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When Washington state legalized recreational marijuana, people wondered if it would mean more people driving around stoned. Well, two-and-a-half years later, one trend is clear. Police are arresting more drivers with pot in their systems. NPR's Martin Kaste reports, what's not clear yet is what that means for traffic safety.
MARTIN KASTE, BYLINE: The first set of numbers comes from the Washington state toxicology lab. They're the ones who test the blood samples from DUI cases, and since legalization, a lot more of those samples have tested positive for marijuana. Three years ago, about 19 percent of the samples contained THC. That's the key ingredient in pot. But this year, that percentage is up to 33 percent. It's almost doubled. And that worries Kevin Sabet.
KEVIN SABET: I think, really, what it says is that people are getting the message from legalization that marijuana's safe.
KASTE: Sabet is the president of Smart Approaches to Marijuana. It's a group that's critical of the new legal pot industry.
SABET: They're making money off of heavy habitual regular users, and my worry is that a lot of those users think it's perfectly OK to get in a - get behind the wheel after they smoke.
KASTE: Still, that 33 percent figure comes with a big caveat. It's not a percentage of all the drivers on the road. It's just a measure of the drivers who've had their blood taken under suspicion of DUI. It could be that the Washington State Patrol and the police are just getting better at recognizing stoned drivers and pulling them over. But there is another statistic, a grimmer statistic which has added to the concern.
SHELLY BALDWIN: What we see is in 2014, we had a fairly good spike in marijuana involvement in crashes.
KASTE: Shelly Baldwin's the spokeswoman for the Washington Traffic Safety Commission. They've done an interesting new analysis of blood tests of drivers in fatal accidents. Last year, they saw an increase in the percentage of blood samples showing THC, but they weren't distinguishing between active THC and what's known as carboxy THC. That's the metabolized version of the THC which hangs around your system long after you've sobered up.
BALDWIN: Carboxy certainly sticks around in the system for a long time, so it didn't tell us what we needed to know about behaviors out there.
KASTE: So what they did is go back to those blood samples and find the ones with active THC indicating more recent marijuana use. And they found that those cases are becoming more common. Before legalization, about half of the fatality blood samples containing marijuana had active THC. Now that's up to 85 percent. And Baldwin says that does point to changing behaviors.
BALDWIN: It's telling me that people are using and driving.
PAUL ARMENTANO: My concern is that we must not conflate the detection of these compounds as evidence of impairment.
KASTE: Paul Armentano is the in-house guru on this subject at the pro-marijuana group NORML. He says you really can't tell how impaired someone is just by looking at THC levels in the blood. And other experts agree with him on this. He also points to new research that shows that even active THC can linger in the body long after the high, especially in people who use a lot of pot, like some Washingtonians.
ARMENTANO: Is this greater prevalence associated with any tangible decrease in overall traffic safety? That's the ultimate question. And there's really nothing in this data that I've seen so far to indicate that it is.
KASTE: And in fact, the total number of traffic fatalities has remained roughly the same over the last five years. Still, Washington state's traffic safety officials call this growing percentage of active THC in blood samples alarming, and it's a trend that they say they're keeping an eye on. Martin Kaste, NPR News, Seattle.
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