Survey reveals prevalence of marijuana and alcohol use among drivers

Jun 28 2017

In just seven years, the number of marijuana-positive drivers increased 50 percent, according to the 2013-2014 National Roadside Survey of Alcohol & Drug Use by Drivers. On the flip side, the percentage of alcohol-positive drivers decreased 77 percent between 1973 and 2013-2014. These results and others will be shared at the 40^th annual scientific meeting of the Research Society on Alcoholism (RSA) in Denver June 24-28.

"Alcohol and marijuana affect drivers differently," said Tara Kelley-Baker, senior research scientist with the AAA Foundation for Traffic Safety. "If you're impaired by alcohol, you run red lights. If you're impaired by marijuana, you have trouble noticing and responding to unexpected events. Both are dangerous, but differently so." Kelley-Baker will discuss these findings at the RSA meeting on June 27.

Of particular concern is the steep rise in drivers testing positive for marijuana. "Using data from both oral fluid and blood samples, we found more than 22 percent of daytime drivers and close to 23 percent of nighttime drivers were drug-positive in 2013-2014," she said. "THC, the active component of marijuana, was the most frequent drug, with almost 9 percent of daytime drivers and 13 percent of nighttime drivers testing positive."

Findings were drawn from two comprehensive projects funded and directed by the National Highway Traffic Safety Administration. First, the National Roadside Studies have been conducted approximately every decade since the early 1970s, examining the prevalence of alcohol among drivers by gathering breath samples at 60 sites across the U.S. For the first time in 2007, data on drug use was also gathered via collection of oral fluid and blood samples. The 2013-2014 study provided the first opportunity to examine trends in drug-positive driving. Second, the Crash Risk Study, was carried out during 20 months in Virginia Beach, ending in 2012. It examined the relative risk of driving while alcohol- or drug-positive. Researchers obtained breath, oral fluid, and blood samples from drivers involved in crashes, and also from a comparison group of drivers not involved in crashes who were driving on the same roads, at the same locations, and in the same direction of travel one week later.

"While these studies alone do not speak to the issue of the legalization of marijuana used for therapeutic or recreational use, they do – along with other research being conducted – provide needed information on drug use by drivers," said Kelley-Baker.