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Sleep Deprivation and the Risk of Road Traffic Accidents

Sleep Deprivation and the Risk of Road Traffic Accidents

Contributor Bio

Dr. Zoya Marinova is a researcher and medical writer. Her research interests are in the fields of epigenetics and molecular neurobiology. She received her PhD in Experimental Neuroscience from Karolinska Institute. Dr. Marinova has co-authored publications in renowned journals, such as Molecular Psychiatry and Journal of Neuroscience. She has worked on basic, translational, and clinical research projects investigating the molecular mechanisms of CNS disorders.

Twenty million to 50 million people are injured each year in road traffic accidents around the world. There are approximately 1.35 million casualties of road traffic accidents globally each year, making road injuries one of the top 10 global causes of death.1 Moreover, between 20 and 50 million more people suffer non-fatal road injuries each year, which in many cases may lead to long-term disability.1 However, the impact of road traffic accidents is not limited to physical injuries. They can also have negative psychological effects, which can sometimes be long-lasting and severe, leading to stress-related, mood-related, or anxiety-related symptoms (signs) or disorders.2 The economic cost of road traffic accidents is also high, with one study projecting the cost of road injuries for the world economy during the period 2015–2030 at USD 1.8 trillion.3 Another investigation of the costs of road crashes found that in high-income countries the average costs of road crashes may reach 3.3% of the gross domestic product.4 The financial burden of road crashes is related not only to medical expenses and reduced life expectancy but also to future lost income, expenses for vehicle repairs or replacement, and legal costs.

Risk Factors for Road Traffic Accidents

Both driver-related and driver-independent factors may increase the risk for road traffic accidents. Drowsy or distracted driving elevates the chance of road crashes. Aggressive driving and speeding increase the risk for a road traffic accident with a 3% higher likelihood for a serious crash with each 1% higher mean speed. Alcohol and certain drugs that affect the mind or behavior (psychoactive drugs) also surge the probability of road traffic accidents. Not using proper safety equipment (such as seat belts or car and booster seats) also elevates the likelihood for serious or fatal injuries. Further, the risk for road traffic accidents can also be increased by unsafe vehicles, unsafe road infrastructure, or inadequate post-crash care.1

The Prevalence of Drowsy Driving

Driving while being tired or sleepy is also referred to as “drowsy driving”.5 Drowsy driving is a widespread problem, and a large survey conducted in 2010 among 2,000 U.S. residents reported that 41% of all drivers had nodded off or fallen asleep while driving at least once in their lifetime.6 The same survey showed that 4% and 11% of the drivers had nodded off or fallen asleep while driving during the preceding month or year, respectively.6

Drowsy Driving, Fatigue and the Risk of Road Traffic Accidents

Drowsy driving has been shown to increase the risk of road traffic accidents. For example, a study that analyzed road crashes involving a vehicle towed from the scene concluded that a drowsy driver was involved in 16.5% of fatal crashes and 7.0% of all crashes in the analyzed dataset.7 Moreover, in an investigation of fatal sleepiness-related motor vehicle accidents, short sleep duration of less than 6 hours during the night preceding the accident was identified as a prominent and independent risk factor.8

Driving when tired has also been associated with an increased risk for road traffic accidents.9 A number of factors may affect how tired a driver feels, including the consecutive time spent driving, the consecutive resting time, the sleep duration within the 24 hours preceding the driving, and the biological 24-hour rhythms (circadian rhythms) during the time of driving.10 

Sleep Deprivation and the Risk of Road Traffic Accidents

The sleep duration needed to support the optimal health of adults has been estimated to be at least 7 hours of sleep per night.11 Contrarily, sleep duration of 6 hours or less is considered insufficient to optimally support health in adults. The effect of sleep duration of 9 hours or more per night on adults’ health is more difficult to assess. While some studies have indicated that sleep duration longer than 9 hours may be associated with some harmful outcomes, no convincing biological pathways underlying this association have been identified.11 Not getting a sufficient amount of sleep, also known as sleep deprivation, is a very prevalent problem that reportedly affects approximately 1 in 3 adults in the United States.12 The recommended amount of sleep for adolescents is slightly higher than that for adults at 8–10 hours per night,13 and sleep deprivation is a phenomenon that is also frequently observed in adolescents.

