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.