Report examines marijuana positive drivers involved in deadly crashes


Washington Traffic CommissionSince Washington legalized the adult use of recreational marijuana, many have asked the Washington Traffic Safety Commission how this change may impact traffic safety. The commission took the first step toward understanding the issue by releasing a new report providing a detailed examination of marijuana positive drivers involved in deadly crashes.

This is the first time in Washington that crash data on marijuana positive drivers has distinguished between drivers who test positive for THC, the impairing substance in marijuana, and those who have residual marijuana, called carboxy, in their system from prior use which may have occurred days ago. This study categorizes marijuana positive drivers into mutually exclusive categories based on the total results of their blood tests.

In Washington, impaired driving is the leading factor in traffic deaths. This includes drivers who are impaired due to alcohol, marijuana, and other drugs—prescription or illegal.

Most drivers received both alcohol and drug testing. The State Toxicology Laboratory tested blood samples for both alcohol and drugs for 1,773 drivers involved in deadly crashes between 2010 and 2014. Of these 1,773 drivers tested, nearly 60 percent (1,061) were positive for alcohol, marijuana, or drugs.

Most drivers who were tested had multiple substances in their system. Among drivers with positive test results, the largest percentage showed combinations of alcohol, marijuana and other drugs. Approximately one-third revealed alcohol only (34 percent), and eight percent tested positive for marijuana only.

Marijuana is the most frequently found drug. Not including alcohol, marijuana continues to be the most frequently-occurring drug among drivers involved in deadly crashes. By itself or in combinations with alcohol and other drugs, 349 drivers tested positive for marijuana.

The report further separates these drivers by those positive for THC and those positive for carboxy.

More drivers tested positive for THC. In 2014, of the 89 drivers who tested positive for marijuana 75 of them (84 percent) were positive for THC. This is much higher than 2010 when 81 drivers were positive for marijuana and 36 (44 percent) of those were positive for THC.

Half of THC positive drivers are above 5 ng/ml. In 2014, among the 75 drivers involved in deadly crashes who tested positive for THC, about half exceeded the 5 ng/ml per se limit.

THC is increasing while alcohol is decreasing, the report says. The 75 THC-positive drivers in 2014 comprised the highest number of THC-positive drivers in any year during the five-year period studied. The 51 drivers who only had alcohol in their systems (and were over the per se limit) in 2014 were the lowest number of such drivers in the study period.

Most THC positive drivers are young men. When looking at drivers positive for THC, either THC-only or in addition to alcohol above the per se limit, nearly 40 percent were men ages 16-25.

The report also notes that drivers combining marijuana and alcohol showed increased risk. Drivers who combined alcohol and marijuana were frequently unbuckled, unlicensed and speeding.

THC positive drivers were more likely to be involved in daytime crashes. A majority of deadly crashes involving drivers with THC alone, or in combination with other drugs, except alcohol, occurred during the daytime hours. A majority of deadly crashes involving drivers with alcohol above the per se limit, alone or in combination with marijuana or other drugs, occurred during the nighttime hours.

The full report, “Driver Toxicology Testing and the Involvement of Marijuana in Fatal Crashes, 2010-2014,” is available here.

For more information on the Target Zero campaign, aimed at ending traffic deaths and serious injuries in Washington by 2030, visit

10 Replies to “Report examines marijuana positive drivers involved in deadly crashes”

  1. This makes perfect sense given the behavior of drivers I’ve seen on the roads. Just last week I was behind somebody doing 5-10 miles under the speed limit going down 212th, then came to the roundabout, made a full stop, and appeared to panic because of the mind-boggling complexity of dealing with a traffic circle.

    I wish people would keep their Cheech and Chong routines at home, or at least don’t do it while operating a car.


    1. So explain to me why you think this driver was under the influence of marijuana. I get behind drivers like that all the time around here in good OLD edmonds, and some of them should not be on the roads either.


  2. Cannabis does cause some impairment, however studies have shown that consumers tend to overestimate this impairment, and that they compensate for it with added caution. Alcohol tends to do the opposite, consumers perceive their impairment to be less that what it actually is and often become overconfident, aggressive, and careless. [Robbe and O’Hanlon. 1993; Robbe. 1995]

    To find out how cannabis use affects crash risk overall, in 2015 the U.S. government completed the largest case controlled study to date regarding DUI of cannabis and crash risk. It involved over 9,000 cases and controls spanning a 20-month period. It found that cannabis use while driving is not associated with increased crash risk once adjusted for confounding variables such as age, race, gender, and the presence of other drugs, including alcohol:

    “This analysis shows that the significant increased risk of crash involvement associated with THC and illegal drugs shown in Table 3 is not found after adjusting for these demographic variables.”

    Further, they found that cannabis did not add to the crash risk for drivers under the influence of alcohol:

    “As was described above, there was no difference in crash risk for marijuana (THC)-positive drivers who were also positive for alcohol than for marijuana (THC)-positive drivers with no alcohol, beyond the risk attributable to alcohol.”

    They found that alcohol greatly increased crash risk:

    “at moderate alcohol levels (0.05 BrAC) risk increases to double that of sober drivers, and at a higher level (0.10 BrAC) the risk increases to five and a half times. At a BrAC of 0.15, the risk is 12 times, and by BrACs of 0.20+ the risk is over 23 times higher.”

