Among private drivers

Survey research in Canada, Europe and USA indicate that driving while tired or sleepy occurs at least once a year for a large proportion of the population. The table below presents findings from studies in four countries.

Country	Author	Key fatigue result
Great Britain	Maycock 1997	29 % of respondents stated that they "had felt close to falling asleep while driving" in the past year
Norway	Sagberg, 1999	10% of male drivers and 4% of females reported to have fallen asleep while driving during the last 12 months; 4% of these events resulted in an crash
Ontario	Vanlaar, 2007	nearly 60% of Ontario drivers admit that they have driven while fatigued at least sometime; 14.5% of Ontario drivers say they actually fell asleep or nodded off while driving at least once in the past year
USA	National Sleep Foundation 2002-2005	60% of adult drivers and 51% of teenage drivers reported driving drowsy at least once a year; 14% of adults and 15% of teens said they drive drowsy at least once a week; 37% of adults and 5% of teens said they had nodded off or fallen asleep at the wheel within the past year

A New Zealand study [20] aimed to obtain reliable estimates of the prevalence of driver sleepiness. A sample of car drivers representative of time spent driving on public roads in a geographically defined region was obtained. 588 car drivers and drivers of light vehicles were surveyed at 69 roadside survey sites. From this sample, it was estimated that in New Zealand 58.7% of driving was undertaken by men. Most driving was undertaken by drivers with Epworth Sleepiness scores in the normal range (The Epworth Sleepiness Scale is a questionnaire intended to measure daytime sleepiness). However, a significant minority was undertaken by drivers with one or more characteristics likely to impair alertness. 3.1% had 5 hours of sleep or less in the previous 24 hours, and 21.9% had 4 or less full nights of sleep in the previous week. 8.1% of those surveyed worked a pattern of shifts likely to interfere with normal sleep. Results also found that 1.6% experienced symptoms associated with sleep apnoea.

The strength of this study is that it measures sleepiness in drivers in proportion to actual driving time on the roads. Therefore, the study directly measures exposure to the risk of fatigue-related crashes and injuries. Previous studies of driver characteristics or vehicle crashes that have considered exposure to risk have most often used driver-kilometres as the denominator, which is highly correlated with driving time but not identical.