This past January, adults in California could line up for the first time to legally buy marijuana for personal, nonmedical use. That is when the nation’s largest state joined seven other states and Washington, D.C., in allowing recreational sales of pot.
While much is known about how alcohol impairs drivers, comparatively little is understood about marijuana’s effect on highway safety. Still, as the number of collisions has gone up nationally in recent years, evidence from insurance claims data in three Western states points to marijuana as a contributor to higher crash risk.
More drivers admit to using marijuana, and it is showing up more frequently among people involved in crashes. Although there is evidence from simulator and on-road studies that marijuana can degrade some aspects of driving performance, researchers have not been able to definitively connect marijuana use with crashes that cause injury or death. However, early evidence suggests that marijuana is leading to higher collision claim frequencies in states with recreational use.
In November 2012, ballot initiatives to legalize recreational marijuana sales passed overwhelmingly in Washington state and Colorado. Voters in Oregon followed suit in 2014. In 2017, the Highway Loss Data Institute published the first study of how legalized marijuana may be affecting crashes reported to insurers in those three states.
Using HLDI data, which is collected from companies representing roughly 85 percent of the private passenger vehicle insurance market, researchers can look at many crashes over time and analyze how risk is changing in the states that legalized recreational marijuana sales compared with nearby states where the law did not change.
The study found that legalized sales in Colorado, Oregon and Washington resulted in collision claim frequencies that were about 3 percent higher than would have been expected without legalization.
Looking at each state individually, HLDI found that the size of the effect varied. Colorado saw an estimated 14 percent increase in claim frequency compared with nearby control states. Washington’s estimated claim frequency increase was 6 percent, and Oregon’s was 4 percent higher.
When states legalize marijuana, it may make pot more socially acceptable. National survey data show that people view driving after using marijuana less negatively than driving after consuming alcohol. The Insurance Institute for Highway Safety recently completed an analysis of roadside survey data gathered over time in Washington. Drivers surveyed in the daytime in the state were more likely to test positive for marijuana after legalized sales of the drug than before. Moreover, drivers who tested positive for marijuana a year after legalization were more likely to admit that they had used the drug recently and less likely to say marijuana impairs driving.
HLDI is continuing to monitor insurance claims data in states that have legalized recreational sales and will be updating results for Colorado, Washington and Oregon soon.
The ongoing analyses indicate the overall effect on collision claims is worsening. Now that California is in the mix, researchers will have a much larger dataset to analyze.
While it is too soon to draw a definitive conclusion, the evidence so far should give states pause on public policy that allows recreational use of the drug. Lawmakers may look favorably on the tax revenue generated by legalized marijuana, but early signals on crash risk are flashing red that this is bad news for highway safety.
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