Why Does Driving Make You Tired?


Driving while drowsy is a serious problem that can lead to serious consequences. Unfortunately, drowsy driving is a common occurrence in the U.S. In fact, research studies have found that up to 41% (1) of drivers reported falling asleep at the wheel since beginning to drive. About 21% of motor vehicle crashes (2) that involved a fatality also involved a drowsy driver.

However, falling asleep while driving is preventable. There are a number of reasons people get sleepy while driving. It is important to learn the warning signs and be able to address them to keep from falling asleep at the wheel.

Why Do I Get Sleepy While Driving?

There are many factors that may lead to sleepiness while driving. One theory is referred to as highway hypnosis, (3) or a state in which your attention slips while driving for a long period of time in a predictable environment, such as a long stretch of highway or a road that is very familiar to you. As your attention starts to slip, the chances of falling asleep and running off the road are higher. Research suggests that after a long drive, drowsiness is higher and alertness is lower when on highways versus side roads. The monotony (4) and predictability of a highway leads to drowsiness and boredom while behind the wheel, especially after a long drive.

What Are Some Causes of Drowsy Driving?

There are some main contributors that cause drowsiness while driving. Long hours, time of day, and sleep-related problems are just a few.

Long Hours on the Road

Many studies have shown that longer drives (5) lead to a decrease in alertness over time. If you are planning a long road trip, be sure to take breaks and switch drivers when possible. While longer drives seem to make drivers the sleepiest, even a shorter drive, between 20 to 25 minutes, can cause significant fatigue in the driver, especially if the environment is monotonous or if it is during a part of the day when they tend to feel sleepier.

Time of Day

Circadian rhythm is our body’s biological clock, which cycles over a 24-hour period. Our body temperature, alertness levels, and energy levels change predictably (6) with the time of day. Even for those who are not sleep-deprived, circadian rhythm can cause sleepiness in the afternoon. Research has found that most sleep-related motor vehicle crashes occurred (7) during the hours of midnight to 7 a.m. and afternoons between 2 p.m. and 4 p.m. It is best to avoid driving during these hours, when possible. Even short drives (8) can be affected by circadian-rhythm-related drowsiness.

Sleep Problems

People who suffer from sleep disorders (9) may be at high risk for sleep-related motor vehicle accidents. The Centers for Disease Control and Prevention estimates that 70 million (10) Americans suffer from chronic sleep problems. Even one night of sleep loss can affect your ability to focus and stay alert while driving. Research suggests that being awake for 20 to 25 hours is comparable to having a blood alcohol content of 0.10% (11), which is higher than the legal limit allowed in all states.

Irregular Working Hours

Working night shifts, long shifts, or irregular work schedules can put you at a higher risk for sleep-related motor vehicle accidents. Working a night shift means you have to sleep during the day, which tends to cause more sleep disturbances (12) and reduces sleeping hours by about 2 to 4 hours on average. Your level of alertness and cognitive performance decreases during the hours of your circadian rhythm dips (late afternoon and night).

Alcohol and Medication

Drinking alcohol impairs your cognitive and physical performance and can add to your drowsiness. Additionally, some medications cause increased sleepiness during the day. It is important to read the labels of medication to see if they may cause drowsiness and to contact your physician if you are unsure.

Age and Sex

Younger males between the ages of about 16 and 29 seem to be at a higher risk (13) for sleep-related motor vehicle accidents. There are many speculations as to why age is a contributor, but one reason may be that adolescents require more sleep than other age groups and are often sleep-deprived (14). Males are reported to be 5 times more likely than females to be involved in sleep-related crashes.

What Should I Do if I Start to Feel Sleepy While Driving?

Sleep-related motor vehicle accidents may be common, but they are preventable. Getting quality sleep on a regular basis is essential for many reasons. Experts recommend that adults get seven to nine hours of sleep every night, and this is the best way to avoid drowsy driving. If you feel yourself starting to nod off or fall into a microsleep, it is important to act fast to remedy the situation. Simply rolling down the windows and turning up the music is not enough. Below are steps you can take to stay safe:

  • Pull Over: Find a safe place to pull off the road.
  • Change Drivers: If possible, switch to a different, well-rested driver and give yourself some time to rest as a passenger.
  • Take a Nap: If you must continue driving, take at least 20 minutes to nap in a safe place. A nap has been shown to increase alertness, but only for short periods of time. Do not rely on napping alone for a long drive.
  • Drink Caffeine: Drinking coffee or a caffeinated drink alone is not enough to keep you safe and alert while driving. Try taking a nap first, then go for a cup or two of coffee.
  • Call for Assistance: When in doubt, call a friend or a cab to pick you up. It is not worth risking your safety or the safety of others.

Drowsy driving is common in the U.S., but we are starting to see more attention on the topic and more preventative measures taking place. Each November, the National Sleep Foundation hosts a Drowsy Driving Prevention Week, which raises awareness and education about the dangers and prevention of driving while sleepy. The rumble strips you feel and hear on the sides of highways are implemented by the Federal Highway Administration to wake a drowsy driver (15) and have been shown to significantly reduce the number of accidents caused by sleepy drivers.

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