The Effect of FMVSS 301R on Vehicle Structure in Rear Impact

Vehicle structures are designed to manage impact forces and transfer crash energy. With the introduction of new rear impact requirements, the design of rear structures has evolved and the use of high strength steel has increased. This study objective was to assess the effect of new FMVSS 301 requirements on vehicle responses. NHTSA conducted 33 offset rear crash tests at 80 km/h with vehicles that pre-dated the newer FMVSS 301R requirements and 86 with vehicles that complied with the newer requirements, with a 2009-2015 model year range. The vehicles were grouped by size and the crush was tabulated. Overall, the struck-side maximum crush decreased in the newer model vehicles. Seven matches with pre and post 301R were identified based on make and model. The matched tests were reconstructed using video analysis and crush measurements of both the barrier and vehicle. Generalized vehicle stiffness was determined for each of the matched tests and indicated that vehicles generally became stiffer with new 301R requirements. The average stiffness was about two-times greater in the post-301R models than in the pre-301R models. The average “B” stiffness was 45.4 kN/cm2 (65.8 lb/in2) and 21.7 N/cm2 (31.5 lb/ in2) respectively. A review of the matched test videos showed greater vehicle structural deformation in the pre-301R vehicles. Occupant kinematics was assessed in two of the matched tests. It showed that the seatback yield occurred earlier in the crash pulse for the post than pre-301R vehicles. A review of the offboard camera views showed greater seatback yield suggesting a decrease in the interaction between the seatback and intruded 2nd row structures with the newer models. The increase in seatback yield is likely due to the decrease in vehicle crush and thus intrusion, as well as an increase in the vehicle stiffness, allowing the seat to yield more completely.