Washingtonians can receive a DUI for driving after using cannabis, the state’s Supreme Court concluded Thursday, a decision that upholds the state’s decade-old law regulating marijuana use behind the wheel of a car.

All nine justices rejected Douglas Fraser’s argument that his 2017 DUI was based on an arbitrary and vague standard for THC levels in the blood. Although the justices acknowledged that the correlation between THC levels and impairment is challenging to pinpoint, they found that blood measurements nevertheless provide a useful and constitutionally acceptable measurement.

“Although this limit may not be perfect in terms of identifying degree of impairment for all individuals, it is reasonably and substantially related to recent consumption, which is related to impairment,” Justice G. Helen Whitener wrote in the court’s majority opinion, which was signed by her eight colleagues.

A Washington State Patrol trooper pulled over Fraser near Everett Mall in July 2017 after seeing him speeding alone in an HOV lane, changing lanes erratically and cutting off other drivers, according to the trooper.

When the trooper approached the car, he noticed Fraser was wearing an employee badge from a local cannabis dispensary, which Fraser then removed.

The trooper said Fraser was shaking, sweating and had dark circles under his eyes.


According to the trooper, Fraser said he had smoked “half a day” earlier but that he no longer felt impaired. After performing several field tests, the trooper arrested Fraser on suspicion of DUI.

A test later showed Fraser had a THC blood concentration of 9.4 nanograms per milliliter, with a margin of error of 2.5. That put his THC blood concentration above the state’s 5 ng/ml limit.

Fraser argued in court that the limit was not correlated to any real measure of impairment and was therefore arbitrary, vague and unconstitutional. He backed his opinion with testimony from a doctor who said the effect of a given level of THC can vary significantly from person to person, depending on body fat and frequency of cannabis use.

The justices agreed that impairment standards based solely on THC blood concentration can’t be generalized to the entire population but disagreed that meant the state’s standard was vague or arbitrary.

For one, that’s because marijuana became legal in Washington via a people’s initiative, so the burden for proving the standard unconstitutional is high. Additionally, for both alcohol and marijuana, the standard is based on perceived impairment or blood levels.

And while driving and cannabis use are both legal, neither is a right, the justices said. The impairment caused by 5 ng/ml of THC in the blood may vary, but the limit serves its purpose by discouraging drivers from taking to the roads after using marijuana.

“The laws aim to deter people who have consumed cannabis from driving when there is a possibility they could be impaired, thus promoting some public interest of highway safety,” Whitener wrote.

It’s reasonable to assume the law will continue to do just that, Whitener wrote, and “the highways will be safer because of it.”