Event data recorders in the analysis of frontal impacts

Evaluations of crash protection safety features require measures for quantifying impact severity. Velocity change (delta-V) is the major descriptor of collision severity used in most real-world crash databases. One of the limitations of delta-V is that it does not account for the time over which the crash pulse occurs (delta-t). Late model GM vehicles equipped with event data recorders capture the cumulative delta-V in 10 ms intervals over the crash pulse. Deceleration can be readily calculated from these data and provides a complementary measure of severity that has not previously been available for real world crashes. The relationship between maximum delta-V and deceleration was examined for different vehicle platforms involved in real world frontal impacts and frontal crash tests. Maximum deceleration was observed to be closely correlated to the maximum delta-V. Many late model vehicles are equipped with an event data recorder (EDR) that records the time history of the forward or longitudinal delta-V during the crash pulse (NHTSA website). The recorded delta-V is available for most late model General Motors’ vehicles and can be downloaded using the Crash Data Retrieval System (Vetronix, Santa Barbara, CA). The on-board EDR continuously monitors the vehicle’s acceleration. Every 312 microseconds, the EDR samples the accelerometer and when two successive samples exceed about 2g of deceleration, the airbag deployment algorithm is enabled (AE). Four acceleration samples are averaged over each 1.25 ms period. The resulting values are then integrated to determine the vehicle’s cumulative delta-V. Values of the computed delta-V are stored by the EDR every 10 ms (Chidester et al., 1999).