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. Union Pacific converts this way to 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 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.
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.