A new study by the Centers for Disease Control and Prevention demonstrates the effectiveness of education and enforcement in reducing drunk driving by teens, but is not a cause for complacency.

Since 1991, the study found, drunk driving by teens has declined by more than half. Students in all 50 states and the District of Columbia responded to an anonymous questionnaire on the subject. In 1991, 22.3 percent acknowledged drinking and driving, whereas 10.3 percent acknowledged doing so last year, a decline of more than 54 percent.

Over that period, all states raised their minimum drinking ages to 21. Many states made it illegal for any teen driver to have any alcohol in their systems, and adopted graduated licensing programs.

The results mesh with accident statistics over the same period, with teen deaths in traffic accidents declining by more than 40 percent.

Despite the decline in teen DUI, it remains a serious problem. Car crashes still are the leading cause of death among teens, claiming more than 2,000 in 2011, and the survey results mean that more than 1 million teens still drove while drunk at least once last year.

Since 84 percent of the teens who acknowledged having driven drunk said they did so after a binge-drinking episode - making that activity a logical target for ongoing education and enforcement efforts.