Driver fatigue – an accident waiting to happenAlthough we often associate driver fatigue with long-haul truck drivers, it can affect all of us. Key text Key textStrange things happen in the dead of night. A car leaves a dark and lonely highway, apparently at full speed, and slams into an unforgiving tree. Nobody sees it happen and the driver is dead. On another country road, a car drifts from its lane for no obvious reason and smashes into an oncoming truck, killing all the car's occupants.More than likely, these crashes were caused by fatigue: drivers either falling asleep at the wheel or so exhausted they made serious – and fatal – driving errors. Fatigue is thought to be one of the biggest killers on Australian roads, rivalling the effects of speed and alcohol. But the full extent of its role is not really known – unlike alcohol and drugs, fatigue can't be tested for in post-mortems. This is the reason for the big difference between the lowest and highest estimates of the role of fatigue in the Australian road toll. One study based on coronial and police reports found that fatigue played a part in only 5 per cent of fatal crashes in 1988. A more recent survey (for 1994) raised this figure to about 18 per cent. It included not only those crashes in which police identified fatigue as a cause, but also cases where the crash description suggested 'loss of concentration' had been a contributing factor. A third review found that around 30 per cent of rural crashes in Western Australia could be attributed to fatigue. And a fourth study, by the Australian Transport Safety Bureau, reckoned that fatigue was a factor in over 16 per cent of the total crashes on Australian roads in 1998.
In the Australian Transport Safety Bureau study, fatigue-related crashes were defined by first excluding all crashes involving alcohol, unlicensed drivers or pedestrians and those occurring in areas where the speed limit was less than 80 kilometres per hour, and then counting all remaining head-on crashes and any single-vehicle crashes between midnight and 6 am, and between 2 pm and 4 pm (the two periods of the day when the effects of fatigue are most evident). This is a pragmatic definition; it has the advantage of being repeatable in other studies, but it risks missing some crashes in which fatigue was a factor and of counting others where it wasn't. Why does fatigue cause accidents? The effects of fatigue on driver performance have been documented in numerous studies in which subjects were required to perform driving tasks after long hours of wakefulness. Fatigue manifests itself in:
The Centre for Sleep Research at Flinders University in South Australia has likened fatigue-induced impairments to those caused by alcohol: a person kept awake for 17 hours will perform at a standard comparable to that of someone with a blood-alcohol concentration (BAC) of 0.05 per cent (the legal limit in Australia). After 24 hours without sleep, a person will have capabilities similar to someone with a BAC of 0.10 per cent. But probably the greatest hazard posed by fatigue is the risk of sleep itself. A fatigued driver who remains awake will probably be able to take some (perhaps belated) action to avert a crash, but one who has fallen asleep must rely solely on luck for survival. Circadian rhythms Researchers have long noted that fatigue-related accidents tend to occur in two distinct periods of the day – between midnight and 6 am, and between about 2 pm and 4 pm. These periods coincide with typical low-points in our daily pattern of alertness, or circadian rhythm (the word 'circadian' is derived from two Latin words: circa, meaning 'about', and dies, meaning 'day'). Most organisms follow a daily routine (circadian rhythm). Songbirds, for example, mark sunrise and sunset with their vocal-chords. Many Australian marsupials sleep during the day and go about their business in the relative cool of the night. Are these routines based purely on external factors? For example, do nocturnal animals simply get up when they notice that the sun has set, or is their behaviour also governed by some internal timing mechanism? Scientists have shown that most organisms have internal 'clocks'. If the sun failed to rise one day, songbirds would still sing their usual tune. Plants whose leaves track the sun will continue to do so if kept in a perpetually dark room – as noted in 1729 by the French scientist d'Ortous de Mairan. Scientists have gathered molecular evidence for an internal clock in humans (Box 1: Circadian rhythms at the molecular level), but circumstantial evidence is provided by the modern phenomenon of jet-lag. Travellers who have moved between time zones – say, from Australia to the United Kingdom (a difference of about 10 hours) – typically find it difficult to sleep, even when tired. It might be 10 pm in London and theoretically bedtime, but according to the body-clock it's 8 am and time to get up. In humans, the circadian rhythm is controlled by a small region of the brain called the suprachiasmatic nucleus (SCN). The SCN is located in the hypothalamus, which regulates many functions of the autonomic nervous system. One of the main ways in which the SCN transmits its time-related information is by stimulating the production of melatonin, a hormone manufactured in the pineal gland at the base of the brain. Melatonin levels typically increase in the body after sunset and reach their peak between 12 midnight and 6 am. This corresponds with the body's lowest levels of alertness and body temperature and its lowest capacity for the processing of incoming information. A second, smaller trough in these functions occurs in the afternoon, commonly between about 2 and 4 pm. These two dips in the circadian rhythm are dangerous for drivers. Fatigue-related crashes are thought to be about twice as high at 2 pm as they are at 10 am, and nearly six times as high at 2 am. What sleep does Scientists have identified five stages of sleep:
