In US railroad terminology, a gondola is an open-topped rail vehicle used for transporting loose bulk materials. Because of their low side walls, gondolas are also suitable for the carriage of such high-density cargos as steel plates or coils, or of bulky items such as prefabricated sections of rail track. Gondolas are distinct from hopper cars in that they do not have doors on their floor to empty cargo. In Australia these wagons are called open wagons. History The first gondola cars in North America were developed in the 1830s, and used primarily to carry coal. Early gondolas were little more than flatcars with wooden sides added, and were typically small – or less in length, and or less in weight. These cars were not widely used at first, as they could only be unloaded by workers shoveling out their cargo by hand, a slow and labor-intensive process. A solution for this problem was developed around the 1860s with the drop-bottom gondola, which had hatches installed in the floor which could be opened at a destination, with workers using shovels to direct cargo towards the hatches. This was an improvement over earlier gondolas, but still required manual unloading. After the American Civil War, advances in technology, especially the development of steel, allowed new and larger gondola designs. New gondolas built with steel sides and frames (though wood was retained for flooring, since it was flexible and cheap to replace) were often built to lengths between , and gradually increased in capacity from around to as much as by the early to mid 20th century. Gondolas began to be built for specialized purposes; depending on their intended cargo, the side heights could range from just for bulk commodities like sand, to or more for loads such as pipes, , or more for light cargos like woodchips. Covered gondolas were also developed for cargos that had to be protected from the elements, such as food and freshly made steel. Starting in the 1950s and 1960s, high-sided gondolas were used for coal, thanks to stronger car construction and the invention of rotary car dumpers, which allowed these gondolas to be emptied automatically. Specialized car types "Bathtub" gondolas In the second half of the 20th century, coal haulage shifted from open hopper cars to high-sided gondolas. Using a gondola, the railroads are able to haul a larger amount of coal per car since gondolas