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Interesting article on impaired-driving

Testing for the influence of marijuana is an imperfect science, and even roadside assessments are legally inconclusive.

Whereas a blood alcohol content of 0.08 percent or higher is accepted as the threshold for a DUI charge, blood tests for marijuana aren’t as reliable a measure of physical impairment. Cannabinoids are metabolized differently depending on the individual and the way it was ingested. As a result, the idea of blood tests for marijuana is “flawed,” according to Matt Allen, who is also on the commission’s impaired driving panel.

“Because marijuana metabolites can remain in the blood for weeks after use, there is no evidence that this is an accurate way to measure impairment,” said Allen.

For example, a first-time user could register a low amount of tetrahydrocannabinol (THC) in their system but still be too impaired to drive, while a heavy user could be unfairly arrested for lingering metabolites, even when they’re not under the influence of the drug.

Additionally, the Massachusetts Supreme Judicial Court unanimously ruled that police officers could not cite their roadside observations to conclude in court that a driver was under the influence of marijuana.

“Because the effects of marijuana may vary greatly from one individual to another, and those effects are as yet not commonly known, neither a police officer nor a lay witness who has not been qualified as an expert may offer an opinion as to whether a driver was under the influence of marijuana,” the court wrote in its decision.

According to Carmichael, officers can still share their observations about a driver’s behavior or demeanor in court, but they can’t make any affirmative “pass” or “fail” declarations.

“They just can’t go up there and say this person failed this test,” he said.

Importantly, even if the ability to convict marijuana-impaired drivers may be limited, nothing is stopping law-enforcement officers from taking away the keys of a driver they think is dangerous.

“Our first priority is getting people off the road,” Carmichael said.

But as with most roadside policing efforts, the ACLU also has concerns about whether they would be equitably enforced. The group put out a report in 2016 that found black people in Massachusetts were three times more likely than whites to be arrested for marijuana possession, despite similar usage rates.