It’s already pretty obvious that putting yourself behind the wheel of a car while drunk or on drugs means that you’re also putting yourself at risk for death. But now, a new study confirms it, finding that people who drive while drunk or on drugs are nearly three times more likely to get into a fatal car crash than those who did neither.

Researchers from the Columbia University School of Public Health used two sets of data from the National Highway Traffic Safety Administration: the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers and the Fatality Analysis Reporting System. Both showed information on drug and alcohol use while being involved in a car crash.

Relative to car crashes in which the driver did neither drugs nor alcohol, they found that that 31.9 percent of fatal car crashes and 13.7 percent of those who were part of the roadside survey tested positive for non-alcoholic drugs, with depressants causing the highest risk, followed by stimulants, narcotics, and marijuana.

People who were in fatal car crashes were overall more likely to be on drugs than those that weren’t. Fifty-seven percent of those in fatal crashes had high blood alcohol levels, compared to only 8.8 percent of those interviewed in the roadside survey, while 20.5 percent of fatal crashes involved drivers who tested positive for alcohol and at least one drug compared to 2.2 percent of the roadside survey participants.

“The possible interaction of drugs in combination with alcohol on driving safety has long been a concern,” Dr. Guohua Li, professor of epidemiology and director of the Center for Injury Epidemiology and Prevention, said in a statement. “While alcohol-impaired driving remains the greatest threat to traffic safety, these findings about drugged driving are particularly salient in light of the increases in the availability of prescription stimulants and opioids over the past decade.”

About 30 people die daily as a result of an alcohol-impaired driver, amounting to one death every 48 minutes, according to the Centers for Disease Control and Prevention (CDC).

Source: Li G, Brady J, Chen Q, et al. Drug use and fatal motor vehicle crashes: A case-control study. Accident Analysis & Prevention. 2013.