Department of Transportation Report Bemoans Lack of Accurate Roadside Marijuana Intoxication Test
The 44-page federal analysis makes some important distinctions between the dangers of drunk and stoned driving, and makes a veiled case for cannabis rescheduling.
Published on August 18, 2017

It’s no secret that stoned driving is hard to detect. Even in states where cannabis is legal and regulated like alcohol, an effective and reliable impairment test has yet to hit the market, leaving law enforcement to use a mix of outdated, ill-informed tests and their own variable guessing games to make weed-related DUI arrests. To drive home the point about the difficulties in testing stoned drivers, the National Highway Traffic Safety Administration (NHTSA), a subset of the federal Department of Transportation, has submitted a report to Congress on marijuana and driving, detailing the need for a consistent detector of cannabis impairment, research into stoned driving and increased training for the nation’s police officers.

Taking shots at urine, hair, sweat, mouth swabs and more, the report is not shy about the inaccuracy of current testing methods, including the most widely discussed and most invasive option, testing a drivers blood and making an arrest if it supersedes an arbitrary 5 ng/ml of THC benchmark.  

“The adoption of a 5 ng/ml per se law for THC would appear to result in the exclusion of a large number of drivers who law enforcement officers believe to be impaired by marijuana but whose blood THC concentrations will fall below this artificial per se threshold during the minimum 1 - 2 or more hours it will take to collect a blood sample following a stop, investigation and arrest.” The report says, adding “Poor correlation between THC concentration and performance was found, which again indicates that blood THC level is not a reliable indicator of impairment.”

Because cannabis stays in the body for weeks or even months after your high ended, any test that doesn’t account for immediate impairment detection is essentially worthless. But even if such a test can debut in the near future, the NHTSA report made it incredibly clear that drunk and stoned driving are not the same thing, and should not be treated as such. 

Citing a 2016 study, the NHTSA writes, “Subjects dosed on marijuana showed reduced mean speeds, increased time driving below the speed limit and increased following distance during a car following task. Alcohol, in contrast was associated with higher mean speeds (over the speed limit), greater variability in speed, and spent a greater percent of time driving above the speed limit. Marijuana had no effect on variability of speed. In the combined alcohol and marijuana condition it appeared that marijuana mitigated some of the effects found with alcohol by reducing the time spent above the speed limit.”

The federally mandated report required the NHTSA not only to examine the status of marijuana and driving in the United States, but to also make recommendations about the future of the enforcement and detection. 

Sticking with the harsh tone of the report’s body, the recommendations focus on extensive police officer training and research into detection tools that actually work. For that to happen, however, marijuana’s Schedule I status might first have to be challenged. And while the NHTSA didn’t specifically recommend that the feds reschedule weed, they did blame the unnecessary Schedule I classification for blocking necessary safety research. 

“Unlike alcohol, marijuana is classified as a Schedule I substance under the Controlled Substances Act. A much smaller number of studies have looked at the impairing effects of marijuana use on driving related skills.” The report explains to Congress. “A clearer understanding of the effects of marijuana use will take additional time as more research is conducted. The extra precautions associated with conducting research on a Schedule I drug may contribute to this relative lack of research.”

Zach Harris
Zach Harris is a writer based in Philadelphia whose work has appeared on Noisey, First We Feast, and Jenkem Magazine. You can find him on Twitter @10000youtubes complaining about NBA referees.
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