Recreational marijuana laws associated with small increase in traffic fatalities

Two new studies find that recreational marijuana laws are associated with small increases in fatalities from traffic accidents in states that have passed them. In one study, researchers looked at data from Colorado and Washington, and found that these laws were associated with an increase of about two deaths per billion road miles traveled in Colorado, but not an increase in Washington. One possible reason for the difference: People may have traveled from states neighboring Colorado (and which don't allow the cannabis sales), whereas Washington's neighbors — Oregon and Canada — themselves later implemented recreational cannabis laws, possibly reducing interstate travel.

In the other study, researchers compared data from the first four states to legalize recreational marijuana — adding Oregon and Alaska — and found a similar increase in traffic fatalities compared to states that didn't have such laws on the books. These findings only represent an association, and the authors of an accompanying editorial write that more research needs to be done to understand how cannabis impairs drivers.