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Vol. 4 Iss. 2

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Crash site evidenCe

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Contents

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Fall 2009 Volume 4, Issue 2

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Estimation of Vehicle Speed and Trajectory Based on Video from a VehicleMounted Camera

By: Dan T. Horak

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“What is 30?”

By: Lenny Simpson and Greg Russell

Momentum - Vectoring in a New Approach

By: C. Gregory Russell

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The latest CDR System Data from GM Vehicles Update

By: Brad Muir

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Honda Gold Wing Motorcycle: Linked Brakes and Their Performance

By: Gary Johnson

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Braking Efficiencies of Motorcycles

By Experienced Riders in Hard Braking Situations

By: Lee E. Jackson and Raymond L. Wangler

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"my Turn At the Wheel" By: Richard C. Rinker Death Investigations and Their Psychological Effect on Police Officers

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By: Brian Smith

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Testing the Last Stop Record in the Mercedes MBE 4000

By: Benjamin N. Smith William F. and Ronnie E. DeMonia

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Automobile Extrication for the Reconstructionist

By: bill Davies

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Perception-Reaction Time: Is Olson (& Sivak) All You Need To Know?

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Comparison of Vehicle Measurement Techniques By: Daniel S. Peterson, P.E. and James

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Melcher, Jeffrey D. Armstrong, Jason D. Jupe, and Michael F. Bosworth

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106 Commercial Vehicle Dynamics For Collision Reconstruction By: Daniel J.

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This issue is exciting because it includes coverage of not one but two 25th anniversary association conferences, the WATAI annual conference and the ARC-CSI data DVD. Collision Magazine Premier Partner the National Association of Professional Accident Reconstruction Specialists (NAPARS) and the Canadian Association of Technical Accident Investigators (CATAIR) both celebrated their 25th year in existence with their annual meetings being held as we go to press. We were lucky enough to get a little information about each to share in this issue and hope to be able to bring you more association information in the future.

The 2010 multi-association Annual Conference (the 2009 Conference being the one lead by NAPARS) will reportedly be back in Ocean City, MD in the fall. CATAIR has reportedly announced their 2010 Conference and AGM for Winnipeg, Manitoba although the date’s not been released yet.

On the topic of conferences, you may have noticed or heard of all the “commotion” regarding the President’s statement this past February that “...You can't go take a trip to Las Vegas or go down to the Super Bowl on the taxpayers' dime. There's got to be some accountability and some responsibility.” As it turns out, for a while this past year some were dissuaded from going to Las Vegas for meetings and conferences. The Mayor of Las Vegas, Oscar Goldman, said in response, “ That’s outrageous, and he owes is an apology, he owes us a retraction.”

While the 09 ARC-CSI conference in Las Vegas was, again well attended and featured three 2009 model year Dodge and Jeep vehicles as part of the crash test series not to mention the other great cars Jim Byrne and the North as Vegas Police Department were able to provide, we have learned that at least one Federal government agency moved their training meeting from Las Vegas this year to Phoenix and, at the end of the day, it ended up costing them three (3!) times as much money to hold their meeting in Phoenix instead of Las Vegas.

So what’s the point here? Well, this issue of Collision includes the 2009 ARC-CSI Crash Conference proceedings (data, video, photos, presentation and more) on a data DVD from that conference in Las Vegas this past June. The 2010 conference is set for May 24-27 and, yes it’ll be in Las Vegas. But why not move it?

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The better question is “why should we move it?” We evaluated many other locations around the US where we could do the many things we do at our conference and still make it so the entrance fee is reasonable. With our tremendous working relationship with the North Las Vegas Police Department, the City of North Las Vegas, Station Hotels and Casinos and the Las Vegas Motor Speedway, we simply couldn't find another location to without the impact of considerably raising registration fees.

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We will continue to do our best to keep registration prices down but, in order to achieve that, we have to keep our costs down while continuing to provide excellence in an annual crash conference that includes multiple state-of-the-art crashes with late model cars every year, leading speakers in their respective field, at a major airport hub for convenient and less expensive travel and accommodations, year in and year out - that means, for now, what happens in Vegas, will stay in Vegas!

Managing Editor

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Collision Publishing LLC PO Box 3383 Kirkland, WA 98083-3383 Toll Free: 800-280-7940 Email: editor@collisionpublishing.com Web: www.collisionpublishing.com ISSN: 1934-8681

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Collision Staff Scott Baker Sean Haight Tonya Baker Shawn Greene

Owner, Managing Editor Sr. Editor Advertising Manager Customer Relations

Adverstising Rates & Information

The Collision Publishing media kit, including demographics, advertising rates, placement and sizes, is available online at: www.collisionpublishing.com

ARC - CSI Conference Data DVD

Advertiser Index

Included with this issue of Collision is the 2009 ARC - CSI Conference DVD. This data DVD includes all the crash test data collected, crash video footage, digital photos and the powerpoint presentations from the presenters.

4N6XPRT Systems ... 120, Inside back cover

All rights reserved, © 2006-9 Collision Publishing LLC. The opinions and conclusions expressed in this publication and attached data disk and throughout the articles attributed to specific authors are the opinions and conclusions of the authors noted and not necessarily the editorial staff or anyone else for that matter.

While some articles have been reviewed for content, the accuracy of reprinted models or equations cannot be fully guaranteed. It is the responsibility of the reader to apply critical thinking to an individual review of the content and make their own personal judgements as to its value to them, individually. At the end of the day, 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 PO Box 3383, Kirkland, WA 98083-3383. By sending correspondence to either 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 and, (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.

ARC-CSI Crash ARC-CSI Crash Conference CDs Conference CDs

ARC-CSI Crash Conference ... page 73 The Cad Zone ... page 94 Calc Zone ... page 1 CDR Users Summit ... page 72 Collision Magazine ... page 12 Collision Safety Institute ... page 13 Crash Data Retrival ... page 45 CSV Pro 2009 ... page 87 EDR Analytics ... page 86 Engineering Dynamics ... page 118, inside front cover Instrumented Systems Technology ... page 95

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Vericom Computers ... 119

WeCARE ... page 80, 86

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Visual Statement ... page 81, and back cover

If you would like purchase back issues of Collision Magazine, please visit www.collisionpublishing.com/backissues.html or call us toll free 800-280-7940.

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Back Issues

MapScenes ... pages 2, 59-62

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If you would like to submit an article to be published in Collision please email us your article for review or call us toll free 800-280-7940. Email: editor@collisionpublishing.com

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From the Desk of the President

For NAPARS, fall means that we found ourselves watching trucks crash into cars (or visa versa) and listening to the tearing and crunching of metal on metal in Ocean City, MD. By the time you are reading this, the 2009 NAPARS 25th Anniversary Joint Annual Conference will be one for the history books. The cars and trucks will have been towed away to the bone yard and rusting. Hopefully, many old friendships will have been renewed and even more new friendships made. And some great heavy truck crash training will have been shared. Our thanks go out to the other associations that helped us make this years conference a success. (A “conference dispatch” is found later in this issue of Collision).

Not surprisingly, there are numerous opportunities across the country for quality crash training. There is the annual CDR Users Summit, the ARC/CSI Conference in Las Vegas, and the many association conferences around the country. We all have opportunities to choose from one day classes, two day seminars, or multi-day conferences. From TAARS in Texas, to IATAI in Illinois, CATAIR in Canada, or to MATAI... who I should mention will be host for the Joint Annual Combined Conference in 2010… there are many great opportunities to enhance your crash investigation and reconstruction skills. As crash reconstruction becomes more technical and technology changes and evolves, individually keeping current is more important than ever!

In addition, networking with fellow reconstructionists allows you to build a group of colleagues and friends to consult with when you find yourself in need of a peer review, or some eclectic drag factor for fiberglass on fresh chip and seal. Forget the image of being a smooth-talking socialite, handing out business cards and shaking every hand in the room, networking today means being able to pass on meaningful information or count on someone getting back to you with timely and reliable information.

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While one of the benefits of attending a crash conference is simply making friends and building relationships with other professionals in the industry, those of us who have attended these events in the past – and will in the future, know these are a cornerstone of doing our jobs better. If you have not attended a crash training conference recently, you don’t know what you are missing.

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2009 marks the 25th year that NAPARS has been in existence, serving our membership and promoting professionalism in our field by supporting research, experimentation, and the exchange of ideas about accident reconstructions. It is our board’s hope - if not our plan! - that we are still helping to support our industy 25 years from now.

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Chuck Veppert President, NAPARS

www.napars.org

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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.

We have annual training opportunities at different locations across the country.

We try to have some sort of actual vehicle testing at each seminar, including full scale vehicle crashes. As a member, you would have access to a vast archive of results from many different and sometimes quite unique tests.

The 30th conference of IAARS will be held in the hometown of one of the founding fathers, Myron Lofgren: Elk River, MN. Meeting location is still to be determined, but they may be held at his home. There is a family-friendly Holiday Inn within about three miles, and there should be rapid transit in place between the nearest airport, Elk River, and the Mall of America by the time the conference begins. The conference will start on Monday, July 19, 2010.

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.

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

www.iaars.org

The early days saw the number of members ASPACI Inc. vary with the base of the association in VicASPACI is a non-profit society whose members have toria, Australia. ASPACI became ASPACI joined to share in the challenge of analysing the complicated issues of road collision investigation.

Membership to ASPACI is open to all persons engaged in collision investigation and its allied fields. The association members include Engineers, Police Officers, Independent Consultants, Scientists, Insurance Corporations, Manufacturers and Safety personnel. ASPACI is not a Trade Association or Political Lobby group, nor is it a Police organisation.

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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.

Incorporated in 1993 in Victoria. Now we boast members from all over mainland Australia, New Zealand., United Kingdom, and the United States, as well as parts of Asia.

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Becoming an Industry Partner of Collision offers many benefits to your organization including a discounted subscription rate to Collision for all your members, dedicated space in Collision Magazine to build awareness for your organization, and more. (c )2

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If your organization is interested in becoming a Collision Industry Partner, please contact Scott Baker at (800) 280-7940 x3 or by email: editor@collisionpublishing.com www.collisionpublishing.com

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2009 25th Anniversary Combined Annual Training Conference

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s I sit here in the Grand Hotel of Ocean City, Maryland writing this article, we are just about to complete the 2009 NAPARS 25th Anniversary Combined Annual Training Conference.

With temperatures in the 70’s and plenty of sunshine on the Boardwalk, the backdrop was set for another great conference.

While NAPARS is the responsible host this year, the conference also includes the memberships of MdATAI, NJAARS, NYSTARS, NATARI, and for the first time: PSFM. Although the training actually started Monday with an ACTAR preparatory class, the conference training began in earnest on Tuesday with an optional 8 hour Bendix Air Brake class. John Hawker, Service Engineer for Bendix Commercial Vehicle Systems provided an overview of commercial air brake systems, components, then reviewed present and future technology.

He impressed the attendees with a description of the state of the art full air disk brake systems being tested on tractor-trailers that are approaching the stopping distance capability of passenger vehicles. This is leading to a probable redesign of the suspension and steering components for future trucks so that they can withstand the extreme forces involved in stopping a heavy vehicle in a very short distance. (Not to mention how to keep a load of steel secured to the deck!)

What were the test vehicles you ask? Six brand new tractor-trailer combinations that were supplied by Perdue Farms of Salisbury, MD. Each was equipped with a different engine (Cummins, Cat, Mack, Volvo, and Detroit) so that the various ECM data sets could be downloaded for review. In between tests, the six shiny new $200,000 rigs were available for a “driving experience.”

Most attendees took advantage of the chance to drive a tractor-trailer on a closed course, under the direction of experienced Perdue drivers.

While I did hear a few gears grinding, the majority of the attendees drove very well and enjoyed the experience. The highlight of the testing was a near head-on collision between two moving vehicles, a 2008 Chevy Silverado and a Perdue donated 2000 Freightliner tractortrailer running at approximately 35 miles per hour. Rather than describe the damage, lets just say that there are few usable parts left on either vehicle!

With one more day to go, the focus will turn to data analysis that will be provided tomorrow on the conference DVD. For those who are with us now at the conference, I hope that you were able to get some good training that you can apply to your daily work.

But I also hope that you made friends, found sources and mentors, and generally had an enjoyable time with us. For those of you who were not able to be here, I hope you consider spending some time with us next year as it will be MdATAI’s turn to host the conference, which they have decided to have right back here in Ocean City!

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Wednesday brought a morning of training followed by an afternoon of testing at the

Ocean City Municipal Airport.

Tests were performed on heavy truck acceleration in a turn, brake testing with ECM data downloads, MCSAP inspection demonstrations, followed by crash testing between a tractor-trailer and passenger vehicles.

Veppert President, NAPARS

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2009 25th Anniversary CATAIR National Conference and AGM

Fall in Nova Scotia...you might think about the leaves turning, a chill in the air and the Canadian Association of Technical Accident Investigators and Reconstructionists (CATAIR) would be having their annual National Conference and AGM. If you thought that, we’ll you’d be mostly right.

The leaves weren’t really turning...not just yet.

September 14-18 CATAIR members from all across Canada met in Halifax, Nova Scotia for not only the 2009 National Conference but the association’s 25th anniversary conference. After 25 years, CATAIR’s 300some members represent crash investigators and reconstructionists from 5 countries and a variety of backgrounds. For the 25th Anniversary Conference the speaker line up was pretty impressive.

CATAIR Founding member Sgt Don LeComte (RCMP, Ret.) Was the keynote speaker and was, throughout the conference, “everywhere.”

Jeff Muttart, Kevin McClafferty, Jean-Louis Comeau, Bill Davies, Brad Muir and others from Canada and the US provided a variety of presentations on a wide range of crash reconstruction topics.

On the second day of the conference, the Collision Safety Institute conducted 3 crash tests including one with a 2004 Saturn Vue. The crash tests highlighted

many aspects of “event data recorder” technology but were also useful for a “do it yourself momentum analysis test.” For example, the third test was a 47mph (76 km/h) closing speed 99 Taurus into a 2000 Cavalier crash which can be used to illustrate the reliability and application of closing speed calculations in reconstruction. The Bosch CDR recovered crash data from the Cavalier gave virtually the same data as the Collision Safety Institute’s instrumentation and demonstrated, again, its reliability and application.

The CATAIR Atlantic Region sponsored and organised the conference lead by Ken Zwicker along with Charlie Hibbert, Dave Neal, Rod Hartlen and Trevor Jones among others who clearly gave of their time and effort to make the conference one of CATAIR’s most memorable.

The current National President, Terry Lolacher as well as a number of the current directors were present as well as several of CATAIR’s past presidents including CATAIR’s first female President and original representative to ACTAR, Deb Anderson.

The conference ended with those in attendance being inducted into the “Order of the Good Time” - an exclusive group, founded slightly before CATAIR (ok, founded in 1606) which was an appropriate ending to the conference that was, indeed a good time!

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CATAIR’s 2010 meeting is reported slated for Winnipeg, Manitoba. While no date has been announced, one might do well to keep an eye on their web site http://www.catair.net/contact.us.php for details on the 2010 conference or for more information on how to join CATAIR.

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Dedicated to providing timely and current crash research and information.

This is the first publication of its kind, featuring conference proceedings, articles of interest, peer-reviewed papers, crash test data, industry news and research. Each issue includes either a CD or DVD with conference proceedings in PDF along with all supporting data including crash test videos and digital photographs.

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Calendar

3/15/2010 - 3/26/2010 Concord, CA Traffic Accident Recon. I WeCARE 3/22/2010 - 4/2/2010 Evanston, IL Accident Investigation II Northwestern University Center for Public Safety

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2/1/2010 - 2/5/2010 Concord, CA Intermediate Accident Investigation WeCARE

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At the time this issue of Collision Magazine went to press, there is only one ACTAR examinations scheduled with sufficient time for registration:

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ACTAR Exams

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2009 WATAI Fall Conference

A brisk rain didn’t dissuade the membership of the Washington Association of Technical Accident Investigators (WATAI) from attending the crash test field day October 26, 2009 held in Federal Way, WA. Nearly 100 braved the “normal October in Seattle weather” (as some put it) to watch a series of what turned out to be 6 instrumented crash tests conducted by the Collision Safety Institute for the association. When the dust settled, the assembled membership witnessed 4 air bag deployment and two non-deployment crash tests which were used to illustrate a variety of concepts.

The following day - in the drier confines of the Washington State Criminal Justice Training Commission’s Burien training center - Greg Russell returned to the northwest and offered a presentation on momentum. Describing different methods of approaching a momentum analysis in a collision, Greg’s presentation parallels the article in this issue of Collision (Momentum - Vectoring in a New

Approach) and focused on vector diagraming and using momentum with no “zero approach” angle.

A presentation by Lee DeChant on the iWitness program (photogrammetry software for vehicle crush modeling) coupled with his team examining some of the damaged vehicles on the crash day explored the program’s applications. Rob Kaufman of the regional NHTSA Crash Injury Research Engineering Network (CIREN) team presented on the CIREN project and crash injury and finally the Collision Safety Institute review of the crash data rounded out the three day conference together with an association membership meeting.

The crash tests provided those in attendance with interesting data related to deployment thresholds and the role the crash duration plays in the deployment decision as well as under/override considerations. The final crash of the day, a two car moving head on, gave those in attendance an opportunity to see how the momentum applications Greg had been talking about on the previous day might be applied.

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Ron Sanders, Joe Champagne, Syb Hiemstra, Marc Champan, Jay Moloney and the rest of the WATAI board put together another great meeting and delivered the membership another opportunity for meaningful, state-of-the-art training.

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y r o t c e j a r T d n a d e e p S e l c i h e V f Estimation o a r e m a C d e t n u o M e l c i h e V a m o r f o e d i V n o d e Bas Dan T. Horak

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bstract The use of vehicle-mounted video cameras is on the increase. They can be seen on buses, trucks, taxis, passenger cars and trains in the US and worldwide. The main purpose of such cameras is to enforce safe driving by allowing supervisors to view unsafe driving events caused by drivers and provide training that reduces such events in the future. The National Transportation Safety Board (NTSB) developed a method for estimating speed and trajectory of vehicles involved in accidents based on videos from such cameras. The method is based on aligning landmark locations in synthesized video frames generated with a model of the camera optics and a survey of the accident site with landmark locations in video frames acquired by the camera.

It is tempting to try to estimate the speed of a vehicle just by watching the video taken by a camera mounted on it. However, the transformation from the 3D scene in front of the vehicle to a 2D video frame is very nonlinear and the camera frame rate is usually

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ntroduction Vehicle-mounted cameras are designed to capture video of accidents and dangerous driving events. Some systems, such as those used on locomotives, always store video of the last several hours of travel. Systems for highway vehicles, such as DriveCam, only store events that were detected when accelerometers built into the cameras measured accelerations that exceeded preset thresholds. The DriveCam II model, shown in Figure 1, installs on vehicle windshields and includes two camera sensors, one facing forward and the other rearward. Each sensor stores a total of 81 video frames per detected event, from 10 seconds prior to the event to 10 seconds after it. The color video is in 640x360 format and the frame rate is four per second per camera sensor. Pressing the red button seen in Figure 1 will start video recording even if the accelerations are below the threshold levels.

Figure 1: DriveCam II (showing the rearward facing side)

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quite low. Consequently, such speed estimates can be very inaccurate. For example, if the estimated speed is 65 mph but the uncertainty of the estimate is ±10 mph, it means that the vehicle could have been traveling at 55 mph or at 75 mph. This is not a useful result because it does not answer the question whether a vehicle involved in the accident was exceeding the speed limit or not.

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The main purpose of the speed and trajectory estimation method presented in this paper is to provide more accurate speed estimates.

The accuracy is achieved by comparing video frames acquired by a camera to synthesized video frames in which locations of landmarks at accident scenes are determined precisely by mathematically mapping their surveyed coordinates onto the frames.

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odeling Camera Optics The simplest camera is the pinhole camera shown schematically in Figure 2. It consists of a closed box with a pinhole in it. Since light travels in straight lines, the photographed object is projected onto the rear wall of the pinhole camera box upside down. Pinhole cameras are not very practical because they require very long exposure time due to the limited light energy that can pass through the pinhole. They do, however, serve as good models of camera geometry.

Figure 3 illustrates the computational process of generating a 2D image in the image plane from a 3D scene in front of the camera.

The blue triangle is an object in the 3D scene. The image plane is the ‘film’ on which the red 2D images are captured. The image plane is located focal length f in front of the center of projection p. As the broken lines in Figure 3 illustrate, point c in the 3D scene is mapped onto point c’ in the 2D image plane which is at the intersection of the image plane with the line that passes though points p and c.

This 3D to 2D mapping process can be performed mathematically for any number of significant points in the 3D scene. These points can be surveyed points on traffic signs, buildings, trees, lane markings, road barriers, etc. Once mapped onto the conceptual image plane, these mapped points would coincide with the corresponding points that an actual pinhole camera would have captured if its location and focal length corresponded to those used in the mathematical mapping exercise.

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arrel Distortion and its Correction At this point, one should be asking whether a real camera, one that uses a lens, can be modeled accurately by a pinhole camera model. The answer is that it depends on the angle of view of the camera. A ‘normal’ horizontal angle of view for a camera is about 40°, corresponding to a 35 mm film or sensor and a lens with 50 mm focal length. Cameras that have only one fixed lens usually have a horizontal angle of view of about 40°. The pinhole camera model is quite accurate for cameras with angles of view of 40° or less.

The pinhole camera model is less accurate for wide angle of view cameras, such as those with 60° or wider angles. The reason is barrel distortion that moves pixels that are far from the center of the image plane toward the center of the plane. The result is a barreldistorted ‘inflated’ image, such as the one shown in Figure 4b. The barrel-distorting wide-angle lens moved pixels near the edges of the image inward. Such distortion can cause estimation errors if the distorted image is used in algorithms that are based on pinhole camera models and do not take the distortion into account.

Figure 2: Pinhole Camera Figure 3 shows an alternative conceptual geometric model of a pinhole camera that is more convenient for modeling camera optics.

By placing the image plane in front of the center of projection, the captured image is not inverted. Otherwise, the image formation geometries in the cameras shown Figures 2 and 3 are identical.

Figure 4: Barrel Distortion Illustration 4a: Undistorted (left) 4b: Distorted (right)

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Images distorted by the barrel effect of wide-angle lenses can be corrected mathematically so that the resulting image is almost free of barrel distortion. The correction consists of moving the pixels that were moved inward back to their ‘correct’ distance from center along the same radial direction. The correction formula is:

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where rd = radial distance of a ‘distorted’ pixel from center r = radial distance of a ‘corrected’ pixel from center a = barrel distortion parameter (negative number) Figure 3: Computational Model of a Pinhole Camera

The parameter a can be found by trial and error. Figure 5 shows an original barrel-distorted image taken with the DriveCam II camera and the corrected image. Note that the shown images are the right

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plane are the images, as seen in the video frames acquired by the camera, of the three vertices of the blue triangle.

Barrel distortion correction eliminates most of the distortion due to the wide lenses of the DriveCam II camera. Therefore, the pinhole camera model is an accurate model of the DriveCam II camera as long as the camera images are corrected for barrel distortion via Eq. (1). The barrel-corrected DriveCam II images have a 70° horizontal field of view.

Now consider Figure 3 to be the representation of the mathematical model of the camera. The focal length f of the camera is known, the (x,y,z) locations of the vertices of the blue triangle are known from a site survey, the three vertices of the red triangle can be seen in the video frame, and their locations in the barrel-corrected video frames can be measured. It is easy to see that there is only one location of the center of projection point p of the pinhole camera model and only one pinhole camera orientation that will map the blue triangle vertices onto the red triangle vertices exactly as the real camera did. This location and this orientation are exactly those where the DriveCam II camera was when that video frame was acquired.

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bottom 533x300 pixels of the full 640x360 frames. Therefore, the differences are most visible on the right and bottom of the images.

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stimating Camera Locations The algorithm for estimating speed and trajectory of a vehicle equipped with a camera is based on estimating the locations and orientations of the camera at the times when the video frames were acquired. These locations form the trajectory of the vehicle and the speed can be estimated by dividing the location-to-location distances by the frame-to-frame time differences.

Consider Figure 3 to be the representation of the image formation process in the DriveCam II camera. The three vertices of the blue triangle in Figure 3 represent three points at the scene of an accident that have been surveyed and their (x,y,z) locations are known.

They could be road markings, points on traffic signs, points on road barriers, etc. The three vertices of the red triangle in the image

Therefore, if by trial and error a location and an orientation of a simulated pinhole camera can be found that map several points at a scene into the same points in the image plane as the real camera did, then that modeled camera location and orientation are those where the real camera was when that image was acquired. Since the camera is fixed relative to the vehicle, locating and orienting the camera also locates and orients the vehicle. The trial and error process that leads to accurate estimates of vehicle location and orientation based on video frames from a vehicle-mounted camera will be described later in this paper and illustrated by an example.

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Figure 5a: Original Image Taken with DriveCam II

etting Survey Data without Surveying a Scene In order to locate a vehicle by aligning landmarks in simulated images with landmarks in real images, the (x,y,z) locations of the landmarks at the scene are required. A survey conducted with a total station can generate such locations, as is done at sites of major accidents. NTSB developed a simpler and less expensive method for generating locations of landmarks at accident sites. It is based on aerial photographs available free on the internet and a video taken at the site after the accident. Figure 6 shows an aerial image of a curved segment of Maryland Route 100, downloaded from Google Earth. This location was used for testing the developed speed and trajectory estimation method and is not related to an accident.

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The broken red line superimposed on the photograph in Figure 6 is an arc with a 473 m radius, fitted to match the outside of the Jersey wall barrier seen as the thick white curved line in the figure. The good fit shows that the curve has a constant radius. There are reflectors on the Jersey walls that are not seen in the aerial photograph. Their spacing is somewhat uneven. These reflectors were used as the landmarks for locating a vehicle with a vehicle-mounted camera driven counterclockwise along the curve shown in Figure 6.

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The spacing of the reflectors was measured by recording a video of the Jersey wall from a car (other than the one equipped with the DriveCam) driven under cruise control counterclockwise along the curve. The video was acquired with a conventional digital camera point-

Figure 5b: Barrel-Corrected Image Taken with DriveCam II 20 Collision Volume 4 Issue 2.indd 20

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ed to the right and held steady by a passenger in the passenger seat of the car. Figure 7 shows a typical frame from that video. The frame captured a reflector that is seen near the center of the frame.

By examining the video frame-by-frame, and by relying on constant speed of the vehicle and constant video frame rate, the spacing of the reflectors on the Jersey wall was estimated with accuracy better than 0.15 m.

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The reflectors were all located on a constant-radius arc so that measuring their spacing was sufficient for estimating their relative (x,y) locations. The absolute locations of the reflectors were determined relative to a pole that held a highway sign. The pole was captured in the video and was also visible in Google Earth. Figure 8 shows the top view of the map of landmarks generated from the aerial photograph and the video of the Jersey wall. The red circles represent the unevenly-spaced reflectors on the wall. The green circle is the sign pole. Blue, magenta and black diamonds are points on a broken white lane line, a solid white lane line and the inner side of the Jersey wall at ground level, respectively. Note that the diamonds do not represent specific measured points. They are evenlyspaced points on curves with known fixed radii. These points are only used for aligning the vehicle lateral position and yaw orientation and, therefore, their absolute locations along the road are irrelevant as will become evident in later sections.

Figure 6: Aerial Photograph of Maryland Route 100 (from Google Earth)

Figure 8 (bottom): Map of Landmarks (top view)

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Figure 7 (top): Reflector on Jersey Wall

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he Main Program The computational model of the camera, shown in Figure 3, looks quite simple. However, the mapping from the 3D scene to the 2D image plane it illustrates is very nonlinear.

An efficient and user-friendly program with a graphical user interface (GUI) and with the nonlinear computations hidden from the user is required to facilitate timely estimation of vehicle locations.

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Figure 9 shows the GUI of a computer program developed at NTSB for estimating vehicle locations based on video from a vehicle-mounted camera. The program is written in Matlab.

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The GUI includes the top view of the map of the landmarks. Superimposed on the map is the vehicle shown as a blue rectangle.

The purple lines originating in the vehicle show the field of view of the camera. The green line marks the intersection of the field of view with the ground. The vehicle can be moved and rotated throughout the map by keystrokes and mouse movements. The blue text shows the current location and orientation of the vehicle.

Figure 9 shows the vehicle at the correct location and orientation as demonstrated by the good alignment of the landmarks in the photograph and the superimposed landmarks. Note that only the first four reflectors are visible in the photograph and the image of the pole is only marginally visible at the elevation of the third green diamond. The blue, magenta and black points on the ground do not correspond to specific surveyed points at the scene. They do, however, clearly indicate good lateral and yaw alignment of the vehicle on the curved road.