Each sleep cycle – comprising the five stages – takes about 90 minutes. Thus, someone sleeping for 8 hours will sleep through about 5½ cycles. The different stages consume different amounts of the sleep quota: stage 1, for example, usually makes up less than 10 per cent of a full night's sleep, while the REM stage might span about 25 per cent (although percentages vary by age group). Surprisingly little is known about the physiological role of sleep and the ways in which it restores the brain to its full functions. But the effects of fatigue on the brain can be measured. Studies have shown that after 24 hours of sustained wakefulness the brain's metabolic activity can decrease by up to 6 per cent in total and by up to 11 per cent in specific areas of the brain – particularly those that play a role in judgement, attention and visual functions. Measures to prevent fatigue-related crashes Changes to road design, such as those listed below, could help prevent fatigue-related crashes:
Public education campaigns to warn of the dangers of driving while fatigued also play an important role in reducing fatigue-related crashes. Managing fatigue It is clear that the best way to manage fatigue is simply to get enough sleep. Medical researchers suggest that 8 hours a night is about the right amount for most people, although some, particularly those with sleep disorders (Box 2: Sleep disorders), might find this difficult to achieve. Other fatigue management techniques might help. For example, recent research at Flinders University has shown that subjects waking from a 10-minute nap demonstrate an immediate significant increase in alertness and mental performance that lasts for at least an hour afterwards. In contrast, a 30-minute nap fails to produce a similar immediate increase (although it does induce an increase about 30 minutes after the end of the nap). One useful practice for fatigued drivers, then, is to pull over and take a short 'power' nap. Various road-safety publications outline other fatigue-management techniques. For example, VicRoads advocates that drivers should:
Maintaining a sensible sleep regime is the key. Driving and drowsiness are not good bedfellows; in the dead of night, it's better to wrap yourself around a pillow than around a highway ghost-gum.
Negative feedback loop According to a simplified model, two genes called period and timeless code for the manufacture of two proteins called PER and TIM respectively. When the concentration of PER and TIM reaches a threshold level they are transported into the cell nucleus where they bind to transcription factors (proteins that initiate the transcription of a gene), shutting down further production of the two proteins; this is called a negative feedback loop. The concentrations of PER and TIM in the cell then declines as the existing molecules degrade; once the lower threshold concentrations are reached, their manufacture commences again. This rise and fall in the concentration of PER and TIM occurs on a roughly 24-hour cycle and is thought to play a major role in governing the circadian rhythm in Drosophila. Resetting the biological clock Similar but much more complex processes have now been identified in mammals. In humans (and many other species) the biological clock appears to work on a cycle between 24 and 25 hours in length. Under normal circumstances the biological clock is regularly ‘reset’ by a range of environmental cues, or ‘zeitgebers’ (‘time-givers’), the most important of which is light; thus, jet-lag is not a permanent condition because the internal clock will eventually be reset to match the new real-world conditions. Related sites
Obstructive sleep apnoea is more common than narcolepsy, affecting perhaps 5 per cent of the population. It 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 and thus to have a fractured and less restful sleep. This in turn means that sufferers are commonly tired during the day and more prone to symptoms of fatigue, including 'microsleeps', which are sleep episodes in inappropriate settings that last a few seconds. Several factors contribute to sleep apnoea, including facial structure (ie, the narrowness of the throat), obesity and the loss of muscle tone with ageing. Symptoms may be made worse by the consumption of alcohol and tobacco. Related site
Australasian Science August 2001 (page 9) Device monitors driver fatigue (by Stephen Luntz) Describes a study to use electroencephalography signals to determine driver fatigue.
