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
- Tremont Street Subway approaching the Pleasant Street Incline in Boston, Massachusetts.
- Cogload Junction near Taunton, UK. Connects two InterCity 125 lines.
- Weaver Junction near Dutton, Cheshire, UK (map)
- Aynho Junction in Aynho, Northamptonshire, UK
- Central Station in Sydney, Australia
- Camberwell railway station in Melbourne, Australia
- Flying Junctions along the New York-Washington section of the Northeast Corridor, and the Philadelphia-Harrisburg section of the Keystone Corridor, both converging together at Zoo Interlocking near 30th Street Station in Philadelphia. All were built by the former Pennsylvania Railroad and are now maintained by Amtrak. 39°58′15″N 75°11′55″W / 39.97086°N 75.19848°W
- 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).
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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