– Whether it’s working the night shift, caring for a newborn, studying all night for exams or simply living in a 24/7 society, Americans are sleep-deprived — and that can be deadly on the nation’s roads.

To draw attention to the problem, some states have passed resolutions, posted messages on highways and required information to be included in driver’s education courses and driver’s manuals. But few have stepped up enforcement, trained police officers to detect when a driver hasn’t gotten enough sleep or enacted criminal penalties if drowsy driving results in a fatality.

This year, legislators in New York and Washington state introduced measures that would have made it a felony for a fatigued driver to cause a crash that kills someone. There was a public hearing on the Washington proposal, but neither bill has passed.

Only two states, Arkansas and New Jersey, have enacted such laws, but meeting the standards for prosecution and conviction is difficult. Arkansas, which considers it negligent homicide, requires that the driver hadn’t slept for the previous 24 consecutive hours; New Jersey, which calls it vehicular homicide, does the same, but it sets the time at more than 24 hours.

But those states have had “limited success” convicting drowsy drivers under the statutes, according to a 2016 report by the Governors Highway Safety Association (GHSA), which represents state highway safety offices. Arkansas has had only three convictions since 2013, when the law took effect.

One reason it’s tricky: When a fatigued driver is stopped by police, adrenaline usually kicks in and he doesn’t appear to be sleepy.

“We don’t have a sleep meter, like we have a Breathalyzer, so it’s difficult to recognize drowsy driving,” said Pam Fischer, the GHSA consultant who wrote the report. “It’s hard to prosecute, hard to make the case, and hard to enforce unless the driver readily admits it.”

Fischer said states need to do a better job training police officers to spot drowsy drivers on the road and to recognize some of the telltale signs if they pull them over or arrive at the scene of a crash. Officers also should ask drivers how much sleep they got in the past 24 hours, put that information in their report and warn them about the dangers of drowsy driving, she said.

A 2014 study by the AAA Foundation for Traffic Safety estimated that, on average, drowsy drivers could be involved in 328,000 crashes a year on U.S. roads, 6,400 of them fatal.

But AAA says the actual numbers may be higher, because the data collected by police at crash scenes is incomplete and there is no universal definition or standard wording for drowsiness or fatigue on crash reports.

Lots of Americans are suffering from sleep deprivation, health officials say. A Centers for Disease Control and Prevention study last year found that more than one-third of adults in the U.S. aren’t getting the seven hours of sleep a day needed for optimal health.

And when they get behind the wheel, drowsy drivers’ judgment may be impaired and their reaction time slowed, just like with drunken drivers. Their driving often mimics alcohol-impaired driving, with the car weaving between lanes or drifting off the road.

Among those most vulnerable: shift and night workers, teens and young adults, and truck and bus drivers.

A December 2016 study found that drivers who miss one or two hours of the recommended seven hours of sleep in a 24-hour period nearly double their risk for a crash. Those who miss two to three hours more than quadruple it. And nearly 1 in 3 drivers said that at least once in the past month, they drove when they were so tired they struggled to keep their eyes open.

Some states are beginning to take modest steps to deal with the problem.

Earlier this year, the GHSA and the National Road Safety Foundation, a nonprofit that promotes safe driving, distributed $15,000 grants to Iowa, Maryland, Nevada, New York and Tennessee to create drowsy driving prevention campaigns. Maryland will launch an educational and social media campaign aimed at medical shift workers. Nevada will train law enforcement officers to recognize drowsy driving behavior and collect more data on the number of traffic stops related to it.

Last year, Iowa hosted the first statewide drowsy driving summit to increase public awareness of the problem. It also broadcasts warnings on highway system message boards, such as “Drowsy? Crash on a Couch Not a Road,” runs public service announcements on TV and social media, and has partnered with a local supermarket chain to spread the word with bag stuffers.

Iowa will use its grant money to post signs, stickers and rack cards in every state rest area reminding people about signs of fatigue and urging them to take a quick nap if they’re tired.

“The main thing is to get people to talk about it,” said Patrick Hoye, bureau chief for the Iowa Governor’s Traffic Safety Bureau. “We need to educate the public that this is a serious issue and it’s causing fatalities in our state.”

Traffic safety experts recommend that states make sure there are enough rest areas available, so tired drivers can pull off the road and take a nap. They say states also need to conduct public education campaigns, install rumble strips on highways, and include information about drowsy driving in driver’s manuals and driver’s education classes.