Car accidents are one of the major causes of injury and death in modern society. One major risk factor associated with increased automobile accidents is driving fatigue. A series of studies published in the Journal of Psychosomatic Research attempted to measure the effects of fatigue on driving performance. This series of tests utilized virtual driving simulators, allowing for computerized analysis to measure and record lateral deviation from a virtual trajectory or reaction times.

Fatigue has a huge impact on driving, and can affect a person’s driving ability in ways similar to driving while intoxicated. Research shows being awake for 17 hours has the same effect on driving ability as a blood alcohol concentration of 0.05. Going without sleep for 24 hours has the same effect as a BAC of 0.1, which is double the legal limit, according to the Transportation Accident Commission.

Fatigue in drivers can cause a slow reaction time while driving and lack of concentration, resulting in errors calculating speed and distance; reduced vigilance and poor judgement; and generally nodding off, creating potentially dangerous situations for the driver and others on the road.

In the first study, researchers utilized a simple reaction-time simulation test to show the effects of fatigue on driving ability, what was found was a strong relationship between duration of driving and fatigue, especially in young drivers. A final, controlled study utilized a driving simulator to test the responses of drivers involved in long-distance journeys.

So where is the best place to find subjects for a study on long-distance driving? On the open road, of course. Researchers approached motorists who stopped at a freeway rest area to find recruits for the study. A total of 114 drivers agreed to participate. That particular stretch of roadway, which links Sweden to Portugal via France, involves a high level of suspected sleep-related accidents and long driving distances.

A sleep questionnaire was given to those who met study protocol and agreed to participate. The questionnaire measured habitual total sleep time, sleep latency, sleep quality and sleepiness, and the Epworth Sleepiness Scale, which quantifies behavioral sleepiness; and included logs of sleep/wake behavior during the year, just prior to departure and during the journey. A second questionnaire measured the duration of driving, the number and duration of stops, and the number of driver changes.

After the questionnaires were completed, subjects completed a virtual driving test, utilizing a simulator set up near the rest stop. A winding road was displayed on the simulator, and participants were asked to keep the front of the vehicle centered between the two lines depicting the road lane. Software recorded the lateral deviation of the car from the center of the lane, reaction time was measured using numeric digits in the four corners of the screen. Participants acknowledged every time the number “2” appeared on either side.

The study found 15.8 percent of participants reported having to stop during the trip because of extreme daytime drowsiness. Based on the questionnaires, 76.3 percent of all subjects experienced reductions in “normal” sleep time in the 24 hours before the interview. Simulator analysis showed drivers performed significantly worse than controls on the driving simulator. The main factor affected was the ability of the research participants to maintain the center of the lane through a virtual curve. “The differences observed between drivers and matched controls confirm that fatigue affects long-distance drivers,” the researchers concluded.

The amount of driving performed before testing was the major predictor of deviation from the center of the lane. “These findings suggest that steering error on a driving simulator could be used to measure fatigue. The fact that drivers have a harder time than controls to maintain a perfect angle in curves could be explained by the fact that this procedure requires good coordination, which is affected by fatigue.” Long duration of driving was associated with sleep restriction, and cumulative factors may mask the effects of sleep deprivation.

The researchers showed simulators could be used to evaluate how fatigue affects driving performance. Continued research on the subject could lead to greater awareness for drivers on long journeys.

The Transportation Accident Commission shared the following tips on preventing fatigue-related accidents:

• Get a good night’s sleep before heading off on a long trip.
• Don’t travel for more than eight to 10 hours a day.
• Take regular breaks – at least every two hours.
• Share the driving whenever possible.
• Don’t drink alcohol before a trip.
• Don’t travel at times when you’d usually be sleeping.
• Take a 15-minute power nap if you become drowsy.

Utilizing virtual driving simulators to highlight the dangers associated with driving fatigue may help raise awareness and make roadways safer for all drivers.

Citation: Philip, P, et al. “Effect of Fatigue on Performance Measured by a Driving Simulator in Automobile Drivers.” Journal of Psychosomatic Research, vol. 55, 25 June 2002, pp. 197–200.

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