The number of U.S. teenagers who drink and drive dropped by more than half from 1991 to 2011, federal health officials said Tuesday.

Nine out of 10 high school students age 16 and over said they did not drink and drive in 2011, according to the U.S. Centers for Disease Control and Prevention (CDC). This represents a decline of 54 percent over two decades.

Still, one in 10 -- or nearly one million students a month -- reported driving after consuming alcohol.

"Drinking and driving is risky for any driver, but especially for young teens," CDC director Dr. Thomas Frieden said. "Young drivers are 17 times more likely to die in a crash when they have a blood alcohol concentration of 0.08 than when they have not been drinking."

Car crashes remain the leading cause of death for teens, Frieden said. "There are more than 2,000 teens aged 16 to 19 killed on the road each year, and many of those deaths are alcohol-related," he said. One in five teen drivers involved in a fatal crash in 2010 had alcohol in their system, he added.

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