STEVE INSKEEP, HOST:
Most people know about the problem of drunk driving, DWI. Colorado now faces the problem of DWS. Marijuana is legal in that state, but driving while stoned is not. There is a dispute over just what counts as dangerous behavior.
Colorado Public Radio's Ben Markus reports.
BEN MARKUS, BYLINE: Like many medical marijuana patients, Greg Duran says he drives in fear, knowing he could be busted at any moment for driving under the influence.
GREG DURAN: It would be devastating if I lost my car. It would change everything.
MARKUS: Duran says he needs marijuana every day to treat the nausea from his vertigo. As he merges onto Interstate 70, north of Denver, he says he's probably over Colorado's new marijuana limit: five nanograms of THC - the psychoactive chemical in pot - per milliliter of blood.
DURAN: OK, obviously, I'm able to function and do everything I am. I'm driving on the highway. I'm guessing I probably am over five nanograms, just because I do want to keep a constant amount in my bloodstream, in order to keep my condition at bay.
MARKUS: The problem Duran says is Colorado's THC limit will surely net innocent drivers, because the drug can stick around in the bloodstream long after a person has smoked.
Criminal defense attorney Sean McAllister says he's getting five calls a week from clients with pot DUI citations.
SEAN MCALLISTER: You know, if you were talking about this concept with alcohol and told people we got a test that can say if you if you drank in the last 24 hours, and if you fail it, we're going to arrest you for DUI, we would be occupying the capitol right now.
MARKUS: McAllister says users don't have guideposts for marijuana impairment. Is half a joint too much? What about two or five bong rips? No one's sure.
Jon Lacey, a traffic safety expert based in Maryland, says marijuana doesn't metabolize predictably like alcohol.
JON LACEY: It makes setting an absolute level where you're going to be - everyone is impaired, like we have for alcohol, much more difficult for marijuana and for other drugs. They just behave differently than alcohol does.
MARKUS: And drivers behave differently on marijuana. They drive slower, but they also have trouble staying in their lane, and they lack quick response time. So Lacey says best to stay off the road. Some studies indicate stoned drivers are 33 percent more likely to be involved in a fatal crash. That's enough of a risk to prompt a new state educational campaign.
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MARKUS: In this TV ad, a man is trying to light a gas grill that's missing a propane tank. Words come on the screen saying: Grilling high is now legal. Driving to get the propane you forgot isn't. And if drivers don't heed the warning...
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UNIDENTIFIED WOMAN: (unintelligible)
MARKUS: State Troopers Nick Hazlett, patrolling around Colorado, will be waiting. Hazlett is certified as a Drug Recognition Expert.
NICK HAZLETT: It is the toughest school that an officer will go through in law enforcement.
MARKUS: The state has added dozens of these specialists to law enforcement ranks. They're needed, since there is no easy way to test for marijuana impairment.
HAZLETT: I wish. I wish we did. But no, we don't have a marijuana Breathalyzer.
MARKUS: The state patrol has just started keeping track of marijuana DUI citations, 288 between January and April. But most police departments don't track the information, so it's not clear what the true scope of the problem is.
Hazlett, who lost an uncle to drunk driving, says he personally hasn't seen a big increase in stoned drivers since pot was legalized. But he says even one is too many.
HAZLETT: I'll never know my uncle because of a drunk driver and his selfishness. It's all it comes down to. Someone that's stoned behind the wheel, someone that's high on cocaine or heroin, it's the same danger.
MARKUS: Hazlett says it's a danger that means if you've smoked pot, best to stay off the road altogether.
For NPR News, I'm Ben Markus, in Denver.
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