Voters in Massachusetts approved a referendum in 2016 to legalize the recreational use of marijuana in the commonwealth. It took more than two years, however, for lawmakers to come up with a structure and regulatory system that would allow for legal retail sales. Last week, the first retail stores finally opened with a great deal of fanfare. In fact, in the town of Northampton, the town’s mayor was the first in line to make a purchase at one of the new dispensaries.

While the debate over recreational marijuana has largely focused on criminal laws—and the differences between laws at the state and federal levels—there are other important concerns as well. Two separate studies recently found a statistically significant increase in car accidents in states that have legalized recreational cannabis. Given the geographic proximity of Massachusetts to Connecticut, motorists in the Nutmeg State may have reasons to be worried.

Crash Rates on the Rise

Both studies were presented at the Combating Alcohol- and Drug-Impaired Driving summit hosted by the Insurance Institute for Highway Safety (IIHS) in October. The first study was conducted by the IIHS’s Highway Loss Data Institute and compared crash rates in states where recreational use of marijuana is legal to neighboring states where recreational use is not. Using crash data from 2012 to 2017, the study found that the rate of accidents rose by about 6 percent in Colorado, Oregon, Washington, and Nevada compared to Idaho, Montana, Wyoming, and Utah. The time period was chosen because recreational use was first legalized in Colorado and Washington in 2012.