Marijuana on the Roads: How High Are the Stakes?

Questioning safety and the impending legalization of weed


Thanks to Cheech and Chong and anything-goes Venice, marijuana has long been a central part of L.A.’s hip, relaxed image—but the drug has never been as accessible as it is now. Pot dispensaries, where weed is doled out to anyone with a headache, a prescription, and $30 bucks, are almost as common in L.A. as car-clogged freeways. Those two things, driving and weed, often go hand-in-hand in a city like ours. The question is: how does legal enforcement define, detect, and prevent stoned driving?

With the legalized use of recreational pot likely on the ballot for 2016, California officials will have the benefit of looking to Colorado and Washington for answers, two states that recently legalized recreational use of marijuana.

Five nanograms of THC, the active ingredient in pot, is the current legal limit for bloodstreams in Colorado and Washington. Figuring out that nanogram level is much more complicated than administering a Breathalyzer test; THC levels have to be measured via blood or urine samples, and obtaining such bodily fluids wouldn’t be possible on, say Mulholland Drive (not to mention, the results would be far from instantaneous). If a cop does manage to get an accurate THC measurement, probably after an accident has taken place, the number is often skewed by THC’s tendency to overstay its welcome in the body. Habitual pot users, both party people and chemo-suffering cancer patients, will have traces of THC in their system even if they haven’t lit a joint in days. Further complicating a true measurement of impairment is the malleable potency of weed; someone can get just as high from a puff of kush as they can from five bong hits of schwag.

Photograph courtesy

Since there is no quick and accurate measure of “highness,” Colorado is focusing on prevention. The state is spending $430,000 to educate drivers on the dangers of driving while too stoned. Posters and broadcast ads will warn users, “Drive High, Get a DUI.” (You can drive high though, just under-five-nanograms-of-THC high.) Critics say the campaign is neutered by a lack of specifics, e.g. how long you should wait to drive after you smoke or nosh on a laced brownie.

Throwing away oodles of money to combat stoned driving is likely a misallocation of resources (since evidence points to drunk driving being far more dangerous), but we do need to do a better job at detecting and policing stoned driving because its occurence will likely rise exponentially what with pot becoming so much easier to obtain. For now, though, stoned driving is still a punch line. Mark Kleiman, a public policy professor at the UCLA School of Public Affairs, used a timeworn reference to illustrate the difference to the New York Times: “The joke with that is Cheech and Chong being arrested for doing 20 on the freeway.”

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  • Robert Chase

    The imbeciles who rule Colorado are pushing a $2,000,000 campaign against drivers using cannabis in the face of evidence that drivers’ substitution of cannabis for alcohol has caused traffic fatalities to drop 9% (see “Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption”); the alcohol peddlers are banking on people rejecting the science that contradicts decades of prohibitionists’ idiotic lies about cannabis. The Establishment will hold fast to the prohibitionists’ propaganda, regardless of the facts, until the day they die, so let’s get about replacing them! The corporate media’s response to the movement to end Prohibition demonstrates the monumental incompetence of these failed institutions — “… we do need to do a better job at detecting and policing stoned driving …” only if we want to keep up the number of deaths on our highways!

  • Krymsun

    Why does most everyone jump to the automatic, knee-jerk, and FALSE assumption that cannabis impairs drivers much the same as does alcohol? Why let uninformed opinions be the basis of new laws? It took me very little time to do a search, and find actual scientific studies which indicate just how incorrect such an assumption is. Examples follow.

    Studies Show Marijuana Consumption Not Associated With Dangerous Driving, May Lead to Safer Drivers
    Anyone who consumes cannabis on a regular basis knows that it doesn’t make you a dangerous driver. Many people find that it makes them a safer, more focused driver; one that’s more aware of their surroundings and the dangers associated with controlling tons of gasoline-filled metal. Not only has this been an anecdotal truth for as long as cars and cannabis have been paired, science has also been clear that consuming marijuana doesn’t make you a dangerous driver, and may make some people safer drivers. More research is needed, but it’s hard to deny that of the research we have, marijuana hasn’t been found to increase a person’s risk of an accident. To back this claim up, here’s a list of studies and research conducted on this very topic, some of which were funded by national governments in hopes of different results.

