Some Data Indicates Increasing Accident Rates in Marijuana States

April 1, 2019

Preliminary research indicates that the legalization of recreational marijuana in 10 states has increased accident rates, the Insurance Information Institute said.

The group cited an October 2018 study by the Highway Loss Data Institute that shows collision claim frequency was 12.5 percent higher in Colorado and 9.7 percent higher in Washington than in nearby states that did not legalize recreational use of marijuana. Oregon also had a 1 percent greater rate of collision claims than neighboring states.

“When a state legalizes marijuana, more people use the drug,” according to the institute’s white paper. “More people using marijuana is associated with more people driving with THC in their systems. The standard personal auto policy does not address driving under the influence of any drug, including alcohol and marijuana.

However, auto insurance rates may be affected by the spread of marijuana legalization, particularly if such legalization is associated with an increase in impaired driving and related accidents.”

Much of the institute’s report is based on a study by the Insurance Institute for Highway Safety and the Highway Loss Data Institute released last fall. HLDI analysts estimated that the frequency of collision claims per insured vehicle year rose a combined 6 percent following the start of retail sales of recreational marijuana in Colorado, Nevada, Oregon and Washington, compared with the control states of Idaho, Montana, Utah and Wyoming. The combined-state analysis is based on collision loss data from January 2012 through October 2017.

A separate IIHS study examined police-reported crashes before and after retail sales began in Colorado, Oregon and Washington from 2012 to 2016. IIHS estimates that the three states combined saw a 5.2 percent increase in the rate of crashes per million vehicle registrations, compared with neighboring states that didn’t legalize marijuana sales.

Another study showed an increase in the number of drivers involved in fatal accidents who tested positive for marijuana use. The National Bureau of Economic Research published in March 2018 found that the share of fatal accidents in which at least one driver tested positive for marijuana increased in Colorado and Washington after marijuana was legalized in both states in 2014. In Colorado the fraction of positive tests increased by 9 percent from 2013 to 2016; in Washington the increase was 28 percent in period.

Blood Test

A separate study by the libertarian-oriented Reason Foundation published last September points out that the presence of cannabis in a blood test does not mean the driver was impaired during the accident because THC remains in the blood long after its intoxicating effects subside.

The Reason Foundation’s report, based on a review of available literature, concludes that there is no definitive pattern related to cannabis legalization’s impact on traffic accidents.

“Some studies, especially concerning medical marijuana, suggest that marijuana legalization might actually reduce fatalities by reducing drunk driving,” the Reason Foundation said. “All in all, no conclusive or definitive patterns related to cannabis legalization have appeared in the data or research to this point.”

James Lynch, the Insurance Information Institute’s chief actuary, notes that there is no “breathalyzer” equivalent to detect marijuana impairment.

Research into accident rates has not included California, where recreational use of marijuana did not become legal until January 2018. Janelle Dunham, a spokeswoman for the agency, said its most recent data on collisions is from 2016.

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