Built in 1912 at the Pennsylvania Railroad Altoona shops, the prototype battery-powered tractors served the Pennsylvania Railroad in Baltimore, MD and Jersey City, NJ, moving box cars in narrow city streets where standard locomotives could not be used. This model represents the switcher as it appeared from about the late 1920s to the early 1950s. The switchers before and after this time period featured different wheels and tires. Modifications in the mid-1950s also included conversion from electric to gas, when a large exhaust pipe was added to the roof. These tractors were often seen caked in heavy layers of dust, mud and grime, especially on the wheels and spokes.
Learn more about the prototype at http://prr.railfan.net/RubberTiredSwitchers.html.
Instructions available at http://www.americanarchetypemodels.com. Wire handrails and other small details are not included, but the instructions explain how to add them.