It’s relatively easy to determine when someone is too drunk to drive. If a driver’s blood-alcohol level is 0.08 percent or higher, that person is considered legally impaired. But a study says that measuring the effects of marijuana on drivers is far trickier, and that blood tests are an unreliable indication of impairment by cannabis. As more states consider legalizing the substance, that presents a challenge to legislators seeking to create laws on driving while impaired by marijuana.
The study, commissioned by the AAA Foundation for Traffic Safety, found that laws in six states that legally assess impairment by measuring how much THC (the active ingredient in marijuana) is in a person’s blood are not supported by science.
“There is no concentration of the drug that allows us to reliably predict that someone is impaired behind the wheel in the way that we can with alcohol,” said Jake Nelson, AAA’s director of traffic safety advocacy and research.
Lawmakers in those states looked to policies on drunken driving for cues on how to legislate against driving while high. But the body absorbs alcohol and cannabis in different ways, the study said. While drunkenness directly correlates to alcohol in the bloodstream, cannabis impairment takes place only when THC makes its way into the fatty tissue of the brain.
Regular marijuana users, including those who take the drug medicinally, often show no signs of impairment after using, according to Jolene Forman, a staff lawyer for the Drug Policy Alliance, a drug-reform advocacy group. She also said that marijuana can stay in the blood for hours, days and even weeks after its effects wear off. As a result, the presence of THC in blood is not a useful indicator of whether the drug is impairing that person’s ability to drive. Furthermore, the study said, “The practical reality of identifying evaluating, arresting and sampling suspected impaired drivers means that the THC concentration measured in the blood specimen reflects neither the concentration in the subject’s blood at the time of arrest, nor the concentration of active drug in the brain.”
In Montana, Washington, Pennsylvania, Ohio and Nevada, drivers are presumed guilty if they have a certain amount of THC in their blood. Colorado also uses a threshold to assess impairment, though it allows suspects to provide evidence at trial that they were not impaired. The AAA study recommended that laws relying on thresholds be tossed out and that other factors be used. Mr. Nelson said that, ideally, those would include the failure of a standard field sobriety test and the results of a drug assessment conducted by a trained specialist. That assessment would include a blood test to confirm whether cannabis (or any other drug) was present in the bloodstream. But Ms. Forman said that using blood tests to establish impairment, even on a partial basis as Mr. Nelson suggested, could result in arbitrary punishments.
“It would be equivalent to a test that shows that you had a glass of wine three nights prior,” she said. “It tells you nothing about whether the driver is safe now. If we have better tests in the future, then by all means we should use them, but right now those tests are not helpful.”
She said that two groups would be especially vulnerable to such tests: patients using medical marijuana to treat illnesses, who would have high levels of THC in their blood regardless of their sobriety; and blacks and Latinos, who commit traffic violations at similar rates to whites but are more likely to be cited for them, data show.
Sam Kamin, a professor of marijuana law and policy at the University of Denver, also objected to the blood tests’ inclusion. He said that though it was meaningful to confirm that someone suspected of driving while high had THC in his or her blood, a jury might weigh that information too heavily in deciding whether that person was impaired.
“I think that the amount of THC in the bloodstream is a relevant factor; I just worry that it’s misleading,” he said.
Over a dozen states are considering legalizing marijuana in some form in 2016, but it is not clear how they would institute laws to prevent people from driving while high. California’s Adult Use of Marijuana Act, which proposes to legalize recreational marijuana, includes a provision for $15 million to be given to the California Highway Patrol over five years to “develop protocols and best practices for determining when a person is driving while impaired, including from marijuana use.” A similar act proposed in Massachusetts, where recreational marijuana is decriminalized but not legal, does not specify how impairment would be assessed.
The AAA study echoes the recommendations of many experts who call for the improvement of technology to evaluate drivers’ saliva for cannabis use. Sean O’Connor, the faculty director of the Cannabis Law and Policy Project at the University of Washington, said that there was promising research into detecting cannabis through saliva and other techniques, but that it was being stymied by the drug’s legal classification as a Schedule 1 substance.
“We are hamstrung by the fact that you can’t do legitimate scientific research unless you have a Schedule 1 license,” he said.
His argument underlines the difficulty for states trying to write coherent policy when the drug is still illegal under federal law. Douglas Berman, a law professor at Ohio State University who edits a blog on marijuana law, policy and reform, said that even our knowledge about the way people drive when high is confounded by the reality that marijuana was illegal when some of that data was collected.
“People had an extra reason to be cautious drivers when they were aware that they smelled like marijuana,” he said. “Now that it’s legal in some jurisdictions, absolutely that may affect not just the willingness of people to get behind the wheel after they’ve smoked, but also how much they’ll worry about getting pulled over.”
By Jonah Bromwich - The NY Times/May 13, 2016
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