Fatal and Severe Injuries in Rear Impact; Seat Stiffness in Recent Field Accident Data

A decade ago, James, et.al. published a detailed study of the available NASS data on severe rear impacts, with findings that “… stiffened or rigid seat backs will not substantially mitigate severe and fatal injuries in rear impacts.” No field accident study has since been advanced which refutes this finding. Advocates of rigidized seat backs often point to specific cases of severe rear impacts in which MAIS 4+ injuries are associated with seat back deformation, coupled with arguments supporting stiffer seatback designs. These arguments are generally based upon laboratory experiments with dummies in normal seating positions. Recent field accident data shows that generally, in collisions where the majority of societal harm is created, yielding seats continue to provide benefits, including those associated with whiplash associated disorders (WAD).

This paper reviews the field accident data to identify from actual accident situations the degree to which rigidified or stiffer seats might affect the injury level of real people in severe and extremely severe rear-end crashes. Harm distributions by injury source, damage extent, and velocity change are presented. Individual case studies are reviewed for accident years between 1979 and 2002. Hard copy cases were analyzed to support the findings from the databases. Individual severe injuries were compared with respect to body region and injury contact source. Harm distributions with severity (delta-V) were presented [8]. Pre-impact out-of-position effects are significant in rear crash injury. The majority of Harm still resides in the lower-severity crashes. Cautions about possible negative net societal effects of stiffer seatbacks remain valid. Recent broad-scale field studies have proven an increased incidence of whiplash injuries related to stiffer seatbacks. Earlier findings are not substantially changed by the more recent data: stiffer seats per se do not reduce the overall incidence of harm due to injury in severe rear crashes.