Driver fatigue

Key facts

  • Worldwide, fatigue contributes to 10-20% of road crashes [1];
  • 4% of fatal crashes in Britain are caused by tiredness [2];
  • Peak times for fatigue-related crashes are within the hours of 02.00-06.00 and 14.00-16.00 when drivers are naturally sleepier [3];
  • Drivers at 6am are 20 times more likely to fall asleep at the wheel than at 10am [4].


Fatigue is a major cause of road crashes in the UK. Fatigued drivers have slower reaction times and suffer from reduced attention, awareness, and ability to control their vehicles [5].

Police statistics show that fatigue contributed to 4% of fatal road crashes and 2% of all collisions in Britain in 2018 [6]. However, it is likely that the true figures are far higher because fatigue is hard to spot; unlike alcohol and drugs, police can’t test for tiredness. Worldwide, it is estimated that between 10% and 20% of all road crashes are fatigue-related [7].

Research has shown that one in eight drivers (13%) admit falling asleep at the wheel, and nearly two fifths (37%) have been concerned about falling asleep while driving [8]. Men are three times as likely as women to say they have fallen asleep at the wheel (17% and 5%). Young drivers aged 18-24 are the most likely to feel being tired does not affect their safety behind the wheel (13% compared to 2%). Almost a fifth (18%) of young drivers also claim they would carry on driving even if they were tired, compared with 3% of all drivers.

Motorways and dual carriageways are the most common roads for sleep-related crashes, due to the monotonous road environment and lack of interruptions or driver stimulation [9]. Crashes caused by drivers falling asleep typically involve vehicles running off the road or into the back of another vehicle. They tend to be high-speed crashes, because drivers do not brake before crashing, so the risk of death or serious injury is high [10]. Even if tired drivers don’t fall asleep, they still pose a danger. Research suggests driving tired can be as dangerous as drink-driving [11], and is a significant factor in many rear end crashes [12].


Many factors can contribute to driver tiredness and increase the risk of being involved in a fatigue related crash. These include:

Lack of sleep or disturbed sleep: This could be due to disruptions in life such as a new baby, busy schedules or stress, or could be due to sleep disorders such as narcolepsy, insomnia or sleep apnoea.

Time of day: The most common times for drivers with normal sleep patterns to fall asleep at the wheel are early morning (2am-6am) and early afternoon (2pm-4pm). These times are when the body clock reaches a natural dip, causing drowsiness and reduced concentration [13].

Stress: Tiredness and difficulty concentrating are typical symptoms of stress [14].

Irregular sleep patterns: This can be a problem caused by irregular work shifts and switching from day to night shifts without having sufficient time off in between for your body clock to adjust. Research has found shift workers are particularly high risk for sleep-related crashes [15].

Driving for long periods: Research has found driving deteriorates after two hours of continuous driving, as you become less able to concentrate, and slower to react to hazards. The longer you drive, the more rest you need to recover driving performance [16]. Breaks are therefore recommended every two hours.

Vehicle engineering: Modern vehicles are usually quiet and comfortable for the driver, meaning a more relaxed drive. This can lull drivers, particularly in vehicles fitted with comfort-enhancing features such as cruise control [17].

Medication: Some prescription and over-the-counter drugs can cause drowsiness and impaired alertness. Medications may carry warnings that are not clear they impair driving, for example small print that only advises not to operate heavy machinery. Learn more about drug driving.

Signs of fatigue

Research shows fatigue does not occur without warning, and most people recognise symptoms but underestimate the dangers of continuing to drive [18]. Warning signs include: increased difficulty concentrating; yawning; heavy eyelids; eyes starting to ‘roll’; and neck muscles relaxing, making the head droop.

A ‘microsleep’ occurs when someone nods off for between two and 30 seconds without realising or remembering it [19], often known as head-nodding. This occurs when people are tired but trying to stay awake, most common in monotonous situations, like motorway driving at night. A Brake and Direct Line survey found one in three (31%) UK drivers surveyed admit having experienced a microsleep at the wheel [20].

After a microsleep a driver may feel like they’ve just briefly nodded their head, but they have actually been asleep. During this time, they will have been completely unaware of the road and unable to control their vehicle. In six seconds, a vehicle being driven at 70mph travels about 200 metres, which is enough time to veer across three lanes of traffic or into the central reservation. Simulator studies have shown a clear relationship between microsleeps and crashes [21].

