Portland metro region avoids millions of pounds of greenhouse gas emissions with TriMet’s switch to renewable diesel


The agency used more than five million gallons of cleaner burning R99 diesel since December 2021, decreasing environmental pollution and lowering maintenance costs

What happens when you take hundreds of buses that travel millions of miles and run them on renewable diesel? You start making a big difference–for the environment and for the people who live, work and play across TriMet’s 533-square mile service district. Since Dec. 2, 2021, our nearly 700 fixed-route buses have run on R99, a blend of 99% renewable diesel and 1% petroleum. Our LIFT paratransit vans and buses along with our WES commuter rail trains made the switch to the greener, cleaner-burning fuel on May 1, 2022. In the past year, we’ve used more than five million gallons of R99, a move which created cleaner air for our community, reduced maintenance costs and helped TriMet exceed milestones on our road to net-zero emissions by 2050. 

The move to renewable diesel, combined with our shift to renewable electricity for the MAX light rail system and all TriMet-owned facilities in June 2021, reduced TriMet’s greenhouse gas emissions by nearly 70%. We estimate that these climate actions will help TriMet avoid more than 193 million pounds of greenhouse gas emissions each year. That is equivalent to taking almost 19,000 automobiles off the road annually, according to the Environmental Protection Agency.

What is renewable diesel?

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. 

R99 replaced the B5 biodiesel blend TriMet had been using in our buses since 2006. Unlike higher concentrations of biodiesel, renewable diesel requires no changes to engines. Renewable diesel is processed in the same way as petroleum and performs better than biodiesel in cold air. In addition, it requires no blending and burns cleaner than biodiesel or petroleum diesel. 

Renewable diesel (left) is chemically identical to petroleum but contains nearly no fossil carbon

Benefits add up

As renewable diesel burns much cleaner than traditional diesel fuel as well as biodiesel, TriMet expects to see significant maintenance cost savings over time. Since making the transition to R99 in our fixed-route fleet one year ago, we have experienced a notable decrease in maintenance issues related to our buses’ emissions systems. That’s because renewable diesel is easier on the exhaust after-treatment systems that are installed on our buses. That ultimately lowers the time and cost required to maintain them. In fact, TriMet estimates annual maintenance cost savings could reach as much as $100,000 per year.

The road to net-zero emissions

TriMet began using R99 in our fixed-route buses on Dec. 2, 2021

As TriMet pursues net-zero emissions by 2050, our adoption of renewable energy helps meet milestones defined in our Climate Action Plan. By purchasing renewable electricity and renewable diesel in the past year, we estimate exceeding our 2022 goal for a 60% reduction in greenhouse gas emissions (from a 2020 baseline), by about 10%.

TriMet continues to test and vet electric bus technologies in our move to a zero-emissions bus fleet by 2040. Earlier this year, we made our first bulk purchase of electric buses, 24 long-range battery-electric buses manufactured by GILLIG. The buses will start arriving in 2023, and will expand TriMet’s current electric bus fleet to 34 vehicles by mid-2024. We continue to explore the potential of emerging technologies including four diesel-to-electric conversion buses, and what is believed to be the world’s first 60-foot, articulated bus converted to 100% electric. Learn more at trimet.org/sustainability.