Union Pacific Railroad is partnering with two California air management districts to repower 10 low-horsepower diesel-electric locomotives into new Tier 4 switchers for its yard-switching locomotive fleet starting in fall.

The new switchers will reduce particulate matter and oxides of nitrogen emissions by more than 90 percent during operations when compared to older locomotives, UP officials said in a press release.

Tier 4 technology is the U.S. Environmental Protection Agency’s (EPA) cleanest locomotive standard, they added. UP is working with Bay Area Air Quality Management District and Sacramento Metropolitan Air Quality Management District on the repower project.

Using its multi-engine genset locomotive, UP is the only Class I operating Tier 4 switchers and is the first Class I to pursue Tier 4 repowers, UP officials said.

“Reducing diesel emissions is an essential element of the air district’s continuing efforts to protect public health in communities that are highly impacted by the Bay Area’s freight movement infrastructure,” said Jack Broadbent, air district executive officer.

Funding for the initiative was made possible through the Proposition 1B: Goods Movement Emission Reduction Program (GMERP), a partnership between the California Air Resources Board and local air districts, aimed at incentivizing freight-moving equipment owners to upgrade to cleaner technologies.

The switcher units are being repowered at a Progress Rail plant in Patterson, Georgia. Since 2015, UP has worked with Progress Rail on an updated Tier 4 switcher design.

“The new low-power switchers will be an invaluable addition to our fleet,” said Mike Iden, UP director of locomotive engineering. “The coordination with Progress Rail and our partnerships with the air districts are pivotal in ensuring this new technology comes online to provide environmental benefits to our California operations.”