At-work drivers are particularly at risk from tiredness, because they typically spend longer hours at the wheel, with four in ten tiredness-related crashes involving someone driving a commercial vehicle [22].

Male drivers are more likely to experience sleep-related crashes than females. Drivers under 30 are at higher risk than older drivers [23], and are most likely to crash due to tiredness in the early morning after little or no sleep [24].

Many drivers continue to take the risk of driving while tired, probably linked to lack of awareness of the risks. A Brake and Direct Line survey in 2014 found almost half (49%) of UK drivers surveyed admit driving after less than five hours’ sleep; this is not enough sleep to prevent fatigue [25].

Legislation on fatigue

Police investigations and penalties for killing someone due to fatigue-related driving

It can be difficult to prove a crash was caused by driver tiredness. A driver who was tired and crashed may not admit to drowsy driving or may die in the crash. It is not possible to test drivers for tiredness. However, if police suspect tiredness they can investigate length of driving, lifestyle (did the driver sleep for an adequate time before driving) and the type of impact (many tiredness crashes are high speed and do not involve braking because the driver is asleep). Lack of skid marks from braking, information from event data recorders and tachographs (see below) and eye witness statements can all help to identify fatigue as contributing to a road crash.

A tired driver who kills someone can be charged with death by dangerous driving (if the nature of their driving was perceived to be dangerous) or death by careless driving (a lesser charge for less dangerous driving). The maximum penalty for death by dangerous driving is 14 years imprisonment [26] and the maximum penalty for death by careless driving is five years. The difference between 'careless' and 'dangerous' driving in the eyes of the law is slight and subjective: it's the difference between someone's driving falling below or well below what is expected of a careful and competent driver.

Learn more about Brake’s Roads to Justice Campaign calling for appropriate sentencing for drivers whose driving causes death and injury.

Commercial vehicle legislation

In the UK, companies operating fleets of vehicles have a legal duty of care to “ensure, so far as is reasonably practicable, the health and safety of all employees while at work” and are responsible for what might happen if this is not done. This “applies to all on-the-road work activities as to all work activities” [27].

Under the Management of Health and Safety at Work Regulations (1999) employers must assess the risks involved in staff use of the road for work and put in place all reasonably practical measures to manage driver fatigue. Employers need to assess which drivers and journeys are at risk and set schedules that do not require drivers to exceed recommended working limits and driver hours [28].

Professional drivers of goods and passenger road vehicles must comply with the UK and EU Drivers’ Hours Rules, maintain log books, record hours of work and rest and ensure medical assessments are up-to-date as required. [29] Many commercial vehicles (trucks and coaches) have a device in their vehicle called a tachograph, which records how long they had been driving and breaks taken; this information, along with any available telematics information from event data recorders, can be studied by police if the vehicle is involved in a crash.

Rules for some commercial vehicle drivers are much stricter than others. In most cases, lorry and coach drivers are bound by European Union driver hours regulations (Directive 2012/15/EC); these regulations are complex but include limiting time at the wheel to nine hours a day or 56 hours a week on routes where all or part of the journey is in more than one EU country. Drivers must legally take a break for at least 45 minutes after 4.5 hours of driving. They must have unbroken rest periods of 45 hours every week, which can be reduced to 24 hours every other week [30].

However, other commercially-operated vehicles, notably vans (commercial vehicles weighing 7.5 tonnes or under) and minibuses with 10-17 seats operated for reasons that aren’t commercial (for example for community transport), are exempt from EU regulations. These vehicles are only bound by much less rigorous GB domestic hours rules. These rules restrict a driving day to ten hours. However, they only stipulate a 30-minute break after 5.5 hours’ driving, or 45 minutes taken at times within an 8.5 hour driving shift.

UK figures show vans are the fastest-growing users of the strategic road network (SRN), rising an estimated 0.9% between 2017 and 2018 [31]. However, growth in van traffic has slowed over the last two years.

Medical restrictions

For some conditions associated with fatigue, such as sleep apnoea (for which effective treatment is available), drivers should inform the DVLA of their condition but can continue driving. For other fatigue-related conditions, like narcolepsy (for which there is no cure), drivers must contact the DVLA on diagnosis to relinquish their licence. Medical practitioners are legally required to instruct drivers to do this, and doctors must also inform the DVLA if they discover their patient is continuing to drive. A driver who fails to notify the DVLA can be fined £1,000 or could face prosecution [32].

