A hopper car with an open top for loading by conveyor or chute and bottom gates for discharge, used primarily for bulk commodities that do not require weather protection such as coal, aggregate, and ore. Open hoppers are heavier-duty than covered hoppers and are built to handle dense, abrasive materials. They dominate the coal and aggregates markets.
A closed-top hopper car with roof hatches for top loading and bottom discharge gates for gravity unloading, designed for dry bulk commodities such as grain, fertilizer, plastic pellets, and cement. Covered hoppers protect lading from moisture and contamination. They are the most numerous car type on North American railroads.
An open-top car with fixed sides and ends, used for heavy bulk commodities such as scrap metal, steel coils, pipe, and coal. Gondolas are loaded from the top and typically unloaded by crane, magnet, or rotary dumper. Coil gondolas have a curved floor to cradle steel coils securely.
A train composed entirely of cars carrying the same commodity between a single origin and a single destination, running as a dedicated shuttle. Unit trains eliminate intermediate classification, reducing transit time and cost. Common examples include coal trains, grain trains, and crude oil trains.