Volume 12, Issue 1

ollision C The International Compendium for Crash Research

Volume 12 Issue 1

Autonomous Vehicle Technology

an Accident Reconstructionist’s Perspective

Fracture Energy Calculations for Wooden Utility Poles

Tire Friction Comparisons in Various Temperature

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Includes the 2017 Digital Download

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Contents

Volume 12 Issue 1

inside 4

Industry Partners

6

Letter From the Editor

5

8

Advertiser Index and Digital Download Information

features 8

24 42 50

62 74

80

88

Three Different Methodologies for Determining the Drag Factor for Motorcycles Sliding on Their Sides

by Michael DiTallo, Brent Munyon, Thomas Green, Eric Paul, Kelley Adamson, Mike Merolli, Kevin Vosburgh, Billy Cox, Robert Anderson, David Hallman, Eric Moody, and James Whelan

62

Tire Friction Comparison of Three Tire Types in Warm and Near Freezing Temperatures

by Peter J. Leiss, Steven Becker and Gary Derian

My Turn at the Wheel: A Dirty Trick to Achieve the Desired Result, or What?

by Erik Carlsson

Motorcycle Center of Gravity Data: Methodology and Reference

by Michael DiTallo, Eric Paul, Kelley Adamson, Thomas Green, Mike Merolli, Brent Munyon, Kevin Vosburgh, Billy Cox, Eric Moody, Robert Anderson, James Whelan and David Hallman

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Fracture Energy Calculations for Wooden Utility Poles

by Nathan Rose

Autonomous Vehicle Technology: Looking One, Five, and Fifteen Years into the Future. An Accident Reconstructionist's Perspective

by Luis Flores

3D Laser Scanners in Crash Testing

by Thomas Green, Michael DiTallo, Eric Paul, Kelley Adamson, Mike Merolli, Brent Munyon, Kevin Vosburgh, Billy Cox, Robert Anderson, David Hallman, Eric Moody and James Whelan Fast Approach to Building Solid Cases: Laser Scanning Provides Important Benefits for Investigator

92

by Chad McFadden

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Evaluation of the MIDE Slam Stick as a Low-Cost Accelerometer and Data Acquisition System for Vehicle Skid Testing

by David Hallman, Robert Anderson, Billy Cox, Kevin Vosburgh, Kelley Adamson, Thomas Green, Mike Merolli, Brent Munyon, Eric Paul, Eric Moody, James Whelan, and Michael DiTallo www.collisionpublishing.com

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Industry Partners IAARS

is one of the oldest associations dedicated to expanding the knowledge and training of automobile crash Reconstructionists. IAARS was started in 1980 as a resource for members to use when the inevitable questions arose while trying to reconstruct a crash. We have members from several different countries as well as many different states across the U.S. The annual seminars not only provide instruction on specific topics by experts in the field, they provide face-to-face discussions on how other people approach reconstructing a crash. The old saying "two heads are better than one" is definitely true in accident reconstruction.

Membership in IAARS has other advantages, including a discount (from IAARS) on a subscription to Collision Magazine; access to electronic delivery of the quarterly publication of the Society of Accident Reconstructionists, and electronic delivery of bi-monthly editions of Accident Reconstruction Journal. Members also receive discounts at our training seminars.

We have annual conferences with training opportunities across the country. IAARS was the first association to do actual crash testing in 1982 with T-Bone and Head-on collisions and we continue to try and have a dynamic full scale vehicle crash or testing at each of our seminars. As a member you have full access to the setup and test with all of its data. As a member you have We have three levels of membership. Our highest level, Felaccess to a vast archive of videos and data from many different low, includes a peer review of a reconstruction project. This and sometimes unique tests. Some of these tests include vehicle differs from many other associations in that with this process for membership it can help the member as peer review is a spe- to vehicle, truck to vehicle, motorcycle to vehicle and vehicle to pedestrian crashes, semi rollovers, tip-over testing and brake cific area of judicial consideration when admitting an expert opinion in court. This review, along with training and experi- efficiency testing. IAARS sometimes partners with other associaence, go a long way if you happen to come across a stickler for tions when providing seminars or conferences. a judge. We offer opportunities for a member to publish work IAARS enjoys working with all of the associations and organizaor research in the reconstruction field and an opportunity to tions that are involved in helping get answers to how and why present materials at our annual conferences. collisions occur and how to make our roads and highways safer.

Hope to see you at one of the conferences.

Our association has "old-timers" that have worked thousands of accidents. If you have a question, chances are they have Sincerely, encountered a similar situation in the past and can give some Butch Thompson insight on how they worked it out. We also have members very President, IAARS familiar with the ins and outs of new technology (Crash Data www.iaars.org Retrieval, Photogrammetry) and are willing to help with any questions or concerns you may have.

The ARC Network

was founded in 1998 and since has grown to be the largest and most respected organization for Accident Reconstruction and Traffic Investigation.

Stiffness spreadsheet program. Extend your savings and sign up as a Police Agency member or Platinum member and receive a complimentary subscription to Collision Magazine!

The ARC Network is more than just an organization it is a research and communications Internet portal for everything accident reconstruction. The ARC Network provides research tools, Expert directory, event calendar, industry news feeds, education directlory and a Member's Only area that gives access to various online databases and information.

In addition, as a member you have the choice of being listed in the most-visited Expert Directory on the Internet. Our Expert directory boasts a #1 ranking in Google searches (a feat worth much more than the cost of membership)!

The ARC Network offers various membership levels to fit your needs and budget. Membership starts at just $89.00 per year.

However, that is where the value of the ARC Network starts.

With your membership you not only get access to everything in the ARC Network, you also receive a, $50 discount to the annual ARC-CSI Crash Conference, a $50 discount to the CDR User's Summit and a free copy of Greg Russell's Excel Crush

Scott Baker President The ARC Network (800) 280-7940 arc@accidentreconstruction.com

www.accidentreconstruction.com

For information on becoming a Collision Industry Partner send an email - sbaker@collisionpublishing.com 4 Collision Magazine - Volume 12 Issue 1

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ADVERTISING RATES & INFO

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Owner, Managing Editor Senior Editor Advertising Manager Subscription Services

All rights reserved, © 2017 Collision Publishing Inc. 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. Dis-

senting 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 e-mail to the editor at editor@collisionpublishing.com or sending a "regular mail" letter to us at PO Box 892885, Temecula, CA 92589. By

sending correspondence to either our e-mail 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 e-mail 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.

If you would like to advertise your products or services in Collision Magazine, rates, availability and other information are available online at: www.collisionmagazine.com

ADVERTISER INDEX

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Inside Back 7 87 22-23 41 40 49, 79 73 Inside Front 1 61 2 45-48 98

Included with this issue of Collision

is the 2017 EDR Summit presentation files (PDF).

Use the link and password below to access the EDR Summit presentation files that were made available.

Link: http://www.edrsummit.com/attendee/ Password: houston2017

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BACK ISSUES

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

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Letter from the editor I've said before that publishing Collision wasn't ever part of the original plan and, in the past, we've devoted pages to the concept of peer review - both pro and con. Over the past year, these ideas have run headlong into the changing dates for both the EDR User's Summit and the ARC-CSI Crash Conference and thrown our production schedule a bit out of whack, but not so bad we'd skip a year or an issue. And as the ARC-CSI Crash Conference is coming up fast (September 2017 as I write this) this issue of Collision boasts the biggest collection of peer reviewed papers based on actual testing ever assembled in one publication. After conducting the largest motorcycle crash test series as part of the ARC-CSI 2016 Crash Conference and publishing some of the results in the most recent issues of Collision (Volume 11), in this issue there are 4 more comprehensive motorcycle crash investigation articles based on the testing done by Mike DiTallo and his assembled crew from the 2016 ARC-CSI Crash Conference. That's not, of course, to take away from the other informative and valuable articles in this issue of Collision which, I'm confident, you'll find deserve your attention as well.

It's exciting to be able to point out that despite the confluence of publication date goals and the two annual conferences and date changes for those, the collection of motorcycle articles based on testing done as recently as 2016 - have been written, reviewed, revised and now go out published more quickly than has ever been done before based on full scale testing. No one else has been able to compile and share the data in as short a period of time as has the crew lead

by Mike DiTallo at ARC-CSI 2016.

headquarters facility is available as a training venue - The Crash Academy! A fully set up classroom for up to 18 people and a large indoor bay suitable for a variety of training and even testing applications will become available starting this fall. The Collision Safety Institute has already booked the venue for November 1-3 for the "Crash Data Retrieval Tool Applications for the Insurance Professional" course. The classroom setting with sufficient power strips for all in attendance to use their laptops as well as the indoor bay supplied with select vehicles to practice hands on CDR Tool data retrieval skills is an ideal setting for this course and others.

Lastly, the 2017 ARC-CSI Crash Conference is fast approaching and together with a new and exciting conference venue (hotel and meeting rooms) we have a variety of topics and crash tests and research projects planned. If you haven't already registered, go to the ARC-CSI Crash Conference web site and get on board today!

Managing Editor

Another bit of news I'm excited to share has to do with an expansion at the Crash Data Group headquarters in Temecula, CA. After a recent move to a larger and more versatile facility, starting this fall, the Crash Data Group 6 Collision Magazine - Volume 12 Issue 1

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Different Methodologies for Determining the Drag Factor for Motorcycles Sliding on Their Sides

Michael DiTallo, Brent Munyon, Thomas Green, Eric Paul, Kelley Adamson, Mike Merolli, Kevin Vosburgh, Billy S. Cox, Jr., Robert Anderson, David Hallman, Eric Moody, James Whelan 8 Collision Magazine - Volume 12 Issue 1

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ntroduction Twenty-six motorcycles were used to conduct tests to determine the drag factor for a motorcycle sliding on its side. Three different methodologies were employed for the testing. The motorcycles in the first test method were already on their sides before they were pulled across the pavement. For the last two test methods, the motorcycles fell to the pavement before sliding. otorcycles The test motorcycles consisted of various ages, styles and manufacturers. The manufacturers included; Harley Davidson, Buell, Honda, Kawasaki, Suzuki, Yamaha, Jonway and Znen. Motorcycle styles included sport, touring, motocross and moped. Photograph 1 shows some of the motorcycles used for the tests. Many of the tested motorcycles had been involved in previous impact testing at the 2016 ARC-CSI earlier in the year. The test motorcycles had standard equipment with some of them having minor pre-testing modifications such as the removal of the seat. One of the sport style test motorcycles had frame sliders. Any modifications were minor in nature and would have no outcome on the results of the drag factor testing.

Each motorcycle was assigned a letter destination for the testing. Figure 1 shows the letter designation, brand, model, VIN, year, and type for each tested motorcycle.

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est Methodology The first test method used a load cell to measure the force required to drag the motorcycles across the pavement (pull tests). The tests consisted of dragging the motorcycle in either longitudinal or lateral pull configurations. A second method used the drop method which involves releasing a motorcycle from rear hydraulic lift of a moving box truck (drop tests).

When the box truck reached a target speed, the motorcycle was released from the lift of the truck, allowing the motorcycle to drop and slide to rest.

The final testing method involved towing a motorcycle behind a moving vehicle with its front tire held in a pneumatic clamp just above the pavement; the front tire was mechanically locked into a stationary position; the tow vehicle gained speed; and the front wheel was released from the pneumatic clamp allowing the motorcycle to drop, slide and/or tumble to rest (clamp test).

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Photograph 1: Test motorcycles The pull test is a static test that only utilized a digital load slide distances were documented with total station meacell to measure force (Dillon ED Juror 5000 lb.). The surements, photographs and/or video. clamp and drop tests are upright dynamic tests and the est Location motorcycles in these tests methods were equipped with Photograph 2 depicts the test area which was a one or more of the following instrumentation: VBOX closed stretch of roadway in North Las Vegas, Sport and Slam Sticks. During some of the moving tests, Nevada. The surface was asphalt and in excellent vehicle carrying speeds were verified by Stalker radar and

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Figure 1: Motocrycle data sorted by letter designator 10 Collision Magazine - Volume 12 Issue 1

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Photograph 2: Google Earth aerial image of the test location (sharp) condition (see Photograph 3). The coefficient of friction of the roadway surface was documented utilizing Antilock Braking System (ABS) and Non-ABS skid testing in a 2016 Nissan Altima (1N4AL3AP4GC253202).

These tests were documented with a Vericom 4000DAQ and a VBOX Sport. These sliding tests were performed on the roadway. The air temperature on test day exceeded 110 degrees F and the roadway was bordered by the open desert to the north and a sidewalk and graveled berm to the south. The results are discussed later in this paper.

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est Results Pull Test Results

A total of thirty-six pulls tests were conducted utilizing nine of the test motorcycles. Each motorcycle was pulled laterally twice utilizing connection points on both tires. Four of the lateral tests were done with the tires leading and five tests were conducted with the tires trailing. Each motorcycle was also pulled twice longitudinally, front tire leading with one connection point at the front of the motorcycle (Photograph 5).

When conducting the testing, the lateral pulling force recorded was the dynamic force noted once each subject motorcycle began sliding; the force required to overcome the static friction was not recorded.

Testing results showed a range of drag factors between 0.36 and 0.64. The average drag factor across all motorcycles tested longitudinally was 0.51.

Lateral pull drag factors ranged from 0.40 to 0.59. The average across all motorcycles tested longitudinally was 0.52.

Interestingly, the results from the lateral pull with tire leading showed an average drag factor of 0.54, while the results with the tires trailing averaged 0.51.

Drop Test Results The drop tests were conducted on twelve motorcycles at speeds ranging from 30.7 mph to 41.1 mph. Motorcycles were placed vertically on a lowered hydraulic lift gate of a box truck at a height of approximately 6 inches above the roadway surface (Photograph 6), the truck was accelerated to the desired speed, and the motorcycles were released off the back of the lift gate. The motorcycles dropped laterally onto the roadway surface and slid to rest. The motorcycles’ path of travel from first contact to final rest were documented by hand measurements. A spotter was used to watch, locate and mark the first contact position.

Photograph 7 shows an example of the instrumentation used in these tests. Motorcycles in this series of tests were equipped with a VBOX Sport which provided reliable data. These motorcycles were also equipped with Slam Sticks, but issues with the data analysis were encountered.

The direction of the motorcycle’s travel path did not co-

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Photograph 3: Test location

Photograph 4: Load cell used during the pull test

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Photograph 5: Pull test example

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Figure 4: Pull test drag factors

Figure 5: Pull test drag factors

Photograph 6: Drop test delivery system example 14 Collision Magazine - Volume 12 Issue 1

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incide with the axis of the Slam stick accelerometer. The difference in axes was constantly changing and was not measured. Therefore, the acceleration data along the motorcycles path could not be resolved. Attempts to obtain the acceleration using the resultant acceleration of our data significantly over reports the actual acceleration because the resultant is combining the acceleration in all directions and not just the motorcycle’s direction of travel. Therefore, the data collected by the Slam Sticks is not useful in this application. The drop tests speed results presented in this paper were determined by VBOX Sport and Radar.

Results from drop tests shown in Figure 8 resulted in average drag factors ranging between 0.28 and 0.70.

Photograph 7: Drop test instrument package

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Figure 7: Photographs of the drop test motorcycles after ARC-CSI Crash Testing

Clamp Test Results

Motorcycles in this series of tests were equipped with a VBOX Sport which malfunctioned and therefore no reThe clamp test was conducted on five motorcycles at liable data was collected. These motorcycles were also speeds ranging from 29 mph to 43.9 mph. Motorcycles equipped with Slam Sticks. The direction of the motorwere placed in-line behind a towing pick-up truck. The cycle’s travel path did not coincide with the axis of the front tire of the test motorcycle was placed and clamped Slam stick accelerometer. The difference in axes was conin a pneumatic rig that held the front tire a few inches stantly changing and was not measured. Therefore, the above the roadway surface. The front tire was chained to acceleration data along the motorcycles path could not be limit rotation and forward movement of the test motor- resolved. Attempts to obtain the acceleration using the cycle after being released. The pick-up truck was acceler- resultant acceleration of our data significantly over reports ated to the desired speed, then the motorcycle was released the actual acceleration because the resultant is combining from the pneumatic clamp. The motorcycle’s front tire the acceleration in all directions and not just the motorcontacted the pavement and since it was chained, the tire cycles’ direction of travel. Therefore, the data collected locked up and the motorcycle lost stability and dropped by the Slam Sticks is not useful in this application. The onto the roadway surface. The motorcycles’ path of travel clamp-drop tests speed results presented in this paper were from first contact to final rest were documented through determined by video analysis. use of a total station.

