"Hybrid electric drive provides an outstanding combination of improved efficiency, reduced emissions, and improved performance," said Stuart Sunshine, San Francisco Muni's general manager. "We are proud to be the first transit agency in California to commit to this promising technology, and we look forward to incorporating the hybrids into our fleet."

These buses, to be delivered in 2006, will be certified to standards for diesel electric hybrid buses recently adopted by the California Air Resources Board (CARB). The hybrid units will provide 25 percent to 35 percent better fuel economy while greatly reducing emissions: 90 percent less particulate matter, 40 percent less NOx, and 30 percent fewer greenhouse gases.

At the heart of the Orion VII hybrid bus is the HybriDrive propulsion system, which uses a single electric motor powered by a diesel-driven generator. A Cummins ISB 5.9-liter high-efficiency engine drives a generator that provides power to a single electric motor, which turns the drive wheels. The generator also charges an energy storage unit that provides additional power for high-demand situations, such as fast starts and hill climbs.

The absence of a mechanical transmission means no transmission overhauls -- a major maintenance item on conventional buses. Another feature of the Orion VII hybrid is a regenerative braking system that uses the drive motor to slow the bus, effectively turning the motor into a generator to help recharge the energy storage system. This feature saves energy and significantly reduces brake wear.

"Our hybrid propulsion technology combines cleaner emissions and reduced fuel consumption," said Hank McGlynn, vice president of Power Systems for BAE Systems, a partner in the project. "This is a powerful combination for transit agencies seeking to both reduce fleet emissions and combat the escalating cost of diesel fuel."

In addition to the successful use of these buses in New York City, the Toronto Transit Commission placed an order for 150 buses of the same configuration.