Rear impact accidents primarily involve neck extension injury. The sudden forward motion of the lower torso causes the head to lag the body. This results in the extension injury or whiplash injury, depending on the rate at which the struck vehicle moves forward. The front seat passengers are equipped with various technologies to help prevent the neck injuries in a rear impact scenario. A range of research has been conducted to investigate the effect of various seat design characteristics on the neck injury during a rear impact. The head restraint on the seat limits the backward movement of the head, thus preventing the serious injury. The neck injury is still a major problem for a rear seat passenger. However, very little effort has been made to improve the rear seat crashworthiness performance relating to a rear impact. Surprisingly, the middle rear seat is not required to comply with the FMVSS 202 standard. This paper demonstrates the possibility of a neck hyper-flexion during a rear impact and the mechanism of a facet dislocation injury for a rear middle seat adult passenger. A biodynamic computational model is utilized to simulate the rear impact accident of an adult male. A MADYMO standard Hybrid III 50th percentile ATD is used to simulate a real world rear impact accident. The accident reconstruction is conducted using PC CRASH to analyze the impact orientation and the change in velocity of the struck vehicle. This information along with the crush on the vehicle is used to develop an acceleration pulse to be applied on the occupant. The rear compartment of the subject vehicle was digitized using a FARO arm to recreate the exact seat structure and interior features for the simulation.This study investigates the inadequate performance of the lap belt in conjunction with roof to seat clearance for the middle seat passenger in reducing the injury severity during a rear impact.
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