States that enacted medical marijuana laws, on average, experienced a decline in traffic-related fatalities.

According to a study conducted by researchers at Columbia University's Mailman School of Public Health, states that passed medical marijuana laws saw an 11% reduction in traffic fatalities, on average, after enacting the laws, and had 26% lower rates of traffic fatalities compared with states without the laws. The findings are published online in the American Journal of Public Health.

Specifically, the researchers observed an 11% reduction of among those aged 15 to 24 years, 12% for ages 25 to 44, and 9% for those 45 years and older. Operational dispensaries were also associated with a significant reduction in traffic fatalities in those aged 25 to 44 years at 5%.

Lacking was strong evidence suggesting reductions among those aged 45 years and older, which is also a group overrepresented in the population of patients registered in state medical marijuana programs. "This finding suggests that the mechanisms by which medical marijuana laws reduce traffic fatalities mostly operate in those younger adults, a group also frequently involved in alcohol-related traffic fatalities," said Julian Santaella-Tenorio, a doctoral student in Epidemiology at the Mailman School of Public Health. In 2004 and 2013, 47% of fatally injured drivers with a blood alcohol content of 0.08 or greater were 25 to 44 years old.

The researchers based their findings on data for 1985-2014 from the Fatality Analysis Reporting System, a nationwide census of traffic fatalities information maintained by the National Highway Traffic Safety Administration. The association between medical marijuana laws and traffic fatalities for drivers, passengers, cyclists, and pedestrians was examined for each state enacting the laws. They also evaluated the link between marijuana dispensaries and traffic fatalities. Overall, a total of 1.22 million deaths were attributed to traffic crashes occurring in the 50 states during the study period.

"It is also possible that states with medical marijuana laws and lower traffic fatality rates may be related to lower levels of alcohol-impaired driving behavior in these states," noted Silvia Martins, MD, PhD, associate professor at the Mailman School and senior author. "We found evidence that states with the marijuana laws in place compared with those which did not, reported, on average, lower rates of drivers endorsing driving after having too many drinks. We can also point to other characteristics such as the strength of public health laws related to driving, infrastructure characteristics, or the quality of health care systems, as a partial explanation for these findings."

"The evidence linking medical marijuana laws and traffic fatalities lays the groundwork for future studies on specific mechanisms," said Santaella-Tenorio. "We also expect another area of study will be the association between the laws and nonfatal traffic injuries."

(Source: Colombia University's Mailman School of Public Health)

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