Safety Restraint System Physical Evidence and Biomechanical Injury Potential Due to Belt Entanglement

For more than 20 years, field research and laboratory testing has consistently demonstrated that wearing a seat belt dramatically reduces the risk of occupant death or serious injury in motor vehicle crashes [1, 2]. The injury prevention benefits of seat belts require that they remain fastened during collisions. Federal Motor Vehicle Safety Standards set forth seat belt buckle performance requirements to address buckle performance in accident conditions. However, several theories of buckle release or separation exist including: false latch, inadvertent release, and inertial release. Forensic investigations of vehicle crashes would benefit with diagnostic criteria which could distinguish between a buckle separation, a properly restrained occupant, and an unused or stowed seat belt.

In the unlikely event of buckle separation, entanglement with the webbing would be expected if the occupant moves substantially as a result of the crash forces. This study investigates physical evidence due to entanglement and injury potential to the occupant due to the interaction with an unlatched restraint system in far side collision events. This is accomplished through the analysis of sled tests in which the buckle was intentionally defeated or unlatched prior to testing. Results of the sled tests indicate that identifiable physical evidence on restraint system hardware is likely to be created on the D-ring and/or webbing surfaces. In addition, pressure sensitive film on the arms of the test dummy indicated significant contact stresses and loading patterns due to the interaction of the seat belt webbing and the occupant. The sled test data were then used to create a MADYMO model. The restraint system evidence from the sled tests combined with the MADYMO model analyses provides a strong diagnostic tool for evaluating the lack of restraint use during crashes versus buckle malfunction.