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Concept
Classification yard
Summary
A classification yard (American English, as well as the Canadian National Railway), marshalling yard (British, Hong Kong, Indian, and Australian English, as well as the Canadian Pacific Railway) or shunting yard (Central Europe) is a railway yard found at some freight train stations, used to separate railway cars onto one of several tracks. First the cars are taken to a track, sometimes called a lead or a drill. From there the cars are sent through a series of switches called a ladder onto the classification tracks. Larger yards tend to put the lead on an artificially built hill called a hump to use the force of gravity to propel the cars through the ladder.
Freight trains that consist of isolated cars must be made into trains and divided according to their destinations. Thus the cars must be shunted several times along their route in contrast to a unit train, which carries, for example, automobiles from the plant to a port, or coal from a mine to the power plant. This shunting is done partly at the starting and final destinations and partly (for long-distance-hauling) in classification yards.
Flat yards are constructed on flat ground, or on a gentle slope, not enough to allow a free-fall operation without locomotives. Freight cars are pushed by a locomotive and coast to their required location.
Gravity yards were invented in the 19th century, saving shunting engines and instead letting the cars roll by gravity was seen as a major benefit, whereas the larger amount of manual work required to stop the rolling cars in the classification tracks was judged to be not that important. Gravity yards were a historical step in the development of classification yards and were later judged as inferior to hump yards, because it became clear that shunting engines were needed anyway (at least in inclement weather like strong winds or icy temperatures when the oil in the bearings became thick), and because manual labour was getting relatively more and more expensive.
Official source
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