A new study shows that many more drivers fall asleep behind the wheel than previously believed.
The Centers for Disease Control and Prevention (CDC) study said Thursday that in 19 states, 4.2 percent of drivers admitted to falling asleep while driving a month before the survey.
The survey was part of the organization's ongoing Behavioral Risk Factor Surveillance System (BRFSS).
Those who said they snored or slept less than six hours per night were the most likely to nod off, said CBS News.
It is estimated that 2.5 percent of fatal motor accidents were due to sleeping while driving.
That is just an estimate given the difficulty in obtaining data.
The CDC said that about 41 million Americans do not get enough sleep.
ABC News reported that men were more likely to fall asleep behind the wheel than woman - 5.3 percent to 3.2 percent.
Younger drivers were also more likely to fall asleep than older drivers.
White people tended to be less likely to admit to driving while drowsy.
Texas had the highest rate of drowsy driving and Oregon the lowest (6.1 to 2.5 percent).
The study was published in the CDC's journal, Morbidity and Mortality Weekly Report.