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When transit agency TriMet added two hybrid buses to its fleet in 2002, the transit agency was not impressed with their performance. But nearly a decade later, TriMet has decided to give hybrid buses, which are powered by electricity and diesel fuel, another test drive along one of its busiest routes.

TriMet last week announced a $2 million award from the Federal Transportation Administration to purchase four new hybrid buses for Line 72 – Killingsworth Street to 82nd Avenue. The line accounts for more than 16,500 trips each weekday.

But while TriMet’s hybrid buses save 8 percent more fuel than its other buses, they also cost 40 to 50 percent more than new diesel buses, according to Alan Lehto, the transit agency’s director of project planning. However, hybrid technology has improved significantly over the past few years, he said, leading more transit agencies to look again at the vehicles.

“Our older hybrids were not penciling in terms of cost, emissions benefits and fuel economy,” Lehto said. “But other transit systems are ordering hundreds of hybrids today because the technology has improved. With this grant, we have an opportunity to track the performance of the new technology.”

A hybrid bus, when traveling at low speeds, runs purely on electric power from a battery pack. At medium speeds, a hybrid bus uses a combination of electric and traditional mechanical power from a diesel engine. Because the electric power is used for a portion of the duties performed by the diesel engine, these vehicles are considered to have greater fuel economy and reduced emissions than diesel buses, Lehto said.

C-TRAN, the transit agency for Vancouver, Wash., in early 2008 purchased 12 Gillig Corp. hybrids after monitoring Seattle’s use of hybrid buses for many years. King County’s Metro Transit, which serves Seattle and its surrounding areas, operates 285 hybrid buses, according to Rochelle Ogershok, public affairs specialist with King County’s Department of Transportation. Those vehicles use 47 percent less diesel fuel and have lower maintenance costs than diesel buses, Ogershok said.

C-TRAN’s hybrid fleet uses 30 percent less fuel than its non-hybrid buses, said Scott Patterson, C-TRAN public affairs manager, which is why the transit agency later this year will purchase another six hybrid buses.

“You’re using the brakes less, so there are fewer brake repairs,” Patterson said. “It’s hard to quantify, but we are saving some money in maintenance as well as fuel costs.”

However, the greater fuel economy and reduced maintenance comes at a price. The cost of a hybrid bus for C-TRAN is approximately $650,000, compared to $450,000 for a new diesel bus. TriMet has not decided yet which manufacturer’s hybrids it will purchase, but Lehto said he expects them to cost more than new non-hybrid buses would.

“The cost of these vehicles is significant,” Lehto said. “But if the price of diesel goes up, the operating savings from the hybrids could outweigh the capital cost to purchase them.”

The new hybrids are expected to arrive within 20 months, said Lehto, who added that he didn’t know when the transit agency might purchase more.

“The hope is to be able to replace a portion of our fleet with hybrids every year or so,” Lehto said. “But we’ve had to defer some of that due to a reduced budget. Right now, the plan is to purchase the four new hybrids and go from there.”