Announcement The Cross Island Line was first announced by then Transport Minister
Lui Tuck Yew on 17 January 2013. The line was planned to relieve congestion on the existing
East–West Line and slated to begin at
Changi on Singapore's eastern coast, passing through the major eastern towns including Pasir Ris, Hougang and Ang Mo Kio. From this point, it would proceed further west toward Bukit Timah, Clementi and West Coast, before terminating in the Jurong Industrial Estate. A branch line was to connect the mainline to Punggol. The line was planned to be 50 km long and open in 2030. Studies on the Cross Island Line began in May 2013.
Line alignment Since its announcement, there has been controversy over the alignment of the line's Bukit Timah stretch crossing the
Central Catchment Nature Reserve (CCNR) and
MacRitchie Reservoir, which prompted the
Nature Society Singapore to call for the line's realignment. Environmental groups urged the Government not to build the MRT line under the CCNR. On 19 July 2013, the NSS put forward two proposed alternative alignments: a northern route that would run close to the
Thomson–East Coast Line, heading west towards
Mandai,
Sungei Kadut and Gali Batu before terminating at
Choa Chu Kang, and a southern route skirting the reserve along Lornie Road. One engineering professor Lee Der-Horng noted the possible feasibility of constructing the line through the reserve without impacting the environment, though he said the decision "shouldn't be just based on transport". A tender to assess the environmental impact of the line was called for on 24 February 2014 to facilitate civil works for the line. In July 2014 the LTA appointed Environmental Resources Management (S) Pte Ltd (ERM) to conduct the Environmental Impact Assessment (EIA) for the section of the line around and through the nature reserve. The EIA was to be conducted in two phases with the first studying the ecosystem and physical conditions along both the straight and skirting alignments as well as assessing how construction and operation of the line would affect the CCNR. The Phase 1 EIA report was released in February 2016. Soil investigation works along the CCNR began in February 2017 and by October, was announced to be nearing completion by the end of the year. The Phase 2 EIA report was released in September 2019. On 4 December 2019, the Ministry of Transport confirmed that the direct route underneath the CCNR had been chosen, with mitigating factors such as tunnelling deeper than usual under the CCNR as well as no surface works in the area. The construction cost is also expected to be $2 billion lower than the alternative alignments. In December 2022, the LTA awarded the contract for the design and construction of bored tunnels between Fairways Drive and Sin Ming Walk to a joint venture between Obayashi Corporation and Shanghai Tunnel Engineering Co (Singapore) Pte Ltd for $758 million.
Phase 1 On 25 January 2019, then Transport Minister
Khaw Boon Wan announced the alignment of CRL Phase 1 (CRL1). This segment of the line, spanning , consists of 12 stations from
Aviation Park station to
Bright Hill station. A new 57-hectare
Changi East Depot was to be built to serve the line. Construction of CRL1 officially began on 18 January 2023. Originally expected to be completed in 2029, the opening date was pushed back a year as a result of restrictions imposed on construction works due to the
COVID-19 pandemic.
Punggol Extension The Punggol Extension was initially conceived as part of the North Shore Line, which was first announced by National Development Minister Lim Hng Kiang in December 1996. The LRT line would connect between Pasir Ris and Woodlands A station box for the future line was constructed beneath the Punggol NEL station. During a national conference organised by the Feedback Unit in April 2005, the transport ministry confirmed that plans for the MRT line were still under study, in response to suggestions for a line between Pasir Ris and Punggol. Nevertheless, the line would only be built in tandem with development plans along the line. On 10 March 2020, the LTA announced details of the CRL - Punggol Extension (CPE). The branch will consist of four stations from
Pasir Ris station to
Punggol station. Similarly to CRL1, the opening of CPE was delayed from its original 2031 opening date to 2032. Member of Parliament
Gan Thiam Poh also proposed to serve residents of
Fernvale and
Yio Chu Kang by extending the CRL Punggol branch to
Yio Chu Kang station; transport minister
Chee Hong Tat rejected the proposal.
Extension to Changi Airport Terminal 5 The LTA was also studying a possible extension to
Changi Airport Terminal 5. This was later confirmed by LTA in January 2019, during the announcement of Phase 1 of the CRL, with the station code "CR1" possibly reserved for a station in Terminal 5. Later that year on 25 May, LTA published the Land Transport Masterplan 2040, which confirmed the extension of both the CRL and Thomson-East Coast Line (TEL) to the Terminal 5, with plans for the TEL to further extend to the existing
Changi Airport MRT station on the
East–West Line and absorb the Changi Airport branch of that line, which includes
Expo and
Tanah Merah stations. On 14 May 2025, during the groundbreaking of Terminal 5, the airport operator Changi Airport Group gave further confirmation of plans to extend the TEL and CRL to the terminal, and the first render of the station design was unveiled. Later on 25 July, the LTA officially announced
Changi Terminal 5 station as an interchange station with the TEL, unveiling the location of Changi Terminal 5 station and the alignments of the extension of both lines. The Changi Terminal 5 station will be located in the terminal's ground transportation centre, which will border the Changi East Urban District.
Phase 2 In December 2021, as part of a virtual exhibition by the LTA, a future system map depicted a series of 11 unnamed stations on the western half of the CRL. The map also showed the western segment interchanging with existing and under-construction stations:
King Albert Park,
Clementi,
Jurong Pier and
Gul Circle stations. The map, along with the virtual exhibition, has since been offline. The LTA explained that the route was a "conceptual alignment" yet to be finalised, with the interchange stations being tentative. On 20 September 2022, then Transport Minister
S. Iswaran confirmed the stations for Phase 2 of the CRL. Expected to open in 2032, the segment spans six stations from
Turf City station to
Jurong Lake District station. Construction of these stations was expected to start in 2023.
Phase 3 The CRL is to be completed in three phases. It is projected that the second and third phases will be about and long respectively. In 2021, LTA published a map of the MRT system in the 2030s as part of a virtual exhibition. The map indicated four stations on Phase 3, with an interchange at
Jurong Pier station and
Gul Circle station on the
Jurong Region Line and
East–West Line, respectively. In February 2022,
The Straits Times projected that civil works for Phase 3 might be completed by the end of 2033, with operations beginning in 2034 or later. However, LTA stated that the exact timeline is unclear and will only be known with the completion of advanced engineering studies, which was still ongoing by July 2025.
Future plans In conceptual plans for the redevelopment of
Paya Lebar Air Base, an additional station has been proposed between
Defu and
Tampines North stations to serve the new developments. ==Network and operations==