The effects of persistent audible seat belt reminders and a speed-limiting interlock on the seat belt use of drivers who do not always use a seat belt

November 2019

Introduction: Vehicle technologies that increase seat belt use can potentially save thousands of lives each year. Kidd et al. (2018) found that a gearshift interlock was more effective for increasing seat belt use than an intermittent 7-second audible reminder, but interlocks may not be more effective than persistent audible reminders lasting at least 90 seconds. Method: Forty-nine part-time belt users who had a recent seat belt citation and reported not always using a seat belt drove two vehicles for 1 week each. Thirty-three drove a Chevrolet with three intermittent 7-second audible reminders followed by either a BMW with a 90-second audible reminder (n=17) or a Subaru with an indefinite audible reminder (n=16). The other 16 participants experienced the BMW audible reminder followed by a speed-limiting interlock that limited speed to 15 mph during unbelted driving. These data were combined with data from 32 part-time belt users in Kidd et al. (2018) who experienced the intermittent reminder for 2 weeks or the intermittent reminder for 1 week and a gearshift interlock the next. Results: Relative to the intermittent reminder, seat belt use was significantly increased 30% by the BMW reminder, 34% by the Subaru reminder, and 33% by the speed-limiting interlock. Belt use was increased 16% by the gearshift interlock, but this change was not significant. More participants circumvented the speed-limiting interlock to drive unbelted than the audible reminders. Response to a poststudy survey indicated that interlocks were less acceptable than reminders. Conclusions: Audible reminders lasting at least 90 seconds and a speed-limiting interlock were significantly more effective for increasing seat belt use than an intermittent audible reminder, but reminders were found more acceptable. Practical applications: Strengthening existing U.S. safety standards to require audible reminders lasting at least 90 seconds for front-row occupants could save up to 1,489 lives annually.