A research letter recently published in the JAMA Internal Medicine Journal examined the correlation between the legalization of recreational marijuana and traffic fatalities. The letter’s authors Kamer & Warshafsky begin with the proposition that marijuana use impairs driving ability. The authors go on to suggests that because there is a correlation between an increase in traffic deaths and the legalization of recreational marijuana, impaired driving must be the cause. The authors of the letter reviewed data collected from four states: Colorado, Oregon, Washington, and Alaska. The authors did not look at traffic deaths in Michigan because there isn’t enough data from Michigan yet.
The authors found that traffic deaths increased by 75 per year in Colorado. The authors did not find an increase in traffic deaths in Washington. Overall, the letter predicts that if every state fully legalizes marijuana, traffic deaths would increase by 6,800 every year in the United States. Time will tell whether Michigan will be like Colorado, and see a large increase in traffic deaths, or like Washington where there was no such increase. And time will also tell if any observed increase in Michigan is actually caused by marijuana impaired drivers. The impaired driving lawyers at the Barone Defense Firm note that correlation is not causation, and that the only thing this letter has established is correlation. The authors admit that much more research is needed on this topic, and that their findings were “mixed.”