Volume 2, Issue 1

>c i]Z 8djgi Gddb " LZ XVc ]Zae Ndj Use our ;M( GZVaBdi^dc (9 to instantly animate your reconstruction results on your 3D scene.

Use our HB68 ;M to simulate or predict collision results.

Present powerful time distance reports and persuasive graphical output.

El[hm^[bc j^[c 7bb <N) ekjfkj _i Z[jW_b[Z WdZ Yekhj WYY[fjWXb[$

     

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

           



        

 

&OR SERIOUS 2ECONSTRUCTIONISTS SEE HOW &8 CAN BE RIGHT FOR YOU

mmm$l_ikWbijWj[c[dj$Yec

'$...$.(.$&).)

In c

up ro

G

a

at

D

ra

sh

c

ID I=: 8DJGI GDDB

In

Ed[ _dj[]hWj[Z mehaifWY[$

Volume 2, Issue 1 - Spring 2007

Use our 8gVh]BVi] application with 720+ reconstruction formulae to get all the answers.

of Steering-induced, On-road, Untripped SUV Rollover

p

Use our 8gVh] ;M momentum tool right on the diagram to generate impact speeds.

Reconstruction & Analysis

ro u

Use ;M( to generate a powerful 3D scene complete with textured surfaces and any models you need.

G

Use ;M( Reconstruction software to download your measurements points and auto plot your scene diagram.

in NHTSA Crash Tests

a

Dc ndjg E8 Ä LZ XVc ]Zae Ndj

The Accuracy of GM EDRs

D at

ID NDJG 9:H@IDE

sh

:WjW9ebb[Yjeh

Presentations & Data

C ra

7YY[b[hec[j[h

9b[Wh j^[ HeWZ _d c_dkj[i

IdiVa HiVi^dc 9dlcadVY

B";M

7

6XXZaZgZM

Conservation of Linear Momentum

2007 CDR User’s Conference CD

00

Use =Vl`:nZ our photogrammetry program to take accurate measurements with your camera.

Analysis of Collisions:

)2

Use our EdX`Zi 8gVh]BVi] – to do preliminary calculations of impact speeds etc.

of EDR Information

(c

Use 6XXZaZgZM on the same Pocket PC to measure deceleration ( drag factor ).

Two-Dimensional Analysis C

Use our B";M Pocket PC data collector with any total station – see your points recorded in 3D.

Volume 2 Issue 1

7

Dc i]Z hXZcZ " LZ XVc ]Zae Ndj

The International Compendium for Crash Research

00

;GDB I=: H8:C:

ollision C )2

software package that contains all the tools required for crash and crime reconstructions. Wether you do a linear momentum analysis, SMAC Simulation or create captivating 3D Animations; You never leave one application - FX3

(c

FX3 from Visual Statement is a state of the art reconstruction solution that allows you to perform accurate reconstructions ranging from simple sketches to detailed 3D Environments. FX3 was designed specifically for reconstructionists who benefit from a

Collision: The International Compendium for Crash Research

/NE #OMPLETE 3OLUTION

Investigations Just Got Easier With Sokkia’s Innovative Crime Scene Technology

Expert AutoStats® Expert AutoStats® is a computer program containing over 37,000 vehicles cars, vans, utility vehicles, and light pickups. 1945-2007 model years are represented.

This program can be used alone or with our Expert Qwic Calcs® and Expert VIN DeCoder® programs. Also accessible from within REC-TEC.

4N6XPRT Systems®

Individual Vehicle Specifications

$40.00-First vehicle, $35.00/Additional Vehicles $20/Additional similar Model-same Make/Year/Order Minimum specifications include: Weight, Length, Width, Height, Wheelbase, & Wheeltrack VIN DeCoding when VIN is provided and Information is available Mid-60's to present also includes (when available) Front O verhang Bumper-to-hood Bumper-to-W indshield Turn circle

Bumper H eight Hood Height G round-to-base of W indshield W heel R adius

G

ro

up

In c

When making your request please identify: Year, Make, Model, & Number of Doors

(c

)2

00

7

C

ra

sh

D

at

a

(Laptop & D esktop IBM C ompatible)

Enter:

Manufacturer and Year

Select:

Model from pop-up window

Output:

Wheelbase Overall Length Height Wt. Distribution

Curb Weight Width Drive Wheels Front/Rear Track

Mid-60's to present output also includes (when available): Front Overhang Rear Overhang Bumper Heights Hood Height Turning circle Wheel radius Bumper-to-Hood Bumper-to-Window

Expert AutoStats® is currently owned by over 660 private individuals and 270 Law Enforcement agencies in the U.S.A., Canada, and South America. Additional information, brochure, and order from can be downloaded from:

www.4n6xprt.com

PICKUP/UTILITY/VAN please also identify: Short/Long wheelbase/bed 2/4 Wheel Drive Std./Super/Crew Cab Cargo/Passenger Van

Motorcycle Specifications (1970+)

$40.00-First vehicle, $35.00/Additional Vehicles $20/Additional similar Model-same Make/Year/Order

NHTSA Crash Test Data + A-B-G Stiffness $40.00 per Test

You can Fax your request 24 hours/day - 7 days/week. Please include your Visa/MasterCard/American Express Card Number-Expiration Date-Name on card- and Card Billing Zip & Address. Data is faxed back at no additional charge, and the hard copy is mailed. Normal response time is 1 working day.

FAX: 1-619-464-2206 or

Call 1-800-266-9778 Monday-Friday 9:30 am to 5:00 pm P.S.T.

An order form can be downloaded from:

www.4n6xprt.com

PROGRAM ORDER FORM (Please Print)

Prismless Mapper: This long-range, prismless instrument is ideal for making challenging measurements. Use it’s extremely narrow, visible red laser to pinpoint and accurately measure difficult positions.

c

Standard Mapper: Designed with the job in mind, this instrument is capable of measuring to prisms and reflective sheets, helping you finish faster, easier and safer than ever before.

D at

a

G

ro u

p

In

LEA Remote Mapper: Accuracy, efficiency and the convenience of single-person operation are all combined in this powerful, fully-robotic instrument.

(c

)2

00

7

C ra

sh

For more information on Sokkia’s LEA product line or to find a dealer near you, contact customer service at 800.4.SOKKIA, or visit www.sokkia.com.

The Bluetooth word mark and logos are owned by the Bluetooth SIG, Inc. and any use of such marks by Sokkia is under license.

©2007 Sokkia Corporation

LEA

Sokkia

Law Enforcement Applications

800.4.SOKKIA • www.sokkia.com

Contact Name: _______________________________________________ Company: ___________________________________________________ Street: ______________________________________________________ City:____________________ State:____ Zip:__ __ Country: _______ Phone: (_____) _______________ Fax: (_____) _________________ E-Mail: ____________________________________________________

Expert AutoStats® Expert Qwic Calcs® 4N6XPRT Ped & Bike Calcs® 4N6XPRT StifCalcs® Expert VIN DeCoder® (pkg) Expert TireStuf®

- $ 595.00 ea.

- $ 275.00 ea.

- $ 375.00 ea.

- $ 475.00 ea.

- $ 475.00 ea.

- $ 85.00 ea.

= ________ = ________ = ________ = ________ = ________ = ________

California Sales Tax Shipping & Handling

- 7.75%

= ________ = ________

S&H - Check = $11.75, Credit Card = $16.75, Govt. P.O. = $21.75

TOTAL (U.S. Dollars)

Enclosed is: Visa ____ MasterCard ____ Am. Ex. ____

= ________

Exp ____/____

Card Number: ______________________________________________ Name on Card: ______________________________________________ Signature: _______________________________________________ Please Make Checks*/Purchase Orders Payable to:

4N6XPRT Systems® 8387 University Ave - La Mesa, CA 91941-3842 - U.S.A. FAX: (619) 464-2206 Phone: (619) 464-3478 W eb: http://www.4n6xprt.com Checks *MUST* be drawn on a U.S. bank. Orders are shipped within 10 working days of receipt. Prices subject to change without notice. Multiple orders and Package discounts available. Please call for details.

Discussion Forum Expert Directory Industry News Research Vehicle Specs DB Crush Stiffness DB 07

C

ra

sh

D

at

a

G

ro

up

In c

Event Calendar AR Newsletter Book Store Education Library of Papers Member Discounts

(c )

20

The ARC Network is the largest research & resource organization for accident reconstruction & traffic accident investigation. We also host the industries largest online expert directory.

Over 850 Members Worldwide and Growing!

Join Today

www.accidentreconstruction.com Publication

CDR System

www.CrashConferences.com

00

7

C ra

sh

D at

a

G

Join the ARC Network as a Police Department or Platinum level member and receive a FREE subscription!

)2

(c

ARC Network members receive a $50 discount to all ARC Network hosted Conferences.

I Got Hit, LLC is an authorized distributor for the BOSCH CDR product line.

Visit the web site to view the current special offers!

ro u

p

In

c

Conferences

www.cdr-system.com

www.CollisionPublishing.com

www.AccidentReconstruction.com Toll Free: (866) 223-4984

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

AT THE SCENE, YOU NEED A PARTNER YOU CAN COUNT ON.

Evidence Recorder 4 is the latest version of the world’s best-selling evidence collection software built specifically for professional reconstructionists.

A good partner brings a lot of attributes to the table. Consider just a few of the features and functions built into Evidence Recorder: Intuitive interface with large finger sized buttons, streamlined menus and user definable shortcut keys help increase your efficiency

Partnering with Evidence Recorder allows you to experience power, precision, and productivity gains associated with being able to visually verify your evidence collection.

REDUCE ERRORS. SAVE TIME. ELIMINATE FRUSTRATION.

Data security including realtime saving as you take your measurements

Evidence Recorder will give you confidence that your evidence data is captured, correct, and comprehensive.

Optional raw file encryption ensures only authorized products and users can access your raw file

Quite simply… this is “a brilliant forensic power tool for better productivity and performance.”

In

p ro u

G

a

Easy linework tools help you draw your scene while you collect evidence

EVIDENCE RECORDER – THE PERFECT PARTNER FOR THE DEMANDING PROFESSIONAL D at

Advanced offset routines for use with prismless total stations

c

Powerful graphics engine help you view your scene in 2D or 3D

Evidence recorder enables you to identify details graphically, confirm you have everything you need, and rectify any errors or omissions – all before you leave the scene.

The power you need, when it’s all on the line. Let’s talk about how you can achieve an unparalleled level of precision. It’s a lot easier than you may think.

Easily sync your Evidence Recorder with your MapScenes desktop program

When accuracy and precision are non-negotiable – fortunately, there is MapScenes.

(c

)2

00

7

C ra

sh

Automatic modes for trilateration and baseline offsets included for LTI lasers

TRAINING, EVIDENCE COLLECTION and DESKTOP MAPPING SOLUTIONS

RELIABILITY. RESULTS. REPUTATION.

YOU KNOW WHAT’S AT STAKE. BUT, WHAT HAVE YOU GOT TO GAIN? WE THINK, QUITE A BIT!

MAPSCENES.COM 800.668.3312 © 2007 MICROSURVEY SOFTWARE INC. MAPSCENES® IS REGISTERED WITH THE U.S. PATENT AND TRADEMARK OFFICE BY MICROSURVEY SOFTWARE INC.

2 Collision www.collisionpublishing.com

4

Contents

of interest

Spring 2007

From the Editor

114 Calendar of Events up

In c

Organization News ro

8

ra

C

Two-dimensional analyses of EDR information 20

07

12

sh

D

at

a

G

features (c )

28

20

Close Range Photogrammetry

28

Compartmentalization Compromised: The Issue of School Bus Passenger Safety

34

Damage-Based Collision Severity Reconstruction Technique

38

Analysis of Collisions: Point Mass Mechanics and Planar Impact Mechanics

52

Carrying out a high-speed crash test for the Dutch police THE FUTURE STRUCTION

OF

ACCIDENT

64

EDR Durability

70

The Accuracy of General Motors Event Data Recorders in NHTSA Crash Tests

78

When Measuring Vehicle Crush... find the Method that Works for You

82

Book Reviews

88

Reconstruction & Analysis Of Steeringinduced, On-road, Untripped SUV Rollover

62

RECON-

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

62

38

88

case study 24

Case Study Problem

61

Case Study Solution Collision

3

from the editor

20

07

C

ra

sh

D

at

a

G

ro

up

In c

As mid year is already upon us, I got to thinking about how time truly “flies.”

It took me back to August of 2002 when the first ARC-CSI Crash Conference was held in Seattle, WA. Although less than 75 people attended, we learned a lot and developed a plan to host the ARC-CSI Crash Conference every year. We moved the Conference to Las Vegas and with the help of the North Las Vegas Police Department, secured a part of the Las Vegas Motor Speedway in 2003. As I write this we have just closed early registration for the 2007 ARC-CSI Crash Conference and we are pleased to announce that our attendance, in just 5 years, has almost quadrupled and has gained a worldwide appeal!

(c )

Last year, as you may remember from the last issue of Collision, we ran 9 instrumented crashes including crashes with a bus, a couple motor homes, motorcycles, passenger cars and a fire engine. This year, we are scaling back the number of crashes but, based on conference feedback, we are going to present more in the way of analysis from the reconstruction of the crashes we run on June 4 - the first day of the conference.

This issue of Collision marks our second year of publication and the second issue including CDR User’s Conference proceedings. Many detailed and valuable presentations were made at the 2007 CDR User’s Conference including making Houston, TX the location for this annual conference. Houston allows us to grow the conference and accomodate everyone who wishes to attend.

The 2008 CDR User’s Conference planning is already well under way. We will be back in Houston January 2830, 2008 and will be covering a ton of fresh material. Mark your calendars now! See, time truly DOES fly!

So, what’s out there on the horizon? As far at the Vetronix/Bosch Crash Data Retrieval System is concerned, everything is! This year at the CDR Conference, Bosch announced Daimler-Chrysler joining the list of vehicles supported for crash data downloads by the CDR System and with the pending implementation of 49 CFR Part 563, the list will likely continue to grow quickly.

For the 08 CDR User’s Conference, we’re planning presentations on reliability and use of Ford “PCM” data (you’ll have to check out the presentations on the included disk for more on that!) as well as introducing the Daimler-Chrysler crash data use, application and results of testing conducted on those systems between now and then.

)2 (c

Yes, things sure have changed and time, without a doubt is just screaming by!

00

7

C ra

sh

D at

a

G

ro u

p

In

c

On the horizon for Collision magazine? New industry partners. We have received interest from a number of professional organizations wanting to include Collision as an integral part of their membership package. The latest association to join the Collision family is The International Association of Accident Reconstruction Specialists (IAARS). Like our primary partner NAPARS, IAARS offers their members Collision magazine as part of their membership benefits package. Other associations are moving toward this as well including two international associations!

Scott B. Baker Managing Editor www.crashdatagroup.com 4 Collision www.collisionpublishing.com

All rights reserved, © 2007 Collision Publishing LLC. The opinions and conclusions expressed in this publication and attached data disk in articles attributed to specific authors are the opinions and conclusions of the authors noted and not necessarily the editorial staff or reviewers of those documents. Really, facts belong to everybody, any other opinions to us. The distinction is yours to draw...otherwise, the opinions expressed herein are not necessarily those of any employer, not necessarily ours and probably not necessary. Dissenting opinions, discussion or conclusions which may express an adverse position to those expressed herein by specifically cited authors can be addressed in writing by sending an email to the editor at editor@collisionpublishing.com or sending a “regular mail” letter to us at 118 Lake Street South Suite G, Kirkland, WA 98033.

By sending an email to any of our email or snail mail addresses listed in this publication you are agreeing that: (1) we are by definition, “the intended recipient” (2) all information in the email is ours to do with as we see fit and make such financial profit, political mileage, or good joke as it lends itself to. (3) This overrides any disclaimer or statement of confidentiality that may be included on your original message. The entire physical universe, including this publication and attached data disk, may one day collapse back into an infinitesimally small space. Should another universe subsequently re-emerge, the existence of this publication and data disk in that universe cannot be guaranteed.

Back Issues

Back issues of Collision are available to purchase online while supplies last. www.collisionmagazine.com

Past ARC-CSI Crash Conference CDs are available for purchase at www.crashdatagroup.com

)2 (c

ARC-CSI Crash Conference CDs

00

7

C ra

sh

Crash Data Group Inc PO Box 892885 Temecula, CA 92589 (800) 280-7940 www.collisionmagazine.com sbaker@crashdatagroup.com ISSN: 1934-8681

c

Content Advisory Committee W. R. Rusty Haight Collision Safety Institute Brad Muir Collision Safety Institute John Meserve President, NAPARS Tom Szabo Biomechanical Reasearch & Testing Judson Welcher Biomechanical Reasearch & Testing

4N6XPRT Systems: Inside Back Cover ABC Surveying: Page 23 ARC Network: Page 1, 117 Bunce Industries: Page 7 CDR User’s Conference: Page 37 Collision Safety Institute: Page 19 Crash Test Service: Page 118 CSI Mapping: Page 118 I Got Hit LLC: Page 27, 119 IST: Page 25 iWitnessPhoto: Page 22 Laser Technology: Page 77 MapScenes: Page 2, 57-60 PhotoModeler: Page 51 Sokkia: Inside Front Cover Visual Statement: Back Cover WeCare: Pages 50, 69

In

(c )

20

Scott Baker Publisher, Managing Editor sbaker@crashdatagroup.com Sean Haight Editor Tonya Baker Advertising Account Manager

p

07

C

ra

sh

D

at

Collision Staff

Index of Current Advertisers

ro u

a

G

ro

up

Bonus spreadsheet software by Greg Russell to go along with the Crush Measuring article in this issue.

G

In c

Presentations by: Rick Ruth, Dave Little, Craig Wilkinson, Tim Reust and others.

The Collision Publishing media kit, including demographics, advertising rates, placement and sizes, is available to view/download online at our web site www.collisionmagazine.com

a

Presentations and material from the 2007 CDR User’s Conference in Houston, TX.

Advertising Information

D at

Bonus Data

Advertise

on the ARC Network

Advertise on the #1 web site for accident reconstruction and traffic accident investigation - The ARC Network. For complete information visit:

www.thecrashhub.com

Collision

5

In c up ro G a at

John H. Meserve NAPARS1@comcast.net

(c )

20

07

C

ra

sh

D

From the Desk of the President

It hardly seems possible that the two years of my first term have ended…but as they say time flies when you are having fun and I have definitely enjoyed being the President of this great organization. I thank the Board of Directors and the membership for their support and encouragement and I am honored to have been elected to serve a second term. I remain committed to enlarging our membership base and to expand our organization’s profile and presence in the accident reconstruction community nationally and world wide. During the past two years I have traveled to a dozen states from east to west and north to south on behalf of NAPARS and I will be continuing those efforts, including sponsoring ACTAR examinations, during these next two years.

The fall NAPARS election created some changes in our leadership. Wendell Cover of Maryland, who has served NAPARS in many capacities since the organization was created in 1984, stepped down from the Board of Directors due to term limits. Many thanks, Wendell, for all you have done NAPARS. His place as a private-sector member was taken by Chuck Veppert, recently retired after an outstanding 20-plus year career with the Ohio State Highway Patrol. Chuck had been a law enforcement member of the Board; his place on the LE side was taken by Tom Sobolewski of New Mexico…welcome aboard, Tom!

In p ro u G a D at sh C ra 7 00 )2 (c

Among those attending that conference was NAPARS member Dale Dent of Ohio (center in photo), winner of our Early Bird Membership Renewal contest, which garnered him a free conference registration. Joining me in congratulating Dale are Board members Kenna Marie Johnston and Tom Sobolewski (left) and Chuck Veppert (far right). Be sure to check our website (www. napars.org) for more member opportunities to win conference registrations (2008 CDR and ARC-CSI Crash conferences) and other prizes!

c

And welcome to the many new members who have joined NAPARS in the last several months, especially those of you who I met at the 2007 CDR Users Conference in Houston in January, which was co-sponsored by NAPARS. This third issue of Collision: The International Compendium for Crash Research contains the data from that conference and much more.

A reminder again to all our members (and potential members too): my door is always open. Please feel free to contact me at anytime with comments, questions, suggestions or complaints; the more we all work together the stronger our organization will be in the days and years ahead. Hope to see you at a future NAPARS-sponsored event!

6 Collision www.collisionpublishing.com

Collision

7

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

Organization News

sh

D

at

a

G

ro

up

In c

ARC Network - www.accidentreconstruction.com - Founded in 1998, the ARC Network is the largest Internet portal web site for the industry of accident reconstruction and traffic accident investigation. This organization provides resources and information for all areas of accident reconstruction and traffic accident investigation including research, news, expert discussion, events, products and services, expert witness directory, book store, education services directory, police department directory and a member’s only section that provide valuable online databases and tools to assist in daily accident reconstruction requirements.

(c )

20

07

C

ra

ASPACI - www.aspaci.org.au - ASPACI is a non-profit society whose members have joined to share in the challenge of analysing the complicated issues of road collision investigation. ASPACI was formed in 1991 by a group of police and collision reconstructionists who felt there was a need for information sharing between police and associated institutions in the Australia, South East Asia, New Zealand and South Pacific area. Its primary function is to assist in the spreading of knowledge and enhancing expertise in the science. The Association seeks to promote a professional approach to collision investigation and to encourage the highest standard of ethics, integrity and honesty among its members.

CA2RS - www.ca2rs.com - CA2RS was created to provide accident reconstruction training and resources to its members. There is a growng need for more local resources in the accident reconstruction field. This organization has grown to over 260 paid members and are always looking for ways to strengthen and increase their membership.

CATAIR - www.catair.net - The Canadian Association of Technical Accident Investigators and Reconstructionists (CATAIR) was founded in 1984 to meet the growing demand for a professional organization that subscribed to a code of professional conduct. CATAIR membership is open to individuals involved in all aspects of road safety. Current membership is in excess of 250. presently, our membership is comprised of active and retired police officers, professional engineers, automotive engineers, engineering technologists, private consultants and representatives from the insurance industry.

FARO - FARO, officially known as Forensic Accident Reconstructionists of Oregon, was chartered in June 1994 under the laws of the State of Oregon. Officially designated as a non-profit, mutual benefit corporation, FARO exists as a voluntary professional association of individuals who practice forensic reconstruction in Oregon.

ro u

p

In

c

IAARS - www.iaars.org - The International Association of Accident Reconstruction Specialists was started in 1980 as a training and networking resource for members. It is believed we are the oldest such crash reconstruction organization. Our membership consists of Law Enforcement as well as Engineers and PhD’s. We have members from 38 states as well as Canada, England, Singapore, Spain and West Australia. Our association is a little different from many others in that we have a peer review process for membership. This peer review is a specific area of judicial consideration when admitting an expert opinion in court. The annual seminars, held in different locations nationwide, not only provide instruction on specific topics by experts in the field, they provide face-to-face discussions on how other people approach reconstructing a crash. The old saying “two heads are better than one” is definitely true in accident reconstruction. The next seminar will be the Big Event in Houston, TX in September 2006.

(c

)2

00

7

C ra

sh

D at

a

G

IATAI - www.iatai.org - The Illinois Association of Technical Accident Investigators was born after several members of the Illinois State Police completed their training in traffic crash reconstruction. They saw the need for a way to share information, experiences and grow as Accident Investigators. These founding members set four goals for the organization; 1. To provide professional standards for members investigating accidents; 2. To promote the continued expansion of members knowledge in the area of technical accident investigation.; 3. To promote Traffic Safety through accident investigations; and 4. To promote improved capability of each agency through training and idea exchange. Since 1986, IATAI has held annual training conferences throughout the State of Illinois. These conferences serve to bring valuable training from across the country into Illinois. Our membership reaches out to 26 states in both the public and private sector.

MATAI - www.mdatai.org - MATAI continues to be innovative and willing to meet the needs of its membership. Over the years, MATAI has grown into a internationally renowned organization. MATAI has sponsored or co-sponsored numerous conferences that have been attended by fellow investigators from around the world. These conferences have included relevant and at times, spectacular test collisions involving cars, trucks, motorcycles, pedestrians, bicycles, and even a Metrobus.

8 Collision www.collisionpublishing.com

D

at

a

G

ro

up

In c

MATAI - www.matai.org - Founded in 1988, the Midwest Association of Technical Accident Investigators (MATAI) was formed to provide a professional affiliation for individuals who have a primary interest in the technical aspects of motor vehicle traffic collisions. The Association is dedicated to the exchange of information and ideas to improve investigative techniques and procedures In addition, MATAI provides a communication source between other individuals and affiliations involved in this vital area of public safety. MATAl’s primary objective is to meet the needs of the people directly involved in the initial investigative process.

(c )

20

07

C

ra

sh

NAPARS - www.napars.org - The National Association of Professional Accident Reconstruction Specialists is a non-profit organization whose members have joined together to share the challenge of dealing with the complex problems of accident reconstruction and to upgrade and ultimately professionalize the accident reconstruction field. NAPARS is open to all persons who are interested in the fields of traffic accident reconstruction and highway transportation safety. Present membership exceeds 1,100 and includes police officers, engineers, consultants and government safety personnel. NAPARS is also the Premier Industry Partner for Collision Magazine.

NATARI - www.natari.org - The National Association of Traffic Accident Reconstructionists and Investigators (NATARI) was established as a non-profit Pennsylvania corporation in 1984. The goal of NATARI is to provide a source of information to be shared among accident professionals on a national basis. This goal is reflected in the NATARI logo comprised of an outline of the nation, a broken wheel signifying a traffic collision and the words “to solve for safety”.

NJAAR - www.njaar.org - The New Jersey Association of Accident Reconstructionists started in 1991 as a dream of a few New Jersey police officers who wanted to create a network of individuals with interests in the field of accident reconstruction. Its membership has grown to encompass individuals from many states in all fields of accident reconstruction. We have a large membership base that includes many professionals not only from the police community, but the private sector as well.

NYSTARS - www.accidentreconstruction.com/nystars - The mission of NYSTARS is to organize into one body, professionals in the field of ground vehicle collision reconstruction and related activities, who support and maintain a high standard of ethics, integrity, credibility and honor in the field of collision reconstruction; to encourage training programs relating to motor vehicle collision investigation and reconstruction through research and communication of matters of mutual interest; to promote traffic safety and foster a spirit of brotherhood among the organization’s members.

SATAI - www.satai.com - Established as a non-profit corporation in 1982, the Southwestern Association of Technical Accident Investigators, Inc. goal is to encourage and promulgate the development of professional technical accident investigation and highway safety; promote research and development of programs leading to better technical accident investigations; and to promote the development and dissemination of new knowledge in the fields of traffic safety, accident investigation and reconstruction. The Association is organized and operated for scientific and educational purposes.

D at

a

G

ro u

p

In

c

SOAR - www.accidentreconstruction.com/soar - An organization of accident reconstructionists dedicated to increasing knowledge, enhancing auto engineering, improving traffic safety and the free exchange of information. Membership is open to all people in all aspects of traffic transportation. Membership is comprised of active and retired police officers, professional engineers, automotive engineers and private consultants.

We have members throughout the world.

(c

)2

00

7

C ra

sh

TAARS - www.accidentreconstruction.com/taars - TAARS was organized in 1986 as an organization dedicated to advancing Research, Knowledge, Education and Safety in the field of accident reconstruction. TAARS is a broad based organization with members from many different fields, including law enforcement, private investigators, engineers and attorneys. TAARS has a current membership of over 220 members.

WATAI - www.accidentreconstruction.com/watai - WATAI was formed in 1979 and is the oldest of the technical accident investigation organizations in the United States. Twenty-five plus years since its inception WATAI remains true to its original mission; “to promote education and research in the field of accident investigation; to encourage interdisciplinary communication between the practitioners of accident investigation; and to cooperate and participate with other organizations dedicated to the science of accident investigations”. To that end WATAI sponsors semi-annual conferences. The Spring Conference usually takes place in May and the Fall Conference generally in the onth of October.

Collision

9

In c up ro G a at D sh ra C 07 20 (c )

International Association of Accident Reconstruction Specialists

The International Association of Accident Reconstruction Specialists is one of the oldest associations dedicated to expanding the knowledge and training of accident reconstructionists. Formed in 1980, we have members from several different countries as well as many different states across the U.S. We have three levels of membership.

Our highest level, Fellow, includes a peer review of a reconstruction project. This peer review feature can be very beneficial to a member seeking expert witness qualification in court. One of the criteria a judge can consider when deciding if a person qualifies as an expert is a peer review of his or her work. We offer opportunities for a member to publish work or research in the field of accident reconstruction. This, also, can be very important when qualifying as an expert witness in court proceedings.

Membership in IAARS has other advantages, including a discount (from IAARS) on a subscription to Collision Magazine, member discounts at our training seminars and others listed on our web page, www.iaars.org.

sh

D at

a

G

ro u

p

In

c

We have annual training opportunities at different locations across the country. This year we are pleased to be partnering with the South Carolina Association of Reconstruction Specialists (SCARS). The seminar will be held in North Charleston, South Carolina from July 22 through July 26, 2007. More information can be found on our web page. Plans have already begun for a joint seminar in the summer of 2008 in Vancouver, British Columbia.

Sincerely,

(c

)2

00

7

C ra

If you have any questions about IAARS or the application process, please feel free to contact me or any of the board members listed on our web page.

Dan Lofgren President, IAARS

10 Collision www.collisionpublishing.com

In c

Special Announcement (c )

20

07

C

ra

sh

D

at

a

G

ro

up

Vetronix Bosch Group Announces The Addition Of Chrysler Vehicles To Its Crash Data Retrieval System (CDR) Product anta Barbara, CA. January, 2007 – Vetronix Bosch Group is pleased to announce an agreement with Daimler Chrysler that will enable the company to add Event Data Recorder (EDR) download capability for North American Chrysler vehicles to its Crash Data Retrieval System (CDR) product. The addition of Chrysler vehicles to the software now enables accident reconstructionists and law enforcement agencies access to download crash data from select Chrysler Vehicles. This will supplement the already-existing support for General Motors and Ford vehicles.

Vetronix Bosch Group is the sole source manufacturer for the Crash Data Retrieval System. The CDR System provides accident reconstructionists with the ability to supplement or verify eyewitness accounts and other traditional reconstruction methodologies with data that may be stored within a vehicles Restraint Control Module (RCM) or Sensing Diagnostic Module (SDM). The CDR tool was initially launched in 2000 with support for select General Motors Vehicles. In 2003, support for select Ford vehicles was added. Support for Chrysler vehicles is currently being added to the product and is expected to become available mid-2007. The company’s goal is also to include support for other domestic and worldwide manufacturers in the near future.

The addition of this coverage will allow accident reconstructionists, law enforcement agencies and the National Highway Transportation Administration to obtain electronic crash data from more vehicles than was previously possible through the Crash Data Retrieval System.

S

bout Vetronix Bosch Group Vetronix was founded in 1984 with the introduction of the very first OEM serial data scantool, and soon became a leading supplier of diagnostic products for the global OE and aftermarket automotive service industry. In 2003 Vetronix was acquired by ETAS, a subsidiary of Robert Bosch, GmbH. In 2006 the Vetronix Aftermarket Group was integrated into the Bosch North American Aftermarket Group.

This newly formed Diagnostics business combines the strengths of the world’s largest automotive supplier with Vetronix, a world leader in automotive diagnostics to provide a complete automotive service solution for the aftermarket. This solution includes diagnostic tools and in-depth software, integrated service information, expert training, technical phone support and quality Bosch parts.

C (c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

A

Collision

11

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Two-dimensional Analyses of EDR Information

Bruno Schmidt

Schmidt Consulting Services LLC

otation conventions In order to discuss various physical quantities (eg, weight, speed, angle, momentum) for two or more colliding vehicles at two or more different times (eg, pre-impact and post-impact), it is necessary to use differ-

N

c

In

p

ro u

G

a

D at

sh

C ra

7

00

)2

A

ent symbols and to differentiate among the different quantities. Numerous conventions have arisen regarding the use of different symbols. Probably the most common convention used in accident reconstruction (and illustrated recently in the excellent text by Daily, Shigemura, and Daily1) is to use v1, v2, v3, and v4 to represent initial speeds (and/or velocities) for vehicles 1 and 2 and final speeds for vehicles 1 and 2, in that order. And for angles of travel, 00, y, q, and f are used for the same sequence of items (initial angles of vehicles 1 and 2, final angles of vehicles 1 and 2). In this context, my use of the words “initial” and “final” are in reference to just the collision event—pre-impact and post-impact.

While the convention used in the Daily, Shigemura, and Daily text is commonly used, the use of multiple symbols for angles of travel can be confusing, particularly in derivations using complex algebraic and geometric equations, and in some simple expressions such as Dv1 = v3 – v1.

Other conventions can be found. For instance, Fricke2 and Haight6 use v1 and v2 for the pre-impact speeds for vehicles 1 and 2 respectively, and v1’ and v2’ for the post-impact speeds for vehicles 1 and 2. Also, q1 and q2 designate preimpact angles for vehicles 1 and 2 and q1’ and q2’ are used for the post-impact angles. With this approach, the number “1” always stands for vehicle 1 and “2” always represents vehicle 2. v always represents speed and q always represents angle of travel. Unprimed quantities are always pre-impact and primed quantities are always post-impact. In doing complex algebraic

(c

bstract Although many accident reconstructionists have focused on the “pre-crash” data provided by some GM event data recorders, in many instances the delta-v data provide a rich source of information for analyzing a collision. While the use of delta-v data has been dealt with in the CDR Analyst’s Course with such topics as PDOF, deltav, and closing velocity, some aspects of that analysis have been limited to in-line, or one-dimensional, collisions, particularly with respect to the relationship between closing velocity and delta-v.

This paper provides additional information regarding the theoretical framework for using PDOF, delta-v, and closing velocity, and addresses the use of those relationships for analyzing two-dimensional collisions. The connections between this analysis and the use of 360 degree momentum conservation will be addressed.

Examples of applying this methodology are given.

