The problem: Identifying pot impairment isn’t as clear-cut as testing for alcohol. There is no broad agreement over what blood level of THC—marijuana’s psychoactive ingredient—impairs driving. Breathalyzers can’t detect marijuana levels, and only a small percentage of police officers are trained to authoritatively identify pot-DUI cases.
When voters in Washington state legalized recreational pot use last fall, they decreed that drivers with five nanograms or more of THC per milliliter of blood—a level that some studies suggest is associated with increased accident risk—are under the influence. In Colorado, which also last year legalized pot possession, lawmakers passed a bill earlier this month that sets the same limit, but gives drivers a chance to prove that they weren’t impaired. In Montana, where medical marijuana is legal, the governor signed similar legislation last month.
But the correlation between THC levels and impairment isn’t scientifically straightforward, said R. Andrew Sewell, an assistant professor of psychiatry at Yale School of Medicine. He said the compound leaves the blood quickly and that regular pot smokers who have built up a tolerance and maintain higher levels may not be impaired at the new legal limits. Setting these limits “is going to cause a lot of impaired drivers to be missed and it’s going to cause a lot of innocent people to get arrested,” he said.
Washington state trooper James Arnold’s experience illustrates the conundrum. In May 2012, he arrested Danny Linh after pulling him over for speeding in Seattle, after which he smelled a “strong odor of marijuana” and observed “bloodshot/watery eyes,” according to his report. The trooper radioed for a drug-recognition expert, but none was available.
A judge in March threw out the officer’s field-sobriety tests after Mr. Linh’s lawyer argued that they weren’t reliable, and prosecutors dropped the case last month. Blood tests also showed Mr. Linh was below Washington’s new legal limit for THC, although that didn’t have a bearing on this case because the law went into effect after the arrest.
Ian Goodhew, deputy chief of staff for the King County prosecutor’s office, said the case may have turned out differently if a drug-recognition expert had been available, noting that there aren’t “enough to cover every DUI investigation.” Robert Calkins, spokesman for the Washington State Patrol, said troopers are well-equipped to deal with drugged drivers. He declined to make the trooper available for comment.
Mr. Linh, now 22 years old, said he wasn’t high and that the sobriety tests were “stupid because they were meant for alcohol.” His lawyer, Blair Russ, said the case shows that “we cannot hastily apply marijuana DUI laws,” because there is a “lack of sufficient research to make a decision about someone’s innocence or guilt, especially given the current tools available to law enforcement.”
Sobriety tests have been developed for drugged drivers, but just 6,837, or less than 1%, of the nation’s police officers are fully trained, according to the International Association of Chiefs of Police, which coordinates and manages the training program. Oregon State Patrol Sgt. Michael Iwai, who coordinates training for Oregon and works with the association, said officers using a 12-step evaluation specifically designed to identify drugged drivers—including a so-called walk and turn, balancing on one foot and an eye examination—are able to detect marijuana impairment.
In part because of the ambiguities in detecting pot-DUI situations, states like Colorado say they need an analog to the blood-alcohol test. “Without a test a lot turns on everything at the roadside and roadside tests related to marijuana impairment are not as clear-cut as the alcohol tests are,” said Tom Raynes, executive director at the Colorado District Attorneys Council.
The Colorado bill on pot DUI passed after six tries and heated debate over setting the appropriate THC limits. White House drug czar Gil Kerlikowske said that “when the science actually catches up with the law, they’re going to find that five nanograms is too high” a limit to be using. He is urging states to adopt laws that ban any trace of drugs, like a bill now being debated in the California Legislature.
Meanwhile, states are still sorting out punishments for drivers who are found to be high. In Washington, drivers arrested or convicted of DUI offenses, for alcohol or drugs, must install a device that prevents the car from starting if it detects alcohol on the driver’s breath. But the ignition-interlock device doesn’t detect marijuana or any other drug.
Stephen Graham, a Spokane criminal defense attorney, said he was “flabbergasted” when the Washington Department of Licensing wanted a client to install one after an arrest for driving under the influence of marijuana.
Brad Benfield, a spokesman for the Washington Department of Licensing, said the department must follow state rules. Part of the rationale for the law is that alcohol and marijuana are often present together in impaired drivers, said Shelly Baldwin of the Washington Traffic Safety Commission. In the future, she said, “we’re going to see technologies that will make testing for marijuana possible.”
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