PISCATAWAY, N.J. — Legalizing cannabis in the United States is linked to an increase in car crashes and traffic-related deaths, according to a new study. Specifically, researchers say the number of fatal crashes jumped by four percent in five states that permit recreational marijuana.
The study reports that number of crashes that led to injury also rose by just under six percent in states with legalized marijuana. Meanwhile, the team did not see a spike in a comparison group of six states that have not legalized the drug.
Fatal crash rates rose by around two percent after cannabis became legal and by the same amount again when shops started selling the drug. Overall, crashes leading to injury rose by six and a half percent after legalization, but fell slightly once marijuana sales began in shops.
“The legalization of marijuana doesn’t come without cost,” says lead researcher Charles Farmer, Ph.D., from the Insurance Institute for Highway Safety in a media release. “Legalization removes the stigma of marijuana use, while the onset of retail sales merely increases access,” Farmer adds. “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.”
The team believes the more pronounced relationship between cannabis and crash injuries, rather than fatalities, may be because some drivers slow down when they drive under the influence of marijuana. They create a larger distance between themselves and other vehicles. Motorists who drive “high” may not be able to avoid a crash at lower speeds, but the accidents that do happen are less likely to be deadly. Earlier studies involving driving simulators have shown that marijuana use can affect reaction time, road tracking, lane keeping, and attention.
Colorado car crashes up the most after legalized marijuana
For the study, the team collected data on traffic crashes and the amount of traffic in 11 U.S. states and from the Federal Highway Administration between 2009 and 2019. Colorado, Washington, Oregon, California, and Nevada all legalized recreational marijuana during the study period.
Arizona, Idaho, Montana, New Mexico, Utah, and Wyoming did not.
The authors adjusted their findings for factors known to contribute to crashes and fatalities, such as including seat belt use and unemployment rate. Colorado had the biggest jump (+17.8%) in crashes leading to injury and California had the smallest (+5.7%) after both legalization and the beginning of retail sales. Nevada’s rate decreased by 6.7 percent.
More fatal crashes occurred in Colorado (+1.4%) and Oregon (+3.8%), but the team found decreases in Washington (-1.9%), California (-7.6%), and Nevada (-9.8%). Dr. Farmer says states thinking about legalizing marijuana should ban people from driving while under the influence.
Researchers note their study shows a correlational, but cannot definitively prove legalized marijuana is responsible for the increase in road deaths and crashes. “Studies looking for a direct causal link between marijuana use and crash risk have been inconclusive,” Farmer concludes. “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.”
The findings are published in the Journal of Studies on Alcohol and Drugs.
South West News Service writer Gwyn Wright contributed to this report.