Reductions in police-reported injuries associated with Michigan's safety belt law

Abstract

This research measured the effects of Michigan's compulsory safety belt use law on traffic crashes and injuries of various severities. Using time-series methods, the authors analyzed monthly frequencies of crash-induced injuries and fatalities from January 1978 through December 1987. Exposure to risk of occupant injury was controlled statistically by including aggregate frequency of crashes as a covariate in time-series models. Effects of economic conditions on traffic crashes were controlled by including an index of unemployment as a covariate. The following statistically significant effects were associated with the safety belt law: (a) In crashes with minor vehicle damage, there was a 14.6% reduction in B-level injuries, an 11.0% reduction in C-level injuries, and a 13.0% reduction in aggregate (KABC) injuries; (b) in crashes with moderate vehicle damage, there was a 16.8% reduction in A-level injuries, an 11.6% reduction in B-level injuries, a 10.7% reduction in C-level injuries, and a 3.6% reduction in aggregate (KABC) injuries; (c) in crashes with severe vehicle damage, there was a 6.3% reduction in fatalities, an 11.8% reduction in B-level injuries, a 4.7% reduction in c-level injuries, and a 5.8% reduction in aggregate (KABC) injuries; (d) for all vehicle damage severities, there was a 14.0% reduction in B-level injuries, an 8.3% reduction in C-level injuries, and a 6.4% reduction in injuries to front-seat occupants. Based on these results, Michigan's adult safety belt law has prevented 31,710 injuries from July 1985 through December 1988.