There is evidence that sleep deprivation is associated with an increased risk for road traffic accidents. For example, increased crash rates have been identified for drivers who generally sleep less than 5 hours per night, drivers who have slept less than 7 hours in the preceding 24 hours, and drivers who have slept at least 1 hour less than their regular sleep duration in the preceding 24 hours.14 Moreover, a recent study analyzed the association between sleep deprivation and drivers’ responsibility for road crashes in a representative sample of 6845 drivers involved in road crashes. There were significantly increased odds for a driver to be responsible for the road crash if they were sleep deprived in the 24 hours preceding the crash. These odds were higher with more severe cases of sleep deprivation: 1.3, 1.9, 2.9, and 15.1 times the odds for drivers who reported 6 hours, 5 hours, 4 hours, and less than 4 hours sleep during the 24 hours preceding the crash, respectively, compared to drivers who were not sleep deprived.15

An association between sleep-related problems and an increased risk for road accidents has also been demonstrated for occupational drivers. For example, a discrepancy between the actual reported slept hours and the desired hours of sleep (defined as sleep debt), has been associated with an increased risk for road accidents for truck drivers.16,17 Moreover, sleeplessness (insomnia), breathing pauses occurring during the sleep (sleep apnea), and excessive daytime sleepiness have also been associated with an elevated risk for road accidents for truck drivers.16,17

Sleep Deprivation, Auto Crashes, and Subjective Sleepiness

Sleep deprivation may be associated with an increased risk for motor vehicle crashes even in the absence of subjective sleepiness. Sleep deprivation may cause drivers to feel drowsy and tired. However, sleep deprivation has been associated with an increased risk of motor vehicle crashes even in cases in which the drivers have not experienced a subjective feeling of excessive sleepiness.18 Thus, a study on 3,201 individuals, among which 222 had been involved in at least one motor vehicle crash during the preceding year, found that sleeping 6 hours per night was associated with a 33% higher risk for a motor vehicle crash than sleeping 7–8 hours per night. When the analysis was restricted only to the 75% of the participants who did not report excessive sleepiness, the association between sleep deprivation and an increased motor vehicle crash risk was preserved.18 

Sleep Deprivation and Drivers’ Performance

A study that systematically reviewed the published literature on how sleep deprivation affects the driving performance of young drivers found that in 50% of the reviewed studies sleep deprivation was associated with more weaving of the car and an increased number of line crossings.19 The authors also concluded that chronic sleep deprivation was associated with speeding and crash events, whereas the effects of acute total sleep deprivation in this review were discrepant.19 Short sleep duration has also been identified as a risk factor for specific types of traffic road accidents, such as single-car accidents and rear-end collisions.20 Since these types of car accidents have been associated with reduced attentiveness, the increased risk in sleep deprived individuals may be due to the negative effect of sleep deprivation on drivers’ performance. 

Driving and Sleep Deprivation Compared to Driving and Alcohol Consumption

Sleep deprivation may impair the performance of drivers similarly to alcohol consumption.

A recent study suggested that the estimated crash risk when driving after only 4–5 hours of sleep is similar to the estimated crash risk when driving with a blood alcohol concentration (BAC) of 0.08 (equivalent to or slightly above the legal alcohol limit in the USA).14 The same study estimated the crash risk after having slept less than 4 hours as comparable to the crash risk when driving with a BAC of 0.12–0.15.14

There are also similarities in the effects of sleep deprivation and alcohol consumption on drivers’ performance since both can slow down the response speed and worsen accuracy measures.21 In a recent investigation that used a simulated driving task, both sleep deprivation and alcohol consumption impaired drivers’ performance, including an impairment in the ability to maintain the speed and road position in simulated driving.22

Recommendations Regarding Sleep and Driving

The National Sleep Foundation coordinated the work of a panel of experts in sleep research and medicine that put out a consensus statement regarding sleep deprivation and motor vehicle operation. After systematically reviewing the existing literature, the experts concluded that individuals who have slept 2 hours or less within the preceding 24 hours are not fit to operate a vehicle.23 They also came to the conclusion that most drivers who have slept only 3–5 hours during the preceding 24 hours are likely to be impaired in their ability to operate a motor vehicle.23

Different strategies have been recommended to prevent sleep deprivation and drowsiness and to attenuate the risk of traffic road accidents:24 1) It is important to ensure that drivers get sufficient sleep. Adults need at least 7 hours of sleep per night, whereas teenagers need at least 8 hours. 2) Consulting a healthcare professional for all sleep-related symptoms and conditions, such as insomnia, sleep apnea, and excessive daytime sleepiness, is imperative to ensure that, if needed, treatment is initiated in a timely manner, and that the risk associated with driving is assessed appropriately. 3) Following a good sleep schedule and routine is important to maintain the sleep quality. 4) If possible, it is advisable to avoid driving during time periods characterized with more pronounced sleepiness, such as between midnight and 6 am and during the late afternoon. These periods of more pronounced sleepiness are defined by our internal biological clock (circadian rhythms).

Certain medications and alcohol can interact with sleepiness and further impair drivers’ performance. Therefore, it is imperative to avoid any alcohol consumption before driving. Finally, it is important to check whether any medications a person is taking may cause drowsiness as a side effect. If a medication may give rise to drowsiness as a side effect, the potential risk associated with driving should be discussed with a healthcare professional, and public transportation should be used when possible.24




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  3. Chen S, M Kuhn, K Prettner, DE Bloom. “The Global Macroeconomic Burden of Road Injuries: Estimates and Projections for 166 Countries.” Lancet Planet Health 3, no. 9 2019): e390–e398.

