BOTH 'name and address supplied' and Mr Clucas have misunderstood the main reason of a 20mph limit, probably because of a limited understanding of kinetics.

A vehicle travelling at 20mph has less than half of the kinetic energy of a vehicle travelling at 30mph.

This means that much less damage occurs on the impact of the vehicle with a stationary body.

There was a campaign a little while ago which pointed out that a child struck by a car at 20mph stood a much greater chance of survival than one struck by a car at 30mph.

Other factors are the distance travelled due to reaction time,and the braking distance on various surfaces.

As for figures published of pollution occurring at different speeds,these must now be taken with a pinch of salt.

I must say that I was unaware that there was a design of roads for low speeds: presumably this means cart tracks? Possibly the writer is thinking of the A56,with it's multitude of traffic lights!

David Olliver, Altrincham