The process of estimating the trajectory and speed of a vehicle starts by loading the map of landmarks into the GUI and placing the vehicle at an initial location on the road. The first video frame is then loaded and the program immediately displays it and superimposes the computed landmark locations onto the video frame. Since the vehicle is not likely to be at the correct location at this stage, the superimposed landmarks will not coincide or even be close to the landmarks in the video frame. The mismatch between the landmarks provides information on the direction in which the vehicle should be moved to bring the landmarks into alignment. The user then utilizes this information and moves the vehicle in an iterative fashion until an optimal alignment is achieved.

It takes a skilled user about fifteen minutes to estimate the first vehicle location. Estimating subsequent locations takes about five minutes each. Ten to twenty vehicle locations are typically esti-

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The photograph in the GUI is the negative of a 340x190 pixel segment from a 640x360 DriveCam II video frame. The video is from a test conducted at nighttime. The red circles superimposed on the photograph are at image locations that correspond to the mapping of the red reflectors in the landmark map onto the image plane by a camera that is at the location and orientation shown in the map.

Similarly, the blue, magenta and black diamonds superimposed on the photograph are the projections of the similarly-colored diamonds on the map. The green circle on the map is mapped into

several green diamonds in the photograph because the circle represents the top view of a vertical pole.

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mated to subsequently derive an accurate estimate of the vehicle speed based on the video from a camera mounted on it.

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Figure 10 shows the landmark alignment at two additional vehicle locations. Figure 10a shows the alignment 1.5 seconds after the case shown in Figure 9 and Figure 10b shows it 5.0 seconds after the case shown in Figure 9.

Figure 10: Alignment of Landmarks at Two Vehicle Locations Frame 12 (left) Frame 26 (right)

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ideo Frame Timing Errors DriveCam II camera sensors acquire new video frames at the variable rate of 10 to 30 fps per sensor and store them in buffers. At precisely 4 times per second, the camera processor moves the frames from the buffers into memory. Assuming the lowest frame rate of 10 frames per second, and since the camera sensors and the storage into memory are not synchronized, the nominal frame spacing of 0.25 seconds (between frame acquisition times) can actually be as short as 0.15 seconds or as long as 0.35 seconds (0.25±0.1). These errors do not add up. If N consecutive frames (spaced nominally by 0.25 seconds) are analyzed, the time difference between the acquisition times of the first and

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The vehicle location in this test was estimated at 13 times spaced by 0.5 seconds, i.e., every other DriveCam II video frame was analyzed. The total distance traveled during these 6 seconds was about 120 meters (394 ft). Since the 12 intervals (each 0.5 seconds wide) were consecutive, the longitudinal error over the entire 120 meter distance was ±0.6 meters, or ±0.5%.

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The largest mismatch is at the sign pole (green diamonds) because its angular deviation from the camera axis is the largest. The first reflector also shows a mismatch compared to the alignment in Figure 9. For a specific video frame, the longitudinal error is smaller if there are landmarks located at larger angles to the camera axis, and it is larger if all the landmarks are almost along the camera axis.

Since the angular deviation from camera axis of the landmark closest to the vehicle varies from video frame to video frame, different

frames have different longitudinal location errors. The average of these longitudinal location errors is estimated to be 0.6 m (2 ft) and this value is used when computing speed estimation errors in a later section.

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Figure 11a shows that a 1° yaw error results in a large mismatch between the landmarks. Therefore, the yaw accuracy is better than 1°. Figure 11b shows that a 0.3 m lateral error also results in a large mismatch between the landmarks. Therefore, the lateral accuracy is better than 0.3 m (1 ft). Figure 11c shows a relatively small mismatch when the longitudinal error is 1.4 meters. The mismatch is relatively small because the landmarks are located ahead of the camera and estimating distance to objects by looking straight at them without stereo vision is difficult.

Figure 11: Alignment of Landmarks at Suboptimal Vehicle Locations (a) yaw error (top) (b) lateral error (middle) (c) longitudinal error (bottom)

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ocation Estimation Accuracy The video acquired by the vehicle-mounted camera is affected by vibrations of the vehicle, road surface irregularities, finite speed of the camera sensor, residual barrel-distortion and other distortions due to the camera lens. The (x,y,z) locations of the landmarks cannot be surveyed without some unavoidable errors. Consequently, the alignment between the landmarks in the video and the superimposed landmarks cannot be perfect. To illustrate the location estimation accuracy that can be achieved with these effects present, Figure 11 shows the case from Figure 9 with the vehicle intentionally moved slightly away from its optimal location and orientation.

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the last frame is nominally (N-1)x0.25 seconds. The actual time difference is somewhere within the (N-1)x0.25±0.1 interval. In the example presented here, the nominal total time was 6 seconds and the actual time was within the 6±0.1 second interval. Therefore, the maximum error of total elapsed time was ±1.7%.

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Such timing errors are unique to this specific camera. Other vehicle-mounted cameras may not have such errors and their frame timing may be very close to exact.

Figure 12: Thirteen Estimated Vehicle Locations

The vehicle locations shown in Figure 12 were analyzed to derive a speed estimate for the vehicle. Figure 13 shows speed estimates computed independently for each of the 12 intervals between the thirteen locations. The frame timing was assumed to be exactly 0.5 seconds (recall that every other DriveCam II video frame was skipped) and the longitudinal error was set to zero. The low value of the speed estimate in the second interval is due to the large timing error of the third frame, as explained above. The broken green line in the figure is the average of the twelve interval speeds. It is at 45.3 mph, very close to the 45 mph cruise control speed setting. This close agreement demonstrates that the timing and longitudinal location errors average out over many consecutive frames.

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Figure 13: Speed Estimates in Individual Intervals

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ehicle Trajectory and Speed The location of the vehicle in the test described here was estimated at thirteen locations.

The estimated vehicle locations are shown in Figure 12. The figure shows that the vehicle was driven centered in its lane at an approximately constant speed.

The estimated speed should be constant because the test vehicle was driven under cruise control (set at 45 mph). Note that the third vehicle location is closer to the second than it is to the fourth. It is because a timing error close to the maximum possible 0.1 seconds occurred when the third frame was moved into memory, so that the time interval between the acquisitions of the second and the third frames was closer to 0.15 seconds than it was to the nominal 0.25 seconds. Also note that, because of continuity of time along consecutive frames, such timing errors cannot add up. Therefore, the spacing between the third and the fourth locations is longer than the other spacings. In other words, the timing error across any number of consecutive frames is at most 0.1 seconds.

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Figure 14 shows speed estimates computed over varying numbers of consecutive 0.5 second long frame intervals. For example, the estimate corresponding to 6 intervals is derived over a 3 second time period (6x0.5=3) that starts when the first analyzed video frame was acquired.

Figure 14: Speed Estimates Derived over Consecutive Frame Intervals 24 Collision Volume 4 Issue 2.indd 24

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These estimates take into account maximum possible timing errors and maximum possible longitudinal location errors and show the resulting error bounds on the graph. The error bounds shrink as the total time gets longer and after 6 seconds (or 12 intervals) the speed estimate is 45.3±1.0 mph. The cruise control in the test vehicle was set at 45 mph.

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The vehicle in this test was moving at a constant speed. This is common in accident scenarios because vehicles just before an accident usually either move at a constant speed or maintain small constant acceleration or deceleration. Significant acceleration or deceleration would be evident in a figure similar to Figure 13 as increasing and/or decreasing interval speed estimates. DriveCam II includes a longitudinal accelerometer and its output, which is recorded over the same time period as the video, would also show that the vehicle speed was varying.

Speed analysis over longer time periods, such as that summarized in Figure 14 for the constant-speed test described in this paper, can also be applied to cases with varying speed. The curves in a figure such as Figure 14 would then represent the average speed over time periods during which the speed is known to be varying.

The average speed in such cases can be viewed as an estimate of the lowest possible peak speed during that time period. It is so because for a vehicle to move a given distance over a given time, the speed pattern with the lowest peak speed is a constant speed equal to the traveled distance divided by the elapsed time, i.e., the average speed. Any deviation from this speed would necessitate the vehicle to move, at least momentarily, faster than this speed. In many accident investigations, the key question is whether the vehicle was speeding or not. The estimate of the lowest possible peak speed is one means of determining with certainty that a vehicle was speeding.

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elation to Standard Photogrammetry The method described here looks similar to photogrammetry techniques used for accident scene mapping and owners of photogrammetry hardware and software should be asking whether those tools can be used to analyze video from vehicle-mounted cameras. They cannot be used.

Photogrammetry is based on triangulation of numerous points that appear in several photographs taken from different locations.

The photography takes place after the accident and is well planned.

Consequently, the number of points is sufficient, the data is accurate, and photogrammetry software automatically produces accurate results.

Video acquired by a vehicle-mounted camera usually captures only a few useful points, they are distributed along the road, they may not appear in more than one picture, and camera locations do not facilitate triangulation. Consequently, the data is neither rich enough nor accurate enough for a mathematical solution that automatically generates practical results.

To compensate for the low amount and the low quality of data, we developed the method described here that combines mathematics with computer-aided common sense-based analysis to produce accurate results.

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onclusions A method for estimating vehicle speed and trajectory based on video acquired with a camera mounted on that vehicle was developed. It yields accurate speed and trajectory estimates for vehicles involved in accidents. NTSB used this method successfully in both highway and rail accident investigations.

www.smartdrive.net

www.smartwitness.com

"DriveCam's exception-based video event recorder is mounted on the windshield behind the rear-view mirror and captures sights and sounds inside and outside the vehicle."

"The Smart Recorder System is an innovative Event recording system, capturing comprehensive vehicle data from triggered Events."

"The drive camera recorder will help provide evidence in the event of a crash of serious accident.

This product is offered with GPS logging as well making it the ideal car safety blackbox camera."

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Additionally, a technique was developed for deriving survey data needed for the speed and trajectory estimation method without performing a conventional survey of the accident scene.

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“What is 30?” (c

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Lenny Simpson Greg Russell

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Accident Analysis Reconstruction Inc.

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he defense attorney approached the witness box to begin his cross-examination of the police investigator. He begins by saying, “According to your testimony, your curriculum vitae is very extensive, enumerating attendance at numerous accident reconstruction courses and conferences.” The investigator answers, “That is correct, sir.”

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“Also, you stated you used the ‘slide to a stop’ equation to calculate the speed of my client’s vehicle, is that correct?”

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“Yes, sir,” the investigator eagerly replied. The attorney then asked, “Can you explain from where this formula is derived?” With the police officer’s confident building, he answered, “Yes sir, the kinetic energy equation.”

There is a silent pause and the defense lawyers asks, “If the distance is the measurement in feet, the f has no units of measurement nor does 30, would you explain to the jury how you can place a value with only feet under a square root radical and it magically spits out speed in miles per hour?”

The police investigator’s confidence drains from his pale face. He pauses and finally says, “That was the way I was taught. It even says that in the course formula sheet.”

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“With the court’s permission, officer, would you step down from the witness stand and write the slide to a stop formula on the flip chart?” The officer goes over to the flip chart and proceeds to write:

The attorney continues, “What is the ‘S’?” The investigator testifies, “That is for speed measured in miles per hour.” “Well, how about the ‘D’?” “That is the distance of the tire skid marks measured in feet or decimal of a foot.” “OK, what does the ‘f ’ represent?” asks the defense lawyer. The officer responds, “That is the deceleration factor, also known as a negative acceleration factor and it doesn’t have any units of measurement.” The defense attorney says, “Oh, I forgot, what is 30?” The confident investigator says, “A math constant.” The attorney asks, “Does it have any units?”

“No it doesn’t have any units of measure, it is a constant,” answers the investigator.

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left is 30, but that is a "math constant", or is it? Was investigator told wrong? Was the investigator short changed and not told the entire story about 30?

Obviously, there is a value under the square root radical that has units of measurement that officer was never told about in class. If an equation produces a value that has units of measure, they, the units, have to come from within the equation. They cannot magically appear out of thin air. So how does the slide to stop equation produce an answer in miles per hour? Could it be the deceleration factor? No that is ratio and ratios don’t have units. The only value

For those using the metric system, the same applies to the value 254. As with 30, 254 has units and serves the same purpose.

The truth of the matter is, 30 does have units of measurement. The value of 30 functions as conversion factor which contains the value of gravity and the constant 2.

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Another “plug and chug” accident investigation training course has left the officer embarrassed and poorly prepared for a strenuous cross examination. All the numbers were correct, the officer double checked the math!

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The “constant” of 30 3600 equals the number of seconds in an hour 5280 equals the number of feet in a mile 32.2 equals the Imperial value for the acceleration of gravity

The “constant” of 254 3600 equals the number of seconds in an hour 1000 equals the number of meters in a kilometer 9.81 equals the Metric value for the acceleration of gravity 2

 3600 sec 1 km  m   2  9.81 2 x    sec  1000 m 1 hr 

2

 3600 sec 1 mi  ft   2  32.2 2 x    sec  5280 ft 1 hr 

Multiply the value of gravity by 2

Multiply the value of gravity by 2

2

 3600 sec 1 km  m   19.62 2 x    sec  1000 m 1 hr 

2

 3600 sec 1 mi  ft   64.4 2 x    sec  5280 ft 1 hr  Multiply 3600 seconds by 1 mile and 5280 feet by 1 hour 2

Multiply 3600 seconds by 1 kilometer and 1000 meters by 1 hour 2

 3600 sec mi  ft   64.4 2 x   sec  5280 ft hr 

 3600 sec km  m  19.62 2 x   sec  1000 m hr 

Square 3600 second miles and 5280 foot hours (note that the units get squared)

Square 3600 second km and 1000 foot meters (note that the units get squared)

12,960,000 sec 2 mi 2 ft x  64.4 2 2 2 27,878,400 ft hr sec

12,9600,000 sec2 km 2 m x 19.62 2 2 2 1,000,000 m hr sec

Divide 12,960,000 by 27,878,400

Divide 12,960,000 by 1,000,000

x  0.4648

2

2

sec mi ft  64.4 2 2 2 ft hr sec

x  0.4648

mi 2  64.4 ft hr 2

Cancel out units

x  12.96

sec 2 km 2 m 19.62 2 2 2 m hr sec

x  12.96

km 2 19.62 m hr 2

Multiply 12.96 by 19.62

Round

x  30

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mi ft hr 2

x  254

km 2 m hr 2

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Cancel out units

x  12.96

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. When the components are placed under the radical, it appears as:

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So 30 is not a constant, but is actually a math value of

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With the exception of one of the standard crush energy equations, where 30 literally equals 5×6, anytime "30" appears in an equation it retains the units of mi² per ft hr². Anytime 30 appears in an equation, the units for the velocity variable in the equation or being solved for, will be in units of miles per hour. Any time 30 appears in an equation, 30 may be replaced with 2×g, and units for the magnitude variable will become feet per second. Therefore, anytime 2×g appears in an equation, it may be replaced with 30, the units of the magnitude variable become miles per hour.

Finally, ask yourself what is 3.86 (11.270) or 2.73 (7.97), are they also “constants?"

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The same rule applies in the Metric system where we find the value of 254. Except the units for the variable will toggle between kilometers per hour and meters per second.

Don’t ignorantly perpetuate the myth, 30 is not simply a math constant! www.collisionpublishing.com

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(c e more accurately: th simplification – or, n became a process is th of t uc od pr s or so, the mann - is that instructio s ver the past 20 year s become known oversimplificatio ulae by practice as opposed to a focu lt ha rm su at fo re g d wh en yin e ich pl Th ap wh . of in les ner g theories and princip ps m” has been taught as “3600 Momentuly unchanged. The on the underlyinifests itself where the student develo a ul an ge m rm lar en “fo ed oft on t ain e os nc m rem has unnecessary relia orough undertions/agencies th an entrenched and most of the institu approach used by Momentum” method developed it sheets” rather than confidence in a 0 60 In .

“3 les n. e th tio cip g in ica in pr appl rst teach standing of basic, fi cess” than an expert into more of a “pro omentum easier to teach and then, of the established an effort to make mr the student to understand, the ap - This article is offered to address many” that simply have ostensibly, easier fo ciated with numerous restrictions “rules” governing “3600 Momentum ll being taught. In proach became assoing the application and use of mo- no basis but are, in some quarters, sti and “rules” concern The most notable and obvious by mentum in crashes.

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 Vehicle departure angles are measured from the position a vehicle’s center of mass at the point of impact to the position of its center of mass at its final resting position.

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 You cannot “use momentum” when there is a secondary impact between the involved vehicles or between one vehicle and another object before the vehicle comes to rest.

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he “rules” While some may go back further, since at least the early 1980’s, some of the “rules” that have been – and in some cases are still being - taught concerning the use of “3600 Momentum” include:

 You cannot “use momentum” when there is a 10 to 1 or greater weight ratio for the involved vehicles relative to one another.

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First, a couple definitions and distinctions. We’ll use “equation” here to mean a mathematical statement of equality. We’ll use “formula” to describe “a conventionalized statement” or a “standard procedure for solving a mathematical problem.” Here, the latter example is intentionally offered in the singular not plural: “a procedure” for solving “a problem.”

 When there are approach and departure angles involved, a “Conservation of Angular Momentum” formula is used and when the vehicles are in-line with each other, one can use the “Conservation of Linear Momentum” formula.

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addition, it will present an alternative approach tos teaching momentum that is absent the restriction that exist with the traditional, formula based meth od.

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 An extension of the previous “rule” was that you cannot “use momentum” when there is driver influence on the point of rest of one of the involved vehicles.

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 The approach and departure angles must be measured in a counterclockwise direction.

The departure angles of the vehicles involved in a crash are measured from the each vehicle’s center of mass in their position at impact to the position of their center of mass at maximum engagement/separation. Here, it’s understood that there may be some defined distinction between the “point of maximum engagement” and the “point of separation;” however, in practical application, the division between the two becomes a paper thin point in time, impossible to identify from the gross information the reconstruction has to work with.

A review of examples of “departure” offered during the lecture portion of a reconstruction class suggests that, at least until about the mid - 1990s more often than not, students are told correctly how to measure the departure angles of the vehicles. However, the follow on application, demonstration and in-class projects are done where the departure angles are draw from the center of mass of the vehicles at impact to their center of mass position at final rest.

When applying a momentum analysis to a collision that involves approach and departure headings which don’t fall on a single system axis, the concept or theory that is applied is that of the “Conservation of Linear Momentum;” however, all too often, such crashes have been referred to as one where the reconstructionist would use “angular momentum.” The misapplied term here (“angular momentum”) was used to “remind” the reconstructionist that there were approach and departure angles involved and is an illustration of an oversimplified formula approach rather than one which focuses on the underlying concepts and principles.

Generally, the practice problems given to the students consist of a scale diagram where the vehicles are drawn on impact and at their final resting position. The students are told to draw an X through the diagonal corners of the vehicle, and then draw a line from the center of the X at impact to the center of the X at final rest to solve for the departure angles (as in Figure 1). Therefore, even though the students may have been told the correct method of finding the departure headings of the vehicles, through practice they learn that the departure headings of the vehicles are measured from impact to final rest. Moreover, they “learn” that the center of mass of the vehicle is related to the corners of the rectangular “vehicle” in the exercise rather than the fact that the center of mass will be related to the relationship on the front and rear axles.

Conversely, when attempting to determine the impact velocity of the heavier vehicle when there are significant weight differences, the data of the lighter becomes nearly irrelevant to the calculations. The greater the weight difference the less influence the lighter vehicle will have on the movement of the heavier vehicles.

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Ironically, the flawed notion that departure angles are measured from impact to final rest is further reinforced, even if indirectly, by many of the computer programs designed to perform momentum calculations. Many of these programs will prompt the user to enter the coordinates and headings of the vehicles at both the point of impact and their final rest. The user will later be prompted with a question asking if the “departure path of the vehicle(s) is curved?” If the answer to the question is “yes,” the user is then prompted to enter a position of the vehicle as close to the beginning of the curve as possible.

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However, as with most myths, there is some basis in truth for the myth. In collision analysis, there are issues that arise when dealing with significant weight difference between the vehicles as it relates to the sensitivity of the end calculated result relative to the greater mass ratio. In such cases, the accuracy of data concerning the post impact movement of the heavier vehicle, as well as it change in direction (difference between its approach and departure headings) becomes critical to the velocity calculations of the lighter vehicle. With significant weight differences, changes in the post impact velocity of the heavier vehicle of only a couple miles per hour may change the impact speed of the lighter vehicle by 10 to 20 miles per hour.

On the downside, this method teaches the students little, provides no meaningful experience to draw from in a “real world application” and does little more than to teach them to “plug and chug” through the formula but it makes grading papers easier on the instructor…

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omentum “doesn’t work” with 10:1 or greater weight ratio In short, momentum is always conserved. There are no weight restrictions or ratio exclusions. When we say that the total momentum in a system before a crash will be the same after the crash, there isn’t an asterisk or footnote leading to a comment such as “it’s conserved except where the mass ratios are…”

For the instructor, the “upside” of this method is that, in class, all of the students should be able to obtain the same angles from the scale diagram to use in their calculations. Therefore, when they perform their calculations if they successfully enter the correct numbers into the correct formula they obtained from their formula sheet, they will all arrive at the same answer. The ability for the entire class to arrive at the same solution will, in theory, increase their individual confidence levels.

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In that context, one might think of the sine or cosine values of the approach and departure headings as little more than “correction” or adjustment factors. Yet many who are active within this field have no idea why the sine and/or the cosine values are taken, other than they are part of the formula that they were taught to plug numbers into.

Compounding this issue is that nearly every problem they are given the vehicles travel in a straight line from impact to final rest, which rarely happens in real life. Therefore, once the students return to work, they more often than not avoid applying a momentum based analysis since the vehicles in actual crashes almost never travel in a straight line post impact, creating yet another restriction on the use of momentum that has no factual underlying basis.

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What often gets lost in the instructional process is that the sole purpose of the application of trig functions - specifically using the sine and cosine of the approach and departure headings of the vehicles under study in a “3600 Momentum” application - is to turn the “angular relationship” into a “linear one,” or, more correctly, to relate their off-axis approach and departure vectors to a system based “X” and “Y” Cartesian grid relationship.

The purpose of this question is to allow the program to properly identify the vehicle’s departure heading. However, typically, the user simply answers “no” when asked if the departure path of the vehicle is curved most likely operating under the mistaken belief that the path has to be a simple, smooth curve of some sort. This causes the program to measure the departure heading from impact to final rest,

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ngular Momentum and Linear Momentum In general, when used in the context of collision reconstruction, when one hears the term “Angular Momentum” being used, more often than not, the speaker is actually referring to an application of the concept of the Conservation of Linear Momentum and not actually referring to what is really angular momentum. Angular momentum is a separate and distinct concept than that of linear momentum. Angular momentum deals with the rotational movement of objects not their linear movement.

The notion of “linear momentum” (or conservation of linear momentum) is that the momentum of a mass (vehicle) can be defined by a straight (linear) line. Angular momentum is associated with a rotating mass and its motion isn’t, then, by definition, defined by “linear momentum.”

The departure angles of the vehicles are measured from vehicle’s center of mass at impact to their center of mass at final rest

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Figure 1

ou cannot “use momentum” when there is a secondary impact between the involved vehicles or between one vehicle and another object before the vehicle comes to rest.

As noted, an extension of the previous “rule” was that you can’t “use momentum” when there is driver influence on the point

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With a roughly 90° (relative) collision where the vehicles are striking front corner to front corner, secondary impacts or “side slaps” are common as the rear of the vehicles rotate toward each other. An example of such a collision and the underlying solution appeared in Collision Volume 2, issue 2. These secondary impacts do not preclude the use of the linear momentum application. In fact, these secondary contacts actually make finding a proper momentum solution easier.

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Many newer CAD/drawing programs contain a momentum feature that allows the vehicle’s speed to calculated within the program.

These programs suffer from the same issues as other programs when determining post impact angles. Unless the user is properly trained in both the use of the program and the application of the conservation of momentum analysis, the departure angles identified will typically be drawn from impact to final rest.

of rest of one of the involved vehicles. These flawed notions simply can’t be any further from the truth. The collision – the interaction between the two vehicles - is over at the point of maximum engagement/separation and that’s when the momentum exchange has, similarly, ended. What happens after that point has absolutely no effect on the momentum exchange that occurred during the crash pulse.

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which would, again, be incorrect, but consistent with what they have learned. (It should be noted that this is not a deficiency with programs, but a deficiency with training of the user. When used properly, these programs do an excellent job.)

Generally, the location where the secondary contact occurred may be easily identified from the physical evidence at the scene. This type of

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secondary impact will occur close enough to the point of maximum engagement/separation that the vehicles have not deviated from their initial departure headings. Therefore, if the departure angles of the vehicles are drawn from the center masses at the point of impact through the center masses at location of the secondary impact, one can be pretty sure that they will have in passed through the point of maximum engagement/separation to get there (to the secondary contact).

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When there is a secondary impact with some other object, such as a curb, guardrail, tree, etc. it similarly does not prohibit using momentum in order to determine the vehicles speeds at impact. Depending on the nature of the secondary impact, it may necessitate a more nontraditional approach, which will be addressed later, but the utilization of the momentum application remains appropriate.

In virtually any trigonometry or calculus textbook you will find a unit circle printed on the inside of the front or back cover. In the unit circle 0° is to the right and the angles traverse the circle in a counterclockwise direction.

This is a standard convention used in mathematics, particularly trigonometry. Since CAD programs are essentially graphical representations of mathematical calculations, they typically follow this same convention. Therefore, the “rule” that approach and departure angles have to be measured with 0 to the right and in a counterclockwise direction has no foundation in the theory of the conservation of linear momentum, instead, it simply was a rule that was based on a convention that is commonly used in mathematics.

There was a time when these “rules” were taught as absolute and inviolate. Though these particular “rules” seem to be heard less commonly among those teaching momentum applications - and are not true - they do have their foundation in mathematics.

Nonetheless, if one chooses, they could measure angles in both the clockwise and counterclockwise direction in the same solution. If angles are measured in differing directions, then the direction they are measured has to be taken into consideration. If the angles that

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The approach and departure angles have to be measured in a counterclockwise direction. Or, the angles must be measured in a quadrant method.

There is no requirement for angles to be measured in either the clockwise or counterclockwise direction. Nor is there any requirement that all of the angles be measured in the same direction. However, measuring the angles in the same direction does keep the analysis “simpler.”

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area measured in a clockwise direction are recorded as positive angles, then those measured in the counterclockwise direction have to be recorded as negative angles.

 The approach heading of Vehicle #1 has to be set to 00  You have to know the post impact velocities of the vehicles in order to use “3600 Momentum”

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Regardless, of the direction the angles are measured, with attention to detail, using opposing directions when measuring the angles will have no bearing on the outcome of the calculations, as is illustrated in Table 1.

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 You have to solve for the impact velocity of Vehicle #2 before you can solve for the impact velocity of Vehicle #1

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 If you cannot determine the post impact velocities of the vehicles you can’t “use momentum”

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 You can’t “use momentum” if either of the vehicles came to a controlled stop

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 The approach and departure angles of the involved vehicles have to be measured relative to Vehicle #1’s approach heading The reason why the previous rules exists simply relates to how momentum has traditionally been taught - which is demonstrably most often a function of teaching “a plug-and-chug approach to formulas” as opposed to teaching a thorough understanding of the concepts behind the application of the “conservation of linear momentum.” The problem with that “traditional” approach to teaching momentum is that in the effort to make the process simpler, the true understanding of the physics behind momentum has become lost and the students become focused on which equation to use and fail to obtain a proper understating of the concept being taught.

When teaching momentum applications, the most effective way to get the material across is to abandon the traditional approach and returned to the basic concepts surrounding the conservation of linear momentum. In this way, many – if not all – of the restrictions that have been placed on the use of momentum have been eliminated, providing the students with a true working knowledge of the use of momentum instead of simply the ability to look up an formula in a formula sheet.

In its simplest form the conservation of linear momentum can be represented as… or … where the change of momentum for Vehicle #1 will always be equal and opposite to the change of momentum for Vehicle #2. This is the basic concept of the conservation of linear momentum which often gets lost when students are taught using the plug and chug mentality. easily derives into a form that is generally associated with the conservation of linear momentum as it relates to collision reconstruction.

Since

In addition to the previously discussed “rules,” It’s still not uncommon to find other restrictions on the use of a “360°Momentum” solution. Ironically, none of the following statements are true.

