Staying up 19 hours can rival a 0.05 blood alcohol level

It’s 1 a.m. You’ve been up since 6 the previous morning, you haven’t had a drink, and you feel fine to drive home. That last judgment is the one worth questioning.

In an Australian experiment published in 2000, 39 volunteers, most of them transport-industry workers, stayed awake for 28 hours. On a separate occasion they drank measured doses of alcohol. After 17 to 19 hours without sleep, a stretch that fell between 10:30 p.m. and 1 a.m. in the study, their scores on some tests matched or fell below their scores at a blood alcohol concentration of 0.05%. For comparison, the National Highway Traffic Safety Administration (NHTSA) notes that it’s illegal to drive at 0.08 or higher in every state, and that Utah’s limit is 0.05.

Fatigue gets less respect than alcohol, partly because there’s no roadside test for it and partly because tired is a loose word. The industries that run around the clock have stopped treating it loosely. Airline pilots, truck drivers and doctors in training all work under written limits. Here is what fatigue does to thinking, how those limits work, what the trials of them found, and why drowsy-driving deaths are counted so poorly.

Sleepiness and fatigue are different states

Sleep researchers separate sleepiness from fatigue. A 2006 review in Sleep Medicine Reviews by J. Shen, J. Barbera and C.M. Shapiro of the University of Toronto called them related but distinct, and noted that people tend to lump both under the everyday word tired. Sleepiness is a pull toward sleep, which the authors tie to a disturbance in the brain’s normal arousal system. Fatigue has no gold-standard measurement at all; it’s judged by what people report, and the review found it under-appreciated by clinicians and researchers alike.

Federal aviation rules capture the wider category. The Federal Aviation Administration defines fatigue for airline crews as “a physiological state of reduced mental or physical performance capability resulting from lack of sleep or increased physical activity…” Lost sleep is one route in. Exertion is another.

Illness is a third, and it behaves differently. The National Cancer Institute describes cancer-related fatigue as physical, emotional or cognitive exhaustion out of proportion to recent activity, and stresses that sleep and rest don’t completely relieve it. The National Institute of Neurological Disorders and Stroke (NINDS) says fatigue in multiple sclerosis can be cognitive as well as physical, showing up as slowed processing speed or mental exhaustion.

The distinction matters because the remedies differ. Sleep is the fix for sleepiness caused by lost sleep. It may do little for fatigue with a medical cause, and that difference is one of the clearest signals for when to get checked.

What the alcohol comparison measured, and what it didn’t

The 2000 study, by A.M. Williamson and A.M. Feyer in Occupational and Environmental Medicine, compared each volunteer against themselves: 30 transport employees and 9 army personnel, tested through 28 hours awake and again after alcohol doses reaching about 0.1%. A 1997 letter in Nature by D. Dawson and K. Reid had drawn the same kind of comparison between fatigue and alcohol.

At 17 to 19 hours awake, response speeds on some tests were up to 50% slower, and accuracy was significantly worse than at 0.05%. With longer wakefulness, performance sank to the level seen at the highest alcohol dose given, about 0.1%.

Read the limits too. These were laboratory tests of speed and accuracy, not on-road driving, and the equivalence held for some tests rather than all. The sample was small and made up of healthy workers. The fair summary is that a long day awake produces measurable impairment of a size that would be illegal behind the wheel in Utah if alcohol caused it. Weeks of slightly short nights pile up a deficit of their own, a separate finding covered in the material on chronic sleep restriction.

You usually feel it coming

A popular belief holds that drowsy drivers fall asleep without warning. The evidence points the other way. A 2021 systematic review in Sleep Medicine Reviews, led by Anna W.T. Cai at Monash University in Australia, reviewed 34 simulated and on-road driving studies. Drivers were generally aware of their sleepiness, and high self-rated sleepiness predicted lane departures and crash events. The authors concluded that stopping when you feel sleepy may significantly reduce crash risk.

Alcohol makes the picture worse. A 2004 experiment from Loughborough University in England, published in the journal Sleep, showed how. In it, women who had slept only 5 hours drove worse on a simulated highway. A small amount of alcohol, about half the legal driving limit, had no apparent effect on its own. Combined with the short night, its effect was profound.

How pilots, truckers and medical residents are regulated

Three sectors have turned fatigue science into hard numbers. The rules come from different bodies and look different, but each sets a ceiling on work and a floor on rest.

