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 collisions
Driver fatigue is a serious problem resulting in many thousands of road collisions each year. It is not possible to calculate the exact number of sleep related collisions, but research shows that driver fatigue may be a contributory factor in up to 20 per cent of road collisions, and up to one quarter of fatal and serious collisions.
These types of crashes are about 50 per cent more likely to result in death or serious injury because a driver who has fallen asleep at the wheel 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.
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 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.
Eyesight
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, 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 deteriorates 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.