Drowsy Driving

Drowsiness, also referred to as sleepiness or fatigue, plays a large and often underestimated role in traffic crashes, injuries, and deaths.[[Gaspar, J. & Carney, C. (2023). Drowsiness and Decision Making During Long Drives: A Driving Simulation Study (Technical Report). Washington, D.C.: AAA Foundation for Traffic Safety.]] Drowsiness refers to the state right before sleep and is characterized by difficulties staying awake, decreasing likelihood “to be responsive to external stimuli” [[Strauss, M., et al. (2022). “Predicting the loss of responsiveness when falling asleep in humans.” NeuroImage 251: 119003]], episodes of microsleep (eye closures shorter than 15 seconds), and impaired attention [[https://www.cdc.gov/sleep/features/drowsy-driving.html]]. If attention is impaired, visual scanning behaviours are likely to show decrements.[[Watling, C. N., & Home, M. (2022). Hazard perception performance and visual scanning behaviours: the effect of sleepiness. Transportation research part F: traffic psychology and behaviour, 90, 243-251]] Drowsy drivers also have slower reaction time for sudden braking and steering and impaired decision making.[[https://www.cdc.gov/sleep/features/drowsy-driving.html]] Drowsy drivers are at great risk of falling asleep at the wheel, especially on monotonous roads [[Thiffault, P. and J. Bergeron (2003). “Monotony of road environment and driver fatigue: a simulator study.” Accident Analysis & Prevention 35(3): 381-391]] where vehicle crashes are associated with a higher risk of fatalities and serious injury since impacts occur at high speeds.[[Reyner, L. and J. A. Horne (1998). “Falling asleep whilst driving: are drivers aware of prior sleepiness?” International journal of legal medicine 111: 120-123]]

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Prevalence:

The fact that crashes often are the result of the combined effects of several factors makes it difficult to determine how much drowsiness contributes to crash events.[[https://www.cdc.gov/sleep/features/drowsy-driving.html]] However, multiple studies indicate that drowsiness is a major behavioural contributory factor to road trauma.[[Salmon, P. M., et al. (2019). "Bad behaviour or societal failure? Perceptions of the factors contributing to drivers' engagement in the fatal five driving behaviours." Applied Ergonomics 74: 162-171.]][[Gottlieb, D. J., et al. (2018). "Sleep deficiency and motor vehicle crash risk in the general population: a prospective cohort study." BMC medicine 16(1): 1-10.]] Drowsiness is identified as a primary cause of road crashes for an average of 20% of all crashes in developed countries, 17% in Australia, and 25% in the UK.[[Gottlieb, D. J., et al. (2018). "Sleep deficiency and motor vehicle crash risk in the general population: a prospective cohort study." BMC medicine 16(1): 1-10.]] In one survey, close to 80% of drivers reported that they had previously driven while sleepy.[[Soleimanloo, S., et al. (2022). "The association of schedule characteristics of heavy vehicle drivers with continuous eye-blink parameters of drowsiness." Transportation Research Part F: Traffic Psychology and Behaviour 90: 485-499]] In other surveys, 66% reported having experienced driving while sleepy.[[Reyner, L. and J. A. Horne (1998). "Falling asleep whilst driving: are drivers aware of prior sleepiness?" International journal of legal medicine 111: 120-123]][[Obst, P., et al. (2011). "Age and gender comparisons of driving while sleepy: Behaviours and risk perceptions." Transportation Research Part F: Traffic Psychology and Behaviour 14(6): 539-542]] Almost 33% of one sample of drivers surveyed had to fight sleepiness occasionally while driving and about 8% of the drivers reported occasional head nodding while driving.[[van den Berg, J. and U. Landström (2006). "Symptoms of sleepiness while driving and their relationship to prior sleep, work and individual characteristics." Transportation Research Part F: Traffic Psychology and Behaviour 9(3): 207-226]]

Obstructive sleep apnea (OSA) increases drowsiness and is a highly prevalent disorder, estimated to affect up to 49% of men and 23% of women in the general population.[[Heinzer R, Vat S, Marques-Vidal P, et al. Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study. Lancet Respir Med. 2015;3(4):310–318.)]] One survey found that: 90% of OSA sufferers drove regularly; 72% drove between 1 and 20 hours a week; 28% reported falling asleep while driving and 5% experienced a crash or near miss related to sleepiness within the previous five years.[[Povitz, M., et al. (2022). "Driving consequences of sleepiness in Canadians with obstructive sleep apnea: A population survey." Canadian Journal of Respiratory, Critical Care, and Sleep Medicine 6(5): 298-303]] Young drivers (18–24 years) appear to be over-represented in sleep-related crashes for several reasons related to late maturation of their brains’ decision-making areas, slower reaction times while sleepy, lower tolerance for sleep loss than older adults, and greater vulnerability to sleep deprivation.[[Soleimanloo, S., et al. (2022). "The association of schedule characteristics of heavy vehicle drivers with continuous eye-blink parameters of drowsiness." Transportation Research Part F: Traffic Psychology and Behaviour 90: 485-499]] Research on drowsy driving-related crash clusters has identified other vulnerable driver groups and patterns: afternoon fatigue crashes by middle-aged female drivers on urban multilane curves; crossover crashes by young drivers on low-speed roadways; crashes by male drivers during dark rainy conditions; pickup truck crashes in manufacturing / industrial areas; late-night crashes in business and residential districts, and; heavy truck crashes on elevated curves.[[Rahman, M. A., et al. (2023). "Understanding the drowsy driving crash patterns from correspondence regression analysis." Journal of Safety Research 84: 167-181]]

