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

In Washington State legal sale 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 one year after implementation. Of almost 2,500 participants, 14.6 percent of drivers, 19.4 percent of drivers, and 21.8 percent of drivers were THC-positive in Waves 1, 2, and 3, respectively.