The AA is calling for average-speed cameras to replace speed humps in order to reduce carbon dioxide emissions.
Research conducted by the AA at Millbrook Proving Ground in Bedfordshire showed that fuel economy fell sharply when cars travelled over speed humps.
The economy of a car that achieved 58.15mpg at 30mph on a flat road fell to 30.85mpg over speed bumps.
Edmund King, the AAs president, said: 'Humps are a crude, uncomfortable and noisy way of slowing people down and this research has shown they are also environmentally damaging.'
The tests also showed that CO2 emissions rose 10% when the speed limit was lowered to 20mph, as car engines are designed to work more efficiently at speeds above 30mph.
However, installing average-speed cameras would cost more: estimates suggest 50 speed bumps in four connecting streets would cost 150,000 to put in place, whereas having the required eight speed cameras to cover the same area would cost 250,000.