SIR - David Herdson (T&A, November 3), in rightly criticising proposals to have a blanket limit of 20 mph throughout the city, wrongly claimed that, where already installed, this reduced accidents.

According to the DTI's own statistics, serious accidents in 20mph zones are a little over 30 per cent more than in the 30mph ones.

In any event, I do not believe that conscientious drivers who adhere to the current 30mph are the ones who cause the accidents.

In the main it is those who respect no speed limits, so I fail to see that a general reduction will be of benefit.

It would only be penalising safe drivers, while yielding no overall benefit.

Philip Bird, Nab Wood Terrace, Shipley