One fairly obvious way to lessen your chances of dying in a car crash: Don't take drugs before getting behind the wheel. Researchers found that a full 25% of drivers who died in single-vehicle accidents between 1999 and 2009 tested positive for drugs, USA Today reports. Of those studied, 22% tested positive for stimulants, 22% for marijuana, and 9% for narcotics. Alcohol doesn't help either: 37% of the dead drivers studied had blood alcohol levels over the legal limit of .08.
And though combining drugs and alcohol is certainly not recommended, researchers found that it made no difference in the drivers' level of impairment: "When a driver is drunk, it doesn't matter what drugs are in their system. The alcohol takes over," says a co-author. Even so, one activist points out that more attention should be paid to "drugged driving separate from the alcohol problem." Only 19 states prohibit any amount of drugs while driving. (Read more driving under the influence stories.)