The basic railroad freight car, the box car, is used to haul many kinds of general non-bulk cargo. Originally built with wood sides, current box cars are now entirely steel-sided. The standard size of the box until the 1980s was 40 feet, but later cars crew to 50 feet. The 89-foot "Hi-Cube" car first used in the 1960s was especially designed for the auto industry to carry car parts.
Flatcars were the original freight cars when railroads first began running in the early 19th century. A wide variety of cargo could be loaded onto a flat car, tied down and hauled away. They serve the same purpose today, though their lengths and specialty designs have increased. Their specialty purposes began in the 1950s when railroads began "piggyback" service by using flatcars to carry trailers to distant cities where they were unloaded and hooked to a truck for a local trips. The piggyback service has evolved into hauling container freight as a link in a three-part transportation system, from ship to train to truck.
Similar to a flat car, but with partial sides, gondola cars are used to haul scrap metal, rolled steal, gravel, large crates, machinery and other general commodities.
Hopper cars are used to carry bulk freight exclusively. Hoppers have sloped drop-bottom chutes that allow for discharge of aggregates such as coal, iron ore or gravel by gravity into a receiving bin below the tracks. One specialty type of hopper, known by the musical pun "coal porter," has rotary couplers so that when placed in an unloading position, the car is rotated to dump its cargo without disconnecting from the rest of the train. Covered hoppers are used to carry bulk cargo that needs to be protected from the elements.
The tank car is a rolling cylindrical tank used to carry all types of bulk liquids, from chemicals and fuels to corn syrup for food processing.
Some railroad freight cars are meant to handle one specific type of cargo. The autorack, used to transport automobiles from the factory, is an example. These tall, enclosed cars with swinging doors and ramps on either end allow a whole train to be loaded in one operation without switching of cars. The autos, driven in from one end of the train, are stored on two or three levels of racks. Other types of specialty railroad cars are designed for heavy or over-sized machinery, or to haul the rails themselves to be laid further up the track.
The caboose is the railroad car perhaps treated with the most nostalgia by the general public. In the past, the red caboose was a railroad car seen at the end of every train, carrying brakemen and conductors who kept watch and protected the train during its travels. Cabooses are no longer seen on regular freight trains as the development of sensors and signaling devices made caboose crews obsolete in most situations.
