More motorists are smoking marijuana on the road than ever before, according to new data released on Friday by the National Highway Traffic Safety Administration of the U.S. Department of Transportation. The agency stated that rates of driving while high have increased by 50 percent in the past seven years.

Their data shows that 12.6 percent of drivers stopped at roadside surveys had the drug in their system in 2014 compared with 8.6 percent of motorists in 2007. Overall, about one in five drivers who were stopped tested positive for at least one drug -- an increase from 16.3 percent in 2007.

In a separate study, the NHTSA tried to characterize the risk that drugs posed to drivers and their fellow motorists. The agency compared drivers that had been involved in crashes over a 20-month period in Virginia Beach, Virginia, to those which had avoided any accidents. Researchers found that marijuana users were 25 times more likely to be in an accident than those who did not use the drug. By comparison, drunk drivers were four times more likely to crash than sober drivers.

However, the researchers also noted that the increased risk of a crash was heavily correlated with other factors, too, like age and gender, and said that these may be greater determinants of an accident than drug use. Next, the agency plans to conduct a study in Washington state, where it's legal to use recreational marijuana, to clarify their findings.  

The same study that measured higher rates of marijuana use among motorists also showed that drunk driving on America’s roads has dropped significantly, with about 30 percent fewer impaired drivers behind the wheel as compared with 2007. When measured against original survey data from 1973, the rate of drunk driving has dropped by almost 80 percent. Last year, about 8.3 percent of drivers had consumed alcohol before driving but only 1.5 percent of them blew a 0.08 or higher for breath alcohol concentration on a breathalyzer test, putting them above the legal limit.

“America made drunk driving a national issue and while there is no victory as long as a single American dies in an alcohol-related crash, a one-third reduction in alcohol use over just seven years shows how a focused effort and cooperation among the federal government, states and communities, law enforcement, safety advocates and industry can make an enormous difference,” NHTSA Administrator Mark Rosekind says in a statement.

The NHTSA conducted roadside surveys at 300 sites last year and paid 9,000 drivers for their voluntary and anonymous participation to record rates of drug use and drunk driving.