News Releases


Union Pacific and ZTR Partner on New Hybrid-Electric Locomotives

Locomotive prototype testing expected in late 2023

Omaha, Neb., October 6, 2022

Union Pacific Railroad and ZTR, a green technology company and leader in locomotive control systems, today announced a partnership to build hybrid-electric locomotives. The locomotives will be built at Union Pacific’s North Little Rock, Arkansas, facility with the first prototype expected to be delivered in late 2023 and five additional units arriving in 2024.

The locomotives work much like today’s plug-in hybrid car, capable of operating in multiple modes with several ways to charge the locomotive batteries including wayside and onboard charging.

“Adding hybrid-electric locomotives to our fleet is another important step for Union Pacific as we work to explore ‘drop-in’ technologies that modify current systems and reduce our carbon footprint”, said Union Pacific’s Senior Vice President of Engineering and Mechanical 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.”

Known as “mother-slug” sets, two locomotives are replaced with one diesel locomotive connected to an accessory or slug. In keeping with its sustainability commitments, Union Pacific converts older locomotives, typically with higher emissions. The slug unit will be converted and equipped with batteries, power electronics and controls supplied by ZTR. This helps achieve fuel and maintenance savings and offers environmental benefits allowing the hybrid-electric “mother-slug” to operate in single engine, battery charging or electric only modes.

As the new locomotives will be used chiefly for yard operations, the engineless slug increases traction motors available to the locomotive, boosting the pulling and braking power that is key for this kind of work.

“ZTR is proud of our long-standing relationship with Union Pacific and excited to partner with them on this hybrid-electric locomotive development,” said ZTR Control Systems President Derek Shipley. “This investment aligns well with our ongoing goal to leverage ZTR’s technical expertise to support railways in their decarbonization and efficiency improvement efforts. This initial hybrid-electric mother-slug application will be the basis of our design for future hybrid-electric, long-haul and fully electric solutions.”

Union Pacific began rolling out “mother-slug” sets with ZTR’s Nexsys control systems in 2017 and currently operates more than 65 in yards systemwide. Depending on the mode of operation, fuel savings and greenhouse gas emission reductions could total up to 80%.
Railroads already are one of the most fuel-efficient means of transportation. Moving freight by rail instead of truck reduces GHG emissions by up to 75%. On average, Union Pacific moves a ton of freight 463 miles on a single gallon of diesel fuel.

Union Pacific published its first comprehensive Climate Action Plan in December 2021, outlining its efforts to significantly reduce emissions within its operations. As part of that commitment, Union Pacific will reduce absolute Scope 1 and 2 GHG emissions 26% by 2030 and achieve net zero greenhouse gas emissions by 2050.

Earlier this year, Union Pacific announced a historic agreement with Wabtec Corporation for 600 locomotive modernizations, the largest investment in modernized locomotives in rail industry history valued at more than $1 billion, as well as the purchase of the world’s largest carrier-owned battery-electric locomotive fleet.

About Union Pacific

Union Pacific (NYSE: UNP) delivers the goods families and businesses use every day with safe, reliable and efficient service. Operating in 23 western states, the company connects its customers and communities to the global economy. Trains are the most environmentally responsible way to move freight, helping Union Pacific protect future generations. More information about Union Pacific is available at

Union Pacific Media Contact: Kristen South at 402-544-3435 or

About ZTR

ZTR is globally recognized technology company that supports locomotive and rail car owners in modernizing their fleets to reduce fuel consumption, avoid emissions, increase efficiency and extend asset life. ZTR is a leading supplier of advanced control systems, intelligent starting technologies, fuel management systems, energy management systems and Railway IoT solutions for Locomotives, Rail Car and Maintenance of Way equipment. More information on ZTR Control Systems is available at

ZTR Media Contact: James Greenhill at

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