Rear-Seat Occupant Responses in NHTSA Rear Crash Tests

This study analyzed FMVSS 301 rear impact tests with an instrumented rear-seat dummy. NHTSA conducted 15 FMVSS 301 rear crash tests with an instrumented and belted 50^th Hybrid III dummy in the rear seat. In series 1, there were three repeat tests with the Jeep Liberty and two others, but no onboard camera view. In series 2, there were 8 tests with 2003-2005 MY (model year) vehicles that had rear head restraints. In series 3, there were two tests with 2004-2005 MY vehicles that did not have rear head restraints. There was an onboard camera view of the rear occupant in series 2 and 3. The dummy responses were evaluated and compared to relevant IARVs (injury assessment reference values). Based on the HRMD, the average height of the rear head restraints was 80.4 ± 3.4 cm (31.6″ ± 1.3″) above the H-point. In series 1, the delta V was 24.4 ± 2.0 km/h (15.2 ± 1.3 mph). The upper neck extension moment averaged 28% ± 10% of IARV and the lower neck extension moment was 56% ± 26% with a head restraint. The neck extension angle was −34.2 ± 10.7 deg. In series 2, the rear impact resulted in 27.7 ± 2.7 km/h (17.2 ± 1.7 mph) delta V in vehicles with rear head restraints. It was 28.4 ± 2.4 km/h (17.6 ± 1.5 mph) in the two tests without a rear head restraint in series 3. The upper neck extension moment averaged 37% ± 20% in series 2 with a head restraint and 45% ± 15% without. The lower neck extension moment averaged 47% ± 21% in series 2 with a head restraint and 82% ± 35% without. The head-to-torso extension angle was −23.0 ± 18.1 deg in series 2 with a head restraint and −63.7 ± 0.4 deg without. All but one of the biomechanical responses were below IARV. In four tests with head restraints, the dummy ramped up the seatback and the head interacted with the roof liner. This resulted in neck compression and extension and may be a factor for mid-sized and taller occupants in rear seats with head restraints.