What will legal marijuana mean for Canada’s road safety?

don’t drive stoned.

As you’ve probably heard, recreational marijuana will be legal across Canada come October 17, 2018. Will stoned driving increase? Will this lead to more accidents and fatalities?

We can’t divine the future, of course.  But perhaps we can learn something from the past. Did roads become more dangerous after states began legalizing recreational pot in the U.S.?

The short answer: probably, to some degree.

  • The more stoned a driver is, the more likely she is to be involved in an accident. Motor and cognitive skills are important for safe driving. Getting stoned makes both these skills worse – and the more stoned a person is, the more these skills deteriorate.
  • The number of “THC-positive” drivers on the road increased after legalization. In Washington state, at least. There’s evidence that the percentage of stoned drivers went up noticeably after the state legalized recreational pot.
  • Fatal crashes involving drivers who tested positive for THC increased. Some studies indicate that more people with “detectible” levels of THC in their bloodstreams were involved in fatal accidents after legalization.
  • Collision claim frequency appears to have increased. Early analysis suggests that states with legal marijuana have higher rates of car collisions than they would have had without legalization.

There is an important caveat to all this. You’d think that figuring out when someone is stoned would be easy. It’s not. Unlike alcohol, measuring marijuana impairment is complicated. THC can remain in a user’s bloodstream for days, even weeks, after getting high. Having THC in her bloodstream at the site of an accident does not automatically mean a driver was stoned at the time of a crash.

To make matters worse, to what degree marijuana impacts one person’s driving skills is also not so clear-cut as you’d think. Marijuana impacts different people differently. Researchers are currently trying to figure out how to account for things like THC tolerance when they measure how much marijuana increases crash risks.

But despite these complications, most evidence suggests that stoned driving is a bad idea – it endangers the driver, passengers, and other drivers. For this reason, Canadian provinces have begun revising their impaired driving laws to come down harder on stoned driving.

So what does this mean for road safety in Canada? It’s still too early to tell, but marijuana legalization in the U.S. should serve as a warning.

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