Analysis of seat belt buckle release forces in post-rollover scenarios: Implications for passenger safety

Seat belts have been in use for nearly 140 years and have a proven track record to be the single most effective tool in reducing fatal and nonfatal injuries in motor vehicle crashes (MVCs). However, belted passengers still contribute to more than 40% of all MVC fatalities. The likelihood of severe injuries and fatalities is significantly greater in rollover crashes. The motivation behind this research is to address some of the contributing factors related to belted rollover fatalities. In the United States, they contribute to about 3% of all motor vehicle crashes but account for almost 30% of all fatalities. The objective of this study was to investigate the ability of adults to unlatch a push-button seat belt buckle in a rolled-over orientation. Fifty-five (55) out of sixty (60) subjects in this study (92%) were able to unlatch their seat belt while in a rolled-over orientation. However, 96% of the female subjects and 83% of the male subjects were unable to exert enough force to exceed the force requirement of 133N specified in Federal Motor Vehicle Safety Standard (FMVSS) No. 209 at any given orientation. For male subjects, a reduction of almost 22%, and for female subjects, a reduction of almost 13% in the mean push force from upright to rolled-over orientation was observed. Results of the study suggest that reducing the maximum buckle release force to 50 N would accommodate the strength capabilities of 95% of subjects to unlatch the seat belt buckle in any orientation. This study emphasizes the need for investigating seat belt standards and regulations, some of which have not been changed since their inception in 1965.