Driver health

A person’s fitness to drive can be affected by a medical condition, by temporary illness, substances such as alcohol and by the environment in which they work, drive and live.

Health impairments, such as stress, sleep disturbance, migraine, flu, severe colds and hayfever can lead to unsafe driving. Sometimes, the treatment for these conditions can also impair someone’s driving. Our advice highlights some of the factors that can make someone unfit to drive and the importance of assessing your fitness to undertake a journey.

Fatigue and road accidents

Driver fatigue is a serious problem resulting in many thousands of road accidents each year. It is not possible to calculate the exact number of sleep related accidents but research shows that driver fatigue may be a contributory factor in up to 20% of road accidents, and up to one quarter of fatal and serious accidents.

These types of crashes are about 50% more likely to result in death or serious injury as they tend to be high speed impacts because a driver who has fallen asleep cannot brake or swerve to avoid or reduce the impact.

Sleepiness increases reaction time (a critical element of safe driving). It also reduces vigilance, alertness and concentration so that the ability to perform attention-based activities (such as driving) is impaired. The speed at which information is processed is also reduced by sleepiness. The quality of decision-making may also be affected.

It is clear that drivers are aware when they are feeling sleepy, and so make a conscious decision about whether to continue driving or to stop for a rest. It may be that those who persist in driving underestimate the risk of actually falling asleep while driving. Or it may be that some drivers choose to ignore the risks (in the way that drink drivers do).

Crashes caused by tired drivers are most likely to happen:

  • on long journeys on monotonous roads, such as motorways
  • between 2am and 6am
  • between 2pm and 4pm (especially after eating, or taking even one alcoholic drink)
  • after having less sleep than normal
  • after drinking alcohol
  • if taking medicines that cause drowsiness
  • after long working hours or on journeys home after long shifts, especially night shifts.


Good eyesight is vital for safe driving. Drivers and motorcyclists must be able to read a standard number plate from a distance of 20 metres (or 20.5m for an old style number plate) wearing corrective lenses if required.

You must wear glasses or contact lenses every time you drive if you need them to meet the ‘standards of vision for driving’.

Although eyesight often gets worse as we grow older, people can develop a range of eyesight conditions at any age. Glaucoma and Cataract are perhaps the most well known conditions, but diabetes and other age-related diseases, if left unidentified and untreated, can also affect vision seriously enough to prevent safe road use.

The general recommendation is to have an eyesight check every two years, or more often if your optician recommends it. This will help to make sure you meet the minimum eyesight standards for driving and will usually identify the majority of common eyesight conditions early as they develop.

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