  4. Wijnen W, H Stipdonk. “Social Costs of Road Crashes: An International Analysis.Accid Anal Prev 94 (2016):97–106.


  6. Tefft BC. “The Prevalence and Impact of Drowsy Driving (Technical Report).” 2010; Washington, D.C.: AAA Foundation for Traffic Safety.

  7. Tefft BC. “Prevalence of Motor Vehicle Crashes Involving Drowsy Drivers, United States, 1999–2008.Accid Anal Prev 45 (2012):180–186.

  8. Kalsi J, T Tervo, A Bachour, M Partinen. “Sleep Versus Non-Sleep-Related Fatal Road Accidents.Sleep Med 51 (2018):148–152.

  9. Smith AP. “A UK Survey of Driving Behaviour, Fatigue, Risk Taking and Road Traffic Accidents. BMJ Open 6, no. 8 (2016): e011461.

  10. Zhang Q, C Wu, H Zhang. “Driving Fatigue Prediction Model Considering Schedule and Circadian Rhythm.J Adv Transport 2020; ID 9496259.

  11. Consensus Conference Panel, Watson NF, MS Badr, G Belenky, DL Bliwise, OM Buxton, D Buysse, DF Dinges, J Gangwisch, MA Grandner, C Kushida, RK Malhotra, JL Martin, SR Patel, SF Quan, E Tasali. “Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion.Sleep 38, no. 8 (2015): 1161–1183.

  12. Liu Y, AG Wheaton, DP Chapman, TJ Cunningham, H Lu, JB Croft. “Prevalence of Healthy Sleep Duration Among Adults — United States, 2014.MMWR Morb Mortal Wkly Rep 65, no. 6 (2016): 137–141.

  13. Paruthi S, LJ Brooks, C D'Ambrosio, WA Hall, S Kotagal, RM Lloyd, BA Malow, K Maski, C Nichols, SF Quan, CL Rosen, MM Troester, MS Wise. “Consensus Statement of the American Academy of Sleep Medicine on the Recommended Amount of Sleep for Healthy Children: Methodology and Discussion.” J Clin Sleep Med 12, no. 11 (2016):1549–1561.

  14. Tefft BC. “Acute Sleep Deprivation and Risk of Motor Vehicle Crash Involvement (Technical Report).” 2016; Washington, D.C.: AAA Foundation for Traffic Safety.

  15. Tefft BC. “Acute Sleep Deprivation and Culpable Motor Vehicle Crash Involvement.” Sleep 41, no. 10 (2018).

  16. Garbarino S, N Magnavita, O Guglielmi, M Maestri, G Dini, FM Bersi, A Toletone, C Chiorri, P Durando. “Insomnia is Associated with Road Accidents. Further Evidence from a Study on Truck Drivers.PLoS One 12, no. 10 (2017): e0187256.

  17. Garbarino S, P Durando, O Guglielmi, G Dini, F Bersi, S Fornarino, A Toletone, C Chiorri, N Magnavita. “Sleep Apnea, Sleep Debt and Daytime Sleepiness Are Independently Associated with Road Accidents. A Cross-Sectional Study on Truck Drivers.PLoS One 11, no. 11 (2016): e0166262.

  18. Gottlieb DJ, JM Ellenbogen, MT Bianchi, CA Czeisler. “Sleep Deficiency and Motor Vehicle Crash Risk in the General Population: A Prospective Cohort Study.BMC Med 16, no. 1 (2018): 44.

  19. Shekari Soleimanloo S, MJ White, V Garcia-Hansen, SS Smith. “The Effects of Sleep Loss on Young Drivers' Performance: A Systematic Review.PLoS One 12, no. 8 (2017): e0184002.

  20. Abe T, Y Komada, Y Nishida, K Hayashida, Y Inoue. “Short Sleep Duration and Long Spells of Driving Are Associated with the Occurrence of Japanese Drivers' Rear-End Collisions and Single-Car Accidents.J Sleep Res 19, no. 2 (2010): 310–316.

  21. Williamson AM, AM Feyer. “Moderate Sleep Deprivation Produces Impairments in Cognitive and Motor Performance Equivalent to Legally Prescribed Levels of Alcohol Intoxication.Occup Environ Med 57, no. 10 (2000): 649–655.

  22. Arnedt JT, GJ Wilde, PW Munt, AW MacLean. “How Do Prolonged Wakefulness and Alcohol Compare in the Decrements They Produce on a Simulated Driving Task?Accid Anal Prev 33, no. 3 (2001): 337–344.

  23. CA Czeisler, EM Wickwire, LK Barger, WC Dement, K Gamble, N Hartenbaum, MM Ohayon, R Pelayo, B Phillips, K Strohl, B Tefft, SMW Rajaratnam, R Malhotra, K Whiton, M Hirshkowitz. “Sleep-Deprived Motor Vehicle Operators Are Unfit To Drive: A Multidisciplinary Expert Consensus Statement on Drowsy Driving.Sleep Health 2, no. 2 (2016): 94–99.