The number of teens and young adults who drive under the influence of alcohol or a combination of alcohol and marijuana is declining, a new study finds.

Self-reported driving under the influence of alcohol declined by 59 percent among those ages 16 to 20 between 2002 to 2014, HealthDay reports. Among young adults ages 21 to 25, the rate dropped by 38 percent.

Driving under the influence of alcohol and marijuana dropped by 39 percent in both age groups, according to the study, published by the Centers for Disease Control and Prevention. There was little decrease in the number of young adults who said they drove under the influence of marijuana alone.

Lead researcher Dr. Alejandro Azofeifa of the Substance Abuse and Mental Health Services Administration (SAMHSA) said the decline in driving under the influence of alcohol is probably due to a combination of factors.

These include a decline in drinking overall, and a drop in binge drinking among high school students. Underage drinking laws are being more strictly enforced, and graduated driving license laws require that young drivers do not drink and drive, he noted.

Drunk driving increased with age, the study found. Only 1.5 percent of 16-year-olds said they drove under the influence of alcohol, compared with 18 percent of 21-year-olds.

“Driving under the influence of alcohol and marijuana is a risky behavior, and can result in a fatal car accident,” Azofeifa said. “Regardless of the encouraging numbers we are seeing in this report, there are still too many people driving under the influence and too many people dying in car accidents.”