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Figure 8: Drop test drag factors

Photograph 8: Clamp test instrument package

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Figure 13: A sample of the Vericom testing data

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Results from clamp-drop tests in Figure 11 resulted in average drag factors between 0.28 and 0.43. It should be noted that motorcycle S in this test group had frame sliders.

Nissan Altima Skid Testing Results The drag factor for the roadway in the area of the slide testing was measured using a Vericom VC4000DAQ and a VBOX Sport, mounted in a 2016 Nissan Altima. The

ABS system was disabled for this testing. Five skid tests were conducted resulting in the results seen in Figure 12 as reported by the Vericom and VBOX Sport:

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iscussion The methodologies used in this paper to study the drag factors of down motorcycles were analyzed and compared. Each method provides complexities in gathering accurate and precise data. In general, the data presented in this paper compares well to other

Figure 14: Testing data sorted by motorcycle designator

Figure 15: Testing data sorted by motorcycle type www.collisionpublishing.com

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Figure 16: Testing data of touring motorcycle type

Figure 17: Testing data of sport motorcycle type

Figure 18: Testing data of motocross motorcycle type 20 Collision Magazine - Volume 12 Issue 1

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Figure 19: Testing data of moped motorcycle type

published and measured test data collected by Northwestern University CPS (1,2,3). These test results also show that of the three methods used for testing, the pull tests resulted in the higher calculated drag factors.

Figures 16-19 provide a summary of the motorcycles tests and the average drag factor for motorcycle’s that were tested in multiple configurations.

Of note, during the pull tests two motorcycles, subjects’ S and D, fell substantially outside the average range of the other seven tested. In both instances, hard points, such as frame sliders, were discovered on each motorcycle allowing a substantial portion of the motorcycle to prevent contact with the roadway.

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ummary While this article provides results for a specific set of test motorcycles and conditions, we believe the process illustrated here could be used to perform additional testing under other conditions and specific applications. Of the three methods used, pull tests are easiest to perform. However, the clamp and drop methods more closely represent real-world experience of the motorcycle dropping and first striking the pavement prior to sliding. We caution the reader to note the testing roadway conditions, roadway material type, roadway physical evidence and motorcycle damage before applying the drag factor results for a particular evidentiary crash.

With all three methodologies, light scraping was produced during the motorcycle and roadway interaction.

Photograph 10: Low deceleration rate attributed to hard contact point (frame slider) www.collisionpublishing.com

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cknowledgements A special thanks to Harley Davidson, FAST Towing, Daniel Vomhof, Jim Byrne and our sponsors for all their project support.

A special thanks to all the members if the 2016 ARC-CSI motorcycle crash team (alphabetically).

Kelley Adamson, Robert Anderson, Billy S. Cox, Jr., Team Leader Michael DiTallo, Jim Dunlap, Thomas Green, Wesley Grimes, Rusty Haight, Sean Haight, David Hallman, Thomas Lawson, Mike Merolli, Eric Moody, Jim Morgan, Brent Munyon, Eric Paul, William Redfairn, Tim Reust, Michael Rosenfield, Kenneth Salisbury, Kevin Vosburgh, and James Whelan.

C ollision e International Compendium for Crash Research

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eferences 1. Medwell, Christopher J., McCarthy Joseph R., Shanahan Michael T., “Motorcycle Slide to Stop Tests,” 970963-Society of automotive Engineers, 1997.

2. Bartlett, Wade, Baxter, Al, Robar, Neil, “Motorcycle Slide-To-Stop Tests: I.P.T.M. Data Through 2006.”

Accident Investigation Quarterly, Issue 46, Spring 2007.

3. McNally, Bruce F., “Summary of Motorcycle Friction Tests,” Accident Investigation Quarterly, Issue 44, Fall 2006

EDR

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Collision Publishing is your Crash Research Point of Contact providing a wide range of crash research related material and training opportunities.

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Tire Friction Comparison of Three Tire Types in Warm and

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he purpose of this paper is to demonstrate the differences in braking capability of different types of tires through data collected from testing. Testing was performed during summer weather near 75°F (24°C), and then again on the same road surface in winter with temperatures near freezing (32°F, 0°C). The main variable in these tests was the type of tire installed.

Three different tire types; summer, all season, and winter, all of the same size, were tested in ambient temperature on wet and dry asphalt surface with a single vehicle. The braking tests were conducted with ABS activated and deactivated for modulated and locked wheel friction comparison of the tire types.

fort braking performance, whether locked wheel or ABS modulated, is influenced mainly by the road to tire interaction and is greatly affected by the tire tread and material.

This paper researches the difference in braking performance of 3 different tires; 3 season, all season, and winter of the same size in two ambient temperatures on a single wet and dry asphalt surface with a single vehicle. The braking tests were conducted with ABS active and deactivated for modulated and locked wheel friction comparison of the tire types.

High performance, “3-season”, tires are increasingly available as Original Equipment ManufacAccident reconstructionists rely on accurate fric- turer fitment. These tires were once reserved for tion coefficients to calculate speeds from skid and sports cars and European performance sedans. yaw marks left at a collision scene. Maximum ef- Today they are available as standard or option24 Collision Magazine - Volume 12 Issue 1

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Peter J. Leiss Steven Becker Robson Forensic Inc.

Gary Derian

Derian Engineering

Near Freezing Temperatures al equipment on domestic Sport Utility Vehicles and compact cars. These tires are not intended to be used when temperatures are near freezing or on snow and ice, necessitating the use of either all-season or winter tires for owners in areas that are susceptible to these atmospheric conditions.

Similarly, winter tires are not intended to be used during warm weather, but drivers may travel to warmer areas or leave their winter tires on during warm conditions.

A total of 144 tests were conducted on both wet and dry pavement conditions.

The vehicle chosen for this testing is available from the manufacturer with either all-season or 3 season tires. The vehicle was left in an as manufactured condition for all tests, with the exception of tire changes and deactivating the Anti-Lock Brake System/Electronic Stability Control Electro-Hydraulic Control Unit for locked wheel tests. The vehicle was braked from about 45 MPH for all tests.

Guidance will be given for modifying the friction coefficient used in reconstruction calculations for the permutations of tires, brake systems, roadway conditions, and ambient temperatures. The results show differences not only between the tire types, but how each tire types’ friction varies between wet and dry asphalt and ABS modulated and locked wheel braking, in moderate and cold climates.

The results show differences not only between the tire types, but how each tire types’ friction varies between wet and dry asphalt, and temperature.

The results also report tire friction values higher than typical published numbers.

Results of the near freezing testing are compared to results of testing in warm temperatures.

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I

ntroduction One of the primary purposes for reconstructing crashes is to establish the initial speeds of the vehicles that are involved. Law enforcement agencies, traffic engineers and others often used the speeds to help plan remedial measures to improve vehicular safety on public roadways

There are many methods crash reconstructionists use to calculate the energy dissipated in the various phases of a crash. The length of skids, yaws or other distances where the primary force imparted to a vehicle is through the tirepavement interface is a very important component of the overall energy dissipation.

Often standard values are used for tire to roadway friction, and sometimes modified to account for specific conditions on the roadway. These standard values are useful, but vehicles today are fitted with a wide variety of different types of tires. This study is intended to test the braking performance of three types of tires to better establish the variances in friction values that should be incorporated into energy dissipation calculations.

Others [1] have conducted similar testing; however this series of tests is the first to use a modern, non-modified vehicle that is available with all-season and summer performance tires as an OEM option. The ABS has been calibrated with both types of tires during development of the vehicle.

The goal of this study was to determine how friction coefficients change when the type of tire is changed on the same vehicle. To maintain the comparison of just the change in tires, other variables that can affect the friction at the tire/ road interface were controlled.

The secondary goal of this study was to measure the friction values under different conditions. As real-world conditions change and vary, testing was conducted with both wet and dry pavement, and with and without anti-lock brakes. The test protocol was developed to minimize all other variables.

Three different categories of tires are tested and measured: Summer only high performance, grand touring all season, and winter snow tires. These three represent the spectrum of tire varieties commonly fitted to passenger vehicles.

Each of these tire types has different characteristics in the three major components of a tire design: tread compound, carcass construction and their tread pattern.

Summer only high performance tires are built to withstand high friction forces and heat buildup. These tires are often used by vehicle enthusiasts for track days or in some cases, used in racing classes where street tires are mandatory. In 26 Collision Magazine - Volume 12 Issue 1

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some racing classes, minimum treadwear grades are also specified. Their tread compound is designed for a high level of hot tear strength at the anticipated temperatures of track use, often over 212°F (100°C).

The tread pattern of these tires contains large solid blocks of rubber which are often interconnected to enhance stability and minimize squirm (movement in the tread blocks). The thin sipes used in other types of tires are not used as they can promote squirm and tearing of the tread rubber. Often wet traction and hydroplaning performance is compromised to some degree in order to place a large amount of rubber contact area in the tire footprint. The tread pattern of the tires tested is shown in Photograph 1.

The tire carcass is made very stiff to reduce the distortion of the tire footprint when stressed under cornering at levels often greater than 1g. The stiff carcass also contributes to high speed performance by raising the speed of onset for standing waves. Severe cornering is often accompanied by high loads on the tire’s shoulder, so extra reinforcement here in the carcass, tread pattern and compound is useful to extend tire lift.

Winter snow tires are the polar opposite of summer only high performance tires. Snow tires are intended for operation at low temperatures ranging from near freezing to very cold sub-zero (0°F, -14°C) conditions. Therefore their tread compound, tread pattern and carcass design is very different, as shown in Photograph 2.

The tread compound is designed to remain flexible at low temperatures. This enables the tread elements to conform to the irregularities on the roadway, or on ice and snow and to improve traction. In addition to soft rubber compounds, the tread blocks are heavily siped to promote flexing of the tread blocks and to present thousands of “biting edges” to icy road surfaces. The tread blocks are separated by wide self-cleaning grooves, both circumferential and lateral, to bite into relatively soft snow and packed snow covered roadways.

Since forces on ice and snow covered roads typically remain below 0.15 to 0.2g, the carcass does not have to withstand high lateral forces and can remain soft to further enhance the tire footprint conforming to irregularities in the road surface.

Naturally a winter snow tire will not be expected to perform well in moderate weather on aggressive pavement.

The all season tire tries to split the difference between the summer and winter tires. This tire has light siping of the tread blocks, an intermediate stiffness of the carcass to provide a firm but comfortable ride, and a tread pattern

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Photograph 1: Summer Michelin Pilot Sport PS2 tire tread

Photograph 2: Winter Bridgestone Blizzak WS70 tire tread www.collisionpublishing.com

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intended to produce good wet traction and resistance to hydroplaning with low noise. The tread pattern of an all season is shown in Photograph 3.

This test is the first in an intended series of tests to evaluate the traction characteristics under braking for the three types of tires. This first series was performed in moderate summer conditions. A follow-up series of testing is expected to be performed under winter type conditions.

T

est Method For the cold testing a 1996 BMW 528i sedan was tested on an asphalt surface. The vehicle brakes were factory replacement type and the odometer displayed about 165000 miles. For the warm testing a 2012 BMW 328i sedan was tested on an asphalt surface.

The vehicle brakes were stock and the odometer displayed about 6500 miles. The vehicles were accelerated to a target speed of 45 mph, with the speedometer indicated speed verified with a radar gun. When the target speed was reached, the driver fully applied the brakes and skid to a stop. The vehicle was equipped with a Vericom VC3000 performance testing computer. The Vericom uses a two channel accelerometer to record acceleration and a crystal clock for time. The microcontroller uses these sensors to show the deceleration and to calculate the velocity and distance versus time at 100 Hz sample rate.

The relationship between acceleration and velocity is the following simple equation of motion solved for velocity:

where a is the acceleration, Ve is the end velocity, Vi is the initial velocity, and t is time interval for the calculation.

The relationship between acceleration, velocity and distance is the following equation:

where X is the distance. Used in the brake testing mode, the test was triggered by the start of deceleration. The unit was calibrated against gravity, and leveled at the start of each test. The Vericom was mounted to the center of the windshield, which is just forward of the center of gravity of the vehicle. The angle of the Vericom was adjusted for the test vehicles pitch when braking before each test.

When the vehicle yaws, some of the deceleration rate longitudinally would be read the by lateral sensor reducing the measured deceleration rate. During the braking tests the driver made certain to keep the vehicle straight during

Photograph 3: All-season Michelin MXM4 tire tread 28 Collision Magazine - Volume 12 Issue 1

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the test. The vehicle is most susceptible to yaw during skid testing without ABS brakes on low friction surfaces.

Compared to other data measurement techniques such as GPS systems, skid sleds, and paint mark measurements, the Vericom is very accurate. Previous work in the literature described and tested different test data acquisition and analysis methods for coefficient of friction [2], but did not conclude any method of data analysis better than another.

Our purpose was to compare tires, so repeatability was our main concern. The reported Vericom accuracy is 1% [3], and the author’s experience in accelerometer testing indicated this to be a repeatable technology. Vericom testing results in less error than a torque transducer based test [4].

The Vericom testing and data analysis conforms to SAE standard J2505 [5].

One test track was dry and another was wet before each test set. A 500 gallon roadway sprayer was used to saturate the road surface. The sprayer dispensed about 450 gallons of water over a 265 m2 area prior to each series of 6 runs for a particular tire and brake modulation test. About 1.1 liters per square meter were applied to wet the road. This is the equivalent of about 1 millimeter of water. The cold testing was conducted with water temperature between 34 and 37 °F (1° and 3° C) [6], the warm testing was conducted with ambient water temperature near 75 °F. Both road surfaces exhibited similar wear and were clean and nearly level (as shown in Photograph 4 and 5).

[7]. The testing was performed when we were certain the roadway was not iced when wetted, but only near freezing.

The warm air temperature was about 75°F (24°C) and it was sunny/partly cloudy during the testing. The road surface temperature was hotter than the air due to the direct sunlight.

All tires used during this testing were a size 225/45R18, mounted to Moda MD11 aluminum wheel, and were changed in complete new sets of four. The winter snow tires were Bridgestone Blizzak WS70, the grand touring all-season tires were Michelin Primacy MXM4, and the summer only high performance were Michelin Pilot Sport PS2. Each tire tread is shown in Photographs 1-3.

Each set of tires were driven between 150 and 200 miles of a combination of highway, city, and rural driving cycles before testing to remove manufacturing chemicals that may prevent the tire from achieving maximum performance.

Tire pressure was adjusted to the factory recommended setting prior to testing.

Testing progressed from wet to dry pavement with the anti-lock brake system active. Then the plug connection to the ABS/ASC control module was unfastened to disable the anti-lock brakes for testing on both roadway surfaces.

We performed 6 tests of each condition; per tire, on wet then dry pavement, with and without ABS for a total of 72 tests for each weather condition.

The cold air temperature was about 34°F (1°C) and it was overcast during the testing. The road surface temperature is often not available to the accident reconstructionist and we did not want to test iced roadway conditions so that the data would be comparable to the moderate weather testing

At the conclusion of each test, the data from the Vericom VC3000 was recorded on a data sheet. This data included the vehicle speed at brake application, braking distance, time to brake, and average deceleration.

Photograph 4: Wet track test site cold testing

Photograph 5: Dry track test site warm testing

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During the locked wheel testing an observer was stationed in the braking area to determine if all wheels locked during the maneuver. In all tests it was observed all 4 tires locked.

The visible skid marks from the locked wheel dry asphalt tests were also measured and compared to the braking distances recorded by the VericomVC3000 in Table 1. There was no discernible difference in the color or darkness of the skid marks left by the different tires. Differences in the pattern of the marks were noted due to the differing amount of voids in the tire treads.

Figure 2 presents the deceleration data from the Michelin PS2 tire on dry asphalt with locked wheel braking. The rear suspension hopping that was produced during the moderate weather testing was not exhibited during the cold climate testing. The average deceleration for the 6 tests was 0.70g with a range of 0.677g to 0.727g.

