Safety restraint injuries in fatal motor vehicle collisions

The presence of an apparent seat belt mark (SBM) on a car crash occupant is often used as evidence for use of a seat belt at the time of the crash and, conversely, the lack of a SBM is used as an indication that no seat belt was used. This study examined whether there are clear indications of seat belt use to be found at autopsy and evaluated the sensitivity and specificity of apparent SBM and whether the use of a seat belt and seating location affects the type and severity of injuries sustained. Information on the type of injuries sustained and seatbelt use was retrieved from autopsy reports and police reports, respectively, for cases of fatal motor vehicle collisions occurring in Sydney, Australia over a 5-year period. In this study, a SBM was only found on restrained occupants. The proportion of restrained occupants with evidence of a SBM was 36% (sensitivity), whilst unrestrained occupants showed no evidence of a SBM (100% specificity). A SBM was also found to reliably reflect the seating position of the occupant. We conclude that restrained occupants can be expected to show evidence of the seat belt in just over one third of cases and that the absence of a SBM is not necessarily an indication that no seat belt was used. Spurious SBM is very unlikely to be present if the occupant was unrestrained.