The Hammersmith & City line is a London Underground line that runs between Hammersmith in west London and Barking in east London. Coloured pink on the Tube map, it serves 29 stations over 15.8 miles (25.5 km). Between Farringdon and Aldgate East it skirts the City of London, the capital's financial heart, hence the line's name. Its tunnels are just below the surface and are a similar size to those on British main lines. Most of the track and all stations are shared with the District, Circle or Metropolitan lines. Over 141 million passenger journeys are made each year on the Hammersmith & City and Circle lines.

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Hammersmith & City line
A Hammersmith & City line train at West Ham, bound for Hammersmith
Overview
Stations	29
Colour on map	Pink
Website	tfl.gov.uk/tube/route/hammersmith-city
Service
Type	Rapid transit
System	London Underground
Depot(s)	Hammersmith
Rolling stock	S7 Stock
Ridership	141.627 million (2019)[lower-alpha 1][1] passenger journeys
History
Opened	10 January 1863; 161 years ago (1863-01-10) (as Metropolitan Railway) 30 July 1990 (renamed to Hammersmith & City line)
Last extension	1936
Technical
Line length	25.5 km (15.8 mi)[2]
Character	Sub-surface
Track gauge	1,435 mm (4 ft 8+1⁄2 in) standard gauge
Transport for London rail lines London Underground Bakerloo Central Circle District Hammersmith & City Jubilee Metropolitan Northern Piccadilly Victoria Waterloo & City London Overground Liberty Lioness Mildmay Suffragette Weaver Windrush Other TfL Modes DLR Elizabeth line London Trams v t e

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In 1863, the Metropolitan Railway began the world's first underground railway service between Paddington and Farringdon with wooden carriages hauled by steam locomotives. The following year, a railway west from Paddington to Hammersmith was opened and this soon became operated and owned jointly by the Metropolitan and Great Western Railway companies. The line was then extended to the east, in stages, reaching the East London Railway in 1884. The line was electrified in 1906, and, in 1936, after the Metropolitan Railway had been absorbed by the London Passenger Transport Board, some Hammersmith & City line trains were extended over the former District Railway line to Barking. The Hammersmith & City route was shown on the Tube map as part of the Metropolitan line until 30 July 1990, when it was redesignated as a separate line.^[3]

Starting in 2015, the signalling system was upgraded as part of a programme to increase peak-hour capacity on the line. The six-car C Stock trains were replaced from 2012 to 2014 by new seven-car S Stock trains.

The line runs parallel to the Great Western Main Line between Paddington and Westbourne Park, and parallel to the London, Tilbury and Southend line between Bromley-by-Bow and Barking.

The line is 15.8 miles (25.5 km) long with 29 stations.^[2] Almost all of its track is shared with the other London Underground sub-surface lines: from Hammersmith to Liverpool Street with the Circle line; from Baker Street to Aldgate with the Metropolitan line, and from Aldgate East station to Barking with the District line.^[32] All its stations are shared with other lines.

The line is electrified with a four-rail DC system: a central conductor rail is energised at −210 V and a rail outside the running rails at +420 V, giving a potential difference of 630 V.^[33] Much of the 2-mile-35-chain (3.9 km) double-track railway from the Hammersmith terminus to Westbourne Park station is on a 20-foot (6.1 m) high brick viaduct.^[7] After Westbourne Park the line passes beneath the Great Western Main Line re-surfacing at Royal Oak station and running alongside the main lines to Paddington station.^[32] The line enters a cutting just west of the station and a cut-and-cover tunnel at the end of the platforms. It meets the Circle and District lines from Bayswater at Praed Street Junction before passing through Edgware Road station in a cutting. After King's Cross St Pancras the line is partly in cutting but mostly in the Clerkenwell Tunnels, just after which it passes over the Ray Street Gridiron that carries the route over the City Widened Lines used for Thameslink services.^[32][34][35] There are bay platforms at Moorgate. Just before Aldgate the line diverges from the Circle and Metropolitan lines to Aldgate East.^[32] The line passes over the London Overground at Whitechapel station continuing on the 2-mile (3.2 km) former Whitechapel & Bow Railway to Bow Road where it surfaces, and then to Bromley-by-Bow, where it runs alongside the London, Tilbury and Southend line from Fenchurch Street. At the next station, West Ham, there is a transfer with the Jubilee line, the Docklands Light Railway and London, Tilbury and Southend line. There is a bay platform at the next station, Plaistow, and the line terminates after two more stations at Barking.^[32]

As of December 2012^[update], off-peak there are six trains per hour, calling at all stations,^[36] and requiring 15 trains for the peak-hour service.^[2] Together with the Circle line, over 114 million passenger journeys are made each year.^[37] The journey from Hammersmith to Barking takes one hour during off-peak times. The central section from Paddington to Aldgate East is in Fare Zone 1; to the west to Hammersmith and east to Bromley-by-Bow is in Zones 2; East Ham is in both Zones 3 and 4, whilst Barking is in Zone 4 alone.^[38]

Services are provided by S7 Stock trains, part of Bombardier's Movia family, with air-conditioning as the sub-surface tunnels (unlike those on the deep-level tube lines) are able to disperse the exhausted hot air.^[39] These trains have regenerative brakes, returning around 20 per cent of their energy to the network.^[40] With a top speed of 62 mph (100 km/h),^[39] a 7-car S Stock train has a capacity of 865 passengers, compared to 739 for the six-car C Stock train it replaced.^[41][42] With a length of 384 feet (117 m), S Stock trains are 79 feet (24 m) longer than 305-foot (93 m) long C Stock trains and station platforms have been lengthened.^[43] Traction voltage was increased in 2017, from the present nominal 630 V to 750 V to give better performance and allow the trains to return more energy to the network through their regenerative brakes.^[42]

The line's depot is at Hammersmith,^{[lower-alpha 3]} close to Hammersmith station, built by the Great Western Railway to be operated by the Metropolitan Railway when the joint railway was electrified in the early 20th century.^[16] Sidings at Barking and near High Street Kensington (Triangle Sidings) stable trains overnight.^[2] Sidings at Farringdon were used during the C stock era; due to the greater length of the new S stock trains, these are no longer in use.

It was planned that a new signalling system would be used first on the sub-surface lines from the end of 2016,^[44] but signalling contractor Bombardier was released from its contract by agreement in December 2013 amid heavy criticism of the procurement process^[45] and London Underground subsequently awarded the contract for the project to Thales in August 2015.^[46]

With the introduction of S7 Stock, the track, electrical supply, and signalling systems are being upgraded in a programme planned to increase peak-hour capacity on the line by 27 per cent by the end of 2023.^[44][47][48] A single control room for the sub-surface railway opened at Hammersmith on 6 May 2018, and Communications Based Control (CBTC) provided by Thales will progressively replace 'fixed block' signalling equipment dating back the 1940s.^[44][49]

The rollout of CBTC has been split into sections, each known as a Signal Migration Area (SMA), and are located on the line as follows:^[50]