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Ajunction, in the context ofrail transport, is a place at which two or more rail routes converge or diverge. The physical connection between the tracks of the two routes (assuming they are of the same gauge) is provided byturnouts (US:switches) andsignalling.[1]
In a simple case where two routes with one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to allow trains to transfer from one route to the other. More complicated junctions are needed to permit trains to travel in either direction after joining the new route – for example by providing a triangular track layout.[note 1]
Rail transport operations refer tostations that lie on or near a railway junction as ajunction station. In the UK it is customary for the junction (and the related station) to be named after the next station on the branch, e.g.Yeovil Junction is on the mainline railway south ofYeovil, and the next destination on the branch isYeovil Pen Mill. Frequently, trains are built up and taken apart (separated) at such stations so that the same train can be divided and proceed to multiple destinations. Forgoods trains (US: freight trains), marshalling yards (US:Classification yards) serve a similar purpose.
The capacity of the junctions limits the capacity of arailway network more than the capacity of individualrailway lines. This applies more as the network density increases. Measures to improve junctions are often more useful than building new railway lines. The capacity of a railway junction can be increased with improvedsignaling measures, by building points suitable for higher speeds, or by turninglevel junctions intoflying junctions, where tracks aregrade-separated, and so one track passes over or under another.[2] With more complicated junctions such construction can rapidly become very expensive, especially if space is restricted bytunnels,bridges or inner-city tracks.
The installation of junctions into a rail system poses many challenges, including increased maintenance costs, and problems in on-time performance.Metro rail systems have a rail network design where the number of junctions is minimized. Passengers, and not trains, move from onetrain station to another.
Media related toRail junctions at Wikimedia Commons