WASHINGTON (CNN) -- Fewer Americans are driving drunk, but roughly one in six drivers on weekend nights is on drugs, according to a data released Monday by the National Highway Traffic Safety Administration survey.
In a survey conducted in 2007, 2.2 percent of drivers had a blood-alcohol content of 0.08 percent or higher, which would exceed the limit for driving while intoxicated in all 50 states and the District of Columbia, the agency said in a news release.
The first such survey, conducted in 1973, found 7.5 percent of drivers above the 0.08 limit, the release said. Other surveys were conducted in 1986 and 1996.
"I'm pleased to see that our battle against drunk driving is succeeding," Transportation Secretary Ray LaHood said in the news release.
"However, alcohol still kills 13,000 people a year on our roads and we must continue to be vigilant in our efforts to prevent drunk driving."
The 2007 survey was the first to also check for drug use while driving. It found that 16.3 percent of nighttime weekend drivers tested positive for drugs, according to the statement.
The drugs used most commonly by drivers were marijuana (8.6 percent), cocaine (3.9 percent) and over-the-counter and prescription drugs (3.9 percent), it said.
"This troubling data shows us, for the first time, the scope of drugged driving in America and reinforces the need to reduce drug abuse," said Gil Kerlikowske, director of the Office of National Drug Control Policy.
The survey involved setting up random sites across the country to question drivers who participated voluntarily and on condition of anonymity.
In total, almost 11,000 eligible drivers entered the survey sites, with 9,413 drivers agreeing to breath-alcohol measurements, 7,719 providing oral fluid samples and 3,276 nighttime drivers submitting blood samples, the news release said.