Many railroads converted the popular President's Conference Committee (PCC) streetcars to run on non-trolley wire right-of-way. They installed a small diesel engine to provide the electric power to drive the electric motors powering the axles, then they removed the trolley poles and used the shroud on the roof for the diesel engine exhaust. Some were very well known such as those used on the New Haven, other roads just used them on branch lines. In some areas they were nicknamed critters as they often were just one of a kind on a particular railroad. Other roads used them in Maintenance-of-Way Service.
Models feature all-wheel drive, a five-pole motor, an interior with working lights and authentic paint schemes.