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In a linear relationship, Δv is nothing more than the difference between a vehicle’s impact velocity and its post impact velocity. Therefore Δv may be written as Δv = v - v´

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Multiply mass through both sides of the equation

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Not only is there no requirement that all of the angles be measured in the same direction, but there is really no requirement that they be measured from the same axis, either. There is no mathematical reason why some of the angles could not be measured off the X axis and other off the Y. However, if this approach is taken then, the reconstructionist has to take into account both the direction the angles were measured in and which axis they were measured from. To make matters more potentially confusing, the sine function would have to be applied on the angles measured from the one axis and the cosine function on those measured from the second axis uniformly.

the above equation may be rewritten as:

Add m2 x v2 to both sides

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Add m1 x v'1 to both sides

es) are known along with the approach and departure headings of the vehicles, then if any two of the four velocities (two impact velocities and two post impact velocities) are known, then the other two may be solved for.

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At first it may not be readily apparent that any two velocities may be solved when the other two are known, since there are four velocity variables. However, the reason is fairly straightforward: if two are known then two unknown velocities remain. It is at this point that it becomes important to recognize that the sine of zero degrees will always equal zero, and zero multiplied by anything will always equal zero. With this knowledge, if any of the angles are set to zero then the related terms will drop from the equation since they will be multiplied by zero. Thereby, if any of the four angles equals zero, three velocity variables will remain in the in the equation instead of four.

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Multiply both side by gravity to cancel terms

Table 2 is the same example data presented previously, except the angles have been measured from a common baseline instead of from the approach heading of Vehicle #1. As a result, none of the angles of the vehicles involved in this collision are now zero, since there is no such requirement.

When teaching and working with momentum, the following equation is the only equation that one needs to know.

(Metric) (Imperial) Here, the difference between the Imperial and Metric versions is simply a function of units. The kilogram is a unit of mass where the pound is a unit of force.

The basic momentum equation is a simple equality where the left side of the equation equals the right. This simple relationship it may be expressed as: or …where the impact momentum of the vehicles involved in the collision equals the post impact momentum of the vehicles involved in the collision.

When dealing with approach and departure headings the basic momentum needs to be modified so that it accounts for the approach and departure headings, allow the angular relationship to a linear one. In these cases basic momentum equation becomes:

Table 2 Often situations that require the application of “360° Momentum” involve a vehicle that has made a left turn in front of an approaching vehicle, or accelerating from a stop. In these situations, the impact velocity of the intruding vehicle may be quantified through a means other than momentum, such as acceleration testing, sampling traffic at the collision scene, the critical speed of the vehicle completing the turn, etc.

From the example data, it will be assumed that the impact velocity of Vehicle #2 has been determined to be 15 mph (23 km/h) and the post impact velocity of Vehicle #1 has been determined to be 25 mph (40 km/h). When these velocities and the other information are entered into the equation, we have:

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With this variation of the equation, there is no requirement that the impact velocity of Vehicle #2 be solved before the impact velocity of Vehicle #1 no, is there any requirement that one has to solve for the impact velocities using the post impact velocities. When working with this form of the equation, it is the investigator who decides which velocities they want to solve for. So long as the weights (mass-

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To adjust one the unknown angles to zero, the angles could be measured again from within the scale diagram. However, having to constantly go back and measure the approach and departure headings from a new baseline would quickly become cumbersome and may lead to unnecessary errors. The easiest way to adjust an angle to zero is to simply subtract the angle from itself. For instance, in this example, if one wanted to solve for the impact velocity of Vehicle #1, the post impact velocity of Vehicle #2 has to be removed from the equation. To do this, 45 would be subtracted from Vehicle #2’s departure heading adjusting it to zero (45-45 = 0). What is done to one angle, the subtraction of Vehicle #2’s departure heading, now must be done to the remaining angles, so the equation becomes:

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As with the basic momentum equation, this variation of the equation remains a simple equality where the left side of the equation has to equal the right side. This variation simplifies to…

It can be quickly seen that at this point there are two unknown velocities in the equation and it cannot be solved simply. However, if one of the angles associated with one of the two unknowns was adjusted to zero, then the related unknown variable will cancel from the equation, because the sine of zero degrees equals zero.

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This is the only variation of the momentum equation that needs to be used when dealing with collisions where the vehicles are not traveling in-line with one another. There is no need to use any other variation of the equation, nor is there any need to ever use a trig (normally seen as the cosine) function.

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When the exact same process is completed with the angles that have been measured from a 00 baseline representing Vehicle #1’s approach heading, the end results are the same. Once 300 has been subtracted from each angle to cancel the post impact velocity of Vehicle #2, the adjusted angles are the same as before.

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At this point there are now two known velocities and one unknown velocity in the equation, which may be easily solved.

At this point it is important to recognize that if the angle adjustment produces a negative value, the sine of that negative value is taken, a negative angle is not arbitrary converted to a positive value.

Solving for Vehicle #2’s post impact velocity

The equation is now worked from this format which only requires some very basic algebra skills.

Take the sine of the adjusted angles

Solve the right side of the equation and multiple all possible terms on the left side

Subtract 54378 from both sides of the equation

Divide both sides of the equation by -1500 to solve for Vehicle #1’s impact velocity

Once the third velocity has been determined the same equation is used to solve for the last unknown velocity. At this point there is no need to cancel an unknown term from the equation; therefore, it is not necessary to make any angle adjustments.

Aside from allowing the investigator to solve for any two of the four involved velocities, this approach only requires the investigator to remember a single basic equation. In addition, the form of the equations retains the equality relationship that exits with the linear momentum application nor is there any need to remember when to take the sine of an angle and when to take the cosine, since a cosine version of the momentum equation is never needed. The only thing the investigator needs to be aware of is the need to adjust an angle to 0 degrees in order to cancel a term from the equation, and to subtract the same angle from all of the angles in the equation. In effort to make this concept a little simpler the momentum equation may also be written with an angle adjustment.

which may be written as:

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From an instructional perspective, classroom experience shows that this process actually does simplify teaching the underlying concepts behind the conservation of linear momentum application whereas the “traditional” method fails to do. Not only does it make the process simpler, it does not require a page of “plug and chug” formulae.

Instead the student only needs to comprehend and remember one basic formula, namely, how to mathematically define how momentum is conserved.

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The fact that there is no requirement that any of the involved angles has to initially set to 00 does not prevent one from setting the approach angle of a vehicle, or any of the other angles to 00. The process of adjusting the angles remains the same. If the angles in the example just completed were measured from a zero degree baseline that represents Vehicle #1’s approach heading, the approach heading for Vehicle #2 would be 95°, the departure heading of Vehicle #1 would be 250 and the departure heading of Vehicle #2 would be 300.

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Divide both sides by 2828 to solve for the post impact velocity of Vehicle #2.

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Where Θa represents the adjustment angle that is to be subtracted from all of the angles. The equation may always be used in this form even then no angle adjustment is needed, since zero subtracted from any value will leave the original value.

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Sgt., Ontario Provincial Police Collision Safety Institute

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eneral Motors has been a leader in providing access to light vehicle event data recorder information since the CDR Systems inception in early 2000. The latest updates to the line of GM vehicles covered continue this trend of accessibility. Since the 2009 CDR Users summit, which coincided with the release of version 3.1 software and hardware updates, further GM coverage has been added with version 3.2 and recently 3.3 releases. In addition to the 3.3 software, additional hardware, in the form two additional umbilical cables, is now available. This article will build on the information presented at the conference and include information through the 3.3 update.

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hanges to current data elements The delta-V display for those modules covered by the 3320, 3321 and 3293 modules has been updated. End users should be familiar with what have become known as the “70/230” and “70/10/220” rules. These systems record a total of 300ms of both longitudinal and lateral velocity change and the rules relate to how much of the crash pulse is displayed before

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The GM updates can be divided into several categories: changes to how data from currently supported vehicles has changed, carry-

over vehicle coverage and fixes for vehicle coverage, new vehicle coverage. By way of example, this would include the change in display for delta-V data as well enhanced explanation for some current data elements, currently supported vehicles / SDMs into new model years, addition of new vehicles such as the Chevrolet Camaro and Traverse and the addition of the RollOver Sensor (ROS).

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Figure 1 – Note no data points at time -100 through -80 and 230 through 300

Figure 2 – Same graph in Version 3.3 40 Collision Volume 4 Issue 2.indd 40

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and how much after the approximate time a deployment is commanded. As a refresher, vehicles supported by these cables will fall into one of these categories. These modules are in the continuously running algorithm category for deployment events. (This may be different – module dependant – for Non-Deployment events – always refer to the Data Limitations for each individual download.)

The “70/230” rule means the module will record 230ms of delta-V in 10ms samples after the deployment is commanded, and up to 70ms before deployment. The “70/10/220” rule means the module will record 220ms of delta-V in 10ms samples after deployment, up to 70ms before deployment, and one sample at “around” deployment. Changes in the 3.1 version of the software removed the “lead-in zeroes” that were displayed in prior versions of the software. This was a graphing scale issue where the lead-in points did not actually have data associated with them (see Figure 1). For all modules in these families the delta-V will now be displayed as shown in Figure 2.

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This lock is what’s known as a “soft” lock and will clear internally after about 255 ignition cycles. The significant affect is that, during that period, one event storage space would be filled with crash data and “locked” such that it can’t be overwritten and in the event the module commanded a Deployment and then a Deployment Level (or “Deployment crash #2) event occurring, only the Deployment data would be recorded.

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IR Warning Lamp Status Two different variations for this data element will be displayed for 3320 cable supported vehicles. Figure 4 and Figure 5 appear to display the same parameters, and in fact they do; however, one must refer to the detail and context provided by a review of multiple parameters in the report to draw proper conclusions regarding this data. The Delphi version of this SDM displays data in the System Status section that includes the data element “SIR Warning Lamp ON Time Continuously (seconds)” referring to how long the lamp was ON; however, it’s important to note the specificity: the lamp being “on” so no conclusion can be made about the OFF time (Figure 4).

Figure 3

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nhanced explanation of data elements for vehicles supported by the 3320 cable Several GM vehicles are supported for access using the 3320 cable and there are different variants of the module all still accessible using that one cable. One implementation is that manufactured by Autoliv, and the other manufactured by Delphi. While the data and elements appear similar, there are subtle differences the CDR Analyst should be aware of. Some of these differences are explained in the data limitations, some are left to more detailed explanations and examples found in Bosch Preferred Training Provider training provided by the Collision Safety Institute.

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s the Non-deployment “locked?”

Occasionally, Analysts report seeing a 3320 cable supported vehicle report a “locked” status for a Non-deployment event (See Figure 3). This may occur for those modules manufactured by Autoliv. There are two general instances where one might see this occur: a situation where there was a deployment of a belt pretensioner only and in a situation where two or more Non-deployment events occur within 5 seconds of one another.

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By comparison, the Autoliv version of this module displays the data element: “SIR Warning Lamp ON/OFF Time Continuously (seconds)” meaning it may be a time for “on” or “off” not just ‘on” as in the previous example. The Analyst needs to refer to the line above that in the report: “SIR Warning Lamp Status” (which will either be ON or OFF) in order to reach a conclusion as to which commanded state (ON or OFF) as in effect at the time reflected in the 3rd line (Figure 5).

Data display for the ROS-B variant for lateral and vertical linear acceleration and roll rate provided 750ms if data before occupant containment device (roll-over curtain) deployment (Figure 8) which is identified as a “Rollover.” For Non-rollover events (the equivalent of a Non-deployment) the ROS-B retains 750ms of data before event conclusion. The ROS-C displays the same data as the ROC-B but for 500ms before roll-over curtain deployment and

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Details on the individual data elements recorded by these modules was presented by Rusty Haight at the 2009 CDR Users Conference in Houston and has become a significant part of the Bosch Preferred training Provider Analyst course curriculum including an analysis of the SDM and ROS reports side-by-side from the same event showing the correlation and report-to-report analysis that has to be undertaken to correctly evaluate this data. For that reason, only a brief overview of the differences will be provided here.

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ddition of coverage for vehicles equipped with a ROS-C / Umbilical cable for ROS-B and ROS-C In recent releases of CDR, GM added support for their stand alone RollOver Sensor (ROS). This is a separate module in the vehicle, and requires a separate download process within the same download run as described in more detail in the Bosch Preferred Trainer Technician Training. An additional menu item and icon were added to support his download (Figure 6). Until the recent release of the 3.3 hardware update, access to the ROS was supported as a “DLC only download.” With version 3.3, Bosch made an off-vehicle umbilical available - F-00K-108-455 - making the ROS-B and ROS-C accessible for direct-to-module imaging (Figure 7) where required.

Figure 7

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then for 250ms after roll-over curtain deployment for these events (Figure 9). For Non-rollover events the ROS-C retains 500ms of data prior to event conclusion, and 250ms after.

(8km/h) as the base recording criteria for a Non-deployment event.

In the case of seat belt pretensioner deployments, head rest deployment and battery cut-off deployments, the module will record and label the event a “Non-deployment.”

In early release version of CDR that included ROS access, Diagnostic Trouble Codes (DTC) related to the ROS were displayed and then there was a separate indication of whether or not they were active. Taking up unnecessary space and often misleading to end users, the system was changed and with version 3.3 only displays ROS related DTCs that were active at the time of the event.

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he future of GM SDMs Beginning with version 3.3 of the CDR software, there is now coverage for 2 additional SDM variants supported by the F-00K-108-452 and -454 cables. For those modules supported by the 452 cable the pre-crash data display is in 0.5 second sample intervals for a total time period of 2.5 seconds before Algorithm Enable (AE). Users with current Preferred Provider training should be familiar with the remaining data parameters for this variant. The supported vehicles include 2008-2010 Pontiac G-8 and the 2009 Holden VE (our first Australian vehicle coverage!). Notably both of these SDMs require a delta-V of 5mph

Beginning in MY2010 (including the already on-road 2010 Camaro) GM began installing a new variant SDM that includes onboard roll over sensing (rather than the separate module previously described) where the vehicle is equipped with roll over occupant containment (curtain) airbags. The SDMs are capable of recording up to 3 events. They follow the “70/10/220” rule for Deployment events for delta-V data, and are a wake-up type system for Nondeployment events, i.e.: up to 300ms of delta-V may be available for Non-deployments. For both events, the longitudinal and lateral delta-V is recorded in 10ms increments. Roll over data most closely resembles that of a ROS-C, however, for deployment events in a roll over condition, the SDM will record the vertical and lateral acceleration (as seen in figure 10) , as well as the roll rate angular data for 490ms before deployment of the side curtain airbags, one 10ms sample at around the time of deployment, and 250ms of data after deployment is commanded (keeping in mind the 10ms resolution for the delta-V data display).

Figure 10 www.collisionpublishing.com

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Using the CDR System is a reading intensive activity and one which requires Analysts to actively work to keep current on developments in supported vehicle lines and even specific systems to properly apply the data to collision analysis. This very brief overview of some of the notable changes in GM systems is a good example of how the systems are evolving and will continue to evolve in the coming years.

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“Event Recording Complete” indicators include overall event status, as well as individual indicators for both Deployment event data and velocity change (delta-V) data. These SDMs will wake up on frontal, side and rollover and rear events and the Data Summary includes which of the algorithm(s) related to that/those impact direction(s) were active during the recorded event(s). In addition to a new data parameter for these modules, specifically the “OnStar Notification Event Counter” other counters available in the Event Data section of the CDR report for these modules including separate “deployment” and “event” counters as seen in figure 11.

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Another new section of the Event Data section is Event Severity Status as depicted in figure 12. This is a yes/no parameter for Roll Over, Rear, Right Side, Left Side, Frontal Stage 2, Frontal Stage 1 and Pretensioner events.

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More detailed on these newer systems and associated parameters is expected to be presented at the 2010 CDR Users Summit in Houston, and the Collision Safety Institute CDR Data Analyst class is being updated to reflect the data elements covered in these newer modules.

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BOSCH CDR 3.3 Hardware & Software

New CDR Release!

With the release of CDR software version 3.3, four new CDR cables are now available so you can take full advantage of the new vehicle coverage included. These new cables allow you to retrieve EDR data directly from late model General Motors and Chrysler airbag control modules and General Motors rollover sensors.

Chrysler ACM Cable: F00K-108-453 $131.00 US | $137.55 CAN

GM ACM Cable: F00K-108-454 $120.00 US | $126.00 CAN

GM ROS Cable: F00K-108-455 $124.00 US | $130.20 CAN

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GM ACM Cable: F00K-108-452 $120.00 US | $126.00 CAN

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Contact CRASH DATA GROUP for ordering and special pricing information.

800-280-7940

www.cdr-system.com

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Honda Gold Wing Motorcycle: (c

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Linked Brakes and THeir Performance Gary Johnson, MSME Vear, Inc.

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To study the effects of the LBS, tests were performed using both brakes simultaneously, the rear brake pedal only and the front brake lever only.

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The rear brake pedal operates the center piston of the rear brake caliper, the center piston of the right front brake caliper and the outer two pistons of the left front caliper. There have been a few reports of the secondary master cylinder being out of adjustment upon delivery of the motorcycle resulting in an incomplete release of the rear brakes and premature rear brake pad wear.

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This article describes the components and operation of the 2001 – 2010 GL1800 Gold Wing LBS (non ABS). The front brakes on the Gold Wing are composed of dual, full-floating 296mm front discs with dual three-piston calipers. The rear brake is a single ventilated 316mm disc with one threepiston caliper. Other components include a threestage proportional control valve that couples the front and rear calipers, a delay valve that smoothes front-brake engagement when rear pedal pressure is applied, and a secondary master cylinder attached to the left front brake caliper. Probably the most misunderstood and least known component of Gold Wing’s LBS is its secondary master cylinder.

On the Gold Wing, using the front brake lever activates the outer two pistons of the right front caliper and the center piston of the left front caliper.

The right front and rear calipers are rigidly mounted like most motorcycle and automotive applications. The left front caliper however, is pinned near the front axle and allowed to rotate slightly with the disk when the brake pads apply pressure to the disk. The upper part of the caliper is attached to the secondary master cylinder mounted to the left front fork. Rotation of the caliper applies pressure to the secondary master cylinder and, via the proportional control valve, brake pressure is applied to the outer two pistons of the rear caliper. An interesting “feature” of this design is that when the motorcycle is not moving, front brake lever application will result in no brake force being applied to the rear brake caliper. Rear caliper pressure is only applied from the rear brake pedal or the secondary master cylinder via front wheel rotation.

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ince 1983, Honda Gold Wing motorcycles have been equipped with a “Linked” or “Unified” braking system. While many people are aware of its existence, few understand its intricacies. Even in the motorcycling press, examples of inaccurate descriptions of how it works can be found: “On the Gold Wing, for example, when applying the front brake lever, fluid pressure will actuate two outer pistons in each 3-piston front caliper.”1 And, “The Honda Gold Wing is typical. Front and rear calipers are actuated by the "rear" brake pedal. Pressing on the rear pedal activates the single rear brake caliper plus one of the two front calipers.”2 As will be shown later, these are both incorrect. One possible explanation is that at one time, this may have been the case, but in 26 years of evolution, Honda’s Linked Braking System (LBS™) has become more complicated, and largely misunderstood.

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The author on his 2006 Honda Gold Wing (non-ABS). Threshold braking from 30 miles per hour.

2006 Honda Gold Wing with fender and left fender cover removed showing the pivot point and secondary master cylinder 48 Collision Volume 4 Issue 2.indd 48

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Front Brake Application

Rear Brake Application www.collisionpublishing.com

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The ambient temperature during testing was 89°F, the asphalt temperature was 113°F and the relative humidity was 90%. All brake tests were performed between 25 and 30 miles per hour. Five tests were performed with both the front and rear brakes applied simultaneously. Three tests were performed with only the rear brake pedal applied and two tests were performed with the front brake lever only applied. All of the plots were recorded using g (acceleration (ft/sec/ sec)) vs. time (sec). The deceleration was measured with an Apple iPhone 3GS running Dynolicious Log Box at 100 Hz. The combined weight of the motorcycle and rider was approximately 1200 pounds.

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onclusions During the 10 tests, the front wheel was inadvertently locked twice. One of the front wheel locks produced approximately an 11 foot long skid mark and a small flat spot on the front tire (pictured). The dip in those two plots is the release and reapplication of the front brake to maintain control of the motorcycle. Impending lockup was nearly imperceptible due to the relatively low g at which it occurred. Rear brake pedal only effectiveness was much better than expected with peaks exceeding 0.7g. When applying only the rear pedal, the braking effectiveness sometimes exceeded the simultaneous application of front and rear (lever and pedal) braking. On the rear pedal only runs 2 and 3, the pedal pressure applied was very hard with no lockup of the front wheel and very good deceleration. One observation comparing the combined braking and rear only braking was that the rear only braking appeared to be taking slightly longer (~0.5 seconds) from start to finish.

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eferenences 1. Brissette, P (2009, January 26). 2009 Honda CBR600RR C-ABS Review. Retrieved July 7, 2009, from Motorcycle.com Web site: http://www.motorcycle.com/manufacturer/honda/2009-honda-cbr600rr-cabs-review-87864. html 2. Hough, D Road Science: Braking Part 4. Retrieved July 7, 2009, from Soundrider.com Web site: http:// www.soundrider.com/archive/safety-skills/RS-braking4.htm

The corresponding flat spot to the skid mark left during the first combined braking test.

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Nearly 11 feet of front tire skid mark left unintentionally starting at ~30 miles per hour. The author’s children: Jordan with the tape measure and Sean with the pyrometer.combined braking test. www.collisionpublishing.com

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Closeup of front tire (above)

At the end of the testing (below)

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Full Page Ad DCS.pdf

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___Braking_Efficiencies________

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of Motorcycles

By Experienced Riders in Hard Braking Situations

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Officer Lee E. Jackson Detective Raymond L. Wangler

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Fort Worth (TX) Police Department

The two scenarios that are being evaluated are a full rear wheel lockup at approximately 20 MPH and a panic brake situation using both front and rear wheels done at 30 MPH. This speed reduces the amount of wear and tear on the equipment and the potential for injury to the operator.

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After both runs by the Motorcycles, the coefficient of friction was then determined for the surface by two methods. The first was a skid test using a police vehicle at a known speed, and by use of a drag sled.

(The purpose was NOT to open another round of “Drag Sled Wars”, but for comparison and validation.)

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eather Conditions On the day of the test, February 25, 2009, the observed weather at nearby Alliance Airport (approximately 2 miles away) was clear skies with winds out of the south at 9 MPH, and the air temperature range was 66° to 73° F. (18.8° to 22.7°C).

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The motor teams have one dedicated training day per month, as well as annual qualifications. The data collection took place during their monthly training day held in the parking lot, at the Texas Motor Speedway on February 25, 2009. Texas Motor Speedway is located in far north Fort Worth. These training days consist of varied activities – classroom, varied practical exercises, Motorcycle Rodeo problems, Dignitary Escort Detail Training. Overall, the unit is highly trained.

The second scenario tested involved Rear Wheel Lockup Braking.

This test was designed to be a 20 MPH run. The goal in the scenario was to stop safely with only rear wheel lockup. The deceleration factor in the scenario was determined by speed and distance.

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ntroduction The test subjects were 15 motorcycle officers of the Fort Worth (TX) Police Department Traffic Division. These officers operate a Harley – Davidson Police Motorcycle normally 40 hours per week, averaging 30 to 40 miles per day. They ride in varying situations – freeway enforcement to neighborhood traffic enforcement to main thoroughfares. They are exposed to numerous hazards.

ethodology The first scenario tested involved Panic Braking. This was designed to be a 30 MPH run, using front and rear brakes. The goal was to bring the Motorcycle to the skid threshold, but not to the point of wheel lockup. The deceleration factor was determined by velocity and time.

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Factors and rates of acceleration will be determined from the compiled data. These will be best case numbers when comparing to those of the average citizen riding a motorcycle, and can be used as upper end values in reconstruction crashes involving motorcycle riders.

tudy In order to verify the speeds at which the motorcycles were traveling, a gate area was setup using a Farmtek speed gate.

The gates were set 3 feet apart. The velocity was deter-

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bstract The purpose of this study is to gather useful, reliable data in regards to braking efficiency of motorcycles among experienced riders. The study will examine braking from rear wheel only situations and front / rear wheel braking situations. Although there is some related data present regarding this topic, the purpose of this study will be to gather what would be deemed as “best case scenarios”, by compiling data from riders who operate a motorcycle daily and are exposed to “panic braking” situations.

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mined from the time required to travel from one gate to the other.

This was used for both the 30 MPH Panic Stop and the 20 MPH Rear Wheel Only Skid to Stop. Afterwards, a car skid test was performed to compare to the factors the motors were achieving.

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The 30 MPH Panic Stop was a timed event. For uniformity, the one person was using a stop watch for the entire experiment. The watch was started when the brake lights came on, and stopped when a spotter (the same throughout) signaled when the motor came to a stop.

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The data gathered in this scenario was:

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• Time through the gates • Time to stop • Calculated time through gates to velocity • Calculated factor (Factor=Velocity/Time/32.2)

The 20 MPH Rear Wheel Only Skid to Stop utilized the same initial setup. The gates were moved after 6 riders to aid in the identification of the skid. The riders were instructed that if they began to lose control, abort the run, and it would be re-done. In this scenario, again for uniformity, the distance was measured by one person. The skid length was determined with the use of a 100 foot long nylon tape measure. The distance measured was from the end of the skid at the tire to the start of the visible skid.

The data gathered in this scenario was: • Time through gates • Distance measured of visible skids • Calculated time through gates to velocity • Calculated factor (Factor=Velocity-squared/(64.4*distance)

The data gathered from the skid tests was: • Time through gates • Length of each skid mark • Calculated average skid length • Calculated coefficient of friction • Repeated to validate • On second run, the PCM (Powertrain Control Module) was imaged

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After the riders had made their passes, a skid test was conducted in the same area to determine the coefficient of friction. The pavement being tested was an asphalt parking lot, and although it was aged, it was not heavily worn. The car used in the test was a 2006 Ford Crown Victoria Police Package. The vehicle’s Anti-Lock Brake Sys-

tem was disabled for this test. The target speed for this test was 35 MPH. The car was equipped with a Stalker Dual Antenna system.

The indicated speed was 37 MPH. The gates indicated that the speed was just over 38 MPH.

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Engine. With the Service Brake light on, a test was done to verify that the brakes were still operating.

The first skid test resulted in a speed at the gate of 38.05 MPH. The average skid mark length was 52.2 feet, resulting in a calculated coefficient of friction of 0.917. The second skid test resulted in a speed

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The results of this test produced good agreement on speed. There were 4 distinct tire marks present for each run, and their length was within 10% of each other. The only issue encountered was that with the ABS disabled, at lockup, the indicated vehicle speed went to zero.

The PCM did not get an indication that brakes were applied. The dash displayed warning lights for ABS, Service Brakes, and Service

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onclusion From the two tests that were evaluated, it was found that overall, the values varied. In the 30 MPH Panic Stop, the data leads to the conclusion that the average braking effi58 Collision

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dditional Studies Bartlett, Wade. PE. Motorcycle Braking & Skidmarks. www.mfes.com

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Lewis, Gary. Determining the Deceleration Rate of Motorcycles for the Analysis of Motorcycle Collisions. Collision Magazine, Vol. I, Issue 2, pgs. 19-21

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K. Vavryn, M. Winkelbauer. Braking Performance of Experienced and Novice Motorcycle Riders – Results of a Field Study.

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In the 20 MPH Rear Wheel Skid to Stop, the speed goal was 20 MPH. The variance was +3.244 to -0.884 MPH. The average speed was found to be 20.834 MPH. The distance to stop, which is again speed dependant, ranged from 20 feet to 39.3 feet, with the average being 28.0 feet. When this data was viewed overall, the factor ranged from this test from 0.402g to 0.649g, with the average being 0.531g.

Again, this is drag factor, and not braking percentage. Insert chart “20 Dx Factor”

Of note, these values are in agreement with other testing performed, and not discovered until researching articles after the testing had taken place.

cknowledgements • Farmtek Speed Gates provided by Collision Safety Institute, San Diego, CA. • The men and women of the Fort Worth (TX) Police Department Traffic Division, Motorcycle Enforcement Unit • Captain Gene A Jones, Traffic Division Captain • Detective Ray Wilson and Detective Christine Demore for their assistance in the gathering of the data

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In the 30 MPH Panic Stop, the speed goal was 30 MPH. The variance was +3.552 to -8.913 MPH (it was determined this was due to a defective speedometer). The average speed was found to be 28.045 MPH. The time to stop, which is speed dependant, ranged from 1.38 to 2.15 seconds, with the average being 1.66 seconds. When viewed overall, the factor from this test ranged from 0.514g to 1.089g, with the average being 0.787g. This is the drag factor, not braking percentage (commonly known as “n” factor). Insert chart “30 MPH No Skid”

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In summation, in a best case scenario from an experienced motorcycle rider, a rear wheel lockup will yield an n factor of 0.52 and a two wheel panic stop with threshold braking will yield an n factor of 0.85. These would be the optimal values to examine as an upper limit in determining a slide to stop speed for a motorcycle. Insert chart “% to mu”

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ummary After the tests, the data was gathered and analyzed. Originally, there were 18 riders, but 3 had ABS equipped motorcycles. So as not to skew the results, those 3 were discounted. Also, the highest and lowest values were removed from the evaluation.

