Don't sneeze and drive
Having a bad cold or the flu can significantly affect a driver's responses, insurers have claimed.
One hundred drivers with a range of conditions including colds, stress and headaches and 50 who were healthy were put through a hazard simulator test.
The research, for Lloyds TSB Insurance, found that drivers with colds scored, on average, 11% worse - equivalent to the effect of a double whisky.
Experts said being ill could affect driving ability.
The study, carried out by PCP research agency, looked at 60 people with colds and flu as well as 40 with other conditions including premenstrual syndrome.
They said that applying the 11% effect to reaction times would add 1m (3.3ft) to stopping distance if travelling at 30mph (48km/h) - on top of a normal distance of 12m (40ft).
It would add 2.3m (7.5ft) onto the normal stopping distance of 96m (315ft) if travelling at 70mph (113km/h).
In a separate YouGov poll of 4,000 people carried out for the insurers, 22 people had had an accident while having a bad cold and five while they had flu.
The company estimated that, as 33.5 million adults drive in Britain drive, extrapolating out the YouGov figures would equate to 125,000 accidents caused last year by motorists with colds and flu.
It warned that being unwell at the wheel, particularly when combined with medication, fatigue or a small amount of alcohol, could all have a significant impact on driving ability.
Paula Llewellyn, a spokesperson for the company, said: "Getting behind the wheel when ill causes thousands of accidents every year.
"Try to avoid driving if you're suffering from cold or flu."
Dr Dawn Harper, who is supporting the campaign, added: "Safe driving requires concentration and good reactions, both of which are significantly reduced, even by just a mild cold.
"I would advise drivers suffering from these conditions to avoid getting behind the wheel until they are better."
'Common sense approach'
Duncan Vernon, road safety manager at the Royal Society for the Prevention of Accidents (RoSPA), said: "If you are not well enough to undertake a journey, it could be dangerous for yourself and other road users.
"Severe bouts of common conditions, such as colds, flu, migraine, stomach upsets, infections and hay fever, can affect a driver's ability to drive safely.
"A heavy cold, for example, can have symptoms that include a headache, blocked sinuses, sneezing and tiredness, and these can impair a driver's mood, concentration, reactions and judgement."
He added: "It is important that, when you are ill, you weigh up how necessary journeys are and whether alternative arrangements can be made.
"A common sense approach is needed as it is possible to drive safely when feeling 'slightly under the weather', but a point may be reached when it is unwise to drive.
"People need to be honest with themselves about their ability to drive safely."