TriMet has a nearly $500 million plan to phase out its diesel buses - significant emitters of carbon into the atmosphere -- while buying a new fleet of electric vehicles over the next 22 years.

The agency currently has no single battery-electric buses in its 658-vehicle fleet. A pilot bus, part of the original five vehicles awarded in a 2016 federal grant, is still being tested and hasn't been deployed yet. The agency this summer won a second federal grant for another five electric vehicles, which are expected to hit city streets by 2021.

The $498.9 million price tag is an estimate based on a slew of market uncertainties and potential technological changes over the next two decades, but TriMet's shorter-term strategy is rooted in reality. The agency said it hopes to use $53 million funneled to TriMet from the 2017 statewide transportation package to order 80 battery-electric buses over the next five years. It needs the TriMet board to sign off on the overall strategy later this month and the state's top transportation commission to approve the funding piece.

This week, TriMet shared with its board for the first time the financial estimates behind its long-term strategy to ditch the diesel fleet. TriMet leaders said the strategy has been in the works for about a year. In addition to transitioning away from diesel, the plan calls for putting another 271 buses on the streets by 2042.

"We want to make an effort to move in this direction" of moving away from diesel, Bernie Bottomly, TriMet's executive director of public affairs, said in an interview, "and address what is a gigantic issue around climate change."

TriMet uses about 6 million gallons of diesel fuel every year, emitting about 57,000 metric tons of carbon dioxide into the region's air, according to its analysis. Diesel vehicles are a large contributor to carbon emissions, and freight traffic, school buses and other diesel-based industries also emit deadly exhaust in Portland's air.

TriMet estimates its riders - by not using cars -- help reduce carbon emissions by 78,000 metric tons annually and its newer buses are equipped with better safeguards for spewing particulars. Nonetheless, it acknowledges diesel buses aren't the long-term solution.

TriMet is not alone in exploring zero-emission or battery-operated buses. Thirty-eight transit agencies have a battery electric bus in hand already or have ordered one, most of which are in the test phase. China has an estimated 400,000 battery buses, Bottomly said this week.

Washington state's King County Metro transit agency is planning to move its fleet to an entirely zero-emission service no later than 2034.

No one is quite sure if battery power will be the answer or not. TriMet plans to leave the door open for potential alternative fuels, like hydrogen or natural gas, to gain steam in the coming years.

"Don't discount hydrogen," Doug Kelsey, TriMet's general manager, told the board this week.

But that hydrogen future isn't yet here, and he said the alternative fuel has a "very significant up-front cost."

Inside the numbers:

658: total TriMet buses

8: TriMet diesel/electric hybrids

118 - C-Tran buses

56: C-Tran diesel/electric hybrids

929 - Total buses TriMet plans to have by 2042, when the new non-diesel fleet would be running

11: TriMet's rank, nationally, in number of total buses today

38: Transit agencies across country have battery-electric buses, most in the test phase

(Source: TriMet/C-Tran)

Kelsey attended a zero-emission bus conference this summer and said uncertainties abound. No one knows, he said, how this will shake out. Some long-time diesel manufacturers like New Flyer and Gillig are shifting to electric vehicles. New companies are jumping in, too.

"They're in an intense, competitive market," Kelsey told the board, but it's unclear if electric vehicles can withstand the maximum 300-mile daily grind some buses need to operate on a given day (the average bus runs 100 miles a day).

TriMet is renovating its bus depot on Powell Boulevard, and Kelsey said the agency is "going to put a stake in the ground" and install electric bus charging stations at that facility. "We've got to start somewhere," he said. TriMet says it would need one charging station for every 50 buses.

At a Wednesday board strategy meeting, Bottomly said the agency is building a contingency plan into the 2024 fiscal year if electric buses aren't the best zero-emission option. That's the point when TriMet would need more money to complete the fleet transition, and when it would expect to more than triple its order of non-diesel vehicles to 62.

At the strategy session, Bottomly told board members the transit agency had started discussing future funding sources to help TriMet pay for the buses. One option, he said Wednesday, could be seeking state money from another source, like a proposed carbon-pricing bill expected to be debated in the 2019 Legislative session.

Gov. Kate Brown's office declined to confirm whether the agency had specifically discussed that possibility.

"Our office has had many conversations with stakeholders about how to achieve carbon reductions at the lowest possible cost," the governor said in a statement. "Ultimately, the Legislature will determine how any proceeds from a cap-and-trade program are invested."

TriMet's board will decide whether to approve the plan Sept. 26.

-- Andrew Theen

atheen@oregonian.com

503-294-4026

@andrewtheen