No need to explain ...
20mph limits 'increase emissions'
David Williams, Evening Standard 25.01.08
Cutting speed limits in London to 20mph could increase emissions of carbon dioxide by more than a tenth, the AA claimed today.
Slowing vehicles down makes engines work less efficiently, and the AA has calculated that even on free-flowing routes, fuel consumption in a petrol car going 20mph can be 5.8 miles per gallon worse than at 30mph.
This is enough to produce an extra quarter of a tonne of CO2 every quarter mile travelled. On congested roads the effect can be even more marked, especially with small-engined cars.
Mayor Ken Livingstone has told London's councils to launch 20mph "safety zones" after evidence that they cut accidents and injuries by half.
But the AA said it wanted "detailed research" into the effects of the lower limit before it became widespread. Its president Edmund King said: "It would be a bitter and unpalatable irony if local authorities that have targeted owners of larger vehicles with environmental charges are found guilty of pumping up CO2 emissions through indiscriminate use of 20mph restrictions."
The London Assembly Green Party said the AA's claims were "misinformed" and its tests, conducted on a proving ground, bore no relation to "real" driving conditions in London.
• Haringey is set to become the first London borough to have a 20mph speed limit on all residential streets in an attempt to cut fatal accidents. Haringey already has 20mph zones in Tottenham, Seven Sisters and Muswell Hill. There are more being considered in Wood Green, Crouch End, Stroud Green and Muswell Hill.