	Airline pilots	Truck drivers (property)	Medical residents
Who sets it	FAA, 14 CFR Part 117 (2012)	FMCSA, 49 CFR 395.3 (last amended 2020)	ACGME requirements effective July 1, 2026
Work ceiling	Flight-time caps that rise with crew size, such as 13 hours for three pilots and 17 for four	11 hours of driving inside a 14-hour window	80 hours a week, averaged over four weeks; shifts of 24 hours plus up to 4 for patient-safety and education tasks, with no new patient care
Rest floor	10 hours before duty, with 8 uninterrupted hours of sleep opportunity	10 consecutive hours off before driving	14 hours free after 24-hour in-house call; one day in seven free
Longer cycle	30 straight hours free in any 168	60 or 70 hours on duty in 7 or 8 days, reset by 34 hours off	In-house call no more than every third night
Fatigue rule	Crew must report rested and affirm they’re fit for duty	30-minute break after 8 hours of driving	Programs must teach residents and faculty to recognize fatigue

A few details show how the thinking works. The FAA guarantees a sleep opportunity, not sleep, since no rule can make anyone fall asleep. Its rule also bars an airline from assigning a flight to a crew member who has reported being too fatigued, and bars the crew member from accepting it. After crossing more than 60 degrees of longitude and spending more than a week away, a pilot gets 56 hours off at home, spanning three nights’ rest.

In September 2025 the Federal Motor Carrier Safety Administration (FMCSA) announced two pilot programs to test flexibility, one letting drivers pause the 14-hour window for 30 minutes to 3 hours and one testing shorter splits of sleeper-berth time. These are studies, not rule changes. October 2026 notices in the Federal Register showed the agency still collecting public comment on data gathering for both pilots; the sleeper-berth study would enroll about 256 drivers for 16 weeks.

The ACGME, which accredits US residency programs, sets its limits as accreditation requirements rather than federal law.

Most workers have no hours limit at all. The Occupational Safety and Health Administration’s worker-fatigue page says long hours may raise the risk of injuries and names reduced alertness as a factor in disasters including the 2005 Texas City refinery explosion and the 2009 Colgan Air crash. It describes fatigue-management programs but sets out no hours standard. A 2019 summary by the National Institute for Occupational Safety and Health noted that almost no workers in agriculture, forestry and fishing have work-hour limits, and that in oil and gas extraction only large-truck drivers do. Shift work disorder, the clinical condition some night workers develop, sits in the library’s coverage of shift work.

The duty-hour trials, and the conclusion they don’t support

The case for limits in medical training came from studies of very long shifts. In a 2004 randomized study in The New England Journal of Medicine, Christopher P. Landrigan and colleagues at Brigham and Women’s Hospital in Boston compared interns in intensive care units on a traditional schedule, with shifts of 24 hours or more every other shift, against a schedule that eliminated those shifts. On the traditional schedule, interns made 35.9% more serious medical errors and 5.6 times as many serious diagnostic errors.

A 2005 nationwide survey in the same journal, led by Laura K. Barger, gathered 17,003 monthly reports from 2,737 interns. After a shift of 24 hours or longer, the odds of reporting a car crash were 2.3 times higher. Each extended shift scheduled in a month raised the monthly risk of a crash on the drive home from work by 16.2%. The data were self-reported, so they show association rather than proof.

Later trials tested loosening the rules, and they’re often misread. The FIRST trial, published in 2016, randomly assigned 117 general-surgery programs to standard or flexible rules that waived shift-length and time-off limits. Across 138,691 patients, death or serious complications ran at 9.1% under flexible rules and 9.0% under standard ones, which met the trial’s test for noninferiority, meaning not meaningfully worse. Residents under flexible rules were less likely to leave in the middle of an operation (7.0% versus 13.2%).

The iCOMPARE trial in 63 internal-medicine programs, published in 2019, found the change in 30-day patient mortality under flexible rules noninferior too. It could not show noninferiority for 30-day readmissions or long hospital stays. Its sleep substudy tracked 398 interns for 14 days. The flexible programs still kept the 80-hour weekly cap. Sleep time and self-rated sleepiness held up, but on a reaction-time test of alertness the authors reported plainly: “Noninferiority of the flexible group for alertness was not established.”

