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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.

Three years of data from the Large Truck Crash Causation Study (LTCCS) were analyzed to identify accidents involving heavy trucks (GVWR >10,000 lbs.). Risk of rollover and ejection was determined as well as belt usage rates. Risk of ejection was also analyzed based on rollover status and belt use. The Abbreviated Injury Scale (AIS) was used as an injury rating system for the involved vehicle occupants. These data were further analyzed to determine injury distribution based on factors such as crash type, ejection, and restraint system use. The maximum AIS score (MAIS) was analyzed and each body region (head, face, spine, thorax, abdomen, upper extremity, and lower extremity) was considered for an AIS score of three or greater (AIS 3+). The majority of heavy truck occupants in this study were belted (71%), only 2.5% of occupants were completely or partially ejected, and 28% experienced a rollover event.

Volunteer subject studies in low-speed rear impacts have shown that significant lumbar spine injuries are unlikely in such collisions. Anthropomorphic test devices (ATD) used in low to medium speed rear impact simulations have similarly revealed an unlikely mechanism to cause lumbar spine injuries. However, low back complaints after rear impacts are common in clinical practice. We attempt here to determine the incidence of lumbar spine injuries from actual field data which may provide an insight into the apparent paradox between experimental data and clinical practice. We examined the incidence of all spine injuries in the NASSCDS (National Automotive Sampling System - Crashworthiness Data System) database from 1993 to 2009. We limited the data to only look at rear-end crashes involving two vehicles.