Mitigating fatigue: driver behaviour

The best way to avoid driving tired is to get plenty of rest beforehand, particularly if setting off early in the morning: at least seven to eight hours is recommended [33]. Research shows that driving on less than five hours sleep results in a one in ten chance of staying awake on a lengthy journey [34]. If driving late in the day, especially after a busy day, having a nap before setting off can help alertness.

Drivers are advised to plan long journeys to include rest breaks of at least 15 minutes at least every two hours [35] and if tiredness kicks in it is important to stop and rest as soon as possible. Trying alternate measures such as winding down the window, listening to music and talking to a passenger do not help [36].

When taking a break, the only cure for tiredness is sleep. Having a nap for 15 minutes is more effective in reducing driver sleepiness than an active break such as getting out of the vehicle and walking around [37].

Drinking a caffeinated drink such as coffee or an energy drink can reduce driver tiredness over short periods, and has been found to reduce crash risk among long-distance truck drivers by 63% [38]. Energy drinks are a more reliable source of caffeine, as levels in coffee vary. Drinking caffeine before taking a 15-minute nap, giving the caffeine time to kick in while you rest, can therefore be helpful in addressing tiredness temporarily. However, this is only a short-term solution, and cannot replace regular breaks and sufficient sleep. Drivers who still feel tired or still have a long way to go should stay put and, if possible, check into a hotel to get some proper rest.

Read: Brake’s advice for drivers on avoiding tired driving.

Mitigating fatigue: road and vehicle design

There are ways to reduce the risk of fatigued drivers on the road, and, in the unfortunate event of a crash, reduce the consequences. Research shows that effective vehicle design and careful infrastructure management can prevent road crashes due to fatigue or mitigate the impact of a crash, should it occur [39].

In-vehicle technology

Driver distraction and drowsiness recognition (DDDR) is an in-vehicle system designed to detect symptoms of fatigue and alert the driver, warning them to take a break. The system monitors eye movement, including slow eyelid closure and rate of blinks, and wider head movements, such as a nodding head. Upon detecting physical indicators of fatigue, the system will send a warning to the driver, indicating that they should take a break. DDDR systems can also be designed to monitor levels of heart rate and brain function; or steering and braking patterns indicative of inattention.

These systems (particularly those that track eye movement) are often available as an aftermarket product, marketed to fleet operators. TRL (the UK’s Transport Research Laboratory) recommend DDDR designed to monitor eye movement as these have the ‘strongest evidence base for real-time detection’ of fatigue [40].

Improvements to the road environment

Should a road crash occur due to fatigue the design of the road can significantly affect the severity of the outcome. Infrastructure interventions that can mitigate the impact of sleep-related crashes include crash barriers (particularly median barriers on motorways and trunk roads). Barriers absorb kinetic energy and protect drivers from hitting other hazards (particularly the danger of hitting oncoming traffic in opposing lanes which increases the risk of death and injury due to the combined speed of a head-on crash) [41].

Infrastructure interventions such as barriers support the ‘safe systems approach’, which accepts some drivers will continue to make mistakes and works to improve the environment and vehicles to mitigate outcomes of crashes. The safe systems principles are supported in Britain’s Road Safety Statement launched in 2015 [42].

Highways England is responsible for the maintenance of England’s strategic road network, England’s motorways and most of its trunk roads. It is currently developing a system to rate accurately the safety standards of roads it is responsible for, based on the International Road Assessment Programme (iRAP) standards [43].

A preliminary study [44] of standards of road safety on the SRN in 2010 starred roads out of five (five being best) and found:

  • 50% of the motorway network was at 3 star and 50% at 4 star;
  • 78% of dual carriageways were at 3 star, with 20% at 4 star, and 2% at 2 star;
  • 62% of single carriageways were at 2 star, with nearly all the remainder at 3 star (only 1% being 1 star).

In light of these standards, Highways England is using a ring-fenced road safety fund (part of the Road Investment Strategy 2015-2020) and is currently making upgrades to roads with lower star ratings, as well as building in safety measures such as barriers as part of its general road improvement and development programmes (such as SMART motorways). 

