Time of Day - This was the most significant factor in a driver showing signs of fatigue. The eight hours preceding dawn are by far the worst for drivers feeling drowsy. This greatly supports the theory that internal circadian clocks attempt to force people to sleep late at night. Time of day was much more significant than the amount of time the driver had behind the wheel at the time the drowsiness struck.

Duration of Driving - The study ran four sets of 20 drivers each. Two sets drove day runs only. Two sets ran progressive rotations of night driving. One group of day and night drivers ran in the U.S. and drove only 10 ours a shift. The other group operated in Canada and their drive shifts were 13 hours. The study showed that time at the wheel played no significant role in the drivers experiencing drowsiness.

Daily Principle Sleep Periods - Drivers reported their ideal amount of sleep was an average of 7.2 hours out of even- 24 hours. They actually got five hours or less for every 24 hour period. (Receiving 2 hours less sleep than is needed puts the person in an immediate sleep debt situation).

Cumulative Fatigue Across Days - The study did show that the week wore to an end. the instances of drowsiness increased, indicating a fatigue related to accumulated lack of sleep.

The quantity of sleep was low. The average driver was getting nearly two hours less sleep a night than they had felt was ideal. Average hours of sleep for the four study groups were: 4.5 hours; 4.8 hours; 3.8 hours and 5.1 hours. The quality of sleep was well within the norms for the drivers.

Some Drivers Are More Susceptible to Fatigue and Drowsiness - There was evidence of large differences between individual drivers when it came to drowsiness. 36 percent of the group never showed any signs of ever being

Forty-nine percent were drowsy 10 or less times during the study, and 15 percent were drowsy more than ten times. The number of drowsy events in this last group varied between 12 and 40 with an average of 22 drowsy episodes each.

Drowsiness During Driving - Fourteen percent of the drivers in the study accounted for 54 percent of the number of occurrences of drowsiness observed in the study. Two of the drivers actually dropped into recordable level one sleep while stiil driving the truck. (There were no accidents with any of the drivers during the study).

Napping - Thirty-five of the 80 drivers, or 44 percent of them, took naps during the study. There were 63 naps out of 360 total trips. The naps averaged 27 minutes in length and increased those drivers average sleep for the day by 11 percent. The drivers who decided to stop and nap were generally observed to be drowsy by the video cameras aimed at their faces.

Driver Self-Awareness - Can drivers tell if they are tired or fatigued? Driver's ability to predict their level of awareness was very poor. They generally rated themselves as being much more alert than they actually were.

Age and Fatigue - There were differences in the test scores between the younger and older drivers, but fatigue was not a significant factor in these differences.

Implications for Educational Approaches -Drivers need to realize the natural results of getting inadequate amounts of sleep. They need to be made aware that many of them will respond to the late night circadian sleep trough. Drivers need to accept that self-diagnosis of fatigue is historically inaccurate. They will also need to be trained to identify the subtle changes in driving behavior that signal the onset of fatigue. (They show up way before the driver closes his eyes and falls asleep at the wheel).