Drivers’ Use of Marijuana in Washington State

In July 2014, Washington State allowed legal sales of recreational marijuana. Working with the Washington Traffic Safety Commission, the National Highway Traffic Safety Administration (NHTSA) assisted the State in conducting a roadside study to examine the prevalence of marijuana use before and after sales began. The study also examined drivers’ use of alcohol and other drugs. National roadside studies have been conducted approximately every decade since the 1970s. This study used a similar research design as the national studies but included several enhancements. It included more than 70 over-the-counter, prescription (antidepressants, sleep medications, etc.), and illegal drugs (cocaine, opioids, etc.) that may impair driving-related skills. This project’s objective was to examine whether the percentage of drivers who tested positive for marijuana increased after sales of the drug became legal and what the effect was on alcohol-impaired driving. Data was collected in three waves: (1) immediately before implementation of legal sales, (2) six months after implementation, and (3) one year after implementation.


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  • Accession Number: 01608625
  • Record Type: Publication
  • Report/Paper Numbers: DOT HS 812 307
  • Created Date: Aug 19 2016 12:21PM