North American railway franchise Union Pacific has partnered with two Californian air-management districts to upgrade ten low-horsepower diesel-electric locomotives of its yard switching fleet, in a bid to reduce their nitrogen emissions.

Under the partnership with the Bay Area Air Quality Management District and Sacramento Metropolitan Air Quality Management District, the locomotives will be converted into new EPA Tier 4 switchers this year.

During operations, the new switchers are expected to reduce particulate matter and nitrogen oxide emissions by around 90% compared to the older locomotives.

“The new low-power switchers will be an invaluable addition to our fleet.”

Air District executive officer Jack Broadbent 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.

“The Air District is pleased to assist Union Pacific in switching their locomotives to meet the cleanest national air emission standards.”

The Tier 4 technology is said to be EPA’s cleanest locomotive emissions standard. Union Pacific is the only Class 1 railroad operating Tier 4 switchers that take advantage of its multi-engine Genset locomotive.

Union Pacific locomotive engineering director Mike Iden said: “The new low-power switchers will be an invaluable addition to our fleet.

“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.”

The switchers are currently being repowered at the Progress Rail facility located in Patterson, Georgia.

Once work is complete, they will join Union Pacific’s yard locomotive fleet in the Bay Area and Sacramento later this year.

Since 2015, Union Pacific and Progress Rail have been working together to develop an updated emission-reducing Tier 4 switcher design.