By Melinda Carstensen
As more U.S. states move to legalize recreational marijuana, new data reveals that pot has become increasingly involved in car accidents.
In a study of more than 23,000 fatal crashes from six states, Columbia University researchers found that drivers tested positive for pot about three times more often in 2010 than in 1999. By 2010, 20 states had legalized medical marijuana.
Those higher rates are because of “the increased availability of marijuana and increased acceptance of marijuana use,” Guohua Li, co-author and director of the Center for Injury Epidemiology and Prevention at Columbia University Medical Center, told NBC News.
However, since traces of THC, the psychoactive chemical in marijuana, can remain in a person's system for weeks after consumption, it can be hard to gauge whether the drug was a factor in a crash. The Michigan Supreme Court ruled in 2010 that natural byproducts created by the body during the breakdown of THC levels don’t impair drivers.
Almost half of the U.S. has legalized medical marijuana since California became the first state to do so in 1996. Since then, Colorado and Washington have legalized the sale of commercial pot, and 16 states — including the Patch areas of Connecticut, Maine and Massachusetts — have decriminalized it. Maryland will follow suit this October, according to NORML, a pro-marijuana group.
- How do you feel about how your state treats marijuana with respect to DUIDs? Do you think driving while stoned puts pedestrians and other drivers at risk, or do you think it's harmless?
As legal pot becomes more accessible, states will be tasked with how to address driving under the influence of drugs (DUIDs).
New York state has an effect-based DUID law, which means drivers who are visibly impaired behind the wheel and are likely high can get in trouble. Most states with DUID laws have these.
Washington and Colorado have “per se” laws. Drivers can get a DUID if they have a certain level of drugs in their system.
Other states, such as the Patch areas of Michigan and Illinois, which have legalized medical marijuana, have zero-tolerance “per se” laws. In Michigan, cannabis metabolites are excluded, but drivers in Illinois found with any trace of marijuana at the time of the offense are subject to a DUID (and up to 12 months in jail if convicted for a first offense).
The New York Times reports that only six states have set legal limits for THC concentration in the blood. In Colorado and Washington, the limit is five nanograms per milliliter of blood.
Although traces of marijuana were present in the bodies of the deceased drivers in the Columbia University study, researchers didn’t indicate whether marijuana itself caused the fatal crashes.
“The prevalence of non-alcohol drugs reported in this study should be interpreted as an indicator of drug use, not necessarily a measurement of drug impairment,” the authors write.
Researchers suspected that drivers under the influence of pot were aware of their impairment, and thus compensated by “driving more slowly and avoiding risky driving maneuvers.”
According to a 2013 Columbia University case study, driving under the influence of marijuana is less risky than driving under the influence of alcohol.
Researchers found marijuana holds a relative risk of 1.83 — in other words, driving 10 miles stoned is just as dangerous as driving 18 sober, writes Abby Haglage, of the Daily Beast.
Texting and alcohol, on the other hand, held relative risks of 4 and 12, respectively. Alcohol was 23.
Perhaps the biggest challenge that local governments face is testing drivers for marijuana.
The standard field sobriety test that drivers take when they’re pulled over on suspicion of being drunk is successful in 88 percent of drivers under the influence of alcohol, the New York Times reports. Only 30 percent of people under the influence of THC failed the test in a 2012 study.
Blood-alcohol levels can easily be measured with a Breathalyzer test on site, but no such tool exists for measuring THC levels.
Plus, drivers suspected of being stoned take blood or urine tests hours after they’re pulled over, Maggie Koerth-Baker, the Times writer, points out. The Centers for Disease Control and Prevention predict THC levels can be detected up to two weeks after use.
As states grapple with how to address DUIDs, at least one paper shows marijuana does impair driving.
In a 2012 paper from the British Medical Journal, which took 3,000 related studies into account, researchers found drivers with THC in their systems were twice as likely to be involved in a car accident.
Kevin Sabet, executive director of Smart Approaches to Marijuana, told the Daily Beast that people are “not getting this message,” and said the fact that more people are driving with THC levels in their system is cause for concern.“I think it's reflective of the growing acceptance of marijuana and the growing ignorance about its harms, especially for drivers,” Sabet says. “Many teens today think driving while stoned is safe.”