Front Seat Performance in Rear Impacts: Effect on 1^st and 2^nd Row Occupant Injury

Methods: The study was carried out for rear impact crashes in the 1991–2006 NASS-CDS. Only cases where there was a 2nd row occupant seated behind an occupied front seat were chosen. Serious injury (MAIS 3+F) was determined for the front and 2nd row occupants. The performance of the front seat was determined using eight NASS-CDS investigator categories, including no failure, seat failure of the adjuster, seatback or track-anchor and seat deformation by the occupant or intrusion. The rear crashes were subdivided into four severities (<15, 15–25, 25–45 and >45 mph). The risk for serious injury was determined for each category of seat performance. Next, individual cases were reviewed from the online NASS electronic files to better understand the determination of seat performance by the NASS-CDS investigators. The data analysis was then repeated using 1988–1997 NASS-CDS data to match an earlier analysis and publication.

Results: There were 535,953 weighted cases (641 unweighted) of front-outboard occupants with a 2nd row passenger seated behind in a rear crash. 79.9% of the cases had no seatback failure, 3.1% had a seat performance failure and 10.7% were listed as deformed by the front occupant or intrusion. There were 5,338 seriously injured 2nd row occupants (68 unweighted). The risk for serious injury (MAIS 3+F) was 1.00% for 2nd row and 0.43% for front occupants. With no seat failure, serious injury risks were 0.46% for 2nd row and 0.06% for front occupants. With a failure, they were 7.58% and 2.88%, respectively. With seat deformation, there were 3.33% and 2.54%. Injury risks increased with crash severity. The number of cases of serious injury is limited so no statistical testing was performed. There were only 2 cases with seat failure and 4 with seat deformation in the 25–45 mph category.

Fifteen online cases involving sixteen rear occupants could be downloaded where seat performance was listed as a failure or deformed. In two cases, a seatback failure was noted but the investigators explanations were “the seatback was very reclined at time of inspection” and “seatback reclined when impacted by the occupant.” The photos showed the seat reclined but not broken.

Conclusions: Seat failure is infrequent in rear impacts. Seat deformation occurs by occupant loading or intrusion. Seat failure and deformation are associated with a higher risk of injury to the front-seat occupant and the one seated behind. However, miss-coding of seat performance was noted and there are a limited number of NASS-CDS cases. Some NASS-CDS cases were coded as seat failure but involved only a reclined seatback after the crash, not an actual failure of seat structures.