So the trials showed that, inside an 80-hour week, letting programs schedule longer shifts didn’t measurably harm patients on most outcomes and cut some handoffs. They did not show that fatigue is harmless, and the alertness question stayed open. The trade-off is real on both sides: fewer handoffs and more continuity, against longer stretches awake. The requirements in force since July 1, 2026, still cap the week at 80 hours and continuous shifts at 24 hours plus up to 4.

Drowsy driving: why the official number is so small

NHTSA’s tally for 2024 is 644 deaths in crashes related to drowsy driving. A February 2026 report for the Governors Highway Safety Association, written by Kara Macek, put the 2023 figure at 633, or 1.5% of fatal crashes.

NHTSA itself says traffic-safety, sleep and public-health experts broadly agree these numbers understate the problem. The GHSA report explains why. There’s no breath test for sleepiness. Police don’t see the driver in the minutes before a crash. And a drowsy driver who survives is usually jolted awake by the impact, which leaves little to record.

Three ways researchers have estimated the real toll

• Modeled from crash investigations. A March 2024 AAA Foundation for Traffic Safety report by Brian C. Tefft built a model from in-depth federal crash investigations and applied it to national fatal-crash records. It estimated that 17.6% of fatal crashes from 2017 to 2021 involved a drowsy driver, with about 29,834 people killed over those five years. Applying that share to 2023, the GHSA report arrived at about 6,326 deaths, roughly ten times the official count. Both are estimates, not counts.
• A federal range. NHTSA’s 2016 drowsy-driving research plan put the share of annual traffic deaths attributable to drowsiness anywhere from 2% to 20%.
• Watching drivers’ eyes. A February 2018 AAA Foundation study by Justin M. Owens and colleagues used in-car video from 3,593 drivers and coded how long drivers’ eyes were closed before 701 crashes. Drowsiness may have contributed to 8.8% to 9.5% of all crashes and 10.6% to 10.8% of the more serious ones involving injury, airbag deployment or significant property damage. It was more than three times as common in crashes at night. The sample contained no fatal crashes.

The 2024 AAA analysis also showed who is most exposed. The share of drowsy drivers was highest at ages 16 to 20, and men were significantly more likely than women to be drowsy. Drowsiness was more common among drinking drivers: 17% of those with a blood alcohol level of 0.01 to 0.07 and 20% of those at 0.08 or higher, compared with 11% of drivers who hadn’t been drinking.

A 2013 CDC report drew on a survey in 19 states and Washington, D.C. In it, 4.2% of adults said they had fallen asleep at the wheel at least once in the previous 30 days. The figure was 6.7% among people who usually slept 6 hours or less, against 2.6% among those sleeping 7 to 9.

Warning signs at the wheel, and what helps

These come from the CDC report, NHTSA and the American Academy of Sleep Medicine (AASM), grouped by what you’d notice.

Signs worth acting on

• Your body: yawning or blinking over and over, eyelids that won’t stay up, a head that keeps nodding.
• Your memory: no recollection of the last few miles.
• Your driving: a missed exit or turn, drifting out of your lane, following too close, or the rumble strip. NHTSA singles out lane drift and rumble strips, especially for drivers alone.

What the agencies say works, and what only buys time

• Stopping. The AASM’s advice is to pull over somewhere safe or hand the wheel to a passenger once signs appear. Given the Monash review, the sleepy feeling itself is reason enough.
• Coffee and a short nap, as a bridge. NHTSA says coffee or energy drinks alone are not always enough. It describes one or two cups followed by a nap of about 20 minutes somewhere safe and well lit as a short-term measure whose benefit fades. How naps and caffeine timing work gets fuller treatment elsewhere in the library.
• Planning before the trip. The AASM suggests sharing the driving on long trips, avoiding late-night or solo drives when possible, and not driving at all when short on sleep. A drive home after a long or overnight shift is the situation NHTSA and the intern crash study both point to.

When fatigue is a symptom, not a schedule problem

Ordinary fatigue lifts with sleep and time off. Fatigue that doesn’t is the kind to bring to a clinician, and several patterns stand out.