    Marijuana and Driving: A Review of the Scientific Evidence
    “Marijuana has a measurable yet relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. Below is a summary of some of the existing data.”

    The incidence and role of drugs in fatally injured drivers
    “There was no indication that cannabis by itself was a cause of fatal crashes.”
    REFERENCE: Washington, DC: US Department of Transportation, National Highway Traffic Safety Administration,
    Report No. DOT HS 808 065, K. Terhune. 1992.

    Marijuana’s effects on actual driving performance
    “Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution. .. Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.”
    REFERENCE: University of Adelaide study, 1995

    Role of cannabis in motor vehicle crashes
    “There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.. The more cautious behavior of subjects who have received marijuana decreases the impact of the drug on performance, whereas the opposite holds true for alcohol.”
    REFERENCE: Marijuana: On-Road and Driving-Simulator Studies; Epidemiologic Reviews 21: 222-232, A. Smiley. 1999.

    “Both simulation and road trials generally find that driving behaviour shortly after consumption of larger doses of cannabis results in (i) a more cautious driving style; (ii) increased variability in lane position (and headway); and (iii) longer decision times. Whereas these results indicate a ‘change’ from normal conditions, they do not necessarily reflect ‘impairment’ in terms of performance effectiveness since few studies report increased accident risk.”
    REFERENCE: UK Department of Environment, Transport and the Regions (Road Safety Division). 2000.

    Cannabis And Cannabinoids – Pharmacology, Toxicology And Therapy
    “At the present time, the evidence to suggest an involvement of cannabis in road crashes is scientifically unproven”.
    REFERENCE: G. Chesher and M. Longo. 2002.,Toxicology%20And%20Therapy.pdf

    Cannabis: Our position for a Canadian Public Policy
    “Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving. Cannabis leads to a more cautious style of driving. However it has a negative impact on decision time and trajectory. This in itself does not mean that drivers under the influence of cannabis represent a traffic safety risk”
    REFERENCE: Canadian Senate Special Committee on Illegal Drugs. 2002.

    “The evidence to suggest an involvement of cannabis in road crashes is scientifically unproven.”
    REFERENCE: Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, 2002
    Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, edited by Franjo Grotenhermen, MD and Ethan Russo, MD (Haworth Press 2002).,Toxicology%20And%20Therapy.pdf

    The Prevalence of Drug Use in Drivers, and Characteristics of the Drug-Positive Group
    “There was a clear relationship between alcohol and culpability. In contrast, there was no significant increase in culpability for cannabinoids alone.”
    REFERENCE: Accident Analysis and Prevention 32(5): 613-622. Longo, MC; Hunter, CE; Lokan, RJ; White, JM; and White, MA. (2000a).

    The Effect Of Cannabis Compared With Alcohol On Driving
    “Although cognitive studies suggest that cannabis use may lead to unsafe driving, experimental studies have suggested that it can have the opposite effect.” U.S. National Library of Medicine, 2009

    Why Medical Marijuana Laws Reduce Traffic Deaths
    “No differences were found during the baseline driving segment (and the) collision avoidance scenarios,”
    REFERENCE: Research published in the Journal of Psychoactive Drugs, 2010

    Top 10 Reasons Marijuana Users Are Safer Drivers
    “20 years of study has concluded that marijuana smokers may actually have fewer accidents than other drivers.”

    Risk of severe driver injury by driving with psychoactive substances
    “The study found that those with a blood alcohol level of 0.12% were over 30 times more likely to get into a serious accident than someone who’s consumed any amount of cannabis. .. The least risky drug seemed to be cannabis and benzodiazepines and Z-drugs.”
    REFERENCE: Accident Analysis & Prevention; Volume 59, October 2013, Pages 346–356

    Cannabis: Summary Report
    “Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.”
    REFERENCE: Canadian Senate Special Committee on Illegal Drugs,Toxicology%20And%20Therapy.pdf

    Acute cannabis consumption and motor vehicle collision risk
    “There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.”
    REFERENCE: British Medical Journal, 1999; M. Bates and T. Blakely

    “Stick *that* in your pipe and smoke it!”