The vehicle- calming measures increase the emissions of carbon dioxide and fuel consumption to two-fold by forcing drivers to brake and accelerate repeatedly, according to a study commissioned by the Automobile Association (AA).

A car that achieves 58.15 miles per gallon travelling at a steady 30mph will deliver only 30.85mpg when going over humps.

The AA employed an independent engineer who used a fuel flow meter to test the consumption of a small and a medium-sized car at Millbrook Proving Ground in Bedfordshire, England.

The results, calculated by averaging the performances of the two cars, also showed that reducing the speed limit from 30mph to 20mph resulted in 10% higher emissions. This is because car engines are designed to be most efficient at speeds above 30mph.

A motorist who observed the speed limit on one mile of 20mph road during a daily journey would produce an extra tonne of CO2 in a year compared with driving at 30mph on the same stretch.

"Humps are a crude, uncomfortable and noisy way of slowing people down and this research has shown they are also environmentally damaging. We accept that traffic speed needs to be controlled in residential areas where there is a problem with accidents and children are playing. We think motorists are more likely to accept average speed cameras than humps," TimesOnline quoted Edmund King, the AA's president, as saying.

Previous research by the Transport Research Laboratory found that air pollution rose significantly on roads with humps. Carbon monoxide emissions increased by 82% and nitrogen oxide by 37%.

The London Ambulance Service has claimed that the 30,000 humps on the capital's roads cause up to 500 deaths a year because its crews suffer delays in reaching victims of cardiac arrest.

King said: "Humps tend to breed more humps. If one street has humps installed, the adjacent street calls for humps and eventually you find no clear roads for movement of emergency service vehicles."