The Effects of Active and Conventional Head Restraints on Front Seat Occupant Responses in Rear Impacts 2020-01-1217

This study assesses front seat occupant responses in rear impacts with active head restraints (AHR) and conventional head restraints (CHR) using field accident data and test data from the Insurance Institute for Highway Safety (IIHS). 2003-2015 NASS-CDS data were analyzed to determine injury rates in 1997+ model year seats equipped with AHR and CHR. Results indicated that less than 4% of occupants were in seats equipped with AHR. Crashes of delta-V <24 km/h accounted for more than 70% of all exposed front seat occupants, irrespective of head restraint design. Rear crashes with a delta-V < 24 km/h included 35.6% fewer occupants who sustained a MAIS 1-2 injury overall and 26.4% fewer who sustained a MAIS 1-2 cervical injury in vehicles equipped with AHR compared to CHR. In IIHS 16 km/h rear sled tests, the biomechanical response of an instrumented BioRID was evaluated on seats with AHR and CHR. HIC₁₅ and concussion risk were calculated from head acceleration data. Test data with AHR and CHR were matched by make and model. First, older model seats with CHR were compared to models with AHR. Then, the models with AHR were compared to newer models with CHR. These analyses generally showed a reduction in head and upper neck responses with AHR compared to prior generation CHR. Further reduction in these responses was observed in newer CHR compared to prior model AHR, in general. Time at initiation of head contact was 89.1 ±13.7 ms (mean ± standard deviation) with older CHR, 62.4 ± 8.7 ms with AHR, and 60.6 ± 9.0 ms with newer CHR. However, contact duration was longest in the AHR tests. The average seatback deflection was 13.6 ± 3.6 degrees with older CHR, 12.3 ± 3.0 degrees with AHR, and 10.4 ± 3.0 degrees with newer CHR. Similar trends of decreasing concussion risk with between AHR and older CHR were observed, and concussion risk was comparable between AHR and newer CHR. However, the risk of concussion was negligible across all tests. The results from this study underline continuous improvement in injury mitigation, regardless of head restraint design.