Exploring the role of delta-V in influencing occupant injury severities – A mediation analysis approach to motor vehicle collisions

This study investigates the impact that delta-V, the relative change in vehicle velocity pre- and post-crash, has on the severity of motor vehicle collisions (MVCs). We study injury severity using two metrics for each occupant – the number of injuries suffered, and the probability of suffering a serious or worse (MAIS 3+) injury. We use a cross-sectional set of generally-representative MVC data between 2010 and 2015 as a basis for our research. Collision factors that influence the crash environment are combined with the injuries that were suffered in MVCs. The influence of delta-V is captured using a mediation analysis, whereby delta-V acts as the focal point between crash factors and injury outcome. The mediation approach adds to existing research by presenting a detailed view of the relationship between injury severity, delta-V and other collision factors. We find evidence of competitive mediation, wherein a collision factor's positive association with injury severity is offset by a negative association with delta-V. Neglecting to include delta-V in our study would have let the factor's association with injury severity go undiscovered. In addition, certain collision factors are found to be related to injury severity solely because of delta-V, while others are found to have a significant impact regardless of delta-V. Our results support the multitude of policy recommendations that promote seatbelt use and warn against alcohol-impaired driving, and support the proliferation of safety-enabled vehicles whose technology can mitigate the bodily damage associated with detrimental crash types.