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As a comparison, a 26 pound drag sled was pulled in the area of the skid marks. A digital scale was used to determine the amount of pull needed. Two pulls were made. The first required 23.5 pound of pull, resulting in a factor of 0.903, and the second pull required 24 pounds of pull, resulting in a factor of 0.923. Both tests validate the other in this aspect.

ciency was approximately 87.5% of available friction. It was noted that experience on the motorcycle had some effect in that the longer on motors, the higher the braking efficiency however, this may be related to the sample size for the “more seasoned officers.” In evaluating the 20 MPH Skid to Stop, the data leads to the conclusion that the Rear Wheel visible skid mark braking efficiency is approximately 52% of available friction. The values did vary overall, and there was no conclusive pattern between experience riding and braking efficiency.

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at the gate of 38.60 MPH. The average skid mark length was 52.67 feet, resulting in a calculated coefficient of friction 0.930. The speed from the PCM for this run was 38.4 MPH.

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"My Turn At the Wheel" By: Richard C. Rinker

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have read the article “Calculating Speed from Skidmarks” in the Spring, 2009 issue and wish to comment on the thoughts presented. The author is correct in his assertion that the marks shouldn’t be averaged in the presented example. However, in the presented example, I suggest this case has bigger problems than speed. If you have a case with 120 feet of difference between the longest and shortest skid, you are dealing with a car with defective brakes. As such, any speed is unsafe for the conditions.

That said, lets look at the facts as presented.

The author suggests setting up an equation looking at each skid mark individually and analyzing the speed equivalent from each mark, taken as a sum of calculations. While his method works, it is not the one which is taught at any of the major Accident Reconstruction courses.

What is taught is to look at the end result, and work backward to the start of the skid. If we do that, we get the first section of 4 locked skids for 40 feet at f=.75 and e=1, which gives a speed of approximately 30 MPH. The second section has 3 locked skids fro 40 feet at f=.75 and e=.69, and gives a speed of 24.9 MPH. The third section has 2 locked skids of 40 feet at f=.75 and e=.40. Speed = approximately 18.9 MPH. Lastly, we have one section of 40 feet at f=.75 and e=.18. This gives a speed of approximately 12.7 MPH. If we combine the above increments we get S²= 2038.51, or S=√45.1 or 45 MPH.

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This of course ignores the speed lost due to rolling resistance of the non braking tires during the respective segments, which I believe the author did during his analysis. If we include rolling resistance ( I used 0.04, and know that is subject to discussion) we end up with a speed of approximately 51 MPH.

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I am left wondering what is going to happen to his case when the opposing expert points out that he used a formula which failed to include all the data and therefore underestimated the speed of the vehicle in question?

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D e a t h Investigations and Their Psychological Effect on Police OffIcers Provincial Constable

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B rian Smith Ontario Provincial Police

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ntroduction Psychological struggles pertaining to death encounters are significant concerns in human psychology. These concerns are of great relevance to the police culture, and in particular for the purposes of this study, the individuals immersed in the collision reconstruction area of policing. police officers have frequent encounters with the death of others in a variety of circumstances throughout their careers. Members of a collision reconstruction squad deal with death and all of the evidence involved on a regular basis. Many psychologists have dealt with the concept of policing and death, however, death on a daily basis has had an insufficient amount, or no research associated to it. The ability to deal with the death of another person on a professional basis requires a psychological mind set that few are able to summon without some sort of long-term psychological effect.

Psychology has long recognized that virtually all human encounters with death are potent reminders of our own mortality and may invoke a myriad of consequences. Whether these encounters involve a casual exposure or are more extreme and personally meaningful, they are emotionally difficult events from which some degree of emotional or psychological trauma is almost certain to develop. An individual’s subjective experience with a death encounter may be magnified or diminished by the presence or absence of individual, social, cultural, and contextual factors and variables (Henry, 2004).

Each scene may bring its own set of variables that in relation to the officers experience and emotional structure may have different outcomes. A veteran officer that attends a death scene involving a elderly person dying of natural causes, for example, is likely to have a very different subjective experience of the event and will perform entirely different tasks than a novice officer who responds to his first fatal traffic collision or a veteran detective who is called to investigate a particularly horrific multiple homicide in which one or more

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”The essence of the job is to be able to confront that body in all its grim carnality, it’s stolid and perfect distance, and its sensory intimacy. You walk up to the thing and you step in it’s blood and juices, you smell it and you feel it, and your job is to get down onto the ground with it and slip underneath the skin and inhabit the skull and make its last seconds live and live again. Every cop maintains that detachment is the key, but the truth is that he gives up a section of his soul to every corpse and he dies a little death at the beginning of every case. (Stroud 1987)

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victims is a child. However, the first death encounter that an officer is required to attend is always recalled, at a later date, with great detail even if this recollection is obtained at the twilight of their career. Each subsequent encounter leaves a declining level of death imprint on the individual. Throughout their career the officer may be subjected to some death scenes that he may have a deep connection with, that connection may be through some sort of family or work relationship. These scenes that the officer feels a connection with may in fact leave a deep imprint. However, the details the officer recalls may not be as sensory laden as the first death scene he attended during the adolescence of his career.

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The issues covered in this paper are both profound and complex in their depth and impact. The body of research and theory relating directly to the meaning of death in a purely policing context is sparse. The very idea that there may be a psychological impact on a police officer, regarding the death of another human being, has until recently been untapped. As Ernest Becker wrote, a predominant and fundamental theme throughout Western civilization has been an unwillingness to deal emotionally or conceptually with death (Becker, 1973). Although research into death has increased in recent years it has been described as the “new pornography” – a topic that contains simultaneous elements of perverse attraction and aversion and is patently unsuited for discussion in polite company (Gorer, 1955). As Freud (1961), Feifel (1959,1969), Aries (1974,1975a), Brown (1959), Becker (1973), and a host of other psychological theorists have emphasized throughout their work, that the fear of death is a primary and fundamental source of human anxiety. Humans engage in various behaviors that function to deny, diminish, or attenuate the fear of death (Henry 2004).

Many studies have chronicled other occupation dealings with death. These studies have provided useful insight that may have some applicable information relating to police officers; however we must be careful because none of these occupations are quite like policing. There are no other occupa-

tions in the world that are required to deal with death in the same manner as a police officer. The training that a police officer has is unlike any other profession. The way that the police service and the reconstruction office is structured differs from any civilian or government organization. In fact, evidence of the impact that death has on officers is more readily available in popular non-academic literature including novels and memoirs. Systematic evaluations of the impact that death investigations have on police officers are made conspicuous by their absence.

Research in the area of stressors in police officers has shown that negative and positive influences in the work environment have a direct relationship to the stress the officer may display. An increase in the amount of negative stress placed on an individual can manifest itself in the form of actual physical symptoms. This idea of stress changing a person physically is also true on a psychological level. Nietzsche wrote, whoever fights monsters should see to it that in the process he does not become a monster. When stressors are prolonged and overwhelming, individuals lose their ability to cope. In a recent study three quarters of police officers’ wives believed that their husbands regarded their police work as more important to them than their own families and wives (Alexander).

With a combination of high stress and isolation from their emotional foundation (i.e. family) their ability to cope with any further stressors may become limited.

Occupational cultures are potent mediators of subjective experience (Deal and Kennedy, 1982). Most literature on police supports the notion that there is a definite police occupational culture. The norms, beliefs, and value systems of that culture differ significantly from other occupational cultures and from the larger culture in important ways, and that the police occupational culture plays a powerful role in shaping officers’ individual and collective experience of reality (Bennett, 1984). Each death encounter plays a role in the socialization of each officer into the culture. This socialization takes place for the divisional officer as well as the reconstruction officer. With each autopsy attended or corpse viewed the transformation into the culture is progressed. The use of macabre humor not only helps the officer to “numb” from the situation presented to him but it also immerses him further into the police culture.

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The Reconstructionist attended scenes that are often extraordinary, macabre, and grotesque

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Every human being is fully aware that at some day in the future they will succumb to some sort of death. Very few people are aware of the type of death that will eventually come to them. For the individuals involved in the field of collision reconstruction the constant close relationship that is afforded them with a style of death that is often horrendous in its carnality, may be an image that they conjure for their own inevitable demise. However intellectually they may be aware of their own demise they fail to act upon this knowledge. It is often the police officer that is driving with a reckless abandon rarely seen by the general public. Police officers are known to have life styles that would border on the upper edge of the high-risk category. Motorcycles, sports cars, and impaired driving are a few of the behaviors that police officers have been involved in.

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The very fact that officers are subjected to the viewing and in some cases handling of dead and mangled bodies exact a high toll on the police officer. This toll can have a range of physical and psychological effects. The most notable of these effects, being varying degrees of trauma. A popular psychological diagnosis has been posttraumatic stress disorder; however, the constant exposure to death in the clinical investigations that a collision reconstructionist undertakes does not fit the definition required for this diagnosis.

It has been proven by numerous studies of the human biochemical systems, that chronic and cumulative exposure to traumatic events causes chemical and biological changes that may be permanent (Anderson, 2002). Through Anderson’s research psychologists have discovered that cumulative exposure to traumatic events elevates the levels of epinephrine and nor-epinephrine (stress hormones) in the bloodstream and may cause anxiety, panics and agitation.

Research has also discovered changes in the cerebral blood flow and brain activity due to this same trauma. MRI studies have revealed structural changes in the hippocampus, which may be permanent.

The hippocampus is a portion of the brain involved in learning and memory. These chemical and physical changes to the body that are as a result of the investigations that the officer is required to undertake, may change the entire personality of the officer.

“to discover in death something towards which one can strive; and that the shrinking away from it is something unhealthy and abnormal… When I live in a house which I know will fall on my head within the next two weeks, all my vital functions will be impaired by this thought; but if on the contrary I feel myself to be safe, I can dwell there in a normal and comfortable way (Jung, 1933).

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Which specific individual death scene, body, or investigation leads to over-saturation in a given officer is idiosyncratic. That which is devastating to one officer may have little effect on another. Most police officers are prepared by their daily work on the street for a single body or a few bodies at “routine” death calls. However, a particularly poignant or awful tableau of sights, sounds, smells, tastes, and touch experiences can assault an officer’s emotional achilles heel (Greene, 2001)

Man’s wish for immortality does not consist of a complete denial in the certainty of death or a firm belief in a literal afterlife. It does however reflect “a compelling and universal inner quest for a continuous symbolic relationship to what has gone before and what will come after our finite individual lives. That quest is central to the human project, to man as a cultural animal and to his creation of culture and history” (Lifton, 1983). The philosopher Jung observed, one of the fundamental images and symbols that has transcended time and is present in every culture, is the idea of immortality. The belief that some form of a life after death may be important psychologically to each individual depending on various factors that have made the individuals state of mental health.

However the concept that life has a finality that may be quantified within a specific time period, may be overwhelming for any officer.

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orking with Death There is a universal perception among human beings of invulnerability and nowhere is this more evident than in the confines of the police culture. The idea that harm only happens to others is not only prevalent among police officers, it is a requirement to cope with the vulnerability that is ubiquitous.

The idea of invulnerability may sustain itself for the duration of most officers careers; however trauma, disasters, victimization and severe stressors may shatter this assumption (Violanti, 1991). When one of the above circumstances has affected an officer it may be presented as a “blow to the ego” causing a feeling resembling a lack of control. The ability to cope with future occurrences resembling this or any other high stress environment may be compromised. It may not be one specific incident that causes the complete breakdown of the coping ability but a compilation of sensory input.

Every human being is fully aware that at some day in the future they will succumb to some sort of death.

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Repeated exposure to death scenes changes the officer’s view of life. What he believes to be of importance to him may be the inverse of what his immediate family considers to be important.

An overgrown lawn or leaking faucet may be what the family feels is of great importance to them. A child’s illness constitutes a crisis of the greatest significance to the family. However, after complete immersion in a continuous cycle of death scenes, the officer’s scale of importance may be contrary to the opinions of the people that care for him.

The officer contemplates and ruminates about many issues of deep personal significance – the sanctity and fragility of human life; the suddenness and capriciousness of death. He experiences great irritation at the stupidity of things that otherwise intelligent people do to put themselves at un-necessary risk. He feels the urgency to savor the “insignificant’ things in life.

He desperately searches for “golden moments”, to help restore his rapidly waning faith, confidence, and trust in his fellow man (Greene, 2001). This amalgamation of psychological constraints is culminated by the overwhelming idea that we are a being with a beginning and more significantly, an end.

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resulting from instrumental violence. The tasks and responsibilities that each member undertakes is specific and generally includes photographing the scene, measuring the scene related evidence, and attending autopsies. None of the scientific or technical tasks performed by Reconstructionist implicitly require interaction with witnesses or with the victim’s family and friends, they are unlikely to develop meaningful relationships with them. This ability to concentrate on completion of several specific tasks and the complete isolation from any direct contact to the family of the deceased, gives the Reconstructionist the ability to distance himself from any internal struggles that may emerge.

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sychic Numbing Knowing that each officer will deal with a death in a different manner depending on his psychological state is not the only criteria that we must assess. The type of death is extremely relevant to the individual being subjected. Several types of death may affect the officer deep in his core beliefs. This effect is subjective for each individual. In order for an officer to continue with his required duties he must set up a psychological construct that is specifically designed for him. A partial professional psychic numbing that permits the officer to maintain his composure in the face of adversity and chaos that may comprise this construct. Sergeant Joe Friday on the Dragnet television series stated “Just the facts ma’am”, this is evidence of a depersonalized demeanor that is a function of partial numbing. Psychic numbing is a defense mechanism that may have been created by past trauma or by a combination of sensory trauma induced by numerous death investigations. The extreme form of psychic closing-off takes place in the face of profound threats, and may be temporary. Less acute forms of psychic numbing eventually become chronic and take on more permanent features of depersonalization, insensitivity, and an impaired capacity to think and feel (Lifton, 1967). The numbing may spill over to other areas of the officers’ life. He may become disconnected to everything and everyone in his life. Research has found that in extreme death encounters, and I believe long term exposure to death, the officer may have a “pervasive tendency toward sluggish despair – a more or less permanent form of psychic numbing that includes diminished vitality, chronic depression, and constricted life space, which covers the rage and mistrust that are just below the surface” (Lifton, 1967). The values, beliefs and the police culture may guide him through each individual scene.

However the totality of an extended exposure to graphic deaths will eventually cause personality changes. Some of these changes may be beneficial to the officer.

The experience of grief and bereavement, resulting from superficial exposures to the death of others as a Reconstructionist, may prepare us to cope with more personally significant losses.

officer is on the job, he does not find some ability to cope, he may become vulnerable to a myriad of emotional problems.

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olice Culture and Tenure Most police officers are bound by the emotional cultures of their departments. The overriding sentiment within most police departments is a view that each officer should operate within a construct that is void of any emotion. Although we have recently understood that this type of behavior may be detrimental to the individuals, any acknowledgment of emotion is still considered “weak”, “unmanly”, or “unprofessional”, by the rank and file of the department. This philosophy is in part related to the myth that “soldiers” or “grown men” ”don’t cry” (Greene, 2001). These outdate concepts still live in some factions of the police force. However, over the past two decades a major shift in thinking has taken place. The new concepts that are being formed within the various departments include the idea that psychological support may be essential to today’s policing cultures.

“ " The police culture has had a long-standing tradition of using humor to dull any type of traumatic event’s impact.

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Most officers with some tenure come to recognize the beneficial aspects that some form of psychic numbing has to insulate themselves from potentially traumatic events (Henry, 2004). Rookies however, may come to recognize the benefits of distancing themselves emotionally from the sensory information that they may be required to assimilate. The public pressure for the officer to maintain an image of professional competence creates an arena designed for partial distancing to take place. Whether the officer is concerned by the constant media scrutiny, the stream of public onlookers, or the presence of victim’s family he still has a job to complete. He may use these distractions as a coping mechanism that enables him to focus on the job at hand. If however, in the first few years that an

The police culture has had a long-standing tradition of using humor to dull any type of traumatic event’s impact. This type of “gallows” humor may actual help the officer deal with any given situation. “You can make cruel jokes. You make light of the fact that people are dead. But you wouldn’t last six months if you didn’t do something like that” (Anderson, 2002) In the realm of psychology it seems to be inconclusive as to whether this type of humor tends to do more harm than good. Humor may help the officer in the short term to deal with a particularly gruesome scene. However, it may just suppress any trauma the officer has experienced. Recently management and Police Psychologists have been trying to change these long-entrenched police culture behaviors with small victories being made. However if the psychological health of a police service is to remain strong, the officers with the least amount of tenure must be educated to the risks involved.

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By ensuring the rookie’s exposure to the deaths of others at the earliest stages of his career, the subculture may be operating functionally to ensure the development of adaptive processes that will prepare the rookie for the greater and more personally significant losses Police work may potentially entail. It may also operate to better prepare young Officers to deal psychologically with potential danger and with future threats to their own mortality (Kutscher, 1973).

A personal identity may commence long before an officer enters the police department. The very act of declaring one’s intension to seek a career in policing is often the first step in redefining the social relationship between self and other (Henry, 2004).

Furthermore, a young officer’s sense of idealism may be quickly eroded and replaced with a protective mantle of cynicism as he struggles to harmonize the seemingly insuperable ambiguities presented by police work (Niederhoffer, 1967). This drastic change in self-identity may be formed from the public opinion now presented to the officer. However the interactions that the officer has with his new colleges may also be responsible for a large portion of this shift in thinking. Police officers are known to segregate themselves emotionally and physically from the rest of society. Officers will usually choose other police officers as their friends and neighbors. Most believe that the general public will not understand what they are involved in and may become too interested in their jobs. Even the culture in the stations is one of a tight knit community that has a lack of trust in its community and the officers they believe to be “not solid” or untrustworthy. These beliefs have evolved in a response to a career that is under constant scrutiny from the public and the management of each officer. Today’s police officer is required to keep a constant guard and record of his daily actions as one complaint may end his career.

By the very nature of their time on the job the rookie officer or even the apprenticing Collision Reconstructionist has usually at-

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tended few death scenes. Even before his tenure in the traffic section, the duties that a rookie performs at a death scene (sudden death) are complex and may be emotionally taxing. The entire process can be very difficult and the rookie is often required to remain in close proximity to the corpse for a prolonged period.

The scene and corpse must be searched; personal effects must be removed and given to the next of kin. Even though there is plenty of work that the officer must complete at a scene, being alone with no immediate tasks can certainly cause one to reflect upon death and one’s own mortality. When this personalization of the scene begins, it may cause the officer to further distance himself he may avoid looking at the victim’s face to consciously avoid thinking of the victim as a person. This distancing begins after the first death encounter the officer is faced with.

The first death encounter that an officer has is usually the most memorable. When Vincent Henry conducted interviews with several officers pertaining to their first death encounter he discovered that “when officers were asked to describe their first death encounter they did not begin by elaborating on their own and others’ emotional states. Instead, their initial narratives focused on factual recapitulations of events… In terms of reducing the degree of emotional trauma they experienced during the first death encounter this was fortuitous: by focusing cognitively on these novel and unfamiliar tasks, they had less time or capacity to attend to the disturbing emotional aspects of the death encounter (Henry, 2001).

Officers could recall their first encounter with great detail even after several years had passed. There first scene was described down to the minute detail and they could still picture the scene “as if it was yesterday”. Officers could remember the names and faces of the deceased, the address and the color of paint on the walls. However when asked, these Officers could not recall their first ticket or arrest. This uncanny ability to remember sights, sounds and smells was not confined to only the grotesque portions of the scene even the most mundane of detail was recalled with great clarity. Some deaths have the ability to remain entrenched in the officers’ mind even several years into their career.

officer may feel an acute loss of both physical and emotional control. Mature coping strategies honed on the street can no longer quash previously unconscious fantasies that flare in the face of “bad scenes”, “bad bodies” (Greene, 2001). These deaths may have a deeper connection to the officer. Generally speaking, the victim may be the same race or socioeconomic background as the officer, which will force him to draw some connection with the victim. In extreme circumstances the officer may be required to investigate the death of another officer in a job related circumstance. These types of deaths may be overwhelming to the officer and become an obstacle that even the psychological defense mechanisms he has constructed cannot control.

A United States Department of Justice research study revealed that during the first 5 years as a police officer there is an increased vulnerability to alcohol abuse. However, tenured officers had an increased risk of mortality, morbidity from cancer, heart disease, hypertension, acute migraines, reproductive problems, chronic back problems, foot problems, and insomnia. These officers also were three times more likely abuse their spouses, five times more likely to abuse alcohol, six times more likely to suffer from anxiety, and ten times more likely to suffer from depression (Harpold, 2002).

As of the date of this report no concrete study has been conducted with respect to the effects that death investigations may have on these numbers. Premature interview data that the author of this report is undertaking suggests that the numbers may in fact be much higher.

An officer that is required to deal with death on a daily basis may replace “requests” with “demands” in regards to their interpersonal relationships. For instance, an officer might order his child to “buckle up your seat belt or we’re not going anywhere” The officer cannot communicate his anger at having witnessed the unneces-

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Sometimes the circumstances of the death are such that routine structuring techniques do not bring immediate physical control of the scene. In these situations, the

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It can be seen that the environment the Reconstructionist immerses himself in helps to protect him from the images he must assimilate. However, partial professional numbing from cumulative exposure cannot entirely screen out the most emotionally traumatic elements. Cumulatively, repeated exposures to these traumas over an extended period of time can lead to a profound kind of numbing that can easily come to permeate the officers professional and personal identity. The greater the quality and quantity of traumatic imagery the Reconstructionist experiences at work, the greater his “need for images of connection, integrity, and movement in his personal and professional life” (Henry, 2004).

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Officers who are in the Reconstruction Squad are first and foremost volunteers. This self-selection process screens out those officers with an unusually high degree of death anxiety. Anyone who has issues with the death of another human will not even begin the process of becoming a member. Members of this squad are often given a sort of “death taint” due to their constant interactions with death. However, this death taint serves to further diminish the applicant pools that are able to cope with the daily exposures. If anything it is expected that those with a fascination or affinity for death images will apply.

Like their fellow officers, the Reconstructionist also uses humor to lessen the effect that a bad scene may have on them. The officers use humor to reformulate the images in a comical and less threatening way. In the same way, such humor reinforces the group ethos, and conveys a sense of connection to other group members, and reinforces the sense of unity and objectivity that is so important to the team’s professional identity.

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Members of the Collision Reconstruction Squad are put through a specific process that unwittingly screens out officers who are particularly vulnerable to death imagery. Reconstruction applicants are usually tenured officers, already experienced in dealing with death; they are highly trained technicians who view their work with scientific detachment.

Their work environment is structured in a highly organized way that narrowly defines duties and delegates specific tasks to specific individuals.

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When a team arrives on a scene they expect the area to be secured and removed of any witnesses who might contaminate a scene.

With the exception of the supervisor and the investigating officer they have few interactions with others. Their attention is focused on the task at hand and on the psychomotor skills they are practicing, but their conversation flows easily between giving instructions or commenting on the evidence and whatever other subject they are discussing. The remarkable ease with which they shift attention from professional to personal concerns also illuminates the extent of their professional numbing and how easily they negotiate the boundaries of the personal and professional identities.

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econstruction Office In light of the tremendous number of death scenes they visit as well as the objective grotesqueness of the images they often confront at those scenes, one might reasonably expect to find that the members of the reconstruction office manifest many psychological problems. Members of this office witness death far more frequently than any other category of police officer. Virtually every death scene they attend involves some sort of body trauma. Their duties often require them to closely examine the corpse and body fluids, in ways that would be repulsive to the vast majority of people. Many members of this office perform these duties and witness these images repeatedly over the course of many years. One might expect the cumulative impact of these images and experiences to have powerful and long-term psychic consequences. Only when you look deep into the mind of a Reconstructionist and the role that is required of them, that it becomes apparent their task envir onment and their professional selves are designed to offer them protective psychological devices that limit the effect that traumatic images have on the officer.

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Officers in the area of reconstruction are prone to psychological problems in spite of the fact that they have designed a system that gives each one of them the ability to cope with the grotesque visual images they are required to deal with.

The Reconstructionists’ scientific orientation and logical approach helps them to maintain a dispassionate and objective view of their work and the images it presents, and it helps them make a particular kind of meaning from their death encounters. To the Reconstructionist each scene is a puzzle to be solved using a variety of technical skills and an acquired body of scientific knowledge. Properly interpreted, every piece of physical evidence at a scene provides a piece of the puzzle leading him to an understanding of the totality of the facts surrounding the death, including its proximate and ultimate causes. “As a formative process, it is inherently vitalizing and to some extent serves to counter images and feeling of disintegration, stasis, and separation that may be presented at the scene” (Henry, 2004). These officers required a total concentration with little tolerance for distractions that may disrupt his protective focus and impede his professional numbing.

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In spite of my generally favorable experiences with the majority of Officers, I continue to be perplexed by the occasional police client I encounter who has generally had a successful career and has been relatively symptom free, who engages in self defeating or self destructive behaviors that on the surface appear to be unprovoked and unexpected. Officers who otherwise appear to be dealing effectively with their personal and professional lives seem to unexpectedly become the subject of an internal investigation because of a foolish and risky action or behavior such as driving while intoxicated, being seductive with a female subject, or taking other risks which could compromise or end their career (Ball)

In addition to the unit’s emotional requirements, the members have a set of formal requirements gained through courses and seminars. These requirements develop a certain mindset or focus: by focusing their attention on the immediate tasks at a scene, it enables the officer to screen out distracting images. Each officer develops a scientific forensic knowledge of physics, pathology, metallurgy, body kinematics, vehicle dynamics, engineering and various other proficiencies. Their scientific and technical orientation can also be discerned through the books and journals they read, and the off-duty courses and seminars they attend. Members of this squad also belong to various professional associations in the field they have chosen. This education provides them with some degree of scientific detachment from the things they witness as a result of the career choice they made.

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sary death of a child in a motor vehicle accident, he may be frightened that this could happen to his child. The officer is usually not aware that these changes in personality may be taking place.

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Although there are psychological issues that an officer may encounter as a direct result of the career path he has chosen, his ability to deal with those issues may be of greatest importance. Over the past two decades great strides have been made in assisting the average officer in their daily struggles within their work and social lives.

However, there is still a great deal of work to be done in terms of

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To some extent police officers erect psychic firewalls between their dual selves (work and home), in order to protect their loved ones from the ugliness they witness. This ultimately comes to inhabit their professional self, but it is also psychologically necessary for them to have a kind of psychic refuge from their hard and cynical working world. The officer who can adeptly move between these two selves and two worlds can access rewarding images that connect with and animate many more and many different aspects or dimensions of his personality. He can, in other words, be a more complete, more fulfilled, and more authentic human being (Henry, 2004).

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The death encounter’s traumatic potential is magnified when it involves exposure to grotesque, violent, or particularly disintegrative images. However, in terms of specific tasks and behaviors shaping the death encounter experience, the duties the task environment prescribes can either attenuate or exacerbate psychic threat. The officers may be required to be in close proximity to the corpse for extended periods of time and may be required to closely examine the remains including attending the autopsy. Furthermore, officers who are required to deal with the death of a fellow officer or a person that they make some mental connection with may have difficulty enacting their emotional distancing.

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When the young civilian decides to join the police force he has already begun the transformation of his feelings and coping skills that will be forever altered. Once the officer begins his career the ideals and humor of the police culture began to take hold of the officers personality. The rookie officer dealing with his first death may lay the groundwork for every subsequent encounter. He learns to disassociate from the images he encounters by creating an emotional distancing that is a requirement as his career progresses. In certain areas of policing, officers are required to create a level of partial professional numbing that enables them to deal with a series of deaths.

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ibliograpghy Alexander, D.A. The impact of Police work on Police Officers Spouses and Families. F.B.I. Behavioral Science Unit (9-17) Anderson, B.J. (2002). The echoes of Violence in the Police Family.

Peace-Officers.com (2003) 1-14 Aries, P. (1974). Western attitudes toward death: From the middle ages to the present (P.M. Ranum, Trans.). Baltimore, MD: Johns Hopkins University Press.