Countermeasures:

Drowsiness is mainly induced by sleep deprivation due to total or partial sleep loss, extended wake duration, and sleep fragmentation or sleep disturbances [[Soleimanloo, S., et al. (2022). "The association of schedule characteristics of heavy vehicle drivers with continuous eye-blink parameters of drowsiness." Transportation Research Part F: Traffic Psychology and Behaviour 90: 485-499]]. This would indicate that the best countermeasure against drowsy driving is a good night’s sleep. Studies show that sleeping 6 hours per night was associated with a 33% increased crash risk, compared to sleeping 7 or 8 hours per night.[[Gottlieb, D. J., et al. (2018). "Sleep deficiency and motor vehicle crash risk in the general population: a prospective cohort study." BMC medicine 16(1): 1-10]] Although drivers can identify that they are feeling drowsy, they appear to be poor at predicting when they will fall asleep [[Kaplan, K. A., et al. (2007). "Awareness of sleepiness and ability to predict sleep onset: can drivers avoid falling asleep at the wheel?" Sleep Medicine 9(1): 71-79]] and appear to resist stopping to take breaks even when they have the opportunity to do so.[[1. Gaspar, J. & Carney, C. (2023). Drowsiness and Decision Making During Long Drives: A Driving Simulation Study (Technical Report). Washington, D.C.: AAA Foundation for Traffic Safety]] Moreover, drivers cite multiple reasons for continuing to drive when they feel drowsy: time pressure, 27%; work requirements, 18%; failure to recognise impairment, 18%; necessity, 16%; shift work, 14%; long trips,13%, and; family and social expectations 10% .[[Salmon, P. M., et al. (2019). "Bad behaviour or societal failure? Perceptions of the factors contributing to drivers' engagement in the fatal five driving behaviours." Applied Ergonomics 74: 162-171]] These reasons combined with a high cultural value for productivity, a social acceptance of fatigued driving, and the lack of a fatigue test create the perception that drowsy driving is not a problem.[[Salmon, P. M., et al. (2019). "Bad behaviour or societal failure? Perceptions of the factors contributing to drivers' engagement in the fatal five driving behaviours." Applied Ergonomics 74: 162-171]]

Automated systems in new car technology, like intelligent cruise control, can increase drowsiness through task underload and monotony.[[Körber, M., et al. (2015). "Vigilance decrement and passive fatigue caused by monotony in automated driving." Procedia Manufacturing 3: 2403-2409]] While driving without technological assistance can also be monotonous, monitoring an automated driving system can be equally or more tedious and over trust in the technology might also decrease drivers’ vigilance to the driving task.[[Kundinger, T., et al. (2019). (Over) Trust in automated driving: The sleeping pill of tomorrow? Extended Abstracts of the 2019 CHI Conference on Human Factors in Computing Systems]]

Drowsy driving countermeasures have been attempted with various degrees of success. The most effective are adhering to work-rest scheduling that permits sufficient sleep, driving primarily during the daytime rather than at night, respecting the two anticipated circadian lulls of the 24-hour day (mid-afternoon and from midnight to 6:00 am), obtaining adequate sleep immediately prior to a long trip, and taking fifteen-minute breaks every two hours during long road trips. Consuming caffeine can provide short-term relief from drowsiness and rumble strips can alert drivers that they may be falling asleep, but these measures only provide temporary assistance. The most trustworthy countermeasures against drowsy driving are to obtain an adequate quality and quantity of sleep [[https://www.cdc.gov/sleep/features/drowsy-driving.html]] and to exercise good judgment. In the words of Garry Sowerby, a world champion long-distance endurance driver, "If you think you are too tired to drive, you are. Pull over and stop." [[Cahill, T. (1991). Road Fever. Knopf Doubleday Publishing Group]]

More information on drowsy-driving counter measures can be found at the following websites:

Drowsy Driving FAQs:

True or False?

Drivers are good at knowing when they will fall asleep.
False
Drowsy driving is not a problem during daylight hours.
False
The risk of a drowsy driving crash after six hours of sleep is equal to the risk after seven hours of sleep.
False
Resting every two hours during a long-distance drive reduces drowsiness.
True