17 Percent of Drivers in Washington Test Positive for THC

More than one third of drivers in the state of Washington tested positive for marijuana, alcohol or other drugs while driving, according to a study sponsored by the National Highway and Traffic Safety Administration.

The majority of drivers tested positive for marijuana, followed by over-the-counter or prescription medications.

Researchers compared trends in the prevalence of marijuana and alcohol exposure among Washington drivers before and after marijuana legalization. They did not find a statistically significant increase in the number of drivers who tested positive after legalization.

In fact, the percentage of drivers driving under the influence of alcohol was lower than expected. About five percent of drivers tested positive for alcohol, but only one percent of drivers exceeded the legal limit of 0.08 blood alcohol content.

“This shines the light on some good news,” Washington Traffic Safety Commission Director Darrin Grondel told the Maple Valley Reporter. “It is the norm in Washington to drive sober.”

Washington legalized the consumption of recreational marijuana in December 2012, and it legalized the retail sale of the drug in July 2014. Opponents of legalization expressed concern about a potential increase in drug-impaired driving after legalization.

Researchers from the nonprofit Pacific Institute for Research and Evaluation conducted roadside surveys before legalization of sales, six months after legalization and one year after legalization. The surveys were conducted during two-hour intervals during daytime on Fridays and during two-hour intervals on Friday and Saturday nights.

The researchers collected breath, oral and blood samples from a total of 6,665 anonymous drivers. They analyzed breath and blood samples for alcohol intoxication, and they examined oral and blood samples for marijuana and other drug intoxication.

In the wave of surveys conducted before legalization, researchers found 14.6 percent of drivers tested positive for THC. Six months later, 19.4 percent tested positive, and 21.4 percent tested positive after sales had been legal for one year. Combined, 17 percent of drivers tested positive for THC.

Percent Positive for THC Participants Surveyed
Before Legalization 16.6 908
Six months after 19.4 672
One year after 21.1 810

Despite the increase in percentages, the authors of the study emphasized that there was not a statistically significant increase in the number of positive tests. The authors also wrote that the presence of THC did not imply impairment.

Roughly nine percent of drivers tested positive for stimulants, mainly amphetamines, and about six percent tested positive for opioids, primarily prescription painkillers. It was impossible to determine whether drivers tested positive for illicitly- or legally-obtained drugs based on the data collected.

The study was also limited by response bias. Since participation was voluntary, drivers who were driving under the influence may have been less likely to stop and participate.

Washington Launches ‘Summer Drive Sober or Get Pulled Over’ Campaign

While the study’s results were promising, Washington law enforcement is still proactively trying to cut down on traffic fatalities.

The Washington State Patrol announced that state troopers will be increasing patrols from Aug. 19 to Sept. 5. Labor Day weekend is the deadliest time of year for drunk-driving deaths, according to the state patrol.

A Washington Traffic Safety Commission report found that 251 traffic deaths involved impaired drivers. Of those drivers:

  • 20 percent tested positive for alcohol intoxication.
  • 20 percent tested positive for one drug.
  • 60 percent tested positive for multiple drugs.

“When someone combines impairing substances, such as consuming marijuana and drinking alcohol, they may experience a greater level of impairment than they expected,” Grondel said. “This data shows that combining alcohol and drugs, or one drug with another drug can be a very deadly mix for drivers.

The campaign is part of the state’s Target Zero initiative, which strives to prevent all traffic fatalities by 2030. The Summer Drive or Get Pulled Over campaign is designed to encourage drivers to avoid impaired driving.

“Don’t risk getting arrested for a DUI, or causing a life-changing tragedy,” Grondel said. “Designate a sober, drug-free driver, catch a ride share, or walk with a buddy.”



Medical Disclaimer: DrugRehab.com aims to improve the quality of life for people struggling with a substance use or mental health disorder with fact-based content about the nature of behavioral health conditions, treatment options and their related outcomes. We publish material that is researched, cited, edited and reviewed by licensed medical professionals. The information we provide is not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be used in place of the advice of your physician or other qualified healthcare provider.

View Sources

  • KIRO 7. (2016, August 17). Study: 1 in 3 drivers tested positive for drugs.
  • Maple Valley Reporter. (2016, August 15). One-Third of Washington Drivers Drug-Positive Study Shows.
  • Mertz, A. (2016, August 19). ‘Driver Sober or Get Pulled Over:’ Extra patrols targeting drivers under the influence.
  • Ramirez, R.A. et al. (2016, July). Marijuana, Other Drugs, and Alcohol Use by Drivers in Washington State. Retrieved from https://www.nhtsa.gov/sites/nhtsa.gov/files/812299-washingtonstatedrugstudy.pdf
  • Target Zero. (n.d.) Home.
  • Washington State Patrol. (2016, August 19). Summer Driver Sober or Get Pulled Over [Press release].

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