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Metro Rings and Loops




Latest update: 4 August 2013.

Metros and subways are abundant throughout the big cities of the world. While metro lines are normally planned to be as straight as possible, a special, very urban kind of infrastructure has emerged in metropolitan areas: the Circle Line.

33 circular lines or pan-shaped loops are currently operational in 26 cities. London, Sydney and Tokyo have two rings each, Madrid and Singapore even three. The average circumference of existing rings is about 20 kilometres, ranging from as little as 3 kilometres (Miami, Chicago) to some 49 kilometres (Seoul). A couple more rings are currently under construction or proposed.

Most circle lines orbit a city centre, some of them since the beginning of the 20th century in order to connect peripheral railway stations within big cities. Circle lines that run around a city centre can increase efficiency of a transport network as they provide valuable connections between sub-centres of the city while releasing burden from lines that pass through the city centre.

Contents:
Terminology and Types of Rings
Usability
Facts and oddities
Complete list of ring lines
Reference


Terminology and Types of Rings

Circle, loop or ring? Circle and loop will be referred to here as types of operation of metro lines. The tracks on which a circle or loop line can run (the 'hardware') will be called a ring. The following types can be distinguished:

Isolated circle
A single line circles a ring endlessly. Examples: Glasgow, Moscow.
Shared circle
Several lines, one of which circles the ring completely while others use only stretches of the ring. Example: London's Circle Line, which is accompanied by Metropolitan, District and Hammersmith&City Lines.
Pan-shaped loop
A line which runs from outside into a ring, around it, and out of it on the same route it came in from. Some loops can be technically operated as circles but aren't (like Chicago's Loop) while others cannot (like Tokyo's O-Edo Line).
Operationally split circle
Several lines of which none runs around the entire ring (or loop) though they technically could, either in the past or at present. Example: Vienna.
Terminal loop
A small unidirectional turnover loop at an end of a line with or without stations. Example: Paris.
Spiral
A loop without a connecting station. Sometimes used for metro lines to follow a steep geographical incline. Examples: Naples, Tokyo.
False circle (not subject of this document)
A circular pattern in a metro network which cannot be circled by trains. Occurs in almost every metro system, e.g. lines 2 and 6 in Paris.

Usability

A circle line crossed by several straight (radial) lines is considered to be the best possible type of metro networks since it provides the best traffic connections within a city [5]. However, the thing which comes to mind first, one big transfer station in the centre of the circle with all radial lines crossing, is inefficient. The radial lines should instead meet in many transfer stations within the circle. Moscow serves as an excellent example to this idea, see map below.

Planners in London have found excellent geological preconditions for metro construction since the beginning of the tube's history. This enabled them to plan for the optimal network type, and they indeed chose a network consisting of a circle line crossed by several radial lines [5].

Moreover, the relatively large number of metro rings currently proposed or under construction seems to prove that circle lines are still a good option to enhance the usability of an existing metro network. Only two cities, Hamburg and Vienna, have given up circular operation by splitting former circle lines into parts currently served by separate lines (Hamburg has corrected its mistake 42 years later). The disjunction of the ring line in Berlin had its cause in the division of the city during the Cold War.

When a ring is shared among different metro lines, this can be unsatisfactory in terms of operation and traffic, as delays can be introduced from the branches and accumulate along the endless route [3]. Isolated circle lines, however, can be very reliable: Moscow's metro operators use the Circle Line as a test bed for new signalling and trains because it is has the most reliable schedule of all lines [7].


Example of a circle-radial network: Moscow 2003.

Moscow's metro system is an excellent example for the circle-radial network type (click here to see more maps).


Facts and Oddities

Train carriages running on a circular line have to be reversed from time to time in order to prevent the wheels from wearing out unevenly [1].

Glasgow's metro network consists of a single circular line which runs entirely underground. It is publicly nicknamed 'Clockwork Orange', according to the colour of its trains and the colour of the line in the official metro map. Unfortunately, the metro operator is going to change the colour to blue.

Urban legend in Moscow has it that when Stalin was asked by city planners what he thought of their metro network design, Stalin set his coffee cup in the centre of the blueprint and left the room silently. After the cup was removed, there was a brown circular coffee stain. The planners took this as a sign of Stalin's genius and started building the metro circle line (Kol'tsevaya Line) [8]. Whether this is true or not, Moscow's circle line is colour-coded brown in most official metro maps.

