Potential effectiveness of seat belt interlocks
Seat belt interlocks are a vehicle safety technology that aims to increase seat belt usage by restricting the vehicle from being driven until occupants have fastened their seat belts. The aim of this study was to estimate the potential effectiveness of mandatory seat belt interlocks on new vehicles. Three data sets were used to obtain vehicle age profiles for unrestrained drivers: an observational study from 2009 (belt use 98%), hospital admission data from 2008-2010 (belt use 89%), and Coroner’s report data from 2008 (belt use 66%). A hypothetical scenario was considered in which seat belt interlocks were made mandatory in all new vehicle models from 2015 onwards. Under this scenario, the vehicle age profiles from each dataset were used to examine the time it would take for seat belt interlocks to be a feature in vehicles driven by those who would otherwise not be wearing a seat belt. These results were used to calculate a ‘best case’ estimate of the potential effectiveness of seat belt interlocks: by 2030 there would be a potential 2% reduction in injuries requiring hospital admission, and a 7% reduction in fatalities. By 2050 these values would approach 5% and 16% respectively. These reductions would apply on top of any casualty savings already made through enhanced vehicle technologies, infrastructure and regulations. Despite the relatively long time required for interlocks to reach maximum effectiveness, their introduction would have low marginal costs.