Rebound After Rear Impacts

Abstract

Objective: A number of field accident studies have found that rebound is a source for occupant injury after rear impacts. Sled tests were run to investigate occupant kinematics and rebound, including head velocity and displacement with 3 different seats, 2 conventional seat designs, and 1 all belts to seat (ABTS). Methods: Nine rear-end sled tests were run with a belted 50th Hybrid III dummy on a Taurus, Mustang, or Sebring ABTS seat in nominally 16.5, 24.1, and 32.5 km/h rear-end delta Vs. There was no sled braking after the rear acceleration to study rebound from the seat. Dummy kinematics were analyzed from high-speed video and biomechanical responses from triaxial head and chest accelerations, triaxial upper and lower neck loads and moments, and seat belt loads. Peak responses were tabulated during seat back rotation rearward and rebound forward. Ratios of biomechanical and kinematic responses were determined comparing ABTS to conventional seat responses for each delta V. Student's t-test was used to determine significant differences between the ratios of ABTS to conventional seat responses. Results: The rebound velocity of the head varied from 2.9 to 6.8 m/s with respect to the sled. Overall, it was 69 ± 22 percent higher than the sled delta V. It was greatest with ABTS in the highest severity test where seat back yielding absorbed energy and reduced rebound in the conventional seats. The time to maximum forward excursion was significantly shorter with ABTS compared to the conventional seats with a ratio of 0.54 ± 0.34 (t = 6.13, df = 5, P < .001). Conclusions: ABTS seats remain more upright in rear-end crashes and transfer greater load to the occupant during rebound than conventional seats that yield rearward and absorb energy in higher severity crashes. Rebound occurs earlier and at higher velocities with ABTS. This displaces the occupant toward the front interior. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.