In 2017, the National Highway Traffic Safety Administration (NHTSA) estimated that there were approximately 91,000 police-reported crashes involving drowsy drivers which led to an estimated 50,000 people injured and nearly 800 deaths. From 2011 to 2015, NHTSA estimated that drowsy driving was involved in 2.3 to 2.5 percent of all fatal crashes nationwide. However, there is a general consensus across the traffic safety, sleep science, and public health communities that these crash statistics significantly underestimate the impact of drowsy driving on crashes. For example, the AAA Foundation for Traffic Safety estimated that sleepiness is associated with 21% of all motor vehicle crashes in which a person was killed and 13% of those requiring hospitalization which result in 328,000 police-reported crashes, 109,000 injuries, and 6,400 deaths in the Unites States each year. These estimates make it clear that the issues of sleep deprivation, fatigue, and drowsy driving remain critical concerns for traffic safety in the United States.
Sleep Deprivation Effects
Sleep deprivation affects a driver’s ability to safely operate a motor vehicle by increasing the likelihood that a driver will fall asleep at the wheel, increasing the number of microsleeps, increasing reaction time, degrading attention and vigilance, increasing distractibility and confusion, decreasing motivation, and increasing the probability of driving performance errors. With respect to mood, sleep-deprived people may experience irritability, forgetfulness, and aversion to effort. In other words, sleep deprivation not only affects a person’s alertness, it also affects critical cognitive processes required to drive a vehicle. For this reason, accidents caused by sleep deprivation are likely not the result of decreased alertness alone.
Factors Leading to Drowsy Driving
Research indicates that the time of day is the most important factor contributing to driver fatigue and alertness levels, with drowsiness episodes being eight times more likely between midnight and 6 am than during other times. One study revealed that drivers have a 20-times higher likelihood of falling asleep behind the wheel at 6 am compared to 10 am. Long-distance truck drivers working overnight or early morning shifts are particularly susceptible to sleep deprivation due to disruptions in their natural sleep patterns. Factors such as total sleep duration, timing of sleep, sleep quality, environmental conditions (e.g., darkness, monotonous driving), underlying medical conditions (e.g., sleep apnea), and drug use (e.g., methamphetamine, sedating medications) also contribute to fatigue.
Federal Motor Carrier Safety Administration (FMCSA) Hours of Service (HOS) Regulations
To address drowsy driving in the trucking industry, the FMCSA implemented federal hours of service (HOS) regulations. These rules include limits on total driving time over specific periods and mandatory breaks. However, these regulations have not fully eradicated drowsy driving crashes, as fatigue and sleep deprivation persist among truck drivers. Surveys indicate that a significant portion (65%) of truck drivers experience symptoms of drowsiness while driving, with a smaller number (13%) even reporting falling asleep at the wheel.
HOS regulations, while addressing some causes of drowsy driving, have failed to address all underlying causes. They still permit driving activities such as early morning driving hours, irregular shifts, overnight shifts, and early wake times. They also do not regulate the amount of sleep a driver actually gets, only that they take set amounts of time away from driving. This means that despite FMCSA’s goal of eliminating drowsy driving crashes, fatigue and sleep deprivation in the trucking industry continue to contribute to crashes every day.
Human Factors Investigations of Drowsy Driving
Drowsy driving crashes are not limited to the trucking industry. All drivers are subject to the effects of fatigue and sleep deprivation with equally dangerous consequences for the driving public. Human factors investigations of drowsy driving crashes evaluate the underlying scientific causes of sleep deprivation and fatigue to determine if the driver was fatigued at the time of the collision and if fatigue was a cause of the collision.
Human factors experts use the methodology developed by the National Transportation Safety Board (NTSB) to answer these essential questions.
Was the Driver Fatigued?
These investigations consider the driver's sleep/wake history, circadian factors, and operator health to assess whether a driver was acutely and/or chronically fatigued at the time of the collision. Data on the driver’s sleep/wake history can be gleaned from driver logs, timesheets, testimony, and an analysis of digital evidence. Information on health conditions can be derived from medical records, testimony, and other sources.
Was Fatigue a Cause of the Incident?
This analysis includes evaluating the driver's performance under the specific conditions present at the time of the collision and analyzing whether the driver was exhibiting the known effects of sleep deprivation at the time of the collision.
Contact a Fatigue Expert
Do you have a case where Fatigue or Drowsy Driving may have been a factor? Contact Dr. Nancy Grugle to explore the role of fatigue or sleep deprivation in the collision.