Sir – Just over a year ago I helped publicise the new national bus card for seniors. I have no regrets about this.

The scheme means that poorer, older people can get out more — thus, in a small way, mitigating the effects of the recession — and more prosperous ones use the bus more rather than the car.

But it must be accepted that there is a downside. A full bus has less of a carbon footprint per user than a car with one or two people in it — but the footprint exists. Buses can get uncomfortably full. The journeys have to be paid for by someone. And using buses rather than walking a few hundred metres is bad for health.

The following is a suggestion not for the frail, the very old, the ill or the disabled but for people like me whose health at 61 is very similar to what it was at 59. Impose upon yourself a ‘four-stop rule’. Do not use the bus for four stops or fewer. The distance between four stops is about 800 metres or less. This can be walked in about ten minutes, giving steady and useful exercise. Stopping and starting buses would take about five to cover the distance and you’d probably have to wait at least the other five for one to appear.

When I see healthy people without heavy bags get on a bus to the city centre from the railway station or St Clement’s, I wonder why they are doing it.

Roger Jenking, Oxford