Why it's so difficult to detect, measure, convict drivers high on marijuana

Earlier this week, David Njuguna was convicted of speeding and operating erratically before crashing into Massachusetts State Trooper Thomas Clardy's cruiser, killing him. A Worcester judge, however, found the medical marijuana patient not guilty of impaired driving, based on scientific grounds, even though he had THC in his blood.

So, why is it so difficult to come up with a simple THC number that indicates intoxication?

"Right from the beginning, we said that we were gonna treat alcohol and marijuana the same," said Walpole Police Dept. Chief John Carmichael.

That's a promise law enforcement has not been able to keep when it comes to the issue of motor vehicle operation after cannabis use. "High drivers" are getting stopped and arrested, but cases routinely fall apart, says Carmichael, for one thing, because unlike drunken drivers who refuse breathalyzers, drivers on cannabis can refuse assessment of their intoxication level without penalty.

"There's no teeth in the law to say OK if you refuse this test you could lose your driver's license," said Carmichael.

For Njuguna, the judge said, "It cannot be determined from the THC level when the person ingested any marijuana, how much the person ingested and how impaired the person is at any time."

What she means is, when you inhale marijuana, the level of THC rises rapidly in the blood, but after a short spike, it rapidly falls and stays low, even though during this period, a marijuana user could very well be very high.

Call this, the cannabis testing conundrum.

In a report to Congress in 2017, the National Highway Traffic Safety Administration put it like this: "Peak impairment does not occur when THC concentration in the blood is at or near peak levels."

Still, Governor Charlie Baker is proposing to penalize drugged driving more like drunken driving.

He tells Boston 25 News, The proliferation of marijuana use across the Commonwealth as a result of legalization is creating a very real threat to our roadways and I urge lawmakers to pass our legislation to allow police officers to do their jobs and get impaired drivers off our roadways."

Carmichael, who was appointed by Baker to serve on the independent, 25-member Cannabis Advisory Board, helped draft recommendations that went into Baker's proposal. His reaction to the Njuguna verdict: "It is tough to swallow for law enforcement to see that this is one of our own that was killed as a result of an impaired driver."

Drugged driving statistics are alarming. According to the National Institute on drug abuse, in 2017, 12 million people older than 16 drove under the influence of illicit drugs.

The government agency reports that marijuana affects psychomotor skills and cognitive functions. It estimates that almost 44% of drivers in deadly crashes tested positive for drugs.

Boston 25 Investigates took a look at the number of drunken and drugged drivers in our state. We found drugged driving is actually outpacing drunken driving.

>> 25 Investigates: Drugged driving outpacing drunk driving in Massachusetts

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