Limitations of the methodology, and limitations of the available data, are pointed out, and uncertainty calculation examples are provided.

12 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

lisions, the coefficient of restitution is defined3 as

separation speed closing speed v2 f − v1 f

e= =

v1i − v2i v1 f − v2 f

=

v1i − v2i

Conservation of energy requires that the kinetic energy before a collision is equal to the kinetic energy after the collision plus any crush energy that went into vehicle damage. This can be written as

E= Ekf + Ecrush ki

m1v1i2 / 2 + m1v1i2 / 2 = m1v12 f / 2 + m1v12 f / 2 + Ecrush

7

C ra

sh

D at

a

G

ro u

p

In

c

Combining the definition of e and the equations for conservation of momentum, it can be shown7 that

This is the same equation used in the CDR course6 if positive, or absolute, values for vc and Dv1 are used. This equation, of course, is useful if Dv can be obtained from the EDR in order to at least find the relative speeds of the two vehicles at collision. It should be noted that a similar relationship can be used to find vc if vehicle 2 has the EDR, rather than vehicle 2-given the symmetry of the relationships, just switch subscripts 1 and 2 in the equation above.

The relationship allowing us to find vc from Dv then opens up the question: Can a comparable analysis be done if the

00

O

The absolute sign brackets ( || ) mean that the magnitude, or positive value, of the quantity inside the brackets is to be taken. Doing this means that the order of subtracting one velocity from the other doesn’t matter.

Two other useful principles for analyzing collisions include conservation of momentum and conservation of energy.

Using m for mass and W for weight (W=mg), conservation of momentum can be written as

)2

ne Dimensional Review Definitions, Relationships, and Important Principles For a collinear, inline collision, the post-impact velocities will lie along the same line as the pre-impact velocities.

The closing velocity vc can be written either as v1i – v2i or as v2i – v1i.

In the first case, it is the closing velocity as seen by an observer in vehicle 2; in the second case, it is the closing velocity as seen by an observer in vehicle 1. Although it is not necessary to do so, there is a common practice of orienting the reference axis so that vehicle 1 is traveling in the positive direction along the reference axis. The closing speed can be either positive or negative depending both upon which observer and which vehicle is the “bullet.”

Similar statements can be made about the separation velocity vs—it can be written either as v1f – v2f or as v2f – v1f. Considering the six possibilities—vehicle 1 traveling to the right and rear-ending vehicle 2, vehicle 2 traveling to the right and rear-ending vehicle 1, the same two possibilities with both vehicles traveling to the left, a head-on collision with vehicle 1 traveling to the right and vehicle 2 to the left, a head-on collision with vehicle 1 traveling to the left and vehicle 2 to the right—it will always be true in an inline collision that if both closing and separation velocities are expressed as relative to the same observer (whether an observer moving with vehicle 1 or an observer moving with vehicle 2), then if the closing velocity is positive, the separation velocity will be negative. If we want both of those quantities to be positive for subsequent calculations that we perform, it is better to work with the closing and separation speeds, which are always positive.

A useful concept in analyzing collisions is the coefficient of restitution e (a helpful view of restitution is the “bounce” that occurs in a collision6). For one-dimensional (collinear, inline) col-

.

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

manipulations, this approach always provides a quick visual reinforcement of what vehicles etc appear where in the equations. In his textbook on engineering mechanics, Meriam3 uses a similar convention.

Limpert4 uses a notation that on the surface, at least, appears to increase the complexity of tracking the various quantities: V11 and V21 represent the pre-impact speeds of vehicles 1 and 2, and V12 and V22 represent the post-impact speeds of the two vehicles. Likewise, the pre-impact angles for the two vehicles are given by a11 and a21 while the post-impact angles are a12 and a22. Thus 1 and 2 represent both the vehicle number as well as the pre-impact and post-impact application.

Brach and Brach5 use 1 and 2 subscripts to represent vehicles 1 and 2, both pre-impact and post-impact, and then use lower case v and upper case V for the speeds pre- and post-impact, but different symbols for the pre- and post-impact angles—q for the pre-impact angles and f for the post-impact angles. Thus, for example, in their notation, q1 is the pre-impact angle of vehicle 1 and f2 is the post-impact angle of vehicle 2.

I prefer the Fricke and Meriam approach since it keeps a consistent approach to symbols and labels. However, there are advantages to having an explicit symbol to represent pre-impact conditions (as opposed to its just being the absence of the prime symbol ’). Having an explicit symbol for pre-impact conditions helps provide a check against inadvertently omitting a prime symbol from a quantity and then later thinking it is a pre-impact value when in reality it is supposed to be a post-impact value. Therefore, this paper will use “i” and “f ” for initial (pre-impact) and final (post-impact) situations.

Collision

13

the collision is not inline, and/or is not collinear? Finding the relationship between vc and Dv is more challenging, because it calls for the addition and subtraction of vectors, not just their magnitudes. wo Dimensional Review of Vector Operations In analyzing collisions that are not collinear (or, even if collinear, are not inline), a correct analysis requires dealing with the vector nature of velocity and momentum.

Vectors have both magnitude and direction, which in two dimensions can vary in direction spanning 360 degrees. There are two equivalent ways of quantitatively describing vectors—by their magnitude and direction, or by their components. The first way (magnitude and direction) provides a geometrical description that helps to visualize and understand vectors and their relationships.

The second way (components) provides a way to describe vectors analytically, or algebraically, and facilitates vector operations such as addition and subtraction. A given vector can be described either way, and the alternate descriptions must be equivalent if they are dealing with the same vector.

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

T

the sum of the x components and the sum of the components of the individual vectors respectively. This is shown in Figure 3.

This is illustrated in Figure 1.

To perform vector subtraction, we utilize the fact that the negative of a vector has the same magnitude but points in exactly the opposite direction—the tip and the tail of the vector simply are exchanged. Thus,

G

ro u

p

and also

A short-hand way of expressing this is to say that    v= ( vx ,v y ) = ( vax + vbx ,vay + vby ) = ( vax ,vay ) + ( vbx ,vby ) = va + vb

c

where

From the drawing, it can be seen that

In

With these geometric relationships, when we see the symbol we should realize that this one symbol represents both a magnitude and a direction, and it also represents two-components (x and y). Two ways to explicitly show this representation is to write

sh

)2

00

7

C ra

To illustrate this, and provide the basis for combining components, we can take the same two vectors as above, but change the sign of vb and add the two resulting vectors tip-to-tail, as shown in Figure 4.

From this drawing, it can be seen that va-vb has x and y components given by

(c

These relationships show that, given one description (magnitude and direction, or components) it is possible to calculate the other description (components, or magnitude and direction). One caution: In calculating the arctangent, calculators and spreadsheets are capable of generating values in only the first and fourth quadrants, so it is necessary to use the signs of the components to determine which quadrant a vector lies in. The quadrants and their relationships to the signs of the components is shown in Figure 2.

The addition of two vectors is achieved by placing the two vectors “tip-to-tail” which is equivalent to the parallelogram method of vector addition. It can also be seen that the tip-to-tail method results in the sum having x and y components which are

D at

a

    va − vb = v + ( −vb )

tion as

We can also write these relationships using just one equa-

Collision www.collisionpublishing.com 14 Collision www.collisionpublishing.com

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

   v = ( vx ,v y ) = va − vb = ( vax − vbx ,vay − vby )

elationships Between Closing Velocity (vc) and EDR Data ( Dv ) in Two Dimensions As discussed earlier, in for one dimensional collisions, we have

R

reached by the CGs of the two vehicles, then they pass by each other, with a significant deviation in their motion. In order for this to happen, they must experience a significant rotation, caused by

e v= (1− c

In that case, were simply able to algebraically move the last quantity over to the left hand side of the equation and then solve for vc. However, in two dimensions, we have

ro u

p

In

c

the torques produced by the offset collision forces, as discussed by Daily and Shigemura1. This rotational effect is shown in Figure 7.

)2 (c

and again we have an exact relationship between vc and Dv1 .

In general, however, the two vehicles do not collide in a collinear fashion, and typically e≈.1-1.5, as illustrated in Figure 5.

However, if we consider a third special case, we can get some insight into some useful approximations that can be applied to get reasonable solutions for a large number of collisions.

Case 3. Collinear Offset Collision. In this this case, the velocity vectors are parallel (or anti-parallel), but they do not point toward the CG of the other vehicle, as shown in Figure 6.

For this type of collision, if a common velocity is not

00

7

C ra

sh

D at

a

G

The right hand side of this equation involves subtracting two vectors before finding the magnitude of the result, and the squares of the x and y components of the two become mixed together as the Pythagorean theorem is applied to find the result.

Thus, we cannot solve the equation for vc unless we know the relative angles between the two vectors.

There are two special cases, however, where we can solve the two dimensional equation exactly, and there is another class of collisions where we can get a good approximate solution.

Case 1. Inline Collision. The two vehicles traveling in a collinear, inline fashion allow us to reduce the two dimensional problem to the special case of one dimensional motion, which has already been analyzed.

Case 2. e = 0. For this situation, the two dimensional equation reduces to the following special case:

Inspection of Figure 7 should make it clear that while the vehicles originally had velocity vectors in the east-west direction (meaning that vc was in the east west direction), the changes in the velocity vectors clearly indicate that Dv1 and Dv2 have large components in the north-south direction. Therefore, vc and Dv1 are not in the same direction. As a result, we do not have a simple solution to the e equation which would have permitted solving the algebra to allow us to write vc in terms of Dv1 . This means that this type of Collision 15

a

G

ro

up

In c

collision is not a candidate for obtaining the closing velocity from the EDR data.

On the other hand, there are collinear collisions where the offset is not so severe as to cause rotation to the extent shown in Figure 7. If the collision-induced rotation is not great, we should be able to approximate the closing velocity as being in the same general direction as the change in velocity, and the collinear inline equation can provide a means for calculating vc in terms of Dv1 with an error that is within reasonable limits. Before discussing the errors in this approach, however, it is useful to examine noncollinear collisions where the offset does not produce the type of rotation depicted in Figure 7.

(c )

20

07

C

ra

sh

D

at

Case 4. Non-collinear Collisions.

Consider two vehicles, moving at right angles, that are about to collide, as shown in Figure 8. The closing velocity vector vc can be found by adding either v1i and -v2i or -v1i and v2i tip-totail. The results are also shown in Figure 8.

velocity are the same in both reference frames. Finally, it can be shown that the kinetic energy loss depends only upon the closing velocity7. Thus the kinetic energy loss is the same in both reference frames, which should be expected since the kinetic energy loss equals the crush damage which should be the same no matter what the motion is of the observer. In fact, the kinetic energy loss (and damage energy) can be expressed as

( 1 − e 2 )m1m2 vc2 E= 2( m1 + m2 )

Now, a particularly useful reference frame to observe and analyze collisions is one moving with a velocity that is defined as

 W1v1i + W2 v2i V0 = W1 + W2

For the numerical example given above, we have

 ( 2500 )( 60,0 ) fps + ( 3500 )( 0,48 ) fps V0 = 2500 + 3500 ( 150000,0 ) fps + ( 0,168000 ) = fps 6000 = ( 25,0 ) fps + ( 0,28 ) fps = ( 25,28 ) fps .

In this reference frame, we have the following velocity vectors:

   v1i′ = v1i − V0 = ( 60,0 ) fps − ( 25,28 ) fps

= ( 35, −28 ) fps    ′ = v2i − V0 = ( 0,48 ) fps − ( 25,28 ) fps v2i = ( −25,20 ) fps    ′ = ( 35, −28 ) fps − ( −25,20 ) fps vc′ = v1i′ − v2i

c

In

p

ro u

G

a

D at

sh

C ra

(c

)2

If we examine the motion of the vehicles from an observer moving with a constant velocity v0 , we can calculate the velocities of the vehicles as seen by that observer simply by subtracting the observer’s velocity from the velocities of the vehicles relative to the earth. If we use primes to represent the velocities seen by that observer, we have

7

 = W1 2500lb,v = 60 fps,v = 0,so = v1i ( 60,0 ) fps 1ix 1iy  = = = = W2 3500lb,v 0,v 0 fps,so v1i ( 0,48 ) fps 2ix 2iy    vc = v1i − v2i = ( 60 − 0,0 − 48 ) fps = ( 60, −48 ) fps

Of particular interest, we see that the ratio of the y component to the x component of each of those three vectors is 0.8, or 4/5 (28/35, 20/25, 48/60). This means that in this particular reference frame, the two initial velocity vectors are parallel (actually they are in exactly opposite directions). Therefore, to this observer, it is a collinear collision. And since forces, energy losses, etc are exactly the same in the two different reference frames, we can analyze this right-angle T-Bone collision as a collinear collision, and any collinear results carry over to this T-Bone collision. Note, though, that in this new reference frames, the closing velocity vector may not point from one CG to the other, but there can be an offset. So the possibility of rotation due to the collision is present.

The other thing of interest regarding this particular reference frame is that if we calculate the momentum as seen by that observer, the total vector momentum is zero. Thus, this is sometimes called the “zero-momentum” reference frame.

Being able to view all collisions, no matter what the approach velocities are, either with respect to magnitude or direction, as collinear collisions, allows us to return to the question of which collisions are suitable for the CDR course equation

00

To put some actual numbers into this example, which will be used later to illustrate the results of some error calculations, and which also will demonstrate the component method of vector algebra, let

= ( 60, −48 ) fps  = vc .

Likewise, since it always involves the difference between two vectors resulting in the terms dropping out, we also have Since for a particular vehicle, Dv is the same in both reference frames, then the collision forces and PDOFs are the same in both reference frames. Also, the closing velocity and the separation

As has been pointed out above, if there is a lot of vehicle rotation,

16 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

ro

up

In c

so that Dv departs significantly from the line defined by vc , then the equation is not particularly valuable. So let us look at collisions which are not inline, but for which is substantial overlap between the vehicles, resulting in the vehicles essentially “bouncing back” with a separation velocity vector that is close to the line defined by the closing velocity vector. Although I have not done anything approaching an exhaustive review of such collisions, it appears that for significant overlap without a lot of vehicle rotation being acquired during the collision, the deviation of the separation velocity vector from the closing velocity vector line is typically less than 20 degrees, and may be less than 10 degrees.

a

at

D

sh

ra

C

07

20

(c )

E

G

rror Analysis It is instructive, therefore, to evaluate the error in calculating vc by using the inline equation but for which there actually is an offset resulting in a different angle for the separation velocity vector. In order to do this analysis, a spreadsheet has been prepared that allows a person to enter vehicle weights, speeds, velocity angles (and vehicle 1 is not required to necessarily be moving along the x axis), coefficient e, and the deviation of the separation velocity vector from the inline case.

The three cases to be considered—inline, substantial overlap with little rotation, and significant rotation (where the vehicles may pass by each other rather than “bouncing back” in the zero-momentum reference frame, are shown in Figure 9.

In order to facilitate this calculation, the spreadsheet starts with the initial velocity vectors as entered by the user, then calculates the quantities in the zero-momentum reference frame, then views those quantities from yet another reference frame—another zero-momentum reference frame that has been rotated an appropriate amount so that the closing velocity vector is along the x axis in that reference frame, which allows the user then to enter a separation velocity vector that is at the desired angle from that x axis, then recalculates the resulting post-impact vectors in the original earth-fixed reference frame. Finally, the spreadsheet calculates

vc using the inline equation and compares it to the actual vc for the offset conditions (as specified by the user in terms of the angle of the separation velocity vector from the inline value). A sample display of the user-input part and the error results is shown in Figure 10. The entire spreadsheet is found in the CD that accompanies this publication, and is available to the reader to be used to perform error analyses.

It has been found that the weights of the vehicles and the magnitudes of their velocities have no effect upon the error in the calculated value of vc . What does affect the error is the initial pre-impact directions of the velocity vectors, the value of e, and the value chosen for the separation angle qs’.

omments Regarding e Restitution, e, has been defined as the ratio of separation speed to closing speed, and it has been referred to as the “bounce6.” Strictly speaking, in offset collisions, the coefficient of restitution (the bounce) is defined as the ratio of the component of the separation velocity that is perpendicular to the colliding surfaces, to the component of the closing velocity that is perpendicular to the colliding surfaces3,8. And that does reflect the amount of bounce. However, when there is sliding that occurs between two colliding surfaces (an extreme example being a sideswipe collision), there is very little “bounce” or restitution that takes place. Yet the separation velocity can be a significant fraction of the closing velocity, which means that e as it has been defined and used in this paper (which is large for a sideswipe collision even if it is not particularly useful for our purposes) while the coefficient of restitution would be much smaller. Therefore we must be careful when we use the phrase “coefficient of restitution.” And we should realize that e as it has been used in CDR analyses is the correct quantity to use in calculating crush energy from the previously discussed equation

p

In

c

C

a

G

ro u

( 1 − e 2 )m1m2 vc2 2( m1 + m2 ) D at

E=

C ra

7

00

)2

(c

S

sh

ome Cautions With Respect to Using Dv to Calculate vc If we obtain Dv from an EDR, we must remember that Dv is measured with respect to a coordinate frame that is associated with the vehicle, and so the “x” and “y” components of Dv are Dv longitudinal and Dv longitudinal respectively, and quite possibly are not in the same direction as the earth-fixed x and y components used in the reconstruction analysis. Thus it is necessary to rewrite the vehicle-fixed components to the earthfixed components, as shown in Figures 11 and 12.

We also must remember that we cannot apply the methodology of calculating vc from Dvc when there is significant rotation of the vehicles caused by less than complete overlap, nor can we apply the methodology to sideswipe collisions. In general, Collision 17

when e is large, the errors in the methodology become large unless the collision is essentially an inline collision. However, the values of Dv from the EDR can have large errors in themselves when large rotations are produced by collisions with significant offset.

onclusions and Final Comments The methodology of calculating vc from Dv1 appears to be a valid one for a large class of collisions, from a theoretical basis. Errors can be large, however, for offset collisions The ARC Network is pleased to ofthat result in the separation velocity being at a large angle to the closing velocity.

For those collisions for fer a FREE Collision Safety Insti- which vc can be calculated, that result can be used to independently calculate crush energy, to tute CDR training a cash determine v2i if v1icourse is known,orand to determine v1i if v2i is known.

Although the theoretical basis for these conclusions appears to be rebate when you purchase a new sound, it is desirable to evaluate it utilizing data from a large numVetronix System ber CDR of controlled crash through tests. This the also would allow a person to have more precise guidelines regarding ARC Network. Also included with which collision situations are suitable for this analysis. your purchase References is a FREE one-year 1.

Daily, and Daily, Fundamentals of Traffic membership to theShigemura, ARC Network.

Crash Reconstruction, Institute of Police Technology and Management, University of North Florida, 2006.

2.

Fricke, Traffic Accident Reconstruction, Northwestern Computer not included Traffic Institute [Now Northwestern University Center for Public Safety], Northwestern University, 1990.

3.

Meriam, Engineering Mechanics, Volume 2, Dynamics, John Wiley 1978. has fast become &anSons, indispensible tool of a complete crash reconstruction program. Police agencies, 4.

Limpert, Motor Vehicle Accident Reconstruction and private Cause reconstructionists, engineers, agencies and other safety researchers have come to Analysis, 5th ed., Lexis Publishing, government 1999.

5.

Brach Accident andcontrol Recon- module and accessible using the Vetronix the realization thatand theBrach, dataVehicle stored in theAnalysis air bag struction Methods, SAE International, 2005.

CDR System is an invaluable part of a complete and thorough crash reconstruction.

6.

Haight, Crash Data Retrieval System Operator’s Certification Course, Collision Safety Institute, 2006.

7.

Schmidt, Haight, Szabo, and Welcher, “System-based energy and momentum analysis of collisions,” SAE 980026, 1986.

8.

Stronge, Impact Mechanics, Cambridge University Press, 2000.

C

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Special Offer

The Vetronix CDR System

CDR System

“Whether for trial, research,

Computer

Air Bag Control Module

sh

D at

a

G

ro u

p

In

c

(not included)

(c

)2

00

7

C ra

or any other crash related safety program, the CDR System has become an integral reconstruction tool”

www.cdr-system.com For complete information please contact the ARC Network Toll Free: (866) 223-4984 Email: arc@accidentreconstruction.com 18 18 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

Collision Safety Institute at

a

G

ro

up

In c

CDR 20

07

C

ra

sh

D

CDR Technician and Data Analyst Training series (c )

Crush Damage And Energy Applications for Collision Reconstruction (CRUSH)

Biomechanics Collision Trauma Biomechanics

Pedestrian & Bicycle Reconstruction of Pedestrian or Bicyclist Involved Collisions

ro u

p

In

c

Human Factors 00

7

C ra

sh

D at

a

G

Human Factors: Understanding Driver Response

(c

)2

The Collision Safety Institute (CSI) is an independent traffic collision research, training and consulting organization. CSI’s mission is to provide state-of-the-art training and technology transfer to both public and private entities involved in the analysis and evaluation of motor vehicle collisions, provide technical support to professional associations and organizations in their training efforts and conduct testing and research on surface vehicle collision topics and related technology.

www.CollisionSafety.net Collision

19

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Close Range Photogrammetry

Lee DeChant, DeChant Consulting Services – DCS Inc

FIGURE 1

ro u

G

a

D at

C ra

7

00

E

sh

nsuing Litigation In deposition, the injured woman (plaintiff) stated she was standing on the sidewalk, but not at the position where the street meets the curb. In brief, she explained how the bus approached and struck her down while she stood on the sidewalk. The accident reconstruction expert hired by the plaintiff’s counsel went to the scene after the incident, measured the along and across-road gradients (i.e. the slope of the roadway), as well as other hand measurements of the scene. Shown in their reconstruction diagram was a simple rectangular shape that represented the bus relative to the street, sidewalk and curbing. The report placed the length of the bus at a slight inward angle of about 85 degrees to the sidewalk where the woman was standing – thus

)2

T

(c

he Incident A witness at the incident stated they saw a middle-aged woman talking on her cell phone, standing on the sidewalk, while waiting for a bus to arrive. The witness also said the woman was facing south, while the southbound metro bus was approaching the bus stop. The woman then changed her body direction from south to north, turning through east – the street direction. As the woman turned, the metro bus struck the woman in the face, leaving evidence of a 1.5” wide ‘spider crack’ in the lower-right hand corner of the bus’ front windshield, as shown in Figure 1.

p

In

I

Witnesses state the woman was thrown off her feet from the impact, and landed a short distance away on the sidewalk. Witnesses also explain that the bus, while proceeding southbound, did not make an abrupt east-to-west lane change before the incident. The bus, after striking the woman, stopped thirty feet south of the actual collision area. The bus driver turned the front portion of the articulated bus away from the curb, at a slight angle, prior to stopping. The rear section of the articulated bus section, however, remained parallel to the street, as it tracked directly adjacent to the curb until its final rest position.

City police arrived, interviewed witnesses, and documented the scene using an Olympus C5050 digital camera. The officers acquired about twenty digital pictures of the incident scene from different camera angles and perspectives. They also placed a 30 inch-high orange traffic cone next to where the woman was laying on the sidewalk after the impact. There was evidence of blood on the sidewalk where the woman fell. She received multiple broken bones to her face as a result of the impact with the bus windshield.

c

ntroduction In accidents involving personal injury, digital photography often plays a critical role in determining the root cause of the incident. Close-Range Photogrammetry (CRP) techniques are used in accident scene reconstruction to derive accurate 3D measurements from photos taken at the time of the event. CRP is a proven measurement technique that can essentially extract three-dimensional information from two-dimensional photographic images.

This article investigates an actual accident were a metro bus hit a woman. The woman was standing on the sidewalk when an articulated bus approached a bus stop. CRP software was used to measure photographs taken at the scene, and to prove whether the bus driver was responsible for hitting the woman as the bus approached, or whether the woman actually stepped over the curb onto the street, hence no fault of the driver.

20 Collision www.collisionpublishing.com

T

In

p

ro u

G

a

00

7

C ra

sh

D at

C

c

onclusion The digital imagery captured by the police, in addition to the iWitness close-range photogrammetry software, provided the necessary information to prove where the woman was stand-

)2

(c )

20

07

C

ra

sh

indicated the cause of the incident. It was the reconstruction expert’s opinion that based on his analysis; the bus had indeed broken the vertical plane of the curbing onto the sidewalk area where the woman was standing.

The defense hired their own accident reconstruction expert, who in turn teamed up with a photogrammetrist, and measured the incident from the police department’s digital imagery captured at the scene.

Determining the Facts Using Close-Range Photogrammetry Image-based measurement software was used to determine whether the bus had moved over the curb and encroached the sidewalk area. Due to the nature of the incident and the small area of interest, accuracy of the 3D photogrammetric measurements was critical – with tolerance required to be within a few tenths of an inch. Several steps were taken to ensure this required accuracy was achieved in the analysis.

The photogrammetrist received a CD of the digital imagery, in JPEG format, that was acquired by the police officers at the scene. These images were imported into the iWitnessTM http://www.iwitnessphoto.com photogrammetry software program and reviewed. iWitness automatically recognized the pictures were taken from an Olympus C5050 digital camera. The imagery was acquired at the widest possible angle for the camera (smallest focal length, or zoom). With this camera information, a preliminary analysis was conducted in iWitness, and it was determined that the imagery would provide accurate photogrammetric 3D modeling of the incident scene.

Five images were selected for measurement within iWitness. To achieve the best possible accuracy, the photogrammetrist visited the police department and calibrated the actual camera used at the time of

he Photogrammetric Analysis It was the defense expert witness’ conclusion that the rear portion (articulated section) of the metro bus could not possibly have been closer to the sidewalk curbing, as it directly follows the front section of the bus.

As the entire side of the bus is straight, it was possible to ‘translate’ the evidence (i.e., spider crack of the windshield) back to the point of impact, regardless of the fact the bus driver had turned the front section of the bus at several degrees away from the sidewalk curbing before stopping. The front portion of the bus had not traveled far enough forward to change the angle of the rear-articulated section of bus. The rear articulated section of the bus and the adjacent curbing became key indexes for the photogrammetric analysis.

The photogrammetrist measured the front and the passenger side of the bus from the police digital images, as well as the aft-articulated section of the bus, as shown in Figure 2.

In addition, four key photo- grammetric points (as indicated by the white arrow in Figure 3) were measured on the top surface of the curbing close to where the impact occurred.

These points established the photogrammetric coordinate system by defining the curb’s horizontal plane. This plane iWitness photogrammetry software was extruded upwards in a CAD model – and this appears as a solid blue “monolith” in Figure 4. This monolith provides a three-dimensional vertically extended plane directly over the sidewalk/curbing and perpendicular to the street space.

If the points measured on the bus encroached this area over the curbing, the bus would therefore have been respon FIGURE 3

sible for violating the sidewalk space where the woman was standing. Conversely, if the measured articulated section of the bus was proven not to have entered this area, the woman must have had a portion of her body over the street area, hence she encroached the space of the approaching metro bus, and the bus would not be responsible.

The iWitness photogrammetric 3D model was imported into The Crash Zone CAD diagramming program to complete the analysis. Accuracy of numerous check distances that were previously measured with a steel tape and the Nikon D70 photogrammetric survey revealed the measurement accuracy of the police measured images was better than ¼” (RMS 1-sigma level). As Figure 2 illustrates, the green photogrammetric ‘point tags’ were measured on the articulated portion of the bus.

These 3D points established the translation (i.e. the physical movement) of the ‘spider crack’, essentially projecting it back to the location of the woman at the time of the incident, which was close to the articulated section of the bus final rest position.

Figure 4 illustrates the extruded ‘monolith’ from the four points on the curb; the same location as indicated by the white arrow in Figure 3.

The photogrammetric measurements of the bus, relative to the sidewalk and curbing, prove the woman must have had her body leaning over the curb and into the street space. Spider Crack The measurements, when imported into the CAD program, revealed the woman’s face was at least three inches into the street space, hence the reason she was struck by the bus.

(c

In c up ro D

at

a

G

FIGURE 2

the incident.

Further to the Olympus camera calibration, the actual bus, bus depot, sidewalk and street were also surveyed using a calibrated Nikon D70 digital camera and the iWitness photogrammetry software. Numerous distances were also measured with a steel tape for verification as ‘check distances’ used in scaling the digital imagery in the photogrammetry process.

Collision

21

C

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

ing when the bus arrived at its destination.

Photogrammetry has proven to be an invaluable tool in police forensic investigation and accident reconstruction mapping applications. However, it is critical that imagery is captured in way that is conducive to accurate measurement using photogrammetry.

Primarily this involves multiple shots of the area of interest from different view points and perspectives, without changing the camera zoom. In this case, the police captured sufficient imagery of the incident to follow-up with an accurate photogrammetric mapping of the scene. This case settled out of court, and the photogrammetric results played an integral role in avoiding further litigation.

22 Collision www.collisionpublishing.com

ABC Surveying Instruments Law Enforcement Applications

Affordable LEA600 Package

07

C

ra

sh

D

at

a

G

ro

up

In c

Accident Reconstruction Package

(c )

20

SCT6 Total Station LEA 400 Data Logger Evidence Recorder Software

$6,400 Complete Package Price

Purchase includes a calibration certificate to NIST traceable standards and training.

Sokkia’s SCT6: This instrument combines high precision with rugged reliability. It is ideal for applications both indoor and outdoor.

In

c

LEA 400: This economical solution provides a level of durability and protection that other PDA D at

a

G

ro u

p

methods cannot touch.

sh

Evidence Recorder: This software enables you to identify details graphically, confirm you (c

)2

00

7

C ra

have all the points you need and adjust any errors or omissions—all before you leave the scene.

Surveying Instruments

ABC Surveying Instruments 1110 S. Glendale Ave. Ste. B., Glendale, CA 91205

Collision

23

818.507.5758

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Case Study

- Rusty Haight

c

00

7

C ra

sh

D at

a

G

ro u

p

In

Editor’s note: In the last issue, the case problem was tied to the “2 in, 3 out” crash test conducted at the 06 ARC-CSI Conference in Las Vegas. The case problem solution indicated that there would be additional information in the next issue of Collision; this issue. As it turns out, Greg Russell - the primary author of the solution to the case problem - will be presenting at the 07 ARCCSI Conference on this very topic and that would mean, in keeping with our normal publishing guidelines, that his presentation would be part of the next issue of Collision. For that reason, to tie into another topic of recent interest in the community and since this issue relates to the CDR User’s Conference, we have decided to present the remainder of Greg’s case study solution in the next issue of Collision and include with that his presentation from the 07 ARC-CSI and include here a CDR related case study instead.

(c

P

at about 190ms into the event. As you look at the tabular delta-V data, you see that at what seems to be “10ms” the delta-V appears to already be about -10.97mph. The question is, if the delta-V was “that big” that early into the event, did the airbag control module really wait until 190ms into the event to deploy the airbags?

More specifically, let’s ask the question another way, for this case problem: from the data as offered for the case problem, what was the delta-V at about the time the deployment was commanded?

)2

roblem #1 On its face, this seems like a simple crash. Two cars met, tried to occupy the same space, left many bits and pieces of car and such on the road....you get to sort out the aftermath....sounds familiar, right? Well here, we have two cars, meeting head on and you have some “bonus information” to work with...you have the event data recorder information for one of the cars as recovered using the Vetronix Crash Data Retrieval System.

For the sake of this problem, we will assume the data is otherwise reliable.

What you see in the excerpts from the downloaded data below is that the “pre-crash data” shows a speed within the last second of impact of 35mph. You will also see, in the data, that the involved vehicle experiences a delta-V of -37.7mph.

So, the question here is, what’s the car’s post impact velocity. Now, we’re asking for velocity, meaning magnitude and direction. Units aren’t important...in this case, magnitude and direction are significant. roblem #2 Here we have a CDR imaged file from a car involved in a crash. The data from the event data recorder component is downloaded and we’re not going to worry about whether or not it’s “reliable,” we will, for this problem, assume it is reliable on its face.

