Driving while intoxicated and distracted driving justifiably get a lot of attention. But in the midst of our too-busy, not-well-rested daily habits, another kind of impaired vehicle operation is worth noting: drowsy driving.

According to the National Sleep Foundation, about half of adult drivers admit to consistently getting behind the wheel while feeling somewhat drowsy. About 20% say they’ve drifted off a bit behind the wheel at some point in the past year — with more than 40% admitting this has happened at least once.

The National Highway Traffic Safety Administration says driving while drowsy is similar to driving under influence of alcohol. Drivers’ reaction times, awareness of hazards and ability to sustain attention all worsen the drowsier the driver is. The NHTSA says driving after going more than 20 hours without sleep is the equivalent of driving with a blood-alcohol concentration of 0.08%, which is the legal limit in Maryland. Also, the agency says, a driver is three times more likely to be in a car crash if fatigued.

The NHTSA says every year about 100,000 police-reported crashes involve drowsy driving. These crashes result in more than 1,550 fatalities and 71,000 injuries. The real number may be much higher, however, as it is difficult to determine whether a driver was drowsy at the time of a crash.

In fact, a recent study by the AAA Foundation for Traffic Safety estimated that 328,000 drowsy driving crashes occur annually — more than three times the police-reported number. The same study found that 109,000 of those drowsy driving crashes resulted in an injury and about 6,400 were fatal.

In the AAA study of more than 700 dash-cam videos, researchers examined drivers’ faces in the three minutes leading up to a crash. Using a scientific measure linking the percentage of time a person’s eyes are closed to their level of drowsiness, the researchers determined that 9.5% of all crashes and 10.8% of crashes resulting in significant property damage involved drowsiness.

In addition to simply not getting enough sack time, drowsy driving can also happen because of medications or untreated sleep disorders such as sleep apnea. One medical estimate suggests that more than 70 million Americans have some type of sleep disorder. Shift workers could also be susceptible to drowsy driving.

The Centers for Disease Control and Prevention says that 35% of U.S. drivers sleep less than the recommended minimum of seven hours daily.

“As many Americans struggle to balance their busy schedules, missing a few hours of sleep each day can often seem harmless,” said Jake Nelson, director of Traffic Safety Advocacy and Research for AAA. “But missing just two to three hours of sleep can more than quadruple your risk for a crash, which is the equivalent of driving drunk.”

Knowing the warning signs of drowsiness can help drivers avoid dozing off behind the wheel. The most common symptoms include having trouble keeping your eyes open, drifting from your lane and not remembering the last few miles driven.

AAA recommends that drivers try to travel at times of the day when they are normally awake, avoid heavy foods and avoid medications that cause drowsiness or other impairment. For longer trips, drivers should schedule a break every two hours or every 100 miles; travel with an alert passenger and take turns driving; or just pull over and take a quick nap.

The CDC and other agencies have also warned that in these weeks following the annual switch back to standard time, people’s circadian rhythms often take time to adjust. Apparently our bodies’ internal clocks need to reset.

So be careful on the roads. Get enough rest and stay alert. We’ll all be safer for it.