Does Legalization Create More Car Accidents Caused By Marijuana?

accidents caused by marijuana traffic light

The growing trend toward legalization of marijuana hasn’t been without consequences. Though not as dire as predicted by some reactionaries, it seems that recreational legalization may have led to an increase in accidents caused by marijuana. Just how much of an increase and whether that increase is entirely due to marijuana legalization is up for debate.

The trouble with measuring the causation of something like traffic crashes is that road accidents are extremely complex, and their causes are unique. We can say for certain after decades of research that drunk drivers — even people below the legal limit for alcohol — cause a huge number of fatal traffic crashes.

We can say this for sure because coroners always test people who died in car crashes for blood-alcohol content. Furthermore, BAC is a standardized, reliable measure of drunkenness.

accidents caused by marijuana BAC chart
Predicting your Blood Alcohol Content (BAC) is as easy as referencing this table. Cannabis intoxication….not as simple.

But coroners don’t always test for marijuana, and when they have in the past, it’s been on a case-by-case basis. This means the data about how much increased marijuana use has led to more car crashes is flawed and incomplete. There’s just no way across the hundreds of jurisdictions with a patchwork of pot testing policies to get solid data on how many crashes can be attributed to weed impairment. Furthermore, there’s not even a standard measurement for cannabis residues in the body.

A marijuana high lasts for a few hours, but THC can be detected in blood tests for up to a month. Furthermore, one AAA study showed THC blood levels have no bearing on whether someone is impaired or not. Some states use blood tests, some saliva swabs and now a new marijuana Breathalyzer device is approaching production.

Here’s a summary of what public health experts know about marijuana and car crashes:

Can I drive if I’ve smoked marijuana?

No. It’s at least as illegal as driving drunk, no matter where you’re driving. More importantly, you could hurt someone or yourself.

Marijuana doesn’t affect your driving as devastatingly as alcohol does, but it still impairs your ability to pay attention and your reaction time — two things that can easily lead to death on the roads.

Read our full article summarizing the research showing exactly how cannabis affects your driving.

What are the statistics on accidents caused by marijuana?

The American Automobile Association (AAA) released a study of fatal crashes from 2010-2014 in Washington State (the years immediately before and after the state legalized recreational marijuana). The data show that the number of drivers who died in fatal crashes that had THC in their blood doubled after the legalization initiative was passed, from 49 (8.3%) in 2013 to 106 (17.0%) in 2014, suggesting that accidents caused by marijuana increased alongside legalization.

accidents caused by marijuana seem to have increased in Washington state
Image from AAA.

Total traffic fatalities and total impaired driver fatalities — whether by drug, alcohol or both — also rose by 14 percent from 2012 to 2013, but held steady in 2014, according to Washington State Highway Patrol reports.

All this study proves, however, is that drivers testing positive for marijuana after fatal crashes had used marijuana sometime a month prior to the crash. Furthermore, half of these people also tested positive for alcohol and other drugs in addition to marijuana. This means the AAA study results are virtually useless for drawing conclusions about how marijuana legalization affects the number of traffic deaths. The Washington State numbers are helpful, but still not enough information to figure out causation.  Adding further confusion, testing for other illegal or prescription drugs wasn’t included in the study.

Yet another study from the American Journal of Public Health published in 2017 showed no increase in fatal traffic accidents in states with legal pot as compared with rates in similar states without legal pot, but that study stops after looking at 2015 numbers.

accidents caused by marijuana
Image from the Denver Post.

The most useful information available about this topic comes from The Denver Post in Colorado. Their journalists did a lot of statistical grunt work to squeeze as much info as possible out of the state’s numbers on traffic deaths after recreational pot legalization, producing one of the most thorough examinations of the issue outside academia. Their conclusion? Yes, legalized pot has probably contributed to a rise in traffic deaths, alongside the inferred increase of accidents caused by marijuana.

“The number of drivers involved in fatal crashes in Colorado who tested positive for marijuana has risen sharply each year since 2013, more than doubling in that time, federal and state data show,” reads the first sentence of the piece. Again, the case for an increase in accidents caused by marijuana is strengthened.

The journalists and experts they cite avoided statistical pitfalls and did the most they could to weed out other variables (pun intended). They made sure in the cases they studied, the exact levels of THC in the drivers were measured, based on established intoxication standards. They removed cases in which the drivers had other drugs and alcohol in their systems. They also looked at the numbers of fatal crash drivers who tested positive for ONLY marijuana, showing those spiked year to year. Writers also looked at the prevalence of testing for marijuana in fatal crashes, and though not every driver was tested, the Post journalist also showed there was no change in testing policy, year-over-year, that could have confounded the results.

How can you prevent high driving?

First, don’t do it.

Second, don’t let your friends drive high, and support efforts that spread fact-based information campaigns telling people high driving is dangerous and illegal.

accidents caused by marijuana hotboxing
A common practice of cannabis consumers is to “hotbox” a car, where the windows are up for the entirety of the smoke session. Apart from the carbon dioxide inhalation, this activity would be legal so long as there is no operation of the vehicle by those who partook in the hotbox.

Some have criticized the cannabis legalization movement for downplaying the dangers of marijuana, portraying it as harmless. Though it’s benign relative to alcohol, it still has a powerful effect on the human brain. Cannabis can’t have near-miraculous pharmaceutical potential many of its advocates assert, but also be without consequence when used recreationally.

Legalization needs tempered with accurate information about risks, as some experts argue in The Atlantic in August of 2018.

“Academics and public-health officials, though, have raised the concern that cannabis’s real risks have been overlooked or underplayed—perhaps as part of a counter-reaction to federal prohibition, and perhaps because millions and millions of cannabis users have no problems controlling their use,” the article states.

Accidents Caused By Marijuana (Additional References):

“Legalizing recreational marijuana is linked to increased crashes”

Insurance Institute for Highway Safety: Highway Loss Data Institute

June 2017


“Marijuana Impaired Driving Report to Congress”

National Highway Traffic Safety Administration

July 2017

About Adam Townsend 50 Articles
Adam Maxwell Townsend has been a journalist for 15 years. His reporting has covered science, technology and medicine. Currently, he edits and writes medical and pharmaceutical articles for consumer websites, including WoahStork.

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