Many sleep-related vehicle accidents (SRVAs) are wrongly attributed to other causes, such as driver inattention and tyre "blowout" (when the tyre deflated as a result of the SRVA). From accident surveys we have undertaken with various UK police forces, on many monotonous UK roads (especially motorways) we have found that sleepiness accounts for about 20% of serious accidents. These are accidents to which the police were called, and there are probably many other SRVAs that are not reported in this way. We maintain impartiality in our assessments of road traffic accidents, by using objective criteria, and are overseen by experienced, independent accident investigation officers. SRVAs are often work-related (e.g. trucks, goods vehicle and company car drivers). Typically, these accidents involve running off the road or into the back of another vehicle, and are worse because of the high impact speed (i.e. no braking beforehand), leading to a higher risk of death or injury. SRVAs peak around 02:00h-06:00h and 14:00h-16:00h, when daily sleepiness is naturally higher. This time-of-day effect also means that alcohol is about twice as potent at these vulnerable times compared with the early evening when daily alertness is high. Blood alcohol concentrations (BACs) can be the same, but the effects on the brain are quite different. Just a small amount of alcohol can be dangerous for the afternoon driver, even with BAC well within the legal limits. Thus, legal alcohol limits for driving in most European countries are usually too high at these vulnerable times. The more one suffers from the afternoon dip - the more potent is the effect of alcohol at this time. SRVAs are more evident in young male drivers in the early morning and among older male drivers mid-afternoon, as the afternoon "dip" tends to become more apparent as one gets older. Of course, young men are more likely to be on the road in the early morning. The effects of sleep loss and sleepiness are more profound in younger than in older people, which the former tend to deny; they are at a greater risk than they realise when driving early morning. Whereas time of day is a more important factor underlying SRVAs than is the duration of the drive, European Union and UK legislation regulating driving hours for truck and bus drivers relates only to driving duration. Many early morning SRVAs are within an hour or two of an "early start" and, in the case of truck drivers, well within the 4.5 hours of continuous driving that is allowed (in the EU) prior to a break. Regulations and advice relating to drivers' working hours often mention the need to get "adequate rest". But few, if any describe what is meant by "rest", and even fewer note that rest can be of little benefit if it contains inadequate sleep. Non-sleeping "rest" is no substitute for sleep. Night-workers are particularly vulnerable when driving home after the shift, in the early morning, when on quiet, monotonous roads, especially after their first night on "nights", and after the shift has lasted 12 hours. Possible pathological causes of driver sleepiness such as sleep apnoea have been highlighted recently, but there is little evidence that this contributes significantly to the overall accident statistics for cars, even though apneics may be more likely to have SRVAs - these car drivers tend to drive less and more cautiously. However, this is not the case for truck drivers, as in the UK too many of them have undiagnosed sleep apnoea, that is also used as a legal defence for their SRVA. SRVAs due to trucks are particularly likely to cause death or serious injury to other road users. Hence, apnoea screening of these drivers is desirable. Using a real-car simulator, we have undertaken laboratory studies of falling asleep at the wheel, and have evaluated practical methods for the driver to overcome sleepiness. These studies have been validated on driving tracks. Sleep does not occur spontaneously without warning, and is preceded by feelings of increasing sleepiness to the point that drivers who have SRVAs have been fighting off sleep - that is, they must be fully aware of this sleepiness. However, after falling asleep at the wheel, drivers are unlikely to recollect having done so, and may even claim that it was an unforewarned "sleep attack". But this does not exist, not even in narcoleptics, or for that matter in patients with Parkinson's Disease who, it has recently been claimed, are liable to these whilst driving. Humans have poor recollection for how sleepy they have been recently, even though they were aware of these feelings at the time. What many sleepy drivers do not appreciate is that sleep can ensue more rapidly than they imagine, and that their driving impairment is worse than they realise. Sleepiness can also cause mild euphoria and increased confidence in one's driving ability - this is particularly so in young drivers. Modern trucks and cars have many commendable safety features, but their cabs and interiors may be too well designed, too comfortable, and perhaps too conducive to sleep. Devices are coming on to the market as "in-vehicle monitors of driver sleepiness", to alert sleepy drivers. In this respect there is much interest in methods to detect blink rate or eye closure, but a significant portion of sleepy drivers determined to stay awake can fall asleep with their eyes open. Moreover, blink rate is affected by air flow around the face, oncoming headlights etc. Thus, more "intelligent" and subtle systems are needed. A driver's own self awareness of sleepiness is still a very reliable method for detecting sleepiness, and is the basis for UK motorways now having numerous, permanent signs stating: "Tiredness can kill - take a break" (which we have helped to establish). Nevertheless, too many sleepy drivers fail to stop at motorway service areas and have their SRVA soon afterwards. In taking a break (e.g. 30 minutes), what should the sleepy driver do? We have shown that short naps (less than 15 minutes) are an effective countermeasure, as is caffeine (150mg - found in about 2 cups of coffee). Ideally, drink this coffee and then take the nap (i.e. before the coffee has its effect). Exercise (e.g. brisk walking) is of little use. Continuing to drive whilst sleepy, and relying on "in-vehicle" methods such as cold air to the face, and turning up the car radio/tape, are of limited benefit, and effective for only a matter of minutes - sufficient only to enable the driver to find a safe spot to take a break. Caffeine (200mg) alone is particularly good for the early morning driver having had little sleep that night. These recommendations for caffeine and naps have now been incorporated into the UK "Highway Code". In sum, better driver education and a greater awareness of the dangers of driving whilst sleepy are the best ways of eliminating sleep-related vehicle accidents. (Author/publisher)
Samenvatting