It is a common myth that 20mph limits increase pollution (Argus, Aug 25).

The effects of slower speeds on vehicle emissions are likely to be mixed and we shouldn’t assume 20mph will be detrimental to local air quality.

Lower limits in urban areas may not have a significant influence on emissions of NOx and CO2,but emissions of particulates will probably decrease at 20mph compared with 30mph.

The main impact on levels of pollution probably comes from different approaches to acceleration and changing gear. The Dept for Transport’s own guidance in Circular 01/2013 says there may be environmental benefits from 20mph “as generally, driving more slowly at a steady pace will save fuel and carbon dioxide emissions, unless an unnecessarily low gear is used”.

So the role of driver behaviour in all of this is crucial.

The majority of drivers will adapt their behaviour because they accept the all-round benefits of less aggressive driving and cutting their speed.

It is only a small, stubborn minority who will refuse to change at all.

As well as the environmental impact of their aggressive behaviour, they will continue to put vulnerable road users at completely unnecessary risk from their speeding, discourage people from being more active, reduce enjoyment of public spaces and, ultimately, impose heavy burdens on all taxpayers.

A lower speed limit doesn't harm people – incompetent driving does.

Chris Murgatroyd York Avenue Hove