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

Vehicle structures are designed to manage impact forces and transfer crash energy, in addition to their primary purpose of connecting all the vehicle powertrain, suspension, steering, HVAC, electronics, occupant accommodation, and weatherproofing. 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 88 with vehicles that complied with the newer requirements, with a 2009-2015 model year range. The vehicles were grouped by size and the permanent crush was tabulated. Overall, the struck-side maximum crush decreased in the newer model vehicles. Seven matches with pre and post 301R were identified on the same make and model vehicle of different generations. The matched tests were reconstructed using video analysis and crush measurements of both the barrier and vehicle. Generalized vehicle rear impact stiffness was determined for each of the matched tests and indicated that vehicles generally became stiffer with new 301R requirements, the amount of energy required per cm of rear crush increased. The average stiffness was over two-times greater in the post-301R models than in the pre-301R models. The average “B” stiffness was 46.3 N/cm² (67.2 lb/in²) and 21.3 N/cm² (30.9 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 typically occurred earlier in the crash pulse for the post than pre-301R vehicles, and in pre-301R crash tests greater intrusion of the barrier occurred before seatback movement. A review of the offboard camera views showed a more effective seatback yield suggesting a decrease or lack of interaction between the seatback and intruded 2nd row structures with the newer models. The increased ability for the seatback to 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 effectively.