Sekundenschlaf – eine unterschätzte Gefahr
Mobility: Around one in four Germans say they have dozed off at the wheel of a car. ‘There are clear warning signs beforehand,’ says psychologist Christian Müller from TÜV NORD.
You drive home exhausted in the evening. It's not actually cold, but your body is shivering. A hand rubs over your heavy limbs, your face, your eyes. Eyelids drooping, gaze fixed on the steering wheel, staring into space. The road seems to get narrower and narrower. Only with the greatest effort is it still possible to keep in lane.
‘It's high time for a break and a nap,’ warns Christian Müller from the Medical-Psychological Institute of TÜV NORD in Cologne. ‘Microsleep could set in at any moment.’ Then you are in the first of four sleep stages, the falling asleep phase, in which the brain gradually enters the sleep state. First, the thalamus, the gateway to consciousness for sensory impressions from the outside world, switches off. The cerebral cortex, which is responsible for conscious thought and action among other things, follows a little later. This initially gives the impression of being awake, even though parts of the brain are already asleep.
It is obvious why this is dangerous. If you doze off for just a brief moment, you lose control of the vehicle. At 50 kilometres per hour, a single second is enough to drive 14 metres ‘blind’ - more than enough to drive into the oncoming lane. At 80 km/h, a car covers almost 70 metres in three seconds.
According to official accident statistics, fatigue is only responsible for around 0.5 per cent of all serious road accidents, reports the German Road Safety Council (DVR). However, this figure only includes those rare cases in which the driver admits to being tired. The DVR estimates that almost one in four fatal car accidents are caused by falling asleep at the wheel.
The German Society for Sleep Research and Sleep Medicine (DGSM) even compares the effect of tiredness with that of alcohol: after just 17 hours without sleep, the ability to react is as impaired as with 0.5 per mille of alcohol in the blood. Anyone who has been awake since 6 a.m. should therefore not get behind the wheel at 11 p.m. And anyone who gets into a car after a sleepless night must even expect to doze off while driving within an hour or so. In an experiment at the University of Wuppertal, this happened to three out of four men. After not sleeping for 27 hours, they nodded off in the driving simulator after an average of 52 minutes.
Lack of sleep - the underestimated danger
Even a night with five to six hours of sleep can have this effect. In an experiment at the Queensland University of Technology in Australia, more than one in ten people fell into microsleep at times in the driving simulator - even though the test subjects were supposed to stop as soon as they could no longer drive safely. The risk increases when sleep is neglected for days on end. Over the course of a week with only four hours of sleep per night, microsleeps occurred more and more quickly, as observed in a study of healthy young men in France.
But it's not just the length of sleep that counts, says psychologist Christian Müller. “Even less restful sleep, for example due to breathing interruptions, can cause microsleep.” External circumstances also contribute to this, such as shift work and long monotonous stretches. Sleepy passengers are also unfavorable, as tiredness is contagious.
It becomes particularly dangerous when there is a lack of insight into one's own limits. Many people cannot or do not want to recognize their fatigue - or at least do not draw the necessary conclusions. Even in a driving simulator, many find this difficult. In a Swiss study, more than half of the test subjects showed no insight. They were asked to drive four times for 40 minutes in a driving simulator after being kept awake the night before. 17 of the 28 fell asleep without giving a signal when drowsy, as agreed.
Caffeine and loud music are no panacea
Nevertheless, a good quarter of German drivers admit to having fallen asleep at the wheel at least once. According to more than one in twenty, this has even happened more often. This was determined by the DVR in a telephone survey in 2016. The majority also reported doing something to combat tiredness: Around 60 percent said they open the window, 38 percent drink something containing caffeine and 30 percent turn up the music.
“But that's not enough,” warns Christian Müller from TÜV NORD. “At the first signs of tiredness, you have to stop, move around and get some fresh air. And if that's not enough or you have a longer journey ahead of you, a short nap is essential,” he warns. However, the alarm clock must ring again after 15 to 20 minutes - otherwise you will fall into a deep sleep and wake up drowsy. “It's best to drink a coffee before your nap, then the caffeine starts to take effect after 15 to 20 minutes.”
To ensure that tired drivers don't miss the right moment, new vehicles in the EU will be equipped with an assistance system that monitors alertness at the wheel from 2024 at the latest. Such “drowsiness warning systems” analyze, for example, barely noticeable steering deviations and prompt the driver to take a break with a signal, such as a flashing coffee cup.
These and other measures such as rumble strips on the side of the road can save lives in the short term. In the long term, however, only one thing helps, says psychologist Christian Müller: “sufficient restful sleep”. And if in doubt, do without a car.
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