Occupant Dynamics during Moderate-to-High Speed Rear-End Collisions 2020-01-0516

Numerous studies have evaluated occupant kinematics and dynamics in “low-speed” rear-end impacts (delta-V ≤ 8 mph). Occupant biomechanics during “moderate-to-high” speed rear impacts (9 ≤ delta-V ≤ 20 mph) has not been thoroughly examined. This study characterized the motions and forces experienced by the head, neck, torso, hip, and left/right femur during these collisions. The publicly available NHTSA rear-end crash test data were examined. More specifically, the FMVSS 301 Fuel System Integrity tests were used. The test procedure involved a 30 mph moving barrier impacting the rear of the vehicles. Instrumented 50^th-percentile male (N = 47) or 5^th-percentile female (N = 4) Hybrid III ATDs were positioned in the driver seat. Occupant data including head accelerations, upper/lower neck shear and axial forces, upper/lower neck moments, lower neck acceleration, torso accelerations, torso deflection, hip accelerations, and left/right femur axial forces were evaluated and compared to published injury tolerance data. The vehicle accelerations, vehicle delta-Vs, occupant position data, seat angular velocity, seat rotation and seatbelt forces and pullout were also examined. Target vehicle peak accelerations were 22.9 ± 6.7 g, with corresponding delta-Vs of approximately 13.6-19.6 mph. The time histories of occupant kinematic and dynamic parameters and their relationships with respect to the vehicle acceleration profiles were evaluated. For the range of delta-Vs tested, the occupant dynamic response parameters were below the injury assessment reference values (IARVs). Examination of the peak occupant data also indicated strong correlations between several kinematic and dynamic parameters. Examination of the relationship between occupant kinematics/dynamics and dummy position measurements also revealed positive correlations between head-to-head restraint distance (backset) and occupant parameters such as head acceleration and upper/lower neck forces. The present study enhances the existing database of occupant dynamics in rear-end impacts with an emphasis on “moderate-to-high” speed collisions. This information may provide insight into injury mechanisms, occupant mathematical modeling, and aspects of seat and head restraint design.