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A new report says crashes have increased in states that legalized recreational marijuana.
The report, published Thursday by the Insurance Institute for Highway Safety (IIHS), cited two studies that compared crash data from a handful of states that approved recreational marijuana to neighboring states that have not enacted marijuana laws. Neither study directly links the cause of vehicle crashes to the use of marijuana.
Washington, Oregon, Colorado and Nevada approved the legalization of recreational marijuana in recent years. The first study by the Highway Loss Data Institute (HLDI) compared collision claims from those four states to claims from Idaho, Montana, Utah, and Wyoming.
HLDI analysts estimate insurance claim rates increased by six percent in the states that sell marijuana. The data compared in the study was collected between January 2012 and October 2017.
"Analysts controlled for differences in the rated driver population, insured vehicle fleet, the mix or urban versus rural exposure, unemployment, weather and seasonality," the report states.
The second study, conducted by IIHS, estimates that the combined rate of crashes per million vehicle registrations in Washington, Oregon and Colorado increased by 5.2 percent.
IIHS researchers compared Colorado with Nebraska, Wyoming and Utah, and they compared Oregon and Washington with Idaho and Montana. The data was pulled from police-reported crashes between 2012 and 2016.
The report acknowledges procedures for drug testing are inconsistent and when drivers are tested it can be difficult to isolate if combined with other drugs. The role of marijuana in vehicles collisions is not as clear as the link between alcohol and crashes.
"Despite the difficulty of isolating the specific effects of marijuana impairment on crash risk, the evidence is growing that legalizing its use increases crashes," said IIHS-HLDI President David Harkey.