Train directions of a circular line can be easily confused by passengers, mainly because there are no terminal stops that can be used to label the trains. Every station can be reached by going in either direction, but for the occasional user, chances are 50% to take a time consuming detour. A way to prevent confusion is to give clockwise and counter-clockwise trains different line numbers (like S41 and S42 in Berlin) or names (like Outer Circle and Inner Circle in Glasgow).

Possibly the best way to name a circle line would be to name it with a number and add an 'a' or 'b'. If, for example, Line 5 stands for the circle line as a whole, Line 5a would refer to the counter-clockwise and Line 5b to the clockwise direction. This would make route descriptions very easy to follow, without looking at maps. Letters 'a' and 'b' can work as memory hooks: just remember that a script letter 'a' is written with a counter-clockwise stroke and 'b' with a clockwise stroke.

Some circular lines are likely to be unpopular among train drivers because the endless tunnel trip, and maybe the steady centrifugal force to the same side, makes them feel uneasy. This has at least been reported from Madrid [7].


Complete List

Data provided: City name - line name - circumference - number of stations on the ring - time for a circular ride - inauguration of first section - completion of ring - remarks.

Isolated circles

Beijing - Line 10 - 57.1 km - 45 stations - round trip 104 minutes - opened 2008 - completed 2013.
Beijing - Line 2 - 28 km - 18 stations - round trip 43 minutes - opened 1984 - completed 1987.
Delhi - Ring Railway - 21 stations.
Detroit - People mover - 4.8 km - 13 stations - round trip 15 minutes - completed 1987 - unidirectional.
Glasgow - Circle Line - 10.4 km - 15 stations - round trip 24 minutes - completed 1896.
Madrid - Line 12 ('MetroSur') - 40.5 km - 28 stations - round trip 75 minutes - opened 2000 - completed 2003 - in southern suburbs.
Madrid - Line 6 - 23 km - 28 stations - round trip 67 minutes - opened 1979 - completed 1995.
Moscow - Kol'tsevaya Line - 19.4 km - 12 stations - round trip 29 minutes - opened 1950 - completed 1954.
Singapore - Sengkang LRT - 10.7 km - 14 stations - opened 1998 - completed 2003 - 8-shaped people mover above ground.
Singapore - Punggol LRT - 10.3 km - 15 stations - opened 2000 - completed 2005 - People mover above ground.
Tokyo - Yamanote Line - 34.5 km - 29 stations - round trip 64 minutes - opened 1872 - completed 1914 - Suburban metro.


Shared circles

Berlin - S41/S42 - 37 km - 27 stations - round trip 62 minutes - opened 1871 - completed 1877 - Suburban metro, circular operation suspended 1961-2002.
Charleroi - all lines - 4.1 km - 8 stations - round trip 14 minutes - opened 1983 - completed 2012 - all lines running around the circle.
London - Circle Line - 22.5 km - 27 stations - opened 1863 - completed 1884.
Miami - People mover - 3 km - 8 stations - completed 1986 - Elevated, rubber-tyred, automated.
Nagoya - Meijo Line - 25 km - 28 stations - opened 1965 - completed 2004.
Osaka - 21.7 km - 19 stations - opened 1874 - completed 1898 - Suburban metro.
Oslo - Lines 4, 5, 6 - 13 km - opened 1898 - completed 2006.
Seoul - Line 2 - 48.8 km - 43 stations - round trip 84 minutes - opened 1978 - completed 1984.
Seville - Cercanias C4 - 5 stations.
Shanghai - Line 4 - 33.7 km - 26 stations - opened 2000 - completed 2007 - shared with line 3 .


