NORTH American Class 1 Union Pacific (UP) and ZTR, a locomotive control systems supplier, have announced a partnership to introduce hybrid-electric locomotives.

The work will focus on what UP describes as “mother-slug” sets, where two diesel locomotives are replaced with one diesel locomotive coupled with an accessory or slug. The slug unit will be converted and equipped with batteries, power electronics and controls supplied by ZTR, helping to “achieve fuel and maintenance savings and offer environmental benefits” allowing the hybrid-electric mother-slug to operate in single-engine, battery charging or electric only modes.

The locomotives will be built at UP’s North Little Rock facility in Arkansas and the first prototype is expected to be delivered in late 2023 with five additional units arriving in 2024. In line with its sustainability commitments, UP says conversions will focus on older locomotives, typically with higher emissions.

UP says the locomotives can operate in multiple modes with several ways to charge the locomotive batteries, including wayside and onboard charging.

The Class 1 adds that the new locomotives will be used primarily for operation in yards with the engineless slug increasing traction motors available to the locomotive, boosting the haulage and braking power that is key for this kind of work.

UP began rolling out mother-slug sets with ZTR’s Nexsys control systems in 2017 and currently operates more than 65 in yards. Depending on the mode of operation, fuel savings and greenhouse gas emission (GHG) reductions could total up to 80%, the Class I says.

“Adding hybrid-electric locomotives to our fleet is another important step for UP as we work to explore drop-in technologies that modify current systems and reduce our carbon footprint,” says UP senior vice-president of engineering and mechanical, Mr Shane Keller. “This pilot will help make our fleet more fuel efficient and further advance our commitment to reaching our sustainability goals, while testing the technology’s capability for expanded use across our locomotive fleet.”

“This investment aligns well with our ongoing goal to leverage ZTR’s technical expertise to support railways in their decarbonisation and efficiency improvement efforts,” says ZTR Control Systems president, Mr Derek Shipley. “This initial hybrid-electric mother-slug application will be the basis of our design for future hybrid-electric, long-haul and fully electric solutions.”