Sir – The report of your investigation into the degree of compliance with the new 20mph speed limit (Almost 90% break limit, September 3) is a bit hard on drivers.

There are many things that a driver in an urban setting must be watching out for, most particularly the erratic behaviour of children, other drivers, cyclists, animals, other signs etc.

Speed signs have to jostle for the attention of the driver. To a large extent, drivers use the speed of the flow of traffic within which they find themselves as a direct guide to the speed they should be driving at.

Fairly frequent reminders of the speed limit, and the gradual recognition of drivers of the new situation will gradually raise compliance, over time.

It is unrealistic to expect instantaneous compliance with changed conditions. Lack of compliance does not imply that drivers are wilfully ignoring the new speed limit.

Chris Osman, Oxford