You can see, in the downloaded data, that the delta-V for the crash is -19.5mph and that the deployment was commanded

P

24 Collision www.collisionpublishing.com

See the solution on page 61

Passenger 1st Stage Time From Algorithm Enable to Deployment Command Criteria Met (msec) Passenger 2nd Stage Time From Algorithm Enable to Deployment Command Criteria Met (msec) Data And ForDeployment Case Problem Time Between Non-Deployment Events1: (sec) Frontal Deployment Level Event Counter Event Recording Complete Multiple Events Associated With This Record One Or More Associated Events Not Recorded

Seconds System Status At DeploymentVehicle Speed

D

at

a

G

ro

up

In c

Before AE (MPH) SIR Warning Lamp Status -5 34 Driver's Belt Switch Circuit Status -4 Passenger Front Air Bag Suppression Switch Circuit35 Status -3 35 Ignition Cycles At Deployment -2 35 Ignition Cycles At Investigation -1 Maximum SDM Recorded Velocity Change (MPH) 35

Engine Speed (RPM) 0 0 0 0 0

7.5 17.5 N/A 1 Yes No No

Percent Throttle OFF 0 BUCKLED 0 Air Bag Not 0 Suppressed 2564 0 2565 0 -19.56 190 0 115

(c )

20

07

C

ra

sh

Algorithm Enable to Maximum SDM Recorded Velocity Change (msec) Time Between Non-Deployment And Deployment Events (sec) Time From Algorithm Enable to Deployment Command Criteria Met (msec)

Seconds Before AE -5 -4 -3 -2 -1

Seconds Before AE -8 -7 -6 -5 -4 -3 -2 -1

Seconds Brake Switch Before AE Circuit Status -8 OFF Vehicle Speed Engine -7 OFF Speed (RPM) -6(MPH) OFF -5 42 OFF2944 -4 44 OFF3136 -3 45 OFF3136 -2 42 OFF2944 -1 0 OFF2496

Percent Throttle 28 28 14 0 0

Brake Switch Circuit Status OFF OFF OFF OFF OFF OFF ON ON

Page 3 of 9

Printed on:

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

3GNEC12T34G195868

1G8ZN12891Zxxxxxx

Page 2 of 7

Printed on: Tuesday,

Collision

25

Data For Case Problem 2:

System Status At Deployment SIR Warning Lamp Status Driver's Belt Switch Circuit Status

OFF BUCKLED Air Bag Not Suppressed 2564 2565 -19.56 190 0 115

In c

Passenger Front Air Bag Suppression Switch Circuit Status

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

Ignition Cycles At Deployment Ignition Cycles At Investigation Maximum SDM Recorded Velocity Change (MPH) Algorithm Enable to Maximum SDM Recorded Velocity Change (msec) Time Between Non-Deployment And Deployment Events (sec) Time From Algorithm Enable to Deployment Command Criteria Met (msec)

Seconds Before AE -5 -4 -3 -2 -1

Vehicle Speed Engine Speed (MPH) (RPM) 42 2944 44 3136 45 3136 42 2944 0 1G8ZN12891Zxxxxxx Deployment 2496 Data

0.00

Seconds Before AE -8 -7 -6 -20.00 -5 -4 -3 -30.00 -2 -1

Percent Throttle 28 28 14 0 0

SDM Recorded Velocity Change (MPH)

Brake Switch Circuit Status OFF OFF OFF OFF OFF OFF ON ON

-10.00

-40.00

20

30

40

50

60

70

80

90

100

110

120

130

140

150

10

20

30

40

50

60

70

80

90

100

SDM Recorded Velocity Change

-10.97

-12.73

-14.04

-16.24

-17.55

-17.99

-18.43

-18.87

-18.87

-19.31

110

120

130

140

150

-19.31

-19.31

-19.31

-19.31

-19.31

(c

Time (milliseconds)

)2

00

7

C ra

sh

Time (milliseconds)

a

10

D at

-60.00

G

ro u

p

In

c

-50.00

C

1G8ZN12891Zxxxxxx

Page 2 of 7

Printed on: Tuesday,

26 Collision www.collisionpublishing.com

Collision

27

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

In c up ro G a at D sh ra C 07 20 (c )

c

In

p

ro u

G

a

D at

sh

C ra

7

00

)2

S

10,000 pounds and an engine located forward of the windshield.

Empty Type C buses weigh in at 22,000-25,000 pounds. The Type C entrance door and driver’s seat are aft of the front axle. Some Type C buses have a shorter chassis and body with fewer seat rows and a reduced seating capacity. Most have the standard 13 rows of seats on both sides of the aisle with a narrow 16” aisle separating 39” wide seats. Seat rows are set closely as possible from the back of the bus forward to assure so that compartmentalization seesaws will better protect students in a collision. The only seat belt and shoulder harness on Type C is for the driver. Compartmentalization is assumed to protect all of the students on board.

Still larger Transit-style or “Type D” school buses also comply with FMVSS 222. With a body installed upon a truck chassis and an engine mounted in the front, midsection, or to the rear.

Type D or transit buses have GVWRs well over 25,000 pounds empty. They have up to 84 elementary school student seating capacity. The entrance door and driver’s seat are forward of the front axle. Type D buses have the same 16” aisles and 15 rows or more of 39” wide seats in tandem. The only three point seat belt-shoulder harness on the bus is for the driver. Compartmentalization in these buses is also designed for all students without the use of any seat belts.

The FMVSS 222 or School Bus Passenger Seating and Crash Protection for School Buses is intended to reduce the number of deaths and occupant injuries resulting from collisions of

(c

chool buses have a unique history of design and construction that over many years has proven that the larger school buses are very crashworthy for their student passengers.

The National Highway Transportation Safety Administration (NHTSA) has enacted many Federal Motor Vehicle Safety Standards (FMVSS) of which at least 55 apply to school bus construction and crashworthiness. The FMVSSs as contained in Title 49 CFR Part 571, apply specifically to school bus occupant protection including FMVSS 220 for School Bus Rollover Protection, which establishes performance requirements for reinforcing the school bus body structure to withstand forces encountered in rollover crashes. FMVSS 221 addresses School Bus Body Joint Strength and establishes performance requirements for the strength of the body panel joints in the school bus and how the bus should perform in a collision. FMVSS 222--School Bus Passenger Seating and Crash Protection establishes performance requirements for school bus passenger seating and restraining barriers.

Both Type A and B vans or buses are under 10,000 GWVR and must have seatbelts for occupant protection. Neither type relies on compartmentalization as identified in FMVSS 222-School Bus Passenger Seating and Crash Protection. Type C or conventional school buses having a seating capacity of up to 72 elementary students or 41 middle or high school pupils must comply with FMVSS 222. This bus type consists of a body installed upon a flat-back cowl truck chassis with a GWVR of more than

28 Collision www.collisionpublishing.com

Compartmentalization Compromised:: Compromised ra

sh

D

at

a

G

ro

up

In c

The Issue of School Bus Passenger Safety

(c )

20

07

C

By Dr. Ray Turner, School Bus Accident Reconstruction, LLC

Type A - School Bus Van

Type B - School Bus

Type B - School Bus Type D - “Transit” School Bus

Type C or D buses have high ground clearance with Delta V forces at the point of impact, or the point of maximum intrusion, occurring under the bus floor while the other vehicle underrides the passenger compartment. Bus passengers are thereby spared the highest

c

In

p

ro u

D at sh C ra 7 00 )2

The larger buses have a considerably larger mass than the majority of vehicles that collide with them giving student occupants a life-saving advantage. Because of the Type C and D construction school buses have different crash force distribution during vehicleto-vehicle collisions.

a

rguments for School Bus Compartmentalization Supporting Student Passenger Safety. The argument FOR school bus compartmentalization for Type C and D buses is based on these data:

(c

A

crash pulse and the best ride down conditions compared to the others in the opposing vehicle.

US Fatality data since 1988 reveals that there were 416,000 fatal crashes of which 1,265 were school bus related. From 1988 to 1997 there were 115 fatalities on Type C and D school buses. Of the school bus collision fatalities 64% or two-thirds were passengers in the other, smaller vehicle. 27% of the school bus fatalities occurred outside the school bus—usually in the danger zone or an area some 10 feet on both sides or to the front of the

G

school bus occupants against structures outside the bus. Compartmentalization alone, however, will be shown below as not protecting students from rear end collisions, lateral collisions and rollovers as well as non-collisions during sudden driving maneuvers such as hard braking, sharp turning, or students being airborne during bus rear end elevation over rough roadways. The conventional interpretation of FMVSS is that by means of compartmentalization large school buses interiors will provide occupant protection so that children are protected without the need to buckle up.[1]

10.6.2005 Chicago, IL

Collision

29

c

In

p

ro u

G

a

D at

sh

C ra

7

chool Bus Compartmentalization Is Not What It Seems…

Does compartmentalization compromise passenger driver safety during school bus collisions? When would compartmentalization work or not work to save student lives? If compartmentalization cannot save passengers lives in catastrophic collisions, and the data in this article cites only fatalities, then how many more major or minor student injuries would compartmentalization prevent or not prevent? Heinrich’s Pyramid [7] predicted the ratio of fatalities to major and minor injuries in industry in general. Heinrich placed fatalities at the top of his pyramid. Mollenhauer [8] in 1998 modified Heinrich’s Pyramid to represent fa-

S

00

A

)2

rguments against School Bus Compartmentalization as Passenger Protection during Collisions. “It is difficult, if not impossible, to develop ways to protect school bus occupants in catastrophic crashes, such as those involving trains and heavy trucks. The crash forces in those crashes are so great that any reasonable structural design cannot maintain the integrity of the vehicle, which is one critical component of occupant crash protection. (National Transportation Safety Board)”[2] We may therefore conclude that in catastrophic collisions compartmentalization does not provide sufficient student passenger safety for some or all passengers. Therefore in all other lessthan-catastrophic collisions how well does compartmentalization work for all student passengers as it was intended?

The National Transportation Safety Board (NTSB) investigated a school bus accident in Conasauga, Tennessee, in which a school bus was struck on the passenger side by a locomotive traveling 51 mph. The NTSB concluded that sidewall components, such as the overhead storage racks, seat frames, and sidewalls, were not designed to be energy-absorbing; These structures could cause injury to occupants by lateral movement during a side-impact collision.[3] As a result, the NTSB issued Safety Recommendation H-01-40 to NHTSA: “H-01-40. Develop and incorporate into the Federal Motor Vehicle Safety Standards performance standards for school buses that address passenger protection for sidewalls, sidewall components, and seatframes.[4] We may further conclude that no such sidewall protection, school bus sidewall components or seat frames have yet been implemented that would protect students from any lateral colli-

sions. Seat frame strengthening or reinforced seat frames have not been developed in the industry since this recommendation was made. Overhead storage racks are no longer manufactured in newer buses. There are many older buses that have storage racks that endanger student passengers during collisions.

In a school bus accident in Central Bridge, New York[5] the NTSB found that seat cushions came loose during impact.

The Board subsequently concluded that the school bus passengers, whether lap belt-restrained or unrestrained, may have sustained more severe injuries because the seat cushion bottoms were unlatched. The NTSB made Safety Recommendation H-00-29 to NHTSA: H-00-29. Modify the Federal Motor Vehicle Safety Standards to include the requirement that school bus seat cushion bottoms be installed with fail-safe latching devices to ensure they remain in their installed position during impacts and rollovers. Because enhanced performance for sidewalls, sidewall components, seat frames, and seat cushion fixation are critical for occupant safety in many accident scenarios, the Safety Board urges speedy action on these recommendations.[6] NHTSA enforcement of seat cushion bottom securement to the seat frame has been adopted by school bus manufacturers.

However, this leaves many older buses in the fleet not meeting that safety standard. When seat cushions become loose during bus lateral collisions or rollovers then compartmentalization is compromised. Without a seat cushion under them those students have no other safety measure to protect them from injury during collisions. Loss of collision integrity of the seat back, the seat cushion and/or the seat frame means compartmentalization cannot work as intended during all rollovers or many lateral collisions.

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

bus. 10% of the fatalities were school bus occupants where compartmentalization may have minimized other fatalities and/or reduced other bus passenger injuries. Of the 10% fatalities in the bus 2% were drivers and 8% were student passengers. Since school bus drivers are always required to wear their three-point lap/shoulder belts compartmentalization for school bus drivers does not apply.

The Most Harmful Events (MHEs). For those 115 school bus fatalities cited above the MHEs came from 29 crashes with other vehicles, 14 fatalities from a collision with fixed objects, 6 fatalities from school bus rollovers, and 66 MHEs from all other bus locations.

Types of Vehicles in School Bus Collisions. Fatalities in the two-vehicle crashes occurred with large trucks with equal or greater GWVRs than the Type C or D buses 89% of the time.

Light Trucks accounted for 7% of those school bus fatalities with the remainder coming from school bus collisions with passenger cars and other vehicles.

Direction of School Bus Collisions. Heavy truck frontal collisions with school buses accounted for 83% of the MHEs, Right-side lateral collisions were 10%. Left side collisions were 5%.

2% were rear-ending collisions. If we can assume that the same locations of collisions with lighter, passengers vehicles will mostly be from the front of the bus, with much fewer lateral collisions from either side of the bus and only 2 out of 100 being struck from the rear end—what does compartmentalization do then to contribute to passenger safety under those conditions?

For Type Two Collisions, or collisions of occupants within vehicles, compartmentalization provides passive occupant protection with energy absorbing, well-padded high seat backs that are strong and closely spaced in rows within the bus.

30 Collision www.collisionpublishing.com

Figure 1

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

tems (CSRS). [9] Children using CSRS are not protected by compartmentalization because they are secured by a seat belt through the CSRS belt channel. The belt must be firmly secured to the seat frame.

The Compartmentalization Envelope (CE) does not apply to any students using Safety Vests that require a cam strap securement behind them and around the back of their own seats. Children seated in booster seats on specially designed bus seats are secured with a three-way harness that is anchored to a reinforced bus seat frame.

Booster seats with built-in harnesses are not afforded CE protection because they are secured with a seat belt.

Lateral Collisions and the Student’s CE. Lateral collisions with students of any size will eject them from their CE and into the aisle or across the aisle against their fellow students who are seated in the row opposite them when moving toward the point of impact. Some students during lateral collisions are ejected from their CE and slammed against the opposite interior bus wall.

Rear End Bus Collisions and the Student’s CE. During a rear end bus collision those students whose heads do not extend above their seatbacks will derive a benefit from their seatback acting as an effective back and neck restraint to reasonably assure their safe ride down.

Older elementary students, or any middle and high school students are vulnerable to neck injuries from neck extension backward over their own seatbacks. In a high intensity rear end collision some students may ramp up and out of their seats backwards toward the point of impact. Students with neck extensions may also be those who are ramped backward and have exited their CEs. They, too, were not adequately protected from injury.

Frontal Bus Collisions and Their CE. When student heads are higher than the height of both seat backs—the seatback in front and the one on which they are seated—during a frontal collision those larger students are likely to suffer neck injuries suffering from neck flexion forward and over the seatback in front of them. Larger students in frontal collisions tend to ramp up and over the seat while moving toward the point of impact. When students ramp up in either direction (forward or backward) their CE is not working.

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

talities and lesser injuries with respect to collisions for both cars and trucks. The Mollenhauer truck injury data is a modified Heinrich Pyramid. The data is comparable to Type C and D school buses which are constructed of heavy truck chassis.(See Figure 1).

School industry leaders and the school bus industry as a whole tend to view compartmentalization as a safety standard fitting all collisions, all students, students in various positions in or out of their seats, students standing, students facing to the rear and other positions and not with their feet flat, facing forward with hands on lap.

The Compartmentalization Envelope (CE) is an envelope of protection--not a safety attitude--for school bus manufacturers, transportation supervisors, directors, and bus operators. Here is what the Compartmentalization Envelope (CE) literally means: The CE is a cubic volume of space starting at the top of the seatback where the student is seated with a plane formed from to the top of students seatback to the next seatback in the row immediately in front. The end of the student’s seat cushion near the bus wall is one of the side planes of the CE extending from the top of the student’s seatback down to that student’s seat base and then extending plane forward to the seatback side and cushion base of the row immediately in front. At the other end of the student’s seat cushion adjacent to the bus aisle is the other side of the (CE) plane that also extends from the top of the student’s seatback to the his seat cushion base and then extending plane forward to the seatback side and cushion base of the row immediately in front. Visualize the base of the CE cubic space as being level plane formed by the underside of the student’s seat cushion (not the bus floor) and extending forward at that level to the seat base of the seat immediately in front. The student’s 39” wide seatback is the back plane of the volume and the seatback immediately in front is the front plane of the CE cubic area. Multiple CEs are formed between each pair of adjacent seats in the school bus.

Further, because seatmates sharing the same CE may collide with one another during a collision the CE should be for one student passenger only so that there would be no other students with which to collide. If other students are present then it is problematic whether the CE can be effectively shared with seatmates.

Lastly, any student secured with any lap belt or harness is by definition not protected within the CE since compartmentalization was defined according to NHTSA as not requiring students to use seatbelts.(See NHTSA citation #1 above.)

Within the compartmentalization envelope (CE) what size of students are best protected by the high-backed, well padded seats at their back and the seatback facing ahead?

The problem of Child Safety Seats. Smaller children with shorter legs that do not extend over the seat cushion and reach down below and outside the base of the compartmentalization envelope have the best protection. However, infants and small children under 40 pounds bodyweight are required to be secured on the school bus using Child Safety Restraint Sys-

Collision

31

c

In

p

ro u

G

a

D at

sh

C ra

7

C

07

20

(c

)2

(c )

C

ra

ompartmentalization Compromised Thirteen rows of seats should each provide a CE for student passenger safety during a collision right? What about the following rows or passenger placements on the bus?

Students with Front Row CE. Passenger side front rows face the stairwell stanchion with little or no padding on the frame and a metal modesty cover for the student seated there. The driver side front row seated students fare no better with the same type of stanchion in front of them and forward to the back of the driver’s padded seat—none of which affords a modicum of padding as do all other padded seat backs in the seat rows behind. During frontal collisions students may be ramped up or ejected into the stanchion opening into the driver or on the passenger side row pummeled down into the stairwell. Damaged front exit doors allow their ejection from the bus. (Conclusion: Students in Front Rows Have NO CE.) Students with Back Row CE. Passengers seated in the rearmost seat rows have the rear exit door and windows behind them.

During a rear-end collision there are no students to ramp over onto them from the rear. However, student in rows forward from them may be ramped back into them. Students seated in the last row may be ejected from the bus through the rear aisle windows or from a rear door when that door integrity is compromised. Further, during that same rear end collision the students seated in the last rows receive the greatest amount of intrusion, are at or nearest the point of impact and experience the largest Delta Vs. (Conclusion: Students in Back Rows Have No CE.) CE for Students in Seat Rows Distant From the Bus Center of Gravity. Students seated in rows progressively further away from the bus center of gravity (CG) are subjected to increasing G forces. During a collision causing the bus to yaw, to slide sideways or to spin without a rollover those students seated in rows most distant from the bus CG are ejected across the aisle to the adjacent seat row or are pressed against the bus wall on their side of the bus with other students ejected into them from the opposite

row. (Conclusion: On either side of the bus aisle those students are outside of their protective CE or some of those students suffer an intrusion by others into their CE.) Students in Seat Rows When Airborne Have No CE. Students are the most vulnerable to lateral displacement outside their CE during sharp turns and bus off-tracking at modest speeds. Onboard bus videotapes reveal that when the bus hits a dip or a speed bump or “curb hops” even at speeds under 10 MPH students will become airborne. (Conclusion: When airborne and off their seat cushions those students are outside or above their CE.) CEs and School Bus Passenger RSIs. When buses are driven at normal speeds, and with no collisions, students in the last rows are jostled hard and continuously. The level of jostling is comparable to a continuous low-G bus collision for them. Adult bus attendants assigned to the back of the bus experience continuous jostling and have legitimately complained of back and neck Repetitive Stress Injuries (RSIs). Research on passenger seat displacement on buses using accelerometer data is critically needed.

Passengers may receive RSIs when seated in the back of the bus when subjected to lateral forces that remove them from their CE while still remaining in their seat rows. (Conclusion: Minor up to major Repetitive Stress Injuries (RSIs) can and do occur because of repeated passenger displacement off their bus seats.)

CEs and Bus Passenger Seat Cushion Displacement.

Higher Delta V bus collisions have caused some passengers to experience seat cushion failures as they return to their seating space after being airborne and out of their CE.[10] Some students are pinned down within the seat frame after the seat cushion was ejected from that same seat frame.[10] Other students may be injured by ejected seat cushions that become projectiles inside the bus or inside the seat row during ride down. (Conclusion: Students with seat cushion failures are extended below or above their CE. Ejected seat cushions can be a danger to all students on a bus in a collision.)

CEs for Passengers In Wheelchairs Does Not Apply. Lift bus lateral movements over rough roads and sharp turns all combine to physically challenge the already physically challenged. Injuries abound with students using manual or power wheelchairs when they are “jostled,” tipped sideways, or ejected from their wheelchair if improperly secured.[5] Wheelchairs users do not have a CE since their chairs are secured with four straps connecting the equipment with bus floor tracking and the student is secured with occupant restraint with a lap and shoulder belt system in place. (Conclusion: Students Using Wheelchairs Do Not Have Their CE.) CE for Wheelchair Users Who Transfer to a Bus Seat.

Wheelchair users who transfer to a school bus seat nearby may not be able to maintain their seated position on the bus without a three-way lap and shoulder belt built into a special, highly reinforced school bus seat.

With no lap belt or a vest

00

sh

D

at

a

G

ro

up

In c

Any students not seated facing forward with bodies turned toward the aisle, toward their bus wall, or facing rearward against the direction of bus movement, or kneeling in the seat facing forward or to the rear, or standing and facing in any direction while the bus is moving or other improper seating positions—all these students are outside their CE. For those ejected only from their seats but who remain within their seat bus row all other surfaces surrounding them are not padded surfaces and will not protect students colliding with bus walls, floors, seat frames, seat legs, the space under the seat in front or the space under their own seat.

Those fortunate enough to remain within their CE may collide with their fellow seatmates, with backpacks, band instruments, lunch boxes, or books not secured to cause injury to those students in the collision mix.

32 Collision www.collisionpublishing.com

C

onclusion: The Compartmentalization Envelope for Most Students on the School Bus Is Compromised. CE as a passive student restraint system is effective only during a narrow range of collision types and intensities. Compartmen-

talization is not an all pervasive safety feature that exists throughout the school bus. Compartmentalization as a safety envelope requires students to be properly seated but fails to keep students safe when they are ejected out of that narrow space during a variety of collisions. Front and back bus rows, lateral collisions, rollovers, any student in a Child Safety Restraint System, a student who wears a vest anchored to the seat back—all these students may not have a CE that is required for their protection. eferences: 1. http://www-nrd.nhtsa.dot.gov/vrtc/cw/BUS_GIJune2000a.pdf dowloaded on 2/21/2007).

2. National Association of State Directors of Pupil Transportation Services, History of School Bus Safety—Why Are School Buses Built As They Are? (The Plains, Virginia: NASDPTS, 2000.

3. National Transportation Safety Board, Collision of CSXT Freight Train and Murray County School District School Bus at Railroad/Highway Grade Crossing, Conasauga, Tennessee, March 28, 2000, Highway Accident Report NTSB/HAR-01/03 (Washington, DC: NTSB, 2001.

4. National Transportation Safety Board.

5. National Transportation Safety Board, School Bus and Dump Truck Collision, Central Bridge, New York, October 21, 1999, Highway Accident Report NTSB/HAR-00/02 (Washington, DC: NTSB, 2000).

6. NTSB, August 6, 2002.

7. Heinrich, H.W., Peterson, D., and Roos, N. (1980). Industrial Accident Prevention. New York: McGraw Hill.

8. Mollenhauer, M. (1998). Proactive Driving Safety Evaluation: An Evaluation of an Automated Traveler Information System and Investigation of Hazard Analysis Data. Unpublished Doctoral Dissertation. University of Iowa, Iowa City.

9. NHTSA Child Safety and Restraint System accessed 2/22/2007 http://www.nhtsa.dot.gov/people/injury/buses/busseatbelt/ page01.htm.

10. National Transportation Safety Board, Highway Accident Report, School Bus Run-off-Bridge Accident-Omaha, Nebraska, October 13, 2001. NTSB/HAR-04/01 (Washington, DC: NTSB, 2004).

11. NTSB Omaha, NE. Pg. 14.

12. ABC World News. November 6, 2006.

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

R

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

secured with a cam strap to their seat backs some of these students will slide out of their seats onto the floor during normal braking or especially when the bus is involved in a minor collision. (Conclusion: Students Using Wheelchairs When Transferred To A Seat May Not Have CE without added belt securements. Yet with belt securement students no longer receive a CE).

Students in School Bus Rollovers are Protected by CE? During school bus rollover collisions the CE for some occupants does not protect them. Some students receive compound collisions to their bodies when ejected from their seating area. Other students receive ejected students colliding against them and the bus wall.

The first collision sequence is the crash pulse may occur in 1/10th of a second as the students onboard farther away from the point of impact are ejected from their seat toward passengers seated in rows nearest the point of impact. Students are slammed directly into their neighbors in the opposite row as they move toward the lateral point of impact or are pressed hard against the wall nearest the point of impact. The entire nation witnessed this instant process when ABCNEWS.com aired on November 6, 2006 on the World News a bus 900 rollover to the bus driver side.[12] When a compound rollover occurs the combined weight of students ejected across the aisle shifts the bus center of gravity. This sudden student bodyweight shift combines with the energy of the striking vehicle for the bus to rollover. The second collision sequence occurs when all students fall together “down” to the bus ceiling. The bus ceiling is not a passenger friendly surface. Like the walls, the floor and other bus surfaces these surfaces cause injuries. Students may fall six to seven feet from their seat rows against the ceiling head, feet- or side-first during rollovers and outside their CEs. If the bus point of rest is upside down there remains the third collision sequence that occurs when students who are conscious and ambulatory attempt to evacuate an upside down bus. Slips, trips and falls and collisions with other students can and does cause further injuries. Should the bus rollover further to 1800 a fourth sequence would occur with students falling from the ceiling to the other side of the bus. Additional quarter-turn rollovers would put students in harms way as though they were clothing tumbling in a clothes dryer. (Conclusion: In all Rollover Collision all Rows are ejected from their Compartmentalization Envelope (CE) on one side of the bus. Wheelchairs users remain upside down and well secured with occupant restraints and wheelchair tiedowns in the bus that has rolled over.)

Students in School Bus Lateral Collisions are Protected

by CE? In lateral collisions students opposite the collision side will be ejected from their CE in any direction that is toward the point of impact. Students on the collision side during a lateral collision will be pinned against each other and against the bus wall nearest that point of impact. At the same time students from the row across are ejected toward their fellow passengers toward the point of impact. (Conclusion: In all lateral collisions compartmentalization does not work for those students unless they are secured by a seat belt or are secured in their wheelchairs. Any person secured by a seat belt, by a three-way seat belt and shoulder harness in or out of a wheelchair may not receive protection from their Comparmentalization Envelope.)

C Collision

33

In c up ro G a at D sh ra C 07 20 (c )

Damage-Based Collision Severity Reconstruction Technique

(For use when crush measurements are only available for one vehicle) Mark S. Erickson ,PE Wilson C. Hayes, PhD

00

7

C ra

sh

D at

a

G

ro u

p

In

c

reconstructionist is retained, just one of the vehicles involved in the collision event remains in existence. This situation further complicates the analysis and immediately raises a red flag, as we know that one of the physical requirements of a crush analysis is that the deformation induced to both vehicles must be considered (6). Although missing a vehicle presents a complicating factor, if good crush profile data are available for one of the vehicles and crush stiffness data, vehicle weights, and impact orientation is known for both vehicles, a force-balance reconstruction technique can often be implemented. This technique allows the damage energy absorbed by the missing vehicle to be calculated based on the peak collision force along with the vehicle’s structure stiffness coefficients. In the following, a general derivation of the force-balance reconstruction methods will be presented. For simplicity, the equations derived will relate to a two-vehicle collision involving uniform crush profiles. That being

)2

S

is retained (often years after the event), physical evidence associated with the collision scene is often scarce. From time-to-time, depending on the severity of the collision, the investigating police agency may have documented the roadway evidence, final rest positions of the vehicles and relevant debris fields. More often than not, reliable scene evidence is unavailable.

Under these circumstances, and given that the damaged vehicles are sometimes available long after the collision, the analyst will often choose to implement a damage-based collision reconstruction.

This technique allows the determination of collision severity level (delta-V) based on the crush damage induced to each vehicle.

Input data required for a damage-based reconstruction includes, but is not limited to, vehicle weights, structural stiffness coefficients and measurements of the postimpact crush profiles for each vehicle.

A further frustration that occurs all too often is that by the time the accident

(c

ince the early 1960’s, the conscious drive to increase automotive safety has greatly advanced the field of accident reconstruction.

Over these years, scientists, engineers and investigators have developed and validated numerous techniques to analyze motor vehicle collision (MVC) events.

These techniques include methodologies based on the conservation of momentum, conservation of energy as well as empiricalbased approaches. Among the input data required for application of these various techniques are: area of impact, post impact rest positions, post-impact trajectories, effective drag factors, vehicle weights, crush profiles, etc. In a controlled crash setting, acquisition of these data represents a fairly straightforward process of scene documentation and vehicle measurement.

However, the complicating factor for the typical accident reconstructionist involved in the realm of civil litigation is that by the time the accident reconstructionist

34 Collision www.collisionpublishing.com

Once the crush profile for each vehicle is obtained, the energy absorbed by each vehicle can be calculated. By definition, the work done during a collision is equal to the product of the collision force and crush distance. Integrating Equation 2 with respect to crush depth (c) and satisfying the appropriate boundary condition, yields the following relationship for energy absorbed during impact (Eqn. 4). This equation provides a straightforward process to calculate the energy absorbed by each vehicle:

Ei =

2

Ai wi Bwc + Ai wi ci + i i i 2 Bi 2

Vehicle #2: 1997 Ford Escort sedan LX (4dr) • Total Vehicle Weight (including occupant): 2705 lbs • Rear Structure Stiffness Coefficients: A = 165 lb/in; B = 46 lb/in2 • Vehicle Width: 67 in • Crush Damage: 11.5 in of uniform crush across entire width of rear bumper (cI = cII = ... = cN)

2

for i = 1, 2 (4)

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

said, the methodology can be expanded to more complex crush profiles if the general shape of the damage pattern is known or can be reliably estimated.

The foundation for this technique rests on basic physical principals. Newton’s Third Law of Motion states that whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body (1). This law of action-reaction applies to all collisions, including impacts involving automobiles. In the context of automobile collision reconstruction, this means that the forces acting on two vehicles during a collision event are at all time equal in magnitude (and opposite in direction).

That is, for a two-vehicle collision, the magnitude of the force exerted on vehicle #1 is equal to the magnitude of the force exerted on vehicle #2 (Eqn. 1).

(3)

D at

a

G

ro u

p

In

c

Vehicle #2

sh

Applying the same crush model to vehicle #2, the equation can be rearranged, solving for crush depth. Since the peak force applied to each vehicle is equal in magnitude, the unknown crush to vehicle #2 can be solved for directly (Eqn. 3)

STEP #1: Calculate Peak Force Acting On

C ra

(2)

Figure 1: Damage Profile of Vehicle #2 (11.5 inches of approximately uniform crush)

STEP #2: Using the Peak Force from Step #1 (Newton’s 3rd Law), Calculate Crush Depth for Vehicle #1

7

F = A1w1 + B1w1c1

(5) (6) Consider the following example: Based on information obtained from a traffic accident report and witness statements, we know that vehicle #2, a Ford Escort sedan with a single occupant, was slowing to a stop for a red light. Vehicle #1, a Honda Civic carrying two occupants, was traveling behind vehicle #1 and for an unknown reason did not recognized that vehicle #2 was slowing and impacted the rear of vehicle #2. By the time a reconstruction was requested, vehicle #1 had already been repaired (there were no photographs of the post-impact damage to vehicle #1).

Vehicle #2 was inspected and crush profile measured.

Determine the energy absorbed by crush and delta-V for each vehicle.

Vehicle #1: 2001 Honda Civic sedan DX (4dr) • Total Vehicle Weight (including occupants): 2914 lbs • Front Structure Stiffness Coefficients: A = 372 lb/in; B = 148 lb/in2 • Vehicle Width: 68 in • Crush Damage: Unknown ???

00

Another fundamental physics principal, Hooke’s Law, states that stress is directly proportional to strain(1).

Essentially, this law states that if the force applied to a structure, along with the stiffness of the structure are known, the resulting structural deflection can be determined (and vise versa). Applying Hooke’s Law to motor vehicle collision reconstruction, McHenry (5) proposed a similar model for use in analyzing automobile deformation.

Implementing this model (Eqn. 2), we can calculate the magnitude of the collision forces based on crush depth (structural deflection) (3). For a two vehicle collision in which vehicle #1 is available for measurement and vehicle #2 is no longer in existence, the peak force applied to vehicle #1 can be calculated by:

)2

(1)

(c

F1 = F2 = F

With the energy absorbed by each vehicle, along with the appropriate vehicle weights, the delta-V sustained by each vehicle can be calculated according to the following(2,6) (Eqns. 5 & 6):

STEP #3: Calculate Damage Energy for Vehicle #1 Collision

35

N

20

07

C

ra

sh

D

at

a

G

ro

up

In c

STEP #4: Calculate Damage Energy for Vehicle #2

omenclature F = peak force acting on vehicles (F1 = F2 = F) E1 = energy absorbed by crush (vehicle #1) E2 = energy absorbed by crush (vehicle #2) M1 = total weight of vehicle #1 M2 = total weight of vehicle #2 A1 = stiffness coefficient (vehicle #1) A2 = stiffness coefficient (vehicle #2) B1 = stiffness coefficient (vehicle #1) B2 = stiffness coefficient (vehicle #2) c1 = crush depth (vehicle #1) c2 = crush depth (vehicle #2) w1 = width of crush (vehicle #1) w2 = width of crush (vehicle #2) ΔV1 = delta-V (vehicle #1) ΔV2 = delta-V (vehicle #2)

(c )

STEP #5: Calculate the Delta-V for Each Vehicle: iscussion As mentioned earlier, the above theory can be expanded to include non-uniform crush profiles and varying Principal Directions Of Force (PDOF). For further details regarding the extrapolation of this theory to more complex cases, the reader is encouraged to see Grimes et al. (4). In this study, a more general derivation of the force balance technique is developed, along with the presentation of validation experiments.

Their results, based on vehicle-to-vehicle crash testing, confirmed the validity of the methodology, showing that the force balance method produces collision severity predictions within 10 – 12% of calculations based on conventional analyses. While the force balance methodology allows for solution of crush energy without inspection or crush measurements of one of the vehicles, the accuracy of these calculations are dependant on the accuracy of the crush measurements of the other vehicle, along with the stiffness data for both vehicles. Given this inherent sensitivity, it is advised that this reconstruction technique be attempted only when reasonably accurate input data are available.

D

R

eferences 1. Cutnell JD, Johnson KW: Physics, New York, NY, John Wiley & Sons, Inc., 2001

2.

