Drowsy driving can mean a number of things, including falling asleep while driving or simply not paying attention while driving due to fatigue or lack of sleep. Much of the research into sleepiness focuses on the human "biological clock".
What Time is Your Body? — Biological Clocks
Your biological clock tells you when it's lunchtime, gives you pep at certain times of the day, and affects your body temperature. Most people's clocks run on a daily rhythm of approximately 24 hours, but individual "body time" varies from person to person.
"Morning people" feel most alert in the early part of the day, while "night people" enjoy staying up late. Many teenagers and young people have clocks that make it easy for them to stay up late and sleep late. As people get older, they tend to wake up earlier and go to bed early.
Certain times of the day are "danger zones" for fatigue. For example, almost everyone's biological clock is programmed to make them feel sleepy in the middle of the afternoon. Many fatigue-related collisions occur between 1:00 p.m. and 4:00 p.m., during this "afternoon lull." Night time is especially risky for drivers. Most people are programmed to sleep when it's dark, and sleep becomes irresistible late at night. Avoid driving during the "low" period between 2:00 a.m. and 6:00 a.m.
To be a safer driver, become aware of your own biological clock. What times of day do you feel most alert? What times do you feel most drowsy? Once you are aware of your personal cycle, you can take extra care when you're likely to be feeling sleepy.
DROWSY DRIVING FACTS
People have a greater tendency to fall asleep while driving on the long, uninteresting stretches of road that are characteristic of many high-speed, rural highways. The New York State Police estimate that 30 percent of all fatal crashes along the New York State Thruway occurred because the driver fell asleep at the wheel.
The U.S. National Highway Traffic Safety Administration (NHTSA) estimates that approximately 100,000 police-reported crashes annually (about 1.5 percent of all crashes) involve drowsiness or fatigue as a principal causal factor. A conservative estimate of related fatalities is 1,500 annually or 4 percent of all traffic crash fatalities. At least 71,000 people are injured in fall-asleep crashes each year. The economic costs are immense: NHTSA estimates that these crashes represent $12.5 billion in monetary losses each year.
Additionally, drowsiness and fatigue may play a role in crashes that are often attributed to other causes. About one million crashes annually - one-sixth of all crashes - are thought to be caused by driver inattention. Sleep deprivation and fatigue make these lapses of attention more likely to occur.