Driver fatigue

A quarter of all crashes on British main roads causing death or serious injury are tiredness-related [1]. Motorways and dual carriageways are particularly high-risk, as this type of driving is monotonous, with fewer interruptions and challenging scenarios to keep drivers alert and attentive [2]. It’s estimated that almost one in five crashes on trunk roads are fatigue-related [3].

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 [4]. Even if tired drivers don’t fall asleep, they still pose a danger. Too little sleep radically affects your ability to drive safely, increasing reaction times, reducing attention, and reducing your ability to control the vehicle [5]. Research suggests driving tired can be as dangerous as drink-driving [6].

Take action: Make the Brake Pledge to take regular breaks and never drive when tired.

Who is at risk?

Male drivers are more likely to crash due to tiredness than female drivers: 85% of sleep-related crashes involve male drivers [7]. Drivers under 30 are at higher risk of sleep-related crashes than older drivers [8], and are most likely to crash due to tiredness in the early morning after little or no sleep [9]. 

At-work drivers are particularly at risk from tiredness, because they typically spend longer hours at the wheel: four in 10 tiredness-related crashes involve someone driving a commercial vehicle [10].

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 found in the past year almost half (49%) of UK drivers surveyed admit driving after less than five hours’ sleep – not nearly enough for safe driving [11].

Take action: Support Brake’s wake up! campaign to raise awareness of the risks of tired driving.

What can increase the risk of driving tired?

Many factors can contribute to driver tiredness and increase your risk of being involved in a tiredness-related crash.

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, making you sleepy and less able to concentrate [12].

Stress: Tiredness and difficulty concentrating are typical symptoms of stress [13].

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 insomnia or sleep apnoea.

Learn more: Read our fact page on sleep apnoea.

Irregular sleep patterns: This can be a problem if you work shifts and switch 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 tiredness-related crashes [14].

Driving for long periods: Research has found that 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 for, the more rest you need to recover driving performance [15].

Vehicle engineering: Modern vehicles are usually quiet and comfortable for the driver, meaning you might be more relaxed when driving. This can increase the lulling effect that long, monotonous journeys have on drivers, particularly in vehicles fitted with comfort-enhancing features such as cruise control [16].

Medication: Some prescription and over-the-counter drugs can affect driving by causing drowsiness and impaired alertness. Unfortunately, medications may carry warnings that are not completely obvious and clear that they can impair driving, for example small print advising not to operate heavy machinery within a certain period of taking the medication. Hence drivers should always check with their doctor or pharmacist if any medication they take can impair driving, and not drive if there is a chance it can.

Learn more: Read our fact page on the dangers of drug-driving.

What is the law on driving tired?

If you cause a death while driving tired, you can be charged with death by dangerous driving. The maximum penalty for this is 14 years in prison.

It can sometimes be difficult to prove that a crash was caused by driver tiredness, as tiredness leaves no physical traces and drivers may not remember feeling tired before crashing. However, the police will investigate how long you’d been driving, what you were doing beforehand (e.g. how long you had been awake for), the type of impact, eyewitness statements, and marks on the road (e.g. for evidence of lack of braking), which can all indicate whether the crash may have been caused by tiredness.

Professional truck drivers have a device in their vehicle called a tachograph, which records how long they had been driving and whether they had taken their legally-required breaks: this will form part of the investigation if a professional driver is involved in a serious crash.

If drivers suffer from a medical condition that causes daytime sleepiness, such as narcolepsy or sleep apnoea, they must inform the DVLA. If they fail to do so, they can be fined £1,000, or prosecuted if they cause a crash as a result.

How can I tell if I’m in danger of falling asleep at the wheel?

Research shows that normal sleep does not occur without warning, and most people can recognise the symptoms, although they may underestimate the dangers of continuing to drive when sleepy [17]. 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 [18], 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 [19].