Figure 3 shows the deceleration versus time for the Michelin PS2 tire on wet asphalt with ABS modulated braking. The average deceleration for the 6 tests was 0.82g with a range of 0.783g to 0.846g.

Vericom Computed Distance (ft) 87.7 80.0 78.2 76.2 88.4 81.3 79.8 67.0 69.9 72.7 75.8 72.1

Figure 4 presents the deceleration data from the Michelin PS2 tire on wet asphalt with locked wheel braking. The average deceleration for the 6 tests was 0.68g with a range of 0.657g to 0.700g.

Table 1: Comparison of visible skid length measurement and Vericom calculated stopping distances for all cold dry surface locked wheel braking tests

Figure 8 presents the deceleration data from the Michelin Primacy MXM4 tire on wet asphalt with locked wheel braking. The average deceleration for the 6 tests was 0.73g with a range of 0.702g to 0.748g.

Tire Type

Run Starting Measured # Speed Skid (MPH) Length (ft) Primacy 1 43.6 83.0 (all-season) 2 40.1 83.5 3 39.9 78.0 4 39.6 74.0 5 43.5 92.0 6 41.5 85.0 Blizzak 1 43.8 81.5 (winter) 2 39.9 76.0 3 40.4 72.0 4 41.2 78.0 5 42.1 77.5 6 40.3 80.0

Figure 5 presents the deceleration data from the Michelin Primacy MXM4 tire on dry asphalt with ABS modulated braking. The average deceleration for the 6 tests was 0.89g with a range of 0.870g to 0.916g.

Figure 6 presents the deceleration data from the Michelin Primacy MXM4 tire on dry asphalt with locked wheel braking. The average deceleration for the 6 tests was 0.71g with a range of 0.683g to 0.729g.

Figure 7 presents the deceleration data from the Michelin Primacy MXM4 tire on wet asphalt with ABS modulated braking. The average deceleration for the 6 tests was 0.98g with a range of 0.929 to 0.995g.

R

Figure 9 presents the deceleration data from the Bridgestone Blizzak WS70 tire on dry asphalt with ABS modulated braking. The average deceleration for the 6 tests was 0.77g with a range of 0.725g to 0.800g.

In the figures below the left-hand y axis is deceleration in units of g and the right-hand y axis is speed in miles per hour (MPH). The x axis is time in seconds (s).

Figure 11 presents the deceleration data from the Bridgestone Blizzak WS70 tire on wet asphalt with ABS modulated braking. The average deceleration for the 6 tests was 0.74g with a range of 0.689g to 0.779g.

esults The Vericom VC3000 data was processed with Vericom’s proprietary Profile 3 software to generate charts of deceleration rate and vehicle speed versus time. The figures below show the deceleration and vehicle speed versus time for the 6 data samples collected for each tire, brake modulation type, and roadway condition.

Figure 10 presents the deceleration data from the Bridgestone Blizzak WS70 tire on dry asphalt with locked wheel braking. The average deceleration for the 6 tests was 0.79g with a range of 0.756g to 0.815g.

Figure 1 presents the deceleration data from the Michelin PS2 tire on dry asphalt with ABS modulated braking. The Figure 12 presents the deceleration data from the Bridgeaverage deceleration for the 6 tests was 0.89g, with a range stone Blizzak WS70 tire on wet asphalt with locked wheel of 0.865g to 0.918g. braking. The average deceleration for the 6 tests was 0.67g with a range of 0.544g to 0.719g.

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Figure 1: PS2 tires, ABS modulated braking, dry asphalt

Figure 2: PS2 tires, locked wheel braking, dry asphalt www.collisionpublishing.com

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Figure 3: PS2 tires, ABS modulated braking, wet asphalt

Figure 4: PS2 tire, locked wheel braking, wet asphalt 32 Collision Magazine - Volume 12 Issue 1

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Figure 5: MXM4 tire, ABS modulated braking, dry asphalt

Figure 6: MXM4 tire, locked wheel braking, dry asphalt www.collisionpublishing.com

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Figure 7: MXM4 tire, ABS modulated braking, wet asphalt

Figure 8: MXM4 tire, locked wheel braking, wet asphalt 34 Collision Magazine - Volume 12 Issue 1

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Figure 9: Blizzak tires, ABS modulated braking, dry asphalt

Figure 10: Blizzak tires, locked wheel braking, dry asphalt www.collisionpublishing.com

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Figure 11: Blizzak tires, ABS modulated braking, wet asphalt

Figure 12: Blizzak tires, locked wheel braking, wet asphalt 36 Collision Magazine - Volume 12 Issue 1

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Table 2 presents the average deceleration values for each 6 test run groupings. The data demonstrates that all tires, except the Blizzak on dry asphalt, produce higher tire friction during ABS modulated braking than during locked wheel braking.

Tire Pilot PS2 Pilot PS2 Pilot PS2 Pilot PS2 MXM4 MXM4 MXM4 MXM4 Blizzak Blizzak Blizzak Blizzak

Wet/ Dry Dry Dry Wet Wet Dry Dry Wet Wet Dry Dry Wet Wet

ABS/Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel

Average Deceleration (g) 0.89 0.65 0.82 0.73 0.89 0.71 0.98 0.73 0.77 0.79 0.74 0.67

Table 2: Average deceleration value for all cold tested configurations.

The average deceleration rates were compared for each tire, both locked wheel and ABS modulated braking, between wet and dry asphalt. Table 3 lists the percent differences for these comparisons. It can be seen with ABS modulated braking the reduction in braking performance between dry and wet asphalt was less than 8% for all three tires. The locked wheel braking performance decreased markedly as the performance nature of the tire went down; the PS2 went up over 11%, the MXM4 up by over 2%, and the Blizzak decreased by nearly 19%.

The PS2 in locked wheel, and MXM4 in both locked wheel and ABS modulated testing exhibited an increase in braking performance in the wet and cold temperatures.

This is thought to be due to the cooling effect of the wet surface on the tire contact patch, helping to maintain the tire’s temperature closer to its optimal point, preventing overheating and reducing the available grip.

Tire PS2 MXM4 Blizzak

ABS -8.80% 9.10% -4.35%

Locked Wheel 11.65% 2.34% -18.65%

Table 3: Percent difference in tire friction between cold dry to wet asphalt The data for each tire was compared to calculate the difference in tire friction between ABS modulated and locked wheel braking on similar surface (wet or dry) and is listed in Table 4. The three tires displayed dramatically different losses of performance on dry asphalt, but on wet asphalt the tires displayed a consistent loss of performance.

Tire PS2 MXM4 Blizzak

Dry -37.77% -25.56% 2.66%

Wet -11.90% -34.90% -10.68%

Table 4: Percent difference in tire friction of the three tires from ABS modulated to locked wheel braking Table 5 presents the average deceleration values for each 6 test run grouping. The data shows that all tires, except the Blizzak on dry asphalt, produce higher tire friction during ABS modulated braking than during locked wheel braking.

Tire Pilot PS2 Pilot PS2 Pilot PS2 Pilot PS2 MXM4 MXM4 MXM4 MXM4 Blizzak Blizzak Blizzak Blizzak

Wet/ Dry Dry Dry Wet Wet Dry Dry Wet Wet Dry Dry Wet Wet

ABS/Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel

Average Deceleration (g) 0.98 0.70 0.95 0.68 0.88 0.73 0.85 0.61 0.79 0.83 0.72 0.54

Table 5: Average deceleration value for all warm tested configurations www.collisionpublishing.com

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The average deceleration rates were compared for each tire, both locked wheel and ABS modulated braking, between wet and dry asphalt. Table 6 lists the percent differences for these comparisons. It can be seen with ABS modulated braking, the reduction in braking performance between dry and wet asphalt was less than 8% for all three tires.

The locked wheel braking performance decreased markedly as the performance nature of the tire went down; the PS2 dropped by the same 3% as calculated with the ABS modulated braking while the Blizzak decreased by 35%.

Tire PS2 MXM4 Blizzak

ABS -3% -3% -8%

Locked Wheel -3% -16% -35%

Table 6: Percent difference in tire friction between warm dry and wet asphalt The data for each tire was compared to calculate the difference in tire friction between ABS modulated and locked wheel braking on similar surface (wet or dry) and is listed in Table 4. The three tires displayed dramatically different losses of performance on dry asphalt; on wet asphalt the tires displayed a consistent loss of performance.

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Tire PS2 MXM4 Blizzak

Dry -29% -17% 6%

Wet -28% -28% -25%

Table 7: Percent difference in tire friction of the three tires between ABS modulated and locked wheel braking in warm testing.

D

iscussion The grand touring all-season tire tested is comparable to the tires used on police vehicles that are frequently used to measure coefficients of friction at accident sites. Comparing the performance data in these tests using that tire as a baseline establishes the adjustments in braking coefficients for summer and winter tires shown in Table 8. Positive numbers in Table 8 indicate the need to use higher tire coefficients of friction, negative numbers lower coefficients of friction.

ABS Braking Dry Wet Summer 0.1% -16.4% Winter -13.6% -24.7%

Locked Wheel Braking Dry Wet -8.8% 0.8% 11.4% -8.3%

Table 8: Tire friction adjustments for near freezing temperatures by tire type for speed from skid calculations, for data based on all season tires.

Summer Winter

ABS Braking Dry Wet 11% 12% -11% -15%

Locked Wheel Braking Dry Wet -4% 11% 14% -11%

Table 9: Tire friction adjustments for warm weather by tire type for speed from skid calculations for data based on all season tires.

Comparing the data in Table 8 with table 9, the similar data from moderate temperature testing results [7], it can be seen the PS2 summer tire displays marked degradation in its relative performance to the MXM4 all-season tire in near freezing temperatures. This was expected since the summer tire has a rubber compound designed to elicit maximum grip in moderate to high temperatures.

The Blizzak performance relative to the MXM4 was not expected. The near freezing temperatures were thought to bring a distinct advantage to the Blizzak, being it is

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designed solely for use in these conditions. It performed comparatively worse to the MXM4 in ABS braking in the near freezing environment as it did in the moderate temperature environment.

Tire

Wet/ ABS/Locked Dry Wheel

Pilot PS2 Pilot PS2 Pilot PS2 Pilot PS2 MXM4 MXM4 MXM4 MXM4 Blizzak Blizzak

Dry Dry Wet Wet Dry Dry Wet Wet Dry Dry

ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel ABS Locked Wheel

Warm Average Decel (g) 0.98 0.70 0.95 0.68 0.88 0.73 0.85 0.61 0.79 0.83

Cold Average Decel (g) 0.89 0.65 0.82 0.73 0.89 0.71 0.98 0.73 0.77 0.79

Table 10: Tire friction comparison by tire and test type between moderate and near freezing temperatures.

The data is further reduced to a percentage better or worse calculation as displayed in Table 11 below. In these calculations the moderate temperature data was treated as the baseline.

Tire Pilot PS2 Pilot PS2 Pilot PS2 Pilot PS2 MXM4 MXM4 MXM4 MXM4 Blizzak Blizzak Blizzak Blizzak

Wet/Dry ABS/Locked Wheel Dry ABS Dry Locked Wheel Wet ABS Wet Locked Wheel Dry ABS Dry Locked Wheel Wet ABS Wet Locked Wheel Dry ABS Dry Locked Wheel Wet ABS Wet Locked Wheel

% Difference Moderate/Cold -9.18% -7.71% -13.89% 7.50% 1.02% -3.01% 15.06% 18.85% -2.78% -4.94% 2.22% 23.15%

Table 11: Tire friction comparison by tire and test type between moderate and near freezing temperatures.

The drop-off in the PS2 performance between moderate and near freezing temperatures was not as great as was anticipated. It is thought the brake testing raised the tire tread temperature to near its designed working value allowing the tire to retain most of its moderate ambient temperature performance. There would likely be a marked difference in lateral grip between the two temperatures.

The MXM4 exhibited similar performance in the near freezing temperatures on the dry surface, with a marked increase in performance on the wet surface. It is thought the more temperature stable rubber compound benefitted the most from the cooling effect of the wet surface.

The lack of increased dry surface performance was not an anticipated outcome of this testing. It was thought the soft rubber compound would benefit the most from the decrease in ambient and surface temperatures. As discussed in the results of the original work [6], the soft compound and heavy siping is thought to disrupt the ability of the ABS unit to accurately determine the amount of available grip.

C

onclusions Different types of tires vary in carcass, compound, and tread pattern, all of which are optimized for their intended usage. These differences create performance variations in all areas of tire performance, including tire to road friction coefficient. The available tire friction is a key factor in determining a vehicle’s braking capability in maximum effort stopping distances.

These differences create performance variations in all areas of tire performance, including tire to road friction coefficient

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Valid coefficients of friction are necessary to provide accurate, reliable findings of vehicle speeds from skids. In the testing described in this paper we have established adjustments to published data to account for different types of tires that can be installed on vehicles involved in collisions.

The comparison of moderate and near freezing temperature data provides a scientific basis for the reconstructionist to modify the roadway-tire coefficient of friction to fit a particular set of circumstances.

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eferences 1. Goudie, D., Bowler, J., Brown, C., Heinrichs, B. et al., "Tire Friction During Locked Wheel Braking," SAE Technical Paper 2000-01-1314, 2000, doi:10.4271/2000-01-1314.

2. J. Eubanks, J., Haight, W., Malmsbury, R., and Casteel, D., "A Comparison of Devices Used to Measure Vehicle Braking Deceleration," SAE Technical Paper 930665, 1993, doi:10.4271/930665.

3. Vericom owner’s manual - VC3000.pdf 4. SAE standard- J345a, “Wet Or Dry Pavement Passenger Car Tire Peak and Locked Wheel Braking Traction”, Published: 1969-03-01.

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5. SAE standard- J2505. “Measurement of VehicleRoadway Frictional Drag”, Published: 2010-08-01.

Average acceleration measurement method.

6. Bound between the air temperature and the USGS website data for the water source - Susquehanna river near Harrisburg, Pennsylvania. http:// nwis.waterdata.usgs.gov/usa/nwis/uv/?cb_00010 =on&cb_00300=on&cb_00045=on&format=g if_default&period=&begin_date=2013-03-04&end_ date=2013-03-08&site_no=01570500 7. Leiss, P., Becker, S., and Derian, G., "Tire Friction Comparison of Three Tire Types," SAE Technical Paper 2013-01-0783, 2013, doi:10.4271/2013-010783.

Contact Information The authors may be contacted via email as follows: Peter Leiss, P.E., C.F.E.I., C.V.F.I.: pleiss@robsonfoensic.com Steven Becker: sbecker@robsonforensic.com Gary Derian, P.E: gary@derianengineering.com

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eel h W The t a rn u T My

A DIRTY TRICK TO ACHIEVE THE DESIRED RESULT, OR WHAT? erik carlsson

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his article is about a traffic accident that perhaps can be de-scribed as more unnecessary than most accidents, if indeed it is even possible to rate different levels of something unnecessary. The tiny driver of a small car, equipped with the then recently mandated air-bag in the steering wheel, was southbound on a four-lane two-way ma-jor highway, traveling at a moderate speed in the ‘slow’ lane. Her mind may have been somewhere else because she did not notice that a traffic signal at an intersection in front of her on the straight road turned red. First when an SUV that was stopped at her right on the intersecting country road began to move forward did she realize she had a red light. She hit the brakes, and almost managed to stop before her car reached the intersection.

The driver of the SUV was making a left turn, and, as many drivers do, cut the corner. He began his northbound turn as soon as the front of his SUV began to cross the first of the two southbound lanes. The ensuing collision happened in that lane.1 The impact was minor, and can perhaps best be described as a sideswipe, with the left front corner of the car hitting the driver side rear half of the now northbound SUV. Both vehicles could have been driven from the accident scene, but the airbag in the car deployed and broke the tiny driver’s wrists. She therefore ended up in a hospital instead of driving her car home.

The driver of the car admitted at the subsequent police investigation that she didn’t see the traffic light turning red and that she only became aware of the red signal when she saw the SUV beginning to move. The driver of the SUV stated that he didn’t see the approaching car until just before the collision. He had been waiting for a green light and was concentrating on the traffic signal.

