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freight train composed of cars carrying a single type of commodity that are all bound for the same destination. By hauling only one kind of freight for one destination, a unit train does not need to switch cars at various intermediate junctions and so can make nonstop runs between two terminals. This reduces not only the shipping time but also the cost. The unit train was introduced by American railroad companies in the 1950s so that they could offer lower shipping rates and thereby make their freight service more marketable. Initially, unit trains were used primarily to haul coal from mines to power plants. By the late 20th century about 50 percent of the coal shipped in the United States was carried by these trains. Other forms of bulk cargo, such as grain and cement, were also transported in this fashion.