Circle line (London Underground)

The Circle line, coloured yellow on the tube map, is the eighth busiest line on the London Underground. It forms a loop line around the centre of London on the north side of the River Thames with, since 13 December 2009, an extension to Hammersmith on its north-western side.

History
The route now known as the Circle line was authorised when Acts of Parliament in 1853 and 1854 empowered the Metropolitan Railway (MR) and the Metropolitan District Railway (MDR) to construct the world's first underground railway in central London. From an initial section between Farringdon and Paddington stations, the route was gradually extended at each end. Financial difficulties in the construction of the section through the City of London, as well as animosity between the two railway companies, delayed completion of the full circuit until 6 October 1884, although it had been known as the Inner Circle since the 1870s.

Trains on the route were originally hauled by steam engines, but electrification was started with an experimental section in 1900. A disagreement between the two companies over the method of electrification delayed the exercise, so that the first electric trains were introduced gradually over the 11 days to 24 September 1905.

The introduction of this line took over many parts of the Metropolitan line, confining it to the north-west and limiting its interchanges with the District line. The Uxbridge branch of the Metropolitan last shared track with the District in 1933, when Piccadilly line services replaced the latter. In the east, the Barking service of the Metropolitan, also sharing track with the District, was designated part of the Hammersmith & City line in 1988, though in practice the Hammersmith & City had been operated as a separate line for many years before that date.

Other circle routes
The success of the Inner Circle led to the operation of three other "circular" routes within the capital, over existing main line routes and sections of the Inner Circle tracks. Like the Inner Circle at the time they were established, none of them was actually a complete circle:
 * Middle Circle: Aldgate to Mansion House via Addison Road (now Kensington Olympia)
 * Outer Circle: Broad Street to Mansion House via Willesden Junction
 * Super Outer Circle: St Pancras to Earl's Court via Cricklewood and South Acton.

These routes failed to attract the passenger numbers hoped for. The Super Outer Circle ran for only two years; the other two routes lasted longer, but were eventually cut back and finally ended (see the map for details). Other services on the lines continued. Today parts of the Outer Circle and Super Outer Circle routes are operated by London Overground trains on the North London Line. Plans to complete an outer rail loop have been relaunched under the name Orbirail.

7 July 2005 terrorist attack
On 7 July 2005 two Circle line trains were bombed. The blasts occurred almost simultaneously at 08:50 BST, one between Liverpool Street and Aldgate and the other on a train at Edgware Road.

Following the attacks, the whole of the Circle line was closed. While most other lines re-opened on 8 July, the Circle remained closed for several weeks, reopening a little less than a month after the attacks, on 4 August. 13 people were killed by the blasts on the Circle line trains. A third attack occurred on the Piccadilly line between King's Cross St Pancras and Russell Square.

Pre-13 December 2009
Prior to 13 December 2009, the Circle line was true to its name and formed a simple loop. This orbital route had 27 stations and 14.5 mi of track. The map below shows what it looked like from a geographic point of view:

The route
The line became known as such in 1949, when it was designated separately from its parent lines, the Metropolitan line and the District line, although it had been shown on Underground maps since 1947 (see history above). It is a "route" more than a real "line", as it does not have any stations for its sole use and only has two short sections of track over which it operates exclusively: the chords between High Street Kensington and Gloucester Road, and between Tower Hill and Aldgate.

The name of the line became inaccurate on 13 December 2009, when trains on the line ceased to run a continuous circuit, taking instead a "lassoo" or "teacup" shape. A complete journey around the line would take approximately 59 minutes, but timetabling constraints mean that each train has a scheduled two-minute stop at High Street Kensington and Aldgate, extending the time required for a full circuit to about 63 minutes. This allows the service to operate with seven trains in each direction with a seven-minute service interval. It has 35 stations and 17 mi of track.

In the north, east and west of central London, the loop part of the Circle line roughly follows the boundary of Travelcard Zone 1, but in the south there is a substantial portion of the zone outside the Circle line. With the extension on 13 December 2009, it ceased to be one of the only two lines operated completely within Zone 1 (the other being the two-stop shuttle the Waterloo & City line). Out of the 35 stations served, a substantial number have Circle line platforms that are wholly or almost wholly underground; while those at Edgware Road, Farringdon, Barbican, Aldgate, Sloane Square, South Kensington, High Street Kensington, Bayswater, Notting Hill Gate and Paddington are in cuttings or under train-sheds. However these are still all below street level, albeit only a few feet, whereas all the stations on the Hammersmith extension are above ground and most of this section is an elevated railway, built largely on brick arches. See below for the changes that took place on 13 December 2009 extending the line to Hammersmith.

Trains
All Circle line trains are in the distinctive London Underground livery of red, white and blue and are the larger of the two sizes used on the network. These trains use C stock, introduced 1969-70, and also in 1978. They are expected to be replaced with S stock by 2012.

Depots
The principal depot for the Circle line is at Hammersmith, but there are several other sidings at Barking, Triangle Sidings (in Kensington) and Farringdon. Sidings at Edgware Road have been decomissioned.

