Study Finds Minor Changes in Traffic Fatalities Five Years Following Adult-Use Legalization

Austin, TX: The enactment of adult-use legalization in Colorado and Washington has been associated with non-significant changes in traffic fatalities, according to data published in the journal Accident Analysis and Prevention.

Investigators with the University of Texas at Austin and the David Geffen School of Medicine in Los Angeles assessed trends in Colorado and Washington in the five years following the enactment of adult-use legalization laws as compared to control states.

Authors reported a slight, overall uptick in traffic fatalities following legalization, finding, "In the five years after legalization, fatal crash rates increased more in Colorado and Washington than would be expected had they continued to parallel crash rates in the control states (+1.2 crashes/billion vehicle miles traveled, but not significantly so."

By contrast, researchers reported that the opening of cannabis retailers was associated with "more pronounced and statistically significant" effects on traffic safety (+1.8 crashes/billion vehicle miles traveled.)

Their findings are inconsistent with trends reported by the same team in 2017 when they "found no significant association between recreational marijuana legalization in Washington and Colorado and subsequent changes in motor vehicle fatality rates in the first three years after recreational marijuana legalization."

Authors suggested that the differing results "might be attributable to the longer follow-up time or to differences in methodology. The previous study included only non-medical marijuana control states and did not adjust for the same population, economic, roadway and traffic factors included in this analysis."

They concluded: "Fatal crash rates increased in Colorado and Washington after recreational marijuana legalization – and specifically after the opening of commercial recreational marijuana dispensaries – when compared with concurrent changes seen in nine control states that maintained stable medical marijuana or anti-marijuana status. … The evidence for increased fatal crashes following recreational marijuana legalization … stands in contrast to earlier studies finding decreases in traffic fatalities following medical marijuana legalization. … [T]hese unexpected findings raise the possibility that legalization of medical and recreational marijuana represent two distinct policy exposures rather than "escalating doses" of the same exposure and pose very different risks. This is an area in need of further study."

Full text of the study, "Fatal crashes in the 5 years after recreational marijuana legalization in Colorado and Washington," appears in Accident Analysis and Prevention. Additional information is available from the NORML fact-sheet, ‘Marijuana and Psychomotor Performance.’