An increasing number of people are using cannabis daily, surpassing alcohol consumption and leading to a higher incidence of impaired drivers on the roads, thus putting everyone at risk.
A study published in the International Journal of Drug Policy in 2023 suggests that the legalization of marijuana could be contributing to an additional 1,400 traffic fatalities in the U.S. annually. Many drivers are unaware of the impairing effects of cannabis: only 70% believe it is very dangerous to drive within an hour of using marijuana, compared to 94% for alcohol, according to a 2022 survey by the AAA Foundation for Traffic Safety involving 2,500 drivers.
Law enforcement agencies are now faced with the challenge of identifying drivers under the influence of cannabis. They are implementing saliva tests to detect recent marijuana use and enhancing officer training to recognize signs of impairment. Despite these efforts, the methods currently in use are only beginning to address the widespread impact of marijuana use on driving, and some experts argue that they are not sufficient.
“There’s no way to tell if individuals using marijuana are impaired by a test,” said Michael Whitekus, science director at Robson Forensic, which provides expert testimony on fatal crashes. Unlike alcohol, which has reliable tests to gauge impairment, testing for marijuana impairment is complex. Urine tests can show positive results for several days, and blood tests, which measure THC levels (the psychoactive compound in cannabis), do not accurately indicate impairment. Field sobriety tests depend largely on the judgment of police officers, most of whom lack specific training to detect cannabis impairment.
Roadside saliva tests offer some assistance to officers, but they only indicate recent use and not the level of impairment. This contrasts with alcohol tests, where levels in the blood, saliva, or urine closely correlate with impairment, according to toxicologists.
Alcohol is water-soluble, leading to a consistent concentration across tissues and organs, making it a reliable measure of impairment. Conversely, THC is fat-soluble and is sequestered from the blood by the brain and other fatty tissues. Barry Logan, president of the Center for Forensic Science Research and Education, explains that THC concentration in the blood drops by about 50% every 17 minutes, even as impairment increases. By the time a driver is pulled over, arrested, and taken to a hospital for a blood sample, hours have often passed.
Challenges and Emerging Solutions
In states that consistently test for marijuana, more drivers involved in fatal accidents are testing positive for the drug. Roadside oral-fluid tests provide a straightforward yes or no result, similar to a home pregnancy test. Officers ask the driver to move a stick or swab around in their mouth. Most testing kits involve a swab or sponge on the driver’s cheeks and under their tongue. The results, which typically come within about 10 minutes, alert law enforcement if there is a certain amount of THC in the driver’s system.
However, the threshold for a positive test varies across different kits, and while laboratory tests can determine THC levels in saliva, they cannot assess impairment.
Alabama was among the first states to adopt these tests in 2018, and they have since been widely used in states like Michigan and Indiana. New York lawmakers are considering a bill to require these tests if law enforcement requests them after a crash. A 2023 review of roadside monitors used in Alabama over five years found THC in 90% of oral fluid samples compared to 75% of blood samples from the same individuals.
Bill Lindsey, Alabama’s traffic-safety-resource prosecutor, said that because oral fluid is easier to collect and test than blood, it helps officers better identify impaired drivers. “We were seeing other drugs on board that would affect and impair drivers, and our officers weren’t thinking about that [before],” he said. Detecting cannabis still requires an officer’s judgment on impairment, highlighting the need for more training.
“It’s basically like a big puzzle that we are starting to piece together,” said Ryan Hutton, a state law-enforcement officer and founder of Extract-ED, which educates police officers nationwide on identifying cannabis impairment. During training, officers observe volunteers who smoke cannabis and then undergo roadside tests similar to those drivers would experience if pulled over. If volunteers consume edibles, officers wait 60 to 90 minutes before testing. They check for signs such as the smell of marijuana, bloodshot eyes, lethargic movements, and difficulty dividing attention. For instance, when asked for their license and registration, people who are high often produce only one. Cannabis can also affect a person’s sense of time, Hutton said, which is evident when officers ask someone to close their eyes and indicate when 30 seconds have passed—those who are high might stop after 10 seconds or wait more than a minute.
Real-World Implications
In 2018 near Charlottesville, Va., a dump-truck driver drove around a barrier onto railroad tracks as an Amtrak train approached. The crash derailed the train, killed a passenger in the truck, and injured nearly a dozen people. Witnesses reported that the truck had ample time to cross, but the driver hesitated, unable to quickly navigate around the second barrier. Investigators found that the driver had used marijuana, likely impairing his reaction time. Although his blood showed marijuana use, they couldn’t determine whether he was high.
A study published in January in JAMA Network Open monitored the driving of 31 regular cannabis users on a simulator before, during, and after smoking their usual amount. Weaving increased, and speed decreased about 30 minutes after smoking, but impairment was not correlated with THC levels in the blood. The researchers found the weaving equivalent to that of a drunken driver. The drivers reported feeling impaired for three hours.
Combining alcohol with cannabis can significantly amplify impairment, according to studies. “It’s not an additive effect. It’s a multiplication effect,” said Eric Jackson, executive director of the Connecticut Transportation Institute.
The institute is tracking a series of wrong-way fatal crashes in the state. Most of the drivers were above the legal limit for alcohol, but other substances that compound the problem are often not tested because blood-alcohol tests suffice for prosecution. “A lot of people stop testing when they find alcohol,” Jackson said. But “if we don’t know what we don’t know, then we can’t fix the issue. We need to understand the magnitude of the problem.”
Read the original article here