CHAPEL HILL -- Drivers who work night shifts, long hours or more than one job are at greater risk of being in a crash caused by falling asleep at the wheel or fatigue, according to a first-of-a-kind University of North Carolina Highway Safety Research Center study.
Other factors strongly associated with having a drowsy driving crash include sleeping less than six hours per night, being awake for 20 hours or longer and frequent driving between midnight and 6 a.m.
"To our knowledge, this is the first study where a large number of drivers in sleep-related crashes were contacted soon after their crash," said Dr. Jane Stutts, the project's principal investigator.
Other drowsy driving studies have involved either surveying the general population of drivers and asking about their experiences with drowsy driving or analyzing police crash data about such crashes.
Researchers interviewed by telephone 1,403 N.C. drivers identified by recent police crash reports and driver records, including 467 involved in crashes caused by falling asleep or being fatigued.
"We found that drivers in sleep and fatigue-related crashes were four to five times more likely than drivers in the control crash group to work night-shift jobs," Stutts said.
Working 60 or more hours a week also increased drivers' risk. Twenty-seven percent of those involved in sleep-related crashes worked 60 or more hours weekly, compared to 17 percent of the drivers in the control group. Drivers in sleep-related crashes were nearly twice as likely as drivers in the control group to work more than one job.
"My impression when I talked to a lot of these people was, 'well no wonder you fell asleep at the wheel!'" Stutts said. "You must have been just exhausted!" The study, funded by American Automobile Association Foundation for Traffic Safety, found that people who had been in "sleep" mishaps often were different from other drivers, she said.
Between 8 percent and 10 percent of drivers in sleep and fatigue crashes reported taking medications while fewer than 2 percent of the control crash group took them. Three percent of the drivers in sleep crashes reported having a diagnosed sleep disorder.
"Drivers who hadn't been in crashes were older and much less likely to be employed," Stutts said. They also were more likely to be female and reported driving less.
"Everyone who doesn't get enough sleep on a regular basis, however, is at risk," the scientist said. "The vast majority of people in our study who crashed as a result of driving while drowsy either got too little sleep on a routine basis and built up what sleep researchers describe as 'sleep debt,' or they got far too little sleep before trying to drive."
In many cases, she said, people involved in such crashes were just average drivers putting in extra hours at work, adjusting to a new baby, staying out late for a party or trying to make it back home after a trip."
"As a society, we don't view sleep as a necessary function but more as a luxury," said Dr. Bradley Vaughn, director of UNC-CH's Sleep Disorders Center. "The consequences are that, in general, we try to shorten the amount of sleep we get and are more sleep-deprived. The study also found that sleep and fatigue crash drivers:
- averaged more than a half hour less sleep per night than controls,
- were twice as likely to report getting too little sleep and suffer from extreme sleepiness
during the day,
- tended not to plan ahead to get more sleep to avoid drowsiness,
- often were unaware of how sleepy they were and
- were three times as likely to rate their sleep as "poor."
"About a quarter of the drivers in sleep crashes said that they had driven while sleepy more than ten times in the past year," said co-investigator Dr. Jean Wilkins, associate professor of psychiatry. "These people may have started to think that driving while drowsy is no big deal.
"They think they can handle it, that they can force themselves to stay awake. Many of us would never think about driving drunk, but by driving when we're sleep-deprived, we put ourselves and others at risk of a crash as severe as an alcohol-related crash."
Note: A news conference will be held at 10 a.m., Dec. 21 at the National Press Club, 529 14th Street NW, Washington D.C. B-roll film is available from the AAA foundation by calling Stephanie Faul at 202-638-5944, Ext. 4. Graphics, drivers' stories and other details will be posted Dec. 21 at:www.hsrc.unc.edu.
HSRC contact: Emily Smith, (919) 962-7803.
UNC-CH News Services contact: David Williamson, (919) 962-8596.