Study leader Dr. Guohua Li, professor of epidemiology and director of the Center for Injury Epidemiology and Prevention at the Columbia University's Mailman School of Public Health, said data came from two national information systems sources sponsored by the National Highway Traffic Safety Administration: the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers and the Fatality Analysis Reporting System.
The Fatality Analysis Reporting System is a repository of investigation data for all crashes that resulted in at least one fatality within 30 days of the crash and that occurred on a public road. This source also contains detailed information about the crash circumstances as well as individuals and vehicles involved in the crash.
The study, published in the journal Accident Analysis and Prevention, found 31.9 percent of the drivers involved in fatal car crashes and 13.7 percent of the drivers interviewed at the roadside survey -- controls -- 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 studied, depressants conferred the highest risk, followed by stimulants, narcotics and marijuana.
In addition, elevated blood alcohol levels were found in 57 percent of the cases and 8.8 percent of the controls; and the risk of fatal crash involvement increased exponentially as these levels rose. About one-fifth of the cases tested positive for alcohol and one or more drugs, compared with 2.2 percent of the controls.
"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," Li said in a statement.