When the light turned green, he “stepped on it” and began his left turn. He had no reason to look out for traffic on the highway because he knew that drivers on the highway had a red light when he got green light.

Overly aggressive airbags! It did not take long after that the mandatory requirements for airbags in the steering wheels in new cars went into effect before it became clear that the airbags were too powerful, or “overly aggressive,” as NHTSA phrased it. The airbags caused in low speed impacts more injuries than they prevented. The reason for the high force with which the airbags deployed was that it was initially believed that for optimal protection of drivers the vehicles should meet the mandatory FMVSS 208 frontal barrier crash test requirements with the driver dummy unrestrained. The airbags therefore had to be more powerful than they needed to be if the vehicles instead were tested with the dummies restrained.

De-powered airbags: The observation that the airbags in low speed impacts caused unnecessary injuries led to a changed safety standard that resulted in less powerful airbags. These airbags were in the beginning called “de-powered airbags.” Owners of cars equipped with the overly aggressive airbags were in some cases permitted to have the airbags disconnected.

Broken wrists led to a law suit. The lady driver’s injuries became a text book example of unnecessary injuries caused by overly powerful airbags. She would probably have escaped injuries completely if the airbag had not deployed as this was a collision that even in the pre-seatbelt and pre-airbag era no doubt would have been considered an insignificant fender-bender.

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An attorney representing the injured driver filed a law suit against the car manufacturer, alleging that what in the legal community was called unwarranted airbag deployment caused her injuries. The attorney supported his claim by referring to the fact that Mercedes-Benz had an airbag system with two different thresholds, where a higher impact force is required to trigger the airbags when the occupants are restrained. With such a system in the car, the attorney alleged, the injured lady’s injuries would have been prevented, as she was wearing her seatbelt. [The defense attorneys did not challenge the plaintiff’s claim that she was wearing her seatbelt as it in the accident report was stated that the driver had her seatbelt on at the time she received assistance to get out of car. The attorneys no doubt realized that they would make fools of themselves if they tried to convince a jury that the injured lady may have managed to fasten the seatbelt after the collision despite her broken wrists.]

No vehicle defect! As expected, the carmaker’s legal team opposed the allegation by the plaintiff’s attorney of a vehicle defect. The accident vehicle not only met the mandatory safety standards, the defense team contended, but in addition also met the carmaker’s own specifications! According to those specifications, the threshold for airbag deployment in a front-end collision was 8-14 mph. The severity of the plaintiff’s accident was within that range, the defense team maintained.2 That such was the case had been determined by the defendant's expert witness, a science teacher at a well known university. In his report, the expert ‘showed’ that the severity of the impact between the small car and the SUV equaled the car hitting a barrier at a speed of 8 mph.

A reasonable tolerance level? A tolerance level of 8 to 14 mph [Equivalent Barrier Speed] for the airbag sensors to trigger the air-bags in a frontal collision seems excessive, but that is what the carmaker’s attorneys stated when they submitted their expert’s report.

A thorough accident reconstruction! The defense expert did a comprehensive job and did not take shortcuts. Rather than relying on already established stiffness coefficients for the two vehicle models involved in the accident, he researched available data bases about conducted barrier crash tests. He found two barrier crash tests for each or similar models of the two vehicles that he considered to be comparable to the collision that led to this legal dispute. Based on those barrier crash tests, he calculated the corresponding stiffness coefficients for each model at the two barrier crash tests. He thus established two sets of stiffness coefficients for each vehicle. Next, he calculated the severity of the collision at issue by using the average of each pair of stiffness 44 Collision Magazine - Volume 12 Issue 1

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coefficients. By using the average of the calculated stiffness coefficients instead of the higher or the lower ones, he indicated that he was fully objective and did not deliberately affect the calculated impact force up or down.

Interesting reading! As is good engineering practice, the defense expert included his computations in his report and did not merely state what the computations showed. The inclusion of the computations in the report led to some interesting reading. At the defense expert’s first computer run, the computer showed that the collision force acting on the car was 3.09 times that of the force acting on the SUV. This may perhaps have been just fine with the defense legal team, who posited that the collision force acting on the car was high enough to warrant deployment of the airbag. The expert, however, realized of course that as a science teacher he could not neglect the law of physics that states that a physical force can only exist when there is an equal force in the opposite direction. The collision force acting on the car could therefore not have exceeded that on the SUV. Clever solution? To solve his dilemma with mismatching collision forces, the defense expert multiplied his well-researched and estab-lished stiffness coefficients for the SUV by 3.09! He then re-run the computations, at which time the computer showed the same collision force for both vehicles. [No surprise there!] Based on the recalculated collision force acting on the SUV, the Equivalent Barrier Speed of the car computed to be eight mph, and thus support the defense le-gal team’s claim about the car meeting the manufacturer’s own speci-fications.

Selectable result. Naturally, the defense expert would have arrived at equally matching collision forces if he instead had divided the stiffness coefficients for the car by 3.09.

He could also have tried a middle way by increasing the assumed stiffness coefficients for the SUV by multiplying it by, say, 1.5, and divide those for the car by a similar number. In either case, the calculated EBS of the car would have been less than eight mph.

Foot-notes: 1. An issue not addressed in the law suit that followed is a state law that specifies that a driver making a left turn onto a two-way street must not start the turn until the front of the vehicle has crossed the lane(s) for traffic approaching from the left.

2. The attorneys obviously meant Equivalent Barrier Speed, not actual vehicle speed.

Anyone who has some questions or comments about what I have described in this article is welcome to contact me at erikcarlsson@live.com.

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Let’s Get Back To Basics How quickly and easily can you deliver a scene for court?

Let’s face it, most of the drawings prepared for case files or courtroom presentations are simple, straightforward 2D diagrams.

The most critical and stressful time spent is at the scene.

The reconstructionist needs the best scene evidence collection software and the best diagramming software.

That’s it.

So how does it work? The process begins with IMS EvidenceRecorder.

With Leica Geosystems IMS, your diagramming begins in the field.

When using IMS Evidence Recorder to take measurements, you’re actually building 2D/3D framework for the diagram in real-time. The user interface is crafted to work very specifically with your workflow to ensure a brisk pace when taking measurements via total station or GNSS receiver.

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The data transfer between IMS EvidenceRecorder and IMS Map360 is unmatched. The diagram you can see in IMS EvidenceRecorder appears in IMS Map360.

The evidence (actual measurements made by the instrument) is available and verifiable. The drafting commands are powerful and flexible. Your final deliverable is both credible and reliable.

Don’t use a total station, no problem. IMS Map360 can use data from many sources.

Other sources of data can also be used such as manual baseline offsets, point clouds from scanners, and imagery from UAS systems.

Animation Extension

Point Cloud Extension

When you do end up working on a scene that requires more visual appeal, Leica Geosystems IMS still has you covered.

With add-on extensions, you can bring your diagrams to life with animation, as well as the ability to view the point cloud data, take measurements, and create your diagram right within the point cloud.

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ed w e i v e R Peer

Motorcycle Center of Gravity DatA Methodology and Reference

2016 ARC-CSI Motorcycle Crash Team Pre-Crash Testing Michael DiTallo Eric Paul Kelley Adamson Thomas Green Mike Merolli Brent Munyon Kevin Vosburgh Billy S. Cox, Jr. Eric Moody Robert Anderson James Whelan David Hallman

A

bstract Over the course of several days before the 2016 ARC-CSI crash conference, the Motorcycle Crash Team conducted detailed inspections and measurements of the test motorcycles. The test motorcycles included five new Harley-Davidson Inc., (Harley-Davidson) motorcycles, which were owned and driven by Harley-Davidson, but were never involved in collisions. The remainder of the test motorcycles had all been involved in some type of collision or event resulting in minimal side damage. None of the test motorcycles previously involved in a collision had sustained frontal damage. The test motorcycles were photographed, manually measured, scanned using a FARO 3D scanner (See scanner usages in Crash Testing Article Volume 12 Issue 1), and the damage and configuration of each

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one was documented. All test motorcycles were measured and weighed “wet” (full gas tank) and several were also measured and weighed “dry” (empty gas tank). One inspection goal was to create a resource containing the longitudinal and vertical center of gravity (CG) for each test motorcycle that could become a useful database in crash reconstruction analysis.

I

ntroduction The same process and methodology of data collection was utilized for all twenty-six motorcycles. The following will describe and illustrate the process of collecting data to determine the center of gravity for Test Motorcycle A as the example. Test Motorcycle A is a 2006 Harley-Davidson Sportster.

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ethods and Materials The test motorcycles’ gasoline tanks were filled with fuel and the engine oil levels were checked to ensure they were “full.” The motorcycle dimensional data was measured and documented including the static weight without an operator. The tire air inflation pressure was checked and filled to recommended pressure.

In all cases the front tire was lifted as high as possible to be between 25 to 45 degrees from level. The hoisted weight on the rear tire was documented as well as the hoisted height of the front axle. The data was corrected for the height of the scale pads. The scales used were a set of Intercomp SW-RFX 1500 wireless PC scale system, which were calibrated, and a certified accuracy to +/- 0.1% of applied load or +/- graduation, whichever is greater.

Once the data was collected the longitudinal and vertical center of gravity was analyzed. We always lifted the front tire, however either the front or the rear tire could have been lifted for this analysis.

Figure 2: Static weight of Test Motorcycle A

Figure 1: Test Motorcycle A being weighed

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Figure 3: Test Motorcycle A being measured for the variable of rh which is the sum of variables r and h

Figure 4: Close-up Test Motorcycle A being measured for the variable of rh which is the sum of variables r and h

Figure 5: Test Motorcycle A being weighed for the variable of wh which in this photograph is the weight of the rear axle 52 Collision Magazine - Volume 12 Issue 1

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Figure 7: Illustration of variables used for the center of gravity calculations

by Northwestern University CPS Traffic Crash Reconstruction 2 Motorcycle Horizontal Gravity Center

of Gravity Height

Figure 8: The variables and formula used for the center of gravity calculations by Northwestern University CPS Traffic Crash Reconstruction 2 Motorcycle Center of Gravity Height

Figure 6: Hoisted weight

R

esults Table 1 (following pages) contains data for all test motorcycles without an operator as previously described. Table 1 identifies the test motorcycle by same letter used in testing and consistent with past and future publications. In addition, a photograph depicts the motorcycle along with specification data and the key measured and calculated data.

Figure 9: The variables and formula used for the center of gravity calculations by Northwestern University CPS Traffic Crash Reconstruction 2 Motorcycle

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A

Wf 263 lb.

Wr 316 lb.

Wh 350 lb.

W 579 lb. h 2.07 ft. r 1.08 ft. l 5.33 ft. lf 2.91 ft. lz 1.82 ft.

B

Wf 325 lb.

Wr 369 lb.

Wh 396 lb.

W 694 lb. h 2.07 ft. r 1.00 ft. l 5.31 ft. lf 2.82 ft. lz 1.49 ft.

C

Wf 347 lb.

Wr 401 lb.

Wh 422 lb.

W 748 lb. h 2.07 ft. r 1.00 ft. l 5.38 ft. lf 2.88 ft. lz 1.36 ft.

D

Wf 357 lb.

Wr 437 ft.

Wh 446 Ib. W 794 lb. h 2.09 ft. r 1.08 ft. l 5.29 ft. lf 2.91 ft. lz 1.22 ft.

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E

Wf 379 lb.

Wr 502 lb.

Wh 535 lb.

W 881 lb. h 2.32 ft. r 1.00 ft. l 5.29 ft. lf 3.02 ft. lz 1.41 ft.

F

Wf 242 lb.

Wr 251 lb.

Wh 304 lb.

W 493 lb. h 2.26 ft. r 0.96 ft. l 4.55 ft. lf 2.31 ft. lz 1.81 ft.

G

Wf 127 lb.

Wr 177 lb.

Wh 195 lb.

W 304 lb. h 2.20 ft. r 1.17 ft. l 4.63 ft. lf 2.69 ft. lz 1.68 ft.

H

Wf 216 lb.

Wr 230 lb.

Wh 240 lb.

W 446 lb. h 2.07 ft. r 0.96 ft. l 4.67 ft. lf 2.41 ft. lz 1.17 ft. www.collisionpublishing.com

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I

Wf 170 lb.

Wr 178 lb.

Wh ----W 348 lb. h ----r ----l 4.76 ft. lf 2.43 ft. lz -----

J

Wf 162 lb.

Wr 181 lb.

Wh 204 lb.

W 343 lb. h 2.60 ft. r 0.96 ft. l 4.90 ft. lf 2.59 ft. lz 1.48 ft.

K

Wf 220 lb.

Wr 196 lb.

Wh 240 lb.

W 416 lb. h 2.29 ft. r 0.96 ft. l 4.58 ft. lf 2.16 ft. lz 1.80 ft.

L

Wf 166 lb.

Wr 189 lb.

Wh 232 lb.

W 355 lb. h 2.62 ft. r 0.87 ft. l 4.67 ft. lf 2.48 ft. lz 1.70 ft.

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M

Wf 261 lb.

Wr 240 lb.

Wh 294 lb.

W 501 lb. h 2.33 ft. r 0.96 ft. l 4.75 ft. lf 2.28 ft. lz 1.87 ft.

N

Wf 289 lb.

Wr 347 lb.

Wh 386 lb.

W 636 lb. h 2.61 ft. r 1.08 ft. l 5.25 ft. lf 2.86 ft. lz 1.64 ft.

O

Wf 242 lb.

Wr 292 lb.

Wh 318 lb.

W 534 lb. h 2.59 ft. r 1.00 ft. l 5.27 ft. lf 2.88 ft. lz 1.45 ft.

P

Wf 287 lb.

Wr 329 lb.

Wh 370 lb.

W 616 lb. h 2.61 ft. r 1.08 ft. l 5.42 ft. lf 2.89 ft. lz 1.74 ft. www.collisionpublishing.com

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Q

Wf 132 lb.

Wr 151 lb.

Wh 198 lb.

W 283 lb. h 2.56 ft. r 1.08 ft. l 4.63 ft. lf 2.47 ft. lz 2.24 ft.

R

Wf 219 lb.

Wr 202 lb.

Wh 277 lb.

W 421 lb. h 2.56 ft. r 0.96 ft. l 4.60 ft. lf 2.21 ft. lz 2.18 ft.

S

Wf 209 lb.

Wr 199 lb.

Wh 235 lb.

W 408 lb. h 2.16 ft. r 0.96 ft. l 4.50 ft. lf 2.19 ft. lz 1.69 ft.

T

Wf 235 lb.

Wr 212 lb.

Wh 253 lb.

W 447 lb. h 2.45 ft. r 0.96 ft. l 4.73 ft. lf 2.24 ft. lz 1.67 ft.

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U

Wf 228 lb.

Wr 241 lb.

Wh 292 lb.

W 469 lb. h 2.75 ft. r 0.96 ft. l 4.67 ft. lf 2.40 ft. lz 1.66 ft.

V

Wf 205 lb.

Wr 216 lb.

Wh 245 lb.

W 421 lb. h 2.62 ft. r 0.96 ft. l 4.67 ft. lf 2.40 ft. lz 1.43 ft.

W

Wf 207 lb.

Wr 206 lb.

Wh 248 lb.

W 413 lb. h 2.29 ft. r 0.96 ft. l 4.58 ft. lf 2.28 ft. lz 1.77 ft.

X

Wf 97 lb.

Wr 155 lb.

Wh 184 lb.

W 252 lb. h 2.54 ft. r 0.71 ft. l 4.25 ft. lf 2.61 ft. lz 1.37 ft. www.collisionpublishing.com

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Y

Wf 83 lb.

Wr 146 lb.

Wh 184 lb.

W 229 lb. h 2.46 ft. r 0.54 ft. l 4.21 ft. lf 2.68 ft. lz 1.51 ft.

Z

Wf 215 lb.

Wr 265 lb.

Wh 298 lb.

W 480 lb. h 2.54 ft. r 1.08 ft. l 5.23 ft. lf 2.89 ft. lz 1.73 ft.

