Hopper car

A hopper car (US) or hopper wagon (UIC) is a type of railroad freight car that has opening doors on the underside or on the sides to discharge its cargo. They are used to transport loose solid bulk commodities such as coal, ore, grain, and track ballast.^[2][3][4] The hopper car was developed in parallel with the development of automated handling of such commodities, with automated loading and unloading facilities.

Hopper cars are distinguished from gondola cars, which do not have opening doors on their underside or sides. Gondola cars are simpler and more compact because sloping ends are not required, but a rotary car dumper is required to unload them. Some "dual-purpose" hoppers have a rotary coupler on one or both ends, so they can be used in both rotary and bottom-dump operations.