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Seattle Metro’s Hybrid Bus Fuel Woes

Seattle Metro’s GM-Allison diesel parallel-hybrid buses are falling far short of the promised fuel savings of 40%—in some cases, delivering worse mileage than the older (and dirtier) dual-mode Breda buses they replaced, according to a report in the Seattle Post Intelligencer.

The paper first reported on the problems with fuel economy for the New Flyer buses in December 2004. (Earlier post.)

Metro owns the largest fleet of the GM parallel-hybrid buses in the world. New York is building its hybrid fleet with series-hybrid buses from Orion, a division of DaimlerChrysler. (Earlier post.)

There appear to be several issues facing the Seattle buses.

First, the hybrids are used on suburban express routes with more highway mileage—a situation in which the electric drive doesn’t contribute to fuel saving as it does in urban stop-and-go driving.

Second was a switch from Cummings diesel engines to Caterpillar engines, along with the need to meet more stringent emissions requirements.

Caterpillar spokesman Jim Dugan said it isn’t fair to compare today’s buses with 1989 buses like the Bredas, which were much dirtier.

“Emissions coming out of our engines today are dramatically better than for a bus of 1989,” he said. “The tradeoff is your fuel economy is not as good.”

Dugan said Caterpillar “optimized” the Metro hybrid engines for lower emissions rather than for better fuel economy.

“As the EPA tightens emission control requirements on truck and bus engines, fuel economy suffers,” [Jim] Boon [Metro’s vehicle maintenance manager] said. “The trucking industry is just going crazy over this right now.”

Despite the higher purchase cost and the “underwhelming” fuel efficiency, Metro believed needed to purchase the buses from an emissions perspective, as the buses will be used in a downtown bus tunnel shared with Sound Transit’s light rail line.

The hybrids, according to Metro, are also savings about $3 million a year in maintenance, are quieter than regular diesels and are faster than the old Bredas on hills and the highway.



Keep in mind that it is CUMMINS Engine Company, not Cummings Engine Company.

tom deplume

How long until diesel exhaust after treatments make diesels less fuel efficient than gasoline.


seems ridiculous to me that when you increase fuel efficiency, you increase emissions. if you're burning less, why would you exhaust more?
to me, it seems like a) mere excuses, and b) GM ... sucking.

little shop

Well that is quite true, you can BURN MORE and make less 'pollution' but not less co2. Basically that means less particulate matter and less smog. Even my gas car often runs at higher idles and uses more fuel to keep the engine warm in the winter. It could be 'programmed' not too at the expense of emmisions. If it was so programmed it would make less co2 and use less gas.

I dont have much faith in the GM parallel hybrid system. A pure city bus would do best with a serial hybrid. A mostly highway bus (as well as a long haul freight truck) has little benifit to being a hybrid.


Each company should bear some responsibilities. GM is not conservative enough with the performance of its hybrid power train. Seattle Metro is not considerate enough to assess the performance of those parallel hybrid. If those hybrid offers the most optimistic performance in terms of cost and environment impact under the stop-and-go traffic, why bother to replace those in the highway-oriented routes?


Power to Seattle for trying. If GM blows, move on and find a better solution.

Richard Burton

so educate me; what is the difference between a "parallel" hybrid, vs a "serial" one, or others, for that matter? Thanks


Parallel hybrid can be powered directly by the diesel motor or the electric motor. Toyota and Honda hybrids are parallel where they have a trasmission that directly connects the internal conbustion motor to the wheel like all conventional non hybrid vehicles.
A series hybrid has an internal conbustion generator charging the batteries, and a separate electric motor that alone powers the wheels at all times. There is no traditional mechanical trasmission.

richard schumacher

It's puzzling why King County Metro continues to buy the problematic Breda hybrid busses. Other transit agencies are getting much better results with hybrid busses from other manufacturers. See for example

tom deplume

Having worked in public transit I could not see the logic of many management decisions. Some decisions were blatant displays of favortism to former managers who went into the transit equipment business after retirement.

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