S

ummary In crash reconstruction analysis the longitudinal center of gravity is often placed into a vehicle drawing. The data needed for this calculation, as described above, is frequently easily obtain from specification sources and/or measured. Having at least the longitudinal center of gravity can assist in the study of rotation, vehicle dynamics (behavior) and distance determination. The data needed for vertical center of gravity is often more difficult to find, often unpublished, and will most often need to be measured. We hope that this article will serve as reference for crash reconstructionists.

This group has also collected some data and is hoping to gather additional data to analyze how the center of gravity of a motorcycle changes (both vertically and longitudinally) with an operator and/or passenger. Once this has been studied, we will provide additional information as a resource.

A

cknowledgements A special thanks to Harley-Davidson, FAST Towing, Daniel Vomhof, Jim Byrne and our sponsors for all their project support.

VinLink (www.vinlink.com) for specification data.

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A special thanks to all the members of the 2016 ARCCSI motorcycle crash team (alphabetically).

• • • • • • • • • • • • • • • • • • • • • •

Kelley Adamson Robert Anderson Billy S. Cox, Jr. Michael DiTallo (Team Leader) Jim Dunlap Thomas Green Wesley Grimes Rusty Haight Sean Haight David Hallman Thomas Lawson Michael Merolli Eric Moody Jim Morgan Brent Munyon Eric Paul William Redfairn Tim Reust Michael Rosenfiel Kenneth Salisbury Kevin Vosburgh James Whelan

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ed w e i v e R Peer

Fracture Energy Calculations for Wooden Utility Poles Nathan Rose

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Kineticorp, LLC.

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I

ntroduction

The following mechanisms of energy dissipation may need to be considered when calculating the initial speed of a vehicle that impacted a wooden utility pole: (1) crushing of the vehicle; (2) full or partial fracture of the pole; (3) moving and tilting of the pole within the ground; (4) acceleration of the pole after a full fracture; and (5) tire, and other dragging forces, acting on the vehicle during its post-impact motion [Daily, 2009; Cofone, 2007 and 2012].i Each of these will be discussed in this article.

However, the focus will be on validating Kent and Strothers’ method for calculating the full or partial fracture energy for the pole [1998].

In general, a vehicle’s kinetic energy at the time of impact with a wooden utility pole can be calculated by adding the vehicle’s post impact kinetic energy to the energies dissipated through vehicle crush, pole fracture, and pole movement (including tilting and accelerating after fracture). This is described mathematically by Equation (1).

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KEimpact = Ecrush + Efracture + Emovement + KEpostimpact

(1)

In Equation (1), the variables have the following meaning: KEimpact = kinetic energy of the vehicle at first contact with the pole Ecrush = energy dissipated in crushing the vehicle Efracture = energy dissipated in fully or partially fracturing the pole Emovement = energy dissipated in moving or tilting the pole KEpostimpact = kinetic energy of the vehicle at separation from the pole Once the kinetic energy at impact with the pole is obtained, this kinetic energy can be converted to the impact speed with the following equation.

but the analysis in this article will only utilized their frontal impact data. Asay and Woolley reported the equivalent barrier speed for each test and the crush profiles that resulted. Their data was used without modification.

As a part of the analysis reported here, a second-order polynomial was fit to this pole impact data using the “add trendline” function in Microsoft Excel. A second-order polynomial was chosen because it produced the best fit out of several possible functional forms. The graph of Figure 1 shows the data from the Craig publications and the Woolley and Asay publications with the maximum vehicle crush plotted on the horizontal axis in inches and the equivalent barrier speed (EBS) plotted on the vertical axis in miles per hour. This graph also depicts the second-order polynomial that was fit to the data, which had the following equation: EBS = 0.0059 C 2 + 0.8262 C + 1.009

(3)

In Equation (3), the variables have the following meaning: C = maximum crush in inches EBS = equivalent barrier speed in mph

(2)

In Equation (2), the variables have the following meaning: W = weight of the vehicle g = gravitational constant

C

rushing of the Vehicle An extensive literature covers methods for calculating the energy dissipated during crushing of the vehicle. This study relied on the frontal impact crash tests cited and analyzed by Craig in Accident Reconstruction Journal [1993, 1995a, 1995b, 1995c, 1995d] and those reported by Woolley and Asay [2002, 2008]. The tests cited

by Craig were passenger car frontal impacts with rigid pole barriers, thus they were tests in which no energy was dissipated by moving, deforming, or fracturing the pole. All of the collision energy could be reasonably assumed to have been dissipated through crushing of the vehicle. Craig had analyzed this data by plotting the maximum vehicle crush versus the equivalent impact speed for each test. Some of the tests were repeated impacts of the same vehicle into the pole barrier, so for these tests, the equivalent impact speed was calculated by adding up the collision energies from the impacts to which the vehicle had been subjected.

Woolley and Asay impacted stationary Ford Taurus and Nissan Sentra sedans with a 12-inch rigid pole mounted to the front of a massive moving barrier (MMB). They conducted tests on the front, rear, and sides of these vehicles, 64 Collision Magazine - Volume 12 Issue 1

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The R2 value for Equation (3) was 0.9333. To obtain a basic quantification of the uncertainty in speeds calculated with this equation, an upper and lower bound was established that would encompass most of the data plotted in Figure 1. These upper and lower bound curves, which are depicted with dotted lines in Figure 1 and labeled “high” and “low,” are shifts of Equation (3) by 5.0 mph in either direction. This value was chosen because it resulted in an envelope that captured most of the data points. Clearly, there cannot be 5 inches of crush for an impact speed of 0 miles per hour, so this uncertainty would narrow at low impact speeds. Nonetheless, in the speed range of 10 to 40 mph, the envelope created by these upper and lower bound curves captures most of data included in Figure 1.

M

oving and Tilting of the Pole Daily [2009] and Cofone [2007 and 2012] discuss a method for calculating the energy dissipated by moving and tilting the pole within the ground. This method is based on Newton’s Third Law, which requires that the force applied to the pole by the vehicle is equal in magnitude and opposite in direction to the force applied to the vehicle by the pole. If the collision force can be calculated based on the vehicle deformation, and then the distance through which that force acted can be determined (this would be the pole displacement at the level of the force application), then the energy dissipated in displacing the pole can be calculated. Daily reports that this energy can be calculated with the following equation:

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Figure 1: The Relationship between Maximum Crush and EBS for Frontal Pole Impact Tests Emovement=EFC · Faverage · dpole movement

(4)

In Equation (4), the variables have the following meaning: Faverage = average collision force dpole movement = displacement of the pole at the level of the collision force" EFC = effective force coefficient The effective force coefficient is a multiplier that accounts for the changing orientation of the force applied to the pole as it rotates. Daily’s publication gives instructions for calculating this factor. Daily recommends using methods of crush analysis to calculate the average collision force for this calculation, though other methods could also be used.

This process will not be detailed here, since the primary purpose of this article is to validate a method for calculating the fracture energy for a utility pole.

P

ost-Impact Motion of the Vehicle There are many references that describe methods for calculating the energy dissipated during the post-impact movement of a vehicle. Carter [2012], for instance, discussed several methods for calculating the energy dissipated while a vehicle yaws across the road surface. Rose [2016] discussed the effects of high post-impact spin rates within this analysis and also discussed the use of simulation for quantifying the post-impact energy dissipation. This process too will not be detailed here, since the primary purpose of this article is to validate a method for calculating the fracture energy for a utility pole.

F

racturing of the Pole Several studies have discussed methods for calculating the energy dissipated by full or partial fracture of a utility pole. The discussion here will focus only on the 1998 study by Kent and Strother, in which they made “a first attempt to understand the energy absorbing processes operating when vehicles strike trees and wooden poles in order to make reasonable estimates of the mag-

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nitude of the tree/pole energy dissipated in the crash.”

Since the time Kent and Strother published their study, additional utility pole impact tests have been added to the literature that can be used to validate their approach [Croteau, 2011].

Table 8 in their article). To obtain a reasonable approximation of the degree to which the energy calculated by Equation (5) should be increased to represent dynamic loading of the pole, a line was fit to the Kent and Strother data. The result was the following equation:

Kent and Strother derived the following expression, which yields the energy to statically initiate fracture of a wooden utility pole (FE0):

CF = -0.007 · d + 1.2294

(5)

In this equation, the variables have the following meaning:

σR = the modulus of rupture for the wood species under consideration IC = the cross-sectional moment of inertia for the pole a = the application height of the force above the ground r = the radius of the pole Er = the radial modulus of elasticity The modulus of rupture and the longitudinal modulus of elasticity for the relevant wood species can be obtained from the Wood Handbook, which is produced by the Forest Products Laboratory of the United States Department of Agriculture Forest Service. A PDF version of this handbook is accessible for free via a Google search. The Wood Handbook does not report the radial modulus of elasticity for the various wood species, but it does report the ratio of the radial to the longitudinal, so the radial modulus of rupture can be calculated. The cross-sectional moment of inertia of the pole can be calculated with the following equation.

(6)

In this equation: d = the diameter of the pole Testing and modeling reported by Kent and Strother showed that the dynamic energy required to fracture a wooden utility pole is greater than the static fracture energy, so Equation (5) will underestimate the fracture energy for a vehicle impacting a utility pole. In their article, Kent and Strother reported the difference between the static and dynamic fracture energies for various pole diameters (see 66 Collision Magazine - Volume 12 Issue 1

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(7)

In this equation: d = the pole diameter CF = the correction factor for Equation (5) The R2 value for this equation was 0.7562.

In addition to the issue of static versus dynamic fracture initiation energy, Kent and Strother noted that “several confounding issues must be addressed when dealing with wood structures. Properties of wood not only vary greatly depending upon species, but they also can be strongly dependent on geographical location, moisture content, grain orientation, grain coarseness, texture, hard mineral deposits, grain irregularities, and treatment.” They state that, of these variables, moisture content is perhaps the most influential and they present the following equation that can be used to adjust any of the mechanical properties of the wood, based on the moisture content. This equation is also listed in the Wood Handbook.

(8)

In this equation: P = the material property under consideration P12 = the material property at 12% moisture content Pg = the material property for green wood M = the actual moisture content of the pole Mp = a reference moisture content (in percent) specific to the wood type So far, this section has laid out a method for calculating the energy required to initiate fracture of the pole. The energy required to fully fracture the pole will be greater than the energy required to initiate the fracture. Based on pendulum testing conducted by Kent and Strother with 1/8th scale poles, they concluded that “a second-order polynomial fit most accurately represents the relationship between the energy to completely fracture the pole specimens and the specimen moment of inertia…” They presented

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the following equation for calculating the fracture energy for poles constructed of southern yellow pine: FEtotal = -0.0051 · Ic2 + 39.782 · IC

(9)

For poles that completely fracture, Kent and Strother recommend first calculating the energy required to initiate the fracture [Equations (5) through (8)]. If the pole is not made of southern yellow pine, then they recommend next calculating the fracture initiation energy for the same size pole as if it were made of southern yellow pine, then based on the ratio of the fracture initiation energies for the actual pole and the southern yellow pine pole, scaling the result of Equation (9) to obtain the total fracture initiation energy. The flow chart of Figure 2 summarizes the approach they propose. ii

V

alidating the Kent and Strother Approach In 2011, Croteau reported seven full-scale crash tests that involved moving barriers impacting wooden utility poles. Five of these tests involved non-deformable moving barriers and two involved deformable moving barriers. The face of the deformable barrier had a stiffness that was representative of the frontal stiffness of a passenger car. Both barriers had a bumper height of 26 inches.

The class 4 utility poles that were tested were constructed of southern yellow pine and were coated with Pentachlorophenol preservative. They were 35 feet tall with a nominal diameter of 10 inches and were buried six feet deep. They were mounted in hard-packed desert soil.

After the tests, the moisture content of each pole was measured. The authors also reported that the poles were surrounded by a four-inch thick reinforced concrete pad to replicate a typical sidewalk. This concrete prevented the poles from moving and tilting within the soil, and so, there was no need to consider these energy dissipation mechanisms in our analysis of these tests. The non-deformable barrier tests also eliminated the need to consider vehicle deformation, and since Croteau reported the vehicle speeds immediately following pole fracture, there was no need to calculate the post-impact speed. This allowed the pole fracture energy to be isolated in the test data and in the calculations.

Table 1 lists the barrier impact speeds and the pole moisture contents for the five tests that utilized a non-deformable barrier. This table also lists the actual change in velocity that the barrier experienced in each test (up to the point of pole fracture), the post-fracture barrier speed, and the actual energy dissipated in fracturing the pole. Table 2 lists the barrier impact speeds and the pole moisture contents for the two tests that utilized a deformable barrier. All five of the crash tests with the non-deformable barrier resulted in complete fracture of the pole. Of the two tests with a deformable moving barrier, one pole fractured (Test #4 @ 33.2 mph) and one did not (Test #6 @ 14.8 mph impact speed).

Figure 2: Flow Chart Summarizing the Kent and Strother Method www.collisionpublishing.com

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Table 1: Non-Deformable Moving Barrier Tests with a 12% moisture content, and the sixth and seventh for the actual reported moisture contents, with the adjustment being made using Equation (8). The adjusted values based on the actual moisture contents were the ones actually used in the calculations. Tables 4 lists similar values for the longitudinal modulus of elasticity and Table 5 for the radial modulus of elasticity.

Table 2: Deformable Moving Barrier Tests

After calculating a range for the fracture initiation energy, Equation (9) was used to calculate the total fracture energy, since all of 5 of the poles fractured completely. Since Calculations for the Tests with the Non-Deformable these poles were made of southern yellow pine, there was Barriers: Equations (5), (6), (7), and (8) were used to calno need to adjust the energy calculated with Equation (9). culate the dynamic fracture initiation energy for the poles Table 6 lists the actual ∆V and energy dissipation during involved in the tests with the non-deformable barriers. the pole fracture for each of the non-deformable barrier There are four species of southern yellow pine (shortleaf, tests along with the range of these values calculated usslash, longleaf, and loblolly). Croteau did not report of ing the Kent and Strother approach. For all five cases, the which species the poles in his tests were constructed. Thus, entire range of calculated fracture initiation energies was in obtaining material properties from the Wood Handless than the total fracture energy, as would be expected. In book, the low and high values were obtained amongst these all but one case, the total fracture energy calculated with four species and used to establish a low-end and high-end Equation (9) overestimated the actual total fracture energy. calculation of the dynamic fracture initiation energy. Table However, all of the calculated barrier velocity changes were 3 lists the range of values employed in the analysis for the within 0.9 mph of the actual value. modulus of rupture. The second and third columns list this modulus for green wood, the fourth and fifth for wood

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Table 4: Range of Values for the Longitudinal Elastic Modulus Calculations for the Tests with the Deformable Barriers: Similar calculations were carried out for the cases involving deformable moving barriers. However, for these cases, in addition to using Equations (5), (6), (7), and (8) to calculate the dynamic fracture initiation energy for the poles, Equation (3) was also used to calculate the equivalent barrier speed for the crushing of the barrier. For the test at 14.8 mph (Test #6), Equation (3) yielded an equivalent barrier speed of 13.2 mph, with a range of 8.2 to 18.2 mph. The mean of this range is 1.6 mph below the actual impact speed, but the range encompasses the actual value.

The pole did not fracture in this case and this would likely be an instance in practice where a reconstructionist would neglect the energy that went into deforming the fibers of the pole. In describing the damage to this pole after the test, though, Croteau noted: “Creasing of fibers is apparent in the bumper contact area and outer-layer fibers on

Table 5: Range of Values for the Radial Elastic Modulus the non-struck side began to pull apart in one small area.”

Realistically, there was some energy absorbed by this pole, but it was below the level necessary to initiate fracture.

Application of the Kent and Strother fracture initiation

Table 6: Comparison between Actual and Calculated Values www.collisionpublishing.com

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model to estimate this energy resulted in a speed range for this case of 14.8 to 16.4 mph, a range that contains the actual speed (this range neglects the uncertainty in the calculation of the equivalent barrier speed for the barrier), but generally overestimates it.

