When are you too high to drive? New tech seeks to answer this question


Raised taste buds on the back of the tongue, aggressive driving, slight sweating, body tremors, poor estimation of time: These observations, among others, are what a Washington state patrol trooper used to get Douglas Fraser III to take a blood test in 2017. The test determined Fraser’s blood had a THC concentration of 9.4, plus or minus 2.5, Nanograms per milliliter (ng/mL). Fraser admitted to smoking cannabis 20 hours prior to his encounter with the state trooper.

Was Fraser driving while impaired? He said he was not, but a trial court said he was. Washington state is one of a few states where adult-use cannabis is legal that has a “per se” limit of THC in blood, meaning if your blood contains 5 ng/mL of THC or more while driving, you are guilty of driving impaired.

Fraser said the state’s per se law was unconstitutional and took his case to the Washington State Supreme Court. On May 12, 2022, he lost.

The court ruled it did not matter that researchers around the country, including those at the DOJ’s National Institute of Justice, have almost unanimously agreed that there is no blood-level THC concentration, no “magic” number, that correlates directly with cannabis impairment. The law doesn’t need to be scientifically sound to be constitutional, the judges said.

But was it justice? 

Its clear per se laws don’t mete out justice by themselves. In fact, some research shows a driver can be impaired with even less THC than most non-zero limits, while others seem to not be impaired with higher concentrations. Its also clear that if you ingest enough cannabis you are definitely going to be too high to drive.

“When cannabis was just blanket illegal, there was no demand to discriminate between whether or not someone had at some point used cannabis versus whether or not they might be under the influence of it,” said Paul Armentano, deputy director of NORML. Now with cannabis fully legal in 19 states, he says people want a “much more narrow window of detection” to determine if you are impaired rather than if you’ve used it at all.

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This shift is driving a new wave of technological innovation to reduce reliance on the subjective observations of an officer putting a driver through roadside tests and the clearly unfounded assumption of guilt based on THC concentrations. Even though cannabis-related conviction rates involving toxicology results are high in many states where cannabis is legal, and courts are clearly unlikely to throw out per se laws, there appears to be a growing cultural push for objectively knowing whether or not a person is too high to drive.

There are phone and tablet-based apps like Druid and AlertMeter that measure a person’s performance in a series of tests meant to determine if you are impaired via testing your reflexes, hand-eye coordination, ability to balance, focus, and sense of time. And while a University of Chicago study found apps like these (unnamed in the study) do detect impairment, there are drawbacks. Primarily, the researchers stated, “If an app like this were to be used as a roadside sobriety test, law enforcement officers would have to compare each persons personal baseline/sober performance to their possibly intoxicated performance to accurately determine whether driving ability was impaired.”

Thus, the researchers said that while performance-based apps “may one day be established and validated. For now, we have a long way to go.”

However, Armentano said, NORML has advocated for the use of these performance technologies to help consumers know whether they are too high to drive and also help employers, who can presumably establish a personal baseline, know about the condition of their employees.

“These are the sort of performance tests that people could theoretically be asked to do on the side of the road to gauge whether or not their performance seems to be impaired,” Armentano said. “But we have to get away from the idea that any test will produce a magic number is going to tell us in that instant whether someone’s impaired or not. We are never going to have that number.”

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A new entry into this field isn’t trying to establish a broad assessment of impairment but is, in its initial development, more geared toward helping the officer at the side of road gain objective evidence of impairment.

Gaize” is a technology that runs on a headset platform and automates the same eye tests an officer performs on the side of the road as part of the Standardized Field Sobriety Tests, which include specific involuntary eye movements seen when a person is high. The program also provides video results for the test.

Ken Fichtler, Gaize’s founder and CEO, hopes to have their product available by the end of summer. He said Gaize is unique in that its tests are already “scientifically validated” to signal cannabis impairment via eye movement, based as they are on established field sobriety tests. 

However, as with all these tech-based impairment measuring tools, the results of the tests are currently not admissible in court. Even so, like other existing tools, Fichtler believes Gaize will be useful in the workplace and eventually for self-testing consumers.

“I think there is a really important role for technology to play in detecting impairment,” Fichtler said.

He added that an arresting officer “is trying to be objective but it’s a real challenge when you’re on the side of the road, lights flashing, traffic zooming by while you’re trying to do these tests. You already believe they are impaired, and so you have a confirmation bias built-in. And I think one of the really important roles that Gaize can play is driving fairness and objectivity into that process.”

Since Gaize and its founder are located in Missoula, Mont., we decided to ask Missoula County prosecutors if any of these new technologies would help enforce DUI laws. In addition to the location of this new company, Montana just began sales of cannabis for adult recreation, is experiencing a rebound in tourism, and also has an inherited per se law of 5 ng/mL.

Matt Jennings, Chief Criminal Deputy County Attorney for Missoula County, said they are not expecting a big surge due to tourism because the “vast majority” of DUIs there involve locals. He said they have seen an increase in cannabis-related DUIs since Montana legalized medical cannabis years ago and now with full legalization, but he added that more suspects are being tested for it as well.

“A lot of the increase is due to law enforcement being better trained to recognize impairment by marijuana in general,” Jennings said. “It’s a good chance that 20 or 25 years ago, law enforcement was mostly looking for alcohol.”

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Since legalization, he said, one of the most common reasons an officer suspects a driver of using cannabis is paraphernalia left out in the open, like a pot pipe in the cupholder. Apparently, legalization has caused some people to forget that having cannabis or a pipe open in their car is still probable cause. 

Typically, he said, suspects charged with cannabis-related DUIs often test far above the per se limit and have a combination of substances involved, such as alcohol or prescription drugs, methamphetamine, etc.

“So, what we often end up getting is more of a package with a blood test. But what we’re really focused on, honestly, is the driving behavior,” he said. “The reason there was an investigation is something was going on with the driving behavior or there was danger to the public that resulted in law enforcement making contact.”

As far as the new technology-based tools, Jennings said he’s “really excited about some of these technological options,” but getting their results admitted in court is another matter. Currently, judges in Montana do not allow alcohol breathalyzer tests as evidence, for example.

However, he added, “any tools are always helpful … So, if there are other alternatives or different pathways to understand what was going on with somebody’s intoxication or their driving behavior, that’s always going to give different avenues to pursue justice in those circumstances.


Jake Ellison has been an award-winning journalist for 30 years in the Pacific Northwest (primarily at the Seattle Post-Intelligencer) covering science, higher education and cannabis legalization. 

Jake Ellison