Day TD, Hargens RL: An overview of the way EDCRASH computes delta-v. SAE 870045:183-198, 1987

3. Fricke LB: Traffic Accident Reconstruction, Evanston, IL, Northwestern Traffic Institute, 1990 4. Grimes WD, Heusser R, Hunter J, Neptune JA: Developing a crush profile estimate by balancing impact forces. SAE 970942:1-19, 1997 5. McHenry RR: Computer program for reconstruction of highway accidents. SAE International 730980:409-435, 1973 6. Robinette RD, Fay RJ, Paulsen RE: Delta-V: Basic concepts, computational methods and misunderstandings. SAE 940915: 1994

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

C

36 Collision www.collisionpublishing.com

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Keeping you current in

Covering GM, Ford & Chrysler Event Data Recorders

January 28-30, 2008 Houston, Texas

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Industry Experts, Fresh Topics in CDR

www.CrashConferences.com

(866) 223-4984 Collision

37

Analysis of Collisions

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Point Mass Mechanics and Planar Impact Mechanics

Raymond Brach

University of Notre Dame Brach Engineering, LLC

Matthew Brach

Brach Engineering, LLC

nalysis of Collisions, Part 1: Point Mass Mechanics Conservation of Linear Momentum: Suppose an intersection collision between two vehicles occurs (Figure 1) where the following are known or can reasonably be assumed to be true based on an investigation:

A

x12 + y12 p ro u a

G

x22 + y22

D at

= d2

c

(1)

and

In

= d1

00

7

C ra

sh

(2) 4. the frictional drag coefficients, f1 and f2, or their equivalent values, of the vehicles from impact to rest.

Note that Figure 1 shows two coordinate systems, x-y and n-t. The x-y system is one fixed to the ground or roadway. The n-t system is orientated along a common crush surface of the vehicles in their crash positions, referred to as the intervehicular crush surface. The angle between these coordinate systems is Γ.

The utility of this second coordinate system will become evident later.

Under such circumstances (and other conditions to be discussed later), the skid-to-stop formula can be used to provide the final collision speeds at separation, V1 and V2 (final impact

)2

I

1. the initial directions of motion of each vehicle at the beginning of contact, that is, angles θ1 and θ2, 2. the final directions of motion of each vehicle at separation from impact, that is, angles q1 and q2, 3. the travel distances, d1 and d2, from separation to rest of each vehicle, where

(c

ntroduction A method used frequently in the reconstruction of collisions has been given the name conservation of momentum. More specifically sometimes it is referred to as the conservation of linear momentum (COLM). This article discusses the assumptions behind COLM, how it is applied with the skid-tostop formula to reconstruct crashes and some problems that can arise if conservation of linear momentum is not applied carefully.

A more general form of COLM is presented including concepts of restitution, force, impulse and PDOF. Energy is discussed, particularly if energy is or is not conserved in a collision.

Part 2 of this article covers planar impact mechanics. This is a more general method of analyzing and reconstructing collisions that takes rotational velocities and rotational momentum of the vehicles into account. Comparisons of reconstruction calculations using planar impact mechanics are made to reconstruction calculations using point mass mechanics. Planar impact mechanics gives more accurate results since it is more rigorous. The improvement in accuracy is illustrated in the comparisons using examples where significant differences occur.

38 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

In c up ro G a at D sh 20

07

C

ra

46.6 ft/s (31.8 mph). Then the solutions (from Appendix A) of Eq 5 and 6 give v1 = 65.4 ft/s (44.6 mph) and v2 = 77.5 ft/s (52.8 mph).

(c )

Figure 1

Figure 2

velocity symbols are capitalized). That is:

Example 1: Suppose two vehicles collide in an intersection as shown in Fig 2 with Veh 1 originally eastbound and Veh 2 northbound. Both vehicles weigh 2500 lb. After impact the center of gravity of Veh 1 travels x1 = 42.0 ft and y1 = 52.0 ft to rest. The center of gravity of Veh 2 travels x2 = 32.0 ft and y2 = 36.0 ft to rest. From impact to rest, both vehicles remain on the same flat road surface with a frictional drag coefficient estimated to be f = 0.70.

The initial speeds of the vehicles can be found using Eq 3, 4, 5 and 6. First, Eq 1 and 2 give d1 = 66.84 ft and d2 = 48.17 ft.

Next, Eq 3 and 4 give V1 = 54.9 ft/s (37.4 mph) and V2 =

a

G

ro u

p

In

c

where V1n is the final velocity of Veh 1 in the direction of the normal coordinate, n, in Fig 1, V2n is the final velocity of Veh 2 in the direction of the normal coordinate, n, v1n is the initial velocity of Veh 1 in the direction of the normal coordinate, n, and v2n is the initial velocity of Veh 2 in the direction of the normal coordinate, n, in Fig 1. The numerator in Eq 7 represents the parting velocity (rebound velocity) and the denominator represents the closing velocity (or approach velocity). The negative sign comes into play because in an impact, the direction of the relative normal (perpendicular) velocity reverses as a result of the impact. All of the velocity components in Eq 7 are measured normal to a common intervehicular crush surface defined by the angle Γ as shown in Fig 1. For all point mass collisions (not just vehicle collisions), the coefficient of restitution is bounded, that is, 0 ≤ e ≤ 1. The common velocity condition (at the instant of separation) normal to the intervehicular crush surface means that e = 0. In words, this means that V1n = V2n and the vehicles do not bounce apart, or in more formal terms, the collision is perfectly inelastic.

For most high speed vehicle collisions, e typically is less than 0.3 [2] and, experimental data show that it is typically very close to zero.

Once the preimpact velocities of the vehicles are known, many more results from the example collision can be found from the mechanics equations of a point mass collision [2]. These results include the magnitude and directions of impulses, the collision

D at

Since most readers already are familiar with COLM, a typical application is presented using the skid-to-stop formulas (Eq 3 and 4) combined with the solution of the conservation of linear momentum (Eq 5 and 6).

(7)

sh

(6) Equations 5 and 6 are two linear algebraic equations in the unknown initial velocities, v1 and v2. They can be solved using methods of algebra; the solution is given in Appendix A (Eq A1 and A2).

V − V1n e = − 2n v2 n − v1n

C ra

(5) and from conservation of momentum in the y direction

7

(4) So at this point the final impact velocities, V1 and V2, are known. Knowing the final velocities, conservation of linear momentum can be used to compute the initial impact velocities, v1 and v2 (initial impact velocity symbols are lower case), of both vehicles. From conservation of momentum in the x direction:

00

V2 = 2 gf 2 d 2

)2

(3)

And

The equations from COLM and skid to stop can provide useful results but are only part of the information mechanics can provide.

When vehicles collide at high speeds (closing speeds of roughly 20 mph or more), they typically are momentarily “stuck together” at their contact surface at the instant of separation; this phenomenon is ordinarily referred to as the common velocity condition [1].

To determine if the solution of the above equations meets the common velocity condition, additional equations of mechanics must be developed. In particular, the concepts of restitution and relative sliding over the contact surface at separation are examined.

When studying collisions it is common to define what is called a coefficient of restitution, e, as

(c

V1 = 2 gf1 d1

Collision 39

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

kinetic energy loss, each vehicle’s ΔV, the PDOF for each vehicle, etc. The equations for such quantities are given in Appendix A. More is covered in what follows.

The assumptions that underlie the COLM and impact equations are very important and must always be checked to make sure they are satisfied for each application. The basic assumptions for point mass impact theory are [3]: 1. The impact represents a single dynamic contact, taking place over a short duration.

2. Forces other than the vehicle-to-vehicle contact force and impulses of forces other than the contact impulse are negligible.

3. Rotational motion (angular velocities) of the masses is negligible.

4. The initial velocities are known and final velocities are unknown (in some special cases the opposite can be true).

5. The deformation is localized and small compared to the size of the bodies (that is, the center of gravity location is not significantly changed by damage).

6. During the contact duration, position changes are negligibly small, velocity changes are instantaneous and accelerations are large.

7. The effects of the normal (crush) and tangential (sliding, shearing, entanglement, etc.) contact processes are known and are described by two impact coefficients.

8. The masses (weights) remain essentially constant.

In accident reconstruction, one of the most important assumptions is number 2. Forces such as the tire-ground forces must be small compared to the force acting over the intervehicular contact surface. This is why the impact equations should be applied to high speed collisions only. With lower contact forces between each vehicle, tire-road frictional forces can be significant for low speed collisions and their collisions must be treated in a different fashion [2].

The use of the skid-to-stop formula also involves assumptions.

One is that each of the vehicles travels from impact to rest with all wheels locked or, at least, with uniform deceleration. Another is that the change in heading of each vehicle (due to impact rotational velocity changes) has a negligible effect on the deceleration.

postimpact distance, or that two of its wheels were locked due to damage and the other two were free to roll, so that f1 = 0.56 instead of 0.70. For this alternative value of f1, the skid to stop equations give V1 = 49.28 ft/s (33.6 mph). The solution of Eq 5 and 6 now gives v1 = 61.9 ft/s (42.2 mph) and v2 = 73.1 ft/s (49.9 mph). More importantly, the coefficient of restitution, e, is equal to 0 and the results of the reconstruction become physically realistic.

In fact, the approach to the reconstruction that provided these new results was to find the value of f1 that gave a value of e = 0. This was done using the search/optimization feature of a spreadsheet. The full reconstruction results are illustrated in Fig 3. oint Mass Impact Mechanics: It was seen above that impact mechanics, even for point masses, is broader, or more general, than COLM. To gain a full understanding, some of the basic concepts of impact mechanics must be understood. Typically, the concept of a force is a beginning point. When two objects come into contact, each transmits an equal and opposite dynamic force, F, to the other (this follows from Newton’s Third Law). For an impact the contact force starts from zero (at the beginning of contact), reaches some peak value and then drops to zero when the bodies separate. The profile of such an intervehicular force is shown in Fig 3. The area under the force-time curve, shown shaded in Fig 4, is defined as the impulse and here is given the symbol, P. An impulse is an accumulation of the action of a force over time. If needed, an average value of the force can be found if the duration and impulse are known. For example, Fig 4 shows the average of that intervehicular force, Favg.

Newton’s Second Law can be stated in terms of impulses and

P

D at

a

G

ro u

p

In

c

Example 1 (continued): The coefficient of restitution for the collision of Example 1 was not needed in the solution of Eqs 5 and 6, but once the initial velocities are known it can be found. Its value can be calculated using Eq 7 and other equations from Appendix A. For a crush surface angle of Γ = 0̊ (see Figs 1 and 2) the coefficient of restitution is:

C ra 7 00 )2 (c

Since e must be greater than zero for realistic collisions, a negative value of e should alert the reconstructionist that something is amiss. A negative coefficient of restitution signifies that the vehicles passed through each other [4] which is physically impossible. At this point it is a good idea to check the assumptions. Perhaps, for example, the motion from impact to rest of one or both vehicles does not satisfy the locked-wheel assumption. This is implied by e being negative and Veh 1 seemingly passing through Veh 2 (see Fig 1).

Suppose the wheels of Veh 1 were not locked for the entire

sh

V − V1n 24.57 − 18.64 e= − 2n = − = −0.14 v2 n − v1n 43.21 − 0.0

Figure 4

40 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

Figure 3

Collision

41

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

where

m=

m1 m2 m1 + m2

v − v1t r = 2t v2 n − v1n

(13)

up

In c

(14) e is the coefficient of restitution and μ is referred to as the impulse ratio. It is equal to the ratio of the tangential impulse component and the normal impulse component:

(12)

Example 1 (continued): Some of the other features of the reconstructed collision can be examined. For example, using Eq 8 and 10 and values from Fig 3, the impulse components have the values:

Px =

2500 (30.95 − 61.90) = −2405.19, lb − s g

Py =

2500 (38.32 −= 0.0) 2977.93, lb − s g

In

c

which produces an impulse magnitude of P = 3827.93 lb-s.

In this example, the intervehicular contact surface is parallel to the y axis, the x-y and n-t axes are coincident and Γ = 0.

Consequently, Px = Pn and Py = Pt. In addition, using Eq 12, the kinetic energy loss is 178,102.7 ft-lb, which is 49.9% of the total initial kinetic energy of the vehicles. Since Px and Py are known, the PDOF of each vehicle can be determined.

The angle of the impulse is

p

(11) In Fig 5 the x-y coordinate system can be thought of as one attached to the ground (road), whereas, the n-t coordinate system can be thought of as one attached to a common crushed contact surface of the masses (vehicles). Using trigonometry and the angle Γ, Appendix A provides equations that permit the impulses to be expressed as components in the n-t coordinate system as well as components in the x-y system.

In a broad sense, energy in a collision is conserved. Some of the energy in a collision is converted to sound, some is converted to damage (crushing, displacing, scraping, gouging, sliding etc.) of the metal and plastic materials. Some energy even can be diverted into injuries of the occupants. But, to a reconstructionist, the most important aspect of collision energy is that in all vehicle collisions, some percentage of the combined initial kinetic energy of the two vehicles (the vehicle system kinetic energy) is lost. This kinetic energy loss can be calculated by computing the initial kinetic energy of both vehicles, computing the final kinetic energy of both vehicles and subtracting them. Another way is to use the equation from Appendix A:

Knowing α, the principal direction of force, PDOF, can be found [6].

ro u

m2V2 y − m2 v2 y = − Py

(17)

G

and

(10)

a = tan −1 ( Py / Px )

a

m1V1 y − m1v1 y = Py

Once P is found, the direction, α, of its line of action can be established using trigonometry from:

D at

(9) The same holds true for the y components, giving two more equations.

(16)

a = tan −1 ( Py / Px ) =tan −1 (−1.238) =128.9° sh

m2V2 x − m2 v2 x = − Px

Pn2 + Pt 2

C ra

(8) Recall that capital V is a symbol that represents a final impact velocity and lower-case v is a symbol that represents an initial impact velocity. Because of the equal and opposite nature of forces (and impulses), a similar equation can be written for m2 , namely:

Px2 + Py2 =

This means that pdof1 = 51.1̊ and pdof2 = -38.9̊.

Additional equations can be written, more examples can be worked, but at some point, a very important question must be asked. Is point mass mechanics the best way to model or analyze a collision? In other words, is there a better, more accurate method?

The answer to the second question is yes. A method called planar impact mechanics is available [7, 8, 9] that can model collisions, including the effects of rotational momentum. Surprisingly, the application of the method isn’t any more difficult than point mass mechanics. An explanation of planar impact mechanics follows in Part 2.

7

m1V1x − m1v1x = Px

P=

00

(c )

20

changes in momentum [5]. For example, from Fig 5, the impulse component, Px, in the x direction is equal to the change in momentum of mass, m1, in the x direction. In mathematical form, this is:

)2

07

C

ra

Figure 5

The quantity μ is sort of an equivalent impulse friction coefficient, but has some important differences from a friction (force) coefficient [2]. The total impulse, P, can be found from its components:

(c

sh

D

at

a

G

ro

(15)

42 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

nalysis of Collisions, Part 2: Planar Impact Mechanics The words planar impact mechanics refer to the analysis of the mechanics (motion and forces) of an impact between two rigid bodies that takes place in a plane. Figure 6 shows two rigid bodies (vehicles) in contact and with a common point C. It shows them separated to display the physical action of each on the other. The term rigid body does not imply that the bodies are not deformable, but rather that they are not point masses; their mass extends beyond their centers of gravity. In other words they possess a moment of inertia. In this case, each moment of inertia is about a vertical axis through the center of gravity and corresponds to rotational motion referred to as yaw rotation. By methodically applying Newton’s Second Law in the form of impulse and momentum, a set of impact equations can be developed that can be used to analyze a vehicle collision taking into account the change in yaw velocity due to the impact.

What is remarkable about these equations is that they can be solved using algebra, that is without resorting to a computer. But more on this later.

In this Part of the article, only the collision is analyzed.

Since postimpact motion of vehicles in actual practice seldom takes placed under uniformly locked wheel conditions, the motion following the collision typically is analyzed separately from the collision using a computerized vehicle dynamic simulation program [9, 10, 11, 12].

The assumptions that underlie planar impact mechanics are identical to those for the point mass impact mechanics with one exception. For planar impact mechanics, Assumption 3 (given above for point mass mechanics) concerning rotational motion (angular velocities) is dropped.

As in Part 1, the impact problem is treated as one where the initial velocities are known and the final values are to be computed.

m1 (V1n − v1n ) = Pn

(18)

m1 (V1t − v1t ) = Pt

(19)

I1 (Ω1 − w= d c Pn − d d Pt 1)

(20)

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

A

The initial velocities are v1x, v1y, ω1, v2x, v2y and ω2. The final velocities are V1x, V1y, Ω1, V2x, V2y and Ω2. Accident reconstructionists would usually like to be able to solve the impact problem the opposite way (determine the initial velocities that cause certain final velocities). Unfortunately, the mathematics will not allow that [4]. To set up the proper equations including the effects of rotation, it is necessary to define a common point C located on the intervehicular crush surface (see Fig 6) called the impact center. Point C is the point of action of the impulse, P. It lies on the contact surface and its location is estimated from viewing the damage to the vehicles. Point C is the point through which the PDOF acts. It is specified (located) by the distances d1, and d2 and the angles ϕ1 and ϕ2 relative to the centers of gravity of the vehicles (see Fig 6).

The heading angle of each vehicle during impact relative to the x-y coordinate system is given by θ1 and θ2, respectively, for vehicle 1 and vehicle 2. These angles are not exactly the same as the initial directions of motion as in the point impact case covered in Part 1.

This is because, each vehicle can have an initial angular velocity, ω, and could even be sliding sideways (although typically this is not the case).

As in Part 1, Newton’s Second law in the form of impulse and momentum can be applied [5]. A change in rotational momentum for each vehicle must now be included. This is done here using n-t-θ coordinates (rather than x-y-θ) for convenience. Applying Newton’s law for each coordinate and for each vehicle gives 6 total impulse and momentum equations. These are:

Figure 6 Collision

43

m2 (V2 n − v2 n ) = − Pn

(21)

m2 (V2t − v2t ) = − Pt

(22)

I 2 (Ω 2 − w= d a Pn − db Pt 2)

(23)

Figure 7

20

07

C

ra

sh

D

at

a

G

ro

up

In c

As before, capital symbols represent final values and lower case symbols represent initial values; this notation includes the rotational velocity symbols, Ω and ω. The velocity components v1n, v1t, v2n, v2t, V1n, V1t, V2n, and V2t are those of the center of mass of the vehicles. The distances da, db, dc and dd are defined in Appendix B. There are 6 unknown final velocity components, V1n, V1t, Ω1, V2n, V2t and Ω2. The impulse components, Pn and Pt, also are unknown. This means there are 8 unknowns and 6 equations.

Two more equations are needed. Two impact coefficients can be defined as was done in the point mass problem. The coefficient of restitution is:

is known. This includes the collision kinetic energy loss, the velocity change, ΔV, of each vehicle, the PDOF of each vehicle and so on.

Equations 18 through 25 form a set of linear algebraic equations in the 8 unknowns. A remarkable feature of these equations is that their solutions can be stated without the use of a computer [2]. The solution equations are:

V1n =v1n + m(1 + e)vrn q / m1 V1t = v1t + mm(1 + e)vrn q / m1 V2 n = v2 n − m(1 + e)vrn q / m2 V2t = v2t − mm(1 + e)vrn q / m2

(26) 27) (28)

Ω1 = w1 + m(1 + e)vrn (d c − md d )q / I1

(29) (30)

Ω 2 = w2 + m(1 + e)vrn (d a − mdb )q / I 2

Other variables, such as q, are given in Appendix B. All of this means that given the initial velocities of any two vehicles’ physical properties (their masses, yaw inertias and dimensions), their collision configurations, their damage profiles (to determine Point C and the angle Γ), their impact coefficients (e and μ) and their initial velocities that their final velocities can be calculated.

Once a solution is obtained, all of the mechanics of the collision

D at

sh

7

00

)2

(32)

(c

vrn = (v2 n − d aw2 ) − (v1n − d cw1 )

C ra

The quantity vrn is the closing velocity which now depends also on the initial angular velocity:

a

G

(31)

Figure 8 contains a spreadsheet version of the solution equations of planar impact mechanics (Eq 27 - 32) for these input values. Table 1 compares point mass results with the planar impact mechanics results in Fig 8. Relatively large differences occur in many of the final quantities. In particular, the final angular velocities from the planar impact mechanics solution are significant, but ignored in the point mass solution. A large difference exists in the kinetic energy loss. This difference is due, in part, to neglecting the rotational kinetic energy in the point mass solution, and also due to the decrease in the tangential impulse when the freedom to rotate exists. The ΔV values are lower from the planar impact mechanics solution and the PDOFs are changed significantly. The accuracy of these quantities is important when assessing injury potential and when using the ΔV values of an EDR in a reconstruction.

c

(25)

Example 1 (revisited): Consider again the above example where an eastbound vehicle collides into the driver’s side of a northbound vehicle (Fig 7). A new analysis is made here using planar impact mechanics that includes rotational effects. To facilitate a later comparison, the initial velocities found from the point mass analysis are used as the initial conditions along with common velocity conditions. The final velocities, impact kinetic energy loss and vehicle ΔV values from the point mass solution and the planar impact mechanics solutions will be compared. Point C in Fig 7 is an estimate of the impact center.

As determined from the vehicle dimensions and crush, d1 = 7.1 ft and d2 = 2.6 ft. The crush surface and impact configuration give Γ = 0̊. Based on the diagram in Fig 5 and Fig 7, ϕ1 = 0̊ and ϕ2 = 90̊. The orientations of the vehicles at impact determine that θ1 = 180̊ and θ2 = 90̊. The yaw moments of inertia are I1 = I2 = 1575 ft-lb-s2. The initial velocities are: v1n = 61.9 ft/s, v2n = 0.0 ft/s, v1t = 0.0 ft/s and v2t = 73.1 ft/s. Based on information from the accident investigation, it is assumed any initial yaw velocity is small, so that ω1 = ω2 = 0.

In

where VCrn is the normal component of the rebound velocity at point C and vCrn is the normal component of the closing velocity at point C (these are expressed more fully in Appendix B). The second impact coefficient is the ratio of impulses,

p

(24)

ro u

(c )

V e = − Crn vCrn

Example 2: Consider an example identical to the Example 1 except where the impact center is now over the driver’s side rear wheel of Veh 2 as shown in Fig 9. All other conditions

44 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

Vin, ft/s Vit, ft/s V2n, ft/s V2t, ft/s Ω1, deg/s Ω2, deg/s KEloss, ft-lb ΔV1, ft/s ΔV2, ft/s Pn, lb-s Pt, lb-s pdof1, deg 51.1 pdof2, deg -38.9

Point Mass Solution Example 1 30.95 38.32 30.95 34.81 178103 (50%) 49.3 49.3 -2404 3318 26.1 -63.9

Planar Impact Mechanics Solutions Example 1 Example 2 30.95 49.17 15.17 13.25 30.95 12.73 57.97 59.89 304.5 265.9 111.5 323.3 117555 (33%) 68257 (19.1%) 34.5 18.4 34.5 18.4 -2401 -969 1179 1029 46.1 -43.9

Table 1

C ra

sh

D at

a

G

ro u

p

In

c

Figure 9

7

C

00

onclusions It is clear from the above examples that not only are rotations important, but that the effects of an offset in the vehicle alignment (as well as angular alignments) in a collision can be significant. A point mass reconstruction of a collision simply is incapable of making any such distinctions and can produce results that are considerably different from an actual collision. A reconstructionist must be very careful when applying various methods based on the assumptions that underlie the method. A reconstructionist must also be very careful when choosing software and making claims about a reconstruction. If the software being used to analyze and reconstruct a collision does not take rotation into account, it should be used only under strict adherence to all of the assumptions that govern point mass collisions.

When an impact center, Point C, is located and the angle, Γ, of the crush surface is determined, the planar impact mechanics solution automatically determines the PDOF of each vehicle.

The importance of these angles has increased in the advent of Event Data Recorders (EDR). Typically the output from an EDR includes the ΔVEDR value of a vehicle for a collision. Currently, this value is obtained by integration of an accelerometer signal where the accelerometer axis is coincident (aligned) with the heading axis of the vehicle. This means that the ΔVEDR value is not the total vehicle change in speed, ΔVVEH, but rather its component along the heading axis. This means that

rotational effects be assessed prior to analysis? Since planar impact mechanics is relatively easy to apply, use both and compare. On the other hand, since planar impact mechanics is easy to apply, it should always be used.

)2

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Results of the planar impact mechanics analysis for this example are shown in Fig 10. Some important results are included in Table 1 for comparison to previous results. Comparison between the planar impact mechanics analysis results from Example 1 with Example 2 shows significant differences. These differences are most evident in the collision kinetic energy loss and the ΔV values but also show up in some of the final velocities and PDOF vales as well. Conceivably, the collision in Fig 9 could be analyzed or reconstructed using point mass mechanics. In that case, it is legitimate to compare the results of the point mass solution of Example 1 to the planar impact mechanics results of Example 2. Table 1 shows again that the differences are dramatic. Among other differences, the point mass ΔV values change from 49.3 mph to 18.4 mph and the point mass energy loss changes from 50% to 19%.

Table 1. Comparison of results for Example 1 from the Point Mass Solution and the Planar Impact Mechanics Solution v1 = 61.90 ft/s, v2 = 73.13 ft/s

(c

are the same as the last part of Example 1. Here, d2 and ϕ2 are different from above and are 6.9 ft and 159.4̊, respectively.

∆VEDR = ∆VVEH cos( PDOF )

(33) This relationship can be useful in reconstructing accidents when an EDR record is available for one or both vehicles.

COLM should not be used to analyze a collision whenever rotational effects are significant. How can the significance of Collision

45

In c up ro G a at D sh ra C 07 20

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

(c )

Figure 8 46 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

Figure 10

Collision

47

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

eferences: 1. DOT HS 805 732, CRASH3 User’s Guide and Technical Manual, US Department of Transportation, February, 1981.

R

2. Brach, Raymond and Matthew Brach, Vehicle Accident Analysis and Reconstruction Methods, SAE, Warrendale, PA, 2005.

3. SAE seminar C-0416, Vehicle Accident Reconstruction Methods, SAE, Warrendale, PA. 4. Brach, R. M., Mechanical Impact Dynamics, Wiley Interscience, New York, 1991.

up

In c

5. Beer, F. P. and E. R. Johnson, Vector Mechanics for Engineers, McGraw-Hill Book Company, New York, NY, 1962.

a

G

ro

6. Russell, C. G., “PDOF, Principal Direction of Force”, Collision Magazine, Vol 1, Issue 2, 2006.

sh

D

at

7. Brach, R. M., “Impact Analysis of Two-Vehicle Collisions”, Paper 830468, SAE, Warrendale, PA, 1987.

20

07

C

ra

8. Woolley, R. L., “The ‘IMPAC’ Program for Collision Analysis”, Paper 8700476, SAE, Warrendale, PA, 1987.

(c )

9. Steffan, H. and A. Moser, “The Collision and Trajectory Models of Pc-Crash”, Paper 960886, SAE, Warrendale, PA, 1996 10. Day, T., “An Overview of the EDSMAC4 Collision Simulation Model”, Paper 1999-01-0102, SAE, Warrendale, PA, 1995.

11.McHenry, B. G. and R. R. McHenry, “SMAC-87,” Paper 880227, SAE, Warrendale, PA, 1988 12. Brach, R. M., “VCRware, A Suite of Spreadsheets for Vehicle Crash Reconstruction”, CRASH 2005, Human Subjects Crash Testing and Scientific Conference, Spine Research Institute of San Diego , San Diego, CA, 2005.

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Appendix A, Solution of Equations 5 and 6 and Other Point Mass Solution Equations:

48 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

Collision

49

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

In c up ro G a at D sh ra C 07 20 (c )

DBD Crush Deformation Jig

By WeCARE Products and Education

In

c

Simplify your crush deformation measurements with the sturdy, freestanding, portable DBD Crush Jig.

)2

00

7

C ra

sh

D at

a

G

ro u

p

Outstanding demonstrative evidence.

Rugged canvas carrying case Fits in standard car trunk Weighs only 20 pounds $599.00 plus CA sales tax, plus shipping and handling. (c

For information, other products and orders, see our Website or phone (916) 782-4654 or fax (916) 782-4878 or mail to: 228 Pleasant Street Roseville, CA 95678

E-mail to: WeCARE@rudydegger.com

http://www.rudydegger.com/WeCARE

See class schedule for “Speed Determination from Crush Analysis” class.

50 Collision www.collisionpublishing.com Collision www.collisionpublishing.com

WITH YOUR CAMERA and PHOTOMODELER

®

a

G

ro

up

In c

* R a p id e v id e n c e c o lle c t io n t o c le a r s c e n e s mo r e q u ic k ly * Cr e a t e 2 d / 3 d mo d e ls o f n e w o r d a ma g e d v e h ic le s * Cr e a t e a c c u r a t e d ia g r a ms o f c o llis io n s c e n e s * P r e s e n t y o u r r e s u lt s in c o u r t

sh

D

at

PhotoModeler is the accepted and proven choice for close-range photogrammetry.

(c )

20

07

C

ra

- Over 16 years of development (est. 1990) - Large customer base in the U.S. and worldwide - The proven choice for police department implementations - The established solution for forensic, engineering and reconstruction firms

- Quick access to phone and email support - Top-rated training by professional reconstructionists

In

c

Some of the features that help you get the job done easier and faster: - Fully integrated support for digital and film cameras - Export your diagrams to your favorite CAD or drawing tool (11 different export formats) - Inverse Camera for working with photographs from unknown film or digital cameras - Excellent tools for review and feedback of project quality - Fully automated camera calibration when high accuracy is required - Full support for control points from total station measurements for refinement, stabilization, resection or coordinate matching - Extract photographic texture for realistic 3D models - ‘Project Merge’ for generating scenes over large distances - Support for single photograph projects - great for forensics - Fully integrated ortho-photos for that "birds-eye" view of your scene - Model with curves and curved surfaces for added realism h - Draw on your surfaces from a single photo to add detail to important rap g o ot scenes easily and quickly ph .

- New Offset Points feature - great for evidence marker use 1

New Version 6 and New Website!

7

re &

00

su

)2

Visit www.photomodeler.com to get a free evaluation copy and to see a full list of capabilities including all the new version 6 features.

me a

ex

(c

3.

C ra

sh

D at

a

G

ro u

p

2. photomodeler

po

rt

Eos Systems Inc. www.photomodeler.com 604.732.6658 Collision

51

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

Carrying out a high-speed crash test for the Dutch police

By Wolfram Kalthoff, Ralf Bührmann, Eckhard Meyer* For the Field Day of the Dutch police at their training center (Verkeersveiligheidscentrum) in Lelystadt, Netherlands, a crash test at over 100 kph was carried out with the aid of innovative technology. Why and how the crash was carried out and the results are detailed in the article that follows. [1]

ntroduction The Dutch police is responsible for the recording of traffic accidents and in part the reconstruction of them for use in criminal proceedings. Each region of the Netherlands has a team of police officers specially trained for this purpose (VOA: Verkeers Ongevallen Analyse).To expand on the required know-how for accident reconstruction the AVOA (Adviesgroep Verkeers Ongevallen Analyse) holds an annual Field Day on the police training school grounds in Lelystadt, NL. Test execution, as well as the exchange of experience is the centre point of these occasions. These tests cover matters that arise in everyday police work and are hence of great practical relevance. In 2004, for example, drift and skid marks were dealt with, including those that arise despite the use of modern stability systems such as ESP, and how to deduce the speeds involved from such evidence.

p

In

c

I

D at

sh

C ra

7

00

)2

F

To demonstrate this fend-off position in practice, a test was carried out which was designed to simulate a car colliding at high speed with a police vehicle positioned according to the rules.

3 Test site The training grounds in Lelystadt offer ideal conditions for such a crash test. The grounds are used as a centre for traffic and driving safety training. The approximately thirty hectare large facility includes not only circuits but a building with conference rooms. It is mainly used by the police but sometimes rented out to others interested parties. There is a circuit of about 2.5 km in length, a motorcycle training area, an 80 x 8 metres smooth traffic lane for skid testing and an off-road area. The grounds also include an 80 x 300 metre tarmac area for use as an acceleration lane for this crash test and provides unrestricted deceleration space (see illustration 3).

(c

end-off Position Apart from deducing speed from such evidence a further subject relevant to the police was dealt with in 2005. Under the Dutch police’s safety rules in the event of a traffic accident on a motorway or main road the first police vehicle arriving at the scene of the accident must be used to shield the accident scene. To do so it must be parked 100 metres away at an angle with the front wheels facing in the direction of moving traffic, the hand brake on and the gear lever in the neutral position (“Fend-off Position“, see illustrations 1 & 2) [2]. The vehicle’s engine should be left running so that operation of the blue light can be ensured over a long period.

a

G

ro u

Illustration 1: Safety distance [2]

52 Collision www.collisionpublishing.com

In c up ro G (c )

20

07

C

ra

sh

D

at

a

Illustration 2: Fend-off position [2]

Illustration 3: Aerial view of the Dutch police training school grounds

est performance and results In this case an Opel Omega collided at a 30° angle with a stationary Peugeot 306 Break. The collision speed of the remotely controlled Opel was 107.1 kph. Illustrations 5 to 8 show the vehicles after the crash.

00

7

C ra

sh

D at

a

G

ro u

p

In

c

T

)2

T

cylinder is via a membrane pressure controller.

To prevent any uncontrolled vehicle movement the system is so designed that if remote control reception fails the steering reverts to the center, the accelerator is released and the car is braked to a halt (“fail-safe“).

(c

est technology To carry out the test at the planned high speed without having the use of any permanently installed crash facility the test vehicle used was remotely controlled. Driving instructions were transmitted from a vehicle driving immediately behind it. The remote control system was based on the NAVIP system as developed by Priester &Weyde [4] built and tested during a practical training course [5] The system’s development is the subject of a new study [6]. That system as described here was used for this test for the first time. Afterwards tests have been conducted with that remote control versus guard rails with speeds up to 185 kph. The equipment used afforded a time saving installation into and removal from the crash vehicle. The system is independent of the vehicle type used, does not hinder airbag operation and makes it possible to position a dummy on the driver’s seat. After a crash test the equipment can be repaired or replicated.

In the remotely controlled vehicle - a powerful car with an automatic gearbox - there’s a transceiver that transmits the signals received to various servomotors. Each adjustable device has two servomotors for safety reasons and in order to apply greater force. A servo motor pair operates the accelerator, allowing finely adjustable vehicle acceleration. Two more servomotors transmit steering commands to the steering wheel, angles of up to ± 20° can be set using them. This range is sufficient to move the car in a straight line and keep it straight (see Illustration 4).

