Flying junction

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Flying junction: with a bridge, trains do not block each other

A flying junction or flyover is a railway junction at which one or more diverging or converging tracks in a multiple-track route cross other tracks on the route by bridge to avoid conflict with other train movements. A more technical term is "grade-separated junction". A burrowing junction or dive-under occurs where the diverging line passes below the main line.

The alternative to grade separation is a level junction or flat junction, where tracks cross at grade, and conflicting routes must be protected by interlocked signals.

Complexity[edit]

Fretin triangle, France: Each side is over 3 km (2 mi) long. A grade-separated wye. TGVs and Eurostars cross it at 300 km/h (186 mph)

Simple flying junctions may have a single track pass over or under other tracks to avoid conflict, while complex flying junctions may have an elaborate infrastructure to allow multiple routings among a variety of tracks without trains coming into conflict, in the manner of a highway stack interchange.

Flying junction without crossings[edit]

In some cases, when two lines each of two tracks merge with a flying junction, they become a four track railway together. This happens regularly in the Netherlands (see #Examples below).

High-speed rail[edit]

Nearly all junctions leaving or joining high-speed railways are grade-separated. On the French TGV high-speed network, the principal junction on the LGV Sud-Est at Pasilly where the line to Dijon diverges from the line to Lyon, and the junction on the LGV Atlantique at Courtalain where the line to Le Mans diverges from the line to Tours, are both fully grade-separated junctions equipped with special high-speed switches (points in British terminology) which permit the normal linespeed of 300 km/h (186 mph) along the direction of the mainline, and a diverging speed of 220 km/h (137 mph).[1]

The French LGV (Lignes à Grande Vitesse) network is large enough to contain four fully grade-separated high-speed triangles: Fretin (near Lille), Coubert (south-east Paris), Massy (south-west Paris) and Angles (Avignon). A fifth triangle, Vémars (north-east Paris) is grade-separated except for a single-track link on the least-commonly used side (southern end linking Paris Gare du Nord to Paris CDG airport).

Examples[edit]

Australia
Canada
  • West Toronto Diamond in the Union Station Corridor
Denmark
France (LGV Triangles)
  • Triangle de Fretin, Lille, France. Connecting Paris, Brussels and London. (map)
  • Triangle de Coubert, Paris, France. (map)
  • Triangle des Angles, Avignon, France. With two parallel 1.5 km (0.93 mi) viaducts. (map)
  • "Triangle de Messy", Paris, France. Partial four-way junction. (map)
  • Triangle de Vémars, Paris, France. (map).
Germany
Netherlands
Flying junctions flank both ends of Weesp railway station

There are between 25 and about 40 flying junctions on Dutch national railways, depending on how one counts the more complex examples.

Flying junctions where the merged lines become a four track railway:

More complex flying junctions, with tracks from four directions joining:

United Kingdom
Taiwan
United States of America
The Uptown Hudson Tubes in Jersey City, New Jersey were built c 1910.
Flying junction on the Tremont Street Subway approaching the Pleasant Street Incline in Boston, Massachusetts.

See also[edit]

References[edit]

External links[edit]