Magic in a Tank: ODOT’s Journey to One of the World’s Lowest Carbon Fleets

Written by: Michael Graham, Columbia-Willamette Clean Cities Coalition

"Historic Hwy 30, Columbia River Gorge, Oregon" by Bonnie Moreland (free images) is marked with CC PDM 1.0

The Oregon Department of Transportation uses a next-generation biofuel. It operates better than fossil diesel and costs almost the same. That saves ODOT and Oregon taxpayers money and carbon emissions.

Like most fleets, ODOT has dealt with fossil diesel, which, let’s be honest, is a dirty fuel.

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It’s not very pure, attracts water, and spews carbon and particulate emissions. For example, a full load of diesel may still meet ASTM specifications but can contain over 3 gallons of water dissolved and 1.5 pounds of dirt suspended in the fuel. A gallon of ULSD can similarly emit 22.4 pounds of carbon dioxide per gallon.

It also comes with maintenance headaches ranging from clogged fuel injectors and filters to biological growth in fuel tanks. These issues add downtime and costs for fleet operators, and its emissions warm the planet.

ODOT fleet managers and staff headed off many of the issues brought on by fossil diesel. They deployed specialized filters and desiccant breathers to reduce dirt, water and biological growth. They instituted routine fuel tank inspection and cleaning regimens fleetwide. Much of the fuel quality issues improved through ODOT management.

To reduce carbon emissions, ODOT incorporated record amounts of biodiesel blends through rigorous education campaigns for maintenance staff and drivers.

As early as 2005, ODOT had introduced blends as high as 40-50%. Depending on the year’s fuel consumption, ODOT’s biodiesel usage today reduces between 5% – 9% of statewide fleet emissions, annually.

Biodiesel is a fuel with properties similar to diesel, made by a chemical reaction from vegetable oils and other organic waste feedstocks. Biodiesel performs well in diesel equipment and is widely used throughout the world.

Fossil Diesel is Bad for People and Vehicles

But the particulate emissions from the fossil portion of ODOT’s fuel usage still caused issues in newer diesel vehicles equipment with advanced emissions aftertreatment systems. If left untreated, diesel exhaust can negatively harm human health, and is even classified as a known carcinogen by Oregon Department of Environmental Quality. Its particulate emissions also impact diesel vehicle and equipment performance.

Source:  Oregon Department of Transportation

Newer diesel vehicles and equipment with advanced emission control technologies, such as DPFs, help substantially reduce the impact of diesel exhaust particulate. This preserves air quality and public health by trapping particulates before they enter the environment.

Consequently, these systems suffer from particulate accumulation on the filter traps. This is especially prevalent in slower-moving and idle-prone diesel duty cycles where regeneration cycles can’t keep up with the accumulated particulate.

The problems can include down time for a forced regeneration cycle – wasting fuel, time, money – and even blown filters costing tens of thousands of dollars. Like many fleets, ODOT was enduring this experience firsthand thanks to fossil diesel’s emissions.

Then in 2016, ODOT received its first shipment of a next-generation biofuel. The problems all but disappeared.

Renewable Diesel is a Better Diesel

Renewable diesel is low carbon and incredibly pure compared to its fossil cousin.

Renewable diesel is not biodiesel but is bio-based. It is a next-generation diesel fuel made by cracking and reforming fats, oils, and grease into a super-pure and high-performance diesel molecule. Both can achieve 60-80% lifecycle carbon emission reductions.

It emits around 30% less particulate matter when combusted, meaning less is available for the DPF system to trap, which improves performance. Columbia-Willamette Clean Cities members anecdotally share that renewable diesel can also extend intervals between oil changes, reduce engine backpressure, and slightly improve fuel economy. ODOT surely noticed.

“Our bridge crew crane used to need the regeneration system/filter repaired regularly due to idling and low RPM operation. We have not had to repair that system since switching [to renewable diesel],” Shane Johnson, assistant district manager, said.

ODOT Maintenance Manager Kyle Elliot, based in Manning, Oregon, noticed renewable diesel’s impact.

“We haven’t had issues with plugging up fuel filters like we used to – especially in the wintertime,” Elliot said. “We have also noticed we haven’t had to drain the fuel water separators as often either.”

Renewable diesel also excels in the cold and often does not need additives to prevent fuel from gelling. This saves ODOT money on cold weather additives or expensive kerosene, which adds $0.03 to $0.11 per gallon, depending upon the vendor.

“R99 is the only fuel we want in the High Cascades,” Dan Metz, transportation maintenance manager, said. “Our equipment runs better on it and we have seen slight improvement in fuel economy. It doesn’t gel or require other chemicals to keep it usable.”

ODOT is a National Leader on Fleet Decarbonization

Thanks to renewable diesel, ODOT hit a milestone in 2020 with the use of over 53% alternative fuels in its statewide operations. That impressive feat also included a 38% carbon emission reduction in 2020. For perspective, their 2017 Sustainability Report stated a 17,165 metric tonne reduction over a nine-year period. With renewable diesel, ODOT reduced 11,200 metric tonnes in just one.

Several market forces helped ODOT fleet leadership in the process, including a new statewide contract and a reinstated $1-per-gallon federal credit, known as the Blender’s Tax Credit.

The biggest bang came from the Oregon Clean Fuels Program – one of only two programs in the country where low carbon fuel producers generate credits, which are bought and sold on a market to petroleum importers and refiners.

The policy helps Oregon and California purchase R99 at- or near-parity with fossil diesel.

For comparison, fleets in neighboring Washington are forced to pay upwards of $4 per gallon for R99. ODOT paid just $1.39 in July 2020 thanks to this program.

ODOT’s Road to a Decarbonized Diesel Fleet

Last year was a landmark for ODOT, and market forces are shaping up for another solid year in 2021. R99 continues to spread across their statewide operations, and 100% alternative fuel usage is well within sight.

“It’s not if, but rather when,” Amy Regimbal, ODOT fuel, surplus, and storeroom supervisor said. She has spearheaded many of the fuel management and maintenance solutions.

Source: Oregon Department of Transportation

The fuel has been a hit with internal fleet operators. Where most fleet managers would need to coax, coerce and convince district managers to adopt and use alternative fuels, ODOT fleet leadership found that word-of-mouth advertising was more than enough. Some are even boasting to peers on regional calls about how well their fleet performs with R99.

“Everyone in the agency is beginning to want it. It burns cleaner and better in our heavy rigs, and it’s a low-carbon fuel helping us achieve our GHG reduction goals. It appears at this point to be one of those rare win-win scenarios, we will take all of those we can get,” Darin Weaver, ODOT fleet services manager, said. “It seems apparent that the future of diesel fuel is not petroleum-based. We are very happy with the performance of the renewable product and we are proud to adopt the future now and help lead the way.”


  1. Please be more correct with your terms, “A gallon of ULSD can similarly emit 22.4 pounds of carbon per gallon.” does not make any sense because a gallon of diesel only weighs, at most, 7.5 pounds per gallon. The source you cited indicates the correct term is pounds of Carbon Dioxide, CO2, which is the carbon in the diesel fuel combined with oxygen from the atmosphere.


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