IIHS Study Reveals Increase in Crash Rates since Marijuana Legalization

by Gwen Newell
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The North Carolina Senate has advanced a bill (S.B. 711) that would legalize medical marijuana, as the state remains one of the few holdouts in the country without such a law – and with other states beginning to legalize the recreational use and retail sale of marijuana, more evidence has emerged that crash rates have gone up as a result of this. A new study by the Insurance Institute for Highway Safety (IIHS) and another by the affiliated Highway Loss Data Institute (HLDI) shows that crash rates spiked with the legalization of recreational marijuana use and retail sales in states like California, Colorado, Nevada, Oregon and Washington.

However, the preliminary results of a separate IIHS study of injured drivers who visited emergency rooms in California, Colorado and Oregon showed that drivers who used marijuana alone were no more likely to be involved in crashes than drivers who hadn’t used the drug. That’s consistent with a 2015 study by the National Highway Traffic Safety Administration (NHTSA) that found that a positive test for marijuana was not associated with increased risk of being involved in a police-reported crash.

More than a third of U.S. states have legalized the recreational use of marijuana for adults 21+ and, not surprisingly, the hefty tax revenues those states are earning have others exploring similar legislation (recent polls indicate that 68 percent of American adults favor legalization). Consumption also appears to be expanding rapidly, with self-reports of past-month marijuana use doubling from 6 percent  to 12 percent of those surveyed between 2008 and 2019.

That’s a potential concern for those who care about traffic safety. Driving simulator tests have shown that drivers who are high on marijuana react more slowly, find it harder to pay attention, have more difficulty maintaining their car’s position in the lane and make more errors when something goes wrong than they do when they’re sober. But these tests have also shown marijuana-impaired drivers are likely to drive at slower speeds, make fewer attempts to overtake and keep more distance between their vehicle and the one ahead of them.

Despite those increases in crash rates, studies of whether marijuana itself makes drivers more likely to crash have been inconsistent. The latest one from IIHS — which used data collected from injured drivers in three emergency rooms in Denver, Colorado; Portland, Oregon; and Sacramento, California — showed no increased crash risk associated with the drug, except when combined with alcohol.

Researchers conducted surveys for more than a year, interviewing and drug-testing more than 1,200 patients in total. The results showed that the crash-involved drivers weren’t any more likely to self-report or test positive for marijuana alone than other drivers who weren’t involved in a crash and were at the emergency room for reasons other than an injury.

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