MR KING again makes assertions with little in the way of statistical backup.

Where is the evidence that merely putting up 20 mph signs has any measurable effect on the incidence of casualties?

To determine whether ‘20s plenty’ has positive effects, it’s necessary to compare like with like, either the number of accidents on exactly the same stretch of road before the introduction of 20mph with those after, or, if looking at all accidents across a whole town, the accidents per kilometre in each speed band.

Without these statistics, we don’t even have a starting point.

The Warrington pilot showed that the average speed of vehicles before the pilot was 24.9mph and after 23.5mph.

In other words, speeds were nowhere near 30mph and I suggest that a mere reduction of 1.4mph is hardly a statistically significant basis on which to base any decision and certainly not a basis for claims that 20mph signs are the sole cause of this insignificant reduction.

Arguably, I could have put a stuffed teddy bear with a slow down sign on the roadside and equally claimed success because of the bear.

Correlation is not the same as causation.

I would also remind Mr King that in the town centre trial, the number of accidents increased from 24.6 before the trial to 37 after, a 50 per cent increase.

Unlike Mr King, however, I would not necessarily claim that this is statistically significant without a lot more knowledge of the factors and events involved.

And neither do I recognise the casualty statistics he claims for the Department for Transport. The Table RAS 10001 for 2013 shows something different to the numbers he quotes.

If we look at the DfT’s statistics for the last three years, we see the number of accidents has fallen on the combined 20mph and 30mph roads, 40mph (built up) roads and the non-built-up 50 to 70mph roads.

Since accidents have fallen in all speed bands, I can see no basis whatsoever for claiming that roads are safer merely because of a classification change from 30 to 20mph.

Not only did he get my name wrong, neither did I claim monies spent on 20mph signs could have been spent on the Sandy Lane recycling centre.

They could, however, have been spent on real traffic calming measures, and that does not necessarily mean more street furniture, as the Danes have demonstrated by taking away the motoring equivalent of a safety blanket and showing that roads can be safer with less.

Richard Buttrey Stockton Heath