California wants to pay you to light up and drive. Sort of.
Recreational use of marijuana has been legal in California since January but traffic laws are lagging behind. While current sobriety tests can detect the presence of marijuana in the driver's system, they can't test for impairment. That's because it's not currently known what level of THC -- the psychoactive compound in marijuana called tetrahydrocannabinol -- significantly impairs drivers.
To address the problem, the California legislature is funding a UC San Diego study that will determine how pot affects driving performance and how soon after smoking pot is it safe to drive.
Researchers are recruiting 180 people for the study, which will consist of having participants smoke varying amounts of marijuana or a placebo and then participate in driving simulations and cognitive tests. Participants will be monitored for 5 to 6 hours after smoking and will be tested about every hour-and-a-half, plus have blood, saliva, and breath samples taken at regular intervals.
“We are not only looking at how impaired a driver is at different levels of smoking, but also how long that impairment lasts,” says Tom Marcotte, co-director of the UCSD's Center for Medicinal Cannabis Research, which is conducting the study.
A law that went into effect this year prohibits marijuana use by the driver or passengers but it is difficult to enforce because unlike alcohol, there is no established legal limit for driving while under the influence of marijuana.
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"The gold standard for any sobriety test is whether the driver is impaired," he says.
Researchers at UC San Diego hope their findings will be used to draft clearer guidelines for police officers.
In the case of a drunk driver, a breathalyzer or blood test is used to determine whether a driver has enough alcohol in their system to be impaired. But similar tools don't exist for marijuana testing.
While a blood test can detect the presence of marijuana, the lack of evidence for what constitutes impairment means the blood test alone isn't helpful, according to Marcotte.
A device that tests the driver's saliva, used by San Diego police, suffers from the same shortcoming.
“Current sobriety tests are good but they provide limited information on the impact of smoking on the driver's performance,” says Marcotte.
"There's a lot of subjectivity on the officers, and it puts a lot of pressure on them, in that moment, to determine what to do without having any forensic evidence to prove it," Lou Shapiro, a Los Angeles criminal defense attorney, told the Los Angeles Times in March.
Critics of current methods, like cannabis entrepreneur Virgil Grant, worry that the lack of an objective standard could lead to increased racial profiling on the roads.
"As a black man in America, I think that's a no-brainer," Grant told the Times. "If we left everything up to law enforcement in our community, we would be getting locked up at even more alarming rates."
The study is expected to be completed in spring of 2019. In the future, researchers hope to also examine the effects of marijuana edibles on driving impairment.
"Edibles act differently in the body than smoking, which gets in the system more quickly," says Marcotte. "Edibles take an hour or two to hit you and the effects lasts longer. So testing requires a different approach."
Researchers have already recruited 100 participants for the study and are looking for the final 80.