• Fatigue out of proportion to what you’ve done. The National Cancer Institute reports that about 80% of patients feel fatigue during chemotherapy or radiation. Its summary links that fatigue with reduced attention and concentration, and lists anemia, depression, sleep disorders and sedating drugs such as opioids among the contributors a care team looks for.
• Mental exhaustion with a neurological condition. NINDS says cognitive impairment affects up to 75% of people with multiple sclerosis. It adds that depression sometimes causes the impairment and should be ruled out first, because impairment from depression can be treated.
• Fatigue with low mood. Depression often travels with exhaustion. The National Institute of Mental Health counts fatigue or feeling slowed down, along with trouble concentrating, remembering or deciding, among its symptoms when they’re present nearly all day, almost every day, for two weeks or longer. If you’re having thoughts of suicide, call or text the 988 Suicide and Crisis Lifeline at 988.
• Nodding off while driving, plus loud snoring. The CDC survey found snorers more likely to report falling asleep at the wheel (5.6% versus 3.2%), and the same CDC report counts drivers with untreated sleep disorders among those at higher risk. A clinician decides whether that pattern warrants a sleep study. Sleep apnea’s long-run effects on thinking get their own treatment in the companion piece on sleep across the decades.
• Drowsiness after a new medicine. The CDC report counts drivers who use sedating medications among those at higher risk, and NHTSA advises checking medicine labels for drowsiness warnings. The prescriber, or a pharmacist with your full medication list, is the right person to judge whether a drug is the cause.

What a clinician checks when fogginess and fatigue persist is the business of the brain fog article.

The takeaway

Treat hours awake the way you’d treat drinks: as a dose with a measurable effect. By 17 to 19 hours, some measures of speed and accuracy look like a 0.05% blood alcohol level, and the people whose jobs depend on alertness work under rules built around that fact. For everyone else, the most reliable early warning is the one you already have. Drivers generally feel sleepiness before it costs them, and the research says to believe it: when the yawning, drifting or missed exits start, the safest move is to stop driving.

