Does Cannabis Use Increase the Risk of Vehicle Crashes?

October 4, 2017

Despite some frustrating speed bumps, the tidal wave of cannabis legalization shows no signs of receding anytime soon, and one of its primary benefits—besides access to safe, high-quality and clean marijuana!—is the flood of research following in its wake.

As we’ve reported previously, two recent studies examine the question of what cannabis legalization does for traffic safety and the affect that cannabis use has on drivers. As you’ll recall, one of the main arguments against legalization is that it would make our roads even more dangerous, unleashing a horde of impaired and confused drivers to an already-dangerous environment.

Statistically speaking, driving impaired is dangerous—resulting in at least 10,000 deaths a year in the United States—but what effect cannabis has on these numbers is not entirely certain.

Cannabis and Crashes: By the Numbers

One of the recent studies found an overall rise in automobile accident insurance claims in states with legal weed. The research, commissioned by the Insurance Institute for Highway Safety, found that compared with their neighbors, legal-weed states saw a roughly 3% rise in these claims.

A second, roughly similar study commissioned by the American Journal of Public Health instead zeroed in on traffic deaths. And rather than comparing cannabis-legal states with their neighboring states, it compared them to states with similar populations and traffic patterns, and found “no significant association between recreational marijuana legalization…and subsequent changes in motor vehicle fatality rates.”

Yet other studies have found a decrease in traffic deaths in regions with legal cannabis. As reported last December by Reuters, states that legalized cannabis for medical use experienced a decline in traffic deaths, according to a study analyzing data from 1985 to 2014.

So if the evidence evens out—very roughly speaking—to “not much of a difference,” perhaps there’s a different way to look at the question. On a physiological level, what happens when we imbibe cannabis and get behind the wheel?

Cannabis in the Body: An Increase in Risky Driving?

Studies indicate that cannabis does affect the parts of the brain that regulate body movement, balance, and coordination. And marijuana’s well-documented effect of altering perceptions of time and speed are obvious red flags when it comes to driving and impairment.

That said, other studies indicate that drivers with only small amounts of THC in their bloodstream tend to be more cautious on the road. And habitual cannabis users tend to experience fewer overall adverse effects when it comes to driving, perhaps a result of their bodies’ increased tolerance.

Cannabis and Driving: Tips to Live By

So if cannabis use increases some risks—even if the dangers aren’t necessarily borne out by statistics—what are some steps you can take to ensure you’re not a liability to yourself or others on the road? Here are three to start with:

  • Wait to drive: The effects of cannabis are most pronounced in the first hour after imbibing (though edibles will generally have a later and more powerful effect). 
  • Don’t combine cannabis and alcohol: While alcohol is objectively much more dangerous than cannabis where driving is concerned, the two potentiate, or strengthen their effects, in combination. Don’t fool yourself into thinking cannabis will “soften” the effects of alcohol or that driving while high doesn't affect you. 
  • Respect Local Laws: While roadside cannabis intoxication tests are in their infancy, police have the authority to arrest any driver they suspect of driving impaired. If there’s any doubt you’re not safe to be on the road, don’t chance it.

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