Families with elderly driving relatives worry most about a decline in their cognitive abilities, according to a survey.
When asked by the Institute of Advanced Motorists (IAM), some 46% of people said they were concerned about things like early dementia affecting their relatives' ability to drive.
Of those people who are concerned, some 42% said they had attempted to discuss the matter with their relatives.
By law, drivers are required to tell the DVLA if they have been diagnosed with dementia.
It may be that those facing the condition are able to drive safely for some time after diagnosis, but eventually they will have to give up to keep themselves and others safe.
IAM chief executive Simon Best 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."
Copyright Press Association 2014