Legalized marijuana linked to spike in vehicle accidents, study finds

Nellie Chapman
October 20, 2018

The HLDI looked at collision loss data from January 2012 to October 2017 in Colorado, Nevada, Oregon and Washington, four states with legal recreational cannabis.

The study said that the frequency of collision insurance claims in Colorado, Nevada, Oregon, and Washington state rose about six percent higher than in nearby states where marijuana is still illegal.

The rates of auto crashes are up by as much as six per cent in Colorado, Nevada, Oregon and Washington where recreational weed is legal, compared to their neighboring states, according to a new report released Thursday by the Institute for Highway Safety (IIHS) and Highway Loss Data Institute (HLDI).

States are quickly moving towards legalizing marijuana. Sales began in October 2015 in OR and in July 2017 in Nevada. They controlled for various factors, including differences in the driver population, insured vehicle fleet, the mix of urban versus rural conditions, unemployment, weather, and seasonality. The findings are being presented at a law enforcement summit organized by the two groups. However, the analysts point out that determining impairment can be a challenge, since unlike alcohol, the threshold for marijuana impairment is not straightforward.

"The new IIHS-HLDI research on marijuana and crashes indicates that legalizing marijuana for all uses is having a negative impact on the safety of our roads", IIHS-HLDI President David Harkey said about the study's results. "States exploring legalizing marijuana should consider the highway safety impact".

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But Harkey admitted that the role that marijuana plays in crashes is much more hard to determine than that of alcohol.

Drivers under the influence of weed tended to weave more when tested in simulators, studies show, although scientists say more research needs to be done to better understand the correlation between blood or oral fluid concentrations and psychoactive effects of tetrahydrocannabinol, the main psychoactive ingredient in cannabis. Policies and procedures for drug testing tend to be inconsistent, and many states don't include consistent information on driver drug use in crash reports.

Investigators found marijuana cigarettes in the truck as well as drug paraphernalia and prescription medication, and a toxicology test detected THC and clonazepam, a sedative, in the driver's system.

In addition to the states in the study, Alaska, California, Maine, Massachusetts, Vermont and the District of Columbia also allow recreational use of marijuana for adults 21 and older, as well as medical use of marijuana.

Recreational use isn't allowed in Arizona, but in 2010 voters approved a proposition making marijuana legal for patients with medical cards.

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