Law enforcement agencies in Maine have two options to ascertain whether an impaired driver is under the influence of cannabis, York County Sheriff William L. King Jr. said.

One option involves having the driver examined by a Drug Recognition Expert, an officer who has specialized training to look for clues that might lead him to suspect the driver is drug impaired, King said. The second option is a blood test, which will show whether a person has been using cannabis recently.

But testing for drug impairment remains problematic nationwide due to the limitations of drug-detecting technology and the lack of an agreed upon impairment limit. The nationally recognized level of impairment for drunken driving is 0.08% blood alcohol content, but there is no similar national standard for drugged driving, according to the National Conference of State Legislatures.

King’s department is investigating a crash in Hollis Sunday night in which four Maine State Police troopers were injured by a driver who appears to have been impaired by marijuana. Tyler Croston, 24, of Westbrook, drove a 2017 Subaru WRX into the troopers, police say. He is charged with aggravated driving under the influence, aggravated driving to endanger and reckless conduct with a dangerous weapon. 

King said Monday that there was “sufficient evidence” to charge Croston with operating while impaired. Investigators at a news conference Monday said evidence at the scene and witness statements indicated the possibility that Croston had been using marijuana.

Croston, who was taken to the hospital following the crash, consented to a series of tests with a Drug Recognition Expert (DRE) at the hospital that indicated he was under the influence of narcotics, police said.


“The DRE is specially trained to look for clues that the person is under the influence of marijuana,” King explained.

Cannabis Impairment Detection Training is offered at the Maine Public Safety Training Institute’s Green Lab in Auburn.

Investigators also took a sample of Croston’s blood to test at the hospital. King said results of that test will be expedited, but he was uncertain when they would be available.

Neither option, however, will give investigators a clear picture of the level of cannabis in a person’s system like a blood alcohol test would, King said.

“Does it present a problem? Absolutely,” King said of trying to determine the source of a driver’s impairment.

“The challenge for law enforcement is tracking how many crimes or traffic related incidents have occurred with cannabis as a causal or contributing factor,” he said.

King would like to replicate Colorado’s Cannabis Conversation program, a statewide initiative involving the public, marijuana consumers, law enforcement and local governments to better understand why people drive high and how to prevent impaired people from getting behind the wheel. Colorado legalized recreational marijuana in 2012.

According to the U.S. Centers for Disease Control and Prevention, a total of 12.8 million Americans reported driving while under the influence of marijuana or other illicit drugs in 2018.

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