In five states this fall 鈥 California, Arizona, Nevada, Maine and Massachusetts 鈥 voters will be deciding whether marijuana should be legal for recreational use. And any of those states that do legalize marijuana will have to wrestle with the question of how to enforce laws against聽stoned drivers.
It has been legal to smoke pot for fun in Colorado since January 2014, and the state modeled its聽marijuana driving-under-the-influence law on the one for alcohol. If a blood test shows a聽certain聽level of聽, the mind-altering compound in marijuana, the law says you shouldn鈥檛 be driving.
It sounds straightforward, but consider the case of Abby McLean,聽a stay-at-home-mom from the Denver suburbs.
McLean, 30, was driving home from a late dinner with a friend two years ago when she came upon a DUI roadside checkpoint.
鈥淚 hadn鈥檛 drank or smoked anything, so I was like, 鈥楲et鈥檚 go through the checkpoint,鈥欌 she recalled.
McLean is a regular marijuana user but she insists she never drives while high.
Still, the聽officer聽at the checkpoint told her he smelled marijuana and that her eyes were聽bloodshot. Eventually he whipped out handcuffs, and McLean said she started to panic:聽鈥淟ike, massive panic attack. And, 鈥極h, my God, I have babies at home. I need to get home. I can鈥檛 go to jail!鈥 鈥
She didn鈥檛 go to jail that night, but she got home hours late. A blood test later revealed McLean had five聽times the legal limit of 聽allowed in Colorado, which is聽five nanograms of THC per milliliter of blood.
It may sound like an open and shut case that could have resulted in any number of penalties. But McLean鈥檚 attorney, , had a field day in court with Colorado鈥檚 .
鈥淓ven the state鈥檚 experts will say that number alone is something, but generally not enough, and we really hammered that home,鈥 he said.聽Aschner got a hung jury and McLean pleaded to a lesser offense.
Still, McLean鈥檚 trip through the criminal justice system is emblematic of numbers that suggest a sharp increase in marijuana DUI arrests in Colorado. So far this year, State Patrol data show that total DUI citations this year rose to 398 through early July, compared with 316 in for the same period 2015.
It turns out, measuring a person鈥檚 THC is actually a of intoxication. Unlike alcohol, THC gets stored in your fat cells, and isn鈥檛 water-soluble like alcohol, said聽, co-director of the Center for Medicinal Cannabis Research at the University of California, San Diego.
鈥淯nlike alcohol, which has a generally linear relationship between the amount of alcohol you consume, your breath alcohol content and driving performance, the THC route of metabolism is very different,鈥 Marcotte said.
That鈥檚 why adapting drunk driving laws to marijuana makes for bad policy, said聽, a professor of public policy at New York University. 鈥淵ou can be positive for THC a week after the last time you used cannabis,鈥 he said. 鈥淣ot subjectively impaired at all, not impaired at all by any objective measure, but still positive.鈥
Still, Colorado and five other states have such laws on the books because pretty much everyone agrees that driving stoned can be dangerous, especially when combined with alcohol.
What police say they聽really need is a simple roadside sobriety test. Scientists at UCSD are among researchers on several apps that could measure how impaired a driver is. One has a person follow a square moving around a tablet screen with a finger, which measures something called 鈥渃ritical tracking.鈥 Another app measures time distortion, because things can slow way down when a person is high.
The THC route of metabolism is very different.
Those tests are still experimental.
Denver District Attorney Mitch Morrissey said the uncertainty doesn鈥檛 mean Colorado should throw out its THC blood test. He said it may not be perfect, but it gives juries another piece of evidence to consider at trial.
鈥淚 think that putting in a nanogram level makes sense,鈥 said Morrissey. 鈥淚 can鈥檛 tell you what level it should be. I don鈥檛 think Colorado鈥檚 is right. I don鈥檛 think it should be as high as it is. I think it should be lower.鈥
Morrissey remembers trying alcohol DUI cases as a young prosecutor. The science wasn鈥檛 settled then either, the blood alcohol standard was about twice as high as it is now, and it took years for it to be lowered.
鈥淚 think that has to do with better testing better technology,鈥 which Morrissey said will improve eventually for marijuana too.
In the meantime, some regular marijuana users, like Abby McLean, are scared to drive for fear of failed blood tests.
鈥淚 haven鈥檛 gone out really since then, because I鈥檓 paranoid to run into the same surprise, 鈥極h oh, there鈥檚 a DUI checkpoint.鈥欌
This story is part of a partnership that includes , , and Kaiser Health News.