Aries, P. (1975a). Forbidden death. In E. Shneidman (Ed.), Death: Current perspectives. Palo Alto, CA: Mayfield.

Ball, S. Self defeating behavior patterns in law enforcement Officers. F.B.I. Behavioral Science Unit (419-421).

Becker, E. (1973). The denial of death. New York: Free Press.

Bennett, R.R. (1984). Becoming blue: A longitudinal study of Police recruit occupational socialization. Journal of Police Science and Administration, 12(1), 47-58.

Brown, N.O. (1959). Life against death: The psychoanalytical meaning of history. Middletown, CT: Wesleyan University Press.

Deal, T.E., and Kennedy, A.A. (1982). Corporate cultures: The rites and rituals of corporate life. New York: Addison-Wesley.

Freud, S. (1961). Thoughts for the times on war and death. In J. Strachey (Ed. And Trans.). Standard edition of the complete psychological works of Sigmund Freud (vol. 14). London: Hogarth Press. Original work published 1924.

Feifel, H. (1969). Death – relevant variable in psychology. In R. May (Ed.), Existential psychology (2nd ed.) (pp. 58-71). New York: Random House.

Feifel, H. (Ed.). (1959). The meaning of death. New York: McGraw-Hill.

Greene, C.L. (2001). Human remains and psychological impact on Police Officers: Excerpts from psychiatric observations. The Australian Journal of Disaster and Trauma studies (Vol 2001-2).

World Wide Web Groer, G. (1955). The pornography of death. Encounter, 5, 49-52.

Harpold, J.A. (2002) Negative Influences of Police Stress. Selected Readings for the Next Millennium, (2) 171-177.

Jung, C.G. (1933). Modern man in search of a soul (W.S. Dell & C.F. Baynes, Trans.). New York: Harcourt, Brace, & World.

Kutscher, A.H. (1973) Anticipatory grief, death, and bereavement: A continuum. In E. Wyschogrod (Ed>), The phenomenon of death: Faces of mortality (pp.40-54). New York: Harper & Row. Lifton, R.J. (1967). Revolutionary immortality: Mao Tse Tung and the Chinese cultural revolution. New York: W.W. Norton.

Lifton, R.J. (1983). The broken connection: On death and the continuity of life. New York: Basic Books. Original work published 1979.

Niederhoffer, A. (1967). Behind the shield: The Police in urban society. Garden City, NY: Doubleday.

Stroud, C. (1987) Close Pursuit. New York, 20 Violanti, J.M. (1991) Post Trauma Vulnerability: A Proposed Model. Critical Incidents in Policing Revised, 365-371

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onclusions Although police officers experience death as a matter of routine during there various investigations throughout their career, little knowledge has been gathered with respect to the particular kinds of impact such exposures have upon individual officers or their occupational culture.

During this short analysis I have tried to bring to light some of the issues and causes that officers and in particular Reconstructionist may encounter. Each police officer, like any human being, can be pushed beyond the limit of his psychological experience and endurance, to a point at which he becomes overwhelmed (Greene, 2001). It may be that one specific scene or a combination of years of work may push an officer to over-saturation. Most police officers are prepared for their daily work through a combination of factors that have brought them to a point where they may or may not be able to deal with the emotional stimuli in front of them.

research and strategies for dealing with officers whose primary role is in the investigation of death. I believe that first and foremost all police departments must acknowledge that investigating death is a unique psychological environment, which requires a special set of rules and procedures for admittance and intermittent testing to maintain the psychological fitness of its employees. The officers in this environment should be trained to recognize, in themselves as well as their colleagues, the signs and symptoms that these issues may present. As I have stated earlier these are highly educated and productive officers whose thirst for knowledge keeps them from succumbing to the difficult images that are presented to them. In this same light, the knowledge presented to them as a direct result of this research may protect them from psychological trauma that may be lurking in the images that are already present in their minds.

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The task environment combined with individual subjective factors creates an environment for officers in the reconstruction squad to invoke partial professional numbing. However, this may allow the officers to function through their work and home life on a daily basis but the cumulative effect of extremely traumatic scenes may exact a toll that will not be protected by the numbing. The members of this group are dedicated professionals who do a psychologically difficult job. They experience the deaths of others more frequently and in some ways more intimately than any other group of officers but nevertheless manage to avoid the complete and immobilizing immersion in disintegrative death imagery one might expect to result from these encounters.

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You won’t find a better opportunity for quality training, networking and practical experience anywhere! www.CrashConferences.com

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There is no other crash conference like it! Witness fully documented, live, full scale crash testing first hand, attend presentations by recognized experts in their field, and then leave with a DVD documenting all the crash data, photos and video of the testing, copies of presentations for later review, related documents and reference material in hand!

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Testing the Last Stop Record

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in the Mercedes MBE 4000

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William F. Messerschmidt

Ronnie E. DeMonia

Messerschmidt Safety Consulting

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Benjamin N. Smith

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ASI Investigations

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ntroduction In 2000, Mercedes Benz began marketing the MBE 900 and MBE 4000 diesels as engines available for Freightliner products sold in North America. The MBE 900 and MBE 4000 diesels are equipped with a unique set of electronic controls, which are comprised of a Vehicle Control Unit (VCU) and a Pumpe-Linie-Dusse (PLD) Control Unit (the PLD is comprised of the electronic controls for the fuel injection system). The twounit system stores data that are very similar to the data contained in the Detroit Diesel Series 50 and 60 engines; the data are also accessed with the same service tools: Detroit Diesel Diagnostic Link (DDDL) and Detroit Diesel Electronic Controls Reports (DDEC Reports). In the MBE systems, the majority of data accessed by DDDL are contained in the PLD Control Unit, and the DDEC Reports data and some fault code data are contained in the VCU. Despite the fact that event data recording technology has been in use in Mercedes Benz engines for over half a decade (beginning with version 12.09 of the MBE firmware), little testing has been done to establish the specific characteristics of DDEC-equipped Mercedes Benz Engine data collection methodology. Until this point in time, most research on Heavy Vehicle Event Data Recorder (HV EDR) systems, including the MBE, has focused on establishing the accuracy of speed and braking data captured before and after an event is triggered (see Reust 2004; Reust & Morgan 2006; van Nooten, et al. 2005; Bayan et al. 2009; Rogers et al. 2009).

One of the challenges that imaged ECM data presents to the crash reconstructionist is the prospect of having to link event records to a specific incident. These difficulties arise when the data captured cannot be linked to the incident under investigation with certainty. Known issues such as clock drift, improper programming, power failures, and other anomalies can create uncertainty about how (and if ) the captured event data relate to the incident that is being investigated. The testing that we discuss in this paper attempted to examine the creation of a new Last Stop Record under circumstances that were outside the “normal” or routine use of the MBE. These tests represent an attempt to assist the crash reconstructionist in linking event records to incidents under investigation.

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verview The testing included performing a total of 18 test runs, with each of the test runs focusing on different scenarios that were meant to address fundamental questions about the way MBE electronic controls record and store data.

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The test vehicle was a 2005 Freightliner Columbia with an MBE 4000 and an Eaton Fuller Ultrashift automatic transmission. The VCU firmware version was 14.21, and the PLD version was 60A. Photograph 1 shows the test vehicle during a braking run.

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We performed two additional tests of the Last Stop Record. In the first of these, the tractor was driven at over 50mph for approximately five minutes, and the DDEC Reports file was extracted with the key switch ON. In these cases, no new Last Stop Record was created. A third trial was performed with the tractor exceeding 60 miles per hour for approximately 10 minutes. The DDEC Reports file extraction was performed with the key switch ON. Again, in the third trial, no new Last Stop Record was created.

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verwriting the Last Stop Record The first issue studied during this testing was how the Last Stop Record is written. The objective in the initial phase of testing was simply to create a Last Stop Record and to identify the conditions necessary to overwrite that event.

The initial hypothesis was that a Last Stop Record would be written when the speed of the drive wheels (as measured at the output shaft of the transmission) reached zero miles per hour, and the associated data would be overwritten when the speed of the drive wheels subsequently exceeded 1.4mph.

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• The effect of simulating a power failure by cycling the key switch to OFF while the vehicle was in motion.

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• The impact of multiple ignition cycles on the Last Stop Record;

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• How an existing Last Stop Record is overwritten by a new Last Stop Record;

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To answer these questions, three types of tests were conducted to determine:

The initial download provided a Last Stop Record stored in the EEPROM of the VCU. During the first test, the vehicle’s driver accelerated to a speed of approximately 15mph and drove approximately 100 yards. The vehicle was stopped using the service brake, and the DDEC Reports file was extracted through the 9-pin Deutsch connector while the motor remained running and the key switch remained ON. The extracted DDEC Reports data showed that the initial Last Stop Record had not been overwritten. Based on these results, it was obvious that wheel speed was not the only critical factor in the writing of a new Last Stop Record, and as a result the working hypothesis was changed. It appeared that either there was a minimum time-in-motion required to create a Last Stop Record, or the key switch position must cycle from ON to OFF.

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The tests discussed in this paper center on the following questions: Is the recording of a Last Stop Record dependent on Key Switch position? Is there a minimum “time-in-motion” required to write a new Last Stop Record? How does a power failure, prior to the wheel speed reaching zero, affect the Last Stop Record?

The test vehicle was downloaded using DDDL 6.41 and DDEC Reports 6.43 prior to beginning the tests. Several programmed parameters were checked against physical vehicle parameters (including tire size and rear axle ratio) to ensure accuracy. The manufacturer’s specifications on the Eaton Fuller Ultrashift transmission were checked against the programmed ratios. The vehicle was also checked to ensure that no active fault codes were present before the testing began. Active fault codes were checked periodically during the tests, and they were also checked after completing the final test run to ensure that no faults were set due to testing.

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The testing was divided into two sets of trials: one set that tested the function of the Last Stop Record, and another set that tested the function of the Hard Brake event feature. Tests that were designed to examine the Hard Brake event also created Last Stop Records. The Last Stop Records are the focus of this paper. The authors’ testing of the Hard Brake event feature is ongoing.

Immediately after the third trial, the key switch was cycled to OFF and the DDEC Reports file was re-extracted. This extraction pro-

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vided a new Last Stop Record. The Last Stop Record was compared to video and DDDL Snapshot data from the third test run, and the Last Stop data were found to correspond with the kinematics of the third test. This indicated that after the vehicle came to a stop, kinematics data were present in the ECM but were not accessible through DDEC Reports until the key switch was cycled OFF.

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Based on these three tests, it appears that the following process takes place within the MBE VCU with respect to the Last Stop Record:

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2. The tractor is turned ON and driven.

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ultiple Ignition Cycles Within the Last Stop Record The first three tests established that terminating an ignition cycle was the catalyst for creating a Last Stop Record. Key switch position is a parameter that is monitored by the VCU and recorded in various trip activity and engine usage reports. It appears that Key Switch Status also affects the transfer of Last Stop data from volatile to non-volatile memory.

Experience with the system indicated that the VCU would always report 1 minute 44 seconds of data for a Last Stop Record. The second scenario that was examined was the condition where a Last Stop Record had been created, and subsequently the engine was turned ON for less than 1 minute 44 seconds. This scenario, which could occur if an accident vehicle were to be driven to the shoulder of the roadway after a crash, presented three alternate hypotheses:

3. During operation of the tractor, the wheel speed reaches 0mph.

1. No Last Stop Record would be recorded if the vehicle was in motion for less than 1 minute 44 seconds.

4. During a period of idle, after the wheel speed has reached 0mph, no new data are written beyond the 15 seconds after the wheel speed is first observed at 0mph.

2. The new Last Stop Record would be “patched” into the previous Last Stop Record and contain elements of both stops.

5. Once the key switch is turned OFF, the data are transferred from volatile memory (RAM) to non-volatile memory (EEPROM) and can be accessed by DDEC Reports.

6. The time at which the key switch is turned OFF is reported as Time = 0:00.

Figure 1: This visual shows the process by which the Last Stop Record data are transferred from volatile memory (RAM) to non-volatile memory (EEPROM) in the MBE VCU.

3. A completely new Last Stop Record would be generated, as the previous Last Stop Record was erased when measured drive wheel speed exceeded 1.4mph.

In order to test these three hypotheses, the following test procedure was used: 1. The ECM was downloaded in order to document the Last Stop Record in the VCU prior to testing.

2. The engine was started and idled for approximately 18 seconds.

3. The tractor was driven forward for 18 seconds, reaching a speed of approximately 10mph and then braked to a stop.

4. The engine was turned off (2 seconds engine shut off time) and remained off for 11 seconds.

5. The engine was started again (3 seconds engine start time) and idled for 6 seconds.

6. The tractor was driven forward for 20 seconds, reaching a speed of approximately 10mph and turned off.

7. DDEC Reports was extracted and saved.

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This 1 minute 23 second test was videotaped with fixed-frame-rate video (30fps) to provide a chronological record for comparison with the Last Stop Record from the ECM. The extracted Last Stop Record and video were evaluated to provide a side-byside chronological event table.

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Figure 2 shows a visual comparison of the DDEC Last Stop Record and the fixed-frame-rate video. The video was analyzed in the same resolution as the Last Stop Record (1 hertz), and the final engine shut down time was set equal to the last stop time (time = 0) from the DDEC Last Stop Record (see test step # 6). www.collisionpublishing.com

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In c ro up G a at D sh C ra 9 00 )2 (c Figure 2: This visual is a comparison of the data captured in the DDEC Reports Last Stop Record and the fixed-frame-rate video.

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During the final test, the tractor was driven at speeds up to 17 miles per hour for approximately two minutes. Video and DDDL Snapshot data were captured during this time. After two minutes of driving, the key switch was cycled OFF and the tractor was stopped using the service brake. The DDEC Reports file was extracted after the key switch was cycled OFF and the tractor had come to rest.

The Last Stop Record accurately captured the vehicle speed while the engine was ON and wrote 0mph values for all parameters after the ignition was turned OFF. The time at which the ignition was turned OFF was reported as 0:00, with 15 seconds of all-zero data following that time. Figure 3 shows the Last Stop Record that was extracted after this test.

It is extremely important to note that these findings are not necessarily applicable to Detroit Diesel ECMs, such as DDEC IV and DDEC V. Testing conducted by the authors along with members of the Wisconsin State Patrol, which was presented at the 2009 Midwest Association of Technical Accident Investigators (MATAI) Annual Conference, clearly demonstrated that in some cases, the DDEC IV and MBE electronic controls store and record data differently.

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imulating Power Failure Using the Key Switch A final test of the Last Stop Record involved cycling the key switch OFF while the vehicle was in motion. This method of examining the effects of a power failure was used by Bayan and Dunn (2009) to test Cummins ECMs.

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imitations This research was conducted with a Mercedes MBE 4000, with VCU version 14.21 and PLD version 60A. Other firmware and PLD versions may behave differently. If data that contradict these findings are observed, the investigator is encouraged to check the version of the VCU and PLD. These data are found on Page 1 of the Calibration Data File, which is extracted using DDDL 6.4x. Figure 4 shows the VCU and PLD versions in the test vehicle.

Although the same software tools are used to extract Calibration and DDEC Reports data, the actual firmware of the VCU and PLD are not the same as (and do not always behave like) the firmware of the DDEC IV and DDEC V ECM.

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The multiple ignition cycle test illustrates that an MBE Last Stop Record will only contain engine parameter data from the last ignition cycle. It is also evident from our results that if an ignition cycle lasts for less than 1 minute 44 seconds, all data prior to starting the engine will be reported as zero.

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The video analysis confirmed that there were at least 48 additional seconds during which the engine was running, but where RPM were reported as 0. The 48 seconds of time contained 20 seconds during which the tractor was in motion, and 28 seconds during which the tractor was stationary at idle. This result indicates that the third hypothesis (that a completely new Last Stop Record would be generated) is correct for the Mercedes MBE engines.

In regards to on-scene investigations that are undertaken by law enforcement, a first responder is the person who is primarily responsible for securing the accident scene and ensuring the safety of motorists and other emergency responders. In many cases, state law dictates that an accident vehicle be driven out of the travel lanes if possible. Although driving an accident vehicle out of the travel lanes may be necessary, it will cause Last Stop Record data to be overwritten, even if the vehicle is only moved from a travel lane to the adjacent shoulder.

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The Last Stop Record that was extracted from the VCU after this test only contained 32 seconds of non-zero data prior to the last stop (time = 0). The collected data showed that all engine parameters beyond -33 seconds were reported as zero, even though the truck was in motion, as illustrated in Figure 2. In short, the Last Stop Record did not accurately reflect the physical movements of the test vehicle.

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iscussion These tests indicate that wheel speed is not the only parameter that is relevant to recording a Last Stop Record in the MBE. Key Switch Status, which is also monitored by the engine, seems to function as the “trigger” that moves data from RAM to EEPROM. This is an important finding because it demonstrates why many collision events fail to set a Last Stop Record. In a case where power to the VCU is lost before the key can be turned OFF, or in a case where the driver is incapacitated, no Last Stop Record will be recorded.

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After synchronizing the Last Stop Record and the video, simple descriptive values were assigned to each one-second increment for both timelines. The descriptive values (run, mobile, off, and combinations of each) illustrate the tractor’s approximate status for each time increment according to both sources.

This testing used the key switch to simulate a power failure. Although this method has been used in other ECM research (Bayan, et al.), it appears that because the key switch status is a monitored parameter in the VCU, it is an invalid method for examining pow-

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Figure 3: The Last Stop Record extracted after cycling the key switch to OFF while the vehicle was in motion.

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Although power loss simulation using the key switch presents the researcher with confounding procedural variables, it can be inferred from the testing as a whole that if power is lost prior to cycling the key switch, no new Last Stop Record will be created.

This suggests the value of specific testing where a power loss at the VCU is simulated.

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onclusions The MBE 4000 generates a Last Stop Record when the key switch is cycled to OFF, regardless of whether the vehicle is stopped, or wheel speed is measured to be 0mph, provided that the vehicle has been in motion (not at idle) during that key cycle. If the ignition cycle lasts less than 1 minute 44 seconds, values of ZERO and OFF function as placeholders in the incomplete report. When the vehicle was turned OFF while still in motion, a new Last Stop Record was created, where time = 0 reflected the last second before the key cycle.

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er failures in the MBE engine. Monitoring of the key switch creates a procedural confounding variable within the research, and future testing should be conducted where power to the VCU is interrupted without cycling the key switch.

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Figure 4: Page 1 of 5 in the Calibration Data File of the test vehicle. The VCU and PLD versions are circled in red.

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Under normal operating conditions, an ignition cycle can be expected to last much more than 1:44; the vehicle will be brake to a stop; and the ignition will be turned OFF some time afterward. In this case, the time when key switch is turned OFF will be set as time = 0:00.

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On the next ignition cycle, the vehicle will be turned ON, and idle for some period of time. If the ignition is turned OFF prior to the vehicle’s being accelerated to over 1.4mph, then no new data will be written when the key is cycled to OFF.

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cknowledgements ASI Investigations and Messerschmidt Safety Consulting (MSC) would like to thank Powell Transportation of Columbia, Mississippi for the generous use of their vehicles. The authors would also like to thank Kelly S. Messerschmidt for her editorial assistance.

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Automobile Extrication the 9

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Collision Safety Institute Canada

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he purpose of this review is to give you an idea of the procedures followed at a crash scene by Fire personnel performing an extrication to achieve patient access for paramedics and ambulance personnel.

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As reconstructionists , we do not want to confuse the witness marks made by extrication heavy hydraulic tools (ie.: the “jaws of life”) and other equipment used by the fire department to affect extrication at a crash scene, (air chisels, pry bars, saws, etc) with crash induced marks.

Some fire departments will also employ tire deflation as a method to help stabilize a vehicle, as deflated tires put more weight on the cribbing and there is less bounce to the car. This may be done by releasing air through the valve stem, removing the valve stem, or by puncturing the tire. So a punctured tire may not be from road debris during the crash. Tire punctures can be made by spiking the tires with a sharp pointed bar, or by pushing a knife into the sidewall between the tire belts.

A hybrid vehicle will also be chocked at the wheels to prevent it moving forward or backward should it start on its own.

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In most instances, the first thing done to the vehicle will be to make it stable for extrication operations. This will involve “cribbing” the vehicle, or placing blocks, chocks, and other set ups to isolate the suspension from the road, so that the vehicle will not shift or lurch

during the use of heavy hydraulic rescue tools. A shifting or lurching vehicle will place more strain on an injured patient.

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In c ro up G a at D sh C ra 9 00 )2 (c Fig 1. Crushing fender to gain front door hinge access.

Fig 2. Spreading the rear door at the latch.

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Fig 3. “A” pillar dash lift

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In c ro up G a at D sh C ra 9 00 )2 (c The roof off manoeuvre is obvious, which involves cutting the “A”, “B” and “C” pillars. However, a roof flap, either forward or rearward can sometimes can accomplish the same desired room without having to lift or move and place the entire roof. A roof flap may save some windshield marks, as the windshield does not have to be removed, but will crack in new places as the roof is cut and moved.

A dash lift or roll is used if there is patient entrapment under the dash or within the pedals, with either the body or extremities. A

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It is often beneficial to try and talk to the incident commander, or the EMS personnel who removed the patient to determine what the steps were followed in the extrication evolution, seat belt usage, original post crash occupant placements, and patient extraction.

How the evolution went, what problems were encountered, and tool usage will shed a lot of light for the investigator on what crash deformation and marks have been changed by the rescue crew.

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A word to the wise: The fire rescue squad will often take pictures of the scene and extrication for training purposes. These photos evoke discussion upon review at the station regarding cribbing and tool placement, alternate evolutions which might prove faster, all to improve the “golden hour” of patient treatment.

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Once the door is open there is an opening if the rescue personnel want to cut the B pillar out of the vehicle, with or without the rear door attached. There is also the opportunity to push the B pillar away from the rest of the body by placing the spreader against the bottom of the B pillar and the seat track to gain room for the front seat area.

Seat belts are often cut if the seat belt latch is hard to reach, or simply unbuckled if the latch mechanism is within reach during a patient check. The resting place of the seat belt may have nothing to do with its involvement in the collision.

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The rear door can be removed in a similar manner to the front door. Some rear doors have secondary pins near the bottom of the door openings, which will distort the door at removal (Fig 2).

Seat movement is also something that tends to be affected by patient removal or packaging, and is one of the areas confused by diagnosis of seat back movement in crashes. It is common practice for rescue personnel to engage the seat back recliner manually or electrically to lower the seat back to slide a patient backward and upward directly onto a backboard. This can involve forcing the recliner mechanism or bending the seat.

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The door hinges or latches will be forced open with the spreaders, or cut using hydraulic cutters, depending upon the preference of the operator, or the power of the tool.

Steering wheel column lifts, and steering wheel removal are less common procedures with the advent of airbags and pyrotechnic steering columns.

These photos often start with a virgin scene with the vehicles at final rest before extrication operations begin. If there is a technical point that you are trying to review, this resource from your rescue friends may be invaluable.

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he Evolution For heavy hydraulics to be effective, an access point has to be made so that the hinges or latches on a door can be exposed. The advent of quality vehicles with narrow fit and finish gaps means that a gap needs to be made near the desired purchase point, large enough to get spreader tips into. This can be as simple as using a large bar at the door gap opening, or crushing a fender with a spreader to access the door hinges (Fig1).

A door can also be distorted to gain entry to a latch or pin.

A dash lift is becoming more common, as the lift is direct and in the area where needed. Look for a cut in the “A” pillar near the hinge or supported area, another cut to the upper apron rail, (the upper structure joining the front cowl to the engine compartment), and a final lift of the dash with the spreaders (Fig 3).

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ools The most commonly used tools at a crash scene today are the hydraulic cutter, spreader, and combination tool. Each tool manufacturer builds tools for specific benefit applications, and you will find light spreaders with smaller openings, or larger spreaders with very wide openings, small and large cutters, as well as combination of both. It is not surprising that rescue tools have gone through redesigns as modern vehicles get stronger, and there are occasions where out dated tools will delay a rescue, as the extrication path will have to be changed to fit the capabilities of the tools, (and sometimes the operators).

dash roll uses a ram which is placed within the door opening to displace the dash forward and upward. This will sometimes block patient access for removal, so often the dash lift is chosen. There is also less opportunity to roll a dash now that there are secondary supports from the dash structure to the tunnel below the dash.

So always remember if there has been fire department or EMS involvement with your vehicle, all may not be as it seems.

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ethod of Access The best method of access will be determined by the Incident Commander, who will direct the rescue. His primary responsibility is actually the safety of the first responders as the rescue evolution progresses, as well as to get the patient out as fast and safely as possible.

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In either case, the rationale is inadequate. PRT is a very complex, situationally-dependent phenomenon that cannot be captured in the canned numbers that are so typically employed. Few who reconstruct accidents know much about the underlying science, where the numbers they quote originate, how they were obtained or what they really mean.

There are two popular opinions and rationales for PRT. The first opinion is that the PRT is 1.5 seconds. The usual basis for 1.5 seconds is that the reconstructionist read it in an accident reconstruction book, learned it in a class or simply believes that it is the “accepted value.” The second opinion is that the PRT is 1.1 (or 1.6 for the 95th percentile driver) based on “Olson.” This opinion almost invariably means that the accident reconstructionist has read one of Olson’s secondary sources, such as a chapter in Forensic Aspects of Driver Perception And Response (2003), or has simply seen it cited somewhere. In fact, the data stem from Olson & Sivak (1986), but Sivak remains anonymous because few have read the original research. For simplicity, I will simply refer to the data as “Olson,” which is how they are usually referenced.

This article addresses the misuse of canned numbers (including the AASHTO 2.5 seconds and computer programs) in general but focuses primarily on the “Olson values.” There are three main problems. First, every research study has limited generality because it is conduced under a specific set of conditions. An accident reconstructionist wishing to apply Olson, or any other research study, to a specific accident should understand the differences between the driving situation in the study and the specific accident. These differences will be smaller in some cases and larger in others, but there will be always

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ccident reconstruction often requires a driver “perception-reaction time” (PRT), the interval between obstacle appearance and driver response initiation, I .e., the foot just touches the brake pedal and/or the hands just start turning the wheel. The PRT number is often a critical factor in establishing causation and subsequently in assigning blame.

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differences. In some cases, Olson does not apply at all. In fact, the concept of PRT itself may not even apply. The discussions below of visibility and the tollbooth problem are examples.

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Second, Olson is a perfectly fine study, but it is only one of perhaps 100+ driver PRT studies. These other studies provide data for other sets of conditions. Knowledge of these studies allows the reconstuctionist to better interpolate and extrapolate PRT for a broader set of conditions. However, there are no existing data for many common accident scenarios, so it is often impossible to determine a PRT with much precision. For example, there are almost no data for PRT at night, when accidents are frequent.

This is a very unusual way to determine PRT. Usually, the PRT clock starts counting at the moment the signal is presented. It is unclear how accurately drivers could say where they were when they first saw the obstacle, so there are questions about what this study actually measured. However, one thing is certain: if the PRT clock had started counting at the moment when the driver first had a clear sightline to the obstacle, then the PRT would have been longer.

Reading the actual study reveals that the methodology was biased to produce short PRT’s. There are many other procedural factors that further promoted very short PRT and that limit the study’s generality for assigning PRT to real accidents.

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1. Drivers were alerted. The term “alerted” unfortunately has two senses, which often creates confusion. Some authors use the term “alerted” to mean that the driver knew that there was an obstacle or even a particular obstacle ahead. In this sense, “alerted” means “expecting.”

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Their results show a median PRT of about 1.1 second to press the brakes, with no difference between younger and older drivers. The 5th percentile drivers responded in .8 second while the 95th percentile driver responded in about 1.6 seconds. Olson has published these results in several later book chapters but without the methodological details.

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In sum, the Olson drivers’ high arousal level, likely produced shorter PRT’s than would occur under many normal driving scenarios. Olson was fully aware of this likelihood when he noted that “The subjects in this study were possibly alert relative to the general population of drivers” and that “the results are probably conservative (I.e., lower) to what would be found in the real world.”

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"Reading the actual study reveals that the methodology was biased to produce short PRT’s."

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2 The testing occurred during the day.

Olson does not specify the times of his testing, but it is likely that much of it was performed when drivers are at a moderate or high point on their “circadian rhythms,” the normal 24hour cycle of arousal that all people experience.

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A close reading of the Olson & Sivak study reveals the important methodological details. Olson tested two groups, a younger group of 49 drivers with an age range of 18-40 and an older group of 15 drivers with an age range of 50-84. The drivers were told only that they would be a study of driver behavior. They drove the test vehicle during daylight at about 27-31 mph with the experimenter sitting in the rear seat. The route took them over a rural road chosen so that there would be no distractions or possible hazards. After 10-15 minutes, the vehicle came to a hill.

