Flying junction.html |
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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.
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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 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
- Cogload Junction near Taunton, UK. Connects two double-track fast lines.
- Weaver Junction near Dutton, Cheshire, UK (map)
- Aynho Junction in Aynho, Northamptonshire, UK
- Central Station in Sydney, Australia
- TGV 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).
See also
External links
- WikiMapia link - aerial photo of Fretin triangle (mentioned above)
- Photo link - flying junction on Pennsylvania Railroad north of 30th Street Station, Philadelphia, Pennsylvania, United States
- Photo link - simpler flying junction at terminus of Market-Frankford transit line, 69th Street Station, Philadelphia, Pennsylvania, United States
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