After a microsleep the driver may feel like they’ve just briefly nodded their head, but they have actually been asleep, possibly for up to half a minute. During this time they will have been completely unaware of anything around them, including hazards in the road or an unexpected bend. This can obviously be fatal: if you nod off for just six seconds while driving on a motorway at 70mph you would travel nearly 200 metres, which is more than enough time to veer across three lanes of traffic and off the road or into the central reservation. Simulator studies have shown a clear relationship between microsleeps and crashes [20].

How can I avoid driving tired?

The best way to avoid driving tired is to make sure you get plenty of rest beforehand, particularly if you are setting off early in the morning: at least seven to eight hours is recommended [21]. Research shows that if you drive on less than five hours you only have a one in 10 chance of staying awake on a lengthy journey [22]. If you’re driving late in the day, especially after a busy day, having a nap before you set off can help you feel alert. Never set off on a journey if you’re already feeling tired.

Plan your journeys carefully to enable you to have sufficient rest beforehand, and to avoid driving at times when you’re likely to feel more tired. Allow enough time to take breaks of at least 15 minutes at least every two hours [23]. If you feel tired or lose concentration sooner than two hours, then you need to take a break as soon as possible.

If you feel tired on your journey, find somewhere safe to rest (not on the hard shoulder) as soon as possible; never try to fight off tiredness. Winding down the window, listening to music and talking to a passenger do not help prevent sleep [24]. 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 [25].

Drinking a caffeinated drink such as coffee or an energy drink is effective in reducing driver tiredness over short periods, and has been found to reduce crash risk among long-distance truck drivers by 63% [26]. 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. Therefore 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.

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

[1] Sleep-Related Crashes on Sections of Different Road Types in the UK (1995–2001), Department for Transport, 2004

[2] Sleep-related vehicle accidents: some guides for road safety policies, Accident Analysis and Prevention, 2001

[3] THINK! Don’t drive tired, Department for Transport

[4] The relationship between driver fatigue and rules limiting hours of driving and work, Transport Research Laboratory, 2009

[5] Exploratory study of fatigue in light and short haul transport drivers in NSW, Australia, Accident Analysis and Prevention, 2008

[6] Long nightly driving comparable to drunk driving, Utrecht University, 2011

[7] Sleep-Related Crashes on Sections of Different Road Types in the UK (1995 - 2001), Department for Transport, 2004

[8] Driver sleepiness—Comparisons between young and older men during a monotonous afternoon simulated drive, Biological Psychology, 2012

[9] Misperceptions about Unforewarned “Sleep Attacks” When Driving, British Medical Journal, 2011

[10] THINK! Don’t drive tired, Department for Transport (undated)

[11] Male drivers urged to wake up to dangers of tired driving; survey finds half have nodded off at wheel, Brake and Direct Line, 2014

[12] Advanced Driver Fatigue Research, Federal Motor Carrier Safety Administration, 2007

[13] Struggling with stress? NHS Choices, 2014

[14] Fatigue a proven killer on the road, says CARRS-Q research, Courier Mail, 2012

[15] The impact of continuous driving time and rest time on commercial drivers' driving performance and recovery, Harbin Institute of Technology, 2014

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

[17] Are drivers aware of sleepiness and increasing crash risk while driving? University of New South Wales, 2014

[18] Microsleep, sleepdex.org, undated

[19] Male drivers urged to wake up to dangers of tired driving; survey finds half have nodded off at wheel, Brake and Direct Line, 2014

[20] Microsleep Episodes and Related Crashes During Overnight Driving Simulations, University of Applied Sciences Schmalkalden, Germany, 2011

[21] How much sleep do you need? BUPA, 2012

[22] According to research by Loughborough University Sleep Research Centre

[23] The Highway Code: rule 90, Department for Transport, 2014

[24] In-car countermeasures hardly effective against driver sleepiness, Swedish Road and Transport Research Institute, 2012

[25] The effectiveness of nap and active rest breaks for reducing driver sleepiness, Queensland University of Technology, 2014

[26] Caffeine reduces crash risk for long-distance truck drivers but can't replace sleep, George Institute for Global Health, 2013


Page last updated: November 2014