Map
Circle line route as of December 13, 2009

Extension
The Circle line extension is the latest extension of the Circle line from Edgware Road to Hammersmith.

On 13 December 2009, the Circle line was extended to Hammersmith, sharing tracks with the Hammersmith & City line (see station list above). Clockwise, the new service runs from Hammersmith to Edgware Road station and then makes a full loop of the circle to arrive at Edgware Road a second time. Anticlockwise, trains leave Edgware Road round the circle and pass through Edgware Road a second time before continuing on to the Hammersmith branch. This means it is no longer possible to travel between certain stations on the line (e.g. Baker Street to Bayswater) without changing trains at Edgware Road, or going "the long way round". However, London Underground has said that giving the line a fixed terminus will help improve reliability and capacity. Despite its new spiral shape, it is still called the Circle line.

No new track was required as this was solely an extension to the service pattern, using existing lines. It now shares the tracks previously used only by the Hammersmith & City line, although empty movements were regularly made over this section to the Circle depot. The extension was announced on 5 March 2009 and opened on Sunday, 13 December 2009.

Other information
The extension is intended to reduce overcrowding on Hammersmith & City line trains between Hammersmith and Edgware Road by doubling the frequency of trains on that section. It is also designed to bring about reliability improvements, not only for the Circle line itself but also for the District, Hammersmith & City and Metropolitan lines.

Disruption on the other sub-surface lines has a knock-on effect on Circle line services, because it shares track with them.

Orbital routes
Orbital routes have an intrinsic timetabling robustness problem. The trains are constantly "in orbit" so there is little scope for "recovery time" if they are delayed. A single delay can have long lasting knock-on effects and be much more disruptive than on a non-orbital railway. Recovery time can be created by timetabling for longer stops at some stations but this increases journey times and reduces train frequency. The current spiral route supposedly removed this problem because of the adequate recovery time at both ends of the route.

Stations


The line then continues to Edgware Road where trains terminate before traversing the loop in a anticlockwise direction toward Hammersmith.

Circle line parties
Circle-line parties have gained in popularity on the line in the 21st century, similar to subway parties in the United States. These involve large groups of people boarding a train and holding an impromptu party in the carriages, often dressing in costume.

A high-profile Circle-line party took place on 31 May 2008 to celebrate the last night of legal alcohol drinking on public transport in London. Thousands of people attended and seventeen were arrested by police due to disorderly behaviour, eventually causing the entire line to be suspended for the rest of the night.

Trivia
The Circle Line Pub Crawl aims to visit each Circle line station in turn, drinking a half pint or shot in a pub near to each.

The Cast Off knitting club sometimes holds knit-ins on the Circle line

TML-Studios announced on 4th October 2010 that they will be developing a simulation game set on the Circle Line, called World Of Subways 3: Circle Line.

Maps

 * Hammersmith - 51.49417°N, -0.225°W
 * Goldhawk Road - 51.50194°N, -0.22694°W
 * Shepherd's Bush Market - 51.50583°N, -0.22639°W
 * Wood Lane - 51.50972°N, -0.22417°W
 * Latimer Road - 51.51389°N, -0.21722°W
 * Ladbroke Grove - 51.51722°N, -0.21056°W
 * Westbourne Park - 51.52111°N, -0.20111°W
 * Royal Oak - 51.51917°N, -0.18806°W
 * London Paddington - 51.51722°N, -0.1775°W
 * Edgware Road - 51.52°N, -0.16778°W
 * Baker Street - 51.52194°N, -0.15694°W
 * Great Portland Street - 51.52389°N, -0.14389°W
 * Euston Square - 51.52583°N, -0.13583°W
 * King's Cross St. Pancras - 51.53028°N, -0.12417°W
 * Farringdon - 51.52°N, -0.10528°W
 * Barbican - 51.52028°N, -0.09778°W
 * Moorgate - 51.51861°N, -0.08861°W
 * Liverpool Street - 51.51861°N, -0.08139°W


 * Aldgate - 51.51389°N, -0.07611°W
 * Tower Hill - 51.51°N, -0.07611°W
 * Bank-Monument - 51.51306°N, -0.08806°W
 * Cannon Street - 51.51028°N, -0.09083°W
 * Mansion House - 51.51222°N, -0.09417°W
 * Blackfriars - 51.51167°N, -0.10306°W
 * Temple - 51.51111°N, -0.11444°W
 * Embankment - 51.50694°N, -0.12194°W
 * Westminster - 51.50111°N, -0.125°W
 * St. James's Park - 51.49944°N, -0.13444°W
 * London Victoria - 51.49667°N, -0.14472°W
 * Sloane Square - 51.4925°N, -0.15667°W
 * South Kensington - 51.49417°N, -0.17389°W
 * Gloucester Road - 51.49472°N, -0.18306°W
 * High Street Kensington - 51.50083°N, -0.1925°W
 * Notting Hill Gate - 51.50889°N, -0.19694°W
 * Bayswater - 51.51194°N, -0.18806°W
 * Hammersmith Depot - 51.49778°N, -0.22528°W