Going into the study, researchers thought crash rates might be higher, as more drivers were assumed to be high. But researchers at Columbia University's Mailman School of Public Health found an 11 percent reduction in traffic fatalities on average in the 23 states and District of Columbia that have enacted medical marijuana laws.
The presence of medical marijuana dispensaries also correlated with fewer traffic fatalities, the study found. The theory is that lower traffic fatality rates might be related to lower levels of alcohol-impaired driving as people, especially younger people, have started substituting smoking pot for booze.
There was little reductions in the traffic fatality rate for people 45 or older, who are disproportionately represented in larger numbers among people enrolled in state medical marijuana programs. The largest reduction in traffic fatality rates in states with medical marijuana laws occurred among drivers ages 15 to 44.