By The Herald Editorial Board

It’s a simple thing to recognize that drowsy driving is a bad idea. More than a few of us will admit to having heavy eyelids and a nodding head while behind the wheel.

But that’s what rumble strips are for, right?

What we haven’t known is just how little a loss of sleep it takes to increase the risk of an accident and that with each hour of lost sleep that likelihood increases to the point where there’s not much difference between driving drowsy and driving drunk.

A new report by the AAA Foundation for Traffic Safety, drawing on original research and existing studies, now serves as a wake-up call for just how impaired we are when we drive without getting enough hours of sleep in a day.

Among other findings, the report says that drivers who have just four to five hours of sleep in the last 24 hours are comparable to those driving with a blood-alcohol level of .08, the level that in Washington and the other 49 states is considered impaired. Drive after having slept for four or fewer hours and the level of impairment is comparable to someone with a BAC of .12 to .15, the AAA report says.

More than falling asleep behind the wheel, the AAA report said, sleep deprivation slows a driver’s reaction time, decreases the accuracy of responses to road conditions and leads to long lapses in attention. And alert drivers also are simply better at avoiding drivers who aren’t.

It doesn’t take much lost sleep to increase the odds of an accident. While a driver with fewer than four hours has an 11.5 percent higher risk of a crash, drivers with four to five hours of sleep were 4.3 percent more likely to be in an accident. Even those with five to seven hours of sleep were still nearly 2 percent more likely to crash.

The study may even underestimate the risks; drawing data from more than 4,500 accidents involving 7,234 drivers, the study did not have data on accidents that occurred between midnight and 6 a.m., a time of day when the effects of sleep deprivation could be greatest.

And the number of people driving without adequate sleep is significant. The Centers for Disease Control and Prevention say that 35 percent of people get fewer than seven hours of sleep in a 24-hour period, and 12 percent reported sleeping less than five hours. Beyond driving, the CDC has declared insufficient sleep to be a public health problem.

Earlier research by the AAA foundation found that 21 percent of fatal crashes involved a sleep-deprived driver. At the statewide level, there were 568 fatalities from auto accidents in 2015, an increase from 462 in 2014 and 436 in 2013. Of 2015’s fatalities, 148 were attributed to alcohol impairment and 156 were related to speed. And while there is overlap of contributing factors, of the 568 fatalities last year, 329 were accidents where one or more vehicles left the roadway, according to statistics for Washington state from the National Highway Traffic Safety Administration.

More specifically, the Washington State’s Target Zero campaign, which has set a goal of zero road fatalities by 2030, attributed 39 fatalities and 194 serious injuries between 2012 and 2014 to drowsy drivers. Impaired driving, speeding and distracted driving remain the most common causes of accidents, the Washington State Patrol reported.

All of this is in the driver’s control. We can be responsible about not driving when we’re intoxicated, about watching our speed, not being distracted by our phones and getting enough sleep.

The National Sleep Foundation offers tips on avoiding drowsy driving at tinyurl.com/NSFdrowsytips. Among them:

Take a 20-minute nap before driving or pull off the road and take a nap during a long stretch of driving, but give yourself time to wake up.

Drive with a buddy.

Avoid driving between midnight and 6 a.m. when you’re accustomed to sleeping.

Have a coffee.

And no, rumble strips are not enough.