Before the
merger of the two major Hong Kong railway operators, the
MTR Corporation (MTRC) and the
Kowloon-Canton Railway Corporation (KCRC) rail networks in 2007, both the
West Rail (opened in 2003) and the
Ma On Shan Rail (opened in 2004) were operated by KCRC. Both railways were envisaged to be extended in the near future and platforms on the Ma On Shan line were
built with reserved structures for extension at a later date. Both MTRC and KCRC independently submitted their own proposals to the
Hong Kong government for developing the Sha Tin to Central Link (SCL) by extending their own existing networks. After numerous revisions of their proposals, the government eventually approved the scheme by KCRC, which involved joining the West Rail and the Ma On Shan Rail via the
Wong Tai Sin and
Kowloon City districts (the phase 1 East West Corridor), and extending
East Rail line to
Hong Kong Island's central business district (phase 2 North South Corridor). After the 2007 network merger, operations of all transport services (East Rail, West Rail, Ma On Shan Rail,
Light Rail, feeder buses and
Guangzhou–Kowloon through train) of the KCRC were leased to the MTRC for 50 years. The MTRC also rebranded the three commuter railways to East Rail line, West Rail line and Ma On Shan linetts like their own railways. Subsequently, the approved SCL schemes fall into the hands of the MTRC. The construction of East West Corridor, which largely followed an alignment proposed by the MTRC in the 1970s as the
East Kowloon line and later shelved, began in August 2016. At the time, it was unclear how MTRC would name the new lines or whether they would retain the provisional names "East West Corridor" and "North South Corridor"; the word "corridor" would set a precedent in the naming convention of MTR lines. Speculation of a "East West Line" arose when a photograph of an info plate printed with "EWL" (東西綫) at
Ho Man Tin station while it was under construction surfaced. The plate was removed before the opening of the station that year as part of the
Kwun Tong line extension to
Whampoa. MTRC eventually announced on 25 May 2018 that the operational name was the Tuen Ma line.
Construction defects and delay The Tuen Ma line was planned to be fully operational in 2019, but after the newly built platforms at
Hung Hom station failed a safety inspection which occurred between December 2018 and January 2019, its full opening was postponed by about two years. The head contractor of the SCL construction, Leighton Asia, subsidiary of the
CIMIC Group, was accused of covering up construction defects until a whistleblower from a subcontractor leaked photo evidence to the press. This led to more thorough investigations, hearings and inspections behind the set concrete for assessing if it would require demolition and rebuilding the structure from scratch. The Hong Kong government also expressed disappointment in the MTRC executives for their incompetent supervision.
Michael Tien, former KCRC chairman, suggested that it was technically feasible to have the Ma On Shan line be initially extended from Tai Wai to
Diamond Hill station instead of delaying the opening of the entire line. This has the advantage of spreading the Kowloon bound traffic between Tai Wai and
Kowloon Tong stations of the East Rail Line, which is overcrowded during peak hours. However, the then MTRC chairman,
Frederick Ma, insisted that they aimed at inaugurating the whole line in mid-2019 to avoid the extra resources required for operating the line in separate phases. On 18 July 2019, the
Transport and Housing Bureau announced that the Tuen Ma line would open in two phases. On 14 February 2020, the Ma On Shan Line was extended from Tai Wai station to
Kai Tak station because the latter has a
crossover track which permits the operation of the station as a terminus. The extension, named Tuen Ma line Phase 1, was expected to alleviate significant congestion on the East Rail line between Tai Wai and Kowloon Tong stations in preparation for the shortening of trainsets as part of preparatory works for the cross-harbour extension of that line. The remaining section of the Tuen Ma line, from Kai Tak to Hung Hom, opened on 27 June 2021.
Future extensions In May 2020, the Government submitted a proposal for the Tuen Mun South Extension to the Legislative Council Subcommittee on Railway Matters. In addition to the "Railway Development Strategy 2014", which includes a proposal for
Tuen Mun South station near the
Tuen Mun Ferry Pier, the MTRCL has proposed in the latest project proposal to add
an additional station in Tuen Mun Area 16. Building an intermediate section in Tuen Mun Area 16 will require the Tuen Mun Swimming Pool to be relocated. A possible relocation for the Tuen Mun Swimming Pool is at the Tuen Mun Golf Centre; the specific plan depends on the technical feasibility study. If, after research, it is confirmed that the above-mentioned location is not suitable, MTRCL will identify other possible locations. Considering that the detailed planning and design of the project will take about two to three years, the Tuen Mun South Extension started construction in 2023 and will be completed in 2030. The government has invited MTRCL to carry out the detailed planning and design of the Tuen Mun South Extension project, and will negotiate with the MTR Corporation on the financing arrangements for the Tuen Mun South Extension on the basis of the "ownership" model for the project. ==Train services==