Risks & Statistics

Driver fatigue is most commonly experienced during the late night and early morning. In an analysis of US interstate truck accidents involving dozing drivers, Harris (1977) found that about twice as many of these crashes occurred between midnight and 8 a.m. as in the rest of the day and about half of the single-vehicle accidents occurred in the early morning hours. Hoback (Lisper et al., 1979) stated that "a driver is fifty times more likely to go to sleep between 2 a.m. and 6 a.m. than from 8 a.m. to noon".

It only makes sense that when our body’s internal clocks or circadian rhythms indicate we are at our sleepiness that there would be more accidents related to driver fatigue.

Daily Rhythm Test Result

Your natural daily rhythm cycle
This chart shows your natural rhythm of
alertness and sleepiness over a 24-hour period.

Research into morning and evening types has been
done by Professor Jim Horne at Loughborough University,
who has produced these graphs by comparing your data to the national profiles.

Why does the chart dip?

  • Having a siesta seems to be hard-wired into us. Most of us have a natural dip in the early afternoon - this is controlled by your body clock (not by how much you eat at lunch).
  • Morning people (Larks) have a longer and more obvious afternoon dip than evening people (Owls).
  • After a poor night's sleep, your afternoon dip would be more noticeable. Your graph would be one notch lower - something you should bear in mind if driving in the afternoon.

Can I affect the dips?

  • Everyone's natural dip is made worse by alcohol - drinking at lunchtime seems to have more of an effect than in the evening.
  • Afternoon tiredness can be overcome by coffee or a 20minute nap (ideally both, since caffeine takes 20 minutes before it gets through your system).
  • If you like to limit your caffeine intake, you may want to save your quota for when you experience your natural dip.