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In rear-end collisions, occupants move rearward relative to the vehicle interior, while compressing the seatback. In low-energy impacts, the stiffness of the non-frame seat components may influence the kinematic response of an occupant. Previous research has reported seat stiffness from experiments for a limited number of seats. Because passenger vehicle seats have evolved, this current work reports a range of seat stiffnesses for modern passenger vehicles. A portable measuring device to characterize vehicle seat stiffness was built to accommodate a wide range of vehicle types. The device measured simultaneously the force applied to the seat and the displacement of the seat cushion. Seats of sedans, crossovers, sport utility vehicles, minivans, and pickup trucks for model years between 2016 and 2020 were tested using the device. For each seat, three measurements were taken for four different seat regions: upper seatback, lower seatback, aft seat bottom and fore seat bottom.

In low-speed, rear-end collisions, the occupant in the target vehicle moves rearward relative to the vehicle and interacts with the seatback and seat bottom. Due to the direct interaction of the occupant with the seat, seat stiffness can affect the kinematics of the occupant. Generic seat stiffness values are often used as input parameters in computer programs, such as MADYMO, that are used to model low-speed, rear-end collisions and simulate occupant kinematics. To create an accident specific simulation, the model could take into account all aspects of the accident including the person involved, the subject vehicle, and the subject vehicle seat. Recent research has demonstrated that the seat stiffness of the compressible structure of the seat, comprised of foam and springs, can vary between vehicles, and also can vary between regions within a single vehicle seat.

Previous studies have shown that occupant kinematics in lateral impacts are different for near- and far-side occupants. Additionally, injuries to far-side occupants in high-speed lateral impacts have been better documented in the scientific literature; few studies have looked at low-speed far-side occupants. The purpose of this study was to determine the risk of lumbar spine injury for restrained and unrestrained far-side occupants in low- to moderate- speed lateral impacts. The NASS/CDS database was queried for far-side occupants in lateral impacts for different levels of impact severity (categorized by Delta-V): 0 to 8 km/h, 8 to 16 km/h, 16 to 24 km/h and 24 to 32 km/h. To further understand the lumbar spine injuries sustained by occupants in real-world impacts, far-side lateral impact tests with ATDs from the NHTSA Biomechanics Test Database were used to estimate lumbar loads in generic far-side sled tests.