Driving lesson

Bill to tackle marijuana-related impaired driving should be rejected

Spurred by the Commonwealth’s legalization of marijuana and growing concerns about an increase in impaired driving, Governor Charlie Baker reintroduced the Trooper Thomas Clardy Act, which states that the presence of any intoxicating substance or its metabolites in a driver’s system as indicated by breath analysis or a chemical test of blood or “oral fluid” will be admissible as evidence that that person is under the influence. Mitigating marijuana-impaired driving is a public safety priority, but testing marijuana use rather than actual impairment is an unnecessary and scientifically invalid approach that would be successfully challenged in court.

These tests can indeed detect THC, the main psychoactive chemical in marijuana, but in fact there is no blood, saliva or breathalyzer test that can determine whether a person who has used marijuana is actually impaired, and there is no level of THC in blood or mouth fluid that can distinguish between impaired and healthy. As noted in a 2017 U.S. Department of Transportation report to Congress, “blood THC level and degree of weathering do not appear to be closely related.” Additionally, THC builds up in fat and other body tissues, but then slowly returns to the bloodstream. So even after a few weeks of non-use, a THC test can still show evidence of previous marijuana use, long after any tampering has subsided.

Notably, courts in Oklahoma (Rose v. Berry Plastics Corp.) and Arizona (Whitmire v. Wal-Mart Stores Inc.), persuaded by scientific evidence, have ruled that a positive doping test does not justify not dismissing an employee who is a medical marijuana patient unless there is also evidence of impairment. It seems inevitable that judges will apply this same reasoning to traffic stops of suspected impaired drivers.

Should law enforcement officers use the standardized field sobriety test instead, as they do with suspected drunk drivers? No, because researchers have shown that this method does not reliably measure marijuana impairment. Its key component is the horizontal gaze nystagmus test, a procedure approved by the National Highway Traffic Safety Administration to observe whether drivers have jerky, uncontrollable eye movements when trying to follow a small object that is moved to one side. to the other. Based on research, Bill’s acceptance of the horizontal gaze nystagmus test as a reliable field sobriety test is grossly misinformed.

But what would be better for combating impaired driving, whatever the cause, is a quick, reliable and objective measure of impairment that can be used during a traffic stop. In short, effective law enforcement requires an assessment of impairment, not substance use. That’s why our company, Impairment Science Inc., has developed an app to assess impairment. Used on a smartphone or tablet and taking just three minutes, the Druid app offers four game-like tasks that measure reaction time, decision-making accuracy, hand-eye coordination, balance and ability to perform divided attention tasks. Independent researchers have validated Druid’s ability to detect alcohol and marijuana impairment. Currently, Druid can be used by employers whose workers are in safety-sensitive jobs, but work to adapt the app for use during roadside stops is only now underway.

It is essential to develop a reliable and objective measure of impairment for traffic stops, but calls to use the mere presence of THC in a driver’s system to define legal impairment should be resisted. The Legislature should reject the Baker bill.

Michael Milburn, a retired psychology professor at UMass Boston, is the founder and chief scientific officer of Impairment Science Inc. He conceived the idea for the Druid app. William DeJong, a retiree professor of public health at Boston University and former board member of MADD, is the Director of Research and Evaluation at Impairment Science.