Circle Line

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The 35.5-kilometre (22.1 mi) Circle line forms an incomplete loop from Dhoby Ghaut in the Central Region of Singapore, north to Serangoon and Bishan, and south to HarbourFront, with a branch from Promenade to Marina Bay station which will be extended to HarbourFront in the future. The fully-underground circular route also makes several links with the other MRT lines. The line begins at Dhoby Ghaut station, which has an interchange with the North South and North East lines, going eastwards and paralleling Bras Basah Road and Raffles Boulevard, before joining the Circle line extension at Promenade, which also interchanges with the Downtown line. From Promenade station, the line goes northwards and towards the east, passing beneath the Kallang Basin. Between Stadium and Dakota, the line parallels Stadium Boulevard and Old Airport Road, then the line continues northwards and follows the route of Paya Lebar Road and Upper Paya Lebar Road between Paya Lebar (which interchanges with the East West line) and Tai Seng.

Extension: Stage 6
On 17 January 2013, the Land Transport Authority (LTA) announced 'Circle Line Stage 6' which will 'close the circle', set to be completed by 2025. The 4 km extension will run between Marina Bay and HarbourFront. The extension will connect commuters between the HarbourFront to Marina Bay stations and expand the rail network to the southern edge of the Central Business District. On 29 October 2015, LTA announced the station locations for Stage 6, with the working names of the stations being Keppel, Cantonment and Prince Edward. Tenders were called for construction between 2016 and 2017.

On 15 May 2017, the LTA invited the public to send in suggestions for names of the three MRT stations or propose to keep their current names. Keppel and Cantonment kept their names, while Prince Edward has been changed to 'Prince Edward Road'.

Construction of Stage 6 commenced in late 2017. A joint venture – by China State Construction Engineering (The Singapore branch) and Nishimatsu Construction – won the contract to build the new Keppel MRT station and its associated tunnels.