Marijuana has been shown to impair drivers. Studies evaluating motor vehicle crash (MVC) fatality rates in states following the legalization of medical marijuana have had conflicting results. This study examined MVC fatalities in two states, Washington and Colorado, for the first three years following the legalization of recreational marijuana. MVC fatality rates were not found to be significantly changed after recreational marijuana legalization.
The authors obtained MVC fatality data from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System (FARS). They used a difference-in-differences approach and compared year-over-year changes in fatality rates, before and after the legalization of recreational marijuana in Washington and Colorado. They compared their findings against contemporaneous data from eight control states that had not legalized medical or recreational marijuana.
The authors found that from 2009 to 2015, for all states, the annual MVC fatality rate decreased from 12.8 fatalities to 11.4 fatalities per billion vehicle miles traveled. In Washington and Colorado, MVC fatality rates increased by a mean of +0.1 (±0.4) fatalities per billion vehicle miles traveled and decreased by -0.5 (±0.9) in the control states. However, the MVC fatality rate changes in Washington and Colorado were not statistically significant compared to fatality rate changes in the control states.
This study does not support a statistically significant correlation between MVC fatalities and legalization of recreational marijuana. Yet, policymakers should remain cautious about the study results as marijuana has known intoxicating effects that can impair drivers. Additional, long term studies are needed to determine the effect on MVC fatalities following marijuana legalization.
Commentary by Theresa E. Tassey, MD, MS. She is the Health Policy and Leadership Fellow at the University of Maryland Department of Emergency Medicine.
OBJECTIVES: To evaluate motor vehicle crash fatality rates in the first 2 states with recreational marijuana legalization and compare them with motor vehicle crash fatality rates in similar states without recreational marijuana legalization. METHODS: We used the US Fatality Analysis Reporting System to determine the annual numbers of motor vehicle crash fatalities between 2009 and 2015 in Washington, Colorado, and 8 control states. We compared year-over-year changes in motor vehicle crash fatality rates (per billion vehicle miles traveled) before and after recreational marijuana legalization with a difference-in-differences approach that controlled for underlying time trends and state-specific population, economic, and traffic characteristics. RESULTS: Pre-recreational marijuana legalization annual changes in motor vehicle crash fatality rates for Washington and Colorado were similar to those for the control states. Post-recreational marijuana legalization changes in motor vehicle crash fatality rates for Washington and Colorado also did not significantly differ from those for the control states (adjusted difference-in-differences coefficient?=?+0.2 fatalities/billion vehicle miles traveled; 95% confidence interval?=?-0.4, +0.9).
CONCLUSIONS: Three years after recreational marijuana legalization, changes in motor vehicle crash fatality rates for Washington and Colorado were not statistically different from those in similar states without recreational marijuana legalization. Future studies over a longer time remain warranted.