Scientists Discover Drug-Positive Drivers Have Triple the Risk for Fatal Car Crashes

There's new evidence that shows people driving under the influence of drugs are more dangerous than ever on the road. Scientists have discovered that drug use is associated with an increased risk of fatal crash involvement--almost three times as high.

In order to learn a little bit more about how drugs and alcohol affect fatal crashes, the researchers examined data from two national information sources: the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers and the Fatality Analysis Reporting System (FARS). In fact, FARS also contained data about the crash circumstances as well as individuals and vehicles involved in the crash.

So what did they find? It turns out that 31.9 percent of the drivers involved in fatal car crashes and 13.7 percent of the drivers interviewed at the roadside survey tested positive for at least one non-alcohol drug. Overall, drivers testing positive for drugs were three times as likely as those testing negative to be involved in a fatal crash. Among the drugs, depressants conferred the highest risk, followed by stimulants, narcotics and marijuana.

That's not all the scientists discovered. They also noted that elevated blood alcohol levels were found in 57 percent of the cases and 8.8 percent of the controls. In addition, they found that the risk of fatal crash involvement increased exponentially as those levels rose. Relative to drivers who tested positive for neither alcohol nor drugs, the odds of fatal crash involvement increased by more than 13 times for those who were alcohol positive but drug-negative, more than two-fold for those who were alcohol-negative but drug-positive and a staggering 23 times for those who were positive for both drugs and alcohol.

"The possible interaction of drugs in combination with alcohol on driving safety has long been a concern," said Guohua Li, one of the researchers, in a news release. "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 decades."

The findings are important for better understanding exactly how dangers drugs and alcohol are when it comes to driving. It could help influence future policies concerning drivers under the influence and gives that much more of an incentive for impaired drivers not to get behind the wheel.

The findings are published in the journal Accident Analysis & Prevention.