The brake pedal cannot be controlled via servomotors, as the force required to do so is too great. A pneumatic system is therefore used. A dual-effect universal cylinder is controlled via a proportional pressure regulator using air from a pressurised tank in this system. The pressure regulator is controlled via a servomotor pair linked by a gear wheel system. Quick complete reversal of the

Illustration 4: Installation of test technology in the crash-initiating vehicle grounds

Collision

53

54 Collision www.collisionpublishing.com

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

Collision

55

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

In c up ro G a at D sh ra C 07 20 (c )

Both cars were equipped with accident data recorders (UDS). The velocity changes due to the accident could then be calculated based on the acceleration history recorded. The Opel Omega was slowed 43.1 kph longitudinally. The Peugeot 306 suffered a longitudinal change in velocity due to the crash of 48.9 kph and of 46.3 kph laterally (resultant 67.3 kph). Illustrations 9 to 18 show vehicle movement during and after the crash. It can be seen post crash that both vehicles were turned pronouncedly.

Due to the angled position of the test vehicles, in particular during the initial point of impact a exchange of force was exerted on the rear of the vehicle including the rear axle of the Peugeot. The impact momentum on the Peugeot was exerted eccentrically. A result hereof was a considerable clockwise turning of this vehicle around its vertical axis. The Opel initially impacted eccentrically and turned counter-clockwise around its vertical axis. The Peugeot came to a standstill after about 45 metres. The prescribed gap of 100 m would hence have sufficed in this case. The Opel, by contrast, performed a circular arc. Had the crash happened on a motorway on the left-hand lane the Opel would have been pushed into the central reservation rail. ummary This article documents a crash test simulating a car crashing into a stationary police vehicle on a motorway.

The high speed was 107 kph in this test which is realistic for Dutch motorways. The high-speed test was made possible by using a remotely controlled vehicle. The test showed that the distance as stipulated by the authorities of 100 metres between a deliberately positioned police car and an accident is reasonable and sensible in this speed range. It also made clear that both vehicles would turn about their vertical axes in any such accident. With the aid of further crash tests the fend-off position can be optimised for maximum effectiveness in as many different accident angle configurations as possible.

S Illustrations 5 & 6.: Peugeot 306

ibliography Kalthoff, W.; Bührmann, R.; Meyer, E.: Kollisionsversuch im Hochgeschwindigkeitsbereich. Verkehrsunfall und Fahrzeugtechnik, 6|2006, Juni 2006, 44.Jahrgang, Vieweg Verlag / GWV Fachverlage GmbH, Wiesbaden “Richtlijn Eerste Veiligheidsmaatregelen bij Incidenten op auto(snel)wegen“, Verkeerscentrum Nederland Incident Management, 9/2004, brochure. http://www.politieacademie.nl/Data/Html/frameset.html; 01/11/06 Ing.-Buero Priester & Weyde; Saarbruecken, Berlin, Michendorf; www.unfallgutachter.de Hanert, Karsten: Praktikumsbericht NAVIP, FHTW Berlin, July 2003 Meyer, Eckhard: Erprobung und Weiterentwicklung einer Funkfernsteueranlage zur Durchführung von Crashversuchen, Studienarbeit, FH Osnabrück, March 2006

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

B

Illustrations 7 &. 8.: Opel Omega

Authors Eng. Wolfram Kalthoff, Eng. Ralf Bührmann, Cand.-Eng. Eckhard Meyer c/o crashtest-service.com, Münsterstrasse 101, 48155 Münster, Germany www.crashtest-service.com

56 Collision www.collisionpublishing.com

C

������������������������������� � �

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

������������������������������������������������

�� ������������������ �� ���������������������������������������� �� �������������������������������������������������������������������������������������������� �� �������������������������������������������������������������������������������������������������������� c

�� ������������������������������������ ro u

p

In

�� ���������������������������������������������������������������������������

sh

D at

a

G

�� ������������������������������������������������� � �����������������������������������������������������������������

(c

������������������������� ��������

)2

00

7

C ra

��� �����������������������������������������������������������������������������������������������������

���������������������������� © 2007 MicroSurvey Software Inc. MapScenes® is Registered with the U.S. Patent and Trademark Office by MicroSurvey Software Inc.

Collision

57

20

07

C

ra

sh

D

at

a

G

ro

up

In c

��������� (c )

�������������� ��������������� ������������������������� ���������������������������� ���������

��������������������� �������������������������� ������������������������ ������������������������ ������������������������� ����������������������� ������������

�����������������������

G

ro u

p

In

c

���������� ������������������������ �������������������������������������� ����������������������������������� ��������������������������������������� �������������������������������������� ���������������������������������������� �������������

(c

)2

00

7

C ra

sh

D at

a

��������� �������������������� ��������������������������������������� ������������������������������������ ��������������������������������������� ��������������

����������������������������

58 Collision www.collisionpublishing.com

�

�����������������������������

20

07

C

ra

sh

D

at

a

G

ro

up

In c

�����������������������������������������������������������

(c )

����������������������������� ������������������������������������������������������ ������������������������������������������������������� ��������������������������������������������������������� ���������������������������������������������������������

G

ro u

p

In

c

������������������������������������������������������ �������������������������������������������������������� ����������������������������������������������������������� ����������

(c

)2

00

7

C ra

sh

D at

a

���������������������������������������������������� �������������������������

Collision © 2007 MicroSurvey Software Inc. MapScenes® is Registered with the U.S. Patent and Trademark Office by MicroSurvey Software Inc.

59

In c

The Rest of the Family

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

Power Tools for the Demanding Professional ����������������������������������������� �����������������������������������������������

�������������������

����������������������������������������� �������������������������������������� ���������������������������������������� �����������

�������������������������������������� ��������������� ������������������������������������������ �������������������������������

c

������������������������������ ��������������������������

In

��������������������������������������

����������������������������������

p

�����������

This desktop forensic mapping software is the most precise available in the world. Feature rich, it enables you to have complete confidence in the evidence you present. For Accident Reconstruction Specialists and Law Enforcement Professionals, no other product offers more precision, flexibility, or drawing power. A few of the many new features in 2008:

�����������

ro u

��������������������������������� ������������������������������������

This is the latest version of our bestselling evidence collection software.

Collect evidence at the scene with unparalleled levels of ease and precision. Evidence Recorder enables you to review all collected evidence in real-time to ensure it is correct and complete. Some of the reasons why Evidence Recorder is the industry standard:

���������������������������������������� �������������������������������������� ������������������������

G

The Tracker Xtreme is the only purpose-built data collector on the market today for the professional investigator. This power tool makes evidence collection fast and accurate in all weather conditions. Here is why the Xtreme is the best:

D at

a

����������������������������������������� ��������������� �������������������������������������������� ����������

�������������������������������������� �������������������������������������������

sh

C ra

7

00 )2 (c

��������������������������������������� ��������������������������������������� ��������

��������������������������������������� ���������������������������������� ����������������������������������� �������������������������������������� ����������������������������������� ����������������

���������������������������������� ��������������������������������������������������������� �������������������������������������������������

800.668.3312 | mapscenes.com

60 Collision www.collisionpublishing.com

��������������������������������������������������������������������������������������������������������������������������������

at

a

G

ro

up

In c

Case Study Solution

(c )

20

07

C

ra

sh

D

- Rusty Haight

c

In

p

ro u

G

a

D at

sh

C ra

7

S

S

00

olution, Problem #1 The solution here is far simpler than a lengthy evaluation of the crash data, it’s really all about an analysis of the values reported. As the problem states, if we assume the data in this head on crash is reliable as it is presented, we’re left with an understanding that the vehicle’s speed at about impact is 35mph and as a function of the crash it has changed speed by -37.7 (let’s round to 38 for simplicity here) mph.

As we examine the data, we recognize that, since this is a head on crash, we may ignore the impact (pun intended) of an off axis impulse. That simplifies the analysis. What we’re left with then is a relatively simple vector analysis. (Elsewhere in this issue of Collision we see the articles by Schmidt and Brach that describe in great detail momentum analysis and those might well be of some assistance here.) This particular case problem is; however, fairly simple.

For this problem, w can apply the vector equation that describes delta-V: delta-V = Vfinal - Vinitial. But here, we know the delta-V and Vfinal which means we have to rearrange that model to read Vfinal = Vinitial - delta-V. So here, we can solve for the after impact velocity by applying the provided information as: Vfinal = 35mph - 38mph which means the post impact velocity (and here the polarity is important) -3mph. THAT means, the car is “backing” at about 3 (some rounding here) mph after impact. “Backing,” relative to the car’s normal “x” axis (see SAE J211) means, as a vector, we would describe the post speed as -3 mph. An answer of simply “3 mph” (without proper polarity) is wrong.

It doesn’t describe the direction. The value of -3mph (negative relative to the “x” axis) would be necessary to make “3mph” the correct answer as a vector: direction AND magnitude.

This crash comes from a full frontal barrier crash test.

The car is propelled into the barrier at 35mph and, after impact, rebounds at about -3 (rounding again, work with it...) mph. Had we been required to deal with redirection the model shown would

olution, Problem #2 The question here is, what was the delta-V at about the time the deployment was commanded? While a lot of the other information included in the case problem description doesn’t help us directly answer the underlying question, the volume and meaning of the of data does. Here, we see 150ms of delta-V data suggesting a specific type of airbag control and a specific recording methodology/system in the SDM line: a module that records for a specific period after a deployment is commanded.

The frequently “confusing” part of the downloaded data is that the “10ms” data point shows an apparent delta-V so “high” (relatively speaking) that if we take it on face value it might suggest that the deployment should have occurred far earlier than the reported point some 190ms into the event. At the “10ms” data point, the delta-V reported is -11mph (rounding again). While we know that delta-V is not “the” actual criteria used to deploy airbags, the change in acceleration required to get from no change to a change of -11mph in 10ms has got to be sufficient to deploy airbags. This should cause us pause but for the realization that this module is one that records delta-V in a specific way.

But the reality here is that the “100 after and up to 50 before” rule applies. This module is one that has a programmed runtime to capture 100 ms of delta-V data after a deployment is commanded and then store whatever is in RAM for the period before the deployment is commanded.

In this case then, since we have data running out to what is marked as “150ms,” we know that deployment was commanded at 190ms into the event, and we know that the system reports 100ms of delta-V data after the deployment is commanded, if we review the delta-V data table, the deployment would have been commanded in the “50ms window” of that data.

Looking at the table (p26), the cumulative delta-V at that point would be -17.65 (round to -18) mph. So the answer to the question “what was the delta-V at about the time the deployment was commanded?” would be “about -17 to -18 mph.”

)2

T

still apply because we’re specifying vectors: magnitude (some number of mph in this case) and direction...vectors. The solution here is that the car was “backing” at 3mph (-3mph) post impact.

(c

he solutions to this issues case problems all come from topics covered in the current Vetronix approved CDR Data Analyst Certification course or they may be deduced as a function of an understanding of some fundamental reconstruction topics. There are no “trick questions” here, just a requirement to understand fundamental concepts.

C Collision

61

In c

Terry D. Lewis

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

rn u T e y “M t Th l” A ee h W

THE FUTURE OF ACCIDENT RECONSTRUCTION

c

In

p

ro u

G

a

D at

sh

C ra

7

00

)2

T

accidents. In order for the officials in the FMCSA to keep their jobs, and the FMCSA itself to continue to exist, they need to produce results. The major variable in this endeavor is the continued advancement and mandatory installation of the new EDR technology. The FMCSA has enlisted the assistance of the NHTSA and other federal agencies, which basically are in the same situation with light duty motor vehicles.

The FMCSA is also enlisting the assistance of the owners of large semi tractor trailer fleets, taxi cab companies, large commercial bus companies, and many other types of trucking companies that would benefit from EDR devices, by being able to monitor their employees’ driving habits and obtain documentation for potential disciplinary action. This could also motivate better employee driving habits, resulting in less abuse of company equipment, and fewer traffic accidents. This obviously would be of significant monetary benefit to trucking company owners.

The insurance industry could save hundreds of millions of dollars in reduced operating expenses, quicker settlement of injury accident claims, and drastically reduce fraudulent claims. The insurance industry is strongly motivated to join the FMCSA and the NHTSA in promoting the development of these new EDR technologies simply based on the potential for huge financial gains.

Law enforcement would be behind this new EDR technology if it only helped in traffic law enforcement and the NHTSA projects it will significantly reduce traffic accident injuries and deaths. Yet, with 35 million traffic accidents occurring annually, the accurate, unbiased analysis of traffic accident causation would also greatly assist law enforcement and the courts. In the analysis of accident causation, much is dependant upon the efficiency of the investigating police officer in documenting the physical evi-

(c

he traditional methods of traffic accident reconstruction are rapidly heading toward obsolescence. The new computer generated technologies are changing the manner in which future accident causation will be established. With the new motor vehicle’s computer regulated engine control modules expanding their parameters with the rate of advancing computer technology, the courts beginning to accept this information, and government agencies and big business promoting it, the manner in which future accident causation is established is definitely going to change, and not in the distant future.

This evolution began with the advent of antilock braking systems that do not leave skid marks, the rapidly evolving development of the engine control modules, and the recording capacities of the event data recorder (EDR). Although this EDR data is not currently mandated by the U.S. Government, motor vehicle manufacturers are voluntarily installing EDR’s in newly manufactured vehicles. The National Highway Traffic Safety Administration (NHTSA) has proposed, beginning in September 2008, that EDR’s record a minimum set of 42 specific data elements, useful in crash investigation and driver safety. These devices would be required to record a vehicle’s speed, seat belt use, brake application, and much more, for up to 5 seconds before impact, in all newly manufactured light duty vehicles.

The Federal Motor Carriers Safety Administration (FMCSA) is the newer government agency that is responsible for the safe operation of commercial motor vehicles used in interstate commerce on our nation’s highways. Officials within the FMCSA have indicated they will reduce the number of fatalities in truck accidents by 50% by the year 2010. That new computer technology holds the key to reducing both the number and severity of truck

62 Collision www.collisionpublishing.com

00

7

C ra

sh

D at

a

G

ro u

p

In

c

tion function on the captured signal, while transferring it to a persistent memory device. To verify that the data has not been tampered with, the stored data is operated on by the same validation function. The audit validation value is compared and the outcome of the comparison is indicated.

The microprocessor receives and captures this data in a readily readable form during a time period, and makes it available from an output port.

Larry Frankel of the American Civil Liberties Union has indicated that EDR’s have beneficial uses, but have a potential to invade our privacy in a very sophisticated manner. The legislation should clearly address the question of ownership of this EDR data, and who has the right to access it. Advancing technology will almost inevitably produce a system that can record video of the driver and conversation inside a vehicle. Unless legislation makes it clear who owns the data, and who has access, the courts will be required to make that decision.

Some of the obstacles facing future EDR data cannot be assessed at this time. Future political considerations could result in legislation restricting EDR access.

Future court decisions could be challenged on the basis of civil rights issues stemming from the U. S. Constitution’s 5th Amendment. The U.S. Supreme Court might rule that no person “shall be compelled in any criminal case to be a witness against himself.” It has been suggested that the 5th Amendment protection could be a means of preventing the admission of EDR evidence in criminal trials.

With several federal government agencies future survival at stake, the law enforcement community, the monetary interests of the insurance industry and large trucking companies, the future of EDR technology appears to be headed toward the greater good theory: Namely, making the highways safer for all drivers is more important than the rights of a few individual drivers, especially since EDR data only documents the truth of what has actually occurred.

The rapidly advancing computer technologies are going to change the way traffic accident reconstruction is performed in the future. The basic EDR based data will most likely be retrieved in the future by law enforcement, greatly reducing the need for post accident reconstruction in criminal cases. Anyone not up to speed on EDR technology is going to be left behind. C

)2

determining how many occupants are in the vehicle, whether they are using their seat belts, and other information that helps emergency responders further anticipate the type and severity of injuries.

The device that could significantly change the accident reconstruction industry is the digital camera. These cameras are similar to those with which television viewers of the Indianapolis 500 can watch the action from the race car driver’s view.

Digital cameras similar to those in race cars can be currently installed in vehicles as an aftermarket product. EDR proponents hope digital cameras will be mandated in newly manufactured vehicles in the near future. These manufacturer-installed digital cameras would record the events leading up to an accident, capture accident data, and record the aftermath. They would be fitted into the rear view mirror, provide a driver’s eye view of an entire accident from beginning to end, and will disclose that information without bias. The digital camera would continuously record video data in a software loop of what the driver observes looking out the front windshield. When an accident occurs, a subsystem senses that the accident signature parameters have been matched or exceeded. This triggers the EDR to permanently store the video sequence. The system time stamps the video, and allows the police, accident reconstructionist, or other authorized party to see the accident develop before and after impact.

Future digital cameras’ central processing units could transmit the video data through a cellular transceiver that encrypts and locks this data to prevent tampering. The result would be images and data transmitted immediately after the accident to a secure computer server, and readily accessible to law enforcement. Future systems could include multiple cameras, driver monitoring and other related features.

The accuracy of EDR data has been questioned by numerous comparisons, tests, and examinations. One proposed approach for improved accuracy of EDR data begins with a self diagnostic capacity within the EDR’s computer-based system itself. This would assure that the EDR data has not been tampered with. An EDR mounted in a vehicle can include digital image sensors, sound sensors, location GPS sensors, vehicle performance sensors, and a capture circuit for storing sensed data signals around a triggering event. A central processing unit and program memory can be programmed to perform a valida-

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

dence at the accident scene. Yet, in some cases no measurements of skid marks, vehicle positions, debris, etc., are documented.

In these types of cases EDR data would become even more valuable, especially in the resulting civil cases.

The current effect EDR data is having on court decisions is somewhat similar in both criminal and civil cases.

EDR’s are being accepted in most courts as an accurate source of evidence that is not biased, subject to approximation, or manipulation. Yet, several studies have indicated that judges still only view EDR data as evidence that needs to be supported by more conventional means of accident reconstruction. EDR evidence currently by itself does not establish an issue in dispute, but it might not be that long before this changes. In many criminal cases where speed is being disputed, if the speed cited can be convincingly disputed by a competent defense attorney, the citation might be thrown out by the judge on a strict letter of the law basis. This would not be the case with the exact speed being established by an EDR and a competent presentation by an expert. The advantages to date to law enforcement in criminal cases, is that local prosecutors have been allowed to subpoena EDR data without the permission, and to the detriment, of the owner.

The existing abilities of the EDR’s to provide accurate information about the causal factors of a traffic accident are amazing. Yet, the additional developing computer assisted advances are even more astounding.

I recently saw a television advertisement that showed a luxury vehicle parallel parking without the assistance of the driver.

Another T.V. advertisement has a car backing out of a driveway, and an audible device sounding when a garbage can is in its path.

Most newly manufactured General Motors vehicles offer an advanced automatic crash notification system (AACN) in their new G.M. models equipped with On Star’s invehicle safety and communication system.

The AACN system works with new and existing sensors in conjunction with advanced intelligence key crash data, including the direction of impact and the impact force.

When the AACN is triggered by a crash of sufficient severity, an emergency voice/data connection will be established with an On Star call center. AACN data in the future may be transmitted electronically to 911 centers, emergency responders, and trauma centers using secured internet connections.

Eventually the system may be capable of

Collision

63

In c up ro G a at D sh ra C 07 20 (c )

Wade D. Bartlett Mechanical Forensics Engineering Services, LLC

c

00

7

C ra

sh

D at

a

G

ro u

p

In

E

)2

I

marize the anticipated success rate of current EDR technology with regard to Rule 563 durability requirements.

DR & Electronics Survivability Background The earliest flight data recorders (ca. 1960) were required to operate at up to 100g for 5ms. Assuming the impact pulse takes the commonly assumed half-sine wave shape, as described by Varat & Husher [2000], this equates to a change in velocity (DV) of 7mph. Clearly the authors of the specification knew the plane crash at that severity level would be the exception, not the rule, but were limited by the durability of mechanical components which were part of those systems, including pen and foil. Even today, typical mechanical relays are only specified to function up to 20g, with a “destruction” pulse of 100g [Omron 2007a], while general-use surface mount electrical devices with mechanical components such as sub-miniature relays commonly have non-malfunction limits in the range of 50g to 100g.

Flight recorders introduced around 1980 shifted to solid state architecture, allowing them to meet the then-new re-

(c

ntroduction In August 2006, NHTSA issued the final rule on Event Data Recorders (EDRs) for passenger vehicles, 49CFR Part 563. Among other things, the rule mandates that EDRs be capable of “surviving” the frontal impacts specified in FMVSS 208 (run at speeds up to 35mph/56kph) and lateral impacts specified in FMVSS 214 (run at impactor speeds of 33.5mph/54kph). The rule does not set any requirements regarding survivability during fire, submersion, or rear end impacts, though they are all discussed in NHTSA’s Federal Register entry regarding the rule [NHTSA 2006].

This article will attempt to accomplish the following: (1) outline the history of EDR survivability in air and rail travel as compared to the Part 563 requirements, (2) describe the impact pulses electronics devices are commonly exposed to, (3) describe the general nature of the crash environments being specified, based on a review of several NHTSA tests conducted on various motor vehicles, (4) discuss EDR survivability observed in some non-specified crash and damage modes, and (5) sum-

64 Collision www.collisionpublishing.com

T

he Test Crash Environment Accelerations & Crush In NHTSA’s full-vehicle tests, the speed at impact is the specified parameter, not a particular average or maximum chassis acceleration or pulse shape. Vehicles

he Real World Crash Environment Wolf and Bratton [2006] concluded that the average speed of all crashes on American roads is approximately 34mph (55 kph). Nolan et al. [2001] identified the average DV for all passenger vehicle tow-away crashes as 12mph (20kph) based on 1990-1995 NASS data. That same study noted that the average DV for crashes in which an occupant received injuries rising to the Maximum Abbreviated Injury Scale value of 3 or higher (MAIS 3+) was 19mph (31kph). Gabauer and Gabler [2006] showed it was more like 12mph (19kph) for occupants protected by an airbag only and 17mph (27kph) for occupants protected by seatbelts and airbags.

While there have been debates about the merits of running tests at “average” speeds rather than something higher, it would appear that the general severity of many (if not most) real-world crashes are well modeled by the standardized crash tests mandated by NHTSA. This provides good confidence that

7

C ra

sh

D at

a

G

ro u

p

In

c

T

00

T

)2

he Final Rule: 49CFR563 Section 563.10 of the final rule outlines the survivability requirements for passenger vehicle EDRs. Specifically, it requires no new tests, but rather that most EDR data be fully recorded and remain “downloadable” for 10 days after the vehicle is tested per FMVSS 208 (frontal impact up to 35mph/56kph, offset frontal barrier 25mph/40kph impact) or FMVSS 214 (lateral impact by 33.5mph/54kph moving dolly). External power may be used during these subsequent downloads.

These tests have traditionally been run with the engine off and without any sort of direct operator input, so the pre-crash throttle setting (% FULL), brake status (ON/OFF), and engine RPM values are not changing, nor are they controlled. Based on concerns for the safety of personnel conducting the tests, it was decided to continue running tests with the engine OFF, and exempt those three data elements from the survivability requirements. However, the rule states that the “complete file recorded (YES/NO)” data element must read “YES” after the test.

with different chassis characteristics will have differences in the pulse shape and response, but the average accelerations have been shown by numerous researchers to be approximately half the peak acceleration values.

The most severe events, in terms of accelerations experienced, are full-frontal barrier impacts with stiff vehicles. Park et al. [1999] showed that 87 of 93 light trucks experienced peak accelerations of 25g to 35g during 35mph barrier NCAP tests.

Six of the 93 light trucks they evaluated garnered only one or two “stars” in the government’s crash testing, and these had peak accelerations of 31g to 44g.

Hollowell et al [1999] showed that average chassis accelerations experienced during 35mph NCAP tests were mostly between 12g and 20g, with all cases being below 25g. Jewkes [2003] showed that offset impacts at 45mph and above with 33 and 50% overlap generated average accelerations comparable to those experienced by vehicles during 35mph full-frontal impacts.

Average and peak accelerations will increase with test speed and decrease with increasing pulse length, as shown in Figure 1. Thirty-five mph frontal barrier impacts dissipate approximately 36% more energy than their 30mph counterpart currently required by FMVSS 208. The average acceleration experienced during a 35mph change in velocity given a 100ms duration is approximately 16g. Peak chassis accelerations measured in 35mph barrier tests tend to be in the 30g to 32g range.

Most airbag control modules responsible for the EDR functionality are located near the vehicle’s center of gravity (CG), with significant distance to the car’s outer shell in all directions.

The frontal barrier tests specified in FMVSS 208 typically generate frontal crush depths of only 20-35 inches (51-89cm) [Hollowell 1999]. IIHS conducts side impact test which are not identical to the side impacts specified in FMVSS 214, but they are similar. Arbelaez et al. [2005] reported an average maximum crush depth from those IIHS tests of 14.6 inches (37cm). This modest compartment intrusion should present no problem with regard to most EDRs’ physical space. For any modules mounted near the door-sills or near the perimeter of the passenger compartment, severe side impacts may involve sufficient compartment intrusion to present a hazard of direct impact damage, though.

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

quirement of 3,400g for 6.5ms [Grossi 1999], or DV ≈ 309mph.

The introduction of nonvolatile flash memory chips in the early 1990s offered further improvements in durability over mechanical mediums such as tape or rotating hard-disks, allowing their use in such demanding environments as naval torpedoes [Lewis 2002].

In June 2005, Federal rules which required installation of railroad event recorders in engines were enhanced with crashworthiness specifications. The final rule required a 55g peak acceleration half-sine pulse over 100ms or a 23g pulse over 250ms [49CFR229 Subpart D]. Both of these approximate a DV of 80mph, and were discussed at some length by Stevens et al. [1999]. The latest FRA rule additionally specifies tolerances for short and long-term heat or flame exposure, static crush loading, immersion in several types of fluid, and water immersion at pressures equivalent to 50 or 100ft depths.

The NHTSA working group on Truck and Bus EDRs made a variety of suggestions regarding the survivability of EDRs in those vehicles [NHTSA 2001a]. Those recommendations included immersion in various fluids, static loading to 500lb, penetration resistance, temperatures to -40F (-40 C), and an acceleration of 300g for 50ms (DV ≈ 210mph). Survivability to fire was not deemed a priority.

The accelerations experienced by common consumer electronics during normal use such as running or dancing can exceed 4g over a quarter second [Galvin 2005]. This equates to a velocity change in excess of 12mph. Electronics devices commonly include acceptance criteria for impact pulses in excess of 150g, with individual components often specified to survive peak accelerations in excess of 1,000g, albeit for a shorter duration commensurate with a drop on the floor, typically 0.1ms to 2ms. Even laptop computers can be purchased off-the-shelf to withstand 15g sustained accelerations and drops from 3 feet (DV ≈ 15mph) [Getac 2007].

Collision

65

c In

D at

a

G

ro u

p

Figure 2: Comparing change in velocity as recorded by the EDR with test instrumentation on the left rear seat cross member (NHTSA Test #3851).

S

sh

ide Impact Example NHTSA Test #4777 involved the side-impact of a stationary 2001 Buick Lesabre by a deformable barrier moving at a speed of 32.9mph (52.9kph) per FMVSS 214. The Buick CG experienced peak accelerations of approximately 16g laterally, 8g longitudinally, and 25g vertically. The last of these was a very short-lived 70Hz spike. The resultant CG acceleration reflected this vertical spike, peaking briefly at approximately 30g, as shown in Figure 3. The average acceleration was closer to 13g. The total speed change was approximately 12mph (19kph) laterally and 3mph (5kph) longitudinally. The module recorded a non-deployment event with DVmax=1.2mph. The maximum crush was approximately 14.4 inches (0.44m).

C ra

F

7

MVSS In 2001, the NHTSA working group reported that they had downloaded EDR data from 21 modules subsequent to their use in various NHTSA testing.

The vehicles included 15 cars, 2 vans, 2 pickups, and 2 sport utility vehicles. The tests included 3 FMVSS 208, 5 side NCAP tests, and 13 frontal NCAP tests. The raw data they reviewed were not provided in the report, but there is no mention of failures in any of the modules. The report specifically noted that there was generally good agreement between the EDR data and the test-contractors’ instrumentation with regard to change in velocity through the test [NHTSA 2001b].

Neihoff, et al. [2005] reviewed 37 crash tests of newer vehicles built by three major OEMs, and compared various data recorded by the test instrumentation with that recorded by the EDR. They found good correlation for the acceleration pulse (to the extent recorded) and 100% accuracy with regard to seatbelt status.

Included in their evaluations were several tests run by IIHS at 40mph (64kph), with no adverse effects on module survivability noted. These IIHS tests represent a 30% increase in energy dissipation over the 35mph tests mandated by NHTSA. Some modules were downloaded by the vehicle manufacturers, as they could not be downloaded using publicly available tools. The manufacturers chose to not share some of the download results, precluding evaluation for this paper. Those modules were described in the paper as “malfunctioning,” though one of the authors has advised that the actual results are unknown [Gabler 2007].

A number of crash test reports are available on the web which include EDR data. The list can be found at http://wwwnrd.nhtsa.dot.gov/database/aspx/eventdata.aspx, while complete reports for specific tests can be located at http://www-nrd.nhtsa. dot.gov/database/aspx/vehdb/querytesttable.aspx. As of this writing, the list included 35mph frontal impacts, one lateral crash test, and one partial-offset crash test which would be covered by Rule

00

(c )

20

07

C

EDRs capable of surviving the NHTSA tests will be survive the great majority of real world crashes.

F

)2

ra

sh

D

at

a

Figure 1: Showing Calculated Average and ½-Sine Peak Accelerations for Impact Pulses of 100ms and 125ms.

rontal Barrier Example NHTSA test #3851 involved a 2002 Chevrolet Avalanche colliding with a stationary barrier at 35mph (56.6kph) per FMVSS 208. Figure 2 shows the change-in-velocity data points recorded by the EDR along with the curve reported for the left-rear seat cross-member. The EDR reported value is clearly very similar to the value reported by the test instrumentation. The vehicle’s change in velocity was reported as 42.0mph (67.7kph), with a total barrier contact time of 144ms. The weighted average crush across the front was reported to be 18.6 inches (472mm) with a maximum crush of 19.8 inches (502mm). The left rear seat crossmember peak acceleration was 30.7g. The EDR functioned without incident.

(c

G

ro

up

In c

563. Additionally, there were a few test-development crashes and two car-to-car crashes which would be outside the scope of the new rule. Three examples of the FMVSS crash tests the new rule requires an EDR to survive are shown below.

66 Collision www.collisionpublishing.com

ffset Frontal Example NHTSA Test #4437 involved a 25mph (40kph) 40% offset frontal impact into a deformable barrier by a 2003 Chevrolet Suburban, per FMVSS 208. The total change in velocity was reported to be 30.9mph (49.8kph) with crush ranging from 17.7 inches (0.45m) on the left to negative values on the right due to bumper deformation. The EDR recorded a non-deployment event and 150ms of the 190ms acceleration pulse. The right rear seat crossmember accelerometer recorded a peak longitudinal acceleration approaching 14g, and a lateral peak of approximately 5g.

O

bove And Beyond The Rule Though not required by the new rule, EDRs have been observed to be fairly durable when exposed to a variety of traumas not part of Rule 563, including high-energy crashes, immersion in fresh and salt water, and mechanical damage.

Several SDMs were removed from scrapped cars by this author for submersion testing. Two of these six were found sitting in standing water inside the passenger compartment. Their exposure time could not be determined, but it had been long enough to stain and corrode the cases. All six modules were allowed to sit at room temperature for several weeks, at which time every one was downloaded without incident using the Vetronix CDR kit.

rozen Two modules, a 1999 Cavalier SDM R (1G1JC1243X7138305) and a 2000 Cavalier SDM G (1G1JC1244Y7427355). each equipped with a wiring harness plug, were placed in gallon jug of water, agitated vigorously several times over 3 hours and placed outside in sub-freezing weather. The water was observed to be frozen solid within two days, and did not thaw during the subsequent 2 weeks. The ice was then allowed to thaw at room temperature. One of the units (the ’99) had been partially submerged when removed from the scrapped car. The case on this unit was noticeably bulged as a result of water intrusion prior to freezing, and though it made “sizzling” sounds when powered up, a download was completed successfully.

The circuit board was not removed from the base prior to the drying cycle. Performing this additional step, or rinsing the unit in an electronics-friendly solvent may have improved the unit’s condition. The base of the ’00 module appeared to be fully potted, and it was the only one of the six test units described here which stayed water-free inside.

In addition to the test described here, several investigators have noted that they have performed successful downloads on modules after chipping them out of the ice in the floorpan area of crashed vehicles.

F

G

a

D at

sh

C ra

7

00

O

)2

F

blique car-to-car: Example NHTSA Test #4955 was a “development” test, involving an oblique frontal impact (330 degree) between a 2000 Cadillac Seville (identified in the report as the Bullet Vehicle) and a 1997 Honda Accord (identified in the report as the Target Vehicle), with both vehicles traveling at 35mph (56kph). The only EDR file from this test came from the Cadillac, and it showed a steady 35mph pre-crash speed, up to the 1second data set, which shows 158mph and 100% throttle. The EDR-recorded DV=19.0 at 110ms when the recording stopped. A manual integration of the longitudinal acceleration recorded at the CG shows DV ≈ 25mph over 160ms. The apparently anomalous 1-second data set is most likely a result of the data buffering phenomenon described in the Limitations section of the CDR Report. The throttle was most likely pushed to the floor by the test dummy’s foot during the im-

(c

resh Water Submersion Two modules, a 1998 Saturn SDM-R (1G8ZF5284WZ159737) and a 2001 Saturn SDM-G (1G8JU52F41Y572516), were each equipped with a wiring harness plug and placed in a bucket of fresh water which was agitated daily for 2 weeks. At the end of that time, both units had water intrusion in the case, so the outer cases were removed to facilitate drying prior to downloading the data. Both modules showed corrosion inside the case and on the circuit board, but both downloaded without incident once dry.