For the test at 33.2 mph (Test #4), Equation (3) yielded an equivalent barrier speed of 16.2 mph (11.2 mph to 21.2 mph). Following the fracture of the pole, the deformable barrier was still moving at 27.3 mph. Application of the Kent and Strother model to estimate the energy dissipated in fracturing the pole and combining that energy with the crush and post-impact energies resulted in a calculated speed range for this case of 32.2 to 32.7 mph, 0.5 to 1.0 mph below the actual speed. This range neglects the uncertainty in the calculation of the equivalent barrier speed for the barrier deformation. If this were included, the full range would encompass the actual impact speed. For this case, Croteau reported a total energy dissipation from the barrier crush and pole fracture of 52,327 foot-pounds.

Calculations with Equation (3) and with the Kent and Strother approach to calculating the dynamic pole fracture initiation energy yielded a total energy dissipation between 42,864 and 47,600 foot-pounds.

In instances when the pole fully or partially fractures, the method proposed by Kent and Strother provides a method for calculating the energy absorbed by the pole.

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iscussion and Conclusions When reconstructing a vehicle collision with a wooden utility pole, the following mechanisms of energy dissipation may need to be considered: (1) crushing of the vehicle; (2) full or partial fracture of the pole; (3) moving and tilting of the pole within the ground; (4) acceleration of the pole after a full fracture; and (5) tire, and other dragging forces, acting on the vehicle during its post-impact motion. One assessment that the reconstructionist will have to make for any particular case is the significance of the energy absorbed in fracturing the pole. In instances where the pole does not fracture (even partially), this fracture energy can reasonably be neglected. However, in instances when the pole fully or partially fractures, the method proposed by Kent and Strother provides a method for calculating the likely energy absorbed by the pole.

This study has examined the degree to which the Kent and Strother method can reasonably be relied on to accurately predicted pole fracture energies. To make this assessment, 7 full-scale tests reported by Croteau were utilized. For all 6 tests in which the utility poles fractured, the Kent and Strother model predicted a fracture initiation energy that was less than the actual pole fracture energy. This is as expected, since the total energy to fully fracture the pole would be expected to be greater than the energy to initiate the fracture. In 4 of the 6 tests in which the utility poles fully fractured, the Kent and Strother method overestimated the total fracture energy. For 2 of the tests with complete fracture, the model underestimated the total fracture energy. For the tests with the non-deformable barrier, all of the calculated barrier velocity changes were within 0.9 mph of the actual value. For the case with the deformable barrier where the pole did fracture, application of the Kent and Strother model to estimate the energy dissipated in fracturing the pole and combining that energy with the crush and post-impact energies resulted in a calculated speed range for this case of 32.1 to 32.6 mph, 0.6 to 1.1 mph below the actual speed (this neglects the uncertainty in the calculation of the equivalent barrier speed for the barrier deformation). For this case, calculations with Equation (3) and with the Kent and Strother approach to calculating the dynamic pole fracture initiation energy yielded an underestimate of the total energy dissipation.

For the case with the deformable barrier where the pole did not fracture, Equation (3) yielded an equivalent barrier speed of 13.1 mph, 1.7 mph below the actual impact speed. Because this would likely be an instance in practice where a reconstructionist would neglect the energy that went into deforming the fibers of the pole, reconstructionists would be likely to slightly underestimate the impact speed (this again neglects the uncertainty in the calcula-

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tion of the barrier impact speed for the barrier crush). Croteau did note some damage to the fibers of the pole after this test. In this case, if a reconstructionist chose to try to incorporate some energy absorption by the pole through application of the Kent and Strother fracture initiation model, the result would be a speed range of 14.6 to 16.3 mph, a range that contains the actual speed, but generally overestimates the actual impact speed. Overall, the Kent and Strother method yielded dissipated energies and ∆Vs that were reasonable, particularly when compared to the possibility of neglecting the energy absorbed by a fully or partially fractured pole, a practice that is unfortunately not uncommon.

stiffness and energy absorbing characteristics based on Lateral Impact New Car Assessment Program (LINCAP) testing [2017]. These tests involve the driver’s door area of the vehicle impacting an 8-inch diameter instrumented pole barrier at a speed of approximately 20 mph. Nordhagen, Warner, Perl, and Kent reported 13 pole crash tests into the rear ends of two 1988 Acura Legends and a 1986 Ford Taurus [2006]. They analyzed the tests and reported stiffness characteristics for the rear ends of the these vehicles.

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eferences 1. Asay, Alan F., Jewkes, Dagmar B., Woolley, Ronald L., “Narrow Object Impact Analysis and Comparison with Flat Barrier Impacts,” Paper Number 2002-01-0552, Society of Automotive Engineers, 2002.

The pole impact data examined in this study was confined to passenger cars. In addition to that, real-world collisions with utility poles can, of course, engage portions of the vehicle other than the front end (the side or rear, for instance). 2. Ault, B. and Toomey, D., "Application of Lateral Pole Impact Force-Displacement Data to the ReconstrucIn cases involving different vehicle types or structures, the tion of Side Impacts with Narrow Objects," SAE Int. analyst would need to apply a different method than that J. Trans. Safety 5(1):2017, doi:10.4271/2017-01described here to determine the equivalent barrier speed 1416. for the vehicle. Durisek, Tanner, Chen, and Guenther examined the structural characteristics of the front end of 3. Carter, Neal, Gray Beauchamp, Nathan A. Rose, a full-size pickup through a series of impacts with a rigid “Comparison of Calculated Speeds for a Yawing and pole at different locations across the front end of the veBraking Vehicle to Full-Scale Vehicle Tests,” Paper hicle [Durisek, 2004; Chen, 2004]. They reported tests at Number 2012-01-0620, Society of Automotive Enginominal speeds of 10, 20, and 30 mph. They showed that neers, 2012. the stiffness characteristics of the body-on-frame vehicle they tested were dependent on impact location.

4. Chen, H.F., Tanner, C.B., Durisek, N.J., Guenther, D.A., “Pole Impact Speeds derived from Bilinear EsWhile this study has focused on frontal impacts, the findtimations of Maximum Crush for Body-on-Frame ings in relationship to the fracture energy calculations Constructed Vehicles,” SAE Technical Paper Number should also be applicable to side and rear impacts, as well.

2004-01-1615, 2004, doi:10.4271/2004-01-1615.

Clearly, application of the analysis techniques discussed here to a side or rear impact with a utility pole would 5. Cofone, Joseph N., The Investigation of Automobile require a different data sets for calculating the crush enCollisions with Wooden Utility Poles and Trees, 2nd ergy for the car. The pole fracture energy model, however, Edition, Institute of Police Technology and Managewould be the same. Varat and Husher described several opment, 2012. tions for quantifying the vehicle crush energy for side impacts with poles [1999]. Warner and Nordhagen reported 6. Cofone, J., Rich A., Scott, J., “A Comparison of Equations for Estimating Speed Based on Maximum Static repeated pole impact tests along the side of a Ford Taurus Deformation for Frontal Narrow Object Impacts,” [2006]. This testing led them to the conclusion that “the Accident Reconstruction Journal, Volume 17, No. 6, front axle and A-pillar regions are much stiffer than the December 2007.

CG and B-pillar areas to narrow rigid pole impact.” Tanner, Chen, Cheng, and Guenther reported a pair of oblique 7. Craig, V.T., “Analysis of Pole Barrier Test Data and side impact tests “in which the only significant variation Impact Equations,” Accident Reconstruction Journal, between tests was the use of a rigid pole barrier in one test, Vol. 5, No. 5, September/October 1993. and the use of a frangible wooden pole in the second test.”

These tests engaged to side of the vehicles in the area of the 8. Craig, V.T., “In-Line and Offset Pole Impact Tests front suspension and wheel arch. The authors concluded of Three Vehicles,” Accident Reconstruction Journal, that “the vehicle suspension is far stiffer than typical side Vol. 7, No. 3, May/June 1995. impact parameters…in fact the stiffness is as much as three times greater.” Ault and Toomey examined side structure www.collisionpublishing.com

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9. Craig, V.T., “Speed Estimation in Head-on Vehicle Pole Impacts,” Accident Reconstruction Journal, Vol. 7, No. 3, May/June 1995.

10. Craig, V.T., “Repeat Pole Impact Tests of Three More Automobiles,” Accident Reconstruction Journal, Vol. 7, No. 5, September/October 1995.

11. Craig, V.T., “Speed Estimation in Head-on Vehicle Pole Impacts - Update,” Accident Reconstruction Journal, Vol. 7, No. 5, September/October 1995.

12. Croteau, Jeffrey, Benjamin Frank, Daniel Peterson, Cleve Bare, George Kyanka, “Timber Utility Pole Fracture Mechanics Due to Non-Deformable and Deformable Moving Barrier Impacts,” SAE Int. J. Passeng. Cars – Mech. Syst. 4(1):279-292, 2011, doi:10.4271/2011-01-0288.

13. Daily, J.G., Daily, J.S., Rich, A.S., “A Method for Vehicle-Wooden Utility Pole Impact Speed Reconstruction,” Accident Reconstruction Journal, Vol. 19, No. 5, Sept/October, 2009.

14. Durisek, N. J., Tanner, C. B., Chen, H.F., Guenther, D.A., “Vehicle Characterization through Pole Impact Testing, Part I: Vehicle Response in Terms of Acceleration Pulses,” SAE Technical Paper 2004-01-1210, 2004, doi:10.4271/2004-01-1210.

15. Kent, Richard W., Charles E. Strother, “Wooden Pole Fracture Energy in Vehicle Impacts,” SAE Technical Paper 980214, 1998, doi:10.4271/980214 16. Nordhagen, R.P., Warner, M.H., Perl, T.R., Kent, R.W., “Accident Reconstruction for Rear Pole Impacts of Passenger Cars,” SAE Technical Paper Number 2006-01-0899, 2006, doi:10.4271/2006-01-0899.

17. Rose, Nathan A., Neal Carter, Gray Beauchamp, “Post-Impact Dynamics for Vehicles with a High Yaw Velocity,” SAE Technical Paper Number 2016-011470, 2016, doi:10.4271/2016-10-1470.

20. Warner, M.H., Nordhagen, R.P., “Development of Pole Impact Testing at Multiple Vehicle Side Locations As Applied to the Ford Taurus Structural Platform,” SAE Technical Paper Number 2006-01-0062, 2006, doi:10.4271/2006-01-0062.

21. Woolley, Ronald L, Asay, Alan F., “Crash Pulse and DeltaV Comparisons in a Series of Crash Tests with Similar Damage (BEV, EES),” Paper Number 200801-0168, Society of Automotive Engineers, 2008.

Footnotes: i. Other energy dissipation mechanisms exist during a vehicle impact with a utility pole – such as energy being dissipated through vibration of the pole or through localized fiber crushing [Kent, 1998]. In cases of full or partial pole fracture, these additional sources of energy dissipation can reasonably be assumed to be captured in the total fracture energy for the pole. In cases where the pole does not even partially fracture, the calculations will typically assume that the energy loss from vibration and localized fiber crushing are negligible. ii. Kent and Strother also proposed a method for instances when the structural properties of the wood cannot be determined. That portion of their study is not covered in this article.

Author Contact Information Nathan A. Rose Director and Principal Kineticorp, LLC Office – (303) 733-1888 Mobile – (720) 839-1995 Email – nrose@kineticorp.com LinkedIn: https://www.linkedin.com/in/nathanarose

18. Tanner, C.B., Chen, H.F., Cheng, P., Guenther, D.A., “Pole and Vehicle Energy Absorption in Lateral Oblique Impacts with Rigid and Frangible Poles,” SAE Technical Paper Number 2008-01-0170, doi:10.4271/2008-01-0170.

19. Varat, Michael S., Husher, Stein E., “Vehicle Crash Severity Assessment in Lateral Pole Impacts,” SAE Technical Paper Number 1999-01-0100, 1999, doi:10.4271/1999-01-0100.

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Autonomous Vehicle Technology Looking One, Five, and Fifteen Years into The Future

An Accident Reconstructionist's Perspective

Luis Flores P.E., ACTAR, CFEI Crane Engineering

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ntroduction I recall a friend of mine asking me about a year ago if I was worried about autonomous vehicles making my job as a vehicle accident investigator essentially obsolete. I retorted: as long as it’s still humans behind the software, there will always be room for, well, human error.

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unctionality As you can imagine, the proliferation of autonomous vehicle technology relies on more than the safety mechanisms introduced by vehicle manufacturers can offer. More importantly, a coordinated effort amongst traffic engineers and the general public is key to its success.

Autonomous vehicle technology operates on the idea that vehicles will be able to: “talk to” or “see” each other; interact with the ever-changing infrastructure they operate on; and account for the non-motorized traffic they encounter (pedestrians, bicycles, wildlife, etc.). Radar and Light Detection and Ranging (LiDAR) technologies sense objects near and far, GPS keeps the vehicle on its route, and computer vision (optics) detect markings and signs along the road.

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evel Up The Society of Automotive Engineers currently identifies six levels of vehicle automation:

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Level 0 is no automation.

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Level 1 is driver assistance (i.e. electronic stability control and adaptive cruise control).

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Level 2 is partial automation (i.e. driver can deactivate automated accelerating, braking and steering and take over).

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Level 3 is conditional automation (i.e. autonomous in limited environments such as freeways).

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Level 4 is high automation (i.e. all environments except severe weather).

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Level 5 is full automation.

xisting Limitations Perhaps the most overlooked item on the autonomous feasibility checklist is cybersecurity. Just last year, WIRED magazine published a story on how a pair of cybersecurity researchers managed to take control of a Jeep Cherokee from its climate control to its audio system. And this year that same pair demonstrated a slew of new attacks perpetrated through the vehicle’s communication network, or CAN bus. It is no coincidence that shortcomings like this one have resulted in a senatorial plan to introduce an automotive security bill in 2015, legislation that would direct the National Highway Traffic Safety Administration (NHTSA) and the Federal Trade Commission (FTC) to establish federal standards to secure personal cars and protect drivers’ privacy.1

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Photo Credit: Texas Instruments

A more obvious and physical deficiency in autonomous vehicle technology is the inability for the distance sensing radar and central computers to operate under perilous weather. A 2014 Hyundai autonomous vehicle competition in South Korea proved just this when on day one of the competition, a Veloster performed a series of tests flawlessly under sunny weather. These varied from following the speed limit to backing into a parking spot. During day two, a rainy and foggy morning, the same vehicle failed more than half of the same tests.

1 YEAR OUTLOOK | The Semi-Autonomous Present Already 2016 has proven to be a year flooded with TV ads on emergency brake assist, or automatic emergency braking, as Volkswagen calls it. Some manufacturers have gone as far as using the word “autonomous” in these ads. Generally speaking, the average driver has a perception and reaction time of 1.5 seconds. This is known as the window of time in which your brain goes from “Oh no!” to when your foot initially touches the brake pedal. Logically, braking time and distance vary based on initial speed. To put things into perspective, a vehicle traveling at 60 mph covers about 130 feet in those 1.5 seconds, more than a third of a football field. In addition to minimizing that time window, the additional pressure applied to the brake pedal when brake assist is activated is vastly larger than that of the average human foot. Eliminating that human factor 76 Collision Magazine - Volume 12 Issue 1

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in an emergency braking scenario has proved so effective in Europe that the European Commission proposed making brake assist standard on new vehicles being sold after 2009.2 Differing from the active brake assist is a passive system known as lane departure warning, designed to keep a distracted or tired driver within the lane markings. This system has naturally evolved into lane keep assist, an active system that will help the driver steer back into position.

While autonomy Levels 4 and 5 are not quite a reality, a start-up company by the name of Faraday Future is scheduled to launch its first hyper-connected electric semi-autonomous vehicle through its Advanced Driver Assistance System (ADAS). These autonomy levels have complex challenges, however. Earlier this year, the Tesla Model S made the news when a driver was killed in a crash with a heavy truck while operating in autopilot mode. As the heavy truck was turning left in front of the Model S, the autopilot sensor failed to detect that an object was ahead due to the trailer’s high ground clearance. In other words, it was a matter of perfect timing exposing an imperfect system.

