A decline in cognitive abilities caused, for example, by the onset of dementia, is the greatest concern that families have about elderly relatives driving, according to the IAM.
In a survey of almost 1,300 people conducted on behalf of the IAM, 46% of respondents admitted to being worried about this issue.
The IAM says that more than 800,000 people in the UK currently have dementia – 17,000 of whom are under the age of 65 years – and this number is expected to increase to more than one million by 2021.
The IAM says that while people with dementia may still be able to drive safely for some time after it has been diagnosed, because of the progressive nature of the disease there will come a time when they have to give up.
Simon Best, IAM chief executive, said: “Staying healthy is the simplest way to ensure you are fit to drive, but an independent and objective driving assessment will also help people make the right decision at the right time.
“Experts warn that the numbers suffering from dementia will continue to grow and it is important drivers seek advice before using their cars.
“Families and friends need to be aware of the early warning signs of dementia and seek advice and medical help as soon as possible.”
The IAM has published details of what it calls “signs that an individual no longer has the skills needed to drive safely”. These include: difficulty judging speed, distance and space; getting lost on familiar roads; straying across lanes or hitting kerbs; failing to observe road signs and traffic signals; and becoming angry or confused while driving.