Classification yard

Flat yards, built on level ground, allow freight cars to coast to the desired location after receiving a push by a locomotive. ==Gravity==

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. They 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 labor was becoming increasingly expensive. Thus, only a few gravity yards were ever built, sometimes requiring massive earthwork (one example is the first German gravity yard at Dresden). The historic technique of a gravity yard is today partly presented in Chemnitz-Hilbersdorf gravity yard (museum). Most gravity yards were built in Germany (especially in the kingdom of Saxony) and Great Britain (such as Edgehill, 1873), a few also in some other European countries, for example Łazy yard near Zawiercie on the Warsaw–Vienna Railway (in Poland). In the US, there were very few old gravity yards; one of the few gravity yards in operation today is CSX's Readville Yard south of Boston, Massachusetts. ==Hump==

Hump yards are the largest and most effective classification yards, with the largest shunting capacity, often several thousand cars a day. They work similarly to gravity yards, but the falling gradient is limited to a small part of the yard, namely the hump. It is the heart of the yard—a lead track on a small hill over which an engine pushes the cars. Single cars, or a block of coupled cars, are uncoupled at or just before the crest of the hump and roll by gravity onto their destination tracks in the area of the yard where the cars are sorted, called the classification bowl. The first hump in Germany (Leipzig) was built in 1858 and in France (Saint-Etienne) in 1863. grip the sides of the wheels on passing cars to slow them down. The speed of the cars rolling down from the hump into the classification bowl must be regulated according to whether they are full or empty, heavy or light freight, varying number of axles, whether there are few or many cars on the classification tracks, and varying weather conditions, including temperature, wind speed, and direction. In regard to speed regulation, there are two types of hump yards—with or without mechanization by retarders. In the old non-retarder yards, braking was usually done in Europe by railroaders who laid skates onto the tracks. The skate or wheel chock was manually (or, in rare cases, mechanically) placed on one or both of the rails so that the treadles or rims of the wheel or wheels caused frictional retardation and resulted in the halting of the railway car. In the United States, riders in cars did this braking. In modern retarder yards, this work is done by mechanized "rail brakes," called retarders, which brake cars by gripping their wheels. They are operated either pneumatically or hydraulically. Pneumatic systems are prevalent in the United States, France, Belgium, Russia and China, while hydraulic systems are used in Germany, Italy and the Netherlands. Classification bowls in Europe typically consist of 20 to 40 tracks, divided into several fans or balloons of tracks, usually with eight classification tracks following a retarder in each one, often 32 tracks altogether. In the United States, many classification bowls have more than 40 tracks, frequently divided into six to ten classification tracks in each balloon loop. towerman operates the retarders at Proviso Yard in Chicago, Illinois (1943) Bailey Yard in North Platte, Nebraska, United States, the world's largest classification yard, is a hump yard. Other large American hump yards include Argentine Yard in Kansas City, Kansas, Robert Young Yard in Elkhart, Indiana, Clearing Yard in Chicago, Illinois, Englewood Yard in Houston, Texas, and Waycross Rice Yard in Waycross, Georgia. Notably, in Europe, Russia, and China, all major classification yards are hump yards. Europe's largest hump yard is that of Maschen near Hamburg, Germany; it is only slightly smaller than Bailey Yard. The second largest is in the port of Antwerp, Belgium. Most hump yards are single yards with one classification bowl, but some, mostly very large, hump yards have two of them, one for each direction, and thus are double yards, such as the Maschen, Antwerp, Clearing, and Bailey yards. Almost all gravity yards have been retrofitted with humps and are worked as hump yards. Examples include Chemnitz Hilbersdorf (today Saxon Railway Museum), Dresden Friedrichstadt and Nürnberg (Nuremberg) Rbf (Rbf: Rangierbahnhof, "classification yard"), in Germany. ==Unique locomotives==

Hump yards sometimes require purpose-built or adapted shunting locomotives (US:switchers) if the chassis of mainline locomotives are so long that they cannot clear the railheads over the hump. British Rail, for example, permanently coupled pairs of Class 08 diesel shunting locomotives to achieve the required tractive effort. In a classic master and slave (US: cow and calf) configuration, the slave unit had its cab removed and both units received added weight to improve traction. Special locomotives for hump yards in the US include the EMD TR family. ==Image gallery==

File:Kornwestheim Ablaufberg 20060318.jpg|A switcher locomotive pushing a car over the hump at Kornwestheim yard File:MannheimRangierbahnhof 2018-08-10 Luftbild.jpg|Mannheim Rangierbahnhof, Germany, two-sided nearly symmetrical systems for opposing directions File:Trainyard.bradleygee.jpg|North Yard in Denver, Colorado, a typical U.S. classification yard in 2009 File:CNW yard, Chicago.jpg|Chicago and North Western Railway's Proviso Yard in Chicago, Illinois, December 1942 File:201805 Nanxiang Station Yard III.jpg|Nanxiang Classification Yard in Shanghai, China ==See also==