The experimenters had placed an obstacle, a 6” x 36” block of foam, in the left side of the lane directly in front of the driver. As the driver ascended the hill, the obstacle came into view. The sight distance to the obstacle was about 150 ft (46 meters), which translated to about 3.3-3.8 seconds time-to-collision (TTC). Instruments measured the time/location at which the driver released the accelerator and pressed the brake. In order to determine the PRT, the driver had to re-travel the route and tell the experimenter where he had first seen the obstacle. Olson then calculated the putative PRT time by measuring the distance from the location where the driver claimed to have first seen the obstacle to the location where he released the accelerator. PRT is this distance divided by speed.

The other sense of “alert” refers to general arousal level. Drivers in the Olson study may not have been expecting a particular obstacle, but they certainly were alert and had a very high arousal level: they were participating in an experiment where their behavior was being monitored. There was even someone sitting in the back seat watching them. Moreover, they had been driving only 10-15 minutes before encountering the obstacle. Arousal level is related to driving time. The well-known phenomenon of vigilance decrement (Mackworth, 1948), a rapid decline in detection, typically starts within a half hour after task initiation. Further, research (Philip, Taillard, Klein, Sagaspe, Davies, Guilleminault, & Bioulac, 2003) has shown that time spent driving is a better predictor of decrease in driver performance than hours without sleep. The short driving time in the Olson study gives the test drivers a significant arousal advantage over a real driver who may have been on the road for an extended period.

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hat Does Olson Actually Say? In order to properly use Olson (or any other study) as a basis for estimating real world PRT’s, the first step is to carefully analyze the experimental procedure. The second step is to determine the differences between research conditions and the accident conditions. The last step is to compensate for the differences. This is the most difficult problem.

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Third, assigning a reasonable PRT requires knowledge that goes even beyond the PRT literature. The issue of driver PRT cannot be snipped off from the larger topics such as perception, memory and learning and examined independently. This is especially true in accident scenarios where no PRT data exist. The assessment of older driver PRT, as discussed later, is a good example.

First, the research was not exactly a study of PRT to an unexpected obstacle. The PRT determination required the driver to return to the scene and to say where he first saw the obstacle. At this point, the obstacle was expected and not a surprise.

For most people, the arousal cycle has lows in the late afternoon and especially in the early morning hours. During these periods, many performance measures, such as accident rates and PRT are at their worst. One study (Wylie, Shultz, Miller, Mitler, & Mackie,

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1996) of long haul truck drivers, for example, found that accidents correlated with time-of-day, early morning hours, but not with time-without-sleep. As a rule of thumb, in fact, it takes about 24 hours before people exhibit major sleep-deprivation losses.

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In fact, when visibility is sufficiently low, the concept of PRT becomes irrelevant. After all, if the driver can’t see the obstacle, then he can’t respond to it. For example, assume that PRT for a pedestrian cutting left-to-right across the driver’s path in good visibility conditions 1.5 seconds. In this case, driver first sees the target in peripheral vision. At night, the same pedestrian wearing dark clothing emerges from outside the driver’s headlamp beams.

When the pedestrian is far to the left, he receives little headlamp illumination and is invisible.

"For the same pedestrian walking the same path, driver will have less time to avoid the collision at night ..."

In sum, the Olson study optimized the PRT by placing the obstacle at the fixation point directly ahead of the driver. PRT will be longer

Situations that are more ambiguous or which develop more gradually require conscious thinking that slows response and drastically increases variability. For example, a driver traveling at night who approaches red and white dots (e g., the rear reflective tape on a truck) at some ill-defined distance must gain “situational awareness.” He must identify the lights, determine the distance, search memory for previous similar experiences, decide what is going to

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5. The obstacle appeared suddenly and unambiguously. Olson’s drivers responded reflexively and did not have to think much because the situation was very clear. There was minimal cognitive processing, little uncertainty and no complexity, so PRT was very short. Moreover, the variability is very small because people are relatively uniform in their speed of making reflexive responses.

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Visual field effects likely explain why Olson & Sivak found a 1.1 median PRT second while studies (Green, 2008a) using lane incursions typically find slower mean PRT’s of about 1.5 seconds.

(About .1 second of this difference is likely due to the difference between using median and mean as measures of central tendency.)

Olson and Sivak’s 95th percentile level was 1.8 seconds while the 95th percentile lane incursion PRT would be about 2.4 seconds, which is also near value used by AASHTO in geometric road design.

Lastly, low visibility conditions also slow cognitive processing by creating uncertainty and by impairing recognition. I explain this further in the next section.

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Lastly, if the target is more than 15o from the sightline, the driver will likely also have to make a head turn. Imagine a driver approaching an intersection or railroad track. He must turn his head to look one direction and then the other. It takes the driver 85th percentile driver .7 seconds to turn his head one way and then another 1 second to turn back the other (Long & Nitsch, 2008). This 1.7 seconds search time is on top of the PRT.

It is possible to precisely estimate of the amount of slowing that will occur at night. However, some qualitative statements are possible. For the same pedestrian walking the same path, driver will have less time to avoid the collision at night because the pedestrian will likely have to be much closer in order to achieve the required visibility.

The difference between day and night PRT will depend on factor such as street lighting, pedestrian clothing, background clutter, etc.

A pedestrian wearing white clothing, for example, will often have better visibility and more approximate daylight visibility conditions than a pedestrian wearing dark clothing. However, there are exceptions (Green, 2008b).

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In contrast, many collision scenarios involve a lane incursion where a vehicle or pedestrian approaches from the side. The obstacle then first appears in peripheral vision, where visual sensitivity is lower and attention is weaker. Moreover, when a viewer detects an object in peripheral vision, he most likely makes a saccadic eye movement toward it. The saccade requires time to move the eye plus a “dwell time” for the viewer to perceive the scene.

The total saccade time about is 1/3 second in good day visibility. At night, the time is likely to be longer. The first saccade may miss the object, so viewers may have to make more than one saccade to “home in” on the target. When the new fixation requires a significant change in distance, such as shifting gaze from a mirror to an obstacle a few hundred feet down the road, the eye’s change of accommodation and vergence can drive the time up to as long as a second (Travis, 1948.)

As pedestrian and vehicle approach, more headlamp illumination falls on the pedestrian. At some point, driver sees the pedestrian. In theory, the 1.5 seconds reaction time clock starts when the pedestrian first becomes visible in the periphery. But when is that? In order to state a well-defined PRT, it would be necessary to know the exact point at which the pedestrian became visible. Even if this could be calculated, then it would still be necessary to specify the point where the pedestrian became conspicuous enough to draw attention and eye movement. This point is likely unknowable with great precision.

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3. The obstacle appeared at the point of fixation. Olson placed the obstacle on the roadway at the crest of a hill and directly in front of the driver. It likely the exact location where the driver was fixating at the moment he reached the 46 meter sight distance. Location of an obstacle in the visual field can affect PRT. The optimal location is along the sightline at the point of fixation. Objects located here cast their images on the fovea, the retinal area of sharpest vision and the focus of attention. Olson placed the obstacle in the ideal visual field location.

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4. The visibility conditions were good. Olson tested drivers in daylight and good visibility, so obstacle visibility was not a limiting factor in driver behavior. PRT is likely to increase at night and under other low visibility conditions.

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Olson’s drivers then likely had this additional arousal advantage over normal drivers in the early morning hours who are at a low point on the circadian rhythm. However, drivers who habitually work nights may have their rhythm “phase shifted,” so the peaks and lows are at different times than normal drivers.

when objects approach from the side as well as for other reasons discussed in subsequent sections.

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Even if the driver decides to respond, the choice of response is sometimes unclear. A driver heading toward a tractor-trailer blocking the road may find that there is no time to brake and that steering to the left will take him into oncoming traffic while steering to the right will put him in a ditch. This is termed an “avoidanceavoidance” conflict where the driver must choose among a set of bad alternatives. In such cases, PRT typically is very, very long.

Often, the driver can’t decide and fails to respond at all before collision. The common example is the underride accident where there is an unfortunate tendency to assume the driver’s failure to respond because he had fallen asleep. In fact, the driver may have been caught in an avoidance-avoidance crisis.

“ " "The driver also has a mental stopping distance and steering model of his ability to brake/swerve his vehicle."

Moreover, most drivers have likely had little or no experience making sudden stops, especially at high speeds. They base their cocoon 92 Collision Volume 4 Issue 2.indd 92

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For this scheme to work, the driver must accurately assess object distance, speed and stopping distance (or time). However, distance perception is highly fallible, especially for small points of light, unfamiliar objects, foggy atmosphere and some other situations.

Drivers are also poor at judging their own speed (Denton, 1980) and there are many situational factors that can cause them to underestimate how fast they are going, I e., fog and, low edge rates (Denton, 1980.) Drivers may also err in their belief of stopping ability when driving an unfamiliar vehicle or on wet or icy roads, sharp downgrades, dark conditions, etc.

7. The “older” drivers were not all old. Olson somewhat surprisingly failed to find any slowing in their “older drivers.” This has caused many to claim that aging has no effect on PRT. However Olson’s “old” group included drivers as young as age 50. While visual abilities start their decline in the early 40’s, the significant effects do not begin until viewers enter the 60’s. Olson does not give the ages of the individual drivers, so it is impossible to know the number who were in their 50’s and early 60’s where aging effects are small.

However, it is very possible that Olson found no aging effect, in part, because their “older” drivers were too young.

Olson’s task further likely minimized aging effects. As discussed elsewhere (Odom & Green, 2008), studies in the basic research literature have repeatedly found that impairments of aging (and other conditions such as distraction and alcohol use) are more pronounced when perceptual and cognitive abilities are taxed under conditions such as low visibility, uncertainty and complexity. The simple, virtually automatic avoidance task in the Olson study required little cognition. It was performed in good visibility, so perceptual abilities were not a limiting factor.

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The driver also has a mental stopping distance and steering model of his ability to brake/swerve his vehicle. This area is like a cocoon that surrounds the driver, providing a buffer zone with obstacles. Drivers believe that they can avoid collision with obstacles outside the cocoon. Ideally, the driver steers his vehicle through the cocoon’s center, adjust speed and direct as the safe field of travel dynamically changes.

The fear of losing control is likely why drivers frequently resort to two-stage braking (Prynne & Martin, 1995). They initially push the brake pedal down part way and then monitor the situation, hoping that they can avoid the collision without and extreme response that risks loss of control. If collision is still likely, then the driver might go to the extreme maneuver.

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The point of the tollbooth example is that there is much more to PRT than perception. Drivers have a mental model of their ability to control their vehicle. The decision to act is always based partly on this mental model. The model’s constituents are the “safe field of travel” and “stopping distance” (Gibson and Crooks, 1938). As a driver travels down the road, he is surrounded by obstacles, cars ahead, curbs and other barriers, pedestrians crossing the road, etc. which define a safe field of travel.

This field changes constantly as new vehicles, pedestrians, etc. appear and change position.

6. The drivers were traveling at a slowly. Olson’s drivers traveled at speeds ranging between 2731 mph. At such slow speeds, sudden, abrupt braking or steering is less likely to cause an unrecoverable loss of control and to have dangerous consequences. In contrast, drivers traveling at 65 mph on a freeway may to hesitate to make sharp swerves or go to full-out braking because of potential control loss.

They have to weigh the hazard of a collision with the hazard created by a loss of control that sends the vehicle over a median or guardrail, into other traffic or that initiates a side-skid and rollover. It is a type of avoidance-avoidance conflict that will likely lengthen PRT.

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Theoretically, PRT would be the time between first sighting of the tollbooth and the pressure on the brake pedal. However, this is not a “reaction” in any conventional sense, so the concept of PRT doesn’t really apply. The driver does not brake because there is no need to act. While the tollbooth problem might seem trivial, drivers face similar problems frequently. Up ahead, they see brake lights or unidentifiable objects, some dim dots of red and light. Should the driver brake immediately or wait until he is sure of the situation?

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The “tollbooth problem” provides a good example. Imagine a driver on a high speed limited-access road traveling 65 mph. Suddenly, he sees a tollbooth up a head about a half-mile away and realizes that he will have to stop. Does he start braking immediately? The answer, of course, is no. Immediate braking wastes time arriving at the tollbooth. Rather, the driver has an internal model of his vehicle’s braking capabilities and has learned the mount of time/ distance needed to stop at a comfortable deceleration (or even at an uncomfortable deceleration.) Eventually he reaches the critical distance and begins to brake.

size on their experiences stopping at lower speeds. Since stopping distance increases with the square of speed rather than linearly with speed, they are likely to underestimate the needed distance.

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happen if he responds and if he doesn’t respond, choose a response, chose how hard to make the response, etc. (Green, 2008). Moreover he must consider his ability to control vehicle speed and direction.

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onclusion Accident reconstructionists should take the Olson results for what they are – the fastest that a driver can avoid an “unexpected” obstacle in highly optimized conditions. Any deviation, such as low visibility, peripheral visual field location, complexity or uncertainty is almost certain to increase PRT. The finding that there is no loss of PRT with age is not generalizable and depends on specific conditions. Lastly, real drivers are unlikely to be as alert as the drivers in the study. Lower arousal level may produce longer PRT’s, especially at low points in the circadian rhythm and after driving for extended periods.

Each of the 7 factors described above would doubtless add time to Olson’s optimized 1.1/1.8 seconds PRT but assigning a precise number is difficult. I have sometimes seen opinions where someone arbitrarily adds 0.5 or 1 to compensate for nighttime or complex conditions. While essentially guesswork, these estimates are doubtless closer to reality than the simple, foveal, daytime, high-arousal values taken at face value. However, there are few if any PRT data for many of these conditions. This is why it is so important to have general knowledge about perception, attention and memory to fall back upon. They are often the only available guides.

Despite the lack of data for many situations, however, I can draw two practical conclusions about assigning a driver PRT. First, estimates will often cover a very broad range because precision is impossible. Second, estimates will often be very high - much higher than are normally seen. Low visibility and violated expectation make the obstacle disappear and even a moment’s hesitation to search or to think or to decide upon response can eat up seconds.

The AASHO Redbook’s view of PRT written in 1973 remains true today:

Green, M. (2008a) "How long does it take to stop?" Methodological Analysis of Driver Perception-Brake Times. In M. Green, B. Abrams, M. Allen, Forensic Vision With Application To Highway Safety, 379-406. Tucson: Lawyers & Judges Publishing.

Green, M. (2008b) "Pedestrian accident analysis" Methodological Analysis of Driver Perception-Brake Times. In M. Green, B. Abrams, M. Allen, Forensic Vision With Application To Highway Safety, 329-348. Tucson: Lawyers & Judges Publishing.

Long, G. & Nitsch, A. (2008). Effect of dead turning on driver perception-reaction time at passive railroad crossings. Transportation Research board 2007 Meeting CD. Mackworth NH (1948). The breakdown of vigilance during prolonged visual search. Quarterly Journal of Experimental Psychology, 1, 5-61.

Odom, J. & Green, M. (2008). Aging Vision. In M. Green, B. Abrams, M. Allen, Forensic Vision With Application To Highway Safety. Tucson: Lawyers & Judges Publishing.

Olson, P. & Farber, E. (2003). Forensic Aspects of Driver Perception and Response. Tucson: Lawyers & Judges Publishing.

Olson, P.L. & Sivak, M. (1986) Perception-response time to unexpected roadway hazards. Human Factors, 28, 96-99.

Philip P., Taillard J., Klein E., Sagaspe P., Charles A., Davies W., Guilleminault C., & Bioulac, B. (2003). Effect of fatigue on performance measured by a driving simulator in automobile drivers. Journal of Psychosomatic Research, 55, 197-200.

Prynne, K. and P. Martin 1995. Braking behavior in emergencies.

SAE Technical Paper 950969.

Travis, R. (1948). Measurement of accommodation and convergence time as part of a complex visual adjustment. Journal of experimental psychology, 38, 395-403.

Wylie, C. D. Shultz, T. Miller, J. C. Mitler, M. M. and Mackie, R. R. (1996). Commercial motor vehicle driver fatigue and alertness study: Project report. Technical Report FHWAMC- 97-002, Federal Highway Administration, Washington DC.

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This discussion of older driver PRT highlights the point that PRT assignment often requires knowledge of the general psychological literature and of scientific methodology. First, it is necessary to actually read Olson’s study in order to learn that he placed drivers as young as age 50 in the old category. This is not a detail that is ever mentioned in secondary sources. Second, the effects of complexity and uncertainty on the size of age-related deficits do not appear anywhere in the driver PRT literature or any computerized PRT program. It is basic science published in basic science sources.

Third, the important issue of representativeness would not be apparent to anyone who was not intimately familiar with the way scientific research is conducted.

Gibson, J.J. & Crooks, L.E. (1938). A theoretical field-analysis of automobile driving. American Journal of Psychology, 51, 453–471.

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Moreover, research with older subjects always raises the issue of representativeness. Olson does not state how he recruited the subject drivers. However, most researchers would routinely screen their subjects, especially older ones, for any visual or other health problems. The older subject drivers are then likely to be healthier, more active, in better visual and cognitive condition than the population as a whole. Moreover, the drivers very likely agreed voluntarily to be in the study. Only the relatively healthy and “spry” senior is likely to volunteer for a research study. In sum, research on screened, self-selected older drivers likely overestimates abilities of the older population as a whole. In any event, the “older” group consisted of only 15 drivers.

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eferences American Association of State Highway Officials (1973). A Policy on Design of Urban Highways and Arterial Streets. Washington, DC: AASHO.

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“Whenever the driver is confronted with a complex traffic or highway situation and is required to make choices, judgments, and decisions, his response time may increase to 2, 3 or even 5 seconds” (p. 278).

Denton G. (1980). The influence of visual pattern on perceived speed. Perception, 9, 393-402. www.collisionpublishing.com

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Comparison of Vehicle Measurement James W. Smith, P.E. Exponent, Inc.

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ntroduction Damage measurements are the underlying foundation for calculations used to estimate the dissipated damage energy involved in a collision, which in turn can be utilized to determine the speeds of the involved vehicles. An investigator often must take measurements of a vehicle in less-than-ideal conditions. Some complicating factors might include a confined work space, weather conditions, time constraints, a remote inspection site, or significant deformation that is difficult to characterize.

Cost of the measurement equipment and ease of use may be factors in an investigator’s decision-making process; measurement systems vary widely in cost, size, weight, and complexity. Given these concerns, the aim of this paper is to evaluate the practicality and accuracy of several methods of measuring vehicle damage profiles.

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Several methods exist, and much has been written about these methods, from semi-automated photogrammetry1 to use of deformable wire-frame models when as little as two photographs of a vehicle are available2. However, little in the way of comparative studies has been published about these different techniques.

This paper compares several methods of vehicle measurement for application in the accident reconstruction discipline. Each method was employed to model a subject vehicle, and the methods are compared to assess measurement accuracy, time required to acquire and process the data, cost of use for the data collection equipment, and general equipment ease of use.

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bstract The application of the principle of Conservation of Energy for an accident reconstruction requires that an investigator determine the amount of residual deformation of a damaged vehicle. Law enforcement officers present at the scene of an accident are operating under time restrictions which frequently do not allow sufficiently comprehensive vehicle damage data to be taken for use in calculations. Instead, an investigator may need to acquire deformation measurements independently. Common measurement techniques include the use of hand measurements, photogrammetric analysis, or a theodylite (total station) survey. A lesserknown 3-dimensional metrology tool is also available.

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Daniel S. Peterson, P.E. Exponent, Inc.

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Tumbas and Smith3 point out that the typical uncertainty in principle direction of force (PDOF) outweighs error from measurement of crush when energy calculations are made using the CRASH3 algorithm. In fact, Smith & Noga4 found that less than 18 percent of the error in estimated delta-V was due to measurement inaccuracy and 70 percent was due to error in the assignment of PDOF. In that study, estimated error in the crush measurements was ±3 inches at the 95% confidence level.

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Again, in a study of several hand measurement techniques, Brown, et al5, concluded that variances of as much as 3 inches in crush depth did not significantly affect estimated delta-V for 35-mph impacts using CRASH3.

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This study will analyze what level of accuracy can be expected from several measurement techniques and, using data from a sample National Highway Traffic Safety Administration (NHTSA) crash test, quantify the effect of measurement variance on calculated vehicle impact speed.

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easurements For this study, a 2002 Volkswagen GTI was used as a subject vehicle for measurements. A single vehicle was used for this comparison to remove variability associated with vehicle selection and measurement point identification.

Implementing these measurement techniques on multiple vehicles, both damaged and undamaged, and in various environments, may have given a more complete picture of the utility of each method, but the added variable would have made a comparison of measurement accuracy far more complicated.

Measurement points were marked on the vehicle with colored ½-inch-diameter adhesive round markers and adhesive marking tape (Figure 1). Measurements were taken at the center of each marker. The markers were placed in locations that could be used to generally characterize the shape of the vehicle. Also, since frontal crush measurements are widely familiar in the accident reconstruction discipline, a series of markers was placed across the front of the vehicle along the hood, bumper, and lower fascia in a C1-C6 measurement station profile as described by Tumbas and Smith3 (Figure 2).

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hotogrammetry The vehicle was photographed both indoors and outdoors to compare the effect of different lighting and slightly varying camera positions on the clarity of the photographs for modeling and the accuracy of the produced data. Indoor photography for use with photogrammetry can be challenging because low light forces the camera to use a shorter depth-of-field (wider f-stop), which can cause parts of the vehicle to be out of focus.

Outdoor photography in full sunlight presents issues with glare and dark shadows, which can obscure points of interest in some photographs.

In both environments, the vehicle was photographed with a calibrated camera from eight directions, at both ground level and elevated positions, for a total of sixteen photographs per model.

Additional photographs were also taken of the interior to capture a number of points marked on the driver seat and steering wheel.

The authors used a Nikon D60 digital SLR camera body (10-megapixel sensor) with an 18-55mm Nikkor zoom lens set to its widest angle. For all photographs, the camera was set to “aperture priority, F9” to maximize depth-of-field without producing unusably dark photographs, and a Nikon SB-800 external flash was used indoors. A tape measure placed on the ground beside the vehicle was used to scale each model. The markers were not disturbed during the re-positioning of the vehicle from indoors to outdoors, except for slight variations of axle and steering wheel positions.

The photographs were imported into EOS Systems PhotoModeler software6 and oriented to each other by marking points on the vehicle that were common among the photographs.

As a general rule, a 20 - to 30-degree or greater angle included between camera positions is desirable for good photogrammetric convergence of data points. Also, a point’s spacial accuracy may be improved by including the point in as many photographs as possible. For this study, the approximate camera positions were pre-planned to allow every measurement point to be included in three or more photographs. Finally, a calibrated high-megapixel camera body and quality lens can give much faster and more accurate modeling results than a lower quality calibrated camera, or worse, an unknown camera (for example, police or insurance adjuster photographs that were taken with varying zoom settings).

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The total station and 3-dimensional (3-D) metrology measurements were acquired at a later date than the photogrammetry and hand measurements. Markers and tape were re-applied to the vehicle at that time following the same pattern as before. Because nearly all of the measured points were located at corners or along edges of body features, the second set of markers could be placed in sufficiently similar locations to the first set. In a few instances, the markers were re-located using measured distances from body features or the vehicle centerline.

An individual familiar with each technique gathered the measurements; thus, common pitfalls associated with user inexperience were avoided and standard practices based on experience were followed.

Figure 1: Adhesive measuring tape and markers applied to the subject vehicle 98 Collision Volume 4 Issue 2.indd 98

Figure 2: Front view of the subject vehicle with measurement points indicated

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and Measurements After the vehicle was photographed, it was measured by hand. A reference line was established on the ground directly below two symmetrical points defined by body panel intersections near the rear wheel well on each side of the vehicle.

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Tape measures were positioned on each side of the vehicle and in front of the vehicle based on this reference line. A hand-held tape measure, plumb bob, and level were used to establish the position of each measured point in a rectangular coordinate system based on the reference line.

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otal Station The vehicle was also surveyed using a Leica TCR 303 total station7 in “reflectorless” mode. In this configuration, the instrument projects a laser beam directly onto the vehicle and calculates a distance based on the elapsed time until the light pulses are reflected back to the instrument. Each measured point is defined in a spherical coordinate system based upon the measured distance and the instrument’s orientation. The data is later converted into rectangular coordinates for comparison with the other measurement techniques.

ment tip at the other. The PDA is mounted to the pole and it processes streaming data from the laser detectors and collects discrete point locations upon command. Data can be collected with the measurement pole held in almost any orientation desired as long as the detectors have clear line-of-sight to the laser transmitters and the pole is kept within a 3-D space for which a pre-measurement calibration has been performed. The system must be calibrated for the intended measurement volume when the transmitters are first set up and any time they are re-positioned; this process takes about five minutes.

The points marked in the vehicle’s interior were not measured with the X-station because the seat and steering wheel positions were not recorded at the time that the photogrammetry and hand measurement techniques were conducted and they had since been adjusted. However, the X-station is well-adapted to interior measurement locations such as these.

Alternatively, a team of investigators can conduct a total station survey of a vehicle or a scene with a reflector mounted to a measurement tool with a known length. However, this method is not possible for an investigator working alone to acquire measurements.

Larger ¾-inch-diameter adhesive markers were placed on the vehicle for this survey, and some of the markers were creased and applied to the vehicle such that one half of the marker was raised and facing in the direction of the total station. The larger size of the markers and the bending of the marker faces provided an improved surface for reflecting the laser pulses back to the total station. If smaller markers had been used, or if markers were not used at all, the glossy nature of the vehicle’s paint and the curvature of the various body surfaces would have in some instances not sufficiently reflected the laser back to the instrument, and point collection failure or incorrect measurements would have resulted.

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omparing The Systems After these four techniques were used to survey the measurement points, all measurement data was imported into AutoCAD and the surveys were aligned to each other.

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-D Metrology Finally, the vehicle was measured with a tool that is lesser-known in the accident reconstruction discipline. ArcSecond’s X-Station (also referred to as “Indoor GPS”, or “iGPS”)8 is a 3-D metrology tool that utilizes multiple stationary laser transmitters and a handheld pole with a palm-size computer, or PDA (Figure 3). The pole is length-adjustable, with laser detectors at one end and a measure-

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"Three laser transmitters were used for this survey, although two will work in most situations."

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Three laser transmitters were used for this survey, although two will work in most situations. More than three are allowable if the system is configured to use a laptop or desktop computer to process the streaming data. Additional transmitters can be used to improve accuracy, especially when large areas such as a crash scene are measured.

The transmitters were mounted on 6-foot-tall tripods; two were placed 30 feet ahead of the aft-most point on the vehicle and 15 feet to each side of its centerline. The third transmitter was placed approximately 9 feet directly behind the aft-most point on the vehicle along the vehicle centerline. This layout, which defined an approximately round measurement area, afforded the most accurate results and the greatest flexibility for measurement pole orientation and positioning. Attempting to measure within an oblong area can produce less accurate results due to poor triangulation between the poles and the transmitters. Such a measurement area setup also tends to create areas in which sightlines from the pole to the transmitters are blocked by the vehicle.

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To capture the greatest number of data points in a limited amount of time, two surveys were taken with the total station, one on each side of the vehicle. The instrument was positioned 30 feet forward of the aft-most point on the vehicle and 15 feet to each side of the vehicle’s centerline as these positions provided good views of the front, sides and top of the vehicle.

Because the total station requires direct line-of-sight to take measurements, points on the rear of the vehicle and inside the vehicle were not measurable from these positions.

Figure 3: Basic X-station equipment

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The data from the two models produced with photogrammetry (hereafter referred to as the indoor and outdoor photomodels) matched almost exactly, demonstrating the high accuracy that can be obtained using a calibrated camera with a high-megapixel sensor. Although this does not mean that either model is perfectly accurate and precise, it justifies the choice of the indoor photomodel as a baseline model to which the others are compared for accuracy.

A vehicle-based coordinate system was assigned to the indoor photomodel using the vehicle axles. The origin was located at the center of the rear axle, and the axes were defined in accordance with SAE sign convention (x-forward, y-right, z-down).

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The other models were aligned to the indoor photomodel using points on the rocker panels, the A-posts at the base of the windshield, and the top of the windshield at the vehicle centerline.

These points, and data describing the accuracy and precision of the alignments, are tabulated in Appendix A. The alignment of the X-station survey to the indoor photomodel is shown in Figure 4.

