Driving High: Marijuana’s Effects Behind the Wheel

Model Car in Bed of Marijuana

Harm reduction. That’s the catchphrase behind the federal Liberal Party’s announcement earlier this year that the government will soon be introducing legislation to legalize marijuana. “We will introduce legislation in spring 2017 that ensures we keep marijuana out of the hands of children and profits out of the hands of criminals,” said Health Minister Jane Philpott when she made the announcement during a special session of the United Nations General Assembly in New York in April. “We are convinced it is the best way to protect our youth while enhancing public safety.”

There can be little doubt that the move reflects general public sentiment: A poll from the Angus Reid Institute released at the same time indicates that 68 percent of Canadians feel pot should be made legal. For most Canadians, it simply doesn’t make sense to potentially criminalize otherwise upstanding teens and youth – and yes, even Gen-Xers, boomers and seniors – for indulging in something that’s become so much a part of modern culture.

As with alcohol, however, while legalizing marijuana may reduce harm on an overall basis, it can sharply increase risks to public safety if users get behind the wheel. Canadian safety advocates and law enforcement authorities are looking to U.S. jurisdictions where marijuana was legalized to see how legalization might affect driving safety in Canada, and the findings are a bit of a buzz-kill.

As a recent CAA-sponsored report from Canada’s Traffic Injury Research Foundation notes, “It is imperative that complementary road safety strategies to prevent and reduce cannabis-impaired driving are considered and developed in concert with this legislation.”

Stoned Behind the Wheel

Rolling Marijuana Joint in Car

Popular sentiment, especially amongst marijuana users, holds that stoned drivers are less of a risk behind the wheel than drunk drivers, and there may even be some truth to it: A 2010 summary report in the American Journal on Addictions concluded that “effects of cannabis use … are more pronounced with highly automatic driving functions than with more complex tasks that require conscious control, whereas with alcohol produces an opposite pattern of impairment. Because of both this and an increased awareness that they are impaired, marijuana smokers tend to compensate effectively while driving by utilizing a variety of behavioural strategies.” (Sewell, R.A., J. Poling and M. Sofuoglu. “The Effect of Cannabis Compared with Alcohol on Driving.”)

In practice, the report found, drunk drivers tend to think they’re just fine to drive and, combined with lowered inhibitions, this tends to lead them to take risks behind the wheel by speeding, following too close and passing recklessly. In contrast, drivers stoned on marijuana tend to believe they’re more impaired than they actually are, and compensate by slowing down, leaving more following distance, and avoiding passing.

But make no mistake: A stoned driver may be marginally safer than a drunk driver, but they’re still seriously impaired, and still at a much greater risk of getting into an accident. The same report noted that impairment with THC (the active ingredient in marijuana) increases reaction times, makes it difficult to divide attention between tasks, and degrades motor coordination, tracking ability, visual functions and other psychomotor skills associated with driving.

Worse still, the report found that when marijuana and alcohol are consumed at the same time, the impairment effects of each were multiplied, so that even at relatively insignificant blood alcohol and THC levels, drivers showed serious degradation of driving performance and inhibition, and they didn’t attempt to compensate for their lost skills like purely stoned drivers did.

Traffic Safety Challenges

Car Key on Marijuana

To gain insight into what legalization of marijuana might mean for road safety, BC’s Council on Health Promotion (a section of Doctors of BC) looked at accident statistics from Washington State and Colorado, two nearby US states that recently legalized marijuana. “In Washington State, fatal crashes among drivers who tested positive for marijuana doubled from eight percent in 2013 to 17 percent in 2014. In Colorado, the number of drivers in fatal crashes who tested positive for marijuana without other drugs in their system tripled between 2005 and 2014 from 3.4 percent to 12.1 percent,” noted Nanaimo emergency physician Dr. Chris Rumball in a British Columbia Medical Journal opinion piece.

A Canadian study by Dalhousie University professor Mark Asbridge and colleagues mirrored these statistics, finding that recent cannabis use almost doubles the risk of having a collision resulting in serious injury or death.

For Canadian law enforcement authorities, the legalization of marijuana presents some real challenges: partly because there aren’t currently any approved devices to quickly and accurately measure THC levels in the blood; and partly because even if a test device was available, there’s a lack of scientific consistency tying impairment to levels of marijuana metabolites in the blood (THC is fat soluble, so it’s hard to link a person’s current state of impairment to a specific blood level).

What all that means is that even if easy roadside tests become available (and that might be coming soon, with UBC Okanagan engineering professor Mina Hoorfar recently announcing the development of an inexpensive handheld microfluidic breath analyzer), it will take the law some time to catch up and establish valid limits. “It’s a bit of a sit-and-wait situation,” remarked Vancouver Police Department Constable Brian Montague. In Washington State, police can use a roadside saliva swab test or can order a blood test to indicate if a driver has recently used marijuana, and the legal limit has been set at five nanograms per millilitre of THC, but any amount of marijuana in the blood can be used “as evidence that a person was under the influence of marijuana.”

