Serious-to-fatal injury to second-row occupants in rear impacts using 1994-2020 field data

Serious-to-fatal injury was analyzed for second-row children aged 0-14 years and adults aged 15 and older in rear impacts by body region, restraint use, and injury mechanism using field data collected by NHTSA.

1994-2015 NASS-CDS and 2017-2020 CISS data were used to investigate the rate for Maximum Abbreviated Injury Scale (MAIS) 3 + F injury in rear crashes involving 1994+ model year vehicles. All second-row occupants were included, irrespective of restraint use and ejection status. The data were analyzed by group: children (0-14 years old) and adults (15+ years old). All available electronic files for seriously injured second-row occupants in the rear impacts were reviewed for mechanism of injury.

The rate of serious injury (MAIS 3 + F) for second-row occupants was 0.93% ± 0.36% in rear crashes; it was 0.76% ± 0.39% for children and 1.22% ± 0.40% for adults. There were 2.8 AIS 3+ injuries per seriously to fatally injured occupant on average. Most serious injuries occurred to the head in children and to the head and chest in adults. Restraint use was only 31.3% for all seriously injured second-row occupants in the rear impacts. It was 45.1% for children and 17.8% for adults. The overall rate of serious injury in rear impacts was 10.0 times higher when unrestrained than restrained overall; it was 5.6 times higher for children and 20.2 times higher in adults. The case review indicated that many young children were improperly restrained or placed in the incorrect child seat. More than 17% of second-row adults were ejected; all were unrestrained. The primary mechanism for child injury was related to intrusion (86.0%). About 14% was not related to intrusion; 12.3% involved the front seat rotating rearward into the child. The primary mechanisms for adult injury differed from those for children; 68.0% was related to intrusion, 21.6% was not related to intrusion, and 10.4% involved ground impact with ejection. Of the non-intrusion-related cases, 19.1% involved acceleration forces injuring the adult and 2.5% involved the front seat rotating rearward.

The primary mechanism for serious injury to second-row occupants in rear crashes was intrusion either by direct force, compression into front components, or acceleration into forward components. The front seat moving rearward was an infrequent cause for injury.