Mechanisms of Injury to Vehicle Occupants Restrained by Three-Point Seat Belts

This paper summarizes the findings of a study undertaken by Transport Canada to examine the primary mechanisms of injury to front seat occupants restrained by conventional three-point seat belt assemblies. The study involved the early retrospective investigation of collisions, in defined geographic areas across Canada, in which at least one occupant involved was fully restrained. The pattern of injury to 314 full restrained occupants who sustained at least one injury at the AIS 2 or greater severity level is examined in the present paper. Overall, the head/face and chest were found to be the most frequently injured body regions. In the case of drivers, facial injuries were invariably associated with the steering wheel, whereas head injury was more likely to be associated with interior side and roof structures. Injuries to the shoulder/chest and pelvic/abdomen regions among drivers were usually associated with direct contact with either the steering wheel or the interior side surfaces. Passengers were found more likely to sustain shoulder/chest and abdominal injuries from the seat belt itself. Injuries to the lower extremity complex consisted largely of knee,lower leg, and ankle-foot fractures. Femur fractures were observed only at the extreme end of the collision severity spectrum. In the absence of any intrusion or rear occupant loading of the front seat back, injuries were generally confined to below the AIS 4 severity level. While further reductions in the incidence of fatal or life threatening injuries will likely necessitate major improvements to the structural integrity of the vehicle itself, there appears to be scope for the further reduction of injuries at the AIS 2 and 3 levels through more careful design of the seat belt and the interior structures.