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The effects of a gearshift interlock on seat belt use by drivers who do not always use a belt and its acceptance among those who do

Kidd, David G.; Singer, Jeremiah P.; Huey, Rick W.; Kerfoot, Laura B.
Insurance Institute for Highway Safety

Introduction: Seat belts reduce the risk of fatal injury in a crash, yet in 2015, nearly 10,000 people killed in passenger vehicles were unrestrained. Enhanced seat belt reminders increase belt use, but a gearshift interlock that prevents the vehicle from being placed into gear may prove more effective.
Method: Thirty-two people with a recent seat belt citation and who admitted to not always using a seat belt as a driver were recruited as part-time belt users and asked to evaluate two new vehicles. Sixteen drove two vehicles with an enhanced reminder for one week each, and 16 drove a vehicle with an enhanced reminder for one week and a vehicle with a gearshift interlock the following week. A group of full-time belt users who reported always using a seat belt drove a vehicle with a gearshift interlock for one week to evaluate acceptance.
Results: Relative to the enhanced reminder, the gearshift interlock significantly increased the likelihood that a part-time belt user used a belt during travel time in a trip by 21%, and increased the rate of belt use by 16%. Although every full-time belt user experienced the gearshift interlock, their opinions about the acceptance of the technology in a post-study survey were fairly positive and not significantly different from part-time belt users. Six part-time belt users circumvented the gearshift interlock by sitting on a seat belt, waiting for the system to deactivate, or unbuckling during travel.
Conclusion: The gearshift interlock increased the likelihood that part-time belt users buckled up and the rate of belt use during travel relative to the enhanced reminder. The system could be more effective if it prevented circumvention.
Practical applications: An estimated 718-942 lives could be saved annually if the belt use of unbuckled drivers and front passengers increased 16-21%