Editing Classification yard (section)

==<span class="anchor" id="Hump yard"></span>Hump==
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[[File:UP DO NOT HUMP.jpg|thumb|Not all cars can be sent over a classification hump. This Union Pacific track maintenance vehicle is permanently labeled "Do not hump" because it is not designed to withstand hump sorting.]]

'''Hump yards''' are the largest and most effective classification yards, with the largest [[Shunting (rail)|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.<ref>{{cite magazine |title=ABC's of Railroading: Terms of the Trade |magazine=[[Trains (magazine)|Trains]] |date=June 1991 |page=22 |publisher=Kalmbach Publishing |location=Waukesha, Wisconsin |issn=0041-0934 }}</ref> The first hump in Germany (Leipzig) was built in 1858 and in France (Saint-Etienne) in 1863. 

[[File:Balkenbremse1.JPG|thumb|upright|The [[Retarder (railroad)|retarders]] 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 [[Retarder (railroad)|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 [[Pneumatics|pneumatically]] or [[Hydraulics|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]].<ref>{{cite book |title=Rangierdienst A-Z |publisher=VEB Transpress-Verlag |location=Berlin |date=1986 }}</ref>

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.

[[File:Proviso hump towerman.jpg|thumb|left|upright|A [[Chicago and North Western Railway|CNW]] 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]], [[Belt Railway of Chicago|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 Marshalling Yard|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.{{Citation needed|date=April 2023}}

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.
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