Fatigue is a state of exhaustion, either physical or mental, that reduces a driver’s ability to operate a vehicle safely. It can be caused by lack of sleep, long working hours, intense activities, or a combination of these factors

The circadian rhythm is the body’s natural wake and sleep cycle that repeats every 24 hours. It is regulated by an internal clock and influences daily patterns of alertness. When sleep is insufficient, the drowsiness felt during natural “low points” becomes more pronounced, significantly impacting a driver’s focus and performance.

The U.S. Sleep Crisis

One in three U.S. adults suffer from insufficient sleep and rest each day, making poor sleep a common issue.
When asked if they’ve nodded off behind the wheel in the last week, all age groups responded similarly, except for those aged 21-29, who were twice as likely as other age groups to have fallen asleep while driving.
About 50 to 70 million Americans have sleep disorders, and 1 in 3 adults do not regularly get the recommended amount of uninterrupted sleep necessary to protect their health.

Getting little sleep and being behind the wheel might seem like an act of irresponsibility, but not everyone who does it is fully aware of the danger they’re putting others in. Doctors working shifts longer than 24 hours, people juggling two jobs, and many other social factors can lead someone to take the wheel without realizing the true consequences.

Breaking Down Drowsy Driving Stats:

According to a recently released GHSA report, nearly 83.6 million drivers using the nation’s highways daily are dangerously sleep-deprived.
According to data from AAA’s Foundation for Traffic Safety report, drowsy driving caused 29,834 traffic fatalities between 2017 and 2021, with 6,726 fatalities occurring in 2021 alone.
Statistics show that 17.6 percent of fatal car crashes between 2017 and 2021 involved a drowsy driver.
Data indicates that drivers are three times more likely to be involved in a car accident if they are fatigued.
In 2015, motor vehicle fatalities rose by 7.7% nationwide, with an estimated 5,000 deaths linked to crashes caused by drowsy driving.
Every year, over 110,000 individuals are injured, and more than 5,000 lose their lives in the U.S. in motor vehicle accidents involving commercial trucks.

Sleep Fatigue Symptoms

As one study reveals, around 1 in 25 adults (aged 18 or older) reported having fallen asleep while driving in the past 30 days. A conservative estimate from the National Highway Traffic Safety Administration (NHTSA) found that drowsy driving was responsible for 72,000 crashes, 44,000 injuries, and 800 deaths in 2013. However, because many drowsy driving incidents go unreported, NHTSA suggests that sleep-deprived drivers may actually contribute to more than 6,000 fatal crashes each year.

It’s a common misconception that sleep fatigue is simply the act of falling asleep at the wheel. In reality, it encompasses several key factors:

Inability to Focus: Driving while tired significantly impairs your ability to stay focused. If you’re struggling to stay awake behind the wheel, your attention is divided, meaning you’re less aware of the road, other vehicles, and potential hazards.
Delayed Reaction Times: Similar to driving under the influence of drugs or alcohol, drowsiness can cause delayed reaction times. Without full alertness, it becomes harder to respond quickly to sudden changes or dangers on the road.
Poor Judgment: Fatigue slows down brain function, affecting your decision-making. This impairment can result in poor judgment, making it more difficult to make safe decisions while driving.
Inability to Judge Distances and Speeds: Due to the combination of slowed reactions and impaired judgment, fatigued drivers are more prone to misjudging distances and speeds. This could lead to driving too fast or too slow, increasing the risk of accidents.
Falling Asleep: The most dangerous risk of driving drowsy is actually falling asleep at the wheel. This can lead to serious accidents, whether by colliding with another vehicle, veering off the road, or hitting a stationary object.

Sleep fatigue is a serious issue, and its impact on road safety extends far beyond simply nodding off behind the wheel.

Commercial Vehicles & Trucks

A recent study examining the sleeping and driving habits of Commercial Motor Vehicle (CMV) drivers found that an unhealthy lifestyle, long working hours, and sleep-related issues were the primary causes of drivers falling asleep behind the wheel.

In another study, it was reported that 17% of CMV drivers had used over-the-counter drugs at the time of a crash, contributing to impaired alertness.

CMV driving often involves prolonged periods of continuous driving, extended hours spent on the road, economic pressures to keep driving while fatigued, physical demands from loading and unloading, and the differences in driving trucks or buses compared to passenger cars. Additionally, the lack of regulation equivalent to Hours of Service (HOS) adds to the risk.

The Driver Fatigue and Alertness Study (DFAS) aimed to observe and measure the progression of driver fatigue and loss of alertness, while developing countermeasures to address these issues. The study found that the time of day was the most significant factor influencing driver fatigue, with drowsiness peaking during night driving. There was also evidence of cumulative fatigue over several days of driving.

The Large Truck Crash Causation Study (LTCCS) reported that 13% of CMV drivers were considered fatigued at the time of their crash.

While restrictions on Hours of Service (HOS) regulations likely reduce the percentage of fatigued drivers, the relationship is complicated by other factors. For example, the difference in fatigue levels between driving for 10 hours versus 11 hours in a day warrants further assessment.

Drivers may be better equipped to judge when their performance is compromised and take necessary actions to reduce risk, such as pulling over to rest, consuming caffeine, or in the long term, adjusting their sleep habits or altering the scheduling practices of the carrier.

Time of Day

A study by the Federal Motor Carrier Safety Administration (FMCSA) found that driver alertness is more closely related to the “time-of-day” than to “time-on-task.” Most people tend to be less alert at night, particularly after midnight. This drowsiness can be further intensified if a driver has been on the road for an extended period.

Accidents caused by drowsiness are most likely to happen during the first hour of driving. Researchers suggest this could be due to sleep inertia—a temporary state of reduced alertness and performance that often follows waking up. This effect may be more pronounced for drivers who rest in sleeper berths. Sleep inertia can impair short-term memory, focus, reaction time, cognitive function, and the ability to stay awake.

