The combination of seat belt use and frontal air bags is highly effective in frontal impacts, reducing frontseat occupants’ fatality risk by an average of 61 percent compared to an unbelted occupant in a vehicle without air bags. Nevertheless, a number of fatalities are still occurring. Whereas the safety community is generally aware of factors that make specific crashes fatal – e.g., extreme crash severity, compartment intrusion, occupant fragility – there is a need for quantitative information on the relative frequency of these factors, and how often they occur in combination.

This study began with in-depth reviews of NASSCDS fatality cases. Case selection was limited to belted occupants in frontal impacts of late-model vehicles equipped with air bags. The reviews focused on coded and non-coded data, and resulted in the identification of factors contributing to the occupant’s fatal injuries. The factors were compiled and analyzed by a team of NHTSA researchers including crash investigation specialists, crashworthiness and biomechanical engineers. Factors were assigned based on their relevance, and emphasized those that have the potential of being addressed through vehicle design improvements.

Many of the fatal crashes occurred under conditions that were considered more severe than what can be reasonably addressed with crashworthiness and restraint technologies. While the physical characteristics of some occupants were found to play a role in their demise, it was more common that the loading conditions from the crash were simply too injurious owing to a reduction in the occupant’s survival space. Impact configurations with insufficient structural engagement or with oblique directions of force frequently result in degradation of structural integrity and occupant trajectories that reduce the effectiveness of restraint systems even in moderate-severity crashes. The findings of this study indicate that corner impacts and oblique frontal crashes should be a priority area for future research.