Drivers who have had too little sleep are no different than those who have had three or four drinks and are too drunk to drive, according to researchers at the AAA Foundation for Traffic Safety.

The report, which draws on original research and past studies to demonstrate the risks of sleep-deprived people who get behind the wheel, said that driving on just four to five hours of sleep was comparable to driving with a blood alcohol content at or above the legal limit, and that the risk of driving with less than four hours was “much greater.”

“The crash risk associated with having slept less than four hours of sleep is comparable to the crash risk associated with a [blood alcohol content] of roughly 0.12 to 0.15,” said Tom Calcagni, of AAA’s Mid-Atlantic office. The legal limit for driving is 0.08.

The report says those who slept for less than 4 of the past 24 hours had an 11.5 percent higher risk of getting in a crash. Drivers who slept 4 to 5 hours had a 4.3 percent higher risk; 5-7 hours had a 1.9 percent higher risk; and 6-7 hours had a 1.3 percent higher risk.

Earlier research by AAA Foundation showed that 21 percent of fatal crashes involved a sleep-deprived driver. The group’s new work uses data from the National Motor Vehicle Crash Causation Survey to delve into how much driving ability decreases based on varying lack of sleep.

Not surprisingly, the less sleep, the higher the risk of a crash.

“You cannot miss sleep and still expect to be able to safely function behind the wheel,” said David Yang, executive director for the foundation. “Our new research shows that a driver who has slept for less than five hours has a crash risk comparable to someone driving drunk.”