ABS Braking Performance and Steering Input

The introduction of ABS (anti-lock braking systems) in motor vehicles has changed the methods an investigator must use when conducting speed analysis from skid marks. ABS is now standard equipment on most new vehicles sold in today=s market. ABS has improved significantly since its introduction. The systems allow a driver to apply the brakes fully while maintaining steering control to avoid a hazard or lessen a collision. An examination was conducted with 20 different vehicles traveling at known speeds being brought to a straight line stop with a full brake application. Tests were also conducted with evasive and lane change steering maneuvers during full brake applications.

The objectives of the experiments were to establish the coefficient of friction for a number of different vehicles in the described situations and to compare the results of each of the test vehicles and with the known actions of vehicles with standard braking systems. An earlier paper written by Cpl. Eric Brewer, RCMP Kamloops, established 65% of the available road surface coefficient of friction as a necessary adjustment when dealing with ABS systems. With the steering induced tests, an effective coefficient of friction was determined and compared to the available coefficient of friction to determine if the 65% factor was applicable. This adjustment consistently produced minimum speed estimates in vehicles experiencing full braking along with extreme steering input.