Restraint System Markings and Occupant Kinematics in Crash Tests With Disabled Seat Belt Restraint Systems

This paper presents an observational study that sought to explore the question of what type of evidence, if any, would be visible on a belt system after a crash at a low severity, or after a crash in which some aspect of the belt system was disabled. Such evidence could be added to the practical knowledge available to the investigator tasked with making a determination of whether a belt system has been used, misused, or has malfunctioned in some way. The study entailed frontal impacts into a barrier angled 30 degrees counter-clockwise. However, to reflect the larger angularity often seen in field accidents, compared to standard laboratory angled-barrier tests, the vehicle was also rotated 30 degrees counter-clockwise, similar to the impactor orientation in the FMVSS 214D test procedure. As with the 214D test, such a configuration re-creates the structural engagement and angularity of the striking vehicle involved in a typical perpendicular intersection collision with both vehicles moving. This common impact mode produces simultaneous lateral and longitudinal loading of the front structure, and much more angular occupant motions as compared to typical laboratory crash tests. A series of three repeated impact crash tests was run, in which the same test vehicle was used for all three tests, rather than using three separate vehicles. Each test included a 50th male dummy in the left front seat and a 5th female dummy in the left rear seat, for a total of six occupant exposures. Each dummy was restrained with a new replacement belt system for each test. In the first test, at 13 mph, both dummies were restrained with a normally functioning seat belt system, with the objective of documenting any marks generated at this lower crash severity. In the second test, at 23 mph, both dummies were fitted with belt systems with defeated buckles. In the third test, at 29 mph, both dummies were fitted with belt systems with disabled retractors. The tests illustrate the effects of crash severity, air bag deployments and belt malfunctions. The resulting physical evidence was documented for each crash test. Occupant kinematics are discussed. When either the buckle or the retractor was disabled, both occupant kinematics and occupant/belt interactions were fundamentally different from what occur under normally restrained conditions. Of course, the specifics of the resulting physical evidence will depend on the nature of the crash, the vehicle (a used 2002 Chevrolet Cavalier in this instance), the occupants, and the belt systems. However, the basic mechanics of the belt/occupant interaction, and the resulting markings documented herein, will help investigators determine whether a hypothesis about belt use, misuse, or malfunction is supported by the physical evidence being examined.