New York's iconic yellow taxis could be about to get a whole lot greener.

Motor engineering company Ricardo, on the banks of the River Adur at Shoreham, has designed a clever electric motor generator which replaces the standard alternator in cars.

The technology, which is being showcased at the New York International Auto Show, means when vehicles idle in traffic jams or stop at lights the engine automatically shuts down.

It restarts when the driver moves his foot from the brake to the accelerator pedal.

The company said the micro system would reduce fuel consumption as well as the amount of carbon monoxide, hydrocarbon and nitrous oxide released into the air.

Demand for fuel-efficient, environmentally responsible vehicles is on the rise as the public, government and manufacturers look for ways to reduce greenhouse gas emissions.

Jeremy Holt, president of Ricardo US, said the electric motor would be ideal for the kind of stop-and-go traffic found in large cities like New York and London.

He said: "Although called a micro hybrid, the benefits can be very significant.

Most vehicles can accommodate this system, including taxis. If this technology were applied to all New York City taxis, Ricardo estimates that 10.8 million gallons of gasoline per year could be saved,reducing greenhouse gas emissions by 105,000 tons of CO2 a year."

Ricardo first started work on the electric motor generator in 2004.

Last month the company announced a ten per cent increase in half-year profits after a turnaround performance by its German operations.

The firm unveiled pretax profits of £4.6 million for the six months to December 31, 2006.

Sales were up three per cent to £84 million, against £81 million last time, while the company's order book had increased 15 per cent to £77 million.

The origins of Ricardo date back to 1906 when Cambridge graduate and engineer Harry Ricardo filed his first patent for a twin-stroke engine.

Since then the company has filed more than 600 patents and its technology can be found in Citroen, Rolls-Royce, Bentley, Fiat, Ford, Volkswagen, Peugeot, Honda and Toyota cars.

The company also makes engine parts for Formula 1 racing cars and tanks.