Outdoor Photomodel Hand Measurements X-Station Total Station, Left Side Total Station, Right Side

Method Mean 0.10 0.11 0.27 0.19 0.25 0.11 0.17 0.10 0.21 0.10

Std Dev 99% 0.04 0.06 0.04 0.05 0.04

Table 1 – Statistical analysis of measurement techniques as compared to the indoor photomodel (inches) Hand measurements are also the most susceptible of these methods to inaccuracy due to the patience and care that must be exercised to generate reliable values regardless of the part of the vehicle that is measured. Complex damage surfaces can be much more difficult to measure repeatably by hand than an undamaged exemplar such as the subject vehicle in this study. This principle was demonstrated by Bartlett, et al9, who found in a hand measurement study that 17 participants profiling the front end of a small van with overlap crush damage produced measurements with a standard deviation of 5.2 inches in crush depth. Hand measurements produced a higher mean measurement deviation than the other methods analyzed in the current study as well.

Total station surveys may be susceptible to inaccuracy depending on how the data is gathered. Some of the variance found in the total station measurements in this study is undoubtedly due to the re-application of the markers following the earlier measurements (this error applies to the X-station survey as well). However, the use of larger markers and the bending of the marker surfaces toward the instrument may have lead to variance caused by measurement of a non-adhered portion of the marker. It is also possible that if the marker, or target, is oriented at a significant angle relative to the instrument or if the target is not sufficiently reflective, an erroneous value may be recorded.

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a Method Mean -0.06 0.03 -0.08 0.13 -0.22 0.04 -0.09 0.08 -0.13 0.07

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Outdoor Photomodel Hand Measurements X-Station Total Station, Left Side Total Station, Right Side

Std Dev 99% 0.02 0.08 0.03 0.05 0.04

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It is interesting to note that the standard deviation of the hand measurements is nearly twice that of the other methods. This illustrates the difficulty in precisely judging the location of certain points that require the investigator to hold a tape measure or a plumb bob steadily over a long distance. To further demonstrate this problem, consider only the hand measurements that require long distance measurements. If only the points at or above the vehicle beltline (the lower edge of the windows) are considered, the mean measurement deviation of the hand measurement points is 0.40 inches, compared to 0.08 inches for the outdoor photomodel.

The longitudinal components of the C1 C6 data mean measurement deviations are shown in Table 2. As expected, accuracy and precision for the C1-C6 longitudinal deviations are generally higher than for the whole-vehicle 3-D deviations. For example, the outdoor photomodel C1-C6 deviation is 0.06 inches with a 99% confidence interval of ± 0.02 inches, but the outdoor photomodel 3-D deviation is 0.10 inches with a 99% confidence interval of ± 0.04 inches.

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Table 1 shows that, in this study, all four methods gave point precision within approximately ¼-inch of the indoor photomodel, and the outdoor photomodel’s mean point precision is within an impressive 0.10 inches of the indoor photomodel. The calculated error is correct to within 0.06 inches at the 99% confidence interval for all of the methods.

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Equation 1

In many cases, an investigator is interested in crush on one particular side of the vehicle. For this reason, the measurement points were laid out on the subject vehicle to allow for an energy/speed analysis. The points that were used to align the models to each other were located in areas that would typically not be deformed as a result of a frontal impact, and three tiers of C1 C6 points were placed across the front of the vehicle.

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recision/Accuracy Once the surveys were aligned in AutoCAD and the vehicle coordinate system was defined, the surveys were individually exported into a spreadsheet and compared, point by point. For each model, 3-D resultant lengths, or measurement deviations, were calculated based on the location of each point and its sister point from the indoor photomodel. Statistical data was then generated based on the measurement deviations. These deviations were found using the Pythagorean Theorem, which states that:

Results will vary for every situation and investigator. All of the methods are vulnerable to error in some way; possible causes can include poor calibration of the X-station or inspection camera, incorrect reading of a tape measure, or simply careless aiming of the total station. However, if the investigator is vigilant and careful in their work, all of these methods are reasonably reliable, as will be discussed later. They will provide data that is within the accuracy and precision required for energy calculations in an accident reconstruction.

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Figure 4: Front view of subject vehicle as mapped by the indoor photomodel (thin solid lines) and the X-station survey (thick dashed lines); at this magnification the models are almost indistinguishable

Table 2 – Statistical analysis of C1-C6 measurements, longitudinal direction only, as compared to the indoor photomodel (inches)

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It is noted that actual measurement variation will likely be random in nature, not consistently overestimating or underestimating the actual measurement; the error discussed above is the largest ex-

$5,300 $130 $5,430

X-station Survey X-station pole kit with PDA and software Two industrial-style transmitters Two survey tripods with soft cases

$10,820 $20,000 $260 $31,080

Table 3 – Sample equipment costs Clearly, measuring by hand requires the smallest investment, and 3-D metrology is the most costly option. Used survey equipment may be available, which could significantly reduce the cost of the complex systems. However, the buyer should beware that used equipment might need calibration or servicing. It also may be obsolete and unsupported by the manufacturer, and communication barriers may exist between old and new technology that will make it difficult to “mix and match” components.

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hotogrammetry Photogrammetry is not typically physically demanding and does not require much equipment. This method may be convenient if the weather is poor, due to the low amount of required on-site time. Application of adhesive markers or adhesive measuring tape can be very helpful in conducting this analysis, but many measurements can be performed without these markers if the investigator has reasons to not use them, such as rain.

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ransport & Ease of Use Other important considerations in choosing the most appropriate measurement system for a project are portability and ease of use. Weight and size can become an issue for travel, particularly by air. The comparative simplicity of some techniques may also be a deciding factor, especially if the investigator has minimal experience with the technique.

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From this relationship, we can say that if the same amount of physical measurement error (0.33 inches) was present in data used to calculate speed for a Golf involved in a collision that produced twice the deformation as the NHTSA test, both the percent measurement error and the percent calculated speed error would be approximately 1%, or half of the speed error in the NHTSA test example. Likewise, if the deformation was only half as severe, the measurement accuracy would have twice as much influence on estimated speed, generating approximately 4% error. This is intuitively expected; with greater crush, a particular amount of measurement error becomes a smaller fraction of that crush.

Total Station Survey Sokkia Set 630R Survey tripod with soft case

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$30 $10 $15 $55

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If energy and crush distance are thus directly proportional to each other, then error in calculated speed must be directly proportional to the error in measurement as well, per Equation 3.

Hand Measurements Four tape measures Plumb bob Standard 24" level

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Equation 2

$450 $1,000 $100 $1,550

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From Equation 2, we can say that impact energy is proportional to both the square of impact speed and crush distance.

Photogrammetry Basic digital SLR camera with lens EOS Systems Photomodeler Collapsible ladder

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Thus, use of the Golf ’s “correct” stiffness coefficients with our maximally-varied measurements affects the estimated impact speed by no more than ± 0.6 mph. In this example, the percent change in speed is about the same as the percent variance in the crush measurements, both approximately 2%.

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To simulate measurements that an investigator might gather, we increase all of the NHTSA-reported crush values by 0.33 inches; this value represents the hand measurements’ 3-D mean measurement deviation with a 99% confidence interval, a worst-case assumption of measurement variance (Table 1). Combining these intentionally adjusted crush values with the “correct” stiffness coefficients we determined previously, CRASH3 generates an impact speed of 29.6 mph. If the NHTSA crush values are decreased by 0.33 inches rather than increased, CRASH3 calculates an impact speed of 28.4 mph.

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First, to neutralize any existing variance in the crush measurements, we use equations from Neptune et al11 to generate A and B stiffness coefficients for the vehicle using NHTSA’s measurements.

By generating stiffness coefficients with only crush data from this particular test, we are assuming that NHTSA’s crush values are perfect (no variance) for our purpose. The crush values can be entered into CRASH3 with the stiffness coefficients we have generated, and the program will output the correct impact speed of exactly 29.0 mph (see Appendix D for sample calculations).

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ost Current estimated costs for the equipment used in this study are listed in Table 3; these values were collected from widely available sources such as online survey supply stores, nationally known home improvement stores or directly from the manufacturer. Equipment costs vary widely between the studied methods, and they could also vary depending on the brand, model and source of the equipment. Companion equipment may also be desirable, increasing cost. For example, more indoor photogrammetry options will be available if an external flash unit is purchased, and more accurate metrology results may be obtained with a greater number of transmitters or with higherprecision transmitters.

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ffect of Measurement Variance on Estimated Impact Speed To demonstrate the effect of the measurement variance found in this study, data from a NHTSA frontal barrier test10 of a 1994 Volkswagen Golf is utilized. In this crash test, the Golf struck a solid, flat barrier at a forward velocity of 29.0 mph and received frontal damage at the bumper level with crush depths of between 10.7 and 15.3 inches. The following exercise simulates a speed calculation an investigator might make by measuring the damaged Golf by hand and entering the gathered measurements into CRASH3 along with known stiffness coefficients for the vehicle.

pected error range. Actual variation in estimated speed for the 29.0 mph impact we have discussed would be ± 0.3 mph using the hand measurements 3-D mean measurement deviation and ± 0.1 mph using the outdoor photomodel 3-D mean measurement deviation.

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Such small variances can become negligible when significant crush is measured, and this level of accuracy is well within the limits prescribed by Tumbas and Brown. As an example, we will demonstrate the effect of measurement accuracy on a speed calculation for a collision-damaged vehicle in the following section.

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Also, if the vehicle is difficult to access (for example, if it can’t be moved from between two other vehicles in a storage yard), photogrammetry measurements may be faster and less physically demanding or risky than direct measurements with a tape measure or with the X-station pole.

A few practices that may help an inspection with the X-station to proceed smoothly are: 1. Check the PDA display before sampling each data point and confirm that the PDA is receiving a consistent signal from the laser transmitters. Erroneous data can be recorded if the data stream is intermittent. Typical causes of poor reception are obstructions between the transmitters and receivers or a shallow incident angle between the pole and a transmitter.

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Tape measures and a camera kit can easily fit into carry-on luggage, so photogrammetry may be preferable if the investigator needs to quickly get to an inspection site, perform the inspection, and return with a minimal amount of luggage. One might carry only a laptop bag and a small camera bag. If a ladder is needed to photograph the important damage area, one can usually be borrowed at the inspection site or rented at a nearby home improvement or tool rental store.

One benefit of the X-station is that measurement points on severely deformed sheetmetal or in complex areas such as engine compartments and interiors may often be easily reached. Exponent has manufactured a simple custom “reverse” measurement tip that can be positioned to measure points on the inside of a door or roof pillar from the outside of the vehicle. These hidden points require much more time to measure with photogrammetry or hand measurements, and may be impossible to capture using a total station.

Another benefit of photogrammetry is that, in one way, the investigator takes the evidence home with them in the photographs. If a particular, important measurement was forgotten at the inspection, it is possible to extract the additional information using the photogrammetry software at a later time. This could save a second trip to measure the vehicle which, in addition to being costly, might not be possible.

2. Be aware of the pole’s adjustable length and the necessity to update the software’s setting if the pole length is changed. Forgetfulness with regard to updating the software can easily invalidate the collected data. It is critical that the pole length be accounted for in the software during both the calibration and measurement phases; otherwise, some or all of the collected data will be incorrect.

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and Measurements Though the equipment is the easiest to transport, hand measurements are perhaps the most physically demanding of the four methods, and the most difficult data to gather reliably. Accurate measurements require patience, time and steady hands. Depending on the points of interest, measurements may also require frequent kneeling, crawling, or lying on one’s back. Inspection facilities are commonly covered in broken glass, automotive fluids, and other potential hazards, so hand measurements can be much more problematic to perform than the other non-contact measurement techniques.

3. Verify that the equipment is fully charged before leaving for the inspection, and bring the chargers on the inspection if possible. It is also a good idea to set up the system in advance of the trip and ensure all connections are working and that every component is accounted for.

A few spare batteries in the carry case might also rescue an inspection if the rechargeable transmitter or PDA batteries are showing shortened life due to a large number of charge cycles.

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-D metrology The X-station system is challenging to take on commercial flights because of its size, weight, and the required number of cases to transport the equipment (reference Figure 5).

The system may require four or more medium-to-large cases. This can be too much equipment to manage without some help.

Shipping the equipment to the inspection location is a reasonable alternative if time allows. Given the airline charges for additional and heavy baggage, it may also be less costly to ship the equipment.

If the inspection is within driving distance, the size and weight of the system does not pose such a problem; all of the necessary equipment can be loaded into a small car.

4. Prior to taking measurements, mark the measurement points with colored markers or a marking pen and photograph the vehicle. This provides a visual record of the point locations, and the photographs can later serve as a backup for use in photogrammetry.

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5. Before leaving the inspection site, download the data to a laptop and review it in a program such as AutoCAD to confirm its accuracy. Saving the data to hard disk also reduces the risk that the data could be lost due to a damaged memory card or a misplaced PDA.

otal station The total station is not as convenient to transport as tape measures or a camera kit, but the system should fit into two cases. Total stations are commonly used by investigators for traveling inspections.

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Like photogrammetry, the total station may also be faster and less physically demanding or risky than direct measurements.

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Another potential disadvantage of the X-station is that measurements can become physically tiring, depending on the circumstances of the inspection and the measurements that are taken. If points of interest are difficult to reach, one may need to hold the measurement pole at arms’ length or maintain an awkward position while finding a pole orientation that affords line-of-sight to the transmitters.

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Figure 5 – Sample weights of minimum required inspection equipment

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One potential benefit of the total station is that, depending on the surface of the inspected vehicle, it may be possible to perform the inspection without touching the vehicle. Additional care should then be taken to verify that the transmitted laser is properly reflected from the intended measurement surfaces. Best practices similar to the X-Station system should be considered for the Total Station also, including proper equipment charging, point marking and documentation, and verification of the collected data.

etup & Measurement Time Every step of the measurements taken for this study was performed by an individual experienced in these methods, and the steps were timed. These times represent a

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points are added to the project, because the setup time is fixed but the per-point data collection time is small. If the measurement points are closely placed, the investigator can capture several points before having to reposition his or her body, further increasing the X-station’s efficiency. This method lends itself to the most detailed and complex surveys.

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best-case-scenario because the data was gathered in a laboratory environment and the desired measurement points were pre-determined.

The overall amount of time required by photogrammetry was greater than that required by the use of a total station. However, when photogrammetry is used, the model of the vehicle is often created later, at a more convenient time and place. The on-site time required for a photogrammetry inspection is generally the least of all the methods: 18 minutes in this case (not including marker placement). Low on-site time could be beneficial for reasons such as poor weather, limited availability of the vehicle, or cost.

In this study, the X-station was the second quickest on-site method and the quickest overall method of gathering data. The efficiency of 3-D metrology increases relative to the other techniques as more

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If only a few measurements are required and immediate results are desired, hand measurements may be a preferable approach. Even less equipment is necessary for this method than for photogram-

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onclusion With factors such as time, cost, portability and ease-ofuse considered, photogrammetry appears to be the most generally convenient technique to use for a remote vehicle inspection. The equipment is small, light, and reasonably priced, and measurement time on-site is often the lowest of these techniques. However, depending on the complexity of the project, more time may be necessary to model the vehicle after the inspection is complete. Severe deformation or other complex shapes require inclusion of additional photographs in the project, which increases modeling time and can lead to computer processor overload.

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Table 4 – Subject vehicle measurement time, not including measurement point planning and marking

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In this study, the additional per-point “time cost” of measurements using each method, excluding time for equipment setup and orientation, was 180 seconds by hand, 43 seconds with PhotoModeler, 37 seconds with the total station, and 17 seconds with the X-station. These time values are only samples generated by the work done in this study; they will easily vary from one circumstance to another and they can change based on the number and location of the points collected.

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Total Station Survey Set up and orient transit Collect data points Download data, stow equipment Align survey halves

11 17 9 37 minutes

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X-station Survey Set up and calibrate system Collect data points Download data, stow equipment

20 210 230 minutes

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Hand Measurements Lay out tape measures Take measurements

15 3 51 69 minutes

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Photogrammetry Photograph vehicle Download photos Model vehicle with PhotoModeler

For example, if an investigator wishes to take measurements inside a vehicle wheel opening, certain points in each photograph may be obscured by the suspension and drivetrain components. The investigator might need to take ten photographs of this small area to ensure that every marked point is visible in at least three photographs that include sufficient angles between the camera positions. If the wheel opening detail was being incorporated into a larger full-vehicle model, which would typically require approximately 12 photographs for an undamaged vehicle, the project might then contain a minimum of 22 photographs. If too many photographs are added to a project, operations on the workstation may be significantly slowed. Eventually, it may become preferable to split the model into several smaller models and assemble them later with drafting software such as AutoCAD. Unfortunately, this process still takes time, and uncertainty is added when the pieces are later combined together.

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Hand measurements were by far the most time consuming method. The collection time might have been lower if only exterior measurements were taken, as accurate interior measurements can be especially difficult and timeconsuming. Rushing through the measurement process may have saved time in this case, but accuracy would have suffered—possibly to the point of significantly affecting calculated crush energy.

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Regardless, several notable differences were observed in the amount of measurement time required for each technique, and several insights can be drawn about the efficiency of these methods under typical circumstances. A summary of the time required for each step is provided in Table 4.

The efficiency of photogrammetry, on the other hand, is not improved as points are added, and it is reduced if the vehicle’s shape is complex and points are difficult to photograph. Each measured point should be included on at least three photographs to provide good positional accuracy. If certain points are only visible in a few photographs, all of these photographs will need to be included in the model to accurately measure each point. With each additional photograph required to capture all of the necessary points, more time is consumed in the modeling phase.

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Time spent upon arrival at an inspection site to become familiar with a vehicle and plan measurements would not be much affected by the measurement system used, so this step is ignored here.

Time spent marking the measurement points, which in this study was about 30 minutes, is also equivalent for each method and is not included.

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metry, and the tools are very inexpensive. However, accuracy will be lower. Also, the accuracy of this method is reduced for difficultto-measure points, and it is susceptible to error if the investigator does not work carefully to gather quality data.

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Use of a total station could be the best option in some circumstances, because it is simple to set up, reasonably quick to use, and it provides accurate data if the surfaces being measured provide good reflectance. As with hand measurements, the total station and the X-station provide immediate on-site results. The disadvantages of using a total station are the potential for error caused by poor reflectance from the vehicle surfaces, and required line-of-sight for taking measurements.

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The X-station is a unique system that provides some benefits that the other methods do not. The equipment is the bulkiest and the most expensive among the options considered here. However, it offers a fast and efficient method of collecting many data points, and it can be the easiest way to collect data from heavily deformed areas or interior locations. It is especially convenient in a semipermanent set up, such as a large garage bay, where calibration is not needed for each project and the equipment does not have to be transported, assembled, stowed and transported home with each project.

All four of the studied methods have been shown to provide sufficient accuracy when used properly. It should be noted that selection of the baseline measurement technique, photogrammetry, certainly affected the reported accuracy of the other measurements.

In addition, the re-application of the adhesive markers during the experiment likely had an effect on the reported accuracy of the techniques used afterward, although the authors believe that sufficient controls were in place to minimize this potential error. In the end, the largest measurement deviation in 3-D space, independent of the chosen baseline technique and including the potential error in marker re-application, was on the order of 0.33 inches. Applying this worst-case potential error to measurements acquired from a 29.0-mph barrier crash test shows that the potential for error in calculating the delta-V would be only ± 0.6 mph.

Each of these measurement techniques offers advantages and disadvantages. They all provide sufficiently accurate data for crush measurements and energy calculations. The investigator must consider his or her situation and the factors discussed here before they can decide which technique will best suit their needs.

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eferences 1. Mills, Dan, and Carty, Gary, “Semi-Automated Crush Determination Using Coded and Non-Coded Targets with Close-Range Photogrammetry”, Accident Reconstruction Network.

2. Rucoba, Robert; Duran, Amanda; and Carr, Lee; “A Three-Dimensional Crush Measurement Methodology using Two-Dimension Photographs”, SAE Report No. 2008-01-0163, 2008.

3. Tumbas, Nicholas S., Smith, Russell A., “Measuring Protocol for Quantifying Vehicle Damage from an Energy Basis Point of View”, SAE Report No. 880072, 1988.

4. Smith, Russel A., Noga, J. Thomas, “Accuracy and Sensitivity of CRASH”, SAE Report No. 821169, 1982.

5. Brown, Douglas R., et al, “Practical Application of Vehicle Speed Determination from Crush Measurements”, SAE Report No. 870498, 1987.

6. EOS Systems Inc., www.photomodeler.com.

7. Leica Geosystems, www.leica-geosystems.com.

8. Metris USA, http://us.metris.com.

9. Bartlett, Wade, et al, “Evaluating the Uncertainty in Various Measurement Tasks Common to Accident Reconstruction”, SAE Report No. 2002-01-0546, 2002.

10. NHTSA report #CR5803, “Vehicle Safety Compliance Testing for Occupant Crash Protection”, FMVSS 208, 1994 Volkswagen Golf III GL, Calspan Corporation, 1994.

11. Neptune, James A., et al, “A Method for Quantifying Vehicle Crush Stiffness Coefficients”, SAE Report No. 920607, 1992.

Appendix A-C: Can be found on the Data disk 4.

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Sample Impact Velocity Calculations 1.

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ing up to a collision and avoidance capabilities, as well as during the impact and post-impact trajectory phases.

An understanding of factors such as articulation, high centers of gravity, rollover propensity, off-tracking in turns, jack-knifes, trailer swing-outs, acceleration rates, and lane change performance is essential in the investigation and reconstruction of commercial vehicle collisions. This paper will provide an introduction to vehicle dynamics concepts applicable to commercial vehicle collisions, with a combination of scientific applications that are unique to heavy vehicles.

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bstract The dynamics of commercial vehicles, especially articulated vehicles, differ greatly from the dynamics of typical automobiles. Professionals trained in standard vehicular crash reconstruction techniques may find that their reconstruction training left them ill-prepared for the investigation and reconstruction of incidents involving heavy vehicles. The performance of commercial vehicles in acceleration, lateral motion, rotational motion, roll and pitch, and handling characteristics can provide insight into the events lead-

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ences. Heavy trucks generally use diesel engines, which provide a higher level of torque than gasoline engines at a lower rpm range.

Trucks require a wide gear ratio selection to get heavy loads from stopped to interstate speeds, and the process of shifting through this range of multiple gears affects the overall acceleration of the truck. Another difference between the acceleration profiles of passenger vehicles and commercial vehicles is the fundamental powerto-weight ratio. Although the engines in heavy trucks are more powerful, a loaded truck cannot compensate for the significantly heavier loads and higher rolling resistance that must be accelerated.

For a truck starting at rest and with the velocity known at some measured distance, the average acceleration can be modeled:

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ntroduction In the field of physics, “Dynamics” refers to the study and calculations of the motion of a body in space and time. It includes the position of the body longitudinally, laterally, and vertically, and how this position changes over time. It also includes the rotational position of the body in the yaw, roll, and pitch planes, and how this rotational position changes over time. Changes in positions, and the rates of changes over time, result in velocities and accelerations in each of these directions. By studying and calculating the inter-relationships between positions, velocities, and accelerations as a vehicle moves through space and time, a collision Reconstructionist can gather important insight into the events leading up to and following a crash event.

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Although the terms “commercial vehicle” and “heavy truck” are often used interchangeably, regulatory and industry groups focus on the commercial aspect of heavy truck use in official definitions.

The Federal Motor Carrier Safety Administration (FMCSA) defines a “commercial vehicle” as a self-propelled vehicle or combination of vehicles used on a highway in commerce to transport passengers or property, when such vehicle has a gross vehicle weight rating of 10,001 pounds or more, is used to transport more than 8 passengers for compensation, or carries hazardous materials. Different vehicle types are included within the scope of commercial vehicles, such as straight trucks, buses, and tractor-trailer combinations. The consistent factors in these vehicle types are weight, length, width, and height greater than that of passenger vehicles.

As a result of the unique demands of carrying the designated gross weight, automotive engineers design very different mechanical systems for commercial vehicles than for passenger vehicles, including the brakes, engines, drive-trains, suspensions, steering systems, and tires.

In 2007, Commercial Vehicles traveled 223 billion miles on United States roads. On a vehicle-miles traveled basis, the total crash rate is lower than for comparable modes of transportation. They were involved in only 6.6% of all reported crashes (approximately 368,000), but the relative severity of crashes tended to be more serious, with Commercial Vehicles involved in approximately 12% of fatal crashes (approximately 4,300). Figure 1 indicates the consistent statistical representation of commercial vehicles in overall and fatal crash rates.

A

An average acceleration for commercial vehicles can be used to model acceleration performance, with data acquired through one of three common methods: 1. Published global values derived from empirical testing of numerous and various trucks, loading conditions, and travel distances. Modeling may incorporate a wide range of driver behaviors, or may involve a subjective evaluation of the nature of the acceleration; for example, "typical," "slow," “moderate, "normal" or "aggressive." The Collision Reconstructionist should attempt to use testing data that closely matches their particular scenario when utilizing a published acceleration factor for a vehicle. Typical average acceleration values for commercial vehicles as reported by Fricke and Proctor are provided in Table 1.

Note that the values in the table are typical acceleration rate ranges. In modeling a specific vehicle’s performance, the Collision Reconstructionist should consider factors such as truck weight (including its loading condition), roadway grade, engine performance, traffic conditions, and subjective elements as reported by the truck's operator.

2. Observational traffic studies of a number of similar size and type vehicles on the same portion of roadway. This method allows for local variations and location-specific factors such as grade and traffic congestion.

3. Testing of the identical vehicle and driver, or an exemplar, in identical or similar conditions. This method addresses vehicle-specific, driver-specific, and locationspecific conditions, but may not always be possible

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cceleration Collision Reconstruction modeling of acceleration performance is a common application in order to determine the location and speed of a vehicle at any given point in time.

However, use of published data for passenger vehicles is inappropriate for heavy trucks due to a number of fundamental differ-

Equation 1

Figure 1: Fatality Analysis Reporting System (FARS) statistics on heavy truck crashes, 2003-2007.

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Acceleration Rate (g)

Source

Low Acceleration: Big Trucks, Loaded

0.01 to 0.05

Fricke

0.03 to 0.10

Fricke

Average Acceleration, First 50 Feet

0.08 to 0.11

Proctor et al

Average Acceleration, First 100 Feet

0.06 to 0.07

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Acceleration from a Stop

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Table 1 – Typical acceleration rates for commercial vehicles – acceleration from a stop.

Speed Range

Low Acceleration (g) Normal Acceleration (g)

Less than 20 mph

0.01 to 0.05

0.03 to 0.11

Between 20 and 35 mph

+/- 0.03

+/- 0.05

More than 35 mph

+/- 0.01

+/- 0.03

for the test truck. It is clear that on a microscopic level the actual acceleration varies over time and does not follow linear behavior, but over time the average acceleration is quite consistent. Through the first 14 seconds of the test the average acceleration remained around 3 ft/sec².

In addition to visual evaluation, the average acceleration can be calculated from the time and the final velocity in ft/sec with Equation 2.

Equation 2 vf = the final velocity at time t For the vehicle test depicted in Figure 1, the calculated average acceleration was consistent with the visual data interpretation:

Once an average acceleration rate has been determined, whether by published values, observational study, or vehicle testing, then the velocity of the vehicle at any point in time can be determined using the following equation:

Table 2 – Typical acceleration rates for commercial vehicles – acceleration in speed ranges.

Equation 3

Figure 1 depicts an example of data acquired from a loaded articulated vehicle accelerating from rest. The high frequency oscillations observed are due to small vibrations in the vehicle as it accelerated. The trend line shows the average acceleration values

An example of applying this method is shown in Figure 2, a graph of vehicle speed for each increment in time based on an average acceleration rate of 2.89 ft/sec^2.

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Figure 2 – Measured acceleration of a partially loaded articulated heavy truck using an Accelerex accelerometer.

Figure 3 – Calculated velocity of partially loaded articulated truck from measured acceleration data. www.collisionpublishing.com

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ff-Tracking and Swept Path in Turns When a vehicle turns, the rear wheels will always follow a different radius path than the front wheels. This phenomenon is referred to as “off-tracking,” and is illustrated in Figure 3. Off-tracking is measured by taking the difference between the turn radius of the front wheels and the rear wheels. The amount of off-tracking is increased as the wheelbase of a vehicle is increased. For example, a bus will experience greater off-tracking than a passenger car. At low speeds, the rear wheels of a single-unit vehicle will turn with a smaller radius than the front wheels, mean-

ing that the rear wheels will track farther to the inside of the turn than the front wheels.