Pan-shaped loops

Brussels - Lines 2 and 6 - 18 stations - opened 1981 - completed 2009.
Bucharest - Lines M1, M3 - 24 km - 16 stations - opened 1979 - completed 1989.
Chicago - different lines - 3.2 km - 9 stations - completed 1897 - The Loop.
Delhi - Gurgaon line - 5 stations - opened 2013 - completed 2013 - Single-track loop.
Hamburg - Line U3 - 17.5 km - 23 stations - round trip 38 minutes - completed 1912 - circular operation was suspended 1967-2009.
Incheon - Wolmido monorail - 5.1 km - 5 stations - opened 2010 - unidirectional monorail.
Kolkata - Circular Railway - 20 stations - opened 1984 - Part of the Kolkata Suburban Railway.
Liverpool - Wirral Line - 4 stations - suburban line, single-track loop.
London - Central Line - 23 km - 14 stations - completed 1948 - near Hainault (operated as loop in peak hours only).
Madrid - Cercanias Line C7 - 16 stations.
Melbourne - several lines - 5 stations - completed 1984 - Suburban metro .
Newcastle - Yellow Line - 26 stations - opened 1980 - completed 1982.
Paris - Line 7bis - 4 stations - opened 1911 - completed 1921 - unidirectional loop.
Singapore - Bukit Panjang LRT - 7.8 km - 13 stations - completed 1999.
Sydney - Suburban metro - 6 km - 6 stations - completed 2000.
Tokyo - O-Edo Line - 28 km - 26 stations - opened 1991 - completed 2000.
Vancouver - Millennium Line - 22 stations - opened 1986 - completed 2002.


Abandoned or operationally split circles

Copenhagen - S-Tog - 20 stations - completed 2005 - operationally split.
London - Overground - 33 stations - opened 2007 - completed 2012 - split at Clapham Junction and Highbury & Islington.
Vienna - Lines U4/U6 - 18 stations - operation as a pan-shaped loop 1925-1978.
Vienna - Lines U2/U4 - 10 stations - operation as a pan-shaped loop for only 2 weeks in 1981.


Rings under construction

Copenhagen - Line M3 (Cityringen) - 15 km - 17 stations - round trip 23 minutes - to be opened 2018 - driverless, shared with line M4.
Naples - Line 1 - 26 stations - opened 1993 - to be completed 2014.
Riyadh - Monorail - 3.6 km - 6 stations - to be opened 2014 - to be completed 2014 - Around KAFD area (King Abdullah Financial District).


Proposed rings

Baku - Line 2 - 23 stations - opened 1985 - Line 2 is planned to become a ring line.
Chicago - Circle line - 20 km - 22 stations - to be completed 2015.
Moscow - Regional rail ring within the city, under discussion.
Moscow - Line 4 - outside line 5 as extension of line 4's Mezhdunarodnaya branch, under discussion.
Moscow - Line 11, part of line 1 - Large metro ring, approved in the 1960's.
Paris - Arc Express - 50 km - 50 stations - round trip 75 minutes - to be opened 2017 - proposed, driverless.
Rio de Janeiro - Line 1 - 23 stations - Line 1 is proposed to become a circle.
Seville - Light rail line 4 - 19 stations.
Singapore - Downtown Line - opened 2013 - to be completed 2018 - Spiral with 9 stations in the middle of a line with 32 stations.
Singapore - Circle Line - 37.3 km - 30 stations - opened 2009 - to be completed 2025 - driverless.
Toronto - Yellow/Purple lines - completion unclear.


Terminal loops

This list may be incomplete.

London - Piccadilly Line - 2 stations - at Heathrow, unidirectional.
Los Angeles - Blue Line - 5 stations - at southern end, unidirectional.
New York - Line 6 - 1 station - going through the glamourous abandoned City Hall station without passengers, unidirectional.
New York - Lines 1 and 9 - 1 station - at South Ferry station, unidirectional.
Paris - Several lines - Paris has the largest number of unidirectional terminal loops worldwide, two of them used with passengers: Nation on line 2, Charles de Gaulle - Etoile on line 6.
Seoul - Line 6 - 6 stations - unidirectional.


Spirals

This rare and unusual type of loop can help rail lines to climb steep geographical inclinations. The one in Naples is completely underground and could go unnoticed by passengers if it weren't plotted in the official metro map. The proposed Downtown Line in Singapore will run through a spiral with 9 stations in the city centre.

Naples - Line 1 - Inclinational spiral at Vanvitelli and Cilea/Quattro Giornate stations, underground, climbing up to 250 m above the city centre.
Tokyo - Yurikamome Line - Inclinational spiral near Shibaura-Futo station, elevated, climbing Rainbow Bridge.





Reference

[1] Bayman, Bob: London Underground Official Handbook. 2000.
[2] Fischler, Stan: Subways of the World. 2000.
[3] Garbutt, Paul: World Metro Systems. 1997.
[4] Groneck, Christoph: Metros in France. 2006.
[5] Schleife, Hans-Werner; et al.: Metros der Welt. 1992.
[6] Schwandl, Robert: UrbanRail.net
[7] UrbanRail.net newsgroup.
[8] Wikipedia: Moscow Metro.





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