Legalized Marijuana Makes Drugged-Driving Study High Priority


Whether you think the grass is always greener on the side where weed is allowed or fear the whole country will go to pot, legalized recreational marijuana has taken root in the U.S. As it spreads to more states, questions about what a legalized America will look like abound, many of which will only be answered through trial, error and experience. One such issue — how to handle the projected increase in "drugged driving" — is about as hazy as a '90s college dorm room littered with black-light posters and Phish CDs.

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Two states already have legalized the recreational use of marijuana — Colorado and Washington — and more than a dozen states are poised to follow suit by 2016. That's in addition to 22 states and the District of Columbia, where the drug already has been OK'd for medical purposes or decriminalized.

According to anti-drunken-driving advocacy group Mothers Against Drunk Driving, alcohol-related driving deaths have declined by half since 1980, but drunken-driving accidents cost the U.S. about $132 billion a year. What's worse, on average 1 in 3 people will be involved in an alcohol-related crash in their lifetime and every day 28 people die in drunken-driving accidents. How will marijuana-related driving accidents impact these numbers?


It's difficult to quantify the direct role marijuana plays in car crashes, and apples-to-apples comparisons to alcohol aren't available. As notes, "many accidents are caused by people using marijuana in conjunction with other drugs, or in combination with alcohol." Still, a National Highway Traffic Safety Administration study found that 4 percent of drivers were high during the day and more than 6 percent at night, and that nighttime figure more than doubled on weekends. Moreover, Columbia University researchers performing a toxicology examination of nearly 24,000 driving fatalities concluded that marijuana contributed to 12 percent of traffic deaths in 2010, tripled from a decade earlier.

NHTSA studies have found drugged driving to be particularly prevalent among younger motorists. One in eight high school seniors responding to a 2010 survey admitted to driving after smoking marijuana. Nearly a quarter of drivers killed in drug-related car crashes were younger than 25. Likewise, nearly half of fatally injured drivers who tested positive for marijuana were younger than 25.

But people are and have been smoking marijuana, regardless of its legal status, so will incentives such as increased ease of access, decreased risk of trouble with the law and a destigmatizing of the drug's users translate to more people stoned behind the wheel? No one knows that for sure, but Colorado has seen a spike in driving fatalities in which marijuana alone was involved, according to The trend started in 2009 — the year medical marijuana dispensaries were effectively legalized at the state level, starting the so-called Green Rush there — and remained stable through 2013, the year after recreational prohibition ended in Colorado.

To combat what it calls "the growing problem of drugged driving," the federal Office of National Drug Control Policy's National Drug Control Strategy includes a goal of reducing drugged driving by 10 percent by making prevention a "national priority on par with preventing drunk driving." The strategy calls for:

  • Encouraging states to adopt "per se" laws prohibiting any trace of the drug in a driver's system while in control of a vehicle, even absent other evidence of impairment
  • Collecting further data on drugged driving
  • Public education
  • Law-enforcement training for identifying drugged drivers
  • Standardized screening methods for drug-testing labs for use in detecting the presence of drugs

Complicating matters of crafting and enforcing drugged-driving laws is limited study of the effects of smoking marijuana specifically on operating a motor vehicle. Soon that won't be the case. NHTSA and the National Institute on Drug Abuse are now in the final months of a three-year, half-million-dollar cooperative study to determine the impact of inhaled marijuana on driving performance. Tests observe participants who ingest a low dose of THC (the active drug in marijuana), a high dose and a placebo to assess the effects on performance, decision-making, motor control, risk-taking behavior and divided-attention tasks.

The study is being performed using what NHTSA calls "the world's most advanced driving simulator," the University of Iowa's National Advanced Driving Simulator, which was previously used to study the effects of alcohol on driving. It's the first time NADS is being used to study the effects of an illicit substance, though researchers hope it will help clear the air on the marijuana issue.

"The mixed results from previous cannabis-dosed driving studies have demonstrated that its effects on driving can be more difficult to detect than the effects of alcohol," NHTSA stated. "The NADS, a more sensitive data collection tool, is capable of detecting the more subtle changes in driving behavior of cannabis-dosed participants."

From a law-enforcement perspective, aside from garden-variety physical signs that a motorist is intoxicated it's difficult for an officer to determine on the spot whether someone has specifically used marijuana, and no reliable Breathalyzer-style test for the drug yet exists. Still, the law doesn't distinguish between drunk and drugged, and substance-impaired drivers can still be charged with driving under the influence.

"A DUI is a DUI," says, "and toxic to a driving record and car insurance rates either way." photo illustration by Paul Dolan; photos by Dario Lo Presti/iStock/Thinkstock, Chad Baker/Jason Reed/Ryan McVay/Photodisc/Thinkstock, defun/iStock/Thinkstock and itayuri/iStock/Thinkstock

By Matt Schmitz | June 6, 2014 | Comments (8)



Every study to date has reported that driving under the influence of cannabis alone does not pose a hazard on our highways.

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 and actual driving performance
“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: U.S. Department of Transportation study, 1993

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”
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

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.”
REFERENCE: 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 And Cannabinoids – Pharmacology,Toxicology And Therapy.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


i'm just impressed with that photo illustration!


So, the problem will be that people who drive after smoking cannabis will be driving slower and more cautiously than those who are not "under the influence" and w/out the road rage. Okay. And this is bad how?


Didn't Mythbusters did an experiment on this already?
Driving stoned is just as bad if not worse than drunk.


I can tell you from experience that driving stoned impacts driving ability. I don't know if it's as bad as alcohol because it's hard for me to compare the two.

I have found myself doing 25mph on the freeway and in bright sunlight it can be hard for me to judge distance and predict what another driver is going to do. In other words my judgment is impaired.

Users need to be kept off the road.

I now use neither but have experience with both including a wreck.


I think an important consideration is personal driving ability. While risking sounding classist, marijuana is most heavily used amongst lower-income people, who also tend to be less alert, responsive, and aware on average. Thus, a study determining the effects will have to account for personal driving ability. I think amongst well-trained drivers, intoxication poses almost absolutely no greater risk than driving sober. The key is learning your current ability (kin to if you were tired) and taking the necessary precautions, while having a set of ingrained plans in case of emergency. Always being aware of the risks and possible solutions is of greater importance than the person's current state.


The ONDCP has a lot of gall advocating "per se" DUID laws. The whole point of "per se" laws is to punish people who are not even intoxicated, especially marijuana users.


Only retards don't understand the meaning of "driving under the influence".

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