Changes in Traffic Fatality Rates Identified Following Adult-Use Legalization

Cambridge, MA: A pair of studies published in the journal JAMA Internal Medicine report a small but significant uptick in motor vehicle crashes in certain jurisdictions following the enactment of adult-use retail marijuana sales.

In one of the studies, investigators affiliated with Harvard University and New York Medical College assessed motor vehicle accident trends in Alaska, Colorado, Oregon, and Washington as compared to trends in other states that did not liberalize their cannabis laws. Authors reported that law changes were not associated with changes in traffic fatalities in the short-term, but that states experienced changes in the most recent year for which data was available. Their finding is consistent with a 2019 study that similarly reported no attributable changes in traffic fatalities in either Colorado or Washington in the years immediately following legalization, but did identify an uptick five years later.

A second study published in the same journal assessed trends in traffic fatalities in Colorado and Washington over the years 2005 to 2017. The authors of the study reported that the “implementation of recreational cannabis laws was associated with increases in traffic fatalities in Colorado, but not in Washington state.” They speculated that the disparate outcomes may be attributable to a variety of factors, including out-of-state tourism, greater use of cannabis among young adults in Colorado, and greater seatbelt adherence among drivers in Washington.

“Findings suggest that adverse unintended effects of recreational cannabis laws can be heterogeneous and may depend on variations in implementation of these laws (e.g., density of recreational cannabis stores),” authors concluded. “These findings suggest the need for policies, public health programs, and enforcement strategies that will prevent unintended consequences of cannabis legalization, such as increased rates of traffic injuries.”

By contrast, available data does not show an association between the enactment of medical cannabis access laws and an increase in traffic fatalities, with some studies showing a sustained decrease in fatalities following medicalization.

Full text of the studies, “Changes in traffic fatality rates in the first four states to legalize recreational marijuana” and “Association of recreational cannabis laws in Colorado and Washington state with changes in traffic fatalities, 2005-2017,” appears in JAMA Internal Medicine. Additional information on cannabis, driving performance, and accident risk is available online.