A 2014 survey of U.S. drivers shows that the issue of impaired driving has changed significantly over recent years. The Roadside Survey of Alcohol and Drug Use by Drivers is conducted periodically by the National Highway Traffic Safety Administration. The survey was first conducted in 1973. Since its inception, the survey has shown a dramatic decrease in the number of drivers with alcohol in their systems. Unfortunately, it has also shown an increase in the number of drivers using marijuana and other illegal drugs, as well as prescription drugs. The survey is voluntary and anonymous.
Since 2007, the number of drivers with alcohol in their blood has fallen by nearly one-third. The number of drivers reporting marijuana use has increased by almost 50 percent. In discussing the alcohol related figure, the head of the NHTSA suggested that it was the result of "a focused effort and cooperation among the federal government, states and communities, law enforcement, safety advocates and industry." A drop in alcohol use by drivers has the potential for enormous safety gains, as roughly 10,000 people are killed each year in alcohol-related motor vehicle accidents.
The results of another study were released in conjunction with the Roadside Survey. The second study involved the crash rates experienced by drivers due to impairment. That study found that a blood alcohol rate of .08 led to a crash risk four times that of sober drivers. The accident rate for drivers at .15 BAC or higher was 12 times that of sober drivers. The study also found an increased rate of accidents among marijuana users as compared to the general public.
Source: Tire Review, "NHTSA Releases Studies on Impaired Driving on U.S. Roads," by Tire Review Staff, 23 March 2015