Fox Valley Models HO Scale USRA 55-Ton 2-Bay Open Hopper, Northern Pacific/NP

Beginning with steam locomotives, railroads needed a way to transport the black diamond of fuel: coal. While gondolas could do the job, specially designed cars were developed in the late 1800s to haul the commodity. As a result, coal hoppers would become one of the most numerous types of cars built. Their specific purpose was to bring coal from the mines to the end customers – railroads, factories and coal yards for home delivery. 

Coal hoppers had a basic design of a large open top area for loading, slope sheets on the interior to aid in unloading, and bays at the bottom with door that would open to quickly unload a car. From there, designers always tried to find a way to increase capacity from a basic design.

When America's railroads were nationalized during World War I, the United States Railroad Administration (USRA) created a series of standardized freight cars. One of the most popular designs was the 55-Ton all-steel open hopper, of which 22,000 were produced. After the war, the USRA adopted the design as its standard practice, and near-clones were built by the tens of thousands – the majority of which worked long enough to be seen through the 1960s and early 1970s.