New Study: Drowsy Drivers Cause 10 Percent of Crashes

Until recently, the official numbers from the U.S government labeled drowsy driving as a factor in only 1 to 2 percent of all crashes. But a new research method called PERCLOS indicates that the older statistics woefully underestimated the incidence of drowsy driving in vehicular accidents. The percentage of collisions associated with drowsy driving turns out to be at least five times higher than previously thought.

The National Safety Council (NSC) estimates that, in 2017, automotive fatalities exceeded 40,000 for the second consecutive year. Accurately measuring the reasons for crashes can help us prevent them. With so many lives at stake, preventative measures imply that thousands more people could be alive who otherwise have died.

PERCLOS: The New Standard for Measuring Driver Drowsiness

PERCLOS stands for “percentage of time that the driver’s eyes are closed during a specified time interval.” In the most recent study conducted by the AAA Foundation for Traffic Safety and published in February, 2018, researchers used PERCLOS to help define when a driver might be drowsy immediately preceding an accident. New technology consisting of cameras in vehicles that recorded a driver’s actions meant that researchers could study video taken immediately before a collision to discover whether the driver’s eyes were closed.

How the Study Was Conducted

From October 2010 to December 2013, more than 3,500 persons in six different U.S. locations agreed to the use of in-vehicle cameras and related technology that monitored their every move for several months. Of the 701 crashes that the researchers examined, drowsiness played a part in 8.8 to 9.5 percent of all accidents. In crashes that involved injuries, significant property damage, or airbag deployment, drowsiness was a factor in 10.6 to 10.8 percent of accidents.

As you might expect, drowsiness was a bigger problem once darkness fell. While many more daytime crashes (489) occurred, researchers determined that only 5.3 percent of them arose from sleepiness. At night, however, a greater percentage of crashes—17.7 percent—were thought to be caused by drowsiness, even though the total number of crashes was only 181. In these cases, evidence of PERCLOS one minute prior to a crash was coded as a contributing factor.

Sleepy Can Be the Same as Drunk

Drowsiness is notoriously hard to track as a cause of accidents. Drivers may not want to admit that they were sleepy, or might not even realize that they had felt drowsy, especially because they are likely to feel wide awake in the aftermath of a collision. No test for sleepiness exists, unlike for drunk driving.

But one study has demonstrated that, after approximately 17 to 19 hours have passed since you last slept, your ability to function behind the wheel is equivalent to a blood alcohol concentration (BAC) of 0.05. By the time you reach 20 to 25 hours without sleep, your driving ability will be impaired as much as if your BAC were at 0.1. The legal BAC in the United States is 0.08 with the exception of Utah, which passed a law in 2017 lowering the legal BAC to 0.05. The law goes into effect December 30, 2018.

In a February, 2016, press release, the CDC reported that more than one-third of all U.S. residents were not getting enough sleep because they slept less than 7 hours per night on average. The recommended amount of sleep for adults is between 7 and 8 hours per night, with more being better. William J. Horrey, Traffic Research Group leader at the AAA Foundation, noted that, “The only true countermeasure to drowsiness is sleep.” If drivers are having accidents because they are drowsy, the only two ways to fix the problem are to sleep more, and not to drive when drowsy.