Police Impaired Driving Checkpoint

For Canadian police, the first line of defence, for now at least, will remain the roadside SFST (Standard Field Sobriety Test) – a test that only trained officers can administer, and that often doesn’t hold up in court. “We can’t simply buy a THC detector and start using it,” explained Cst. Montague, “it needs to be approved for use in the legislation.”

To be effective in catching drugged drivers, police forces will likely require greater numbers of SFST-trained officers, and Canadian police forces have started moving in this direction. In Vancouver, many of the police department’s traffic and patrol officers are SFTS-trained, while in Ontario the Waterloo Regional Police Service and Ottawa Police Service have gone a step further, making SFST training a standard part of academy training for all officers. A Standard Field Sobriety Test may not be as easy to administer as an alcohol breathalyzer test, but it has the advantage of being a universal test, able to recognize impairment regardless of cause. As OPP Constable Jason Folz notes, “any amount of illicit or legal drugs that impairs your ability to drive is already contrary to the criminal code of Canada.”

Ultimately that’s the whole point, and it’s a point that law enforcement and traffic safety advocates may find easier to communicate once marijuana is legal. “Under a system where cannabis is illegal, it’s really hard to get information about its potential harms,” says researcher Daniel Werb with the Toronto-based International Centre for Science in Drug Policy. Evidence indicates that Canadians will smoke marijuana whether it’s legal or not, explains Werb, and to reduce the number of stoned drivers, authorities would do best to take the same nuanced approach used to combat drunk driving. “You can see on TV that there are ads around drinking saying, ‘Don’t drink and drive.’ There aren’t ads that say ‘Drinking is evil; you shouldn’t do it.’”

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Simon Hill

Simon Hill

Simon Hill rebuilt his first engine, an air-cooled Volkswagen, at 14. He started writing professionally about cars in 2009 and was also the editor of Boat Journal magazine. He lives in Vancouver, BC.
  • Jay Carter Brown

    lies lies and more lies. Pot does not impair driving. England did a study on cannabis impaired drivers to determine if new pot driving laws were required. They found that pot does not impair drivers but decided to implement new pot driving laws anyways.

  • http://www.autotrader.ca/ autoTRADER.ca

    This is not a sponsored article, FYI.

  • Lars VanKessel

    just one full of lies and misrepresentations. So why would anyone believe that?
    It’s one thing to claim “more dead drivers are found with marijuana in their system” but completely another to ignore how many of them had alcohol as well? Not to mention the fact that MORE people use cannabis and more people are going to die with it in their systems. Having it in their system does not mean that was the cause of their death! Actual scientific tests show that there is no corelation to cannabis use and an increase in motor accidents. Also studies done by the US department of transportation (in 1993) show that cannabis use did not increase risk of accident.

    some quotes from the study (which are completely absent in this article – as well as actual quotes from the studies mentioned… just the author’s slanted take)
    “It appeared that the effects of the various administered THC doses (100-300 g/kg) on sdlp were equivalent to those associated with bacs in the range of 0.03-0.07 g%. Other driving performance measures were not significantly affected by THC. Plasma concentrations of the drug were clearly related to the administered dose and time of blood sampling but unrelated to driving performance impairment.”
    “Table 1 shows that a modest dose of alcohol (bac=0.034 g%) produced a significant impairment in city driving, relative to placebo. More specifically, alcohol impaired both vehicle handling and traffic maneuvers. Marijuana, administered in a dose of 100 g/kg THC, on the other hand, did not significantly change mean driving performance as measured by this approach.”
    and probably most relevant of all
    ” Therefore an important practical implications of the study is that is not possible to conclude anything about a driver’s impairment on the basis of his/her plasma concentrations of THC and THC-COOH determined in a single sample.”

    Cannabis and alcohol are different, vastly different. To treat them the same is terrible policy. To expect them to affect people the same is terrible science. To create rules that could put an innocent person in jail, or ruin their life forever – simply to appease a few ignorant folk – is terrible politics.

  • Brandon Haist

    I’d have to say that I agree that pot should be treated the same as alcohol. When I used to smoke it was for 1 reason, to fall asleep. What I mean is that every single time I smoked pot it’d make me sleepy. This isn’t the case for every single person however the same could be said about alcohol. Smoking a small about before going for a drive is w/e, but smoking more than half a joint should be the cut off for being allowed to drive.

    Having laws to regulate pot so that people don’t get hurt is a GOOD thing, seeming as though it doesn’t effect everyone the same way, the same as alcohol.

