Time of day

United States organisations have amassed considerable amounts of knowledge and undertaken many initiatives into sleep related road crashes. The National Highway Traffic Safety Administration (NHTSA) is the United States Federal Agency whose mission is to save lives, prevent injuries and reduce traffic related healthcare and other economic costs.

The risk of a crash related to sleepiness increases during night-time hours among both younger drivers (25 years of age and younger) and drivers between the ages of 26 and 45. However, younger drivers have no increased risk during the afternoon, when the predictable circadian sleepiness peak is expected. Drivers ages 45 through 65 have fewer night-time crashes, with a peak at 7:00am. Drivers aged older than 65 are more likely to have "fall-asleep" crashes during the mid-afternoon (Pack et al., 1995; Wang, Knipling, Goodman, 1996).

Ages 25 yrs & below Ages between 26 yrs & 45 yrs inclusive
Ages between 46 yrs & 65 yrs inclusive Ages 65 yrs & above
Figure 3. Time of occurrence of crashes in drivers of different ages in which the crashes were attributed by the police to the driver being asleep but in which alcohol was not judged to be involved. The four panels show plots for drivers of the following ages: (A) drivers 25 years of age or younger; (B) drivers between 26 and 45 years of age, inclusive; (C) drivers between 46 and 65 years of age, inclusive; and (D) drivers older than 65 years. In each panel, the X axis is the time of day and the Y axis is the number of crashes. However, the scale of the Y axis is different for each panel. The data are for the years 1990 to 1992, inclusive. Reproduced with the written permission of the National Highway Traffic Safety Administration, United States.