    [Compton and Berning. DOT HS 812 117. Drug and Alcohol Crash Risk. U.S. Department of Transportation – National Highway Traffic Safety Administration. 2015.]

    It is clear that DUI of alcohol is far more dangerous than DUI of cannabis. That said, at some point one could potentially be high enough to significantly increase crash risk, something roughly the equivalent of 0.08% BAC, and DUI laws should reflect that, and be based on actual impairment, not unscientific “per se” limits. However it is rare for anyone that high to want to actually drive a car, whereas it is commonplace for someone very drunk to attempt to drive.


    –Robbe and O’Hanlon. DOT HS 808 078. Marijuana and actual driving performance. U.S. Department of Transportation – National Highway Traffic Safety Administration. 1993.
    –Robbe H. Marijuana’s effects on actual driving performance. HHMRC Road Research Unit, University of Adelaide. 1995.

    Colorado legalized recreational cannabis in Dec 2012 (Jan 2014 for retail sales) and did not see a statistically significant change in fatal traffic accidents:

    2012: 474 (Population: 5.19 million, 0.0091%)
    2013: 481 (Population: 5.27 million, 0.0091%)
    2014: 488 (Population: 5.36 million, 0.0091%)
    [SOURCE: Colorado DOT & “As Reported” to NHTSA by FARS]

    Recreational cannabis use was legalized in Washington state in Dec of 2012. Retail sales began in July, 2014. There has not been a significant change in fatal traffic accidents:

    2011: 421 (Population: 6.82 million, 0.0062%)
    2012: 403 (Population: 6.97 million, 0.0057%)
    2013: 401 (Population: 6.97 million, 0.0057%)
    [SOURCE: Washington State Department of Transportation – 2012, 2013 Annual Collision Summary]


  3. Sadly it’s not just an either/or thing. A lot of people in deadly crashes have ingested multiple things and the interaction between them is what makes it so dangerous. They don’t give a percentage here but simple math tells us that 349 people tested positive (that number’s up there) out of 1773 people, so 20% of people involved in deadly crashes had marijuana in their systems.

    It also points out that that number is increasing.

    Getting high and driving a car IS dangerous, don’t kid yourself.


  4. There have been 5 studies done by the National Highway Transportation Safety Agency that has reported that cannabis use is not endangering our highways.
    Just last month the NIDA/ONDCP and NHTSA released a study where drivers with 3 times the 5 nano limit in states with marijuana DUI laws and reported that marijuana did not impair drivers enough to endanger other drivers. Drivers using cannabis drove more cautiously than drivers using nothing and di not display any of the aggressive and competitive traits alcohol produces.
    They also reported that measuring the amount of THC in a persons system did not prove impairment.
    Where all these articles are coming from is the companies trying to develop a machine to measure THC in a persons saliva or blood. If they can keep the fear going it could be worth billions if they can sell them to every law enforcement agency.

    HIGH is not drunk,,get over it.


  5. Elisi I think you read the report wrong. Only 8 percent had ONLY pot in their system. But the majority had pot and other drugs or alcohol too.too bad the report won’t go any farther than just a few small sites. Too much money involved in pot sales and thats the whole idea. The idea of legalizing pot is a joke. The areas that have this law will live to regret it. We have politicians now who grow/sell.


  6. Norman You must be kidding. I grew up in the 70s. Don’t tell me pot has no affect on anything it’s just great. It is a starting drug for other drugs, Most people who smoke pot are drinking something alcoholic with it..cotton mouth??? It does nothing for society positive. I’ve seen multiple people start with pot (takes all drive away from said person and they become slugs). My first husband ruined his life starting on pot. Most people I know have at least one family member who have suffered starting with pot. And I believe most of these people drive while on pot and booze. Even if it’s to McDonald’s.


  7. Sweet Jesus, you can do all the “studies” you want, they’re testing the blood of people who have managed to kill themselves in accidents. It’s sad that we had to wait until that happened to find out what kind of stuff people were putting in their bodies, but we now have the data.

    People who are high are getting in fatal wrecks. Period. There’s no question about it, the time for theorizing is past.

    Are they endangering ME? I have no idea. Usually I see them poking along ten miles under the speed limit and looking confused about how to operate their own cars. Some of those people evidently get going fast enough to demolish what they are driving though, and if someone is too zonked to deal with the traffic circle at five corners, they sure aren’t capable of driving on I-5.

    Sorry, if you think pot should be legal that’s fine, but that doesn’t mean it’s harmless. It’s a long way from harmless and people who can barely tie their shoes have no business operating cars.

    Every one of these discussions seems to turn into “yeah but alcohol is worse” — maybe it is, maybe it isn’t, but so what? That may have been an argument in favor of legalization, but congratulations, you won that fight. If you want to make driving stoned legal, good luck with that.


    1. John and Joy, thanks for speaking out; I agree with you 100%. Pot is a starting drug that makes those young people who take it lethargic, their “get-up-and-go-got-up-and-went”. It is THE dream killer.


Leave a Reply

Your email address will not be published. Required fields are marked *