5 YEAR OUTLOOK | Adventures in Ridesharing It is difficult to dispute the impact that ridesharing services like Lyft and Uber have had on the average commuter. Taxi cab drivers can certainly attest to that. So it wasn’t surprising when, in September of this year, Lyft announced

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Photo Credit: Florida Traffic Crash Report

a partnership with General Motors to launch GM’s first autonomous electric vehicle in 2021. Set to arrive on the market in 2017, the Bolt EV and its all-electric range of 238 miles was built with autonomy in mind. Not to be outmatched, Ford also has plans to embrace full autonomy by 2021 by doing away with steering wheels and pedals altogether on ridesharing vehicles. This year alone Ford is testing 30 autonomous Fusion Hybrid Sedans in California, Arizona and Michigan. Also in September of this year, Uber put the world’s first self-driving car on the roads of Pittsburgh, though a driver was on board for safety reasons.3 Imagine doing away with the minutiae of waiting in line to pick up a rental car and instead having said rental pick you up where you need it. The phrase “We’ll Pick You Up!”4 will take on a whole different meaning. Now imagine getting in the backseat and arriving at your destination without having touched a steering wheel. Rental car companies are set to capitalize from autonomous vehicle technology.

Passenger vehicle crashes can be hazardous enough, but topping out at 80,000 lbs., the catastrophe left behind after most heavy truck accidents is multiplied tenfold. Expectedly, doing away with the liability of an inattentive or sleep-deprived truck driver is appealing to the more than 700 billion dollar a year trucking industry. An additional benefit to the driverless truck is the ability for a fleet www.collisionpublishing.com

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manager to monitor and control fuel economy through telematics. This year the Freightliner Inspiration Truck, the first autonomous commercial truck, was approved for use in Nevada public roads and in April, a fleet of Daimler Trucks clocked 1,200 autonomous miles across Europe.

manufacturers of the water heater, range, furnace and other appliances are put on notice. I predict that the manufacturers of equipment and infrastructure related to object sensing and navigation in the subject autonomous vehicles will similarly be put on notice.

In essence, the lesson is that anything that moves people or goods has potential for autonomy; one that will revolutionize every aspect of business and life from the service industry to emergency vehicle transportation (ambulances, firetrucks, etc.).

Furthermore, what happens when the decision-making aspect of an autonomous vehicle is tasked with deciding whether to protect a pedestrian or its occupant, essentially playing God? An article by MIT Technology Review from July of 2015 touched on this most philosophical aspect of driverless cars, where the ethical rubber meets the technological road. A scenario was posed in which a self-driving car must decide between hitting a child suddenly dashing into the road or running into an oncoming van. The human answer ultimately lies in altruism, but what happens when we are no longer dealing with conventional human decision-making? Ultimately, four primary strategies to avoiding an accident are to accelerate, swerve, stop or do nothing.

15 YEAR OUTLOOK | The Great Curve It took 37 years from the first conception of the airbag in 1952 by John W. Hetrick to its mandatory implementation on new vehicles in 1989. While comparing this safety advancement in vehicle technology to autonomous driving is not a perfect parallel, it can serve as a guideline for what’s to come in the next decade and a half. After all, electronic stability control was introduced in the 1990s.

By the early 2030s, there should be ample studies regarding autonomous vehicle accident statistics. Currently, 92 people die on American roadways each day. That is roughly 30,000 per year. According to NHTSA, 94% of crashes are caused by human error.5 Arguably, it is still too soon to simply label all autonomous vehicles as more intrinsically safe, but as they slowly begin to take over our roads, statistics are slated to favor them. Still, humans are stubborn by nature and, to some extent, there is an unquantifiable joy in taking a ride on a sunny day, which means that even fifteen years from now, with autonomous vehicles ubiquitously available and, with safety statistics likely favoring autonomy, there will still remain a large percentage of human driven vehicles on the road. It is also likely that, much like the wonder of looking up and seeing an airplane in the sky as a child faded over time, so too will the public perception of autonomous vehicles as gleaming and mysterious.

Odds are that a joint effort by the government and private industry will be necessary to remove all non-autonomous vehicles, which will take time. iability Forensic engineering careers like accident reconstruction exist because of liability. So in the event of an accident in the current semi-autonomous stage that we are in, who owns the liability? Is it the vehicle manufacturer’s division in charge of software? And when full autonomy is in place and a collision occurs between two autonomous vehicles, who will own the liability then? It could be akin to the event of a house explosion, where the

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Whole New World Since its inception, accident reconstruction has evolved from a career demanding the application of the laws of physics to vehicular accidents to one requiring a valid and logical interpretation of Event Data Recorder data. Meaning that a vehicle that used to communicate the events of an accident through its damage can now further corroborate said damage with a crash data report containing pre-crash status information ranging from individual tire pressures to the various accelerations experienced.

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As vehicles continue to evolve, so will the approach to investigating the accidents that they are involved in. Accident reconstruction will require a basic understanding of how and why an autonomous vehicle made the decisions that it made during an accident, making a rudimentary understanding in computer language a necessity.

Footnotes: 1.

http://www.markey.senate.gov/

2.

http://www.motorauthority.com/

3.

https://newsroom.uber.com

4.

Registered mark of Enterprise

5.

https://crashstats.nhtsa.dot.gov

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ed w e i v e R Peer

3D Laser Scanners in Crash Testing

Thomas Green Michael DiTallo Eric Paul Kelley Adamson Mike Merolli Brent Munyon Kevin Vosburgh Billy S. Cox, Jr. Robert Anderson David Hallman Eric Moody James Whelan

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bstract A series of motorcycle crash tests was conducted at the 2016 ARCCSI Conference. The crash plan was aggressive, with 27 separate crash tests performed over 3 days. One day of crash testing was open to attendees of the conference. Accurate and efficient data collection was a necessity. A decision was made to use several 3D laser scanners simultaneously during the physical measurement process of the crash tests. The FARO S-120 and FARO X-330 3D scanners were used for these tests.

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ntroduction During the 2016 ARC-CSI Conference, a large group of motorcycle crash tests was performed. An article published in the February 2017 issue of Collision Magazine entitled “Motorcycle Crash Testing: Advanced Boot Camp Was Born” describes the crash testing process and lists the motorcycles used during the testing. Other aspects of the testing pro-

cess and data acquisition results are described in another article in this issue of Collision Magazine. See “Evaluation of the MIDE Slam Stick X As a Low Cost Accelerometer And Data Acquisition System For Vehicle Crash Testing.” The motorcycle crash testing included motorcycle-to-barrier, motorcycle-tostationary vehicle and motorcycle-to-moving vehicle impacts.

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ethods and Materials To ensure the results of any testing are useful, reliable, and repeatable, certain testing parameters must be accurately measured and recorded. For our crash testing, these parameters included vehicle weight, vehicle dimensions (pre and post-crash), vehicle positioning (pre and post-crash), impact speed and crash acceleration. During these motorcycle crash tests, we used the following instrumentation and equipment: custom MIDE Slam Sticks and IST 3-D 6-degree of freedom accelerometers to measure the crash pulse; Intercomp SW-RFX 1500 racing scales to measure vehicle weights; FarmTek Polaris timer, V-Box Sport and Garmin VIRB to measure vehicle impact speeds; high-speed and regular digital video cameras to record the tests, and total stations and 3D scanners to measure physical dimensions.

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Figure 1: FARO X 330 and S 120 3D Laser Scanners Used in This Project

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ackground Laser scanners have proven to be useful in a variety of industries, including construction, archeology, architecture, civil engineering, process industry, reverse engineering and forensics, including crime and crash scenes. Popular brands include FARO, Leica, Riegl, Teledyne, Topcon and Trimble. See Figure 1 for an image of two FARO 3D laser scanners.

3D laser scanner usage in crash reconstruction includes the measurements of crash scenes, including physical evidence, roadway layout, site line obstructions, signage and lighting locations. Measurements of the exterior, interior and undercarriage of the crash damaged vehicles, and undamaged exemplar vehicles, are also easily captured by using a 3D laser scanner.

This paper is not intended to be a detailed discussion about the science of 3D scanning, nor is it intended to be a detailed discussion on how to use scanners and process scan data. Rather, this paper is meant to show how 3D scanners can be used as an effective tool to rapidly collect data in a crash-testing environment. Although Faro scanners were used in this testing, this process can be applied to most 3D scanners.

The crash testing performed at ARC-CSI is unique in that it allows the conference attendees to witness the crash testing live and then go onto the test track area in order to perform their own visual examinations and collect documentation of the crashed vehicles.

For the ARC-CSI motorcycle crash tests we used two 3D laser scanners that quickly and accurately captured the final 82 Collision Magazine - Volume 12 Issue 1

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rest positions of the crashed vehicles and resulting physical test surface evidence, prior to the attendees being allowed into the test areas. Other types of measuring devices, such as total stations, were also used to measure the post-crash rest positions and other physical evidence but were not used as the primary means of data collection in this testing.

The Faro 3D laser scanner is a line-of-sight scanner, so it measures everything that it “sees.” 3D scanning allows rapid and accurate documentation of crash scenes and vehicles. According to published data, the Faro 330 scanner utilized measures with a range of 0.6m to 330m with a ranging error of +/- 2mm and the Faro 120 scanner with a range up to 120m with a ranging error of +/- 2mm at a distance of 25m. Using the scanners allowed post-crash data collection to occur quickly and efficiently. The time between crash tests was kept to a minimum, so that a large number of crash tests could be performed in a relatively short period of time. See Figure 2 for a view of a FARO X330 scanner in use following one of the crash tests.

In addition to the two FARO scanners that we used, several crashes were also documented with a Leica Scanner.

All 10 of the crash tests on the first day of the conference were documented with a Leica total station.

Prior to the actual crash testing, all of the test vehicles were scanned so that we would have accurate undamaged vehicle dimensions. Examples are shown later in this article.

While scanning the post-crash test site, the damaged profiles of the involved passenger cars were also collected.

Once the crashed vehicles were removed from the site, additional scanning of the test site was performed. Future an-

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Figure 2: FARO X330 Scanner In Use Following a Motorcycle-Car-Crash Test alytical work will include the study of motorcycle and car deformation and the potential relation to impact speed.

Thus, accurate vehicle deformation and crush measurements are critical for this future analysis.

the damage to the crash tested Volkswagen (VW). Figure 6 is a scale drawing showing the post-crash vehicle positions and the VW pre-crash position. Figure 6 was created from the orthographic image shown in Figure 4.

esults 3D laser scanning produces a point cloud which typically consists of millions of three-dimensional data points. Additional work is necessary to produce “deliverable” products that can be useful to crash reconstructionists. These “deliverable” products can include point cloud images, orthographic images (created from the point cloud), site drawings, vehicle crush drawings, 3D models and web-based sharing services (which allows the users to make their own measurements within the point cloud).

We relied on the drawings and measurements made from our scans to complete the analysis.

Figures 7 and 8 show scan images from point clouds of undamaged motorcycles used in the crash testing. Figure 9 shows a scan image from the point cloud of an undamaged VW Passat.

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For our use we created point clouds, orthographic images, site drawings and vehicle crush drawings. Examples are shown in Figures 3 through 11. Figure 3 is a scan image showing the final rest locations and damage profiles of the vehicles from one of the crash tests. Figure 4 is an orthographic image from the same crash test showing the final rest positions of the involved vehicles. Orthographic images, like Figure 4, created from the scan data have the photorealistic appearance of an aerial photo, but are actually scaled two-dimensional images. They can be used to make measurements, in most CAD systems, as necessary.

Figure 5 is a scale drawing showing the post-crash vehicle positions. The drawing was created from the orthographic image shown in Figure 4. Note that Figure 5 also shows

Figure 10 shows an orthographic image of an undamaged car, prior to a crash test. This orthographic image was cre-

3D laser scanning produces a point cloud which typically consists of millions of three-dimensional data points

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Figure 3: Scan Image of Post-Crash Test Vehicle Locations

Figure 4: Orthographic Image Created From the Point Cloud of Motorcycle-to Volkswagen (VW) Passat Crash Test Scans

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Figure 5: Scale Drawing Made From Orthographic Image Showing Final Rest Positions of Crash Test Vehicles. This Drawing Also Shows the Damage to the VW and Motorcycle

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Figure 7: Scan Image of An Undamaged Motorcycle Point Cloud, Shown Pre-Crash

Figure 6: Scale Drawing Made From Orthographic Image Showing Final Rest Positions of Crash Test Vehicles and VW Pre-Crash Position

Figure 8: Scan Image of an Undamaged Motorcycle Point Cloud, Shown Pre-Crash

Figure 9: Scan Image of an Undamaged Crash Test Vehicle Point Cloud, Shown Pre-Crash

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Figure 10: Orthographic Image of a Test Vehicle Point Cloud, Shown-Pre-crash

Figure 11: Scale Drawing Made From the Orthographic Image Shown in Figure 10 ated from the point cloud of the exemplar vehicle. Figure 11 shows the scaled drawing made from the point cloud of the undamaged car.

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ummary The use of 3D laser scanners for crash testing documentation allows researchers to quickly and accurately gather critical data. This allows a large number of crash tests to be performed in a short period of time while measuring a far greater amount of 3D points as compared to other methods. The point cloud allows the user to virtually revisit the crash scene and take measurements as needed. However, properly identifying and marking the associated physical evidence is recommended.

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cknowledgements A special thanks to Harley-Davidson, FAST Towing, Daniel Vomhof, Jim Byrne and our sponsors for all their project support.

A special thanks to all the members of the 2016 ARC-CSI motorcycle crash team (alphabetically).

Kelley Adamson, Robert Anderson, Billy S. Cox, Jr., Team Leader Michael DiTallo, Jim Dunlap, Thomas Green, Wesley Grimes, Rusty Haight, Sean Haight, David Hallman, Thomas Lawson, Michael Merolli, Eric Moody, Jim Morgan, Brent Munyon, Eric Paul, William Redfairn, Tim Reust, Michael Rosenfield Kenneth Salisbury, Kevin Vosburgh, and James Whelan.

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ed w e i ev R l ia r o t Edi

FAST APPROACH TO BUILDING SOLID CASES

LASER SCANNING PROVIDES IMPORTANT BENEFITS FOR INVESTIGATORS Chad McFadden

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Trimble od Green has been doing accident and crime scene reconstructions for 14 years. In addition to collecting and analyzing information, Green is working to improve the reconstruction process on-scene and in the office. His work is drawing attention in Washington and surrounding states.

A 21-year veteran with the Washington State Patrol (WSP), Green is using his experience and knowledge to simplify and speed the work in collecting and analyzing information and evidence at accidents and crime scenes. Green’s blend of high-tech hardware and software tools together with common sense approaches has produced measureable improvements in scene reconstruction.

Like many law enforcement agencies, WSP has adopted laser scanning as a tool for scene measurement and documentation; Green has spearheaded the move. He has worked on every aspect of scene reconstruction, from data collection and processing to the production of drawings. But, for Green and others, the technology takes a back seat to the core mission of public safety and law enforcement. “I’m not so concerned with how pretty the point cloud looks as I am with getting the details—all of the details—to accurately gather measurements of the scene for reconstruction,” Green said.

Green believes that laser scanners’ ability to gather vast amounts of information can play an important part in producing reports, drawings and exhibits that contribute to the successful resolution or prosecution of a case. But for scanners to become mainstream tools, they must seamlessly blend into the work of people who are already very, very busy.

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ime, Safety and Comprehensive Data

On-scene investigators at fatal collisions and crime scenes face a variety of challenges. They must collect comprehensive information in an accurate, systematic manner. Often working at night or in bad weather, investigators need to capture data quickly while the scene is fresh and before rain or snow can cause evidence to erode or wash away.

Speed is also essential to reduce the duration of road or lane closures, which are costly and inconvenient to the public. According to a 2015 report by the National Highway Transportation Safety Administration (NHTSA), costs attributed to congestion caused by fatal crashes in 2010 including travel delay, excess fuel consumption, greenhouse gases and pollutants totaled $189 million.

On average, a fatal collision resulted in a closure of nearly 3.75 hours. By using laser scanners for data collection, Green and his WSP colleagues demonstrated that they could reduce the time on site while significantly increasing the quality and quantity of information they gather.

Collision investigators must also guard their own safety. In many incidents, they are working near traffic or other hazards. Other measurement methods such as total stations and baseline-and-offset

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techniques may require several people to capture and record the data and can result in closing more lanes. Total station measurement often requires someone else at the site to hold the prism rod; that person could be working on some other aspect of the investigation.

