The nation's biggest fleet of hybrid buses is about to triple. King County Metro Transit announced Wednesday that it will order up to 500...

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The nation’s biggest fleet of hybrid buses is about to triple.

King County Metro Transit announced Wednesday that it will order up to 500 hybrid buses in the next five years, adding those to its 237 hybrids already on the street.

The diesel-electric hybrids, meant to reduce global warming, will be purchased mainly with federal grants, combined with a local sales-tax increase approved by voters last fall. The ballot measure, known as “Transit Now,” will fund more frequent bus service throughout the county.

An initial shipment of 22 hybrid buses will arrive next year. They cost $719,000 each.

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The purchase of up to 500 buses could cost as much as $400 million, depending on inflation and the types of buses the county orders.

A batch of 100 buses would come in 2009, when Metro launches a new bus rapid-transit service for Ballard, West Seattle, Shoreline, the Redmond-Overlake-Bellevue corridor, and suburbs south of Seattle-Tacoma International Airport. The 2009 buses will have three doors instead of the normal two and a larger entryway up front.

Later orders would include some shorter, 40-foot buses.

A hybrid bus operates much like the Toyota Prius and other hybrid automobiles. Petroleum powers the primary engine, and when the vehicle coasts or brakes, kinetic energy from the rolling wheels is used to regenerate the batteries for the electric drive system. The electric motor can propel the vehicle at low speed and assist the diesel engine at higher speeds.

Metro last year operated more than 1,400 buses: 1,035 diesel buses using 20 percent plant-based fuels; 237 hybrids, which also use biodiesel; and 159 electric buses powered by overhead wires. Tests by the U.S. Department of Energy showed that a King County hybrid used 30 percent less fuel than a diesel bus in laboratory simulations. In real Seattle traffic, fuel savings averaged 27 percent, the federal study said.

Most transit agencies have not leapt into the hybrid market as eagerly as King County.

Portland’s Tri-Met, for instance, with two hybrid buses, reports fuel savings of 20 percent. “We’re waiting for the price of hybrids to come down,” said spokeswoman Mary Fetsch. Tri-Met also is interested in future hydrogen fuel cells, she said. Like many agencies, it operates ultra-low-sulfur diesel buses, to limit smog.

Only 2 percent of the nation’s 53,971 transit buses were hybrids last year, according to the American Public Transit Association.

Affordability is a challenge for many cities, as a hybrid bus generally costs $200,000 to $250,000 more than a diesel, said Kevin Walkowicz, co-author of the federal study.

Metro officials say they paid less because of their huge order. Hybrids cost 15 percent less to operate than diesels because of fuel savings, said Jim Boon, Metro’s fleet manager, while parts and maintenance cost about the same. “They’re just a good bus,” he said.

Public awareness of global warming has increased since Metro’s first hybrid order in 2004, while King County Executive Ron Sims has gained a national reputation for trying to lower fossil-fuel use.

The new contract allows Metro to buy some cheaper diesel-only buses, but Sims said there’s only one scenario where he’d do so: “global freezing.”

Mike Lindblom: 206-515-5631 or

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