The AA’s claims that 20mph zones on longer, relatively free-flowing residential roads ‘can pump up carbon emissions by more than 10%’ have been dismissed.
Highways authorities and environmentalists did not accept the claim that 30mph roads were ‘more environmentally-friendly’, as research for the AA suggested.
The AA employed ‘an independent engineer’ to test the consumption of a small and a medium-sized car on a test track. It said commuting a quarter-mile stretch of road at 20mph would use an extra 1.9l of petrol in one week. AA president, Edmund King, is contesting the push for blanket 20mph limits. He said it would be ‘a bitter irony if local authorities targeting owners of larger vehicles with environmental charges pump up CO2 emissions through indiscriminate use of speed restrictions’.
The motoring organisation claimed the Green Party was promoting 20mph limits across London, ‘perhaps without realising that this would backfire environmentally’. But Portsmouth City Council, introducing 20mph limits on all residential streets, including relatively long stretches on its grid-system network, expected ‘no appreciable increase in emissions’.
A spokesman told Surveyor: ‘We are expecting to reduce average speeds by around 3mph, which will have a negligible impact on petrol consumption. ‘On most of our narrow roads, it’s impossible to drive at 30mph, unless you are a dangerous driver – our 20mph zones will target those going too fast for the conditions.’
Reducing such driving would encourage walking and cycling, thereby cutting emissions. ‘We consider that the environmental impact will be neutral at most,’ he claimed, stressing that traffic calming, which the AA’s study suggested doubled emissions, would not be used. London Green Party assembly member, Darren Johnson, said: ‘Driving round a test-track is one thing, driving around London, where the average speed is already below 20mph, is completely different’.
The evidence was that 20mph limits ‘can make driving smoother, reducing emissions’. Vertical traffic calming might increase localised emissions, according to a 1999 Swedish study, but have a beneficial environmental effect over a larger area. The Department for Transport is considering producing guidance on the benefits of introducing 20mph zones (Surveyor, 8 November 2007).
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