New Scientist 3 November 2001 (pages 44-47) Out of control (by Mark Young and Neville Stanton) Discusses the hidden dangers of giving drivers too little to do, and notes that the Australian National Road Transport Commission has voiced its concern that automatic fatigue-detection systems may lead drivers to ignore their own judgment.
21 July 2001 (page 24) You drive me crazy (by Ian Sample) Describes dashboard devices designed to keep drivers awake.
24 March 2001 (page 24) Asleep at the wheel (by Duncan Graham-Rowe) Describes an Australian-designed system that can detect when a driver is losing concentration.
3 June 2000 (pages 28-31) Rhythm and blues (by Lisa Melton) Explains how disruptions to our biological clock can affect our health.
3 July 1999 (page 16) Bang on time (by Jonathan Knight) Discusses biological clocks and what resets them.
Scientific American September 2002, pages 40-47 Times of our lives (by Karen Wright) Describes different biological clocks, including those that synchronise our bodily functions with day and night.
January 2000, pages 58-63 Narcolepsy (by Jerome M. Siegel) Describes the symptoms, causes and possible treatment of the disease that causes persistent daytime sleepiness.
Provides an overview of driver fatigue. In addition, you can access
more information about specific topics (eg, 'Facts about sleep and fatigue'
and 'Problem definition and countermeasures').
Driver fatigue (National Roads and Motorists' Association, Australia) A series of questions and answers designed to alert people to the warning
signs of fatigue and how to avoid it.
Managing driver fatigue (VicRoads, Australia) A brochure for the general public covering causes and management of driver fatigue.
Fatigue and fatigue research: The Australian experience (Monash University Accident Research Centre, Australia) This 1998 paper reviews the extent and nature of driver fatigue in road
crashes and summarises the kinds of investigations undertaken by driver
fatigue researchers.
Fatigue-related crashes: An analysis of fatigue-related crashes on Australian roads using an operational definition of fatigue (Road Safety Research, Australian Transport Safety Bureau) The executive summary of this 2002 report discusses the effectiveness
of the operational definition that was used in the study and presents
an overview of the findings. You can download the complete report from
this page as a PDF file.
2001 Road Safety Conference papers (Murdoch University, Australia)
Australian Broadcasting Corporation (transcripts)
There are 20 common amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. autonomic nervous system. The part of our nervous system that regulates essential functions such as heartbeat and breathing, functions that occur without conscious involvement. It is sometimes called the involuntary nervous system. For more information see The autonomic nervous system (Neuroscience for Kids, University of Washington, USA) and Autonomic nervous system (National Dysautonomia Research Foundation, USA). blood alcohol concentration (BAC). The concentration of ethanol in the blood, which is a key measure in determining the effect of ethanol on the body. It is measured in grams of ethanol per 100 millilitres of blood. For example, people with a BAC of 0.05 grams per 100 millilitres – the legal limit for most drivers – have 0.05 grams of alcohol in their body for every 100 millilitres of their blood. DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts. gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule. hormone. A substance produced in one part of the body and carried by the blood to another part of the body where it causes a response (eg, insulin, produced by the pancreas, that promotes the uptake of glucose by body cells). For more information see The hormones of the human (Kimball's Biology Pages, USA) and The hormones (Center for Bioenvironmental Research, Tulane and Xavier Universities, USA). hypothalamus. A part of the brain that is connected to, and controls activity in, the pituitary gland. It also controls various aspects of homeostasis such as regulation of body temperature and appetite. There are regions of the hypothalamus that are associated with aggressive behaviour. melatonin. A hormone that can influence the hypothalamus and pituitary gland and may affect appetite and sleep. It is derived from the amino acid, tryptophan. protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein. Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).
External sites are not endorsed by the Australian Academy of Science. Page updated June 2006. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by NRMA
– ACT Road Safety Trust.
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