A Supplemental Analysis of Selected Two-Vehicle Front-to-Rear Collisions from the NASS/CDS 2013-01-0223
The National Automotive Sampling System/Crashworthiness Database System (NASS/CDS) is a well-known digital repository containing statistics on hundreds of thousands of vehicle crashes that occurred over the past 30 years. Many of the NASS crashes contain estimates of Delta-v calculated using WinSMASH, a common software reconstruction package. Recent work indicates that WinSMASH typically underestimates Delta-v in frontal impacts, and that inclusion of restitution significantly improves the estimate of Delta-v to within 1% of the value recorded on EDR-equipped vehicles . Prior experiments have shown that in front-to-rear collisions, restitution is a strong inverse function of closing velocity (the difference between the respective pre-impact speeds in the bullet and target vehicles) , with calculated restitutions ranging from 0.265 down to 0.0 for closing speeds varying from 11.4 mph to as high as 36 mph. This work uses front-to-rear impact data from the NASS/CDS to examine the effect of coefficient of restitution on calculated Delta-v values for both the bullet and target vehicles. The WinSMASH-based values of Delta-v and dissipated energy contained in the NASS/CDS were compared to Delta-v values computed using traditional analytical (energy and momentum) equations. With restitution set equal to zero, the mean value of the calculated values of Delta-v (for bullet and target vehicles) ranged between −1.76 and 1.47 percent of the values contained in the NASS/CDS. However, including values of restitution computed iteratively using pre-impact closing velocity increased the computed values of Delta-v for both bullet and target vehicles by an average of 10.38 - 13.17 percent over those provided (in the absence of restitution) by the NASS/CDS. In addition, it was found that small errors in reported values of vehicle mass or dissipated energy (2% - 10%) produced similar or smaller percentage variations in calculated Delta-v values for both the bullet and target vehicles.