FREIGHT CARS. Freight cars, also known as rolling stock, have always been used to handle the bulk of business for railroads. Cargo moving in boxcars, coal moving in hoppers, oils and liquids moving in tank cars and machinery or other big loads moving on flatcars were, and are longtime mainstays of railroads. In the modern era, covered hoppers loaded with grain and chemicals; auto racks moving autos and trucks; long flatcars carrying trailers and intermodal well cars double-stacked with