Fatigue behind the wheel does not start with a sudden fall asleep. Usually, it is preceded by heavy eyelids, frequent yawning, difficulty focusing, wandering thoughts and a feeling that the last few kilometers have passed almost automatically. These are signals that the driver can no longer reliably assess the dangers on the road.
After 17-19 hours without sleep, driving skills can deteriorate to a level comparable to a concentration of about 0.5 per mille of alcohol. The conclusion is based on a study with 39 participants, in which reactions in some tests were up to 50 percent slower after prolonged wakefulness. The European Observatory for Road Safety and the American National Institute for Occupational Safety and Health indicate the same relationship. The comparison describes the degree of impairment, and does not mean that lack of sleep leads to the actual presence of alcohol in the blood.
Microsleep leaves the car out of control
The most dangerous moment is microsleep — a brief episode of involuntary sleep, in which the driver loses control of attention and reactions. According to the US National Highway Traffic Safety Administration, such episodes can last four to five seconds in a person who is seriously sleep-deprived. At a speed of 90 km/h, this means about 125 meters traveled without full control of the car.
Signs that fatigue is already critical include deviating from the lane, passing over noisy markings at the edge of the lane, missing traffic signals, delayed reactions and the inability to maintain a constant speed. Short-term memory lapses are also possible — the driver does not remember part of the last minutes or kilometers. Fatigue impairs not only attention, but also information processing and judgment of dangers.
Stopping is the only safe reaction
At the first sign of drowsiness, the driver should pull over to a well-lit and safe place, outside the active lane. The National Highway Traffic Safety Administration emphasizes: “Sleep is the only preventive measure against drowsy driving.“ A short nap of 15-30 minutes can temporarily increase alertness, and coffee can help for a short period, but none of these measures replace sufficient sleep.
The risk increases with night driving, long trips, shift work, accumulated sleep deprivation, and taking medications with a sedative effect. Loud music, an open window, and physical exercise around the car can create a feeling of alertness, but do not eliminate the cause of fatigue. If the driver is already yawning, losing concentration or does not remember the last section of the road, continuing the journey turns fatigue into an immediate risk of a traffic accident.
Source: oem.bmj.com