  • Greg Mooney

    I am a lover of the weed, and a complete advocate for its legality. I don’t drive when I am stoned, it is an impairment, far less serious than alcohol, but an impairment non the less. That being said I have known many people who are better drivers/workers/ productive people when they are stoned, it helps with focus and awareness for many people I know, me excluded. Perhaps there needs to be more trials done other than that famous test done in Britain giving driving on weed a green light. If you give a non weed smoker a bong hit of shatter they are not good to drive; but then they aren’t going to anyway 😉 . Just stay safe on the roads, there are families and friends in the other lane.

  • David G Smith

    Pot and alcohol are nowhere close in any relation.When did you smoked pot? FFs you look like you are a teenager. If you are aware of what is really going on with marijuana you would know that there are well over 600 different strains of cannabis.You were probably smoking an Indica if it made you sleepy.The law will make sure we pay fines that are UNJUST.I have driven using cannabis many many times.I have a totally 32 years 5 star clean driving record.

  • Matt Llewellyn

    One, anyone can be a bad driver. Two, having bad drivers intoxicated while doing a test does mot prove accurate results. I could smoke an oz of Marijuana, and drive safer than most Canadians. Marijuana effecys everyone differently so have a test to generically subjective people into a categories, i feel disgusted by. You stack a stoner up with any other drug user and they don’t even compare. I am sure people have crashed with just coffee in their systems, amd no one freaks out or with nicotine in their system. Why? Because they are legal so the stigmata of society is ok with those DRUGS, and feel they don’t need to follow up with studies. If people were dying on THC related car crashes, then there would be deaths to date from Marijuana. Marijuana. Currently has no deaths to date. We should just legalize it and leave it alone. Who cares if kids smoke pot, they be less likely to go do something dumb. People don’t fight when high on THC or CBD’S. I smoked pot since i was 12, so one the system that is in place anyways already fails. Two, i still became a business owner, that helps my community. I am going to school to become an astronomer, and i am high on THC All day long because i am in pain and choose to not use pharmaceutical opiads. The amont of energy used to fight Marijuana, humans could have cured cancer or sent man to Mars. Reality is the system has to change or society is going to get the same results time and time again; it is insanity.

  • Jacob Black

    Nobody is saying that you shouldn’t smoke dope, or that you can’t be a successful, valuable member of society if you do. Just like alchohol, there’s nothing to stop you using the stuff and being fully functioning human beings who are vital to society.
    But, just like alchohol, if you’re under the influence of dope, you shouldn’t drive. Simple as that. Pot impairs you. If it didn’t – it would be a crappy pain reliever.
    Do pot, smoke til you can’t see if you like… just don’t drive when you do.

  • Brandon Haist

    I never stated pot and alcohol are closely related at all. I simply stated that in both cases these 2 things effect people in different ways. You can be a happy stoner or a sad stoner or a hyper stoner, just like you can be a happy drunk or a sad drunk or a hyper drunk.

    The point I was trying to make is that pot effects everyone differently, just like alcohol has a different effect on everyone. It doesn’t matter which strain you smoke, just like it doesn’t matter which type of alcohol you drink.

    I simply stated my belief that because smoking pot can cause SOME people to become drowsy, it should be regulated in the same way as alcohol when it comes to driving. Just because you have a tolerance to pot and have never been in an accident in 32 years of driving while high as a kite, doesn’t mean someone else with a low tolerance couldn’t end up in a car crash because they fell asleep at the wheel while under the influence of marijuana.

    I’m 100% for the legalization of marijuana, but having smoked it myself and almost every member of my family having smoked it their entire adult lives, we believe it to be something meant for adults and something meant to be done while at home, not on the road.

    A large amount of people who smoke pot do not have access to the strain of their choosing when it comes to pot. Therefor 90% of the time they do not know what kind of pot they’re smoking when they go to their dealer. Therefor it’s Russian roulette on whether or not the next person to get behind the wheel is under the effects of an indica strain.

    Regardless of what some people believe, for me personally I would prefer it to be treated like alcohol. Also might wanna check California before you claim that you’re going to get some unjust fines attached to your pot purchases. Chances are they’ll charge 10$ a gram with regular pst hst and gst taxes. Which amounts to 15 cents per dollar give or take. That’s absolutely justifiable and in no way unjust if you ask me.

    In regards to someone driving stoned, I’d bet they’d employ the same fine as alcohol dui’s.

  • Pete

    We’re starting to see more articles like this with very little or NO DATA being presented from places where Legalization has already passed. Meanwhile, just about anybody who has EVER smoked even a >little< marijuana must realize, it's going to be tricky to get an accurate test because alcohol is NOT the same as Weed. It affects different people in RADICALLY different ways,(far more so than booze) and at vastly different dosages. In addition, there are mountains of data that suggest THC stays in your bloodstream a long long time after the 'psycho-active' effect or 'high' has passed