Knowledge of the causes of driver fatigue is important for deciding on appropriate countermeasures. We would like to share the findings from a research study titled “European Road Safety Observatory (2006) Fatigue, retrieved May 9, 2008 from www.erso.eu
” and the findings about the contributing factors to driver fatigue.
This study identified 5 general causes of fatigue in general and driver fatigue in particular:
- Lack of sleep or poor sleep
- Internal body clock
- Monotonous tasks
- Individual characteristics including medical conditions
1. Lack of sleep or poor sleep
The average person needs 8 hours sleep every 24-hour cycle. Sleep prior to work is the most prominent factor that influences the waking state, the level of alertness of the driver. A chronic lack of sleep is the result of not having enough sleep during a long period.
An acute lack of sleep can occur after just one bad or short night. If there has been too little sleep during a 24-hour period, we refer to it as a partial, acute lack of sleep. There is a complete, acute lack of sleep if, within a period of 24 hours, there has been no sleep at all.
Besides quantity of sleep, the quality of the sleep is also of great importance. If sleep is regularly interrupted, this leads, just as too little sleep does, to day-time fatigue. The quality of sleep is influenced by, among other things, sleeping disorders e.g. sleep apnoea (a temporary breathing stoppage while sleeping) and narcolepsy (the tendency to suddenly fall asleep). But it can also be a side effect of chronic diseases and/or medication or the result of external factors, such as a noisy or unpleasant sleeping environment.
2. Internal body clock
Fatigue is linked to the circadian rhythm. The body’s circadian rhythm is an internal biological clock. It coordinates the physiological priorities for daily activities, including sleep, body temperature, digestion, performance, and other variables. Therefore, it has a direct affect on alertness, mood, motivation, and performance.
The body’s natural cycle, or circadian rhythm, plays an important role in how fatigue affects people. The brain and the body are so accustomed to the normal body cycle that they resist changes (such as caused by work-schedules). The human body has a greater need for sleep at certain times in the 24-hour cycle than at other times (approximately between midnight and 4 a.m.; and, to a lesser extent, 2 p.m.- 4 p.m.). At these moments, there is a natural tendency to sleep and, if this cannot be given way to, a sleepy feeling occurs.
Shift work for instance interferes strongly with normal sleep patterns. Pronounced sleepiness is therefore a typical characteristic amongst most shift workers.
Prolonged activity inevitably leads to physical and mental fatigue. Researchers have related the duration of activity, or the so called time-on-task, to fatigue symptoms. One of the causes of driver fatigue is the time-on-task, i.e. the time spent driving. The fatigue-inducing effects of prolonged driving may be decreased by taking frequent breaks.
For professional drivers, the relevant time-on-task is better seen as the total work time (including the time of driving). Professional drivers often perform many more tasks than the job of driving. For professional drivers, long working hours often go together with early waking and reduced sleep.
4. Monotonous tasks
A task is monotonous when its stimulants don’t change or the changes are predictable or there is a high level of repetition. Suburban highways where road environment changes are limited and there is a small volume of traffic match this definition. O’Hanlon and Kelly pointed out that driving on a monotonous road is equal to a vigilance task, thus driver vigilance decrement is an expression of fatigue.
Thiffault & Bergeron found that in a monotonous driving situation, driver steering wheel movement is greater and occurs more often, showing that the fatigue effect and effect on driver vigilance caused by a monotonous road situation is relatively large. Also, driving on a relatively long and monotonous driving environment also has a clear negative effect on driver valid peripheral visual field .
5. Individual characteristics including medical conditions
Individual characteristics such as age, physical condition, use of alcohol etc. also influence how fast drivers get fatigued and how well they can cope with fatigue. For example, older people (70+) and persons with poor physical condition are more susceptible to fatigue.
Changes in sleeping habits accompany the transition from teenager to young adult; teenagers may experience chronic sleep loss which may make them extra susceptible for temporary effects of fatigue induced by alcohol, drugs or bad sleep.
Alcohol use has a sedating effect, but alcohol consumed within an hour of bedtime appears to disrupt the second half of the sleep period. Some particular individual characteristics concern sleep disorders.
Narcolepsy is a rare sleeping disorder affecting 1:2000 persons. Sufferers commonly have ‘sleep attacks’ in which they fall asleep without warning. This often occurs in inappropriate settings and even after a good night sleep.
Obstructing sleep apnoea is characterised by the restriction of a person’s airflow during sleep, caused by the closure of the upper airway. People with sleep apnoea receive inadequate quantities of oxygen while asleep, causing them to wake frequently, resulting in a fractured and less restful sleep. Sufferers are commonly tired during the day and more prone to symptoms of fatigue, including ‘micro-sleeps’ (sleep episodes in inappropriate settings that last a few seconds). Symptoms of sleep apnoea may be made worse by the consumption of alcohol and tobacco.
For information on Fatigue and Road Safety also view the following: