Editing Flying junction

{{Short description|Type of railway junction}}
{{Refimprove|date=June 2011}}
[[Image:Flying-junction-both-tracks.svg|thumb|right|300px|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 separation|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 intersection|at grade]], and conflicting routes must be protected by interlocked [[railway signal|signal]]s.

==Complexity==
[[File:Fretin-triangle-diagram.svg|thumb|right|300px|Fretin triangle in France: Each side is more than {{convert|3|km|mi|abbr=on|sigfig=1}} long. A grade-separated [[Wye (rail)|wye]]. [[TGV]] and [[Eurostar]] trains cross the junction at {{convert|300|km/h|mph|abbr=on|sigfig=3}}.]]
Simple flying junctions may have a single track pass over or under other tracks to avoid conflict; complex flying junctions may have elaborate [[infrastructure]] to allow multiple routings without trains coming into conflict, in the manner of a highway [[stack interchange]].

==Flying junction without crossings==
Where two lines each of two tracks merge with a flying junction, they can become a [[Quadruple-track railway|four-track railway]] together, the tracks paired by direction. This happens regularly in the Netherlands (see [[#Examples|Examples]] below).

==High-speed rail==
Nearly all junctions with [[high-speed rail]]ways are grade-separated. On the French [[Lignes à Grande Vitesse]] ([[TGV#Tracks|TGV]]) high-speed network, the principal junction on the [[LGV Sud-Est]], at Pasilly where the line to Dijon diverges, and on the [[LGV Atlantique]] at Courtalain where the line to Le Mans diverges, are fully grade-separated with special high-speed switches (''points'' in British terminology) that permit the normal line speed of {{convert|300|km/h|mph|0|abbr=on}} on the main line, and a diverging speed of {{convert|220|km/h|mph|0|abbr=on}}.<ref group=note>See "[[:fr:Courtalain|Courtalain]]" on the French language Wikipedia.</ref> 

The LGV network has four grade-separated high-speed triangles: Fretin (near Lille), Coubert (southeast Paris), Claye-Souilly (northeast Paris) and Angles (Avignon).  A fifth, Vémars (northeast Paris), is grade-separated except for a single-track link on the least-used side, linking [[Paris Gare du Nord]] and [[Charles de Gaulle Airport|Paris CDG]] airport.

== Examples ==
;Australia
* [[Bowen Hills railway station]] in [[Brisbane]]
* [[Burnley railway station, Melbourne|Burnley railway station]] in [[Melbourne]]
* [[Camberwell railway station, Melbourne|Camberwell railway station]] in Melbourne
* [[Central railway station, Sydney|Sydney Central Station]]
* [[Glenfield railway station, Sydney]]
* [[Strathfield railway station]]
* [[Sandgate Flyover]], [[Newcastle, New South Wales|Newcastle]] – main line flies over coal branch line
* [[Goodwood railway station]] in [[Adelaide]]
* [[Bayswater railway station, Perth|Bayswater railway station]] in [[Perth]]

;Canada
[[File:Columbia flying junction.jpg|thumb|300px|Flying junction just east of [[Columbia station (SkyTrain)|Columbia station]] in [[New Westminster]] in Canada]]
* [[Columbia station (SkyTrain)|Columbia station]] in New Westminster, BC – [[Expo Line (SkyTrain)|Expo Line]] branches for [[King George station|King George]] (top) and [[Production Way–University station|Production Way–University]] (bottom)
* [[Bridgeport station (SkyTrain)|Bridgeport station]] in Richmond, BC – [[Canada Line]] branches for [[YVR–Airport station|YVR–Airport]] and [[Richmond–Brighouse station|Richmond–Brighouse]]

;Denmark
* Hvidovre, Copenhagen ({{coord|55.664158|N|12.483701|E|display=inline|region:DK_type:landmark}})
* Junction of M1 and M2 lines on the [[Copenhagen Metro]]
* Lunderskov ({{coord|55.473772|N|9.301164|E|display=inline|region:DK_type:landmark}})
* Roskilde, south of ({{coord|55.607374|N|12.046496|E|display=inline|region:DK_type:landmark}})
* Sydhavnen, Copenhagen ({{coord|55.641273|N|12.548343|E|display=inline|region:DK_type:landmark}})
* Vigerslev, Copenhagen ({{coord|55.657331|N|12.505050|E|display=inline|region:DK_type:landmark}})

'''Finland'''
* Railway junction of two main lines at Kytömaa, [[Kerava]]

;France (LGV Triangles)
* Triangle de Fretin, Lille, connecting Paris, Brussels and London
* Triangle de Coubert, Paris
* Triangle des Angles, Avignon, with two parallel {{convert|1.5|km|mi|adj=on}} viaducts
* Triangle de Claye-Souilly, Paris, partial four-way junction
* Triangle de Vémars, Paris
;Germany

*[[Bruchsal Rollenberg junction]]
;Hong Kong

* Where [[Airport Express (MTR)|Airport Express]] and [[Tung Chung line]] diverge from each other at [[Tai Ho Wan]]
* [[Tseung Kwan O line]] to the east of [[Tseung Kwan O station]]
;Netherlands
[[Image:Fork Gaasperdammerweg Aansluiting.svg|thumb|300px|Flying junctions flank both ends of [[Weesp railway station]]]]
There are between 25 and about 40 flying junctions on Dutch railways, depending on how more complex examples are counted.
* Near [[Harmelen]]. Before conversion to a flying junction, this was the site of the [[Harmelen train disaster]].
* At [[Breukelen railway station]]
* At [[Lage Zwaluwe railway station]]
Flying junctions where the merged lines become a four track railway:
* Near [[Den Haag Laan van NOI railway station]]
* North of [[Leiden]] where lines from [[Haarlem]] and [[Schiphol]] merge
* At [[Boxtel railway station]] where lines from [['s-Hertogenbosch]] and [[Tilburg]] merge
* West of [[Gouda, South Holland|Gouda]] where lines from [[Rotterdam]] and [[The Hague]] merge
More complex flying junctions, with tracks from four directions joining:
* Around [[Amsterdam Sloterdijk railway station]]
* Around [[Duivendrecht railway station]]
* Northwest exit of [[Utrecht Centraal railway station]]
* West and northwest exit of [[Rotterdam Centraal railway station]]
* At both sides of [[Weesp railway station]] (see diagram at right)

;Norway
* Lillestrøm ({{coord|59.952571|N|11.027455|E|display=inline|region:SE_type:landmark}})
* Lysaker ({{coord|59.914903|N|10.627711|E|display=inline|region:SE_type:landmark}})
* Sandvika, east of and west of ({{coord|59.896373|N|10.536113|E|display=inline|region:SE_type:landmark}}) ({{coord|59.890663|N|10.508148|E|display=inline|region:SE_type:landmark}})

;Sweden
* Flemingsberg ({{coord|59.214247|N|17.939363|E|display=inline|region:SE_type:landmark}})
* Järna, north of ({{coord|59.121566|N|17.613176|E|display=inline|region:SE_type:landmark}})
* Järna, south of ({{coord|59.071478|N|17.539807|E|display=inline|region:SE_type:landmark}})
* Lund ({{coord|55.712348|N|13.185570|E|display=inline|region:SE_type:landmark}})
* Hyllie ({{coord|55.558971|N|12.961761|E|display=inline|region:SE_type:landmark}})
* Myrbacken ({{coord|59.678161|N|17.826828|E|display=inline|region:SE_type:landmark}})
* Lernacken ({{coord|55.562779|N|12.931545|E|display=inline|region:SE_type:landmark}})
* Södertälje hamn ({{coord|59.181793|N|17.643503|E|display=inline|region:SE_type:landmark}})
* Södertälje syd ({{coord|59.159427|N|17.637278|E|display=inline|region:SE_type:landmark}})
* Tomteboda ({{coord|59.352646|N|18.015546|E|display=inline|region:SE_type:landmark}})

;Taiwan
* Start of [[Shalun line]], south of [[Zhongzhou railway station]]

;United Kingdom
* [[Pelaw Metro station | Pelaw]] Junction where both the [[Tyne and Wear Metro]] green line to [[South Hylton Metro station | South Hylton]] joins the [[Durham Coast Line]] and yellow line continues to [[South Shields Metro station | South Shields]] – both diverging on the bridge itself
* Springhead Junction on the [[North Kent Line]]
* Southfleet Junction on the [[High Speed 1|HS1]]
* [[Norton Bridge railway station|Norton Bridge Junction]] near Stone, Staffordshire
* [[Hamilton Square railway station|Hamilton Square underground station]], [[Birkenhead]], on [[Merseyrail]]
* [[Aynho Junction]] in [[Aynho]], [[Northamptonshire, England|Northamptonshire]]
* [[Worting Junction]] near [[Basingstoke]], [[Hampshire, England|Hampshire]] (the flyover is called Battledown Flyover)
* [[Cogload Junction]] near [[Taunton]]
* [[Weaver Junction]] near [[Dutton, Cheshire]]
* [[Shortlands_railway_station|Shortlands Junction]] in south London
* [[Harrow-on-the-Hill_station#Railway_geography|Northwest of Harrow-on-the-Hill]], in the north London suburbs
* [[Hitchin flyover]], [[Hertfordshire]].
* [[Werrington Dive Under|Werrington Junction dive-under]], northern suburbs of [[Peterborough railway station|Peterborough]], Cambridgeshire
* [[Reading railway station#2009–2015 redevelopment|Reading]] West Junction
* [[Bleach Green Viaduct]]s & Junction, [[Whiteabbey]], [[Northern Ireland]] 
* [[Manchester Metrolink]], [[Greater Manchester]], immediately southwest of [[Cornbrook tram stop]] where the [[Eccles Line]] diverges from the [[Altrincham Line]]. 

;United States
[[Image:PATH junction.jpg|thumb|upright|The [[Uptown Hudson Tubes]] in [[Jersey City, New Jersey]] were built {{Circa|1910}}.]]

[[Image:Zoo Substation. Philadelphia, Philadelphia Co., PA. Sec. 1101, MP 87.25. - Northeast Railroad Corridor, Amtrak route between Delaware-Pennsylvania and Pennsylvania-New Jersey HAER PA,51-PHILA,694-20.tif|thumb|[[Zoo Junction]] in Philadelphia in 1977]]

[[Image:Pleasant Street Incline junction.jpg|thumb|Flying junction on the [[Tremont Street subway]] approaching the [[Pleasant Street incline]] in [[Boston]]]]

* Northeast U.S. ([[Amtrak]])
** Along the [[New York City|New York]]–[[Washington, D.C.|Washington]] section of the [[Northeast Corridor]], and on the Philadelphia–[[Harrisburg, PA|Harrisburg]] section of the [[Keystone Corridor]]. Both converge at [[Zoo Junction]] near [[30th Street Station]] in Philadelphia.  All were built by the former [[Pennsylvania Railroad]] and are now maintained by Amtrak.
* [[Boston]], Massachusetts area
** An abandoned underground junction on the [[Tremont Street subway]] approaching the [[Pleasant Street incline]]
** The B branch splits off from the C and D branches of the [[MBTA]] [[Green Line (MBTA)|Green Line]] via an underground flying junction just west of [[Kenmore station]].
** The Union Square spur splits off from the [[Green Line Extension]] of the [[MBTA]] [[Green Line (MBTA)|Green Line]] via an aerial flying junction on the Red Bridge viaduct in the Inner Belt area of [[Somerville, Massachusetts]] just north of [[Lechmere station]] in Cambridge. Lead tracks to the GLX maintenance facility also split off from the junction slightly further west.
** The two southern branches of the [[MBTA]] [[Red Line (MBTA)|Red Line]] in Boston split via a flying junction just north of [[JFK/UMass station]].  In addition, lead tracks to Cabot Yard maintenance facilities branch off from the junction.
* [[Chicago]], Illinois
** On the [[Chicago "L"]], where [[Orange Line (CTA)|Orange Line]] trains diverge from [[Green Line (CTA)|Green Line]] trains north of 18th Street, as well as underground where a non-revenue flying junction separates [[Red Line (CTA)|Red Line]] trains heading to [[95th/Dan Ryan station|95th]] from those heading to the [[South Side main line (CTA)|South Side main line]], which is occasionally used for emergency reroutes to [[Ashland/63rd station|Ashland/63rd]].
**The [[Milwaukee–Dearborn subway]] (now part of the [[Blue Line (CTA)|Blue Line]]) was constructed to have a flying junction where turning between Lake Street and Milwaukee Avenue at Canal Street. The outbound tunnel and its stub, designed to continue west under Lake Street, was bored at less depth than the inbound tunnel and its Lake Street stub, in order to allow future Lake Street trains (now part of the [[Green Line (CTA)|Green]] and ([[Pink Line (CTA)|Pink Line]]s) to run under or over the opposing Milwaukee Avenue trains while entering or exiting the shared portion of the Lake Street tunnels. Plans in 1939 called for tunnels to replace the elevated Lake Street tracks east of approximately Racine Avenue.<ref>City of Chicago, Department of Subways and Traction, ''Second Annual Report of the Department of Subways and Traction, City of Chicago, for the Year Ending December 31, 1940'' (Chicago: City of Chicago, December 31, 1940).</ref><ref>Chicago Department of Subways and Traction, ''Comprehensive Plan'', 2-29, III-VII.</ref> By 1962, the planned Lake Street tunnels to/from Racine Avenue would have curved south to Randolph Street and bypassed the Milwaukee-Lake-Dearborn tunnel entirely.<ref>Chicago Transit Board, ''Plan for Expanding Rapid Transit Service in the Central Area of Chicago'' (Chicago: Chicago Transit Board, April 20, 1962).</ref>
** A flying junction immediately north of [[Belmont station (CTA North Side Main Line)|Belmont/Sheffield]] is used by [[Brown Line (CTA)|Brown Line]] trains to access the [[Ravenswood branch|Ravenswood Branch]] while avoiding crossing the Red Line and [[Purple Line (CTA)|Purple Line Express]] tracks.
* [[Denver]], Colorado
** On the [[Regional Transportation District]] in Denver between the Southeast Corridor and the I-225 Corridor: the Southeast Corridor is on the west side of I-25 and the I-225 Corridor is in the median of I-225. The grade separations of the junction are woven into the grade separations of the interchange between the two highways.
* [[New York City|New York]], New York
** On the [[New York City Subway]] there is an above-ground example at Hammel's Wye on the [[IND Rockaway Line]], as well as numerous below-ground examples across the network
** Connecting [[Metro-North Railroad]]'s [[New Haven Line]] and [[Harlem Line]], near [[Wakefield (Metro-North station)|Wakefield]] station in the [[Bronx]]
* [[Philadelphia]], Pennsylvania
** Amtrak's [[Zoo Junction]], where the [[Northeast Corridor]] meets the [[Keystone Corridor]] and sorts into [[30th Street Station]]'s lower and upper level platforms. Also known as Zoo Interlocking, the name comes from the [[Philadelphia Zoo]], which is located in the crescent shaped pocket between the junction and the river.
** On [[SEPTA|SEPTA's]] [[Cynwyd Line]], diverging from the Keystone Corridor west of [[52nd Street station (SEPTA Regional Rail)|52nd Street]].
** On SEPTA [[Airport Line (SEPTA)|Airport Line]], diverging from the Northeast Corridor south of [[Penn Medicine Station]]
** On SEPTA's [[SEPTA subway–surface trolley lines|subway–surface trolley lines]], where the Route 10 diverges from Routes 11/13/34/36 west of [[33rd Street station (SEPTA)|33rd Street]].
** On SEPTA's [[Broad Street Line|Broad Street subway]], where Broad-Ridge Spur trains diverge at [[Fairmount station (SEPTA)|Fairmount]]. There are also provisions for flying junctions north of [[Erie station (SEPTA)|Erie]] for the Roosevelt Boulevard Subway, and north of [[Olney Transportation Center|Olney]] for an extension on North Broad Street; both are maintained as layup tracks.
*[[San Francisco Bay Area]], California
** The [[Oakland Wye]], where all of [[Bay Area Rapid Transit]]'s mainline operations converge near downtown [[Oakland, California|Oakland]]
** On the [[Market Street subway]] in [[San Francisco]] where the [[J Church]] and [[N Judah]] lines join the main line of the subway. The subway portal is east of the intersection of Church Street and Duboce Avenue in the [[Duboce Triangle]] neighborhood, immediately north of a [[Safeway Inc.|Safeway]] supermarket and south of the [[San Francisco Mint|San Francisco branch of the United States Mint]].
* [[Washington, D.C.|Washington]], District of Columbia
** All main-line connections on the [[Washington Metro]] – adjacent to the Pepco power plant on Benning Road (near the Stadium-Armory station) is a large three-track structure with a turnback pocket where the Blue, Silver and Orange Lines meet.  This would have been part of the Oklahoma Avenue station, had it been built.  South of the King Street station in Alexandria is a series of tunnels where the Blue and Yellow Lines meet.  There are also flying junctions near three underground rail stations:  Rosslyn (Blue, Silver, and Orange Lines), L'Enfant Plaza (Green and Yellow lines), and the Pentagon (Blue and Yellow lines).

==See also==
*[[Double junction]]
*[[Interchange (road)]]

== Notes ==
{{reflist|group=note}}

== References ==
{{reflist}}

== External links ==
{{Commonscat|Flying junctions}}
* [http://www.wikimapia.org/#lat=50.573126&lon=3.1457376&z=15&l=0&m=a WikiMapia link – aerial photo of Fretin triangle (mentioned above)]
* [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]

{{Railway track layouts}}

[[Category:Rail junction types]]
[[Category:Railway bridges]]