In Colorado, it’s legal to smell like marijuana while driving and to have paraphernalia in the car. It’s even legal to have marijuana in the car as long as the weed’s in a sealed container away from the driver.
But it's illegal to drive impaired from cannabis, just like it's illegal to drive drunk. And the number of deaths due to car crashes involving marijuana is rising, says Sam Cole, a spokesperson for the Colorado Department of Transportation.
"It's still small compared to all the other reasons we're seeing for fatalities out there," he says. In 2016, 51 people died in crashes that involved drivers whose blood tested contained a certain level of active THC. That’s 8 percent of all crash fatalities in 2016. "The data indicates it's a growing problem." And CDOT has allocated almost a million dollars, all from marijuana tax revenue, to educate the public about the danger of driving while high.
And yet, confirming that someone has actually been driving while impaired by marijuana is remarkably tricky. But that doesn’t stop Colorado lawyer Chris Halsor from teaching law enforcement officers to recognize the signs of marijuana impairment.
"It's a brave new world," he says to a room full of Colorado State Patrol officers. There are now more dispensaries in the state than there are Starbucks coffee shops, he tells the students as they learn how to correctly perform roadside sobriety tests.
To complicate matters, as CDOT's Sam Cole notes, "the only roadside device that's allowed to be used, by statute, is an alcohol device." It’s largely up to officers to determine on the side of the road if a person is impaired from pot.
As part of the training, Halsor assigned the officers to go shopping at local dispensaries, so they could get a sense of what pot products are out there. Then, a group of volunteers arrived, introduced themselves to the officers, and promptly proceeded to an RV parked in the hotel parking lot where, as payment for their participation, they could legally consume as much pot as they wanted from a plastic tub of edibles, vape pens, joints and other pot products.
When the volunteers returned to the hotel, the officers tested them on a number of measures meant to distinguish the impaired from the sober.
How many quarters are in $1.75? A person who’s impaired might take a while to figure it out.
Walk nine paces, touching toe to heel, along a line, then return. Someone who’s impaired might forget the instructions or have trouble balancing.
Follow a pen with your eyes as an officer moves it around your face. An impaired person’s eyes often show something called “horizontal gaze nystagmus,” in which the eyes jerk when they move to the side. When the pen moves toward the nose, an impaired person’s eyes often show “lack of convergence” -- their eyes can’t cross in sync, drifting or shifting around rather than converging on the tip of the nose.
The usefulness of many of these tests are backed up by scientific evidence, but the methods don’t always apply to everyone equally. And they are all subject to -- even dependent upon -- an officer’s observations, biases, and interpretation.
Indeed, one of the volunteer’s results were clear-cut. “She’d be going to jail,” said Rich Armstrong, an officer with Colorado State Patrol, and the others all agreed. But the other three were not.
Officers disagreed about the second woman, who did well on some parts of the tests and poorly on others. “It was a tough one,” said Trooper Tom Davis, also with CSP.
“Yeah, this is one of those subjective areas,” said Rich Armstrong.
The officers determined that, in real life, they would not have arrested the two male volunteers for impairment, even though the male volunteers had consumed a comparable amount of cannabis to the female volunteers.
Enter the scientists. At the Boulder branch of the National Institute of Standards and Technology, nestled among buildings that house atomic clocks and giant lasers, there is a group of researchers dedicated to forensic science. And right now, a few them are all about pot. Measuring it precisely, of course.
Chemical engineer Tara Lovestead is working hard to lay the groundwork for a pot breathalyzer. As federal employees, she and her colleagues can't actually develop commercial breath tests, but they’re doing the nitty gritty basic research like measuring the fundamental physical properties of THC. The findings could help companies and researchers create reliable devices that correlate chemicals in a person’s breath to their level of impairment.
From Lovestead’s point of view, the current system for determining marijuana impairment relies too much on an officer’s interpretation. “It’s too subjective. I’m not comfortable with that. The public, I don’t think, is comfortable with that,” she says.
At least two companies are working on devices, including Cannabix Technologies and Hound Labs, but they’re still in the testing phase. And though officers in California are already using a marijuana detection device called the Drager DrugTest 5000, it does not detect a person’s level of impairment -- only the presence of THC in their saliva.
Often, when officers deem an erratic or dangerous driver to be impaired from marijuana, they bring the driver in for a blood test. According to state law, if a milliliter of the person’s blood contains more than 5 nanograms of active THC, the person can be “presumed” to be impaired. But researchers have shown that the 5-nanogram limit can be misleading, possibly incriminating someone who last smoked days before driving, and possibly missing someone who just consumed cannabis.
“It’s a very challenging problem and a lot of work needs to be done,” says Lovestead, whose research group previously worked on technology that could sample tiny amounts of chemicals in the air to detect things like explosives or buried bodies.
While scientists and companies chip away at developing marijuana breath tests, Sam Cole at CDOT is exploring another big question: what’s behind Colorado’s rise in crash fatalities involving marijuana.
"The 64 million dollar question is: Is it because of legalization?" he says. Data on crash fatalities and marijuana is spotty before 2013. So the answer, Cole says, is unclear.