King County Metro Transit's fleet of 159 trolleybuses need to be replaced soon, but what they should be replaced with is up for debate.

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About one-fifth of all King County Metro Transit rides are made on an electric bus, powered by a nonpolluting trolley wire overhead.

But the agency hasn’t purchased a new trolleybus since 1979.

Since then, Metro bought new bus bodies and fastened old electric motors onto them. They pulled out the diesel engines from a fleet of dual-mode buses, so they ran only on their electric motors. These minor miracles saved the public tens of millions of dollars.

Now the day of reckoning has arrived.

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By 2014, the agency expects its fleet of 159 trolleybuses to wear out.

At the Sodo maintenance base, trolleybus-maintenance manager Mike Eeds pointed to a crack in a steel roof member, near the rear door of a bus. It’s not a safety hazard but could cause leaks — and cracks are expected to spread through the fleet. Worn-out teeth were being replaced on the same bus’s drive axle. Metro has been cannibalizing spare parts, but those will run out by 2016, he said.

County elected officials must decide by next year whether to retire the old trolleybuses, buy new-generation models or switch to some other technology.

An audit last year suggested tearing out the overhead wires and switching to hybrid buses, whose diesel engines are supplemented with onboard batteries. Doing so could ostensibly save $8 million a year compared to trolleybuses, by reducing electrical-maintenance costs and making route schedules more flexible, the audit says.

But many residents along the routes, and Seattle transportation director Peter Hahn, insist on preserving electric buses because they are quiet and nonpolluting. Seattle ranks third of only six cities in the U.S. and Canada that operate trolleybuses, behind San Francisco and Vancouver, B.C. Edmonton removed its trolleybus wires last year, but Laval, Quebec, is considering a brand-new system using local hydropower.

More than pollution

The debate here involves issues far beyond pollution and noise, with a major consideration being torque — electric motors have superior power to turn bus axles coming off a dead stop.

“San Francisco and Seattle have hills that are alike, up and down. There’s no way you can put diesel buses on the hills,” says Nathanael Chappelle, Metro’s 2007 co-operator of the year. Eeds agrees, saying a “straight hybrid” wouldn’t work.

Midway up Queen Anne Hill, a former cable-car route, the Number 2 and Number 13 buses stop for passengers on a 15 percent slope. When the wheels turn again, the acceleration pushes people firmly into their seat backs. The best drivers wait for all to find a seat, or feather the accelerator pedal, so as not to topple unstable riders in the aisle.

Larry Nelson, living in a fourth-floor hillside apartment, says sparks fly off the wire or the tires spin on damp pavement. Still, that’s better than smelling diesel, he says.

In the overhead network, there are dead spots where electricity is interrupted, so a bus must build momentum to coast through, but not faster than 10 mph.

Take a curve too fast, and the power poles fall off the charged wires — trolleybus driver Chai Kunjara compares the physics to a waterskiier who swings wide faster than the powerboat.

Despite the quirks, he says, the steering handles smoothly, the dashboard console is simple and one can navigate by following the wires, though sometimes drivers forget and stray off them.

The downside of trolleybuses is inflexibility. In the ice storm of December 2008, several trolleybuses on First Hill became stuck, paralyzing the central-city service as the following buses couldn’t pass. Diesel buses can go around stalls — Metro says it will “dieselize” its electric Number 70 route for three years because of the upcoming Mercer Street reconstruction.

Trolleybuses cost $1 million or more, compared with $720,000 for diesel-hybrids. Auditors also point out there’s only one North American trolleybus maker, exacerbating the risk of higher costs.

On the other hand, Vancouver is happy with its 2007 models by Winnipeg-based New Flyer, and expects them to last more than 20 years each. Dayton, Ohio, imported Czech buses for final assembly in the U.S. Hahn argues there’s no danger a robust international trolleybus industry will go extinct.

Exploring options

The County Council has ordered a technical study. Councilman Larry Phillips, D-Magnolia, argues electric buses support the fight against sprawl, by making busy city neighborhoods more pleasant.

The timing is awkward. Hydrogen vehicles or plug-in electric buses seem promising, but Metro can’t wait until those technologies mature. That leaves other options:

• Order a trolleybus with supplementary batteries charged through overhead power and regenerative braking — so the bus can sometimes detour off-wire.

• Combine overhead power with a supplementary diesel motor, for long or short stretches off-wire.

• Travel wire-free using electric batteries and high-torque motors, to be recharged by a diesel motor running at a steady, fuel-efficient rate. Metro General Manager Kevin Desmond also hopes to research whether there’s a bus available to use overhead power in-city, then continue off-wire several miles farther out.

Just last year, Metro published a paper describing a better “Rapid Trolley Network” that provided trips as frequent as every six minutes. There could be off-board payment and roomier vehicles, like a train. New wires over Denny Way, Yesler Way and East Madison Street would fill gaps in trolleybus routes.

When the county took over Seattle bus lines in 1973, the deal guaranteed “electric trolley service” shall continue, transportation Director Hahn’s letter emphasizes. The city is writing a new transit plan that likely would keep or even expand the lines, he said in an interview.

“We believe, in terms of climate change, greenhouse-gas goals, this is the most reliable technology.”

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com