Young drivers are less likely to drive under the influence of alcohol than they were a decade ago, according to research by the Centers for Disease Control and Prevention.

A recently published study looked at the prevalence of alcohol or drug use among drivers between the ages of 16 and 25, and how this behavior has changed between 2002 and 2014. The CDC used data from the National Survey on Drug Abuse and Health, issued by the Substance Abuse and Mental Health Services Administration.

That survey asked 383,700 people between the ages of 16 and 25 about their alcohol and drug use. Some of the questions focused on whether the respondents had driven under the influence of alcohol, marijuana, or both substances in the 12 months prior to the survey.

In the 16-20 age group, the share of respondents who said they had recently driven under the influence of alcohol fell from 16.2 percent in 2002 to 6.6 percent in 2014. Among those between the ages of 21 and 25, the share reporting that they recently driven while impaired by alcohol fell from 29.1 percent in 2002 to 18.1 percent in 2014.

The CDC found that drivers were more likely to operate a vehicle under the influence after they reached the legal age for consuming alcohol. Only 1.5 percent of 16-year-olds said they had driven while impaired by alcohol in the 12 months before the survey, while the share rose to 18.1 percent among 21-year-olds.

The share of drivers between the ages of 16 and 20 who reported driving under the influence of marijuana dropped from 3.8 percent in 2002 to 3.1 percent in 2014. Those between the ages of 21 and 25 were slightly more likely to drive after using marijuana, with 3.3 percent reporting that they did so in the 12 months before the survey.

The CDC notes that these results run counter to the findings of the National Highway Traffic Safety Administration's most recent National Roadside Survey. This report determined that the frequency of weekend night driving while under the influence of marijuana rose from 8.6 percent of drivers ages 16 and older in 2007 to 12.6 percent in the 2013-2014 survey. The CDC says factors leading to this disparity may include a self-reporting bias in the National Survey on Drug Abuse and Health as well as the fact that the psychoactive ingredients in marijuana remain detectable long after their impairing effect has worn off.

Only 1.4 percent of the 16-20 age group said they had driven under the influence of both alcohol and drugs in the year before the 2014 survey, down from 2.3 percent in 2002. Among drivers between the ages of 21 and 25, the share dropped from 3.1 percent to 1.9 percent.

Previous research by the CDC, published in 2012, found that the prevalence of drinking and driving among drivers between the ages of 16 and 19 was at 10.3 percent. This share was down from 22.3 percent in 1991.

The CDC credits the decline in impaired driving among young drivers to several factors. These include enforcement of rules prohibiting drivers under the age of 21 from driving a vehicle with any alcohol in their system, roadside testing at sobriety checkpoints, graduated driver licensing laws, and educational campaigns in the media.

However, the report says there is still room for improvement to reduce drug and alcohol impairment among young drivers. In addition to the fact that vehicle accidents are still the leading cause of death among 16- to 25-year-olds, the National Survey on Drug Abuse and Health found that alcohol and drug use was common among young respondents. Sixty percent said they had consumed alcohol in the past month, 38 percent reported binge drinking, and 20 percent said they had used marijuana.

There are also certain limitations in the survey data. The CDC says that since respondents reported their own behavior, some may have decided not to admit to driving under the influence. Respondents may also have responded inaccurately if they drove under the influence of alcohol or drugs but did not consider themselves to be impaired.

The number of young drivers who drove a vehicle under the influence of marijuana was likely underreported, as the survey only considered those who used marijuana and no other illegal drugs. A total of 35.9 percent of marijuana users who admitted to using another illegal drug in the past year were not included in the analysis of drivers who got behind the wheel while high.

The report recommended continuing education and prevention efforts to encourage young drivers not to drive under the influence of alcohol or drugs. The CDC says improved field tests are also needed for measuring marijuana impairment in drivers, since there is currently no standard test to determine this effect.