Effect of Delta-V Errors in NASS on Frontal Crash Risk Calculations

The most important factor in predicting the risk of injury or death in a frontal crash is the crash severity, which is expressed as the velocity change, or delta-V, experienced by the vehicle during the crash. The National Automotive Sampling System (NASS) is the largest database in the world linking injury outcomes with delta-Vs, which are obtained from field reconstructions. The accuracy of these reconstructions was assessed by analyzing 228 NASS cases involving single event frontal crashes in which the vehicle’s frontal delta-V was also measured directly by an onboard event data recorder (EDR). Compared to the EDR measurements, the delta-V values in NASS averaged 19% lower with a standard deviation of 8.6 kph. The effect of this error on injury and fatality risk calculations was investigated using NASS data from 1997 – 2006 for frontal crashes with a known delta-V. Injury and fatality risk functions were calculated by curve fitting the distributions of the delta-V values associated with injury and fatality incidence normalized by the fitted crash exposure distribution. Individual delta-V values were linearly scaled to correct for the bias error, and the delta-V distributions were corrected for scatter error using a numerical deconvolution technique. Correcting for delta-V bias error shifted the calculated risk curves to the right and correcting for delta-V scatter error shifted the curves back to the left, but to a lesser extent. The effects of occupant age, gender, and belt use on injury and fatality risk were substantial.