Automotive Research

An eye-opening look at drowsy driving

How dangerous is it to drive while tired? Most drivers can recall at least one time they had trouble keeping their eyes open while behind the wheel, but drowsy driving doesn’t receive the same attention as drunken driving and drugged driving.

Research from the AAA Foundation for Traffic Safety suggests it should: It found that drivers who only get 4-5 hours of sleep can more than quadruple their crash risk compared to those who get at least 7—which is the same risk associated with driving over the legal limit for alcohol. And while the federal government estimates that drowsiness is a factor in only 1-2% of crashes, AAA's research found that 9.5% of crashes involved drowsiness.

A man yawning in the rear-view mirror of a car

How dangerous is drowsy driving? 

As part of the AAA Foundation’s survey, 96% of drivers said they see drowsy driving as “completely unacceptable” behavior that threatens their safety. Even so, almost 1 in 3 also admitted that, at some point in the previous month, they themselves had driven while having a hard time keeping their eyes open.

1 in 3 drivers

in the U.S. sleep less than 7 hours a night

1 in 5 fatal crashes

in the U.S. involve drowsy driving

 

How commonly is drowsy driving involved in crashes?

It's difficult to measure the proportion of crashes that are related to drowsy driving, as drivers may not want to reveal that they were driving while fatigued. And unlike drugs and alcohol, there's no way to test for fatigue after a crash. By examining dashcam footage from more than 700 crashes and analyzing the percentage of time that drivers' eyes were closed, research from the AAA Foundation for Traffic Safety found that 9.5% of all crashes, and almost 11% of crashes that led to significant property damage, involved drowsiness. This is far higher than the federal estimate of 1-2%.

Crash risk for drivers who get less than 7 hours of sleep

1.3x

6-7 hours

1.9x

5-6 hours

4.3x

4-5 hours

11.5x

< 4 hours

Warning signs may come too late ... or not at all

traction_control_light.svg

Trouble keeping eyes open

hazard_highway.svg

Trouble staying in lane

ban.svg

Memory lapses

There are a few warning signs that may indicate somebody is too tired to drive safely. These include having trouble keeping one’s eyes open, drifting into nearby lanes, and not remembering the last few minutes of driving. However, more than half of drivers involved in fatigue-related crashes didn’t experience any physical symptoms before falling asleep behind the wheel—their first “warning” was a crash. Given that motorists have a hard time judging their own fatigue before it can put them and others in danger, getting at least 7 hours of sleep remains the best way to avoid drowsy driving.

What you can do

Get the recommended 7 hours of sleep

This is the most important thing motorists can do, and it comes with many health benefits beyond safer driving.

Avoid eating heavy foods before driving

The so-called “food coma” can tip a tired driver over the edge if they’re already beginning to feel fatigued.

Drive at times you would normally be awake

Being behind the wheel when your body expects to be asleep can make you more likely to doze off.

Avoid medications that make you drowsy

Check the label; many drugs carry warnings not to “drive a motor vehicle or operate heavy machinery” for this reason.

Travel with passengers & take turns driving

If your trip is long enough that taking a break every 100 miles isn’t practical, drive in shifts with 1 or more other drivers.

Take a break every 2 hours or 100 miles

Hours of continuous driving, especially on monotonous highways or at night, can lead drivers to zone out.

Information taken from “Missing 1-2 Hours of Sleep Doubles Crash Risk,” December 6, 2016, AAA Foundation for Traffic Safety, and "Drowsy Driving: Don't Be Asleep at the Wheel," February 8, 2018, AAA Foundation for Traffic Safety.

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