Marijuana, Other Drugs, and Alcohol Use by Drivers in Washington State

In Washington State legal sales of marijuana began July 8, 2014. A voluntary, anonymous roadside study was conducted to assess the prevalence of drivers testing positive for alcohol and other drugs, including marijuana, on Washington’s roads. Data was collected in three waves, before implementation of legal sales, about 6 months after implementation, and 1 year after implementation. Of the almost 2,400 participants who provided an oral fluid or blood sample, 14.6 percent of drivers, 19.4 percent of drivers, and 21.4 percent of drivers were delta-9-tetrahydrocannabinol (THC)-positive in Waves 1, 2, and 3, respectively. There were no statistically significant differences between waves. There was a statistically significant increase in daytime prevalence of THC-positive drivers between Wave 1 (7.8%) and Wave 2 (18.4%), and also between Wave 1 and Wave 3 (18.9%). There was an increase in the percentage of THC-positive nighttime drivers with each successive wave, but these increases were not statistically significant. Synthetic marijuana was found in only 2 of the participants.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; Maps; References; Tables;
  • Pagination: 73p

Subject/Index Terms

Filing Info

  • Accession Number: 01609738
  • Record Type: Publication
  • Report/Paper Numbers: DOT HS 812 299
  • Contract Numbers: DTNH22-11-D-00226-0004
  • Created Date: Sep 1 2016 9:27AM