The King County Water Taxi is shifting from standard diesel to renewable diesel to power its fleet. Why? Because renewable diesel cuts greenhouse gas emissions and works in any diesel engine!

“Reducing greenhouse gas emissions is key to fighting climate change. Converting waste into renewable diesel transforms our water taxis and showcases repurposing in action,” said King County Executive Shannon Braddock. “As one of the few major transit agencies working towards a 100% zero-emissions fleet, Metro is driving King County toward a cleaner, healthier future.”

 “The Marine Division is always working on ways to reduce its carbon footprint. The shift to renewable diesel is a step in that direction,” said Marine Division Director Terry Federer. “Metro has always been a leader in zero-emission efforts, and being the first agency on the Seattle waterfront to shift to using renewable diesel continues that tradition.”  

Renewable diesel is made of nonpetroleum renewable resources such as natural fats, vegetable oils (like soybean oil), and greases. After these raw materials are refined into fuel, renewable diesel generally has fewer impurities than conventional fossil-fuel diesel, so it burns cleaner, creating less air pollution (such as particulate matter, carbon monoxide, and nitrogen oxide).

The two primary Water Taxi vessels, the Doc Maynard and the Sally Fox, each use 125,000 gallons of fuel per year, on average. The transition to renewable diesel will reduce greenhouse gas emissions and air pollution as these vessels operate from downtown Seattle to West Seattle and Vashon.

Using renewable diesel also lowers Metro’s greenhouse gas emissions. Because renewable diesel is sourced from renewable resources, the total carbon emitted during the lifecycle of the fuel, from refining the source material to burning the fuel in an engine, can be 60% lower than petroleum diesel.

One great advantage of renewable diesel is that it is a “drop-in” replacement for conventional fossil diesel. Because renewable diesel has the same chemical structure as petroleum diesel, renewable diesel can be used in engines designed for conventional diesel with no modifications. This is where renewable diesel differs from biodiesel, another sustainable alternative to petroleum diesel. Biodiesel has a different chemical structure than petroleum diesel and is often mixed, or “blended”, with petroleum diesel to avoid damaging engines.

In addition to using renewable diesel, Metro’s Marine Division is actively exploring new, high-efficiency vessel designs and zero-emission propulsion systems for the next generation of its fleet. Whether it’s the use of renewable diesel or the commissioning of battery-electric vessels, the Marine Division is committed to being part of King County’s zero-emission future.