The module from a scrapped 1998 Chevrolet Cavalier was found completely submerged, as the car had filled to the doorsills with water. The total duration of the submersion was not known, but it was estimated to be “months” when the module was removed. Repeated attempts to download the module were unsuccessful, and it was placed on a shelf. Several months later, another

ro u

p

A

S

c

Figure 3: Buick CG resultant acceleration

alt Water Submersion Two modules, a 1996 Lumina SDM A/B/E (2G1WL52M4T1188179) and a 1998 Grand Prix SDM R (1G2WP52K8WF339827), were each equipped with a wiring harness plug and were placed in a bucket filled with water drawn from the North Atlantic and agitated daily for two weeks.

After removal from the salt water, both units had water intrusion inside the cases, so the covers were removed, and the internal circuitry was rinsed with fresh water prior to being allowed to air-dry for several hours. Both units downloaded without incident. One of these units (the ‘98 Grand Prix) was originally found partially submerged in water.

In

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

download attempt was successful on the first try.

A 1998 GMC Jimmy was involved in a crash which left it submerged in brackish water for approximately 3 months. After recovery, the vehicle was air-dried for some time prior to removing the module. The module case was corroded and stained, but it did not appear to have experienced significant water intrusion. It downloaded on the first try after removed from the vehicle.

Collision

67

pact, generating the 100% throttle condition. Damage sustained by the vehicle early in the crash most likely caused a voltage spike in the speed sensor circuit which was interpreted by the Powertrain Control Module (PCM) as a speed of 158mph. The SDM simply recorded the speed transmitted by the PCM. xtreme Crashes The NHTSA Special Crash Investigation unit has downloaded a number of modules from vehicles involved in crashes which appear significantly more severe than the Part 563 mandated tests. In particular, one crash involved a 2000 Buick Regal traveling at an SDM-reported speed of 60mph immediately prior to a perpendicular impact with a flat-faced concrete bridge support. Vehicle crush exceeded 40 inches (101cm) across the entire front surface, as shown in Figure 4. This is clearly more severe than any test commonly conducted by NHTSA, and yet the module and its data survived. [NHTSA 2000].

C

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

E

onclusion Given the modest acceleration requirements of the specified FMVSS 208 and 214 tests, as compared to the observed durability of individual components as well as completed EDR assemblies, it does not appear that the current passenger vehicle EDRs will have any difficulty in meeting the survivability requirements newly outlined in 49CFR563. In fact, the current crop of EDRs have commonly been seen to survive crashes much more severe in nature than anything specified in the FMVSS regulations, including fires, physical damage, and submersion.

eferences Gabauer, D.J. and Hampton C. Gabler (2006) Comparison of Delta-V and Occupant Impact Velocity Crash Severity Metrics using Event Data Recorders.

Proceedings of the Association for the Advancement of Automotive Medicine. Chicago IL. Online at http://www.me.vt.edu/gabler/gabler_publications.html. Accessed 22 January 2007.

R

Gabler, Hampton C. (2007) Personal communication. 22 January 2007.

Galvin, Gregory J. (2005) “Inertial Sensing for Hard Disk Drive Drop Protection.” INSIGHT Magazine. 2nd Quarter 2005. International Disk Drive Equipment and Materials Association. Santa Clara CA. Online at http://www.kionix.com/Press-Releases/Releases/IDEMA%20White%20Paper.pdf. Accessed 22 January 2007.

Getac Computers (2007) Online at http://www.ruggedlaptops.us/ getac/a770.html. Accessed 22 January 2007.

Grossi, Dennis R. (1999) Aviation Recorder Overview. Proceedings of the International Symposium on Transportation Recorders.

Arlington VA. Online at http://www.ntsb.gov/Events/symp_rec/ proceedings/authors/grossi.pdf. Accessed 22 January 2007.

c

Henderson, George (2002) “Shock Testing Miniaturized Products.”

Evaluation Engineering. April 2002. p52. Online at http://www. evaluationengineering.com/archive/articles/e0402enviro.pdf. Accessed 22 January 2007.

G

sh

C ra

)2

00

7

Jewkes, Dagmar Buzeman (2003) Vehicle acceleration and compartment intrusion for far- sided occupants versus near-sided occupants in frontal offset collisions. SAE International. Warrendale PA. Paper 2003-01-0159.

(c

In addition to high-speed crashes, modules have been observed to record and preserve data properly in cases where the vehicle was crushed to the point of breaking the outer SDM case, or the vehicle was crushed to the point of requiring module extraction from below (by cutting away the floor panel) or above (through the seat cushion). Though a severe enough fire can certainly destroy the current crop of passenger vehicle EDRs, it is not uncommon to find them still readable after a vehicle fire. This is usually a result of protection afforded them by various structures in the passenger compartment as well as their very low position in the vehicle.

D at

a

Figure 4: Module download successful after barrier impact at 60mph.

ro u

p

In

Hollowell, William T., Hampton C. Gabler, Sheldon L. Stucki, Stephen Summers, James R. Hackney (1999) Updated Review of Potential Test Procedures for FMVSS 208. http://www-nrd.nhtsa. dot.gov/pdf/nrd-11/airbags/FMVSS_208_II.pdf. Accessed 02 February 2007.

Lewis, Mark E. (2002) “Flash Emerging As Top Storage Choice.”

INSIGHT Magazine. Spring 2002. International Disk Drive Equipment and Materials Association. Santa Clara CA NHTSA (2000) Special Crash Investigations Case 182-00. Report 39550. Available online http://www-nass.nhtsa.dot.gov/SCIREPORTS/39550/RPT39550.pdf. Accessed 2 February 2007.

68 Collision www.collisionpublishing.com

NHTSA (2001a) Summary of Findings by the NHTSA Truck and Bus EDR Working Group. Final Report for Docket NHTSA-2000-7699. Online at http://dmses.dot.gov/docimages/pdf1a/183185_web.pdf. Accessed 22 January 2007.

NHTSA (2001b) Summary of Findings by the NHTSA EDR Working Group. Final Report for Docket NHTSA-99-5218. p 60. Online at http://www-nrd.nhtsa.dot.gov/edr-site/uploads/ edrs-summary_of_findings.pdf. Accessed 22 January 2007.

a

G

ro

up

In c

NHTSA (2006) “Motor Vehicle Safety Standards: Event Data Recorders.” Federal Register. Vol. 71, No. 166. Monday, August 28, 2006. Docket: NHTSA-2006-25666. p50998.

Park, Brian, James Hackney, Richard Morgan, Hansun Chan, Johanna Lowrie, and Heather Devlin (1999) The New Car Assessment Program: Has It Led to Stiffer Light Trucks and Vans over the Years? SAE International. Warrendale PA. Paper 1999-01-0064.

Stevens, Thomas, Robert Onley, and Robert Morich (1999), “Design of a Crash Survivable Locomotive Event Recorder.” International Symposium on Transportation Recorders. Arlington VA. Online at http://www.ntsb.gov/events/symp_rec/proceedings/authors/stevens.pdf. Accessed 22 January 2007.

(c )

20

07

C

ra

sh

D

at

Niehoff, P., H.C.Gabler, J.Brophy, A.Chidester, J.Hinch, and C.Ragland (2005) Evaluation of Event Data Recorders in Full Systems Crash Tests. Proceedings of the Nineteenth International Conference on Enhanced Safety of Vehicles. Paper No. 05-0271.

Washington DC.

Omron (2007a) General Purpose LY-Relay Data Sheet. Online at http://ecb.omron.com.sg/pdf/relay/general/LY.pdf. Accessed 23 January 2007.

Nolan, Joseph M., Charles A. Preuss, Sara L. Jones, Brian O’Neill (2001) An Update on the Relationships Between Computed Delta-V and Impact Speeds for Offset Crash Tests. Proceedings of the Sixteenth Conference on Enhanced Safety of Vehicles. Online at http://www-nrd.nhtsa.dot.gov/pdf/nrd-01/Esv/esv16/98S6O07. pdf. Accessed 22 January 2007.

Varat, Michael, Stein Husher (2000) Vehicle Impact Response Analysis Through the Use Of Accelerometer Data. SAE International. Warrendale PA. Paper 2000-01-0850. Eqn. 6.

Wolf, Kathleen L. and Nicholas Bratton (2006) “Urban Trees and Traffic Safety: Considering US Roadside Policy and Crash Data.”

Arboriculture & Urban Forestry. 32(4): July 2006. p170. Online at: www.cfr.washington.edu/research.envmind/Roadside/TransSafety_ArbUF.pdf. Accessed 22 January 2007.

C

Accident Reconstruction Calculator TM

By WeCARE Products and Education

Why do your calculations by hand?

In

C ra

sh

D at

a

G

ro u

p

Momentum Energy Time-Distance Force Basic Motion Delta-V Low-Speed Crush Auto-Pedestrian Projectile Motion and more…

c

The Accident Reconstruction Calculator™ provides you with a complete suite of equations.

(c

)2

00

7

The equations you grew up with. Take the guesswork out of your work with this user-friendly program that has benefited over 500 police agencies and accident reconstruction firms throughout the United States. Visit our website for current price and order form. While browsing our website, take a look at other collision reconstruction products and our training classes as well.

WeCARE Products 228 Pleasant Street Roseville, CA 95678 Bus. (916) 782-4654 Fax (916) 782-4878 WeCARE@rudydegger.com http://www.rudydegger.com/WeCARE Collision

69

In c up ro G a at D sh ra C 07 20 (c )

c In p ro u G a D at sh C ra 7 00 )2

A

maximum recording time of the SDM, but there was no clear trend between speed change accuracy and collision duration. This study provides a set of speed change accuracy data for higher severity collisions and provides a better understanding of the parameters that can affect this accuracy.

(c

bstract The accuracy of the speed change recorded by General Motors (GM) sensing and diagnostic modules (SDM) in non-deployment events has been systematically evaluated for vehicle-to-barrier and vehicle-to-vehicle collisions. However, there has been little published as to the accuracy in collisions severe enough to require airbag deployment. To quantify the accuracy of SDM recorded speed change in deployment events, 23 NHTSA crash tests of 2000 to 2005 GM vehicles were evaluated. The maximum SDM recorded speed change was compared to the data recorded by onboard accelerometers during the test. In the majority of the vehicle-to-barrier tests, the SDM recorded speed change underestimated the accelerometer speed change with a maximum underestimate of 9 km/h. In one long duration vehicle-to-vehicle collision the underestimate was about 11 km/h. In a few of the crash tests, the SDM recorded speed change slightly overestimated the accelerometer speed change by a maximum of 2 km/h. In non-deployment events, the algorithm-enable acceleration threshold has been shown to have a significant effect on the accuracy of the SDM recorded speed change.

Evaluation of deployment events found that there is a much smaller effect due to the initial acceleration threshold. In some of the high severity tests, the duration of the collision was greater than the

70 Collision www.collisionpublishing.com

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

The Accuracy of General Motors Event Data Recorders in NHTSA Crash Tests Craig C. Wilkinson Jonathan M. Lawrence David J. King MEA Forensic Engineers & Scientists

c In p ro u G a D at sh C ra 7 00 )2

I

tematic evaluation of the reported speed change accuracy in high speed or deployment events. A previous study looked at SDM recorded speed changes in NHTSA crash tests and compared the

(c

ntroduction The majority of modern passenger vehicles are equipped with some form of event data recorder as part of their supplemental restraint system. The Vetronix Crash Data Retrieval (CDR) system allows collision investigators to download the crash record from 1994 and newer General Motors (GM) sensing and diagnostic modules (SDM). This crash data is being used in the investigation of collisions with greater frequency so establishing the accuracy and limitations of the recorded data is of interest to all investigators.

Previous studies found that the speed change reported by GM SDMs always underestimate the actual speed change of a collision for collision severities below 16 km/h (Correia et al., 2000; Lawrence et al., 2002; Wilkinson et al., 2005). To date, there has been no sys-

Collision

71

72 Collision www.collisionpublishing.com

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

In c up ro G a at D sh ra C 07 20 (c )

c

In

p

ro u

G

a

D at

sh

R

C ra

I

esults Aligned Barrier Tests There were 21 aligned barrier tests analyzed in this study. The accelerometer speed changes ranged from 42.8 to 67.2 km/h (Table 2, Figure 2). In all of the aligned tests, the maximum difference between the two integrated accelerometer signals was less than 2.3 km/h. The majority of the SDM reported speed changes underestimated the accelerometer speed changes.

However, there were four tests in which the SDM reported speed change slightly overestimated the actual speed change. The maximum underestimate was 9 km/h in the 2003 Chevrolet Silverado 56 km/h barrier test. The maximum overestimate was 2 km/h in a

7

nstrumentation The test vehicles were all equipped with multiple linear accelerometers mounted in various locations. Where possible, the data from both a left and right side mounted accelerometer were used. In all cases, only floor mounted accelerometer data was evaluated. The NHTSA reports for each test indicate that the acceleration data were digitally sampled and recorded at 12,500 samples per second and processed per SAE J211.

Collision data from the SDMs were downloaded using a CDR system (Vetronix Corporation, Santa Barbara, CA.). The CDR reports provided on the NHTSA public database (NHTSA, 2005) were all generated using software version 2.70.

00

M

D

)2

ethods The US National Highway Traffic Safety Administration (NHTSA) has performed thousands of crash tests for both vehicle safety and research purposes.

In twenty-three frontal crash tests of GM vehicles, the SDM was downloaded post-collision and the data included in publicly available reports (NHTSA, 2005). The test vehicles were all within the model years 2000 to 2005. There were 21 flat rigid barrier tests, one offset rigid barrier test and one offset and angled vehicle-tovehicle collision (Table 1).

ata Reduction The vehicle speed change in all but two of the collisions was determined by integrating two of the NHTSA accelerometers. In the majority of the tests, accelerometers mounted at the left and right rear sills were integrated. However, if the integrated signals were not similar in shape or magnitude, other frame mounted accelerometers (such as from the front sills) were integrated. All accelerometer traces were also examined for any abnormalities or clipping. A range of speed change for each test is presented based on two accelerometer signals. The accelerometer data was all downloaded from the NHTSA database and then integrated using PlotBrowser, a NHTSA utility for plotting data files (Figure 1).

The maximum SDM recorded velocity change was compared to the integrated NHTSA accelerometer data. In SDM download reports in which there was not a maximum velocity recorded, the highest value from the speed change table was used for comparison.

An algorithm-enable threshold of 1.0 to 1.4g for a 2003 Cavalier (Wilkinson et al, 2005) was used to determine what speed change the 2003 Cavalier had gone through prior to the SDM beginning to record the event.

The durations of the barrier collisions were estimated using the barrier-mounted force cell data. Time zero on the plots was defined as the start of contact. The end of contact, or the end of the collision, was determined by locating the return of the load cell force to zero or near zero.

(c

speed changes recorded by the SDMs 100 ms into the crash with the speed change recorded by NHTSA accelerometers after 100 ms (Niehoff et al., 2005). Comparing the SDM and accelerometer speed changes at 100 ms does not evaluate the maximum difference between the two as most of the collisions were significantly longer in duration than 100 ms.

The primary objective of this study was to evaluate the accuracy of the maximum SDM reported speed change in NHTSA crash tests compared to the total speed change recorded by NHTSA accelerometers. A secondary objective of the study was to evaluate what parameters have the largest effect on the accuracy of the SDM-reported speed change in higher speed collisions. The results of this study should provide investigators with better understanding of the accuracy and limitations of the crash data recorded by GM SDMs in high speed collisions.

Collision

73

In c up ro G a at D sh ra C 07 20 (c )

This is less than 0.1% of the final speed change of the collision. ffset Barrier Test The offset vehicle-to-barrier test (NHTSA test 4437) consisted of a 2003 Chevrolet Suburban striking a rigid 40% offset barrier at 39.91 km/h. The single offset barrier test was evaluated in the same fashion as the aligned tests. The reported data did not include lateral acceleration data so there was no way to calculate a resultant speed change. The SDM data was compared to the recorded longitudinal speed change only. The maximum recorded SDM speed change underestimated the NHTSA longitudinal speed change by up to 5.36 km/h and overestimated the NHTSA speed change by up to 0.93 km/h (Figure 4). As shown

O

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Saturn Vue 48 km/h barrier test. In terms of percent, the SDM-reported speed change ranged from a 1.5% overestimate to a 13.3% underestimate. The duration of each collision was determined using the load cell data from the NHTSA rigid barrier. The difference between the calculated duration and the length of the SDM recording was plotted against speed change error (Figure 3). The difference between the actual duration and the SDM-recording time represents the duration of collision not recorded by the SDM. There was no clear trend between difference in duration and SDMreported speed change error. In the 2003 Chevrolet Cavalier test (4445), the longitudinal acceleration exceeded the algorithm enable threshold of 1.0 to 1.4g in the first 0.0024 s of the collision.

The cumulative speed change at this time was less than 0.02 km/h.

74 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

tudinal and lateral speed changes of the Cadillac at each of the five locations are shown in Table 3. The average speed changes from the sill-mounted accelerometers are 41.8 km/h longitudinal, 6.8 km/h lateral and a resultant of 42.3 km/h, which are comparable to the center of gravity speed changes.

The SDM reported a longitudinal speed change of 30.6 km/h. The SDM-reported speed change underestimated the integrated longitudinal accelerometer speed change at the center of gravity by 10.4 km/h and underestimated the resultant accelerometer speed change at the center of gravity by 10.8 km/h (Fig 5).

The duration of the SDM speed change recording was 110 ms and the approximate duration of the collision from the accelerometer data was about 120 to 160 ms. The accelerometer speed change continued to increase after the CDR recording ended.

(c

in the figure, the SDM-reported speed change closely matched the right rear accelerometer speed change until the recording finished.

The maximum recorded SDM speed change occurred after the last point recorded in the speed change table. Offset Angled Vehicleto-Vehicle Test The offset angled vehicle-to-vehicle test (NHTSA test 4955) consisted of a collision between a 1997 Honda Accord sedan (the target) and a 2000 Cadillac sedan (the bullet). The target impact speed was 56.6 km/h and the bullet vehicle impact speed was 55.9 km/h. The NHTSA test report describes the alignment as a 30 degree left front oblique, 50% offset.

The bullet speed change was calculated using both longitudinal and lateral accelerometer data from five different locations on the test vehicle. These are defined as left front sill, left rear sill, right front sill, right rear sill, and the center of gravity. The longi-

Collision

75

eferences Correia JT, Iladis KA, McCarron ES & Smolej MA. Utilizing data from automotive event data recorders.

Proceeding of the Canadian Multidisciplinary Road Safety Conference XII, London, ON, 2001.

R

Lawrence JM, Wilkinson CC, King DJ, Heinrichs BE & Siegmund GP. The accuracy and sensitivity of event data recorders in low-speed collisions (2002-01-0679). Advances in Safety Test Methodology (SP-1664). Warrendale, PA, Society of Automotive Engineers, 2002.

c

Wilkinson CC, Lawrence JM, Heinrichs BE, King DJ (2005). The accuracy and sensitivity of 2003 and 2004 General Motors event data recorders in low-speed barrier and vehicle collisions (200501-1190). In: Accident reconstruction (SP-1930). Warrendale, PA: Society of Automotive Engineers.

sh

D at

a

G

ro u

p

In

Niehoff, Gabler, Brophy, Chidester, Hinch, Ragland (2005). Evaluation of Event Data Recorders in Full Systems Crash Tests. International Technical Conference on the Enhanced Safety of Vehicles.

Paper No. 05-0271

00

7

C ra

NHTSA Vehicle Crash Test Database Website. http://www-nrd. nhtsa.dot.gov/database/nrd-11/veh_db.html

)2

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

D

the SDM stopped recording, so a significant amount of the collision was not recorded. It’s important for an investigator to observe that the SDM speed change data was still rapidly increasing when the recording stopped, an indication that important data may have been missed. The collision engagement and the physical vehicle damage are also indicative of a long duration, high severity collision so the SDM underestimate can be readily explained.

A second cause for the speed change underestimate is the location of the SDM. The SDM is mounted under the right front seat of the Cadillac, so the rotation of the Cadillac in response to the collision causes the right sill accelerometers to see a lower effective acceleration, resulting in a lower speed change on the right side of the vehicle. The SDM recorded speed change is much closer in value to the right sill accelerometers than the left sill or center of gravity values (~6 km/h difference).

Another factor in the SDM underestimating the actual speed change in the vehicle-to-vehicle test is the angle of the impact and the post-impact rotation of the vehicles. The tested SDM only records longitudinal crash pulse data, so any lateral force or rotation will result in increased error with respect to the actual speed change. Caution must be exercised when using SDM data from a collision where rotation of the vehicle is suspected.

Augustus “Chip” Chidester, NHTSA; John Hinch, NHTSA; Thomas C. Mercer, GM Corp.; Keith S. Schultz, GM Corp, 1999, “Recording Automotive Crash Event Data,” International Symposium on Transportation Recorders, Arlington, VA

(c

iscussion The SDM-reported speed change underestimated the actual speed change of the collision in the majority of the aligned barrier tests and both of the offset tests. The causes for the error were not the same as those found in previously published non-deployment collision tests (Lawrence et al., 2002; Wilkinson et al., 2005). The effect of the algorithm enable threshold was found to be minimal as the frontal acceleration exceeded 1 to 2g in the first 10 ms in all tests and in less than 3 ms in the majority of the tests. For the 2003 Cavalier test, this represented a cumulative speed change of less than 0.02 km/h.

The effect of the collision duration was not consistent between the tests. During the offset barrier collision and the vehicle-to-vehicle test, the collision duration was much longer than the SDM recorded and the missed portion of the collision was still significant. However, as was shown in Figure 3, there was no clear trend between difference in duration and speed change error in the aligned barrier impacts. Duration can still be a major factor in the SDM underestimating the actual speed change, but the extent depends on the shape of the collision pulse.

In all tests, the SDM-reported speed change curves were similar in shape to the NHTSA accelerometer speed change traces, but there was always a discrepancy in the actual speed change value. It was found that the SDM speed change data could be fit to the integrated accelerometer data by applying a scale factor and an offset. The data was fit by minimizing a sum of squares error. For SDM-recorded speed change data in which the first recorded speed change was 0.0 km/h, the data was shifted by 10 ms.

A scale factor and offset were determined for each aligned barrier collision. The maximum scale factor was about 1.1 and the minimum scale factor 0.95. The maximum offset was 5.9 km/h. In most cases, the scaling resulted in a close fit between the accelerometer data and the scaled SDM data (Figure 6).

While it is not conclusive, the ability to scale the SDM data to match the NHTSA accelerometer data is consistent with uncertainty in the calibration for the accelerometers mounted in the SDMs. The maximum calculated scale factor was 10%. This is the same value previously suggested as a maximum error primarily due to uncertainty in the SDM-mounted accelerometer data (Chidester,1999). This is also consistent with the sensitivity of the type of accelerometer used in many of the General Motors SDMs. If each accelerometer has a potential uncertainty of up to 10%, using a uniform scale factor for each SDM across a vehicle platform would result in the types of errors observed in the NHTSA barrier tests. This is best illustrated in the three tests performed on 2002 Saturn Vue’s. In the three barrier tests, the speed change error ranged from an underestimate of 4 km/h to an overestimate of 2 km/h. The calculated scale factors ranged from 0.96 to 1.0 and the offset varied from 0 to 5.6 km/h. For this vehicle, it appears that the calibration factor for the SDM accelerometer data is appropriate as the recorded data falls within 6% of the NHTSA data both above and below. In the majority of the SDM’s, it appears that the accelerometer calibration has been biased towards underestimating the actual speed change. The data from the offset angled vehicleto-vehicle test demonstrates the importance of understanding the limitations of the SDM before relying on the data it records. In the test collision, the SDM underestimates the actual speed change for several reasons. One source of error is that the actual collision duration is much longer (10 to 50ms) than the duration of the SDM speed change recording. The collision was not finished when

C

76 Collision www.collisionpublishing.com

Collision

77

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

When Measuring Vehicle Crush...

c

In

p

ro u

G

a

D at

sh

C ra

7

C

00

lose-Range Photogrammetry Of the numerous methods for measuring vehicle crush, Close-Range Photogrammetry is becoming a more widespread and popular method of choice. Close-Range Photogrammetry is the science and technology of extracting accurate three-dimensional (3D) data from two-dimensional (2D) images (nowadays, generally images from digital cameras).

The first stage of the photogrammetric measurement process typically involves acquisition of multiple, overlapping images of the object of interest, each of which is recorded from a different view angle. This image recording procedure is straightforward, as all the photographer has to do is set the lens at a given focus and zoom setting and capture the images.

Next, the digital images are imported into a photogrammetric software system where the 2D coordinates of corresponding feature points on the images are determined through a process termed referencing. Once this ‘marking’ of corresponding points is achieved, an optical triangulation computation is performed by the software, and the 3D coordinates of the marked feature points are computed. It is also possible to form line segments, polylines, polygon meshes and photo-realistic textures of the objects to provide a

)2

O

virtual 3D view.

In accident reconstruction, photogrammetry has proven itself to be a fast and accurate means of collecting 3D data for homicide scene mapping, crash scene diagramming and vehicle crush modeling, to name just a few applications. Photogrammetry is a measurement technology well recognized and accepted by the courts, and is widely used by private reconstructionists and law enforcement agencies.

One leading photogrammetric software system that has been specifically developed for accident reconstruction is iWitness.

With the iWitness system, fullyautomatic measurement of an object such as a vehicle or crime scene can be performed through the use of special coded-targets, to accuracies which can exceed hundredths of an inch. Moreover, the necessary photography can be acquired very rapidly, at the scene, With an off-the shelf camera such as a consumer grade digital SLR. In the case of a vehicle crush measurement, the targeting of the object that precedes photography can take place in a matter of minutes and the recording of the photographs is both fast and free of lengthy setup times necessary for alternative measurement techniques.

Whether the user is in the office or in the field, he can import the acquired images into iWitness to automatically produce a 3D reconstruction of the damaged vehicle. In addition to automatic 3D measurement using color (RGB) images, iWitness supports the determination of additional measurement of non-targeted feature points via an operator assisted referencing process.

Such data could be, for example, the 3D polylines indicated in the figure below, which shows within the iWitness workspace both a marked image of the vehicle and a view of the reconstructed object points and features. Moreover, additional measurements can be performed either at the time of the event or months and even years later; the imagery provides a permanent visual record.

Once the image-based 3D modeling is complete, the 3D

(c

fficers and accident reconstructionists measure vehicle crush in different ways. The goal, however, is always constant—to recreate the damage to those vehicles involved and compare it to the original vehicular specification. The “vehicle crush” is determined based upon the difference between these findings.

This article is the first of a two-part series that presents several methods for measuring vehicle crush. Part One will explore the close-range photogrammetry, laser, and manual measurement (spreadsheet) methods. Part Two will cover scanner systems, using a crush jig, and using a total station.

78 Collision www.collisionpublishing.com

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

...Find The Method That Works For You PART ONE

Bob Galvin RS Galvin & Assoc

c

In

p

ro u

G

a

D at

sh

C ra

7

00

M

)2

anual Measurements (Excel crush spreadsheets) The next method of documenting vehicle damage is designed to work in conjunction with an Excel spreadsheet program (included in this issue of COLLISION MAGAZINE’S companion CD). This a low-cost to no-cost method of accurately documenting the entire vehicle and its damage.

The only equipment required is a 100-foot tape measure, a handheld tape measure and some type of mechanism to secure the 100-foot tape measure to the ground (sections of rebar or large screwdrivers work well for this task). Once data from the damaged or exemplar vehicle has been entered into an Excel spreadsheet measurement program, which converts the measurements into a X-Y-Z coordinate format, the data may be imported into a variety of CAD programs and displayed as points.

Measurement Setup: The 100-foot tape measure is used to create a rectangular box around the vehicle. Make sure the four corners of the box are square and that the entire vehicle fits within the confines of the box created with the tape measure.

When laying out the 100-foot tape, the beginning of the tape measure should be secured near one of the four corners of the vehicle. Next, extend the tape across or alongside the vehicle in a counterclockwise direction until it has been extended beyond the confines of the vehicle being measured. Once the tape measure has been extended a sufficient length it should be pulled tight and turned 90 degrees to form the next leg of the box that will enclose

the vehicle. To ensure that this first corner is square, which is essential, form a right triangle comprised of the first and second legs of the tape measure and another tape laid across the first two legs.

The result should be a triangle whose sides measure three feet, four feet and five feet. Remember, this precise measuring process must be repeated for each corner of the vehicle.

Measuring the Vehicle: Once the box has been properly established around the vehicle, all of the measurements will be made from the 100-foot tape measure surrounding and inward toward the vehicle. These measurements are recorded in an X-Y-Z format. The X value reflects the value that appears on the 100-foot tape surrounding the vehicle; the Y value represents the measurement from the 100-foot tape inward toward the vehicle; and the Z value represents the vertical distance of the measurement.

Use of the Spreadsheet: The measurement program can only work once measurements are entered in Excel. Before entering any measurements into the spreadsheet program, the length and width of the box around the vehicle must be entered. Click on the “Enter Length and Width” button to open a dialog box, which will prompt you for the length and width of the box surrounding the vehicle as well as for the corner that was used to establish the tape measure’s base point.

When the “Enter Measurements” button is selected, the dialog box where all of the measurements are entered will appear.

Once a set of measurements has been entered they must be assigned a line code. This code allows the program to draw lines between coordinates with like codes. The codes must be sequential.

For example, if points 1,2,6, 7 and 9 contain the line code “A”, and points 5, 6 and 8 contain the code “B”, the program will draw one line connecting points 1,2,6,7 and 9, and a separate line connecting points 5, 6 and 8.

The color code field controls the color of the line when it is drawn in Excel. This line color does not carry over into the CAD

(c

photogrammetric point cloud can be exported as a DXF file and used in powerful CAD programs such as The CAD Zone’s Crash Zone diagramming software. Photogrammetry enjoys many other advantages, as it is relatively inexpensive, very easy to use and requires no controlled environment. Presently, a suitable photogrammetric measuring system comprising a SLR camera, software system and accessories can be purchased for as little as $2000.

Collision

79

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

program when the data is exported.

Before the “End” button is selected, the user should make sure current measurements logged in have been recorded by clicking on the “Next Measurement” button. When the “Enter Measurement” button is selected on the main screen, the measurement dialog form will reappear, permitting the user to continue entering measurements.

The “Draw Car” button will draw the vehicle based on the information that has been entered. The diagram is drawn to scale, though not to a specific scale. The rectangle surrounding the vehicle represents the 100-foot tape. The “Write Text” button will create a text file that can be used by a CAD program that supports the importing of coordinate data text files, such as Map Scenes,

80 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

c

In

p

ro u

G

a

D at

sh

7

C ra

Author Listing: 1. Close-Range Photogrammetry – Lee DeChant, DeChant Consulting Services—DCS, Inc. (www.iwitnessphoto.com) 2. Manual Measurements (Excel crush spreadsheets) – Charles Gregory Russell, Accident Analysis & Reconstruction, Inc. 3. Measuring Crush With a Laser – John Howell, John Howell & Associates, LLC

00

M

)2

easuring Crush With a Laser By using an LTI Impulse laser mounted on a bi-pod/ pole system, a reconstructionist can effectively measure crush on a vehicle in 3D and produce a wire frame to underlay a scale exemplar vehicle. I use a TDS Recon for a data collector and LTI specific Pocket Zone software, from The CAD Zone, as the collection software. You’ll also need a 300-foot fiberglass tape, four tent pegs or nails, depending on the surface, two markers (traffic cones work well), a ten-foot folding carpenter’s rule, and a 90-degree angle finder. A good extra item to get is some Scotch 3M brand reflective tape for making quarter-inch squares you can easily peel off and stick at target points.

Prepare your scene adequately for measuring. You might use the front of the vehicle as you begin taking measurements.

Make sure the vehicle has about ten feet of room on each side.

Mount the LTI laser onto its bi-pod/pole. Then set up the TDS Recon with Pocket Zone, making sure it is set for LTI with NO ANGLE ENCODER, and that the cross section command is activated. Next, take the folding carpenter’s rule and create a six-foot log middle piece with two-foot end sections as opposing 90-degree angles to the center. Place this rule on the ground against the front tire and put a temporary tent stake at the end. Stretch the beginning of the 300-foot tape six feet further than the front of the vehicle and place a stake there, attaching the tape to it. Move the carpenter’s rule to the rear wheel on the same side and stretch the tape to a point six feet past the end of the vehicle and place another stake, wrapping the tape around it. Repeat this procedure until there is a right angle box around the vehicle.

Once this is all done, place the LTI laser with the pole just touching the tape and a traffic cone about three feet beyond the first corner, to your left as you face the vehicle. Shoot four distinct CL (Crush Layer) zones as you work your way around the

vehicle. These zones include the bottom of the car’s body, center of the body, hood and trunk line, and roofline. Also shoot the top and bottom of all pillars and the center of the axels for reference points.

The laser devices are reflectorless, and most shots can be taken that way. But if you encounter one of those that just won’t work, affix a small piece of the 3M tape on the spot and it will record.

After you have shot all the points, save the diagram as well as the POINT LIST. This is critical! Back at your office, open your CAD program and import the POINT LIST into a blank diagram. This will place your point with X, Y, and Z coordinates and connect like points with a colored line, which will form your wire crush diagram. Then, place it into your pre-prepared exemplar vehicle using the axels as reference, outline and hatch your crush.

The three crush measurement methods discussed here represent just a few of the many methods available. While crush measurement methodology is a matter of choice, it is crucial to ensure that whatever method is chosen, crush, angular displacement, crush width, vehicle speed, and a battery of other related data are accurately collected and a scaled, detailed diagram can be created.

