Josephine Drum says her daughter was "cheated out of life" when she was killed while driving to work in Seattle in 2012, hit by a man in a Jeep whose blood tested positive for marijuana. "I feel if you smoke marijuana and you have to smoke it, that you should not be able to drive under the influence," said Drum, of Stockton, Calif. "I'm 84 years old. To have lost my daughter is something hard for me to accept."
With the push to legalize marijuana surging in popularity, states want to assure the public that roads will be safe. But they face a perplexing question: How stoned is too stoned to drive?
"The answer is: Pretty damned stoned is not as dangerous as drunk," said Mark Kleiman, professor of public policy at the University of California, Los Angeles, who served as Washington state's top pot consultant.
He said Washington state has a law that's far too strict and could lead to convictions of sober drivers, with many not even knowing whether they're abiding by the law.
With no conclusive research, states are all over the map as they try to assess intoxication by measuring blood levels of THC, the main ingredient in marijuana. There's no easy way to do it, with marijuana stored in fat cells and detectable in blood long after it's smoked or consumed, depending on individual tolerance and level of use.
Washington state and Colorado, the only two states to fully legalize marijuana, have set a limit of 5 nanograms of active THC per milliliter of blood. In Washington state, legalization proponents included the language in the ballot initiative approved by voters in 2012. "It appealed to the voters, but it's nonsense — it's not a good measure of whether somebody's impaired or not," Kleiman said.
In California, lawmakers recently rejected an even tougher standard. The state's Assembly Committee on Public Safety voted to kill a bill that would have set the limit at 2 nanograms per milliliter of blood. And in Arizona, the state Supreme Court last month struck down part of the state's zero-tolerance law, saying it could result in convictions of sober drivers.
"What we have to understand is that arbitrary rules or zero tolerance lead to unconstitutional policing," said Diane Goldstein of Tustin, Calif., a former police lieutenant and a member of Law Enforcement Against Prohibition, a pro-legalization group that opposes the laws.
While police can use Breathalyzers to easily measure the amount of alcohol in one's bloodstream, the best way to determine marijuana intoxication is by examining a blood sample. Last year, the U.S. Supreme Court complicated the situation for states by ruling that police must get a warrant before testing blood for a DUI.
"Drawing blood is not a roadside activity for a cop," Kleiman said. "Drawing blood is a medical procedure and you need a licensed phlebotomist. So you're not going to be able to do stoned-driving checkpoints."
Ultimately, he said, a mouth swab that uses a driver's saliva to detect the presence of marijuana may be the answer, if test results can be used to track impairment.
"The problem is that science is lagging really far behind with drugs versus alcohol," Goldstein said.
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As the debate heats up, both sides can point to competing research.
In February, researchers from Columbia University's Mailman School of Public Health reported that fatal crashes involving marijuana use had tripled over the past decade, with 1 of every 9 drivers now involved in a deadly accident testing positive for pot.
But legalization advocates cite statistics showing that the number of DUI fatalities has decreased slightly in both Washington state and Colorado since 2012.
Kleiman of UCLA sees good news and bad news in the issue. "The bad news is at the moment we don't have anything sensible to do about stoned driving," he said. "The good news is that it's only a moderate-sized problem. . I would be nervous about over-criminalizing it."