In the past year Sussex has introduced eighteen 20mph zones to increase safety on the roads. It plans to introduce 17 more during the next 12 months. These safety measures may be saving lives but could they be destroying the environment? JESSICA BAULDRY reports.

According to the AA, drivers are adding to global warming by slowing down.

The motoring organisation is so concerned about the effects of driving slowly, it is launching a campaign called Fuel For Thought to make motorists more aware.

Alarming new evidence is placing pressure on highways bosses to reconsider their priorities.

While the introduction of 20mph zones could be potentially lifesaving in some areas, the environment will pay the ultimate price.

Tests by the AA show a cut in the speed limit from 30mph causes a ten per cent rise in carbon dioxide emissions.

And the AA says the situation worsens with other speed reduction measures, such as speed bumps.

If these are installed, evidence has shown CO2 pollution jumps by a further 41 per cent.

The campaign is timely as highways authorities across Britain look set to follow the example of Portsmouth, which will become the first city in the country to introduce a 20mph blanket limit.

London is expected to follow suit after announcing plans for 20mph zones controlled by speed cameras throughout the capital.

Cities such as Brighton and Hove may not be far behind.

AA president Edmund King said: "We are concerned blanket 20mph limits are being considered without recognising cars will be pumping out more emissions.

"It is hypocritical for local authorities to bring in 20mph limits that have a negative impact on the environment while introducing other measures dressed up as environmental policies which are really all about making money.

"We have to find ways of slowing traffic down in urban areas and outside schools but we need a more common sense approach to speed limits."

The AA commissioned an independent engineer to carry out tests to back up its claim.

The results showed fuel consumption was higher in petrol cars travelling at 20mph than at 30mph.

They showed a typical car would travel 5.85 fewer miles to the gallon at the lower speed - the equivalent of a ten per cent increase in CO2 emission.

Tests along a stretch of road with speed bumps showed vehicles travelled fewer miles to the gallon than along a road without bumps.

The results showed a 41 per rise in fuel consumption and emissions.

Even more alarming was the comparison between a Band G car tax gas guzzler which produces more than 225g of CO2 per kilometre and a Band B vehicle giving out less than 120g/km.

The AA calculated the bigger car produced an extra 42.4g of CO2 per quarter of a mile stretch of road at 30mph.

But the smaller vehicle produced 11 times more CO2 driving at 20mph along the same road than the larger vehicle.

Mr 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 AA boss has called for more research into the environmental impact of 20mph zones.

Despite the evidence, the AA has not dismissed using 20mph in areas where they are needed.

There are 16 variable speed limits outside schools in Sussex which drop to 20mph when pupils are arriving and leaving.

The AA has backed this scheme and others restricting speeds on residential roads not used by buses and lorries.

But it warns highways bosses should not rush headlong into introducing 20mph limits when faced with its evidence.

While the campaign is gathering momentum among environmental organisations, it has its opponents.

The Green Party has fiercely campaigned for 20mph limits in all built-up areas, including villages.

It has criticised the AA's tests as unrealistic and insists reducing speeds can cut CO2 from vehicles.

A spokesman said: "The AA's tests were not conducted under realistic conditions and they don't relate to driving in a city."

Should we be slowing down to protect our children or worrying more about the environment?