It’s essential to measure the damage and then apply it correctly to acceptable formulas. Again, keep in mind that the goal here is to accurately reproduce the vehicular damage and compare it to the original vehicle specification. Without a complete damage profile of the crushed vehicle, which your chosen crush measurement must produce, this goal will not be met.

(c

Crash Zone and Vista FX. This button opens and writes the data into Word Pad as comma-separated values, in a point number, X measurement, Y measurement, Z measurement, line code format.

This Word Pad file should then be saved as a text file so that it may be imported into your CAD program.

C

Collision

81

Book Reviews

c

In

p

ro u

G

a

D at

sh

C ra

7

00

B

(S.I.) systems. The text is intended to serve a need for investigators who possess a good knowledge and understanding of elementary algebra and trigonometry, and who have successfully completed at least an at-scene traffic crash investigation course and wish to further their knowledge towards competency in advanced traffic crash investigation and reconstruction.”

I couldn’t have said it better myself. (Which is why I plagiarized the advertisement above.)

This is one of the few books you’ll find that has a disclaimer up front. No, it’s not one of those “Viewer Discretion Advised” or “Parental Guidance” admonishments, but you will have to read it for yourself. Rivers starts out discussing Newton’s Three Laws of Motion. Yes, those are rather basic items, but hey, this is a Basic Physics book, you know.

Chapter 2, Measurements in Physics, covers: derived units; acceleration rate; the Pound, Slug and Newton; vectors and scalars.

Chapter 3 delves into gravity and mass. Uniform Circular Motion is the topic of Chapter 4. Chapter 5 is all about Work while Chapter 6 covers Power. The remaining five chapters take you through Energy, Force, Friction, Momentum, and Pressure & Force Multipliers.

For those readers who utilize a drag sled, be sure to read the section in the chapter on Work. Here Rivers gives you the equation that takes into consideration the angle at which you drag the sled. Then later in the chapter on Friction, Rivers talks about coefficient of friction and drag factor and explains Drag Sled Concepts.

A neat thing about this book is that the author doesn’t dwell on and on with dreary details. For instance, the Energy chapter is only three pages. After defining Energy, it talks about potential energy, kinetic energy and conservation of energy.

You’ve heard people use the expression “Centrifugal Force.” We all know there is no such thing.

Yes, I know, you can look it up and most dictionaries define it thus: “A force, arising from the body’s inertia, which appears to act on a body moving in a circular path and is directed away from the centre around which the body is moving” [Concise Oxford English Dictionary, Eleventh Edition].

American Heritage Dictionary calls it “The apparent force, equal and opposite to the centripetal force, drawing a rotating

)2

asic Physics

By R.W. Rivers In 2004, Charles C Thomas Publishers (and yes, there’s not supposed to be a period after the C) published and distributed a book on basic physics cleverly titled Basic Physics. I reviewed it back then and yet the text of that review seems to have vanished.

I revisited the book today and want to share it with you. First, you should know that the book is not a massive 90-pound tome that will take a year just to wade through the introduction. Nope, this is a 124-page (140 if you count the title page, table of contents, index and so on) “spiral bound” book subtitled Notes for Traffic Crash Investigators and Reconstructionists. The subtitle is subtitled: An Introduction for Some, a Review for Others.

CHARLES C THOMAS • PUBLISHER, LTD. has been producing a strong list of specialty titles and textbooks in the biomedical sciences since 1927. They are also one of the largest producers of books in all areas of criminal justice and law enforcement. How do I know that? Says so right at their website, http://www.ccthomas.com/. You’ll also find many R.W. (Bob) Rivers books listed plus the following publisher’s blurb about this particular book: “The purpose of this book is to bring to the student an understanding of the basic physics involved not only in traffic crash investigation and reconstruction but also in crimes or other incidents where the movement of objects or persons is involved. The range of topics included are those considered to be fundamental and which best serve the purposes of illustrating the methods and procedures vital as an introduction to physics. Essentials of the subject as related to vehicle motion are stressed. The mathematics used is kept simple and in straightforward, easy-to-understand language. Comments and examples and a very comprehensive list of terms and definitions, supported by many illustrations and diagrams, are provided to give the reader a unified view of basic physics. All materials are prepared in both the English (U.S.) and metric

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

by Joseph E. Badger

82 Collision www.collisionpublishing.com

ational Directory of Expert Witnesses

By Steven, Ellen, Alex and Karen Babitsky It’s quite possible those names don’t ring an immediate bell, but because of them we have a company known as SEAK, named, obviously, after those family members. Steve is the SEAK patriarch, Alex manages their product line and Karen is the marketing director.

One of SEAK’s features is what they call a National Directory of Expert Witnesses, a “proven way to generate new expert witness referrals.” It is not, however, what I would call the world’s largest directory of experts, at least not as far as accident reconstructionists go. I searched their database for Accident Reconstruction Experts in All States and found only 28 – and none in Indiana. But what they market and publish are books.

Steven Babitsky has been an attorney since he was admitted to the Bar in 1972, so he has had a long time to deal with and depose experts. And that prompted him to write books. A lot of books. Babitsky has written or co-written many texts (http://www. seak.com/webstore/default.asp) with such titles as: • How to Become a Dangerous Expert Witness – Advanced Tech niques and Strategies • Cross-Examination – The Comprehensive Guide For Experts • National Guide to Expert Witness Fees and Billing Procedures – The Definitive Guide to Expert Witness Fees • How to Excel During Depositions – Techniques for Experts That Work But the one I thought you might be most interested in is his latest: The A – Z Guide to Expert Witnessing by Steven Babitsky, James Mangraviti, Jr. and Alex Babitsky. Don’t ask me why (because I don’t know), but when I first received the book I started reading at the back. For those of you who have done accident reconstruction and testified at trials and depositions for years or if you are just starting out in this challenging field, you may also wish to start reading the book from the back.

Among the goodies found in the 26 appendices are sample consulting agreements, model CVs and fee schedules. There are directories of referral organizations plus the names, addresses, phone numbers and Web addresses of all the state bar associations.

This hardbound book of 626 pages teaches you such things as how to best connect with and persuade a jury, how to market yourself professionally and cost-effectively. It helps you with testifying skill and how to handle abuse by attorneys. It explains how to bulletproof your CV and written reports. Each of the 24 chapters has a Conclusion and if you are in a hurry, read just the conclusions…

Then if you find something pertinent to your situation, you can read more about it in detail.

But I found a great deal of interesting material especially valuable to those just getting into expert testifying. For instance, in the chapter on Qualifications, it explains who is qualified and who is not and cites case law.

There was the mechanical engineer – in Example 6.14 – who was found not qualified to testify as an accident reconstructionist because he didn’t have any training or experience in the field. Or – Example 6.28 – an engineer found not qualified due to

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

N

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

body away from the center of rotation, caused by the inertia of the body.” [Emphasis mine.] All that is covered in the Force chapter.

Rivers notes: “The term centrifugal force, although not designating a real force, is an acceptable, relative term, widely recognized alongside inertia, where failure to generate adequate centripetal force is present.”

Basic Physics, by R.W. Rivers, is a valuable addition to any accident investigator or reconstructionist’s library. It is available through the aforementioned website or by calling CHARLES C THOMAS • PUBLISHER, LTD. (800) 258-8980 [Outside the U.S. 217-789-8980]. Write to them at 2600 S. First St., Springfield, IL 62704, or send an e-mail to books@ccthomas.com.

The base price is $28.95. Shipping and handling is $6.95 in the U.S. and Illinois residents must add sales tax. Foreign orders require payment in U.S. currency with your order. The actual shipping costs will be charged for shipping and handling. They also have an “Examination Policy” designed for instructors who are considering purchasing 10 or more copies for their course.

“And if you order multiple copies of any one of Thomas’ titles, you can receive a quantity discount. Check with the Publisher for further details.”

(About the reviewer: Joseph E. Badger is an internationally known accident reconstructionist who has had over 100 articles published in such periodicals as Law and Order magazine, Accident Reconstruction Journal, Accident Investigation Quarterly, and others. Having retired after 20 years with the Indiana State Police, Mr. Badger resides in Bloomington, Indiana.)

Collision

83

vidence In Traffic Crash Investigation And Reconstruction By: R.W. Rivers International Network of Collision Reconstructionists member, author, 33-year RCMP veteran, traffic crash investigator, reconstruction consultant and all-around good guy R.W. (Bob) Rivers has just penned his 11th and – he says – final book. He spent a lot of time writing the title.

EVIDENCE IN TRAFFIC CRASH INVESTIGATION AND RECONSTRUCTION: Identification, Interpretation and Analysis of Evidence, and the Traffic Crash Investigation and Reconstruction Process.

A blurb of the book posted at the publisher’s Web site indicates the book has 324 pages. Well, that’s a stretch. To be honest, the last numbered page is 295. But gee, it has the “About the Author” page, a title page, list of contributors page, a dedication page, a forward AND a preface…. And it has a “Note,” a “Disclaimer” and a word about the Metric System. Then a 10-page table of contents. So, yeah, 324 pages. It also has 175 illustrations and 13 tables.

Rivers has always maintained that there is a lot more to traffic crash investigations than “speed analysis,” and therefore for his ultimate text he covered the entire investigation/process in his new manual. And yet he still covers most of the essential ingredients of speed analysis.

One thing I like about the book aside from its contents is that it’s full of friends and memories. For example, Russ Arend wrote the Foreword. I remember Russ from his heading the “Long Course” at Northwestern University Traffic Institute (now the Center for Public Safety). He went on to establish the Institute of Police Technology & Management (IPTM) at the University of North Florida. Rivers dedicated his book to Dr. R.C. (Dick) Hodge, IPTM’s editor and without whom my own book Trailer Underride: Conspicuity, Human Factors, and Rear Bumpers would never have found the light of day.

Contributors to Rivers’ “Evidence Manual” include two INCR members, Al Baxter and George Bonnett. Another contributor and colleague of mine, with whom I was embroiled in a few cases, was the late Bernard Abrams. Rivers also acknowledged INCR members Frank Navin, John Ruller and my friend the late Charlie Kirk. The fact that on page 31, Bob Rivers listed one of my articles under the heading “Recommended Reading” didn’t hurt.

Speaking of recommending reading, the bibliography in the back of the book lists a whole bunch of people you know and whom I consider personal friends… Besides the folks whose names I dropped earlier, you will find Tony Becker, Bob DuBois, James Collins, Vic Craig, John Daily & Nate Shigemura, Mike Lofgren, Rudy Limpert, Jim Mitchell, Dan Parkka and Gary Stephens. (Yes, I know, I didn’t list Nate’s name alphabetically because he is inexplicably firmly fixed to John Daily.)

Now that we have all that out of the way, I suspect you’d like to know what’s actually IN the book. It begins with an Introduction to Traffic Accident Investigation. This is not a three or four paragraph description of the investigation process. It’s almost 30 pages explanation of the investigator’s duties, the accuracy

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

E

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

a delayed visit to an accident scene.

There is a chapter titled “Bulletproofing an Expert’s Report” that contains several examples of things NOT to put in a report. The authors remind readers: “Wise experts do not draw legal conclusions (for example, ‘The plaintiff was guilty of contributory negligence’). [That sentence provoked defense counsel to ask], ‘Can you please explain to the jury the four elements of negligence, Mr. Harding?’” [I believe the authors are referring to (1) duty, (2) breach of duty, (3) causation, and (4) damages, but don’t quote me.]

There is a great chapter on “Methodology.” It contains citations of well over one hundred cases where expert testimony was admissible or inadmissible. Those cases involving accident reconstructionists, engineers, biomechanics, and doctors – where testimony was excluded, barred or disallowed – make interesting reading.

Mr. Babitsky wins my prize for the World’s Best Politically-Correct Expression. In Chapter 14, “Direct Examination,” he discusses juries thus: “When preparing his responses, the expert should keep in mind that he will be attempting to persuade a jury of lay people, many of whom may be scientifically unsophisticated.” [Emphasis mine.]

If you have been cross-examined dozens of times, you may already aware of much of the information in Chapter 15, but if you are relatively new to the industry, study “Cross Examination” well before you spend much time on the witness stand. Chapter 19, “Fees, Billing, and Collections” is mandatory reading for anyone who has been stiffed by a client or made to jump through hoops in order to get paid. And if you feel that you have ever been “abused” when giving a deposition, read the section in Chapter 24 about the attorney who was disbarred after being obnoxious to an expert witness.

I asked Mr. Babitsky if he could give only one piece of advice to an expert what would it be? He said, “Develop and stick to a protocol that you use in all of your forensic expert witness work.

This will help you to do quality work and not miss crucial aspects of the case.” What major pitfall should experts avoid? He said, “Trying to please the current client by telling him what he wants to hear despite evidence to the contrary.”

If you are pressed for time and can read only one chapter, Babitsky recommends Chapter 18, “Marketing an Expert Witness Practice.” It gives you a lot of dos and don’ts when it comes to advertising your business.

The A – Z Guide to Expert Witnessing is available by phone, fax or Website. The price is $135 plus $9 shipping. You can order by phone by calling 508.457.1111 or go to http://www.seak.com/ and click on Webstore.

Questions? You may write to them at SEAK, Inc., P.O. Box 729, Falmouth, MA 02541 or inquire by email: Mail@seak. com. If you would like to contact the author personally, use his e-mail address: sbabitsky@aol.com.

84 Collision www.collisionpublishing.com

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

first place. Each chapter could be a book all by itself.

At Chapter Ten, we have Al Baxter’s “Evidence Manual [for] Motorcycle Crash Investigation.” This chapter discusses, among other things: rake, trail, acceleration, braking and turning.

And it explains the dreaded lean angle equation for determining the amount of lean required to successfully negotiate a curve. There’s a section on calculating the minimum speed of a skidding or sliding motorcycle (and a sliding rider, whether he’s wearing leathers or, heaven forbid, polyesters).

The book’s appendices offer all manner of U.S. and SI conversion tables and they are followed by a “Quick-Find Index” which refers to particular paragraphs rather than page numbers.

That way, you go straight to what you’re looking for rather to just a page where you would have to scan the whole page to find what you wanted. “Finally,” quoting the publisher’s blurb, “there is a comprehensive quick-find index that takes the reader directly to any topic, formulae, or subject matter - or any combination of these.”

The book – EVIDENCE IN TRAFFIC CRASH INVESTIGATION AND RECONSTRUCTION: Identification, Interpretation and Analysis of Evidence, and the Traffic Crash Investigation and Reconstruction Process – comes in both hard cover ($86.95) and soft cover ($56.95) and is available through Charles C Thomas, Publisher, LTD., 2600 S. First St., Springfield, IL 62704. (http://www.ccthomas.com) Or you may e-mail questions to books@ccthomas.com.

(c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

and errors involved, an expert’s responsibilities, plus there’s a nifty checklist – a “Series of Events” – to make sure you don’t miss anything.

The Introduction goes on to define the difference between a fact witness and a lay witness. It explains what the investigation should be prepared to do for trial. Also it presents a history of the Accreditation Commission for Traffic Accident Reconstruction (ACTAR) taken straight from the ACTAR Web site. (Except Rivers chose to substitute “Crash” for “Accident” even though most English-speaking lay persons still calls them accidents. And Bob, we’re not changing the acronym to ACTCR. I mean how would you pronounce that?)

Chapter Two is all about the human element in accident investigation and reconstruction. Written by Martin Kurke and Anne Corbin the chapter delves into human reliability, error, and risk-taking. Bernard Abrams wrote Chapter Three, “The Role of Vision, Visibility, and Discernibility in Driver Performance.”

Okay, so there’s no such word as discernibility. Abrams was an optometrist, not a lexicographer, so I’ll cut him some slack. We all know the word is discernability, a noun meaning “distinctness that makes perception easy.” Bernie gets into photopic and scotopic vision, acuity, and factors that can affect vision.

Chapter Four is a two-part chapter dealing with pathology (written by James Ferris) and the medical examination (written

by Los Angeles County Medical Examiner Dr. Lakshmanan Sathyavagiswaran). And while the name Lakshmanan Sathyavagiswaran doesn’t fall trippingly off the tongue, you may recall the name mentioned a time or two in the infamous O.J. Simpson trial.)

There are at least two people named Michael Sweet. Probably the more famous Michael Sweet is a Christian rock singer and co-founder of perhaps the most popular Christian rock band ever, Stryper. He had absolutely nothing to do with Bob Rivers’ book.

The other Michael Sweet – the Bloodstain Pattern Analysis Consultant Michael Sweet – from Edmonton, Alberta, wrote Chapter Five. Which, not surprisingly, is all about Bloodstain Pattern Analysis.

Chapter Six, “Forensic Photography and Scene Measurements,” is in two parts.

Robert Wyman handles the photographic applications section while Bob Rivers covers scene measurements and plan drawings. Rivers managed to write Chapter Seven, “Trafficway Evidence,” all by himself. Trafficway Evidence is what some of us might refer to as “Facts from the Road.” This chapter covers traffic control devices, signals, detectors, timing, pavement edges, glare, debris, scrapes, scratches and grooves, chips, chops and gouges.., and all sorts of tire marks. Bob includes pages of great photos to assist the reader in identifying physical evidence on the roadway.

Chapters Eight (Vehicle Examinations) and Nine (Speed Analysis and Determinations) are both by Rivers. These two chapters – which make up 40 percent of the text – may be why you bought the book in the

Collision

85

c

In

p

ro u

G

a

)2

00

7

C ra

sh

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

There are any number of accident reconstruction books out there and most cover a wide gamut of situations and are full of equations and messy physics stuff. A few texts, however, target specific types of collisions – such as the wonderful Trailer Underride: Conspicuity, Human Factors, and Rear Bumpers. But now there’s a book that targets specific accident locations. I call it Traffic Signal Intersection Accident Reconstruction or TSIAR. The actual mouthful title is Accident Reconstruction at Traffic Signal Intersections: A Manual for Law Enforcement Personnel, Accident Reconstruction Professionals, Traffic Engineers, and Forensic Engineers by Daren E. Marceau, P.E. The author is a former Raleigh, N.C police officer who is now traffic signals project manager at Kimley-Horn and Associates in Raleigh. That company, according to Fortune magazine is one of its 100 Best Companies to Work For in 2005 and 2006. Says so right at their website: http://www.kimley-horn.com/kha/ In his Introduction, Marceau tells the reader: “This text is not intended to be an exhaustive book on the precise details that go into traffic engineering. It is intended to serve as a manual for reconstructing traffic accidents that occur at intersections controlled by traffic signals.” Marceau adds, “This is the first edition of this text. The reconstruction methods and traffic engineering explanations presented here are reliable and time-proven. As any experienced investigator knows, however, more than one way to solve any given case usually exists.”

You may purchase the book without the book. Let’s go over that again. For $39.99 you can purchase a CD-ROM version.

For $10 more you can get a printed version of the book. I like having the printed text because I can keep it on a shelf and refer to it without having to crank up the computer.

That said, there are advantages to the CD. For instance, where the book’s photographs are black and white, the CD pictures are in color. Any and all text, as well as the photos and diagrams, may be copied to the clipboard and pasted in a report or other document.

There are, however, a few places – at least in the Glossary – where you cannot copy an entire paragraph.

The CD ver-

sion of the book includes the entire text and graphics in PDF form, plus you get version 7.0 of Adobe Acrobat to download if you don’t already have it. On the off chance you would like to print the entire book yourself, there are separate PDF files of the front cover and inside cover.

Also, even though the book has an index, there always seems to be something you want to find that isn’t listed in the Index or Table of Contents. Speaking of the Glossary, if you happen to look under “Protected/permitted,” you will see a reference to a “permitted green ball.” Green ball, however, is not defined in the Glossary. So it’s handy to be able to search the text to see the term explained on page 26.

Or you may come across this statement: “Without this understanding of the difference between permitted and protected left turns, some crashes occur when drivers think they can turn left in front of oncoming traffic during the display of a circular green signal indication.” You may ask, “What’s a circular green signal indication?” Again, that handy search feature is, uh, handy.

Among the text’s 187 pages are seven case studies or as Marceau calls them, “Accident Scenarios.” I don’t know if they are actual cases or made-up situations to illustrate particular points.

Chapter topics include Traffic Engineering Basics; Traffic Signals, Controllers, Phasing, and Design; Traffic Signal Timing; Vehicle and Pedestrian Detection; Signal Preemption; Detailed Case Studies; and of course, Accident Reconstruction at Traffic Signals.

Section 3.14 is about “Pedestrian Signals.” You know, I always thought those little “Pedestrian Buttons” on traffic signal poles were probably not hooked up to anything, but that they were just put there to appease pedestrians into believing that one day the light would change. But the device buttons really are programmed to convey an actuation to the controller for pedestrian and wheelchair subjects to eventually get a green light. There are some illustrations that may be confusing, such as the ones called “Two-Phase Signal with Multiple Preemption Directions” and “NEMA Controller with Concurrent Phase Combinations.”

If you’re working a signalized intersection collision and you obtain a similar diagram from the highway department, you may just want to have the prosecutor or civil attorney subpoena someone at the highway department who can interpret the diagram for the jury. Some such graphs may be more difficult to describe than explaining where the 30 comes from in “30df.”

You can find out more about Accident Reconstruction at Traffic Signal Intersections: A Manual for Law Enforcement Personnel, Accident Reconstruction Professionals, Traffic Engineers, and Forensic Engineers or place an order by contacting Kinetic Energy Press, 4676 Commercial Street SE #177, Salem, Oregon 97302. Phone (503) 540-3244 – FAX (503) 540-3479. Online at http://www.kineticenergypress. com/. Note that the prices mentioned above will increase on January 1, 2007.

D at

T

raffic Signal Intersection Accident Reconstruction

By Daren E Marceau

(c

About the reviewer: Joseph E. Badger is an internationally known accident reconstructionist who has had over 100 articles published in such periodicals as Law and Order magazine, Accident Reconstruction Journal, Accident Investigation Quarterly, and others.

Having retired after 20 years with the Indiana State Police, Mr. Badger resides in Bloomington, Indiana.

C

86 Collision www.collisionpublishing.com

Collision

87

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

In c up ro G a at D sh ra C 07 20 (c )

Reconstruction And Analysis Of Steering-induced, On-road, Untripped SUV Rollover Tests (Part 1) Michael Gilbert, P.E. Gilbert Engineering, LLC

c

In

p

ro u

G

a

D at

sh

C ra

7

00

A

The vehicles involved in the testing were a 1991 Ford Explorer XLT 4x2 and a 1997 Toyota 4Runner SR5 4x2. This paper focuses on the rollover test involving the Explorer. A subsequent paper will examine and analyze the 4Runner rollover test. These tests were run using the vehicles' own engine and drive train to accelerate the vehicles. A remote radio signal was used to control the accelerator, brake and steering wheel during the pre-yaw period. The vehicle speeds and steering inputs that lead to the rollover are presented.

)2

bstract Two steering-induced, on-road, untripped rollover tests of SUVs were conducted. This paper identifies and documents the physical evidence generated as a consequence of one of these rollovers and examines how this evidence is related to the motion of the vehicle during the rollover sequence. The second rollover test will be examined in a subsequent paper.

The vehicle evidence resulting from the rollover included scratch patterns, tire damage, rim damage, suspension damage, window damage and roof crush. The roadway evidence included pre-roll yaw marks, paint transfers/scrape marks, glass deposits, rim gouges, rim imprints, tire scuffs, vehicle debris, and fluid stains.

The vehicle motion was documented and analyzed during the test using video cameras. Analysis of the vehicle motion was used to determine the cause of the resulting vehicle and roadway evidence. The vehicle dynamics during the rollover sequences were also analyzed. The rollover dynamics include number of rolls, rollover distances, speeds, accelerations, roll rates, yaw angles, and yaw rates.

Daniel A. Godrick

ntroduction A rollover is defined as an event in which the vehicle rotates at least 90 degrees about its longitudinal axis and its tires are no longer in contact with the ground. [1] In 2005, a total of 31,322 occupants died in motor vehicle accidents.

[2] Of those 31,322 occupants, 10,770 (or 34%) died in rollover crashes. [2] By contrast, rollovers only accounted for 3% of all motor vehicle crashes. [3] The risk of fatal injury in a rollover accident is exacerbated by the type of vehicle involved the rollover accident. In 2005, rollovers involving cars accounted for 24% of all

I

(c

Lawrence A. Wilson, P.E. Wilson Consulting, LLC

88 Collision www.collisionpublishing.com

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

deaths for occupants in cars. [2] Whereas, rollovers involving SUVs accounted for 60% of all deaths for occupants in SUVs. [2] The disparity between the frequency of rollover crashes relative to other crashes (3%) and the high fatality rate associated with rollovers (24% for cars, 60% for SUVs) indicated that rollover accidents are usually associated with serious and fatal injuries. Therefore, rollover accidents are costly with regard to human life, medical care, and insurance/legal matters.

Currently two types of dynamic rollover tests are typically conducted to determine a vehicle’s performance in rollover. To examine the vehicle’s performance up to the point of roll, vehicles are tested while equipped with outriggers. To examine the vehicle’s performance after rolling over, dolly tests are used.

In the outrigger tests, the outriggers serve two primary purposes: to insure the safety of the test driver and to prevent irreparable damage to the test vehicle. Given that outrigger contact usually occurs shortly after two-wheel lift, the vehicle is prevented from actually experiencing rollover.

In a dolly rollover test, the vehicle is subject to a rollover following the protocol prescribed by FMVSS 208 [4]. This protocol specifies that a vehicle is oriented 90 degrees relative to its direction of travel and tilted 23 degrees with respect to its roll axis. It is then accelerated to approximately 30 mph and released from the dolly. Table 1 lists the vehicle characteristics as it is released from a dolly.

Speed

Yaw Angle

Yaw Rate

30 mph

90 degrees

0 deg/s

Table 1: Dolly Rollover Dynamics as Vehicle is Released (Point of Roll)

ehicle and Test Set Up Vehicle Set Up Two steering-induced, on-road, untripped rollover tests were conducted on two different occasions. The vehicles were a 1991 Ford Explorer XLT and a 1997 Toyota 4Runner SR5. The Explorer test, the focus of this paper, was conducted on April 1, 2005 at the Colorado State Trooper Training Facility in Golden, Colorado. The 4Runner test was conducted as part of the 2006 ARC-CSI Crash Conference in Las Vegas, Nevada and will be examined in a subsequent paper titled Reconstruction and Analysis of Steering-Induced, On-Road, Untripped SUV Rollover Tests (Part 2). The vehicle and tire data for the Explorer is listed in Table 3.

V

1991 Ford Explorer XLT 4-door 4x2 VIN: 1FMDU32X5MUD76298 GVWR: 5040 lbs Engine: 4.0L V-6 GAWR (Front): 2520 lbs Transmission: Automatic GAWR (Rear): 2900 lbs Occupant Load: Sandbags, 5 x 150 lbs for each available seat (750 lbs total) Actual Tires Model: Goodyear Wrangler RT/S L Size: P235/75R15 108S R Size: P235/75R15 105S Range 36 to 63 mph 16 to 72 deg 2 to 65 deg/s

Table 2: Vehicle Dynamics for Actual On-Road, Untripped Rollovers

State-of-the-art technology has allowed for the remote control operation of the braking, accelerating, and steering of vehicles in rollover tests. However, remote control operation of vehicles subjected to on-road untripped rollovers is a difficult and costly endeavor, particularly since the consequence of a successful test is an irreparable vehicle. The National Highway Traffic Safety Administration (NHTSA) has implemented the use of remotecontrolled vehicles as part of their rollover testing protocol for their New Car Assessment Program (NCAP) Rollover Ratings. [6]

p

ro u

G

C ra

sh

D at

a

Remote Control Set Up (Steering, Throttle and Braking) The set-up for the remote control mechanisms (steering, throttle and braking) for the Explorer has been previously described in detail [8]. A brief overview of this set up is presented in this section.

The steering, throttle and braking maneuvers were controlled by a remote control transmitter (Photograph 1a). The receiver (Photograph 1b) brought the steering, throttle and braking signals into the vehicle and transmitted these signals to the different control mechanisms in the vehicle. The steering and braking control signals were transmitted via hardwire to a DC motor controller (Photograph 1c). The motor controller transmitted the steering signals to the steering motor and controller (Photograph 1d) and transmitted the braking signals to the brake actuator (Photograph 1d). The throttle signals were transmitted via hardwire directly

7

45 deg 31 deg/s

00

Yaw Angle Yaw Rate

Table 3: Vehicle and Tire Specifications for Explorer Test

)2

Average 50 mph

(c

Vehicle Parameter Speed at Roll

In

c

Table 2 lists typical values of speed, yaw angle, yaw rate, and roll rate for SUVs involved in on-road, un-tripped rollovers [5]. Comparing Table 1 with Table 2, there are significant differences in motion between vehicles launched from a dolly compared to the motion at point of roll for vehicles involved in actual rollovers. The most significant differences at the point of roll between the test and the real world accidents include: speed, yaw angle and yaw rate. These differences at point of roll affect the motion during the rollover including: the number of rolls, rollover distance, roll rate, yaw and yaw rate.

However, these vehicles are equipped with outriggers to prevent rollover. The extent of published data related to steering-induced, on-road, untripped rollovers is limited to a test by Robert Larson, et al. In this test, a 1985 4x4 Toyota Pick-Up was towed to a speed of 78 mph. At this point, a pre-programmed Right-Left-Right steer was inputted using a remote-control, which caused the vehicle to roll. [7]

Collision

89

Pre-Roll and Rollover Sequence - Summary Figure 1 is an overview of the evidence on the roadway as a consequence of this rollover test. The Explorer's pre-roll path and rollover trajectory are shown in Figure 2. The Explorer entered the test grid and yawed counter-clockwise in response to the initial left steer. It then yawed clockwise in response to the counter steer to the right and rolled, driver's side leading. During the period from initial left steer to point of roll, the Explorer left 143 feet of yaw marks and experienced an average deceleration of 0.10 g. The Explorer rolled four times and traveled 164 feet before coming to rest on its wheels. The roll sequence lasted for 4.6 seconds and the average deceleration was 0.41 g. A summary of the Explorer's rollover sequence is presented in Table 5.

ehicle Evidence Summary The evidence on the vehicle as a consequence of this rollover test included: scratch marks on the vehicle body (scratch patterns), tire damage, rim damage, suspension damage, window damage and roof crush. Photographs 2a-c show overall view of the damage to the Explorer. Figures 3a and 3b are color-coded summaries of the scrape marks on the Explorer.

V

Each color represents a specific roll.

Roll 1 Yellow Roll 2 Blue Roll 3 Red Roll 4 Green

ro u

p

In

c

A scratch pattern area with alternating colors indicated that the authors were unable to determine which roll generated these specific scrape marks. For example, the alternating red/blue scratches on the driver's D-Pillar (Figure 3a) meant that these marks could have occurred during Roll 2 (blue) or Roll 3 (red).

The driver's side scratch patterns on the Explorer are shown in Photographs 3a-3f. The scratch patterns in these photos were highlighted with the same color-coded sequence given in Figure 3a. The passenger's side scratch patterns on the Explorer are shown in Photographs 4a -4d. The scratch patterns in these photos were highlighted with the same color-coded sequence given in Figure 3b. Photos 5a and 5b show rollover damage to the hood and roof, respectively.

The character of the scrapes marks was indicative of when during the rollover sequence the scrape marks were formed during the rollover sequence. The character of scrape marks was defined by the elements listed below: • Severity (How deep scrapes go, into paint, into primer, down to bare metal, or through the bare metal) • Directional Uniformity (Are all scrapes in a group straight and in the same direction) • Density (How close are the scrapes to each other)

G

R

D

a

esults Some of the test results have been previously presented and reported. [8] However, this paper examines the physical evidence generated as a consequence of this rollover in more detail and examines how this evidence is related to the motion of the vehicle during the rollover sequence.

iscussion Vehicle to ground interaction during the pre-roll and rollover left physical evidence on the ground and on the vehicle. The vehicle evidence resulting from the rollover included scratch patterns, tire damage, rim damage, suspension damage, window damage and roof crush. The roadway evidence included pre-roll yaw marks, paint transfers/scrape marks, glass deposits, rim gouges, rim imprints, tire scuffs, vehicle debris, and fluid stains. The vehicle motion was documented during the test using video cameras. Analysis of the vehicle motion was used to determine the mechanisms causing the vehicle damage and roadway evidence.

D at

Scene Setup - Explorer A 40 foot by 240 foot grid, with 20 ft X 20 ft intervals, was laid out on the pavement as a visual reference to aid with the video analysis of the vehicle motion. Orange cones, alternately small and large, were placed along the edges of the grid at 20 foot intervals. Numerous cameras were stationed at positions along both sides of the test grid. Three video cameras captured overhead views using bucket trucks. One camera was stationed at the end of the test grid and captured the rollover sequence head-on. Two radar guns were stationed at both ends of the test grid.

Table 5: Summary of Explorer Rollover Sequence

sh

The steer angles reported in Table 4 use a centered steering wheel position as a reference. Therefore the actual amount of steer from the left to the right is 596 degrees (240 degrees + 355 degrees). The first 240 degrees of the right steer take out the first left steer and cause the wheels of vehicle to straighten, while the next 355 degrees of steer cause the vehicle’s wheels to turn to the right.

1.4 s 0.8 s 0.9 s 1.5 s 4.6 s

C ra

Table 4: Summary of Explorer Steering Profile

84 ft 34 ft 23 ft 23 ft 164 ft

Average Roll Rate 250 deg/s 450 deg/s 400 deg/s 250 deg/s

Time

7

600 deg/s 600 deg/s

1 2 3 4 Total

Average Speed 41 mph 29 mph 18 mph 11 mph

00

Steer Rate

Distance

)2

07

C

ra

Steering Amplitude 240 deg 355 deg

20 (c )

Steer Direction Left Right

sh

D

at

a

G

ro

up

In c

Steering and Initial Speed The steering profile was derived from a rollover test involving a 1993 4-door, 4x4 Explorer equipped with outriggers.

