Driving While Stoned

By Laura Stack
With thanks to Ed Wood for his input on this article

Driving while high on marijuana is a serious problem among American youths; legalization of marijuana makes it worse and more difficult to police. Curiously, there’s no gender gap involved, as there often is with other aspects of drug use; as of 2017, about the same number of boys and girls comprise the roughly 13% of teens who admitted to driving stoned in the past month. Alcohol is still the drug of choice for intoxicated adult drivers, but not so for intoxicated teen drivers; a comparatively low 5% reported driving drunk in the study.

Sadly, after his death, I found selfies and videos Johnny took of himself on his phone while driving and vaping marijuana. In one video, he took a clip of himself vaping while driving and then flipped the camera around to show the road ahead of him and where he was. No one around him knew they were in such danger.

The legal system has barely started to get a handle on stoned driving. In a 2013-2014 roadside survey conducted by the National Highway Traffic Safety Administration (NHTSA), 22.5% of weekend, nighttime drivers tested positive for drugs, some illegal. The problem with this statistic is that testing positive for drugs is not the same as proving that the drivers were under the influence of drugs at the time of the test. By 2016, drivers killed in crashes tested positive for marijuana 18% of the time, up from 8% in 2007. By 2017, the percentage of 33,375 drugged drivers (non-fatalities) who tested positive for marijuana alone came to 38%. That accounted for 13% of all nighttime, weekend drivers.

What is unclear is whether a driver is acutely impaired. A recent study showed the most driving-related skills are predicted to recover within ∼5-hs (and almost all within ∼7-hs) of inhaling 20 mg of THC. However, other factors, such as dose, post-treatment time interval, and type of skill, influence the degree of impairment observed. daily, heavy marijuana users are already chronically impaired. Since the terminal half-life of THC is over 4 days, chronic users never get rid of the body’s load of THC, so they remain chronically impaired, even when not acutely impaired. 

Pot Behind the Wheel

Based on a recent survey, one big reason is for the rise in stoned driving  is that about 48% of American marijuana users believe they can drive just fine while on marijuana. One source claims the number is closer to 60%. The fact is marijuana messes with one’s perception, judgment, and reaction time and causes an increase in fatalities. The AAA Foundation found the proportion of fatal-crash-involved drivers who were THC-positive is approximately double the level observed before marijuana legalization. An estimated 21% of all drivers involved in fatal crashes in Washington State in 2017 were THC-positive, higher than in any other year in the 10-year period examined.

Unfortunately, due to the false narrative and normalization of marijuana, many people believe it’s okay to drive stoned. My home state of Colorado is typical. According to the 2019 Healthy Kids Colorado Survey, the most recent available, 11.2% of high school students in Colorado have driven a car after using marijuana in the past month; however, because 20.6% of high school students are users of marijuana, 11.2%/20.6% shows that 54% of Colorado high school marijuana users have driven after using marijuana! According to a related source, 19.1% of high school students were passengers in a car driven by those who had recently used marijuana. According to an analysis of stoned teen driving in the United States in general, published in December 2020, as of 2017 48.8% of all teen pot users have gotten behind the wheel after using.

Many of these kids may not even have known they were doing wrong. According to a study conducted by Students Against Destructive Decisions (SADD) and Liberty Mutual Insurance, one third of teens in states where marijuana is legal for adult recreational use think it’s legal to drive after or while smoking pot, and 27% of their parents believe that also.

Nationwide, marijuana ranks as the second most common cause of drugged driving after alcohol. According to the Colorado Department of Transportation, the number of deadly crashes caused by drivers using marijuana has risen annually from 11 in 2013, the year after legalization, to 77 in 2016. It’s undetermined how many of the drivers were teens.

The Testing Gap

Teen marijuana users may choose to drive while stoned because they believe they won’t get caught. Unlike alcohol, roadside breathalyzers cannot be used to support evidence of stoned driving in court. Officers use them to ensure the arrest is valid and determine if the driver should be subject to either blood testing or evidential breath testing. For years, police departments and similar agencies were unwilling to split cannabis use out of the general DUI statistics.

THC disappears from blood within hours for occasional users. Only the secondary metabolite carboxy THC remains for weeks. Since the terminal half-life of THC is over 4 days, chronic users never get rid of the body’s load of THC and they remain chronically impaired, even when not acutely impaired. 

Further, there’s no standard for THC level in blood to prove DUI per se, like we have for drunk driving. The standard for stoned driving is impairment; however, marijuana affects different people in different ways. We test the blood as a surrogate to learn what’s in the brain. A high blood alcohol concentration often trumps other drug use since it’s easier to detect. Blood is a good surrogate for water-soluble alcohol but a terrible surrogate for fat-soluble THC, which is quickly stripped from the blood by the brain and other fatty tissues, making any blood level an unreliable indicator of brain level.

How Are We Handling This?

Roadside testers that can detect THC in a driver’s bloodstream are just starting to come on the market, after researchers at the University of Texas in Dallas invented one in spring 2020—not quite a year ago as of this writing. The breathalyzer claiming to be the first to detect THC also claims to detect recent THC use; however, proving presence of THC in oral fluid won’t prove either guilt or innocence of DUI—they only prove the presence of THC.

Because individual states nearly always assert their authority over their citizens in preference to Federal authority, states define stoned driving differently, such as impaired to the slightest degree or incapable of safe driving. In Colorado, we have a permissible inference law. If a driver has a level higher than 5 nanograms per milliliter (ng/ml) of THC in their bloodstream, law enforcement can reasonably infer the driver is impaired by THC if there is other evidence to support such a claim. Eleven states (see the above link) have zero tolerance for any THC detected. Six states have set legal limits ranging from 1-5ng/ml. A legal limit doesn’t prove someone is stoned—it only proves they are above the legal per se limit. All other states require the individual to be under the influence of THC, with that determination left up the court, based on the evidence provided by the prosecutor and testified to by the officer.

What Now?

It took decades and many tragedies for us to catch up with the reality of drunk driving. Evidence from roadside breath testers for alcohol cannot be used in court as evidence that a driver was either drunk or over the alcohol per se limit. That requires an evidential breath tester or blood testing. Evidential breath testing is done at the station house or in rare cases, in a “BATmobile,” a special van outfitted with a calibrated evidential breath tester and a qualified operator. The same will be true of roadside tests to determine THC-intoxication.

Because there is no set THC level that proves acute impairment, we will likely continue to have a mixture of THC laws from state to state, like we do with alcohol. In Colorado in 2018 only 9% of drivers arrested for DUI who tested below 5 ng/ml were convicted of DUI. But 97% were convicted of DWAI – impaired to the slightest degree. So, it’s up to us—Johnny’s Ambassadors—and our allies to monitor and discourage stoned driving by anyone, and especially among teens, to stop them from killing themselves and others.