It has been 50 years since American railroads began phasing out steam locomotives and replacing them with more efficient diesel power. A similar evolution may be about to occur.

The Union Pacific Railroad Co. (Omaha, NE) has been testing a hybrid, battery-powered switcher in its vast Chicago railyards to determine if it is a feasible alternative to conventional diesel-electric locomotives. The hybrid switcher is called the “Green Goat,” because “goat” in railroad slang refers to a locomotive used in railyards.

The electric traction motors on the axles are powered by a large bank of custom-designed lead acid batteries. The batteries are kept charged by a small generator driven by a 130-hp diesel engine.

“The Green Goat test is an opportunity for us to try a novel technological approach in our never-ending search for an alternative fuel for locomotives,” says Mike Iden, general director of car and locomotive engineering at Union Pacific. He claims the new technology promises to be cheaper to purchase, cheaper to run and cheaper to maintain, while producing considerably less pollutants than today’s standard diesel switchers. The experimental locomotive could also reduce the emissions of nitrogen oxides (NOx) by as much as 90 percent.

“Hybrid power technology has already demonstrated, in automotive applications, its ability to perform more economically and reduce emissions,” adds Frank Donnelly, chief technology officer of RailPower Technologies Corp. (North Vancouver, BC), the manufacturer of the switcher. “The Green Goat locomotive, we believe, can provide a similar opportunity for the railroads, but at a comparatively better economic entry point than was initially experienced by the automotive industry.”

Union Pacific began testing the green locomotive at its Roseville, CA, railyard last year. The locomotive was moved to Chicago for cooler weather testing in January.

Donnelly claims the batteries in the hybrid switcher produce the same amount of energy as a locomotive powered by an electrical generator attached to a 2,000-hp diesel engine, which is used primarily in railyards. Typically, 3,000 to 4,400-hp locomotives are used to pull freight trains between cities.

While the diesel only runs as required to keep the batteries at the desired state of charge, power is always available without delay from the batteries. “Since the load of the diesel-generator doesn’t vary—it’s always charging the same batteries—during the periods when it is running, it runs at a constant speed, and thus can be tuned to be very efficient,” Iden points out. “The result, compared to a conventional diesel-electric switcher, is a much quieter and more efficient locomotive that produces much less pollution.”

The Green Goat’s outward appearance also sets it apart. The locomotive is built on a conventional GP9 frame. Its hood has been chopped, giving excellent visibility in all directions. “The batteries take up the majority of the space under the long hood,” says Iden, “with a small space left over for the prime mover and generator.”