We’re all familiar with drunk assholes behind the wheel: Random lane changes, making-the-jump-to-hyperspace speeding, rampant swerving—they all multiply your chances of crashing into a fiery oblivion.
But the ramifications of driving while on weed may be less obvious. Whether it’s caused by paranoia or an overwhelming sense of calm, many Americans believe that stoned individuals drive more carefully: In fact, one-third of teens (and more worryingly, 27 percent of parents) believe that driving under the influence of marijuana is perfectly legal in green states, according to a recent survey. Even more concerning, 32 percent of teens and 24 percent of parents think that driving under the influence of pot is totally safe.
PSA: Driving while high is illegal, can result in a DUI and is also dangerous.
But since legalization seems to be complicating these issues, let’s take a moment to run down everything we know about weed and driving.
How Weed Affects the Driver
First and foremost, marijuana impairs several key driving skills: Reaction time, tracking ability and target detection. But a recent report by the National Highway Traffic Safety Administration found that—compared with sober drivers—those under the influence of cannabis do drive slower, take fewer risks and follow at greater distances. This is presumably because stoned drivers overestimate their level of intoxication, and overcompensate by driving extra attentively.
Additionally, smoking one-third of a joint (or less) has virtually no impact on driving performance (for most people, at least), according to a 2009 study published in the American Journal on Addictions. The same study found that driving drunk is 10 times more likely to result in fatal accidents than driving under the influence of marijuana—more encouraging still, habitual smokers develop a tolerance that actually increases their ability to drive while intoxicated.
That said, more problems emerge the larger the dose. Epidemiological studies show that smoking one-half of a joint (or more) drastically increases the likelihood of accident, compared to driving sober. And when you combine marijuana and alcohol (America’s two favorite drugs, after tobacco), that’s where things get really messy. Per a 2017 study: “Relative to drivers who tested negative for both alcohol and marijuana, the estimated odds of fatal crash involvement increased 16-fold for those testing positive for alcohol and negative for marijuana, 1.5-fold for those testing negative for alcohol and positive for marijuana, and over 25-fold for those testing positive for both alcohol and marijuana.”
So if you’re going to drive, put away that whiskey bong.
How Weed Affects Traffic Safety
Generally speaking, legalization has had little impact on traffic safety nationwide. A 2017 study published in the American Journal of Public Health found no increase in vehicle crash fatalities in Colorado or Washington post-legalization, while a recent study conducted by the Insurance Institute for Highway Safety found only a three percent increase in collision claims (presumably for minor crashes) in states that have legalized marijuana. Considering these results, it seems plausible that legalization could lead to a slight increase in minor, non-fatal accidents (another semi-win for super chill stoner drivers habitually going 10 under the speed limit).
On the flip side, Colorado has seen a decrease in DUI arrests since legalization, according to Larry Folk, chief medical officer of the Colorado Department of Public Health. “There’s a substitution effect when legal access to marijuana is available,” explains Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws. “Some individuals use cannabis in lieu of using alcohol—it’s simply that overall reduction in alcohol use (and other drug use) that may be related to an overall reduction in traffic fatalities, or an increase in traffic safety.” In that regard, another 2017 study published in the American Journal of Public Health found that medical marijuana states experience an overall reduction in traffic fatalities.
But wait! A recent viral study claims that fatal car crashes increase by 12 percent on 4/20, the unofficial holiday of herb enthusiasts. In this case, though, the data is misleading. “That’s so absurd it’s almost not even worth commenting on,” Armentano emphasizes, arguing that the study also found that 18 states experience an overall decrease in fatal car crashes on 4/20. The states showing the largest increase—Wyoming, Georgia and Texas—have essentially zero large-scale weed culture, argues Armentano. Nor do they throw significant public events to celebrate 420. All of which means this study should be taken with a grain of hash.
How High Driving Is Being Policed
Make no mistake about it: Driving while under the influence of drugs—including legal-use marijuana—is illegal in all states. Period.
While some states have attempted to establish a legal standard for judging whether someone is driving under the influence—generally five nanograms of THC per milliliter of blood (which equates to about a quarter of a joint)—actually combating marijuana-impaired driving has proven challenging. Since cannabis is fat-soluble, it may linger in the fatty parts of the brain for hours, days or even weeks, meaning you could theoretically come in over the limit because of the joint you smoked last weekend.
Research also shows that consuming pot in edible form has less of an impact on blood levels of THC, which could potentially provide a loophole for users planning to get behind the wheel.
All of this means that police currently rely heavily on field sobriety tests and drug recognition experts (who check for physical manifestation of cannabis use, like bloodshot eyes) to detect and arrest marijuana-impaired drivers. Police can also use on-the-scene evidence—like the scent of marijuana—as grounds for probable cause, which legally allows them to perform a search, make an arrest and hold someone for trial.
From that point on, prosecutors rely on the totality of evidence—results from the field sobriety test, testimony from the drug recognition expert and a toxicological exam indicating the recent consumption of marijuana—to make a conviction. In the majority of these cases, Armentano says, a guilty verdict will be rendered. Case in point: California had a DUI conviction rate of 74 percent in 2012 and 73 percent in 2011.
If you get convicted, you could face a $10,000 fine , which is—despite the risks to other road users being wildly different—the same amount of money that drunk drivers are penalized.
And so: Yes, you regular smokers are probably safer behind the wheel than someone who’s just chugged a double Bacardi and diet on the way home; yes, you regular smokers are more likely to be negatively affected by an inaccurate test than someone pulled over halfway through their second six pack; and yes, you will still be punished just as harshly regardless.
When it comes to figuring out the laws on weed, we’ve got a long way to go.