It is difficult to determine how many crashes are due to sleepiness.
Sleepiness increases the likelihood of such lapses.
A Gallup poll conducted for the National Sleep Foundation reported that 31 percent of adults said they had fallen asleep at the wheel and 4 percent had had a crash they attributed to fatigue. Such polls indicate police crash reports may significantly underreport the extent of fatigue-related crashes. Seventy-eight percent were male. Studies suggest that 20 to 30 percent of shift workers have had a fatigue-related driving mishap within the last year. This group is at risk because of the number of miles they drive and because many of them drive at night.