Conclusions

• The most general factors that cause fatigue are lack of sleep, bad quality sleep and sleep demands induced by the internal body clock
• Besides these general factors, prolonged driving (time-on-task) can increase driver fatigue, especially when drivers do not take sufficient breaks
• For specific groups of drivers, e.g. professional drivers, these general factors often play a more persistent role due to long or irregular work schedules
• For a small part of the general population (a few percent), obstructive sleep apnoea contributes to above average day-to-day sleepiness.