A fundamental difference between typical passenger vehicles and many commercial vehicles is the point of articulation, such as the fifth-wheel and kingpin connecting a truck-tractor to a semi-trailer (Figure 3). Articulated vehicles have an additional degree of freedom in their dynamic motion, as the tractor and the trailer are capable of independently pivoting relative to one another around the kingpin. Articulated vehicles, including tractor-trailer vehicles, experience even greater off-tracking. The amount of low-speed off-tracking is greater for articulated vehicles. At higher speeds, tractor-trailer off-tracking will result in a greater radius for the trailer wheels, meaning that the rear wheels will track farther to the outside of the turn than the front wheels due to dynamic effects including radial acceleration and tire slip. Dynamic effects on offtracking calculations can be complex and depend on several factors including the kinematic geometry, truck speed, road surface type, tire properties, three dimensional terrain features, roadway superelevation and environmental factors.

Equation 4 Equation 5 Equation 6

Figure 4: Articulated Vehicle Off-tracking (AASHTO). From the Highway Engineering community, a simplified method published

by AASHTO for estimating low-speed off-tracking is based on a static analysis of the geometry using the following equations:

r1 = Front axle path radius r2 = Tractor rear axle radius r3 = Trailer axle path radius rk = Kingpin path radius W = Tractor wheelbase KO = Kingpin offset WT = Trailer wheelbase Δ = Off-tracking From the Automotive Engineering community, another way of determining maximum off-tracking width is through the use of curve fits from experimental data. SAE recommends the following method for determining off-tracking.

Equation 7 W = Wheelbase of the tractor WT = Wheelbase of the trailer measured from the kingpin Using the sum of the wheelbase squares on the horizontal axis and the appropriate curve representing the front axle path radius (r1), the off-tracking can be located on the vertical axis.

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Articulation is an advantage for maneuvering extremely long vehicles around curves, but even with articulation it can be very difficult for long commercial vehicles to successfully negotiate tight spaces. Due to the effect of trailer off-tracking, a large portion of roadway area is utilized by the vehicle in the process of completing a turn. Published turning radii and swept path templates are published and available for modeling of a general scenario, covering typical 90-degree turns and generic vehicle types. However, the actual swept path varies based on a number of factors, especially axle locations, track widths, radius of turn, and angle of turn. If an extremely detailed analysis of swept path is necessary, software applications include AutoTurn or Vestra Civil 3D, software packages compatible with the AutoCad platform. Several commercially available collision simulation software packages can also model swept paths of articulated vehicles based on speed and steering inputs. These tools can be used by road designers to provide adequate turning radii at intersections where turning trucks are expected, or can be used in a collision reconstruction application.

Figure 5: Turning articulated truck geometry for low-speed calculation of off-tracking.

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In c ro up G a at D sh C ra 9 00 )2 (c Figure 6: SAE chart for calculating maximum off-tracking from sum of wheelbases squared.

For roadways designed with wide turn radii and large open maneuvering spaces, tractor-trailers can operate without any impingement on surrounding traffic. However, as turn radius tightens it becomes increasingly difficult to successfully navigate a turn within the allotted space. There are two collision scenarios that often result from the large swept path covered by turning tractor-trailers: 1. Turning Wide: When turning from a two-lane road onto another two-lane road at a tight intersection, tractor-trailer drivers are instructed to pull out straight ahead into the oncoming lane of the cross-street before making

the wide turn and returning to the intended destination lane (“button-hook” turns). By pulling out in this manner, the trailer can complete the turn. Where there is a single travel lane in the origin direction, it is considered improper to begin the turn by pulling laterally into the opposing lane of the origin roadway (“jug-handle” turns).

Since it involves using part of an opposing lane of traffic, the only way a proper button-hook turn can be completed is by relying on other drivers on the cross-street to adjust their speed and path to accommodate the turning tractor-trailer.

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2. Corner-Cutting: When turning from a multiple lane roadway, articulated vehicle drivers are able to initiate their turn from the 2nd lane of the origin roadway. By doing so, they are able to avoid conflicts with opposing cross-street traffic. However, impatient drivers behind the heavy truck will sometimes attempt to pass on the right, and these passing vehicles will be caught in the swept path of the turning trailer, leading to a collision.

In the United States, warning signs are commonly placed

Figure 7: Swept path area for articulated heavy truck turning 90 Figure 8: Steering path options for articulated vehicles to account for off-tracking at tight intersection. degrees. www.collisionpublishing.com

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on the rear of large vehicles to educate other drivers of this potential hazard.

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irectional Control Loss in Articulated Vehicles Although articulation provides numerous benefits for tractor-trailer movement, a vehicle dynamics effect can occur during times of emergency braking or other traction loss.

In a passenger vehicle, only two traction loss scenarios are possible – the front end locking up will result in plowing straight ahead, while the rear end locking up will result in a spin-out. The additional degree of freedom in articulated vehicles results in three potential traction loss scenarios, all of which result in differing degrees of control loss.

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1. If the front axle (or “steer” axle) of an articulated vehicle is the first to lock up or lose traction, then the entire vehicle will simply continue in a line straight ahead in the direction of its momentum. This scenario is commonly called a “plow-out”, and the driver will not be able to regain directional control or steering capability until traction is regained at the sliding wheels. By taking his foot off the brake pedal, a driver can ultimately regain control.

Figure 9: Steering path for articulated heavy trucks to account for off-tracking without impinging on opposing traffic at wide intersections.

2. If the drive axles of the articulated vehicle are the first to lock up or lose traction, then the result is a traditional “jack-knife”, in which the drive axles will swing out around the steer axles, effectively pushing the front of the tractor to one side or the other. The trailer will continue straight ahead in the direction of its momentum, while the tractor will reach a nearly 90-degree angle relative to

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Figure 10: Jack-knifing occurs when the tractor's drive wheels lock up first, causing the tractor to rotate.

Figure 11: Trailer swing-out occurs when the trailer's wheels lock first, causing the trailer to rotate.

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Figure 12: The dynamic friction circle for tires. the direction of travel, effectively side-sliding as shown in Figure 2. Once a jack-knife is initiated there is no opportunity for the driver to regain control. For this reason, the jack-knife scenario is usually considered the most serious.

3. bIf the trailer axles of the articulated vehicle are the first to lock up or lose traction, then the result is a “trailer swing-out”, in which the tractor will continue in its original direction but the trailer will swing to one side or the other as shown in Figure 3. Many drivers incorrectly call this a jack-knife, making it important for the investigator to acquire detailed and clear descriptions of the event, along with accurate recording of tire marks and other evidence at the accident scene. If the driver is able to detect the initiation of trailer swing-out early, it is possible to regain control by modulating braking and the vehicle can resume normal operation. However, once the trailer swings out too far, it will continue around past 90 degrees until the side of the trailer actually impacts the rear of the tractor cab. This impact between a trailer and its own tractor can cause the tractor itself to subsequently lose control.

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Inclement weather and pavement conditions, such as ice, deep water, sand, oil, or similar slick surfaces are often factors in all three control loss events. Bald tires, worn pavement surfaces, and improper brake system balance can also be contributing factors that an investigator should evaluate. Ultimately, driver performance and issues related to appropriate speeds for given environmental conditions play a significant factor in articulated vehicle directional control losses.

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ateral Acceleration and Lane Change Fundamental mechanical differences of heavy trucks in steering and suspension, in combination with the heavy mass being carried, reduce their ability to safely generate large lateral accelerations when compared to passenger vehicles. Studies of normal lane changes by tractor-trailers indicated typical average lateral acceleration values of 0.02 to 0.06 g for normal maneuvers at highway speeds. Emergency avoidance capabilities are similarly reduced by the same mechanical factors, and by a commercial ve-

Figure 13: Rigid vehicle turning to the left experiencing a lateral acceleration to the right creating a destabilizing moment.

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In c ro up G a at D sh C ra 9 00 )2 (c Figure 14: Roll compliance of the sprung weight on the suspension consequently causing a lateral shift of the center of gravity toward the right.

Figure 15: Tire compliance due to added weight on outside tires exacerbating lateral shift of the center of gravity to the right.

hicle’s higher roll propensity as discussed in a later section. Testing of professional drivers in commercial vehicles in emergency steeraway situations indicated a maximum acceleration capability in the range of 0.13 to 0.22 g.

database compiled by the U.S. Department of Transportation has shown that 13% of all fatal large truck crashes involved a roll-over occurrence. The danger of roll-over crashes is a particularly significant factor in the safety of professional drivers, as 58 percent of truck driver fatalities in the United States occur in rollover collisions.

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ollover Propensity Commercial vehicle rollovers are one of the more dangerous types of crashes, making stability a primary criterion in trailer design. The Fatal Accident Recording System (FARS) 114 Collision

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Fcen = Centrifugal Force (equal and opposite reaction to centripetal force) W = Vehicle weight v = longitudinal velocity g = acceleration due to gravity r = radius of curvature

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As with all vehicles, limitations exist for the ability to make a lane change in addition to braking application in an emergency situation. The friction-circle concept documents that less friction will be available for braking if steering forces are involved, increasing the brake-to-stop distance. Since the total available friction of commercial vehicle tires is less than passenger tires due to structural and material differences, this should be considered in avoidance analysis calculations.

As a tractor-trailer follows a curve, the truck accelerates toward the center of the curvature. The stabilizing reaction force to this inward acceleration is known as the centrifugal force. The centrifugal force is calculated using Equation 10.

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Articulation creates a dynamic effect in the consideration of lateral acceleration and especially in emergency lane change or steer-away maneuvers. The trailer will eventually follow the path of tractor, but the peak lateral acceleration of the trailer will be greater than the peak lateral acceleration of the truck, and the peak lateral acceleration of the trailer will time-lag behind that of the truck.

When viewed statically, without dynamic effects or time factors, a vehicle will theoretically roll over when its lateral acceleration exceeds the “static rollover threshold”. The rollover threshold is a

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namic factors contribute to the destabilization of a heavy truck in a turn or traveling along a lateral incline, including the suspension roll compliance, the tire compliance, lateral shift, load shift and the secondary destabilizing moment.

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The differences between passenger vehicles and commercial vehicles, and the influence of dynamic factors on commercial vehicle roll propensity, are shown in Table 3:

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Vehicle Type Automobiles Sport Utility Vehicles Commercial Vehicles Commercial Vehicles, Dynamic Considerations

Rollover Threshold > 1.0 g 0.8 to 1.2 g < 0.5 g < 0.35 g

Table 3: Typical rollover threshold values for different vehicle types.

The sprung weight is separated from and suspended above the axles by springs of varying type and size. The sprung weight is able to move independent of the axles. When a tractor-trailer is turning in one direction, the sprung weight reacts in the opposite direction. The inside spring is put into tension and the outside spring is put into compression, working in conjunction to resist the primary destabilizing moment As a consequence of the spring compression, the center of gravity of the sprung mass shifts away from the center and further destabilizes the load. This effect is called the roll compliance. A virtually identical effect occurs at the tires, as each tire acts essentially like a spring in compression during a significant lateral acceleration. The combination of roll compliance resulting from spring compliance and tire compliance is the second most significant factor in commercial vehicle roll stability.

Figure 16: Lateral shift of the sprung weight due to a force balance of lateral forces to the elastic resistance of the suspension in the lateral direction further shifting the center of gravity to the right. dimensionless function of only the height of the center of gravity and the track width.

Equation 9 T = Track width h = Height of the center of gravity from the ground Using the static stability analysis the maximum possible moment is equal to the vehicle weight times the rigid stability factor, or else the vehicle will tip over.

The rotation of the sprung mass due to roll compliance has a secondary effect as well. The sprung mass shifts laterally relative to the axles, moving the center of gravity further away from the curve radius center. This creates a secondary moment, one that reduces stability and increases roll propensity. As all of these factors are dynamic in nature, and compounding one another, it is understandable that commercial vehicles can transition from a stable state to a rollover rather quickly.

The dynamic rollover threshold value depends on the amount of roll compliance experienced by the subject vehicle, and can be calculated by analyzing the degree that the center of mass moves relative to a static mode. As shown in the corresponding equation, all of the dynamic factors discussed have a negative effect on roll stability, reducing the maximum lateral acceleration that can be attained before rollover ensues. The dynamic rollover threshold value will always be less than the static stability factor: Equation 12

Equation 11

Loading of the trailer or load shift during operation can further affect the dynamic stability of the truck. As a truck cargo compartment leans it is possible for the load to shift and exacerbate the destabilization of the vehicle. This is particularly true for vehicles that carry liquid cargo. A partially filled liquid trailer will necessarily experience load shift during turning. A liquid cargo trailer also experiences liquid slosh as the material moves from side to side. The dynamic motion of the fluid, particularly the phase of the liquid motion compared to the lateral motions of the truck, can intensify the destabilizing moment.

When studied dynamically, the primary destabilizing factor is still the moment generated by centrifugal force acting on the center of gravity, as reflected in the static rollover threshold. However, the stability of a vehicle in the roll plane becomes complex for commercial vehicles in a dynamic analysis environment. Several dy-

Liquid trailers use a variety of methods to control destabilization by load shift. The most common and well known treatment is baffles, which are a grid of materials that physically disrupt and restrict the motion of the load. A second treatment is tank compartmentalization, where the tank is subdivided into sections. Each section

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Destabilization occurs when the contact force on the inside wheel equals zero.

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W = Loaded vehicle weight ay = Rollover threshold value

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In c ro up G a at D sh C ra 9 00 )2 (c Figure 17: Locations of the center of gravity of a partially filled liquid tanker experiencing lateral forces. A partially filled tanker is far more likely to experience an untripped rollover that other heavy vehicle types. is emptied at each drop-off location reducing slosh by having completely empty or completely full compartments. A third design treatment is the elliptical cross-section of cargo tanks, so that as the liquid load shifts laterally during turns, the center of gravity follows an elliptical path and subsequently minimizes destabilization.

Since commercial vehicles are often laden with cargo, and are often over 13 feet in height, their high centers of gravity make them more prone to rollover than passenger vehicles based purely on static factors. A commercial tractor-trailer is six times more likely to experience an untripped rollover than a passenger car. When dynamic factors such as suspension systems, load mobility within the cargo compartment, shifting of liquid loads, torsional compliance, and steering inputs are considered, it is not unusual for a commercial vehicle to have a dynamic stability factor below 0.35 (Figures 18 and 19). Considering roadway designs often incorporate curves assuming design lateral accelerations of 0.25 to 0.35 g, rollovers are a serious problem for commercial vehicles.

sity phenomena can be useful in two ways. If a commercial vehicle has rolled over, an analysis of its static and dynamic rollover factors can aid in determining the speed at which it overturned for a given radius of travel. If a vehicle has successfully completed a turn maneuver without rolling, an analysis of its roll stability factors can provide known limits on the speed or radius of the maneuver. Roll stability issues also affect reconstruction calculations for potential steering avoidance maneuvers, as the peak lateral acceleration assigned to a vehicle should not exceed the rollover propensity of that vehicle.

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ollision Dynamics The collision dynamics of an articulated vehicle involved in an impact will differ from a straight truck or passenger vehicle. The degree of freedom resulting from a hinge at

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For a collision reconstruction, understanding of rollover propen-

Figure 19: Dynamic rollover threshold values for a commercial vehicle scenarios.

Figure 18: Static rollover threshold values for a variety of vehicles and load magnitudes.

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the fifth wheel location tends to result in rotation about this articulation point during the impact phase of a collision rather than the vehicle’s center of gravity. This phenomenon should be noted when studying the post-impact movements of articulated vehicles and matching vehicle dimensions to scene evidence. For example, a straight truck or tractor, without a trailer, will rotate about the tractor's center of gravity when impacted, just like a passenger vehicle. However, a connected tractor or trailer will rotate about the fifth wheel connection when impacted (Figure 20).

This factor should be considered in both qualitative sequence analyses and quantitative reconstruction calculations.

and a sensitivity analysis is completed to determine the robustness of calculations, it may be possible to utilize momentum in more extreme weight disparity situations, but the analyst should be careful to document and consider these issues. Given the articulation and additional degree-offreedom involved in the dynamics of combination vehicles, the use of a momentum analysis that assumes point-mass behavior may also lead to inaccurate results if not properly considered and evaluated. In some circumstances, the entire combination vehicle may be moved by the collision, but in other situations either the tractor or the trailer could rotate around the fifth wheel / king pin connection without imparting any motion or significant forces on the other portion of the vehicle.

“ " "The investigation and reconstruction of a heavy truck crash is a complex and complicated task."

Common methods of reconstructing collisions include physics models of crush damage and conservation of linear momentum. Unfortunately, crush damage models are based on documented crash tests, and little testing has been completed to demonstrate a relationship between the damage done to a commercial vehicle during a collision and the vehicle’s speed loss. Therefore, crush/energy speed loss techniques are currently not applicable for the commercial vehicle, although they remain viable for a passenger vehicle striking a massive and stiff commercial vehicle.

In the case of a collision involving a heavy truck and a passenger vehicle, caution and care must be applied in utilizing a conservation of linear momentum analysis to determine impact speeds.

Mathematical sensitivity can result from large differences in relative weight, making significant consequences for small variations in the pre-impact incident angle and the post-collision departure angle for the tractor trailer. Given the disparate weights, the analysis may become very sensitive to small variations in travel distances, drag factors, vehicle weights, and path angles. The equations for calculating the pre-impact velocity of two vehicles in a full impact collision using conservation of momentum are shown below.

Equation 13 Equation 14

When a commercial vehicle collides with a passenger vehicle, the height of the bumper or structure of the passenger vehicle should be taken into consideration relative to the bumper height or engaged structural member of the heavy truck. If the passenger vehicle under-rides some portion of the commercial vehicle, this can make the use of energy/crush analysis on the passenger vehicle difficult, requiring careful study of override/underride issues. The Reconstructionist must be diligent in noting the crush profile of the passenger vehicle and making appropriate adjustments.

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onclusions The investigation and reconstruction of a heavy truck crash is a complex and complicated task. Investigators need to become properly trained in heavy vehicle dynamics, truck mechanical systems, braking systems, and roadway design factors that affect the dynamics of the collision. The ultimate goal of any crash investigation should be to determine what human, vehicular, and environmental factors contributed to the crash. This information can ultimately be used to develop a safer trucking transportation system. To acquire the information needed for a complete

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One standard rule of thumb states that momentum analysis should be avoided when the weight ratio between vehicles exceeds a factor of ten. If extremely detailed data is available for all variables,

When a heavy truck collides with a passenger vehicle the heavy truck will typically maintain its pre-collision trajectory with a relatively insignificant change in both magnitude and direction of velocity. An energy/crush analysis of the speed change experienced by the passenger vehicle can be combined with a linear momentum calculation to calculate the relatively low change in speed for the heavy truck. Since mass ratios are critical in both aspects of this calculation, the loading condition of the commercial vehicle is an important consideration.

Figure 20: Tractor rotation for free trailer and trailer connected to a trailer at its fifth-wheel connection.

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reconstruction analysis, crash investigators should document any of the following factors that may be relevant in a given crash:

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• Determine the expected acceleration, deceleration, and lateral acceleration rates for the vehicles involved through a review of published information or through actual testing.

• Determine whether the roadway geometry was adequate to accommodate large trucks.

• In turning situations, determine the swept path and amount of off-tracking of a vehicle.

• Analyze tire marks and vehicle dimensions to determine whether there may have been jack-knifing or trailer swing-out.

• Document load weights and distributions for total vehicle weight, and for analysis of rollover or non-rollover.

• Lane-change avoidance possibilities should be carefully evaluated to determine whether such maneuvers are reasonable for the crash scenario.

• Investigators and Reconstructionists of heavy truck crashes should carefully analyze the dynamics of the collision, and consider appropriate analytical techniques to account for the unique truck dynamics.

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eferences American Association of State Highway and Transportation Officials, 2001. “A Policy on Geometric Design of Highways and Streets.”

Dunn, et al., 2003. “In-depth Analysis of the Influence of HighTorque Brakes on the Jackknife Stability of Heavy Trucks.” SAE 2003-01-3398, Society of Automotive Engineers.

Ervin, R. D. 1983. “The Influence of Size and Weight Variables on the Roll Stability of Heavy Duty Trucks.” Michigan University, Ann Arbor, Transportation Research Institute. Report No. SAE 831163.

Fatality Analysis Reporting System (FARS), 1997-2007, “Large Truck Involved in Fatal Crashes”, National Highway Traffic Safety Administration Fittanto, Dan A, et al. “Dynamics and Roll Stability of a Loaded Class 8 Tractor-Livestock Semi-Trailer: An EDVDS Application.”

WP# 2000-4. Engineering Dynamics Corporation, University of

Illinois at Urbana-Champaign and Ruhl and Associates – Forensics, Inc. FMCSA, Analysis Division, Federal Motor Carrier Safety Administration, 2003. “Large Truck Crash Facts, 2001” Fricke, 1990. “Traffic Accident Reconstruction.” Northwestern Traffic Institute.

Gertsch and Eichelhard, 2003. “Simulation of Dynamic Rollover Threshold for Heavy Trucks.” SAE 2003-01-3385, Society of Automotive Engineers.

Harwood, et al., 2003. “Review of Truck Characteristics as Factors in Roadway Design.” National Cooperative Highway Research Program, NCHRP Report 505, Transportation Research Board.

Lawson, et al., 2004. “Optimization to Improve Lateral Stability of Tractor Semi-Trailers During Steady-State Cornering.” SAE 2004-01-2690, Society of Automotive Engineers.

Proctor, et al., 1995. “Analysis of Acceleration in Passenger Cars and Heavy Trucks.” SAE 950136, Society of Automotive Engineers.

Rakheja and Sankar, 1993, “Roll stability of Liquid Tank Vehicles”, Accident Reconstruction Journal, Volume 5, Number 4 Road Traffic Management Corporation, 2005. “Road Traffic and Fatal Crash Statistics, 2003-2004.”

Seluga, et al., 2004. “Articulated Vehicle Yaw Stability During Braking ~ A Parametric Study.” SAE 2004-01-2630, Society of Automotive Engineers.

Suh, et al., 2000. “A Simulation Program for the Braking Characteristics of Tractor-Semitrailer Vehicles.” SAE 2000-01-3415, Society of Automotive Engineers.

Sutphen and Varner, 2003. “Commercial Vehicle Accident Reconstruction and Investigation.” Lawyers & Judges Publishing Company, Inc. Tampere University of Technology, 2009, “Phenomenon and Processes involved in tire-road friction”, European Tire School – Module 10 Winkler, 2000. “Rollover of Heavy Commercial Vehicles.” UMTRI Research Review, University of Michigan Transportation Research Institute (UMTRI).

Winkler, et al., 1992. “Roll-Stability Performance of Heavy-Vehicle Suspensions.” SAE 922426, Society of Automotive Engineers.

March 1 - 5, 2010

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To learn more about the workshops offered at the 2010 HVE Forum, visit: www.edccorp.com/2010HVEForum

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Hotel Contessa – On the Riverwalk San Antonio, Texas

EnginEEring Dynamics corporation 8625 SW Cascade Blvd. Suite 200 Beaverton, OR 97008 USA Phone: 503.644.4500 Fax: 503.526.0905 email: forum@edccorp.com www.edccorp.com

Volume 4 Issue 2.indd 118 EDC Forum Ad.indd 1

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Vericom VC4000DAQ Performance Computer Z

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New tri axis 2G to 6G accelerometer up to 1000 Hz sample rate. Infinite storage time.

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External accelerometers 10G to 100G.

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2G to 100G 1 to 1000 Hz

Super easy to install and completely portable, single suction with ram mount, auto digital leveling (self leveling).

Compatible 5 Hz

♦ OBDII & CAN input. ♦ Up to 16 sensors input.. ♦ Firmware & software updates from internet. ♦ Simple calibration check.

Vehicle Rotation begins

GPS Speed

Vericom Speed

0.00

60

Angular Rate Gyro

GPS Speed

-0.10

50

-0.20

Lateral G

Vericom Distance

-0.30

Compass Heading

40 Gyro (Deg/Sec)

-0.40 -0.50

Deceleration

-0.60

Braking

-0.70 -0.80

30

CSY

20

10

-0.90 -1.00

0

Display Average Table 2/18/2008 Date & Time 9/24/2002 09:18 AM 9/24/2002 09:19 AM 9/24/2002 09:21 AM 9/24/2002 09:22 AM 9/24/2002 09:23 AM 9/24/2002 09:25 AM 9/24/2002 09:27 AM

Time Sec 1.95 1.95 1.95 3.46 3.41 3.35 4.13

Acceleration Average G -0.891 -0.887 -0.882 -0.897 -0.897 -0.895 -0.892

Speed MPH 38.10 37.95 37.74 68.07 67.06 65.74 80.80

Distance Feet 56.6 55.8 56.2 178.5 172.4 168.4 253.4

2.89

-0.891

56.50

134.5

13

14 15 Time (Sec.)

f 0.80

16

17

18

19

Range Table Speed Result 57.88

0.81 0.81 0.83

58.24 58.60 58.96

0.84 0.85 0.86 0.87 0.88

59.31 59.66 60.01 60.36 60.71

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Average of Runs

Run No. 4 5 6 7 8 9 10

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Time (Sec.)

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Acceleration (G)

(compass) built-in.

PC Communication by • USB port.

• Bluetooth up to 100 meters.

• SD Card.

• 3 RS232 ports.

• Streaming data.

GPS

0.10

N 360° magnetometer

Built-in angular rate gyro (yaw or pitch)

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Phone 763-428-1381 USA or Canada 800-533-5547 fax 763-428-1381 info@vericomcomputers.com www.vericomcomputers.com 14320James Road - Suite 200 - Rogers, MN 55374

www.collisionpublishing.com

Volume 4 Issue 2.indd 119

Collision 119

11/2/2009 12:33:34 PM

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We have the STIFFNESS data you need for your calculations!!

4N6XPRT StifCalcs®

puts the NHTSA Crash Test database on YOUR 32 bit MS-Windows computer PLUS calculates A-B-G values and Test Specific Crush Factors based on the NHTSA test data, with no need for you to get on the internet, all for the price of only $570.00*!

Can you do this yourself “for free”?? Only if you value YOUR time at $0.00!!

For more information, program order form, and additonal sample printouts please visit our web site at http://www.4n6xprt.com.

4N6XPRT StifCalcs® is provided by 4N6XPRT Systems

8387 University Avenue - La Mesa, CA 91941 - USA Phone: 800-266-9778 / (619) 464-3478 Fax: (619) 464-2206

Individual Vehicle Stiffness Data So, you want Stiffness data for a vehicle, QUICKLY & CONVENIENTLY, but you don’t want to buy a program? Order your data on a vehicle-by-vehicle basis from us at only $40.00 per test!

Year: _________ Make: _____________________ Model: ____________________________________ Impact on (circle one): Front - Side - Rear Impact speed (circle one): High - Low YOUR CONTACT INFORMATION

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Name: ________________________________________ Company: _____________________________________ Address: ______________________________________ City/State/Zip: _________________________________ Phone: _______________________________________ Fax:__________________________________________ Email: ________________________________________

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4N6XPRT Systems

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Send Order to:

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Visa/MC/AmEx:________________________________ Exp.:____/____ Case Reference: ___________________

Fax: 619-464-2206 Ph: 800-266-9778

8387 University Avenue / La Mesa, CA 91941 / USA E-mail - 4n6@4n6xprt.com

Volume 4 Issue 2.indd 120

11/2/2009 12:33:36 PM

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Vol. 4 Iss. 2

The International Compendium for Crash Research

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• mFX was built for reconstructionists - handheld data collection not just adapted from other software • Save time with all the features you would expect with none of the complexity. With a simple and easy to use interface, data collection is made quick and easy • Use your own hardware whether it be Windows Mobile or a CE based device • Seamless download by directly downloading from mFX to FX3 instead of wasting time downloading into a third-party program

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Det. Mark A. Rice #1457 • Division Reconstructionist • Columbus Division of Police

A TRIMBLE COMPANY

TOLL-FREE: 1.888.828.0383

WWW.VISUALSTATEMENT.COM

ONE STEP AHEAD

Volume 4, Issue 2 - FALL 2009

I’ve used many different tools and software to collect crash scene measurements.

But I can say without any hesitation that FX3 and mFX is by far the best program I’ve ever used. I look forward to many years of use out of mFX and Vista FX3 software.

Collision: The International Compendium for Crash Research

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Volume 4 Issue 2

MINIMIZE ROAD CLOSURES AND SAVE TIME WITH mFX

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2009

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FALL 2009

What is 30?

Momentum

Vectoring in a New Approach

Auto Extrication for the Reconstructionist

Commercial Vehicle Dynamics

For Collision Reconstruction

Death Investigations & Their Psychological Effect

11/2/2009 12:38:56 PM