THE move by the Department for Transport (DfT) to increase urban safety by reducing speed limits to 20mph without traffic calming measures will push up vehicle CO2 emissions.
The claim is being made by Professor Peter Russell, creator of the Eco-Advanced Driving Test which aims to improve fuel mpg by 15%.
In a public statement Professor Russell said: “Government proposals for a 20mph speed limit in towns across the UK have highlighted two great deficiencies.
“There are no current speed cameras capable of accurately measuring 20mph. And many who advocate an in-town 20mph limit are actually supporting the change in order to reduce pollution. However, to drive at 20mph or lower (instead of 30mph) requires use of lower gears; and that demands higher engine speeds – that demand more fuel. That is what gears do.
“Hence it takes half as long again to cover at 20mph the same distance as at 30mph. Therefore wherever vehicles are restricted to lower speeds they must increase their exhaust pollution by 50%.”
The Road Safety Minister Paul Clark, however, says that 20mph zones with traffic calming measures had made a real difference to road safety, adding: “Allowing councils to put in place 20 mph speed limits on more streets without speed humps or chicanes will mean that they can introduce them at a lower cost and with less inconvenience to local residents.”
A report published in the British Medical Journal in December 2009 found that 20mph zones in London had led to a dramatic reduction in the number of accidents in those areas. It called for more 20mph zones and limits to be put in place.
Official car stopping figures say it takes three car lengths (12m) to stop at 20mph; at 30mph this increases to six car lengths (23m).
Expert warns of CO2 rise in urban areas
