Conclusions

Based on American data, over one-third of the adult population has impaired functioning due to sleep loss during one or more days each month
Surveys suggest that over half of all drivers drive while being drowsy at least once a year. Actually nodding off or falling asleep behind the wheel within the last year occurs for a sizeable proportion of the populations (range 10% up to 40%).
Amongst young drivers, driving while drowsy is quite common due to lifestyle factors. Adolescents need more sleep than adults and fatigue may affect youngsters more than adults.
Most professional drivers and shift workers have to cope with fatigued driving on a frequent basis due to work-related factors. According to surveys, half of professional drivers take less than normal sleep time before a long-distance trip
Even the more acute stages of fatigue, e.g. dozing off behind the wheel, happen at least once a year for a considerable proportion of all professional drivers.