Flying junction

Flying junction

A flying junction 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 is 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

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.

High-speed rail

Nearly all junctions leaving or joining high-speed railways are grade-separated. On the French LGV high-speed network, junctions allow 300 km/h+ (normal linespeed) along the direction of the mainline, and a limit of 160 km/h for the diverging path.

The LGV network is large enough to contain four fully grade-separated high-speed triangles: Fretin (Lille), Coubert (south-east Paris), Massy (south-west Paris) and Angles (Avignon). A fourth 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

* Weaver Junction near Dutton, Cheshire, UK [http://maps.google.co.uk/?ie=UTF8&ll=53.300595,-2.63762&spn=0.009105,0.019956&t=k&z=16&om=1]
* Aynho Junction in Aynho, Northamptonshire, UK
* Central Station in Sydney, Australia;TGV Triangles
* Triangle de Fretin, Lille, France. Connecting Paris, Brussels and London. [http://maps.google.co.uk/?t=k&ll=50.57,3.145&z=14]
* Triangle de Coubert, Paris, France. [http://maps.google.co.uk/?t=k&ll=48.693,2.721&z=14]
* Triangle des Angles, Avignon, France. With two parallel 1.5km viaducts. [http://maps.google.co.uk/?t=k&ll=43.946,4.741&z=14]
* "Triangle de Messy" , Paris, France. Partial four-way junction. [http://maps.google.co.uk/maps?t=k&ll=48.951,2.715&z=14]
* Triangle de Vémars, Paris, France. [http://maps.google.co.uk/?t=k&ll=49.055,2.565&z=14] .

ee also

*Double junction
*Interchange (road)

External links

* [http://local.live.com/default.aspx?v=2&cp=39.968157~-75.195093&style=o&lvl=1&scene=1915422 Photo link - flying junction on Pennsylvania Railroad north of 30th Street Station, Philadelphia, Pennsylvania, United States]
* [http://local.live.com/default.aspx?v=2&cp=39.962832~-75.2613&style=o&lvl=1&scene=1891525 Photo link - simpler flying junction at terminus of Market-Frankford transit line, 69th Street Station, Philadelphia, Pennsylvania, United States]


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