Although rear impacts are numerous, most are of low severity and therefore are not frequently sampled in detailed field accident data bases. Only in recent years has there been sufficient data collected to develop a clear picture of injury contact sources and harm distributions for the occupants involved in rear impacts.

Much attention has been focused on reducing severe and fatal injuries that occur in rear impacts by seat design alternatives, primary among which have been proposals to reduce seat back deformation. In this study, field accident data have been evaluated to determine the types of severe and fatal injuries that occur in rear impacts, and their likely injury mechanisms.

Severe and fatal injuries in rear impacts are relatively infrequent. Most severe and fatal rear impact injuries occur in very high energy accidents where seat back deformation is not a factor, either because the injury is the result of other impacts, or because the seat back was supported by deformed vehicle structure. The majority of rear impact Harm is concentrated in non-severe and non-fatal injuries resulting from much more frequent low- and moderate-speed impacts. These data support the conclusion that stronger seat back designs aimed only at reducing severe and fatal injuries may increase exposure to less severe injuries and actually increase the total rear impact Harm.