Drowsy driving is estimated to be responsible for tens of thousands of car accidents and hundreds of deaths every year in the United States. Although the vast majority of drivers know that drowsy driving is dangerous, many people drive while sleepy at least occasionally, and about a quarter of people admit to doing so one or more times a month.

People generally are not good at judging how sleepy they are or how impaired their driving is by drowsiness. For these reasons, it is important to have tools that can assess if a person is at risk for drowsy driving. A team of French researchers recently created one such tool—a questionnaire called the Bordeaux Sleepiness Scale (BOSS).

What is the Bordeaux Sleepiness Scale?

Researchers designed the Bordeaux Sleepiness Scale (BOSS) to determine the likelihood that a person will have a car accident or near miss due to sleepiness. Unlike other questionnaires used to measure sleepiness, the BOSS focuses exclusively on sleepiness in the context of driving. 

The BOSS has been tested among people with sleep disorders and in the general population, and it appears to be better at assessing the risk of a car accident than other questionnaires commonly used to measure sleepiness. It is highly effective at predicting car crashes, and is even more predictive of near misses. 

How Does BOSS Evaluate Risk?

The BOSS evaluates risk by asking five questions about the personal characteristics of drivers and their experiences both behind the wheel and as passengers in cars. For example, it asks people to report how many miles they drive per year and whether they experience excessive sleepiness when they spend a few minutes stopped in traffic.

The responses provided are used to generate a global score on a scale of one to eight. A score greater than three indicates that a person is at risk of having a car accident or near miss due to sleepiness.

Who Is Most At Risk for Drowsy Driving?

Anyone who is sleep deprived is at risk for drowsy driving, but some people are more likely than others to regularly drive while sleepy. Those most at risk include include:

  • Teenagers and young adults 
  • Older adults 
  • Commercial drivers 
  • People who work extended shifts or night shifts 
  • Individuals with untreated obstructive sleep apnea 
  • Those who have trouble falling or staying asleep, including those with insomnia 
  • People who take sedative medications 
  • People who drink alcohol 

“One of the most dangerous aspects of driving when tired is a phenomenon called ‘micro-sleeps.’ A drowsy driver may briefly fall asleep behind the wheel and not even realize it — posing a danger to themselves and others.”

Dr. Dustin Cotliar, Sleep Physician

What Are the Warning Signs of Drowsy Driving?

Drowsiness can express itself through physical sensations, emotions, compromised mental processes, and even unconscious or “automatic” behaviors.

  • Bodily sensations and movements: People engaged in drowsy driving may yawn or blink more often than usual, rub their eyes, have trouble holding their heads up, or feel that their eyelids are heavy.
  • Emotions: People might feel cranky or restless if they are driving while drowsy.
  • Mental warning signs: Drowsy drivers may struggle to remain alert and react quickly. They may also find that their minds frequently wander or drift into daydreams—or that they can’t recall the last several miles they have traveled.
  • Automatic behaviors: Drowsy drivers might run stop signs, miss turns, or pass their exits. They might also unintentionally drift between lanes or tailgate cars in front of them.

Ideally, people should avoid getting behind the wheel of a car if they feel tired and either rest or arrange for alternate transportation. However, if signs of drowsiness develop while a person is driving, they should immediately find a safe place to pull over and take a brief nap.

Learn more about our Editorial Team

2 Sources

  1. Philip, P., Micoulaud-Franchi, J. A., Taillard, J., Coelho, J., Tisserand, C., Dauvilliers, Y., & Sagaspe, P. (2023). The Bordeaux Sleepiness Scale (BOSS): a new questionnaire to measure sleep-related driving risk. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 19(5), 957–965.

  2. Gurubhagavatula, I. (2023 October). Drowsy driving: Risks, evaluation, and management. In T. Scammell & A. Eichler (Ed.). UpToDate., Retrieved November 10, 2023, from


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