End notes

[1] European Road Safety Observatory, Fatigue 2018

[2] Department for Transport (2019), Reported road casualties Great Britain: 2018 annual report, table RAS50001

[3] Horne, J. and Reyner L. (1995), Sleep related vehicle accidents

[4] PACTS (2014), Staying awake, staying alive: the problem of fatigue in the transport sector

[5] European Road Safety Observatory, Fatigue 2018

[6] Department for Transport (2019), Reported road casualties Great Britain: 2018 annual report, table RAS50001

[7] European Road Safety Observatory, Fatigue 2018

[8] AA Charitable Trust (2018), AA-Populus 11-17 September 2018, online poll of 20,561 drivers

[9] Flatley, D. et al (2004), Road safety research report no. 52: Sleep-related crashes on sections of different road types in the UK (1995–2001)

[10] PACTS (2014), Staying awake, staying alive: the problem of fatigue in the transport sector

[11] Verster, J. et al (2011), Prolonged nocturnal driving can be as dangerous as severe alcohol-impaired driving, Journal of Sleep Research 20(4), 585-588

[12] Hui Zhang et. al (2016), The effect of fatigue driving on car following behaviour, Transportation Research Part F: Traffic Psychology and Behaviour 43, 80-89

[13] Horne, J. and Reyner L. (1995), Sleep related vehicle accidents

[14] NHS (2019), Stress

[15] Lee, L. et al (2016), High risk of near-crash driving events following night-shift work, Proceedings of the National Academy of Sciences of the United States of America 113(1), 176-181

[16] Lianzhen, W. and Yulong, P. (2014), The impact of continuous driving time and rest time on commercial drivers' driving performance and recovery, Harbin Institute of Technology

[17] VINCI Autoroutes Foundation (2013), Cruise control may cause drivers to be less attentive and more susceptible to fatigue

[18] Williamson, A. et al (2014) Are drivers aware of sleepiness and increasing crash risk while driving? University of New South Wales

[19] PACTS (2014), Staying awake, staying alive: the problem of fatigue in the transport sector

[20] Brake and Direct Line (2014), Fit to drive: driver tiredness

[21] Golz, M. et al (2018), Microsleep episodes and related crashes during overnight driving simulations

[22] Flatley, D. & Rayner, L. et al (2004), Sleep-Related Crashes on Sections of Different Road Types in the UK (1995–2001)

[23] Filtness, A. et al (2012), Driver sleepiness—Comparisons between young and older men during a monotonous afternoon simulated drive, Biological Psychology 89(3), 580-583

[24] Horne, J. (2002), Misperceptions about Unforewarned “Sleep Attacks” When Driving, British Medical Journal 324

[25] Brake and Direct Line (2014), Fit to drive: driver tiredness

[26], Road Traffic Act (1988)

[27], Health and Safety at Work etc. Act (1974)

[28], Management of Health and Safety at Work Regulations (1999)

[29] Lee, L. et al (2016), High risk of near-crash driving events following night-shift work, Proceedings of the National Academy of Sciences of the United States of America 113(1), 176-181

[30], Drivers’ hours – Great Britain domestic rules

[31] DfT (2019), Road traffic estimates: Great Britain 2018

[32] Driver and Vehicle Licencing Agency (2016), General Medical Council Guidelines reproduced by General information: assessing fitness to drive

[33] Noia, A. (2018), Understanding sleep, BUPA

[34] Flatley, D. et al (2004), Road safety research report no. 52: Sleep-related crashes on sections of different road types in the UK (1995–2001)

[35] Department for Transport, The Highway Code: rule 90

[36] Schwarz, J. et al (2012), In-car countermeasures hardly effective against driver sleepiness, Swedish Road and Transport Research Institute

[37] Watling, C., Smith, S. and Horswill, M. (2014), The effectiveness of nap and active rest breaks for reducing driver sleepiness, Queensland University of Technology

[38] Sharwood, L. et al (2013), Caffeine reduces crash risk for long-distance truck drivers but can't replace sleep, George Institute for Global Health

[39] Merat, N., and Jamson, A. (2012), The effect of three low-cost engineering treatments on fatigue: a driving simulator study

[40] Reed, N. et al (2015), Benefit and feasibility of a range of new technologies and unregulated measures in the fields of vehicle occupant safety and protection of vulnerable road users

[41] International Transport Forum (2016), Zero road deaths and serious injuries: leading a paradigm shift to a safe system

[42] Department for Transport (2015), Working Together to Build a Safer Road System British Road Safety Statement

[43] International road assessment programme (iRAP), undated, Road Safety Toolkit

[44] As presented by iRAP to road safety stakeholder meeting convened by Office Of Rail and Road, September 2016

Page last updated: March 2020


Tags: fatigue tiredness impairment