New Report Shows Multiple Drug Use Responsible for One in Four Washington Traffic Deaths in 2016

State traffic safety advocates advise caution as “420 Day” approaches, an unofficial celebration dedicated to cannabis

Olympia – The Washington Traffic Safety Commission (WTSC) released a report today on the significant increase of multiple drug (alcohol and other intoxicants), or poly-drug use, in drivers involved in deadly crashes.

Driver impairment is the most common factor in deadly crashes in Washington, present in more than half of all traffic deaths in 2016. Poly-drug use is the most common type of impairment and is double the number of alcohol-only drivers and five-times higher than the number of marijuana-only drivers. The report also shows that poly-drug use is an increasing factor in traffic fatalities.

“All studies agree that combining alcohol and marijuana inflates the level of driver impairment and crash risk,” said Staci Hoff, PhD, Research Director, Washington Traffic Safety Commission. “The deadly consequence of combining these two impairing substances is already apparent in Washington fatal crash data.”

Poly-drug use means that a driver’s blood test was positive for alcohol and a drug or multiple drugs. Among drivers who tested positive, nearly 45 percent tested positive for more than a single substance. The most common combination found together is alcohol and marijuana.

Information from several self-report surveys show that driving after using marijuana is common. Among young drivers who admit to driving after marijuana use, more than half believe marijuana makes their driving better. However, marijuana use effects many critical functions involved in driving including memory, reaction time, vision, and divided attention tasks.

Some people who use marijuana celebrate April 20 as a day to celebrate cannabis culture. “This report highlights the need to plan before you party, as marijuana and poly-drug use become more common in our state’s traffic deaths,” said Darrin Grondel, Director, Washington Traffic Safety Commission. “Simple planning, like choosing a designated driver, can prevent crashes, and that’s even more important if someone is using more than one substance.”

The full report can be viewed and downloaded at
Poly-Drug Line Graph:
Poly-Drug Circle Graph: