SPANAWAY, Wash. — Bethel School District is adding nine propane-fueled school buses to its fleet.

The new Blue Bird Vision Propane buses will be equipped with engines that are 90% cleaner than the Environmental Protection Agency’s current heavy-duty engine standard, and produce nitrogen oxide (NOx) emissions at 0.02 NOx, according to Roush CleanTech.

“Bethel School District is the first district to receive school buses that meet the absolute lowest optional NOx level on the market,” said Joel Stutheit, the district’s assistant director of transportation. “We’ve lowered the carbon footprint of our school bus fleet with propane school buses, and will continue our commitment to the community with these new buses.”

The district, which began adopting propane school buses five years ago, initially purchased 10 Blue Bird Vision school buses equipped with Roush CleanTech propane fuel systems. The district has since increased the number of propane buses in its fleet to 32, and has taken advantage of funding opportunities, using one grant to replace two diesel school buses and another grant to help with future purchases.

In addition to expanding its fleet, Bethel School District has grown its propane fueling infrastructure. The district started with bobtail refueling, which is the delivery of bulk fuel using bobtail trucks, while a new transportation center was being built, and then installed a fueling station with three 1,000-gallon tanks and two dispensers. The tanks are expected to be replaced this spring with a single 4,000-gallon tank, leaving room to add another tank when needed, according to the district.

Overall, Stutheit said, the district has been pleased with its transition to propane school buses "because of the efficiency and the low cost of repairs of the engine,” and "drivers like them because they’re quiet and don't have the exhaust of diesel buses." In the coming years, he said, the district is going to focus on replacing its diesel-fueled special-needs buses with propane buses.