Fatigue
ACRS Policy Position
ACRS supports measures to increase public awareness of the contributors to and dangers of driver fatigue, to promote awareness of countermeasures, and further research on these factors and the nature of fatigue and its effect on performance.
Objective
To improve safety by improving knowledge of the causes, contributing factors and effect of fatigue on performance.
Discussion
Fatigue is believed to make a primary contribution to between 4 and 30% of crashes (Moore & Brooks 2000, NRTC 2001). There is however no agreed definition of fatigue and no reliable and exhaustive means of determining whether or the extent to which fatigue contributed to a particular crash (Neville Inquiry, 2000). It is possible that crashes attributed to fatigue are actually the result of the driver falling asleep, and that those crashes represent the lower bound of a much larger number. Some crashes attributed to other causes such as inattention or failure to anticipate could well have fatigue as a factor behind the identified cause.
Whatever the true figure, fatigue is a serious safety problem. Better knowledge of fatigue and factors contributing to it may help the driving public to adopt practices that minimise fatigue and prevent fatigue related crashes from occurring. There has been a considerable amount of research on fatigue in the last decade or so and although much of that has been carried out with respect to the road transport industry, the fundamental physiological factors apply to all.
Australian research on fatigue has tended to characterise fatigue operationally, focussing on mental and physiological effects. The symptoms or effects of fatigue include impaired performance (loss of attentiveness, slower reaction times, impaired judgement, poorer performance on skilled control tasks and increasing probability of falling asleep) and subjective feelings of drowsiness or tiredness. Contributory factors include long periods awake, inadequate amount or quality of sleep, sustained mental or physical effort, disruption of circadian rhythms (the daily cycle of waking and sleeping), inadequate rest breaks and environmental stresses (heat, noise and vibration).
Adequacy of sleep and length of time awake are probably more important than duration of actual work. Two pieces of Australian research (Dawson & Reid 1997 and Williamson et al 2000) have found that being awake for 17-19 hours (eg, from (say) 6am to around 11pm-1am) brought a deterioration in performance on some tests equivalent to having a blood alcohol concentration (BAC) of around 0.05%, the legal limit. After 24-27 hours, impairment was equivalent to a BAC of 0.1%.
Circadian rhythms have an important effect. The body is governed by inbuilt biological rhythms that are attuned closely to the cycles of day and night. There are two ‘low’ points in the circadian rhythm when there is a strong propensity to sleep: from about midnight to 6am and a lesser one in the early to mid afternoon. Work is best performed during the day when the bodily system is (other things being equal) awake and alert; the best sleep is obtained at night. Sleep at other times of the day is less ‘efficient’; work performed at the low points of the cycle may be more prone to error.
Sleep is a biologically determined drive, and fatigue can only be relieved by sleep. If restorative sleep is not obtained, then impairment and progressive deterioration in performance occur, and sleep will follow. If sleep deprived to a significant extent, a person may fall asleep without warning, either into deep sleep or ‘microsleeps’ of a few seconds’ duration.
One reviewer (Swann, 2000) has noted that at lesser levels of sleepiness drivers may have significant withdrawal of attention from road and traffic demands which can affect collision avoidance ability (selective) or collision avoidance and vehicle control (general). At these impaired levels of information processing drivers may not detect critical events such as stop signs and red lights and may fail to appreciate high crash risk situations.
Simple measures are available to avoid the dangers of fatigue. The most important are:
- Get a good night’s sleep before travelling: repay any sleep debt
- Many people leave for holidays after work on Friday. This should really be avoided if possible. The effect of a full day’s wakefulness and a day’s work will affect alertness, judgement and anticipation
- Plan the trip to allow for rest breaks
- Take frequent breaks. There is no research evidence on a ‘good’ rest interval, but the usual suggestion of a break every two hours is good advice.
- Know what signs to look for. Passengers can look for some of these too and alert the driver.
- Wandering in the lane or over lane lines
- Changes in speed, especially slowing down without reason
- Yawning
- Nodding
- Lapses in concentration.
References
Dawson D and Reid K (1997) Equating the performance impairment associated with sustained wakefulness and alcohol intoxication, Centre for Sleep Research, University of South Australia
Moore B & Brooks C (2000) “Heavy Vehicle Driver Fatigue: A Policy Adviser’s Perspective, Proceedings, 4th International Conference on Fatigue and Transportation, Coping with the 24 Hour Society, Fremantle 19-22 March 2000
National Road Transport Commission and Smithworks Consulting (2001) Heavy Vehicle Driver Fatigue: Review of Regulatory Approach Discussion Paper NRTC
Williamson A, Feyer A-M, Friswell R and Finlay-Brown S (2000) Development of measures of fatigue: using and alcohol comparison to validate the effects of fatigue on performance, Consultant Report CR189, Australian Transport Safety Bureau, Canberra
Swann P (2000) Heavy vehicle driver health and sleep disorders, AP-148-00, Austroads