About 12 million Americans drove while high on marijuana in 2018, while 20.5 million people drove drunk, according to new data from the Centers for Disease Control and Prevention.

The findings come amid growing concern over the prevalence of driving while high. The data, based on a survey of nearly 48,000 people in 2018, indicates that 4.7% of Americans 16 or older said they'd driven while on marijuana during the last year, while 0.9% – 2.3 million people – said they'd driven under the influence of an illegal drug and another 8% reported driving drunk.

"Impaired driving is a serious public health concern that needs to be addressed to safeguard the health and safety of all who use the road," CDC researchers said.

The new figures represent an uptick in drugged driving since 2014, when 10.1 million people 16 or older said they'd driven on marijuana or other drugs in the last year. They also show a decline in drunk driving: 27.7 million Americans reported drunk driving in 2014, previous survey data shows.

In 2018, men and people ages 21 to 25, followed by those 16 to 20, were the most likely groups to drive with marijauana in their system, the report found. Drug use among teenagers is of "special concern," researchers said, because younger, more inexperienced drivers are already at higher risk of crashes.

Reducing drunk driving has been a decadeslong public health and safety goal in the U.S., and its prevalence among people 16 to 25 plummeted between 2002 and 2014, previous research shows. Still, an estimated 10,511 people died in drunk driving accidents in 2018 – 29% of all traffic deaths.

Yet "effective measures that deter driving under the influence of drugs are limited," researchers said. There's no chemical test equivalent for marijuana to blood alcohol content, and roadside tests aren't currently "practical and feasible," according to a 2017 report to Congress on marijuana-impared driving.

In an effort to curb high driving, states could develop strategies to curb marijuana use "and potential subsequent impaired driving, especially among teenagers and young adults," researchers said.