Sources

1. Occupational and Environmental Medicine. “Williamson AM, Feyer AM. "Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication." Occup Environ Med, 2000. PubMed. DOI: 10.1136/oem.57.10.649.” pubmed.ncbi.nlm.nih.gov
2. Nature. “Dawson D, Reid K. "Fatigue, alcohol and performance impairment." Nature, 1997. DOI: 10.1038/40775.” nature.com
3. Sleep Medicine Reviews. “Shen J, Barbera J, Shapiro CM. "Distinguishing sleepiness and fatigue: focus on definition and measurement." Sleep Med Rev, 2006. PubMed. DOI: 10.1016/j.smrv.2005.05.004.” pubmed.ncbi.nlm.nih.gov
4. Sleep Medicine Reviews. “Cai AWT, Manousakis JE, Lo TYT, Horne JA, Howard ME, Anderson C. "I think I'm sleepy, therefore I am – Awareness of sleepiness while driving: A systematic review." Sleep Med Rev, 2021. PubMed. DOI: 10.1016/j.smrv.2021.101533.” pubmed.ncbi.nlm.nih.gov
5. Sleep. “Barrett PR, Horne JA, Reyner LA. "Sleepiness combined with low alcohol intake in women drivers: greater impairment but better perception than men?" Sleep, 2004. PubMed. DOI: 10.1093/sleep/27.6.1057.” pubmed.ncbi.nlm.nih.gov
6. The New England Journal of Medicine. “Landrigan CP et al. "Effect of reducing interns' work hours on serious medical errors in intensive care units." N Engl J Med, 2004. PubMed. DOI: 10.1056/NEJMoa041406.” pubmed.ncbi.nlm.nih.gov
7. The New England Journal of Medicine. “Barger LK et al. "Extended work shifts and the risk of motor vehicle crashes among interns." N Engl J Med, 2005. PubMed. DOI: 10.1056/NEJMoa041401.” pubmed.ncbi.nlm.nih.gov
8. The New England Journal of Medicine. “Bilimoria KY et al. "National Cluster-Randomized Trial of Duty-Hour Flexibility in Surgical Training." N Engl J Med, 2016. PubMed. DOI: 10.1056/NEJMoa1515724.” pubmed.ncbi.nlm.nih.gov
9. The New England Journal of Medicine. “Silber JH et al. "Patient Safety Outcomes under Flexible and Standard Resident Duty-Hour Rules." N Engl J Med, 2019. PubMed. DOI: 10.1056/NEJMoa1810642.” pubmed.ncbi.nlm.nih.gov
10. The New England Journal of Medicine. “Basner M et al. "Sleep and Alertness in a Duty-Hour Flexibility Trial in Internal Medicine." N Engl J Med, 2019. PubMed. DOI: 10.1056/NEJMoa1810641.” pubmed.ncbi.nlm.nih.gov
11. National Highway Traffic Safety Administration. “Drowsy Driving: Avoid Falling Asleep Behind the Wheel.” nhtsa.gov
12. National Highway Traffic Safety Administration. “Drunk Driving.” nhtsa.gov
13. National Highway Traffic Safety Administration. “Data/Surveillance (Drowsy Driving chapter, Countermeasures That Work).” nhtsa.gov
14. AAA Foundation for Traffic Safety. “Tefft BC. Drowsy Driving in Fatal Crashes, United States, 2017-2021 (March 2024).” aaafoundation.org
15. AAA Foundation for Traffic Safety. “Owens JM, Dingus TA, Guo F, Fang Y, Perez M, McClafferty J, Tefft BC. Prevalence of Drowsy Driving Crashes: Estimates from a Large-Scale Naturalistic Driving Study (February 2018).” aaafoundation.org
16. Governors Highway Safety Association. “Macek K. Wake Up Call: 2026 Report Update (February 2026).” ghsa.org
17. Centers for Disease Control and Prevention (MMWR). “Drowsy Driving: 19 States and the District of Columbia, 2009-2010 (MMWR 61(51), January 4, 2013).” cdc.gov
18. American Academy of Sleep Medicine (Sleep Education). “Prevent Drowsy Driving: Stay Awake at the Wheel! (January 5, 2022).” sleepeducation.org
19. Federal Aviation Administration, via Legal Information Institute, Cornell Law School. “14 CFR 117.3 Definitions.” law.cornell.edu
20. Federal Aviation Administration, via Legal Information Institute, Cornell Law School. “14 CFR 117.5 Fitness for duty.” law.cornell.edu
21. Federal Aviation Administration, via Legal Information Institute, Cornell Law School. “14 CFR 117.11 Flight time limitation.” law.cornell.edu
22. Federal Aviation Administration, via Legal Information Institute, Cornell Law School. “14 CFR 117.25 Rest period.” law.cornell.edu
23. Federal Motor Carrier Safety Administration. “Summary of Hours of Service Regulations (last updated March 28, 2022).” fmcsa.dot.gov
24. Federal Motor Carrier Safety Administration, via Legal Information Institute, Cornell Law School. “49 CFR 395.3 Maximum driving time for property-carrying vehicles.” law.cornell.edu
25. Federal Motor Carrier Safety Administration. “Trump's Transportation Secretary Sean P. Duffy Launches New Initiatives to Improve Trucker's Quality of Life on the Road (news release, September 15, 2025).” fmcsa.dot.gov
26. Federal Register (Federal Motor Carrier Safety Administration). “Agency Information Collection Activities; New Information Collection: Hours of Service of Drivers: Pilot Program To Allow Commercial Drivers To Pause Their 14-Hour Driving Window (October 6, 2026).” federalregister.gov
27. Federal Register (Federal Motor Carrier Safety Administration). “Agency Information Collection Activities; New Information Collection: Hours of Service of Drivers; Pilot Program To Allow Commercial Drivers To Split Sleeper Berth Time (October 7, 2026).” federalregister.gov
28. Accreditation Council for Graduate Medical Education. “ACGME Common Program Requirements (Residency), effective July 1, 2026.” acgme.org
29. Occupational Safety and Health Administration. “Long Work Hours, Extended or Irregular Shifts, and Worker Fatigue.” osha.gov
30. National Institute for Occupational Safety and Health. “Wong I, Swanson N. NIOSH Working Hours, Sleep and Fatigue Forum: A Recap and Future Directions (NIOSH Science Blog, October 7, 2019).” cdc.gov
31. National Cancer Institute. “Fatigue (PDQ) Health Professional Version.” cancer.gov
32. National Institute of Neurological Disorders and Stroke. “Multiple Sclerosis (MS) (last reviewed December 17, 2025).” ninds.nih.gov
33. National Institute of Mental Health. “Depression (NIH Publication No. 24-MH-8079, revised 2024).” nimh.nih.gov