A new study finds that among 44,000 U.S. drivers involved in fatal single-vehicle car crashes between 1998 and 2009, 25% tested positive for drug use. The most common drugs were marijuana, cocaine and amphetamines.
It’s not clear whether drugs caused the accidents. The connection might make sense intuitively, but there isn’t much data on the impact of drug use on traffic deaths, according to the new study in the Journal of Studies on Alcohol and Drugs, which sought to clarify the link.
“The suspicion is there, because when you look at drivers who’ve been in fatal crashes, the percentage using drugs is a good deal higher,” said study co-author Robert B. Voas of the Pacific Institute for Research and Evaluation in Calverton, Md., in a statement.
Analyzing data from the national Fatality Analysis Reporting System (FARS), the researchers found that drivers in a quarter of crashes studied tested positive for drugs and 37% had blood-alcohol levels higher than the legal limit of 0.08. About 58% had no alcohol in their systems.
Stimulants were linked to all reasons for fatal crashes, including speeding, failure to obey other traffic laws, inattention and not using a seatbelt. Marijuana use was linked to speeding and failure to use a seatbelt.
Given the difficult nature of testing for drug use in drivers — some drugs linger in the body longer after use — and the fact that there is no consensus on the definition of drug-impaired driving, U.S. states differ in how they deal with drug use on the road. In at least a dozen states, there’s a “zero tolerance” policy — no amount of drugs allowed. But the specific drugs that are prohibited vary.
The study also looked at interactions of drug and alcohol use in fatal crashes and found that the combination did not appear to contribute to more impaired driving. In other words, when alcohol was involved, it was the main reason for impaired driving; it didn’t matter whether drivers had also used other drugs. Drugs appeared to play a role only when drivers hadn’t been drinking, the study found.
“Alcohol is still the largest contributor to fatal crashes,” said study co-author Eduardo Romano.
A separate study released this week questioned the safety of driving with a blood-alcohol level of even 0.01 — far lower than the legal limit. That study found that consumption of any amount of alcohol, even just a light beer, was associated with a higher risk of accident and more severe accidents than sober driving.
Moral of the story? Don’t drink or use drugs and drive.