Envautomental

The largest transit agency in North America has ordered 850 diesel-electric buses and will have the world”s largest fleet of hybrids when the vehicles hit the streets of New York in 2010.

The systems once the vehicles are delivered, officials said.

Daimler said the buses use about 30 percent less fuel than conventional models. The Orion VII is a series hybrid, meaning it is powered entirely by an electric motor. The small diesel engine runs a generator that charges the vehicle”s lithium-ion battery. The buses also use regenerative braking in which braking forces produce current to charge the batteries. Daimler claims the Orion VII emits 90 percent less soot than conventional buses because the diesel engine runs at a nearly constant speed.

Transit systems around the world are increasingly turning to hybrids to reduce pollution and fuel costs. Daimler said of Ottawa ordered 202 Orion VII buses on Monday, bringing to 2,600 the number of Orion buses ordered since it launched the hybrid model four years ago.

in Seattle uses were 15 percent less than conventional buses.

buses -  beginning in 2012, a move officials said would cut carbon dioxide emissions by 200,000 tons annually.