freight car, railroad car designed to carry cargo. Early freight cars were made largely of wood. All-steel cars were introduced by about 1896 and within 30 years had almost completely replaced the wooden variety. Modern freight cars vary widely in shape and size, but virtually all of them evolved from three basic types that had been in use since the early 1800s: the open-top car, the boxcar, and the flatcar.
Open-top cars may be either gondola or hopper cars. Hoppers are used to haul bulk freight such as coal, gravel, and grain; they have either several discharge hatches or a collapsible bottom for rapid unloading. Gondola cars have fixed bottoms and must be unloaded from above with the help of a crane; they are used to transport manufactured goods. Boxcars are enclosed cars with sliding doors on the sides; they serve to transport manufactured goods requiring protection from the weather and pilferage. Certain types of boxcars, known as refrigerator cars, are heavily insulated and specially cooled to convey fresh or frozen foods over long distances. Another variation of the common boxcar is the stock car with slatted sides, which is used to transport cattle, sheep, and other livestock. The flatcar has long been utilized for hauling heavy construction machinery and military equipment. During the 1950s British Railways and various other European railroad companies developed high-capacity flatcars suitable for carrying huge demountable containers filled with a variety of cargoes and standardized for use on container ships and flatbed trailers as well. About the same time, American railroads introduced the piggyback car, a flatcar modified to hold as many as two truck trailers in place. Later piggyback-car designs utilized double-stacked trailers on interconnected flatcars. The two-level and three-level rack cars widely used in the United States and Canada for conveying new automobiles are also examples of redesigned flatcars. A similar innovation is the transporter wagon, or car van, employed by some continental European and American passenger trains to haul the automobiles of touring motorists who wish to travel part way by rail. One other specialized freight car is the cylindrically shaped tank car constructed to carry a variety of liquids, including industrial chemicals.