Impact of State Ignition Interlock Laws on Alcohol-Involved Crash Deaths

Background: Despite a range of drunk driving prevention policies and programs, alcohol-impaired drivers are still involved in 1/3 of fatal crashes, killing 11,000 people annually. Ignition interlock devices require a driver to pass a breath alcohol test before starting the car. Interlocks reduce recidivist drunk driving arrests, but their impact on crash deaths is not known. Since 2004, 18 states have mandated interlocks for all drunk driving convictions. We investigated the impact of this universal interlock requirement (UIR) on deaths from crashes involving an alcohol-impaired driver.

Methods: Using publicly available data from the CDC and the National Highway Traffic Safety Administration Fatality Analysis Reporting System, we performed a state fixed effects difference-in-differences analysis of the UIR on alcohol-impaired crash deaths (AICD). We used generalized linear mixed models to account for clustering within states. We included relevant time-varying state characteristics as covariates.

Results: Policy impact was apparent 3 years after implementation. After controlling for year, state fixed effects, state vehicle miles travelled, and additional motor vehicle safety policy changes, adjusted AICD was 6.1 (6.1-6.2) per 100,000 in non-UIR states and 5.1 (4.7-5.5) in UIR states; absolute difference 1.0 (0.6-1.4) per 100,000, p<0.001. This corresponds to approximately 1140 lives saved in UIR states over the study period. There was no significant effect on crash deaths not involving alcohol.

Conclusions: Requiring ignition interlock devices for all drunk drivers led to a decreased rate of drunk driving crash deaths, above and beyond less stringent interlock laws and other drunk driving prevention policies.