BOB Downie (Letters, March 26) corrects Muriel Goodall for suggesting that to set a 20mph speed limit there needs to be accompanying speed bumps.

However, Mr Downie also makes the mistake of thinking that the introduction of a 20mph speed limit will in itself reduce the speed of vehicles to 20mph.

Before introducing a blanket speed limit at the proposed lower level it would be helpful to know what the average speeds actually are on our roads and what percentage of vehicles are driving in excess of the current speed limit. I suspect that such a survey will reveal that speeds could be reduced by effectively identifying those exceeding the current speed limit and ensuring that these limits are observed.

Sandy Gemmill,

40 Warriston Gardens, Edinburgh.