Sir - My car trip computer tells me my average speed for combined motoring hardly ever goes above 20mph. In the city, reducing speed from 30 to 20mph over the ever-shorter stretches where such speeds can be maintained has a negligible overall effect on journey time.

There is always a queue at the next junction, even after the rare 40mph sections. A city-wide 20mph limit would convince many would-be cyclists that it was safe enough to ditch the security of a car in the rush hour, would certainly reduce accidents and shorten some queues.

Why would we not want to implement this? Of course, we'd need more cycle parking.

David Oughton, Oxford