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Cannabis Legalization Linked To Increased Road Accidents, Study Finds

Though no direct causal link between cannabis use and car crashes has been found, new data suggests accidents increase after legalization.


Ben Taub

Freelance Writer

clockJul 20 2022, 13:32 UTC
Driving under the influence of cannabis
The impact of cannabis legalization on road safety remains debatable. Image credit: Mitch M/

The legalization of recreational cannabis use may be associated with an increase in traffic accidents, according to new research in the Journal of Studies on Alcohol and Drugs. To date, in the US, 18 states plus the District of Columbia have legalized weed for adults over the age of 21, and while the new study only assesses the impact of this legislation in five of these states, the findings are nonetheless worthy of consideration.

The study authors collected data on road accidents in 11 states for the period 2009 to 2019. Of these, Colorado, Washington, Oregon, California, and Nevada all legalized cannabis during this timeframe, while the remaining six states maintained a ban on recreational use.


Overall, traffic crash injuries rose by 5.8 percent in the five states that legalized weed, while fatal accidents jumped by 4.1 percent. Importantly, no such increase was observed in the six control states.

Interestingly, the initial surge in crashes was found to occur immediately after legalization but before the onset of retail sales. Typically, states require a year or more in order to create a legal framework for the sale of cannabis, which means legalization is often followed by a period of time in which the drug is legal to possess and use but illegal to buy or sell.

Data indicates that traffic injuries rose by 6.5 percent after legalization before falling by 0.7 percent once retail sales began. Fatalities, meanwhile, increased by 2.3 percent after legalization and a further 1.8 percent after dispensaries were allowed to open.


Explaining this discrepancy, study author Charles M. Farmer said in a statement that “legalization removes the stigma of marijuana use, while the onset of retail sales merely increases access. But access to marijuana isn’t difficult, even in places without retail sales. Users who previously avoided driving high may feel that it’s okay after legalization.”

A deeper dive into the data revealed that the impact of the new legislation was not uniform across the five states: Colorado, which was the first to legalize, saw a 17.8 percent rise in crashes after both legalization and the onset of retail sales. In California, however, this increase only reached 5.7 percent, while Nevada’s accident rate actually fell by 6.7 percent.

In terms of fatal crashes, Colorado and Oregon experienced increases of 1.4 percent and 3.8 percent respectively, while decreases of 1.9 percent, 7.6 percent, and 9.8 percent were seen in Washington, California, and Nevada.


“The differing crash effects in California and Nevada could be attributable to lessons learned from the earlier states [to legalize],” write the authors. For instance, they say that tougher law enforcement against stoned driving and “more effective public service announcements about responsible use of marijuana” may have helped to reduce the harms associated with legalization.

Regarding the fact that non-fatal accidents appear to have risen more sharply than deadly crashes, the researchers say that stoned drivers tend to compensate by slowing down and keeping more distance from other cars. While this tactic may not be sufficient to prevent crashes, it does at least help to limit the severity of these collisions.

Although the new study helps to highlight some of the obstacles that must be addressed when ending the prohibition of cannabis, Farmer is keen to point out that the data presented is merely correlational and does not prove that legalization causes crashes. “Studies looking for a direct causal link between marijuana use and crash risk have been inconclusive,” he said. 


“Unlike alcohol, there is no good objective measure of just how impaired a marijuana user has become. Until we can accurately measure marijuana impairment, we won’t be able to link it to crash risk.”

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