Driving High? Experts Can’t Figure Out How to Measure Impairment

The number of fatal Washington crashes involving drivers with marijuana in their system rose to 79 last year — more than double that of 2012 when voters legalized its recreational use.

In Yakima County, however, the number has remained essentially unchanged at an average of about five a year, according to the state Traffic Safety Commission.

But experts caution the statistics focus only on fatal crashes and don’t provide a complete picture of the impact pot is having on road safety.

When issuing impaired driving citations, most police agencies don’t differentiate between alcohol, pot or other drugs. They’re simply categorized as DUIs.

As a result, data regarding marijuana- impaired drivers isn’t complete. No statewide data is kept on serious injury accidents involving marijuana because of reporting inconsistencies by local police agencies, according to the safety commission.

From a traffic safety standpoint, the state wasn’t ready for the legalization of recreational marijuana, said Nathan Weller, a Pullman-based consultant helping Washington State University with a marijuana-impairment study.

“The amount of challenges that went along with it was unknown at the time (of voter approval) and now we’re playing catch-up,” he said.

Most officers use a standard field sobriety test that initially focuses on impairment rather than determining whether a driver is over the legal limit, said Washington State Patrol Sgt. Brandon Villanti, who works in the impaired driving unit in Seattle.

“We look for impairment and inability to provide attention, motor skills, ability to operate a motor vehicle,” he said. “So our officers are not making an arrest on legal limit but on impairment, and that is confirmed with a blood or breath test.”

But those tests may not be adequate considering the variables of involving marijuana intoxication. Eating pot products can take one to five hours before the peak affect kicks in, compared to the more immediate affect produced by smoking it. That can make it difficult to determine the level of impairment at the time of an accident, Weller said.

For example, someone who smoked it may have a low level of THC in their blood an hour later even though they were high when they were driving, he said.

A person who ingests pot may not have been high at the time of driving but later test positive at a police station, Weller said.

And pot is hard for users to regulate compared with alcohol. For many people it’s safe to drive one hour after a drink, two hours after two drinks, and so on because the amount of alcohol in each drink is regulated.

Participants described getting higher off some products that claimed to have lower THC concentrations than others, he said.

“It’s a rabbit hole right now,” Weller said. “We’re just scratching the surface.”

Researchers in the WSU study are working on developing a Breathalyzer similar to ones used to detect alcohol, he said.

Similar work is being done in Colorado, where fatal crashes involving marijuana have shot up since legalization there in 2012.

Villanti said there are times when a blood test may not reveal the impairment an officer sees on the road. Depending on the case, a drug recognition expert may be brought in to investigate. There are 200 recognition experts in the state who can not only identify a substance of drug but calculate what a person’s level of intoxication was hours before a test, he said.