Effects of lowering the legal BAC to 0.08 on single-vehicle-nighttime fatal traffic crashes in 19 jurisdictions.

BACKGROUND In the past few decades, numerous policies, including those that lower legal blood alcohol concentration limits, have been enacted to reduce alcohol-impaired driving. In the US, 41 states and the District of Columbia have enacted 0.08 per se laws, which specify that if a driver's BAC is at or above 0.08, a violation has occurred even if the driver does not show signs of intoxication. OBJECTIVE We examined effects of lowering the blood alcohol concentration limit to 0.08 per se on fatal traffic crashes in 18 states and the District of Columbia, and whether effects of the law varied by state or by baseline rates of fatal traffic crashes. METHOD Data on fatal traffic crashes were obtained from the Fatality Analysis Reporting System, including all states that enacted 0.08 per se prior to 2001 in the contiguous United States. Effects of the 0.08 law were examined in each state separately, and the overall effect across states was examined using a mixed-model Poisson regression on single-vehicle-nighttime fatal traffic crashes. RESULTS State-specific analyses showed that fatal traffic crashes significantly decreased in three of the 19 states following the introduction of the 0.08 law, prior to adjusting for potential confounders. The mixed-model regression showed a statistically significant 5.2% reduction in single-vehicle-nighttime fatal traffic crashes associated with the 0.08 law across all states, after adjusting for administrative license revocation, the number of Friday and Saturday nights in a month, and trends in all other types of fatal traffic crashes. Findings indicate that the effect of the 0.08 law does not vary significantly by state or baseline rate of fatal traffic crashes in a state, and no significant statistical interaction exists between 0.08 and administrative license revocation policy effects.