Marijuana and alcohol make a terrible mix on the road, significantly increasing a driver’s chances of causing a deadly crash, a new study warns.
The risk of being the person to start a crash if you’ve used both pot and alcohol “increases by more than fivefold when compared with drivers who used neither of the substances,” study author Dr. Guohua Li, a professor of epidemiology at Columbia University’s Mailman School of Public Health, said in a school news release.
Researchers looked at data from nearly 15,000 fatal two-vehicle crashes in the United States between 1993 and 2014.
Drivers who caused the crashes were much more likely than blameless drivers to test positive for alcohol (28 percent vs. 10 percent), marijuana (10 percent vs. 6 percent), or both alcohol and marijuana (4 percent vs. 1 percent).
Drivers who tested positive for alcohol, marijuana or both were more likely than those who tested negative to be male, aged 25 to 44, and to have been in a crash or had traffic violations within the previous three years.
The most common driving error that caused a fatal crash was failure to stay in the proper lane. That error occurred in 43 percent of crashes. Failure to yield right of way and speeding were each the cause of about 20 percent of the crashes.
The researchers also found that on their own, alcohol and marijuana increase a driver’s crash risk by 437 percent and 62 percent, respectively.
“While alcohol-impaired driving remains a leading cause of traffic fatalities in the United States, driving under the influence of marijuana and other drugs has become more prevalent in the past two decades,” Li said.
“Countermeasures targeting both drunk driving and drugged driving are needed to improve traffic safety,” Li concluded.
The study was published in the journal Annals of Epidemiology.
The U.S. National Library of Medicine has more on impaired driving.