1.6 Braking System Involvement in Accidents
1.6.2 National Accident Databases – Braking Accident Causation
The national accident databases discussed next contain statistical data that may be used to compare vehicle component/system performance, including braking systems, prior to and after a design change was implemented. For example, a brake engineer may decide to compare the crash involvement of a specific model vehicle before and after an ABS brake system was installed. In order for the data analyst to properly filter the databases, specific information such as road conditions, precrash driver braking and steering maneuver, roadway geometry, or stopped traffic ahead must be provided by the brake engineer.
1.6.2.1 National Accident Statistical Sampling - NASS
NASS is composed of two systems - the Crashworthiness Data System (CDS) and the General Estimates System (GES). Both systems are based on approximately 5000 cases selected yearly from a sample of police crash reports
and investigated in depth. NASS collects detailed data on representative, random samples of minor, serious, and fatal crashes involving passenger cars, pickup trucks, vans, large trucks, motorcycles, and pedestrians (Ref. 1.12).
The following are variables that are brake related:
1. Antilock.
2. Skidding longitudinally.
3. Skidding laterally – clockwise.
4. Skidding laterally – counterclockwise.
5. Mechanical failure, such as brakes, steering, tires, or other vehicle problems.
6. Vehicle Contributing Factors: Brake System.
7. Braking (no lockup).
8. Braking (lockup).
9. Braking (lockup unknown).
10. Releasing brakes.
11. Braking and steering left.
12. Braking and steering right.
13. Braked/slowed.
On vehicles equipped with Air Bag Event Data Recorders, the precrash brake status is shown. Examples of defects not considered safety related are ordinary wear of equipment that has to be inspected, maintained, and replaced periodically such as shock absorbers, batteries, brake pads and shoes, and exhaust systems.
In a particular application NASS was queried to look at certain model-year pickup trucks equipped with vacuum (gasoline engine) or hydro-boost (diesel engine) power brake systems. The hydro-boost system used a single steering pump for both braking and steering assist, and in the case of combined braking-and-steering maneuvers with brake pedal forces greater than 450 to 500 N (100 to 110 lb), the braking system overrides (starves) the steering assist. For the vacuum power brake, the steering pump is used only for steering assist.
The NASS data, when filtered with respect to combined braking right-turn maneuvers in an attempt to avoid the crash, showed 85.1% were diesel engine trucks compared to 14.9% gasoline trucks. In combined braking left-turn maneuvers, the percentages were 38.9% and 61.1%, respectively.
In another case a fatal accident had occurred. The road was wet and an earlier accident caused all traffic to stop. The driver of a 1999 Plymouth Voyager approached the vehicles in front, not realizing quickly enough that they were stopped. He steered to the right, avoiding the stopped traffic, only to crash into a guardrail. His vehicle slid along the guardrail and collided with the trailer of a tractor-trailer. The driver side A-pillar smashed into the right rear corner
of the trailer, killing the driver. Inspection of the mechanical condition of the Voyager revealed no brake or steering system defects. The subject Voyager was equipped with standard brakes, although ABS was available as an option. NASS was accessed to look for 1995-2001 Plymouth Voyagers with and without ABS brakes that were involved in accidents in which the critical precrash event was a stopped vehicle in the lane on wet roads. The numerical codes in NASS identify the following brake system equipment:
1. ABS not available
2. Four-wheel ABS, standard 3. Rear ABS-only, standard
4. ABS standard, wheel location unknown 5. Four-wheel ABS, optional
6. Rear ABS-only, optional
7. ABS optional, wheel location unknown 8. (not used)
9. Unknown
Only codes 1 and 2 need to be considered. The data showed that there were 84.8% non-ABS-Voyagers versus only 4.9% ABS-Voyagers involved in all accidents on wet roads; however, none involved a stopped vehicle ahead.
Readers are cautioned that without a proper accident reconstruction NASS data may be misleading. The most difficult issues in the Voyager case were related to the driver’s pedal force application, because no front brakes locked in the accident (the driver was able to steer his vehicle away from stopped traffic on a wet road) and, if the driver had applied the brakes, would ABS have made a difference in view of the reduced friction (wet road) and short distance in which to stop or lower the impact speed to mitigate injuries?
1.6.2.2 Fatality Analysis Reporting System – FARS FARS is a nationwide census providing yearly data regarding fatal injuries suffered in motor vehicle crashes. FARS data are derived from a census of fatal traffic crashes in the U.S., the District of Columbia, and Puerto Rico.
To be included in FARS, a crash must involve a motor vehicle traveling on a traffic way customarily open to the public and result in the death of a person (occupant of a vehicle or a non-motorist) within 30 days of the crash. FARS was conceived, designed, and developed by the National Center for Statistics and Analysis (NCSA) of NHTSA in 1975 to provide an overall measure of highway safety, to help identify traffic safety problems, to suggest solutions, and to help provide an objective basis to evaluate the effectiveness of motor vehicle safety standards and highway safety programs.
The following are brake-related variables:
Codes “01–19” — These are preexisting conditions not caused by damage in the crash. It refers to the condition of vehicle components as indicated in the police accident report (PAR). The report may indicate that a component, such as the braking system, is inadequate, inoperative, faulty, damaged, or defective.
The condition may be due to owner/user neglect, poor maintenance, tampering, or defective manufacturing. The vehicle condition(s) noted only indicates the existence of the condition(s). They may or may not have played a role in the accident.
Chapter 1 References
1.1 Limpert, Rudy and Franco Gamero, “The Velocity-Time Diagram:
Its Effective Use in Accident Reconstruction and Court Room
Presentations,” The Accident Investigation Quarterly, Issue 48, Fall 2007.
1.2 Strothers, Charles E., “Velocity Histories as An Accident
Reconstruction Tool,” SAE Paper No. 850249, SAE International, Warrendale, PA, 1985.
1.3 Burckhardt, Manfred, Fahrwerkstechnik: Bremsdynamik und Pkw Bremsanlagen, Vogel Verlag, Germany, 1991.
1.4 Limpert, Rudolf, Motor Vehicle Accident Reconstruction and Cause Analysis, Lexis-Nexis, 6th edition, 2009.
1.5 Burckhardt, Manfred, Reaction Times in Emergency Braking Maueuvers, Verlag TUV Rheinland, Germany, 1985.
1.6 Mitschke, Manfred, Vehicle Dynamics, Springer-Verlag, Germany, 1972.
1.7 Limpert, Rudolf, “A Critical Review of Federal Motor Vehicle Safety Standard 105(75) - Its Requirements, Test Procedures and Safety Benefits,” SAE Paper No. 760217, SAE International, Warrendale, PA, 1976.
1.8 Nieman, G., Machine Elements, Vol. 1, Springer-Verlag, Germany, 1981.
1.9 Kuhlman, A., Introduction into Safety Sciences, Verlag TUV Rheinland, Germany, 1981.
1.10 Kuhlman, A., et al., Prognose der Gefahr, Verlag TUV Rheinland, Germany, 1969.
1.11 Forkenbrock, Garrick J. , et al., “NHTSA’s Light Vehicle Handling and ESC Effectiveness Research Program,” Paper No. 05-0221, NHTSA and Transportation Research Center, 2005.
1.12 www.nhtsa.gov/DOT/NHTSA/NCSA/Content/PDF/NASSbrochure.