November 8, 2008 London's iconic double-decker buses may soon add a green heart to their familiar red exterior. Having already made an impact in North America, buses equipped with BAE Systems’ diesel-electric HybriDrive propulsion system are soon to be trailed on the other side of the Atlantic. The first of 17 evaluation units built by Britain’s Alexander Dennis Limited (ADL) and BAE Systems was delivered this week to bus operator Transport for London and Metrobus.

The hybrid system uses a generator, an electric motor and lithium-ion battery storage along with a regenerative braking system. The diesel motor about half the size of those normally used to run buses runs the generator and a computerized propulsion control system manages power delivery to the electric drive - when accelerating quickly for example, power is pulled from both the batteries and the generator. Because the system uses no mechanical transmission there's less maintenance and the bus delivered to the London uses an new, lighter energy storage system that increases battery life, reduces vehicle weight and therefore improves fuel economy and cuts emissions.

The diesel-electric drive system is already in use on more than 1,500 buses in New York, San Francisco, Houston, Toronto, and Ottawa. BAE estimates that buses equipped with BAE Systems’ HybriDrive propulsion system have so far saved five million gallons of diesel fuel and prevented more than 50,000 tons of carbon emissions.

“Our hybrid technology is the most proven in the industry, with more than 70 million miles of revenue service to date,” said Rob Lindsey, BAE Systems director of transport systems for the U.K. and Europe. “Joining with Alexander Dennis brings the combined benefits of improved fuel economy, lower production of greenhouse gases and other emissions, and reduced vehicle maintenance to the transit system and to the residents of London.”

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