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One approach to this wye has been abandoned, but it and the two remaining legs are still visible.

Double track triangle, drawn in one-rail style

A wye in North American railroad terminology, known as a triangle in English language terminology outside North America, is a triangular shaped arrangement of tracks with a switch at each corner. With a sufficiently long track leading away from each corner, a train of any length can be turned.

Turning is required for any directional piece of railroad equipment, such as most steam locomotives, or indeed many passenger trains, especially those that have a dedicated tail end car such as an observation car.

Individual locomotives and railroad cars can be turned on a turntable, but obviously whole trains cannot. A wye or a loop are the only ways of doing that.

Railroads in North America have more wyes than railroads elsewhere, and North American locomotives and cars are much more likely to be directional than those elsewhere. This is due to the fact that in most places in Canada and the United States, the railroad came first, or at least early, and therefore builders had much more freedom to lay down tracks where they wanted. Similarly, at many rural railway locations in Australia, triangles were also used as an alternative to turntables for much the same reason. In Europe, extensive use was made historically of bi-directional tank locomotives and push-pull trains, and more recently most diesel locomotives and electric locomotives ordered in Europe have been fully bi-directional.

Sefton railway station, Sydney, lies on one corner of a triangular junction. The triangle junction allows trains to branch off in either direction, without the need to terminate or change end. One train a day from Birrong to Sefton does terminate at Regents Park station, in order to clean the rust off the crossover rails. There is also a goods branch from Chullora, and a proposed separate single track freight line. The three passenger stations at the vertices of the triangle have island platforms which makes it convenient to change trains. The sharp curves of the triangle and especially the turnouts on those sharp curves restrict train speeds to between 10 km/h and 50 km/h.

The Keddie Wye in Keddie, California, was built by the Western Pacific Railroad and is a remarkable engineering feat. Two sides of the wye are built on tall trestles and one side is a tunnel bored through solid rock.

There are a number of British examples, including the one known as the Maindee triangle in Newport, South Wales. Here the ex-GWR South Wales mainline from London to Swansea is joined by another GWR line from Shrewsbury via Hereford. The significance of it is that steam-hauled trains can run to Newport and their engines be turned using the triangle. Its OS National Grid location is grid reference ST316887. Shrewsbury also has a triangular route formation that was used to turn steam locomotives, and is still available.

Tsumeb railway station in Namibia has two triangles. The first and smaller one is for turning engines. The second and larger one is to bypass the deadend station at Tsumeb for trains travelling directly between the new extension towards Angola and Windhoek. [1] This direct bypass line could save 60 minutes shunting time, particular if the train were longer than the loops in the station.

The earliest British (and possibly worldwide) example is the double-tracked triangle within Earlestown railway station on the Liverpool and Manchester Railway, which was completed by the Grand Junction Railway in 1837. The triangle has two passenger platform faces on each of its three sides and five of the six platforms are in frequent (half-hourly etc) use by passenger trains. When steam engines were in regular use the triangle (which is of course also traversed by freight trains) was also used to turn locomotives and could still be so used.

The land within a triangle tends to be cut off from the adjacent suburbs, and has marginal value, mainly for railway uses, such as maintenance depots. The triangular shape tends to be unsuited for rectangular buildings. On electrified lines, substations tend to be located inside triangles, in part because the land is cheap, and also because it provides the most convenient and flexible sectioning arrangements. Indeed Sefton triangle contains such a substation. Because it is difficult to see approaching trains, the Sefton triangle depot has a level crossing protected by flashing lights.

• Winnersh Triangle railway station