Drowsy Driving by Length of Drive

Drowsy driving is not limited to long trips. In fact, 30% of drivers report nodding off during drives shorter than one hour, which contradicts the common belief that longer drives are the primary cause of fatigue-related driving. This underscores the importance of staying alert on all trips, regardless of their length.

The Limitations of Caffeine

Caffeine takes several minutes to enter your system and provide the energy boost you’re expecting. If you’re already feeling fatigued when you consume it, the effects may not kick in as quickly as you need. Additionally, for regular caffeine users, the impact tends to be much weaker because their tolerance to the substance is significantly higher.

Overusing caffeine can also backfire, leading to insomnia, headaches, irritability, and nervousness—further compounding the issues of fatigue and focus.

Drowsiness Compared to DUI

Studies show that being awake for 18 hours impairs your abilities as much as having a blood alcohol concentration (BAC) of 0.08%, the legal limit for intoxication. Driving under these conditions poses an equally high risk of a crash.

When drowsy, you lose key functions like quick reflexes, sharp memory, and the alertness that sober drivers rely on for safe decision-making.

Challenges with Police Reports

Police investigators, typically not trained to identify fatigue after an incident, are often reluctant to classify it as a factor in crash reports. This hesitation arises from the fact that they would be required to justify their decision in court if they attribute a crash to driver fatigue. When a vehicle is not equipped with the appropriate technology, determining whether fatigue contributed to the crash becomes highly difficult. And even when a vehicle is properly outfitted, there are still cases where it remains unclear whether fatigue was a major contributing factor.

Drowsy Driving Deaths Likely Underreported

Determining fatigue as the sole cause of an accident can be incredibly challenging, as other factors—such as mechanical failure or the actions of other drivers—often play a role. However, fatigue may exacerbate these situations, particularly through the driver’s impaired reflexes.

Some experts attribute the rising problem of drowsy driving to America’s “always on” work culture, which contributes to widespread restlessness. Others point to increased light and sound pollution, which ironically worsens as cars become more prevalent on the roads. As we juggle the demands of daily life, “sleep often falls by the wayside,” with many people prioritizing other activities over getting enough rest.

A conservative estimate by the NHTSA found that drowsy driving caused 72,000 crashes, 44,000 injuries, and 800 fatalities in 2013. Since many drowsy driving accidents go unreported, NHTSA believes sleep-deprived drivers could be responsible for over 6,000 fatal crashes annually.

Pre and Post 2004 Hours Rule

In 2004, a law was enacted to regulate the long hours that drivers could be required to work, setting a time limit. The consequences of this regulation varied. In Pennsylvania, accidents gradually decreased, while in Oregon, the number of accidents began to rise, as if the rule had never been implemented.

The majority of drivers (72-76% in 2004 and 69-70% in 2005) reported that their daily driving times were about the same as before the rule change. However, in both 2004 and 2005, approximately one-fifth of drivers said they were driving more hours daily under the new rule. Additionally, a significant percentage of drivers in both states reported getting more sleep on a daily basis under the new work rule than they had under the old rule. At least 72% stated that the restart was now part of their regular schedules.

In Pennsylvania, the percentage of drivers who admitted to driving their trucks while feeling sleepy at least once during the past week increased from 43% in 2003 to 48% in 2004, then declined to 43% in 2005. In Oregon, the percentage reporting sleepy driving was 36% in both 2003 and 2004, but increased to 41% in 2005. The percentage of drivers reporting that they had dozed off at the wheel at least once during the past month increased over time in both states, with the difference between 2004 and 2005 being statistically significant.

International Data

Although these numbers are from two decades ago, they reflect a time when distracted driving wasn’t as prevalent.

There has also been some international research on this topic. In England, for instance, Horne and Reyner (1995) discovered that 16 percent of all vehicle crashes were related to sleep deprivation. More recently, Garbarino and colleagues (2001) found that 21.9 percent of highway crashes in Italy between 1993 and 1997 were caused by drowsiness. While these studies do not focus specifically on truck crashes, they do offer insight into the significance of driver fatigue as a contributing factor to accidents.

Tips to Prevent Fatigue and Enhance Safety for Everyone

A 2005 study suggests that three out of every four Commercial Motor Vehicle (CMV) drivers report having made at least one driving error due to drowsiness.

If you catch yourself yawning or blinking frequently, missing exits, hitting rumble strips, or having trouble remembering the last few miles, the CDC advises pulling over to rest or switching drivers.

Avoid driving when your body is naturally drowsy, particularly between 12 a.m. and 6 a.m. or 2 p.m. and 4 p.m.
Skipping meals or eating irregularly can lead to fatigue and cravings. Going to bed with an empty stomach or right after a heavy meal can also disrupt your sleep.
If you’re feeling drowsy or less alert, take a short nap. A nap should last at least 10 minutes, but ideally up to 45 minutes. After waking, allow at least 15 minutes to fully recover before driving. Short naps are more effective at restoring energy than coffee.
Naps aimed at preventing drowsiness are generally more effective in maintaining a driver’s performance than naps taken when already drowsy.
Cold medications are common culprits of drowsiness. If you must drive while having a cold, it’s safer to endure the symptoms than to drive under the effects of the medicine.

Sources:

Drowsy Driving More Dangerous Than People Think

Drowsy Driving Statistics and Facts 2024

CMV Driving Tips – Driver Fatigue

Drowsy Driving Deaths May Be 10x More Frequent Than Official Stats Show

Fatigue, Hours of Service, and Highway Safety

Most Obvious Study Ever: MILLIONS OF SLEEP-DEPRIVED DRIVERS ON THE ROAD EVERY DAY!