TriMet drives Oregon’s transportation industry toward a cleaner air future with shift to renewable diesel


Oregon’s largest consumer of diesel to cut carbon footprint by more than half in less than a year’s time

On Wednesday, Oct. 27, 2021, TriMet’s Board of Directors unanimously supported TriMet’s latest step to reduce our carbon footprint—shifting to renewable diesel to power our diesel fixed-route buses. As Oregon’s largest consumer of diesel, TriMet will lead the state’s transportation industry toward reducing greenhouse gas emissions with the move to renewable diesel that has less toxic impact on our air.

TriMet’s change to renewable diesel will happen as soon as supplies on the West Coast allow, which could come as early as December. Coupled with TriMet’s switch to 100% renewable electricity in June 2021, running buses on renewable diesel will cut the carbon dioxide-equivalent emissions produced by our agency by *about 63% within a year’s time. TriMet expects to avoid more than 155 million pounds of greenhouse gas emissions every year. That’s the equivalent of taking more than 15,000 cars off the road
*emissions reduction data has been updated

The move to renewable diesel is an important one while TriMet transitions to a zero-emissions bus fleet by 2040.

“TriMet is part of the solution to address climate change, and we are taking all roads we can to cut greenhouse gas emissions,” said TriMet General Manager Sam Desue, Jr. “Our zero-emissions bus fleet is coming, but as this transition occurs, we are actively pursuing greener operations now for the health of our community and state.” 

Renewable diesel benefits outweigh costs

Renewable diesel is chemically identical to petroleum, but it contains nearly no fossil carbon. It is made from 100% renewable and sustainable resources like natural fats, vegetable oils and greases. Also referred to as renewable hydrocarbon diesel, it produces fewer emissions, resulting in a cleaner, low-carbon fuel. 

TriMet’s move to renewable diesel is projected to lower the greenhouse gas emissions from our fixed-route bus fleet by about 61% compared to the current Ultra-Low Sulfur Diesel (ULSD) and 5% biodiesel blend we use. *While it is expected to increase our bus fuel costs by $.09 a gallon, based on a 2019 pilot of renewable diesel, we no longer could see maintenance labor and material costs decrease by as much as $100,000 a year. 

TriMet purchases about 435,000 gallons of diesel a month for our fixed-route buses. In September 2021, the cost was $1,006,764. The same amount of renewable diesel would have cost $1,045,914.

TriMet buses have been running on a 5% biodiesel blend since 2006, when we became the nation’s first transit agency to use the cleaner form of diesel. Biodiesel and renewable diesel are derived from the same or similar resources, but their production processes and end results are different

Also, 5% is the highest blending level for biodiesel allowed by TriMet’s bus engine manufacturer, without needing to make significant and expensive changes to the required preventive maintenance schedule to preserve our warranty coverage. Our engines are compatible with renewable diesel, but we will use an R99 blend, made up of 99% renewable diesel and 1% petroleum, which provides required lubrication for the engines.  

Renewable diesel doesn’t retain water the way biodiesel does, and it performs better during cold weather as no winterization additives are required. And, according to Neste, the company that will supply our renewable diesel, there’s less soot, reducing build up in fuel filters over biodiesel. TriMet’s 2019 pilot test of R99 backs that up. Inspection of our test buses’ exhaust systems at that time revealed significantly less particulate buildup. 

Renewable diesel comes on the bumper of renewable electricity

In 2020, TriMet took a deep look at the sources of the greenhouse gas emissions produced by the agency. We found that our full diesel fleet (buses, LIFT vehicles, maintenance vehicles, WES trains) and the electricity we used were our two biggest sources of carbon output. In partnership with Portland General Electric and Pacific Power, TriMet moved to 100% renewable energy earlier this year to power our MAX light rail system and all TriMet-owned facilities, as well as our electric buses. 

On the road to a zero-emissions bus fleet

TriMet unveiled its first electric buses, powered by 100% wind energy, in April 2019

TriMet made a commitment in 2018 to transition to a clean energy, zero-emissions bus fleet by 2040. We began the journey toward that with the launch of our first five all-electric buses in 2019. In a U.S. transit agency first, those buses have been powered by 100% wind energy. Those buses are short-range electric buses that stop at a charging station along the route several times a day. 

Earlier this month, we launched a test of five long-range electric buses that are meant to run all day and charge at night. We also have just begun testing an 11th electric bus believed to be the first of its kind in the world. The bus, dubbed Desert Rose, is a 60-foot articulated bus purchased from Valley Metro Transit in Phoenix and converted from a diesel bus to an all-electric bus.Learn more about our climate actions at