Professional and truck drivers
Fatigue is a particular problem for professional drivers, and especially truck drivers. In practice, the particular job demands of long-haul transport industry often interfere with normal rest. World-wide transport industry work practices include working long hours, prolonged night work, working irregular hours, little or poor sleep, and early starting times. Many truck drivers work more than 12 hours per day, of which at least 60% is usually spent driving . A working week of over 70 hours is common practice for many owner drivers. These long hours of work may result in drivers obtaining less than the necessary 7 to 8 hours of sleep and cause fatigue . In the USA about 20% of all crashes and fatalities involving a long-haul truck, occur between midnight and 6am, the peak period of driver fatigue (Blower et al., cited in: ROSPA ).
French research into lorry driver working times and habits showed that risk levels vary with three key factors as regards the general problem of fatigue . There is an increased risk of crashes at night, an increased risk the greater the length of the working day, and also with irregular working hours.
Research points to an increased crash risk the greater the number of hours driven. However, studies show different results concerning the length of driving time needed before risk increases. Mackie & Miller  found some aspects of driving performance deteriorated after 8 to 9 hours driving. They analysed 750 truck crashes which clearly involved driver fatigue or were single vehicle crashes (which made it very likely they were driver fatigue related). They found twice the probability of a crash in the second half of a trip, as compared to the first half of the trip, and the odds of a crash started to rise after 5 hours driving. Folkard  undertook a meta analysis of several studies of hours of driving and crash risk. Folkard found that there was a rise in likelihood of a crash at two hours into the trip before risk dropped back to starting levels at 4 hours into the trip. The likelihood of a crash then started to rise again the more hours driven until at 11 hours the risk was higher than at any previous time. The US Federal Motor Carrier Safety Administration  has published data showing the relative risk of a fatigue crash and hours driven. As in Folkardís 1997 data and Hamelin , crash risk starts to rise after 10 to 11 hours of driving. The US data shows that the risk of a crash rises seven fold after this period of driving. In summary, the results of various studies are not quite consistent and should be interpreted with some caution. In these studies, the effects attributed to hours of driving may also have been influenced by a down turn in the circadian rhythms or by prolonged wakefulness .
The US National Transportation Safety Board (1995) examined 107 single heavy goods vehicle crashes where the drivers survived and records of their activities over the previous 4 days were available. 58% of those crashes were judged to be due to fatigue; and in 18% of those crashes the driver was asleep at the wheel. In the fatigue crashes the Safety Board found that more drivers had: an inverted sleep/waking cycle; driven at night with a sleep debt (chronic sleep shortage); had slept only 5.5 hours in the past 24 hours compared to 8.8 hours in other crashes not due to driver fatigue; and had fragmented sleep between night and day.
A Dutch survey study amongst 537 truck drivers investigated determinants of both chronic and acute fatigue (defined as actually dozing off or falling asleep behind the wheel) . Surprisingly, drivers who worked for 60-65 hours per week did not feel more tired than drivers who worked for shorter time (52-56 hours). Factors that were linked to chronic fatigue were, in decreasing order of importance: few possibilities to learn new skills, competence or apply creativity; not taking the time to eat well; sleeping problems; relative ill health; being a parent; use of medicine; large pressure of working times on family life; smoking; large pressure of family life on work; lack of vegetables intake. Indirectly, long working hours play a role in the causation of chronic fatigue. The two factors indicating interference between professional and private life belong to the most important factors in explaining chronic fatigue.
In that same study, the factors that were most strongly linked with acute fatigue were in decreasing order of importance: lesser general health; amount of alcohol intake; good (comfortable) cabin climate; more frequent violations of official work and driving times regulations; being busy with other things besides driving (e.g. using mobile phone); driving singly instead of in a team; more often having work progress meetings; not having a fixed contract.