This vehicle was operated by a test driver inputting a left-right steer and had an initial speed of 39 mph. The target speed for the 1991 Explorer rollover test without outriggers was 45-50 mph.

Therefore, the steering profile from the outrigger test was modified so that the vehicle path would have the same lateral movement when run at the higher target speed (45-50 mph). The left-right steering profile is summarized in Table 4.

Roll

(c

from the radio receiver to the throttle servo located under the hood (Photograph 1e).

90 Collision www.collisionpublishing.com

density and high directional uniformity are typical to rolls with long distances and high translational speeds like Roll 1.

As the Explorer rolled from its roof (3rd frame, Figure 5b) onto its passenger's side (4th and 5th frames, Figure 5b) it experienced a substantial change in yaw and yaw rate. Comparing the scratch pattern from Roll 1 on the hood and roof (Photographs 5a and 5b) with the scratch pattern on the right rear quarter panel (Photograph 4d), the direction of the scrape marks increased from 50 degrees to 90 degrees. This sequence shows that the direction of scrape marks can vary significantly in the span of one-quarter roll especially if the vehicle is on the road for a significant distance.

Once the Explorer yawed to 90 degrees relative to its travel direction at the end of Roll 1, the lower portion of the right rear quarter panel and the right rear wheel dug into the gravel/dirt shoulder and the right front rim struck the asphalt pavement (5th Frame, Figure 5b). Video analysis and radar gun data indicated that this vehicle-to-ground interaction caused a deceleration in the vehicle's speed and a dramatic increase in the roll rate. Figure 5c is a scaled diagram of Roll 1 showing the orientation of the Explorer as it traveled through Roll 1. The yellow vehicle icons in this figure represent the first roll.

Roll 1:

Roll 2:

7

C ra

sh

D at

a

G

ro u

p

In

c

As discussed in the previous section describing the vehicle motion in Roll 1, the vehicle-to-ground impact at the end of Roll 1 decelerated the vehicle while simultaneously accelerating the roll rate.

Roadway evidence related to Roll 2 is shown in Photograph 10b and Photograph 12. Notable roadway evidence related to Roll 2 included scrape marks/paint transfers, a glass deposit, and a rim gouge in the gravel/dirt shoulder. Figure 6a is a scaled diagram of this roadway evidence.

The video frame sequence shows that the initial vehicle-to-ground contact during the second roll occurred as the driver’s side rear quarter panel and roof struck the ground (Frames 1-3, Figure 6b). As the Explorer rolled from its roof onto the passenger's side, the glass from the right rear door window was deposited onto the pavement and the right rear rim dug into the gravel/dirt shoulder (Frames 4 and 5, Figure 6b and Photograph 12). Inspection of Figures 3a-3b and Photographs 3a-3f and 4a-4d in conjunction with the video

00

Photograph 10a shows the roadway evidence at the beginning of Roll 1.

Notable roadway evidence in this photo included the initial rollover contact point, a gouge in the gravel shoulder, and the long, continuous scrape marks and paint transfers on the asphalt pavement. The corresponding vehicle damage for the initial rollover contact point in the gravel shoulder is shown in Photograph 3f. Photograph 10b shows the roadway evidence at the end of Roll 1. Notable roadway evidence in this photo related to Roll 1 included the continuation of the paint transfers and scrape marks on the pavement. But most importantly, Photograph 10b shows a heavy gouge in the gravel/dirt shoulder and a rim imprint in the asphalt pavement. This evidence was generated by vehicle-to-ground impacts that significantly affected the Explorer's rollover dynamics. Figure 5a is a scaled diagram of this roadway evidence.

The video frame sequence (Figure 5b) shows that the Explorer starts the rollover sequence at a shallow yaw angle.

The scrape marks related to Roll 1 along the driver's side roof line (Photographs 3b3f ) were 30-35 degrees from horizontal.

As the Explorer rolled from the driver's side roof line at initial ground contact (1st frame, Figure 5b) to its passenger's side roof line (3rd frame, Figure 5b), it traveled approximately 50 feet. The scrape marks related to Roll 1 on the driver's side roof line (Photographs 3b-3f ) to the scrape marks on the passenger's side roof line (Photographs 4b-4f ) progressed from 30 degrees (driver's side) to 50 degrees (passenger's side).

Inspection of Photograph 5b shows that these marks are continuous and therefore related to the same roll. As the Explorer continued to roll and slide from its roof onto its passenger's side A-pillar, the scrape marks have became even more severe. The scrape marks from Roll 1 on the passenger's side A-pillar completely wore through the paint and primer and partially wore through the metal (Photograph 11). Referring to Photographs 3b-3f, 4a-4d, 5a-5b and 11, the scrape marks associated with Roll 1 were very close together (high density) and ran closely parallel to each other (high directional uniformity). High severity, high

)2

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

R

left front tire yaw mark leading to the point of roll (Photograph 8) caused scuffing on the left front tire. Photograph 9b shows this scuffing on the outer edge of the left front tire tread.

(c

oadway Evidence Summary After the rollover was completed, the evidence on the ground related to this rollover was identified, measured, and photographed.

This evidence included pre-roll yaw marks, paint transfers/scrape marks, glass deposits, rim gouges, rim imprints, tire scuffs, vehicle debris, and fluid stains. The evidence and roadway geometry was measured using a laser transit surveying instrument. Figure 1 is a scaled diagram of the evidence on the ground as a result of the Explorer rollover test. Figure 2 shows the Explorer's path from it entry into the grid to its final rest position.

Pre-Roll Trajectory - Left-Right Steer Sequence, The yaw marks created by the Explorer as a result of the left-right steer sequence are shown in Photographs 6a-6c.

Figure 4a is a scaled diagram of the pre-roll yaw marks generated by the Explorer as a result of the left-right steer sequence. The position and orientation of the Explorer as it travels through its pre-roll path is shown in a video frame sequence (Figure 4b) and a scaled diagram (Figure 4c).

Tread scuffing is common when vehicles are subject to the lateral accelerations that result in the type of yaw marks shown in Photograph 6a. In this test, the Explorer exhibited scuffing on the outer edge of the right front and right rear tire treads as a result of the initial yaw (Photograph 7a and 7b).

Referring to the 4th frame of Figure 4b and the highlighted vehicle icon in Figure 4c, two-wheel lift (TWL) occurred more than 25 feet prior to the point of roll.

The point of roll was defined by the end of the yaw marks. Photograph 8 and Figure 4a show a rim gouge beginning 12 feet from the end of the left front yaw mark.

Two-wheel lift (TWL) occurred more than 13 feet before the start of the rim gouge.

Therefore, the rim-to-pavement interaction that caused the gouge shown in Photograph 8 was not the physical mechanism that induced TWL and ultimately, rollover.

This rim gouge was a consequence of the vehicle rolling to the point that the sidewalls of the tires, instead of the treads, contact the pavement. The sidewalls flexed and deformed, allowing rim-to-pavement contact. The rim to ground interaction caused vehicle damage in the form of scrapes on the left front rim (Photograph 9a).

Additionally, the creation of the

Collision

91

onclusions The data presented in this paper is a reliable and valuable source of information to automotive engineers interested in accident reconstruction of SUV rollovers and rollover testing of SUVs. This paper described the vehicle dynamics during the rollover sequence including rollover distances, speeds, accelerations, roll rates, yaw angles, and yaw rates. It documented the vehicle damage correlated to the physical evidence on the ground and the vehicle motion during the rollover sequence.

Specifically, an acceleration of the roll rate was precipitated by a heavy ground-to-rim or ground-to-undercarriage impact. The direction of scrape marks could vary within each roll. Therefore, the character of scrape patterns on the vehicle (severity, directional uniformity, and density) must be considered in correlating specific scratch patterns to a specific point in the rollover sequence.

G

ro u

p

In

c

C

D at

C ra

sh

A

a

cknowledgements The authors would like to acknowledge the Colorado State Patrol for use of their training facility. We would like to thank Bob Caldwell and Ponderosa Engineering for their help in providing knowledgeable staff in helping to set up the test and document the rollover test. The survey of the rollover test evidence that was used to generate the scene diagrams in this paper was conducted under the supervision of Arnold Wheat.

We would like to thank Arnold Wheat and Steve Arndt for providing numerous photos that were used in this paper. Finally,

7

The rim-to-ground impact at the end of Roll 3 caused the vehicle to vault with the front of the Explorer pitched upward. Notable roadway evidence from Roll 4 (Photograph 13b) included a gouge in the gravel shoulder caused by the left rear undercarriage and a fluid stain from the engine compartment. Figure 8a is a scaled diagram of this roadway evidence. The video frame sequence (Figure 8b) shows that the Explorer continued to pitch during Roll 4 as it traveled from the substantial impact at the left rear (Frame 2, Figure 8b) to the roof and hood (Frame 3 and 4, Figure 8b). The right rear quarter panel struck the ground as the vehicle rolled onto its passenger’s side (Frame 5, Figure 8b). At the end of Roll 4, the Explorer continued to roll, almost onto its driver's side, (Frame 7, Figure 8b) before it reversed its roll direction and returned to its wheels (8th frame, Figure 8b). Inspection of Figures 3a-3b and Photographs 3a-3f and 4a-4d in conjunction with the video frame sequence (Figure 8b) show that the scrape marks from Roll 4 vary in direction, but have a consistently light character, as previously defined (severity, directional uniformity, and density). These marks are not deeper than primer level, have no consistent direction, and have a relatively wide spacing. The lack of a consistent direction was a function of the translational speed of the Explorer relative to pitching and yawing motions.

At low speeds, rotational motion about the vehicle's Y-axis (pitch) and Z-axis (yaw) affect the direction in which the vehicle scrapes against the pavement. This effect is minimal early in the roll sequence when the vehicle has a high translational speed, but is more pronounced during the final roll when the translational speed is slower.

This yawing and pitching motion during rollover is also known as "footballing".

Figure 8c is a scaled diagram of Roll 4 showing the Explorer at each quarter roll as it travels through Roll 4. The vehicle icons in this figure are colored green to represent the fourth roll.

D

00

Roll 4:

ebris Thrown Forward During Rollover The right rear cargo area window and the windshield were thrown forward during rollover and came to rest approximately 20 feet beyond the Explorer's final rest position (Photograph 15). The cargo window was thrown from the vehicle at the start of Roll 2 (Figure 9a) and the windshield was thrown from the vehicle at the start of Roll 4 (Figure 9b).

The cargo window traveled approximately 80 from the point at which it was thrown from the vehicle to its final rest position.

By comparison, the windshield was thrown approximately 20 feet. The cargo window traveled a greater distance because the Explorer had more energy (translational and rotational) at the cargo window's point of release than that of the windshield.

)2

(c )

20

Roll 3 was a short roll that started and ended with sets of rim gouges.

Photograph 13a shows the roadway evidence from the start of Roll 3 to the Explorer at final rest. Notable roadway evidence in this photo related to Roll 3 included the detached left rear wheel, the left rear rim imprint in the asphalt, the detached right front wheel and the right front rim imprint in the asphalt. Photograph 13b shows the roadway evidence from the end of Roll 3 to the Explorer at final rest. Notable roadway evidence in this photo related to Roll 3 included the detached right front wheel and its corresponding rim imprint in the asphalt and fluid spray from the Explorer's battery. Figure 7a is a scaled diagram of this roadway evidence.

The video frame sequence (Figure 7b) shows that Explorer started to pitch dramatically during Roll 3. The first frame from the video frame sequence shows that the Explorer's left rear wheel struck the asphalt while the rest of the Explorer was airborne. This impact generated forces sufficient to break the left rear wheel from the rear axle. The imprint in the asphalt can be seen in Photograph 13a and the corresponding damage to the left rear rim can be seen in Photograph 14a. Subsequent to this impact, the Explorer continued to roll as it went airborne (Frames 2 and 3, Figure 7b) until it struck the right front rim and fender (Frames 4-6, Figure 7b). This impact caused the right front wheel assembly to detach from the Explorer. The right front wheel and the corresponding imprint in the asphalt can be seen in Photographs 13b and 14b. Inspection of Figures 3a-3b and Photographs 3a-3f and 4a-4d in conjunction with the video frame sequence (Figure 7b) show that the scrape marks from Roll 3 are limited to the left rear corner and the right front corner of the Explorer, due to

the Explorer's pitching motion. Figure 7c is a scaled diagram showing the Explorer at each quarter roll as it travels through Roll 3. The vehicle icons in this figure are colored red to represent the third roll.

(c

C 07

Roll 3:

ra

sh

D

at

a

G

ro

up

In c

frame sequence (Figure 6b) show that the Explorer experienced a heavy impact on the driver's side and the roof. As the the vehicle rolled onto to the passenger’s side roof, the vehicle-to ground contact was sufficient to cause the right rear door window and right front door window to shatter.

The right front fender struck the ground as the Explorer continued to roll from its roof onto the passenger’s side. Figure 6c is a scaled diagram showing the Explorer at each quarter roll as it traveled through Roll 2. The blue vehicle icons in this figure represent the second roll.

92 Collision www.collisionpublishing.com

we would like to thank Wade Bartlett for capturing the speed of the vehicle via radar. eferences 1.

Gillespie, Thomas D., Fundamentals of Vehicle Dynamics, Society of Automotive Engineers, Inc. 2.

Fatality Facts 2005, Insurance Institute for Highway Safety (IIHS).

Traffic Safety Facts 2004, National Highway Traffic Safety Administration (NHTSA).

Code of Federal Regulations 49CFR571.208, Code 49, Section 571.208, Standard Number 208, Occupant Crash Protection.

Wilson, Lawrence A., D. A. Godrick, S. Kildare, "Vehicle Dynamic Characteristics of SUVs in On-Road, Untripped Rollover Accidents", Collision-The International Compendium for Crash Research, Volume 1, Issue 2, Fall 2006.

NHTSA NCAP Larson, Robert E., et al., “Vehicle Rollover Testing, Methodologies in Recreating Rollover Collisions”, SAE Paper 2000-01-1641.

Gilbert, Michael, et al., "1991 Ford Explorer XLT 4x2 Automated Untripped Rollover Test", The SOARce-A Journal for The Society of Accident Reconstructionists, Summer 2006.

D

sh

ppendix A - Photographs

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 1c: DC Motor Controller

)2

A

Photograph 1b: Futaba R138DP Dual-conversion PCM 1024 8-channel Radio Receiver

(c

8.

(c )

6.

7.

20

07

C

ra

5.

at

a

G

ro

4.

up

3.

In c

R

Photograph 1a: Futaba T7CAP 7-channel Radio Transmitter Photograph 1d: Steering Motor-Controller and Brake Actuator

Collision

93

In c up ro G a at D sh ra C 07

Photograph 2c: Overall View of Damage to Explorer -

(c )

20

Photograph 1e: Throttle Servo

Photograph 2a: Overall View of Damage to Explorer - Driver's Side

Photograph 2b: View of Damage to Explorer - Passenger's Side

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 3a: Explorer Driver's Side Front Fender

Photograph 3b: Explorer Driver's Side A-Pillar

94 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07

Photograph 3f: Explorer Driver's Side Cargo Area/Roof

(c )

20

Photograph 3c: Explorer Driver's Door/Roof

Photograph 4a: Explorer Passenger's Side Front Fender

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 3d: Explorer Left Rear Door/Roof

Photograph 3e: Explorer Driver's Side C-Pillar/Roof

Photograph 4b: Explorer Passenger's Side Doors

Collision

95

In c up ro G a at D sh ra C 07 20

(c )

Photograph 4c: Explorer Passenger's Side Right Rear Quarter Panel (Lower)

Photograph 5b: Explorer Roof

sh

D at

a

G

ro u

p

In

c

Photograph 4d: Explorer Passenger's Side Quarter Panel (Upper)

(c

)2

00

7

C ra

Photograph 6a: Initial Yaw Marks

Photograph 5a: Explorer Hood

96 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 6b: Transition from Initial Yaw Marks to Final Yaw Marks

Photograph 6c: Final Yaw Marks

Collision

97

In c up ro G a at D sh ra C 07

Photograph 9a: Rim Scrapes on Left Front Tire

(c )

20

Photograph 7a: Right Front Tire Tread Scuff from Initial Yaw

Photograph 9b: Left Front Tire Tread Scuff from Initial Yaw

Photograph 8: Left Front Rim Gouge Prior to Point of Roll

Photograph 10a: Roadway Evidence at Start of First Roll

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 7b: Right Rear Tire Tread Scuff from Initial Yaw

98 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07

Photograph 13a: Roadway Evidence - Start of Roll 3 to Final Rest Position

(c )

20

Photograph 10b: Roadway Evidence at End of Roll 1 and Start of Roll 2

Photograph 11: Heavy Scraping from Roll 1 on Passenger’s Side A-Pillar

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Photograph 13b: End of Roll 3 to Explorer at Final Rest

Photograph 12: Roadway Evidence from Second Half of Roll 2 Photograph 14a: Damage to Left Rear Rim

Collision

99

In c up ro G a at D sh ra 07

C

Photograph 15: Debris Thrown Forward During Rollover

(c )

20

Photograph 14b: Damage to Right Front Rim and Tire

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

A

ppendix B - Figures

Figure 1: Overview of Rollover Test Evidence

100 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

Figure 2: Overview of Vehicle Trajectory

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 3a: Explorer Scratch Patterns - Driver's Side

Collision

101

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 3b: Explorer Scratch Patterns - Passenger's Side

Figure 4a: Evidence from Pre-Roll Sequence

102 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

Frame 2

Frame 3

Frame 4

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Frame 1

Frame 5

Frame 6 Figure 4b: Pre-Roll Video Sequence

Collision

103

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 4c: Pre-Roll Vehicle Path

Figure 5a: Evidence from Roll 1

104 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20

Frame 3

Frame 4

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Frame 2

(c

(c )

Frame 1

Frame 5 Figure 5b: Roll 1 Video Sequence

Collision

105

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 5c: Roll 1 Vehicle Rollover Trajectory

Figure 6a: Evidence from Roll 2

106 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

Frame 2

Frame 3

Frame 4

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Frame 1

Frame 5 Figure 6b: Roll 2 Video Sequence

Collision

107

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 6c: Roll 2 Vehicle Rollover Trajectory

Figure 7a: Evidence from Roll 3

108 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

Frame 2

Frame 3

Frame 4

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Frame 1

Frame 5

Frame 6 Figure 7b: Roll 3 Video Sequence

Collision

109

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 7c: Roll 3 Vehicle Rollover Trajectory

Figure 8a: Evidence from Roll 4

110 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

Frame 2

Frame 3

Frame 4

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Frame 1

Frame 5

Frame 6 Figure 8b: Roll 4 Video Sequence

Collision

111

In c up ro G a at D sh ra C 07 20

Frame 8 Figure 8b (cont.): Roll 4 Video Sequence

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

(c )

Frame 7

Figure 8c: Roll 4 Vehicle Rollover Trajectory

112 Collision www.collisionpublishing.com

In c up ro G a at D sh ra C 07 20 (c )

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Figure 9a (above): Right Rear Cargo Window Frame Separation from Vehicle Figure 9b (below): Windshield Separation from Vehicle

C Collision

113

Calendar

August ‘07 up

07

C

ra

sh

D

at

a

G

ro

7/9/2007 - 7/20/2007 Basic Crash Investigation SRR Training North Las Vegas, Nv

In c

July ‘07

conferences, training, and meetings

(c )

20

7/13/2007 - 7/14/2007 SATAI Annual Meeting Phoenix , AZ

8/6/2007 - 8/10/2007 Interviewing Techniques For The Traffic Crash Investigator IPTM Miami, Florida

7/16/2007 - 7/27/2007 At-scene Traffic Crash/traffic Homicide Investigation IPTM St. Petersburg, Florida

8/13/2007 - 8/17/2007 Basic Forensic Mapping Mapscenes West Chester, Oh 8/20/2007 - 8/24/2007 CATAIR Ontario Chapter Meeting Aylmer, ON 8/20/2007 - 8/22/2007 8/23/2007 - 8/24/2007 Mapping With Crashzone / Crimezone Riverside, Ca

7/23/2007 - 7/27/2007 SCARS Annual Meeting Charleston, SC

8/27/2007 - 8/31/2007 Advanced Crash Zone IPTM Jacksonville, Florida

In p ro u G sh C ra 7 00 )2 (c

7/30/2007 - 8/3/2007 Inspection And Investigation Of Commercial Vehicle Crashes IPTM Jacksonville, Florida

D at

a

7/23/2007 - 7/27/2007 Energy Method And Damage Analysis For The Traffic Crash Investigator IPTM Allegheny County Police Training Academy

c

7/16/2007 - 7/20/2007 Crash Zone IPTM Jacksonville, Florida

7/30/2007 - 8/3/2007 Interviewing Techniques For The Traffic Crash Investigator IPTM Jacksonville, Florida 114 Collision www.collisionpublishing.com

In c

September ‘07

10/1/2007 - 10/3/2007 Human Factors And Visibility SRR Training Boston, Ma

C

ra

sh

D

at

a

G

ro

up

9/10/2007 - 9/10/2007 CDR Technician Certification Course Collision Safety Institute North Las Vegas, Nv

October ‘07

10/22/2007 - 11/2/2007 Advanced Traffic Crash Investigation IPTM St. Petersburg, Florida G

9/18/2007 - 7/21/2007 IATAI Annual Meeting Bloomington, IL

10/22/2007 - 10/26/2007 Human Factors In Traffic Crash Reconstruction IPTM Jacksonville, Florida

c

9/10/2007 - 9/12/2007 Forensic Digital Photography For Crash And Crime Scene Investigators SRR Training Northampton, Ma

10/15/2007 - 10/19/2007 Mapscenes Prescott, Az

In

9/15/2007 - 9/18/2007 CDR Data Analyst Course Collision Safety Institute Bloomington, Ill

10/8/2007 - 10/19/2007 Traffic Crash Reconstruction IPTM Jacksonville, Florida

p

9/14/2007 - 9/14/2007 CDR Technician Certification Course Collision Safety Institute Bloomington, Ill

10/2/2007 - 10/4/2007 Pa. State Police Reconstruction Seminar State College, Pa

ro u

(c )

20

07

9/11/2007 - 9/14/2007 CDR Data Analyst Certification Course Collision Safety Institute North Las Vegas, Nv

)2

00

7

C ra

sh

D at

a

10/22/2007 - 10/26/2007 NYSTARS sponsored Annual Joint Association Conference Endicott, NY (c

9/24/2007 - 9/28/2007 Pedestrian/bicycle Crash Investigation IPTM Jacksonville, Florida 9/24/2007 - 9/28/2007 Crush Damage Analysis SRR Training North Las Vegas, Nv

If you would like to list an event in future issues, please send us an email with complete information to editor@collisionpublishing.com

Collision

115

Calendar

January ‘08 In c

November ‘07

conferences, training, and meetings

1/28/2008 - 1/30/2008 2008 Crash Data Retrieval User’s Conference ARC - Network, Collision Safety Institute Houston, TX

07

C

ra

sh

D

at

a

G

ro

up

11/5/2007 - 11/5/2007 CDR Technician Certification Course Collision Safety Institute Seattle, Wa (c )

20

11/6/2007 - 11/9/2007 Cdr Data Analyst Course Collision Safety Institute Seattle, Wa 11/5/2007 - 11/9/2007 Crash Zone IPTM Jacksonville, Florida

If you would like to list an event in future issues, please send us an email with complete information to editor@collisionpublishing.com

(c

)2

00

7

C ra

sh

D at

a

G

ro u

p

In

c

11/12/2007 - 11/16/2007 Traffic Crash Reconstruction Update Jacksonville, Florida IPTM

1/31/2008 - 2/1/2008 CDR Technician Course Train the trainer Course Collision Safety Institute Houston, TX

116 Collision www.collisionpublishing.com

Collision

117

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

118 Collision www.collisionpublishing.com

7

00

)2

(c sh

C ra D at a p

ro u

G c

In

(c ) 07

20 sh

ra

C a

at

D up

ro

G

In c

(c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

CDR Product Catalog - order online at www.cdr-system.com

CDR System Hardware Kit (software not incl.)

Part #FOOK10139 $2845.00 US Comes w/free CDR Cert Class or Rebate

Version 2.9 Software Subscription Software subscriptions are available in one-year or three-year subscriptions.

One Year: Part # FOOE900038 $395.00 US Three Year: Part # FOOE900040 $1185.00 US

CDR System2.8 Update Bundle Part #FOOK104702 $495.00 US Comes w/module, cable #02003320, cable #02003321 & 2.8 software

Cable # 02003293 $95.00 US

Cable # 02002888 $70.00 US

Cable # 06501340-006 $15.00 US

Cable # 02003002 $70.00 US

Cable # 02002828 $70.00 US

Cable # 02002829 $70.00 US

Cable # 02003090 $75.00 US

Cable # 02002837-01 $75.00 US

Cable # 02003003 $70.00 US

Storage Case # 02002880 $145.00 US

Power Booster # 02003108 $70.00 US

Cig. Outlet Pwr # 03001070 $35.00 US

Cable # 02002877 $75.00 US

Cable # 02003004 $70.00 US

I Got Hit LLC is an authorized distributor of Robert Bosch LLC Crash Data Retrieval products.

Prices are subject to change without notice

)2 (c

I Got Hit LLC 118 Lake Street South, Suite G Kirkland, WA 98033 P: (866) 223-4984 E: service@igothit.com www.cdr-system.com

00

7

C ra

sh

D at

a

G

ro u

p

In

c

Cable # 02003274 $95.00 US

Power Adaptor #02001723 $36.00 US

Cable # 02003043 $95.00 US

AUTHORIZED DISTRIBUTOR OF ROBERT BOSCH LLC CRASH DATA RETRIEVAL PRODUCTS Collision

119

Missed the 1st Volume of Collision? (c )

20

07

C

ra

sh

D

at

a

G

ro

up

In c

C Volume 1, Issue 1

Volume 1, Issue 2

a

G

ro u

p

In

c

Keep your library up to date...

(c

)2

00

7

C ra

sh

D at

Back issues are available in limited quantities. order online @ www.collisionpublishing.com/backissues.html or call toll free (800) 346-9571

120 Collision www.collisionpublishing.com

Investigations Just Got Easier With Sokkia’s Innovative Crime Scene Technology

Expert AutoStats® Expert AutoStats® is a computer program containing over 37,000 vehicles cars, vans, utility vehicles, and light pickups. 1945-2007 model years are represented.

G

ro

up

In c

This program can be used alone or with our Expert Qwic Calcs® and Expert VIN DeCoder® programs. Also accessible from within REC-TEC.

at

a

(Laptop & D esktop IBM C ompatible)

Manufacturer and Year

Select:

Model from pop-up window

Output:

Wheelbase Overall Length Height Wt. Distribution

(c

)2

00

7

C

ra

sh

D

Enter:

Curb Weight Width Drive Wheels Front/Rear Track

Mid-60's to present output also includes (when available): Front Overhang Rear Overhang Bumper Heights Hood Height Turning circle Wheel radius Bumper-to-Hood Bumper-to-Window

Expert AutoStats® is currently owned by over 660 private individuals and 270 Law Enforcement agencies in the U.S.A., Canada, and South America. Additional information, brochure, and order from can be downloaded from:

www.4n6xprt.com

4N6XPRT Systems®

Individual Vehicle Specifications

$40.00-First vehicle, $35.00/Additional Vehicles $20/Additional similar Model-same Make/Year/Order Minimum specifications include: Weight, Length, Width, Height, Wheelbase, & Wheeltrack VIN DeCoding when VIN is provided and Information is available Mid-60's to present also includes (when available) Front O verhang Bumper-to-hood Bumper-to-W indshield Turn circle

Bumper H eight Hood Height G round-to-base of W indshield W heel R adius

When making your request please identify: Year, Make, Model, & Number of Doors PICKUP/UTILITY/VAN please also identify: Short/Long wheelbase/bed 2/4 Wheel Drive Std./Super/Crew Cab Cargo/Passenger Van

Motorcycle Specifications (1970+)

$40.00-First vehicle, $35.00/Additional Vehicles $20/Additional similar Model-same Make/Year/Order

NHTSA Crash Test Data + A-B-G Stiffness $40.00 per Test

You can Fax your request 24 hours/day - 7 days/week. Please include your Visa/MasterCard/American Express Card Number-Expiration Date-Name on card- and Card Billing Zip & Address. Data is faxed back at no additional charge, and the hard copy is mailed. Normal response time is 1 working day.

FAX: 1-619-464-2206 or

Call 1-800-266-9778 Monday-Friday 9:30 am to 5:00 pm P.S.T.

An order form can be downloaded from:

www.4n6xprt.com

PROGRAM ORDER FORM (Please Print)

California Sales Tax Shipping & Handling

- 7.75%

= ________ = ________

p

In

c

= ________ = ________ = ________ = ________ = ________ = ________

S&H - Check = $11.75, Credit Card = $16.75, Govt. P.O. = $21.75

TOTAL (U.S. Dollars)

a

LEA Remote Mapper: Accuracy, efficiency and the convenience of single-person operation are all combined in this powerful, fully-robotic instrument.

- $ 595.00 ea.

- $ 275.00 ea.

- $ 375.00 ea.

- $ 475.00 ea.

- $ 475.00 ea.

- $ 85.00 ea.

ro u

Standard Mapper: Designed with the job in mind, this instrument is capable of measuring to prisms and reflective sheets, helping you finish faster, easier and safer than ever before.

Expert AutoStats® Expert Qwic Calcs® 4N6XPRT Ped & Bike Calcs® 4N6XPRT StifCalcs® Expert VIN DeCoder® (pkg) Expert TireStuf®

G

Prismless Mapper: This long-range, prismless instrument is ideal for making challenging measurements. Use it’s extremely narrow, visible red laser to pinpoint and accurately measure difficult positions.

Contact Name: _______________________________________________ Company: ___________________________________________________ Street: ______________________________________________________ City:____________________ State:____ Zip:__ __ Country: _______ Phone: (_____) _______________ Fax: (_____) _________________ E-Mail: ____________________________________________________

= ________

C ra

Exp ____/____

00

7

Card Number: ______________________________________________ Name on Card: ______________________________________________ Signature: _______________________________________________

)2

For more information on Sokkia’s LEA product line or to find a dealer near you, contact customer service at 800.4.SOKKIA, or visit www.sokkia.com.

sh

D at

Enclosed is: Visa ____ MasterCard ____ Am. Ex. ____

©2007 Sokkia Corporation

LEA

Sokkia

Law Enforcement Applications

800.4.SOKKIA • www.sokkia.com

Please Make Checks*/Purchase Orders Payable to:

(c

The Bluetooth word mark and logos are owned by the Bluetooth SIG, Inc. and any use of such marks by Sokkia is under license.

4N6XPRT Systems® 8387 University Ave - La Mesa, CA 91941-3842 - U.S.A. FAX: (619) 464-2206 Phone: (619) 464-3478 W eb: http://www.4n6xprt.com Checks *MUST* be drawn on a U.S. bank. Orders are shipped within 10 working days of receipt. Prices subject to change without notice. Multiple orders and Package discounts available. Please call for details.

software package that contains all the tools required for crash and crime reconstructions. Wether you do a linear momentum analysis, SMAC Simulation or create captivating 3D Animations; You never leave one application - FX3

;GDB I=: H8:C:

G

ro

up

In c

FX3 from Visual Statement is a state of the art reconstruction solution that allows you to perform accurate reconstructions ranging from simple sketches to detailed 3D Environments. FX3 was designed specifically for reconstructionists who benefit from a

D

at

a

Dc i]Z hXZcZ " LZ XVc ]Zae Ndj

00

7

C

ra

sh

Use our B";M Pocket PC data collector with any total station – see your points recorded in 3D.

(c

)2

Use 6XXZaZgZM on the same Pocket PC to measure deceleration ( drag factor ).

Use our EdX`Zi 8gVh]BVi] – to do preliminary calculations of impact speeds etc.

Use =Vl`:nZ our photogrammetry program to take accurate measurements with your camera.

6XXZaZgZM

7YY[b[hec[j[h

9b[Wh j^[ HeWZ _d c_dkj[i

IdiVa HiVi^dc 9dlcadVY

B";M

:WjW9ebb[Yjeh

ID NDJG 9:H@IDE Dc ndjg E8 Ä LZ XVc ]Zae Ndj Use ;M( Reconstruction software to download your measurements points and auto plot your scene diagram.

Use ;M( to generate a powerful 3D scene complete with textured surfaces and any models you need.

Collision: The International Compendium for Crash Research

/NE #OMPLETE 3OLUTION

Use our 8gVh] ;M momentum tool right on the diagram to generate impact speeds.

Ed[ _dj[]hWj[Z mehaifWY[$

In

c

ID I=: 8DJGI GDDB >c i]Z 8djgi Gddb " LZ XVc ]Zae Ndj

p

ro u         

G

 

a

D at

sh (c

)2

00

7

C ra

Use our HB68 ;M to simulate or predict collision results.

El[hm^[bc j^[c 7bb <N) ekjfkj _i Z[jW_b[Z WdZ Yekhj WYY[fjWXb[$

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           



Use our ;M( GZVaBdi^dc (9 to instantly animate your reconstruction results on your 3D scene.

Present powerful time distance reports and persuasive graphical output.

     

          



&OR SERIOUS 2ECONSTRUCTIONISTS SEE HOW &8 CAN BE RIGHT FOR YOU

mmm$l_ikWbijWj[c[dj$Yec

'$...$.(.$&).)

Volume 2, Issue 1 - Spring 2007

Use our 8gVh]BVi] application with 720+ reconstruction formulae to get all the answers.

ollision C The International Compendium for Crash Research

Volume 2 Issue 1

Two-Dimensional Analysis of EDR Information

Analysis of Collisions:

Conservation of Linear Momentum

2007 CDR User’s Conference CD Presentations & Data

The Accuracy of GM EDRs in NHTSA Crash Tests

Reconstruction & Analysis of Steering-induced, On-road, Untripped SUV Rollover