Daytime drowsiness increases the risk of accidents

Daytime drowsiness increases the risk of accidents

The human factor

Apr 2016

A perennial hazard on the roads is fatigue or drowsiness, also defined as “sleep-related fatigue”. It is hard to gather data on this particular hazard because no breath or blood test can give the police any indication of fatigue, unlike with the consumption of alcohol or drugs, for example. As a result, fatigue is frequently not registered in statistics as a cause of accidents, hence the potential for a high number of unrecorded cases.

Fatigue as the potential cause of an accident is indicated in studies in which those involved in an accident are asked about its cause directly afterwards. For example, questioning 9,200 Norwegian people involved in accidents (Sagberg, 1999) revealed that falling asleep at the wheel and drowsiness were the causes of 3.9% of all accidents. This factor played a massive role in nighttime accidents (18.6%), accidents in which the vehicle left the road (8.3%), accidents occurring after the driver had already covered more than 150 kilometers (8.1%) and accidents with casualties (7.3%). A detailed scientific analysis of accidents involving trucks on German highways (Evers & Auerbach, 2003) showed that fatigue was the cause of between 16% and 19% of truck accidents in which people were killed or seriously injured.

Even if the statistical data on drowsiness as the cause of an accident can be interpreted only to a limited extent, the data generated by the Federal Statistical Office of Germany (2015) at least indicates that fatigue as the cause of accidents has increased over the past ten years.

Severe impact on performance

Fatigue and drowsiness have a major impact on a driver’s performance because they lead to impaired attention, concentration, reaction times and judgment, for example of speed or distance. An experiment showed that the participants who undertook a nighttime test for detecting hazard stimuli were significantly worse at identifying the critical stimuli in potentially hazardous traffic scenarios (Höger, Marquardt & Walter, 2011). The ability of drivers to identify road hazards seems to be worse among beginner drivers compared with more experienced drivers (Smith, Horswill, Chambers & Wetton, 2009). Overall, it can be concluded that some road accidents are caused by the driver’s fatigue-impaired ability to identify road hazards.

Another hazard for tired drivers is the “microsleep”, a person briefly nodding off. This can occur particularly on long, monotonous drives. But, depending on its speed, a vehicle can cover many meters in just a few seconds. During this period, drivers who have nodded off not only risk losing control of their vehicle and, possibly, leaving the road, but they will also fail to spot other road users.

Fatigue can have many causes, including a lack of sleep due to external circumstances such as shift work, medication intake or alcohol/drug abuse. Shift workers, for example, frequently have to battle fatigue and daytime drowsiness. Another reason for daytime drowsiness are sleep disorders and sleep-related respiratory dysfunction such as sleep apnoea. If a person is diagnosed as suffering from some form of sleep disorder, it is important that the attending doctors indicate to what extent the disorder could potentially affect that person’s ability to drive. The same applies when people are prescribed medication that leads to increased drowsiness.

What should you do if you experience fatigue at the wheel?

Most importantly, you should do anything possible to avoid the risk of suffering fatigue while driving. Make sure that you get enough sleep and rest, particularly before embarking on long journeys. Remember that driving for long periods on monotonous stretches of road (e.g. highways) can make you particularly tired, so make sure that you schedule a sufficient number of breaks. Physical activity during these breaks increases oxygen levels in your blood and brain, helping you to combat fatigue. If you feel your eyelids getting heavy and that you are losing concentration, take a break at the next available opportunity. In such cases, a short rest – “power nap” – can help you to reduce the risk of causing a fatigue-induced accident. Drivers who regularly or periodically have to take medication – including antihistamines in anti-allergy treatments – should definitely consult their doctor to find out whether their medication causes drowsiness. The consumption of drugs or alcohol can also – even on the day after – impair performance and cause drowsiness.

PS: Driving with a passenger also reduces the risk of causing a fatigue-induced accident.