But large point clouds come with their own challenges. “There are people who look at a point cloud and say they can’t see the details,” Green said. “That is usually because it wasn’t scanned or processed correctly. We want to avoid the trap of not seeing the evidence for the cloud. We do not want just a huge cloud; we want better manageGreen knows of some jurisdictions that have ment of the cloud.” The solution comes from inclosed busy street or arterial for 6 hours or more tegrating the processes from collection through to to accommodate measurements with a total sta- final reports. tion. In contrast, a laser scanner, which operates autonomously, can reduce the time and number That integration begins in the field, where WSP of people needed for measurement and documen- uses a Trimble TX5 scanner. The scanner simplitation while also lessening exposure to traffic. fies the work for scene investigators by providing preset scanning modes that capture data at differIt’s not just the work in the field. In addition to ent levels of resolution. Similar to preset modes on-scene measurements, reconstructors must also on a digital camera, users can select the scanning manage and process the data to produce the in- mode to fit the detail needed at each setup on the formation needed by investigators and district site. Green has developed guidelines for WSP inattorneys. They need to focus on the pertinent vestigators that suggest which mode is appropridetails while maintaining data integrity and the ate for capturing different types of details and evichain of evidence. Their finished products are ex- dence. “We like the presets,” he said, “because we hibits, reports and analyses that provide the basis can teach our people what mode to use in a given for the accurate depiction of the scene and events. situation without having to calculate resolution.”

Green has developed a combination of hardware, Scanning at higher resolution requires a bit more field procedures, software and data management time but can capture small details. “I might need that reduces time on site and yields greater depth to capture shell casings or faint tire marks; for of detail throughout an investigation. that we might scan at high-resolutions,” Green explained. “But for other setups we can run at orensic Scanning: Focus on Evidence To some degree, scanners have been uti- lower resolution, which is much faster. We can lized in scene reconstruction for nearly 20 gain a lot more detail much faster, by as much as years. A scanner uses laser technology to 2/3rds than with other scanners.” collect a large number of closely-spaced measure- When data from the scanner arrives in the ofments and produce a “point cloud” of 3D points. fice, detectives use Trimble RealWorks software By setting the scanner in several locations around to combine the scans and begin analyzing the a scene, investigators can capture multiple point scenes. The software can use “plane-based” and clouds to develop a 3D snapshot of the location. “cloud to cloud“ registration to merge multiple Even small or subtle features such as shell casings scans—the technique helps reduce the need for or tire marks can be captured using the scanner on-scene investigators to handle the spherical tarand point cloud. gets commonly used in many scanning projects.

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After the on-scene work is complete, the scan data is transferred to office computers for archival and processing. The multiple scans are combined into a single point cloud, which provides a complete view of the scene.

Although target spheres are needed in some situations, Green said the plane-based and cloud to cloud approach is much simpler and faster for field investigators—so much so, it’s become the default method.

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Figure 1: A point cloud of a collision scene. Parasite images of troopers are caused as personnel moved through the scene during scanning.

Figure 2: After parasite points are removed, investigators can focus on pertinent information.

The removed points are kept in a layer that can be switched off.

Eliminating the targets is just one way the software component of the integrated system helps make the job of on-site personnel and office faster and easier. For example, even when working at low resolution the scanner may collect thousands of points on a road— far more than needed to correctly depict the surface. The software can reduce the 90 Collision Magazine - Volume 12 Issue 1

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density of the points to preserve the accuracy of the information while eliminating clutter that could potentially distract or confuse a jury.

According to Green, the main advantage of RealWorks is the cleaning of unneeded points. Because troopers need to

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work within the scene and traffic during scanning, they are sometimes measured by the scanner resulting in superfluous or “parasite” points.

The software’s Auto Classification function can place designated objects (ground, poles, vegetation, buildings) into designated layers and also remove the parasite measurements from the finished point cloud. The feature allows for quick processing to finalize the cloud by removing all unneeded measured points.

With the main point cloud in place, the office work moves to the phase of creating reports and diagrams. Using EdgeFX reconstruction software, Green can create drafted maps and models in 3D. Points that are superfluous or irrelevant to the case can be moved to separate layers that are switched off, but are still preserved to meet the essential chain of evidence requirement while and maintain integrity of the scene’s data. When the point clouds are completed, the clouds and analyses can be supplied to prosecution teams.

RealWorks includes simple viewing software that enables attorneys to view and “walk through” a point cloud to gain a detailed understanding of a scene.

Figure 3: WSP Trooper Rod Green inspects multiple views of point cloud captured at a collision scene. The point cloud can be used for analysis, modeling and animation to recreate the collision.

At a second location, officers investigated a vehicle collision that also included a shooting. Although capturing the complicated scene required 31 separate scan setups, The reconstruction software enables Green to add evi- Green estimated the scanning was completed in less than dence markers, vehicle models, trajectories and more—it two hours. When the scan data arrived in the office, he can even simulate how cars are crushed in a collision. The needed only six hours to perform the registration, cleanup information can be used to produce diagrams and anima- and drafting. Depending on the review process, Green said tions for courtroom presentations or can be sent to other that the entire timeline to produce a full report could be systems for specialized analysis. The end result is a concise less than two days. representation of the scene and events—all backed by deOne of scanning’s most valuable features is the ability to tailed, defensible data. preserve a scene while it is fresh and enable personnel to aster Performance to Produce Better Re- revisit the scene “virtually” after the fact. For example, an sults object not deemed pertinent early in an investigation may The speed of the scanning system can be illus- turn out to be important. By using the point cloud, investrated through Green’s experiences. He described tigators can return to the virtual scene at any time. They a recent murder investigation in which a local jurisdiction can use the virtual return visits to extract or confirm dehad mapped the crime scene—a series of trails leading tails on the object and its location long after the on-scene from a trailer park to a swamp. Using a total station, it events and investigation. took three people to do the work. The team needed roughly six hours and required five setups of the total station. The key to Green’s success lies in his understanding of They captured a total of 600-700 points just to produce what goes on at the scene and beyond. By using a holistic the drawing. To demonstrate the power of scanning, they approach to reconstruction data collection and analysis, repeated the mapping using the TX5 scanner. The work in Green is helping to simplify the work of officers in the field the field required only 75 minutes and captured the same and office alike. His work is enabling investigators to comtrails. With millions of points instead of a simple drawing, plete their work faster, more safely and with better results. the team produced a full 3D point cloud ready for drafting that contained far greater detail than the total station work.

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ed w e i v e R Peer

Evaluation of the as a Low-Cost Accelerometer and Data Acquisition System for Vehicle Skid Testing David Hallman, Robert Anderson, Billy S. Cox, Jr., Kevin Vosburgh, Kelley Adamson, Thomas Green, Mike Merolli, Brent Munyon, Eric Paul, Eric Moody, James Whelan, and Michael DiTallo

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bstract This study was conducted as a continuation of the testing outlined in the Collision Magazine article “Evaluation of the MIDÉ Slam Stick X as a LowCost Accelerometer and Data Acquisition System for Vehicle Crash Testing” (Volume 10, Issue 2). The purpose of the study was to evaluate the use of a customized MIDÉ Slam Stick X and a new, unmodified Slam Stick S (Figure 1) for vehicle performance analysis such as skid testing.

eter-based device. The Vericom VC4000DAQ (Figure 2) used for this analysis is a stand-alone data acquisition and collection system. The MIDÉ Slam Stick also contains both an accelerometer and data acquisition system. The purpose of this study was to compare data collected with the Slam Stick X, the new Slam Stick S and the Vericom VC4000DAQ, and to evaluate the Slam Sticks as a tool for skid testing.

Skid testing was conducted at a meeting of the 2016 ARCCSI Motorcycle Crash Team on July 30, 2016 and June 10, 2017.

Figure 2: Vericom VC4000DAQ

Figure 1: Customized Slam Stick X and Slam Stick S mounted in one of the test vehicles

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ntroduction Skid testing is commonly conducted to determine the coefficient of friction at a crash location. Although there are a number of methods to determine the coefficient of friction, this is often accomplished using an accelerom-

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Figure 3: Nissan test vehicle

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ethods and Materials The July 30, 2016 tests were performed using the customized Slam Stick X and a Vericom VC4000DAQ during a series of automotive skid tests. The Slam Stick X was customized with a capacitive 200 g MEMS accelerometer and was one of the same units used in the 2016 ARC-CSI Motorcycle Crash Testing.

This test was conducted on a closed stretch of roadway in North Las Vegas, Nevada. The test surface was comprised of asphalt and in excellent (sharp) condition. A 2016 Nissan Altima (1N4AL3AP4GC253202) was utilized as the test vehicle (Figure 3). Multiple tests were conducted with the Antilock Braking System (ABS) activated and deactivated. The ABS was deactivated by removing the ABS fuse.

The ABS light on the dash was on and the tires locked during non-ABS braking. For this testing, the Vericom VC4000DAQ was mounted to the windshield with a suction cup. The MIDÉ Slam Stick X was mounted with double sided tape on a fabricated instrumentation package that had been used for previous motorcycle crash testing.

a range of 100 to 2000 g’s. Data can be collected from the low-g accelerometer at rates up to 3200 Hz and from the high-g accelerometer up to 20 kHz. The Slam Stick S contains two independent data acquisition systems that can collect accelerometer data either individually or simultaneously.

The raw data from the Slam Sticks was downloaded using the Slam Stick Lab™ software. The software default is to export the data with the average or mean removed (subtracted) from the data set to zero (adjust) accelerometer thermal drift. The data set was then exported into a .csv format with the “mean removal” option set to “none” to avoid distorting the data collected over a short time interval. The exported data was zeroed manually, when necessary, by inspecting a portion of the acceleration data where the vehicle was stationary and then adding or subtracting the difference from zero to the entire data set. The Slam Stick software truncates data in the time column, which creates the appearance of unequal time steps. This must be corrected or accounted for in post-processing. In the The June 10, 2017 testing was performed using the cus- Slam Stick software, under File, Recording Properties, and tomized Slam Stick X, a stock Slam Stick S and a Vericom Channel Information, the actual sample frequency for VC4000DAQ during a series of automotive skid tests. The each channel is listed. The inverse of the sample frequency testing was conducted on a quiet section of commercial is the time interval between data points. roadway in Lake Zurich, Illinois. The test surface was worn polished asphalt. A 2017 Hyundai Sonata (5NPE24AF- In this study, the data was imported into DSP Develop3HH569840) was utilized as the test vehicle (Figure 4). ment Corp., DaDisp™ software, so that each data channel Multiple tests were conducted and the ABS activated on could be properly displayed and processed by specifying every test. The instrumentation in this test was mounted the actual time step. Other software, like a spreadsheet, would require replacing or correcting the exported time similarly to the previous testing. column. The Slam Stick data was filtered at 6 Hz for display and comparison with the Vericom data. The 6 Hz filtering was utilized as described in the March 2013 USDOT NHTSA Laboratory Test Procedure for Dynamic Rollover, The Fishhook Maneuver Test Procedure which is also a dynamic test procedure.

Figure 4: Hyundai test vehicle

Data was collected using the Vericom in brake mode which collects data at 100 Hz. That accelerometer data could not be filtered because of its low sampling rate. However, it was exported with a smoothing factor, which can be set from 0 to 9. In this testing, it was set to 3 which is a typical default setting. Based on evaluation of previous data sets, it is presumed that this indicates that data has been smoothed with a moving average consisting of 3 points.

The filtered Slam Stick S and X data was compared to the Vericom data.

The Slam Stick S is MIDÉ’s latest Slam Stick and has two separate accelerometers capable of measuring low frequency accelerations. The low-g accelerometer has a range of 16 g’s and the high-g accelerometer can be specified with

The Slam Stick data collected during the hard-braking portion of the test was extracted and averaged to arrive at the average coefficient of friction and compared to the average of the exported Vericom data. The Vericom reported drag factor(s) is arrived at within the software. The braking al-

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gorithm is activated after the acceleration surpasses the default, user modifiable, -0.2 g’s and stops when the vehicle comes to a complete stop (1). The braking algorithm has been previously shown to accurately report the acceleration of a braking vehicle (2). As such, a Vericom device is an appropriate device to test and analyze the use of the Slam Sticks for coefficient of friction testing. For the 2016 testing the VBOX Sport was used, however because the device is GPS based, the data was not part of this evaluation of accelerometer based devices.

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esults / Analysis The raw data collected from the Slam Stick X appears pixelated and noisy due to the data resolution. Figure 5 shows an example of Slam Stick X data collected during testing of the 2017 Hyundai Sonata.

The data appears coarse with a resolution of only 0.1 g which gives the graphed data its pixelated appearance. As seen in Figure 5, filtering the coarse output data produces a smoother representation of the actual acceleration.

Slam Stick X and Vericom data collected during skid testing of the 2016 Nissan Altima is shown in Figure 6 and

it shows good correlation. The first portion of the graph is about 0.1 g, since the Nissan is still accelerating prior to brake application. The coefficient of friction from the Vericom data was 0.775 g compared to 0.721 g obtained from the custom Slam Stick.

The magnitude of the Vericom acceleration was consistently found to be slightly higher, but with a slightly shorter duration when compared to the Slam Stick data. The duration in the Vericom data can be explained by the way it processes the data, for example, waiting for a -0.2 g activation and when the vehicle comes to a complete stop.

The results from one of the June 2017 hard-braking tests were used for the following data comparison. The Vericom data shows a coefficient of friction of 0.828 g compared to the Slam Stick X at 0.772 g, the Slam Stick S 16 g at 0.856 g and the Slam Stick S 100 g accelerometer at 0.860 g. A comparison is shown in Figure 7 of the results of the acceleration from the Vericom, the custom Slam Stick X, and the high-g and low-g accelerometers in a stock Slam Stick S.

Figure 5: Comparison between filtered and unfiltered Slam Stick X data www.collisionpublishing.com

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Figure 6: Nissan Altima test data

Figure 7: Hyundai Sonata test 96 Collision Magazine - Volume 12 Issue 1

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Figures 8 and 9 show the results of analysis and comparison of the July 2016 and June 2017 testing. The results show that the Slam Stick X was within 10.4% of the Vericom VC4000DAQ data, but consistently under-reported.

Both accelerometers in the Slam Stick S were found to be within 4% of the Vericom VC4000DAQ results.

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onclusions Comparison of the data collected utilizing the Vericom VC4000DAQ and the customized Slam Stick X and Slam Stick S shows good correlation. The Slam Stick data requires additional post-collection processing as described, while the Vericom processes the data internally and reports the coefficient of friction or roadway drag factor directly. The coefficient of friction obtained using the processed Slam Stick X data, and Slam Stick S data was found to compare favorably with the result of the Vericom VC4000DAQ indicating that the Slam Stick is an appropriate device for obtaining roadway coefficient of friction. The data collected utilizing the Slam Stick S more closely matched the Vericom results likely due to the improved resolution of the Slam Stick S over the Slam Stick X. The effective use of a Slam Stick for friction coefficient or other vehicle testing requires use and knowledge of the techniques briefly described within this paper.

A ence.

Tim Reust, Michael Rosenfield, Kenneth Salisbury, Kevin Vosburgh, and James Whelan.

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eferences 1. Vericom Familiarization Traffic Crash Investigation, September 2014

2. Luker, Craig, “Comparison of Devices for Measuring Acceleration vs. Time in Braking Tests”, 2008-01-0180-Society of Automotive Engineer, 2008.

3. Laboratory Test Procedure for Dynamic Rollover, The Fishhook Maneuver Procedure, NCAP, March 2013, USDOT, NHTSA

cknowledgements The authors wish to thank the ARC Network and Collision Safety Institute for making this testing possible during the 2016 ARC-CSI Crash Confer-

Thanks to all the members of the 2016 ARC-CSI motorcycle crash team (alphabetically): Kelley Adamson, Robert Anderson, Billy Cox, Team Leader Michael DiTallo, Jim Dunlap, Thomas Green, Wesley Grimes, Rusty Haight, Sean Haight, David Hallman, Thomas Lawson, Michael Merolli, Eric Moody, Jim Morgan, Brent Munyon, Eric Paul, William Redfairn,

Figure 8: Data comparison summary from July 2016 testing

Figure 9: Data comparison summary from June 2017 testing www.collisionpublishing.com

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