Citation

Dye D. Collision 2007; 2(2): 46-51.

Copyright

(Copyright © 2007, Collision Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Accelerometers currently are the preferred method of determining roadway/tire drag coefficients. Since many vehicles now include antilock brake systems (ABS), questions have been raised about which friction value obtained from an accelerometer is applied to variously equipped vehicles which undergo a yaw motion or other collision-related event. Accelerometers often provide peak and average friction values; and testing can be performed with or without the ABS enabled. Experience and research have identified variables that affect roadway/tire drag coefficients or friction values. This brings into question which of the accelerometer outputs should be applied to an ABS-equipped vehicle involved in a particular action. This study examines the proper application of the accelerometer outputs to ABS-equipped vehicles and the effect of ABS application to a vehicle involved in a yaw or critical speed sideslip. The tests found that the application of an ABS, during the course of critical speed sideslip, does not affect the ability of the investigator to accurately predict vehicle speed through the chord and middle ordinate method. Additionally, the average friction values of conventional skid tests provided by the accelerometer consistently predicted the actual speed during the critical speed yaw. Conversely, the peak friction values, regardless of the status of the ABS, consistently overestimated the speed of the vehicle. These results seem to dispel the idea that ABS-affected yaw requires friction tests to be performed with an ABS activated. The roadway/locked tire interface provides the great accuracy with the least chance of speed overestimation.