Americans now spend an estimated 15 billion hours under the influence of marijuana each year — rising numbers that worry health professionals who say the car-loving country mistakenly believes that stoned driving is much less risky than drunk driving.
In 2017, 13% of nighttime weekend drivers were found to have marijuana in their system, according to the Centers for Disease Control, up from 9% in 2007. In fact, active marijuana ingredient THC, and not alcohol, is now the most commonly detected intoxicant in U.S. drivers, according to a drug-policy study out this month.
And unlike alcohol, one challenge lies with stopping a potential pot-related accident before it happens: accurate, low-cost roadside marijuana tests don’t exist. THC is not really a detectable intoxicant simply by using a breath test.
It’s a development — one of the downsides to the expanding decriminalization and legalization of cannabis — that challenges policy-makers and health-care professionals who believe that drivers don’t consider the reaction-slowing and depth perception-altering effects of smoking pot to be an issue when operating their vehicles, argue Mark A.R. Kleiman, Tyler Jones, Celeste J. Miller and Ross Halperin in their study and policy proposal published in De Gruyter’s Journal of Drug Policy Analysis.
In that regard, policy emphasis may have to focus on convincing users simply not to drive at all when stoned as there’s little sign that cannabis consumption itself will ease. More than 30 states have opted for medical-use approval and a handful has embraced recreational sales. A national legalization campaign could also find traction in the wake of Canada’s own approval earlier this month. Some studies find that millennials prefer the mood effects and lower cost of marijuana over alcohol.
Still there’s a real challenge in limiting pot-and-driving behavior, in part because its impact is hard to measure. Marijuana affects driving-related skills but its direct link to the cause of any specific crash is hard to pinpoint.
“While it is certain that the risk of driving under the influence of cannabis alone is much lower than under the influence of high levels of alcohol, it is difficult to determine levels of impairment after cannabis use,” said study author Kleiman, a professor at New York University.
“A few facts are certain: stoned-driving adds to accident risk, especially in combination with alcohol and other drugs,” he stressed.
The Governors Highway Safety Association largely agrees, reporting earlier this year that drug tests of car drivers killed in crashes found that significantly more had marijuana and opioids in their system than just a decade ago.
For traffic regulators, practical, reliable testing of drivers may be a ways off. Oral-fluid testing can demonstrate recent use but not the level of impairment and thus a blood test must be carried out by health professionals at a medical facility. A further challenge is that blood THC levels drop very sharply even after minutes. A blood test is also a poor indicator of how recently the drug was used or the extent of impairment, Kleiman and the researchers found.
Marijuana can remain in the human body for days and weeks after use, depending on how much and how often a person uses, although its driving-impairment effects may have worn off much sooner. What’s more, laws on legal limits vary by state.
And if an accurate test is pushed into active use? Stoned driving, the Kleiman-led group argued, should be discouraged through legal means, but within reason.
“Even assuming that an acceptable test can be developed, stoned driving alone and not involving alcohol or other drugs, should be treated as traffic infraction rather than as a crime, unless aggravated by recklessness, aggressiveness, or high speed,” the authors said, stressing that an anti-stoned driving campaign could find the same legs that efforts to reduce drunk driving has had.