Circle Line (Singapore)

History

Original plans

The Circle Line dates back to 1989, when then-Minister for Communications and Information, Yeo Ning Hong, stated that such a system would be "feasible when the population reaches four million", noting the slow population growth and demand.

In October 1997, the Land Transport Authority (LTA) announced the Marina line, a Light Rapid Transit (LRT) line. The 12 km line, mostly underground, would start from Kallang station, and serve Marina Centre and a new district at Marina South with multiple branches to People's Park and Dhoby Ghaut stations. The Marina line was planned to have 18 stations, with possible extensions to Tanjong Pagar and Paya Lebar stations. Plans for the line were confirmed and approved by the government on 12 June 1998. However, due to the high costs and lack of development in Marina South, the Chinatown branch was later removed in November 1999 and the line was reduced to 6 stations from the Dhoby Ghaut to Stadium stations. A part of the removed leg later became part of the Downtown Line. On the other hand, a further extension towards Upper Paya Lebar was announced on 28 April 2001.

The Marina Line was eventually merged with a planned Light Rail Transit line that went from Paya Lebar to Buona Vista via Serangoon and Bishan to form Circle Line Stage 3 on 20 January 2003, and subsequently Circle Line Stage 4 and 5 on 12 December 2003 when Stage 4 was extended from Buona Vista to World Trade Centre to close up the link and to provide connectivity from the west to Sentosa, becoming the Circle Line. On 8 August 2001, SMRT won the bid and was appointed the operator of the Circle Line. Names for the stations for the first three stages of the Circle Line were finalised in July 2005 after the Land Transport Authority (LTA) conducted a public consultation exercise on the naming of stations.{{Cite web|title=Annex A Finalised Names For Circle Line (CCL) Stages 1-3 Stations

Construction of the initial stages

Construction started on 13 March 2002 for Stage 1, 5 September 2002 for Stage 2, May 2003 for Stage 3, and January 2005 for Stages 4 and 5. Initially planned to be opened in stages from 2006 to 2010, at an estimated cost of S$6.7 billion, the Nicoll Highway collapse delayed the opening of the first stage to 2009. When the line fully opened on 8 October 2011, the cost of construction had risen to nearly S$10 billion. Due to the collapse, the station was relocated to a new site two-thirds the size of the original 100 m away. Three stations on the Circle Line were initially designed as 'shell stations', but the decision was made to open two of them, Caldecott and Haw Par Villa (previously Thomson and West Coast respectively), leaving Bukit Brown as the only unopened station on the line.

The first section of the line, Stage 3, a 5 km five-station segment stretching from Bartley to Marymount, opened on 28 May 2009. Initial ridership on this section was lower than estimated, at 32,000 passengers per day (ppd) instead of the estimated 55,000 ppd. Tunneling works for the entire line were completed on 17 August 2009. Stages 1 and 2 started operations on 17 April 2010, followed by Stages 4 and 5 (from the Marymount to HarbourFront stations) on 8 October 2011. A two-station extension to Marina Bay opened on 14 January 2012.

Circle Line stage 6

On 17 January 2013, then-Minister for Transport, Lui Tuck Yew, announced Circle Line Stage 6 which would "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. The Keppel and Cantonment stations kept their names, while Prince Edward station was changed to Prince Edward Road station.

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 station and its associated tunnels.

Stage 6 of the line is now expected to be completed by 2026 instead due to delays caused by the COVID-19 pandemic. Tunnelling works for the CCL6 were completed on 12 January 2022, with a final tunnel breakthrough from Prince Edward Road station into Cantonment station. The tunnels between Cantonment station and the adjacent Prince Edward Road station were constructed only 6.7 m below the former Tanjong Pagar Railway Station. Prior to the tunnelling works, an extensive survey was conducted to ensure that the tunnels do not cross through the building's foundations. Structures were erected to protect the railway station's facade and interior, and monitoring instruments were installed to watch out for any building settlement. To construct the tunnels to Keppel station, the Keppel viaduct had to be closely monitored while underpinning the viaduct with new micro piles. Three bored piles were removed for the tunnelling works.

On 6 December 2024, it was announced that Stage 6 will commence operation in the first half of 2026. During peak hours, trains will no longer terminate at either Pasir Panjang or Paya Lebar except for withdrawal trains; instead it will run from Dhoby Ghaut to Prince Edward Road. During off-peak hours, trains will only run up to Stadium, and the full loop will run all day (known as clockwise loop or counter-clockwise loop).

Incidents

Nicoll Highway collapse

Main article: Nicoll Highway collapse

On 20 April 2004, a section of the tunnel being built for the Circle Line collapsed, when a retaining wall used in the tunnel's construction gave way. This incident occurred near the proposed site of the Nicoll Highway station, not far from the Merdeka Bridge. The accident left a collapse zone that was 150 m wide, 100 m long, and 30 m deep. Four workers were killed, and three were injured.

A criminal inquiry found the main contractor Nishimatsu Construction Company and joint venture partner firm Lum Chang Construction Company and their officers, as well as key Land Transport Authority officers responsible for the collapse. Several other officers and subcontractors were reprimanded and issued warnings in connection with the accident.

As a result of this accident, the first phase of the Circle Line, previously scheduled to open in 2008, was completed in 2009 instead. The affected station has been shifted about 100 m away from the accident site and is now located at Republic Avenue.

This accident also resulted in stricter safety regulations for the construction of all future MRT lines. The shifting of the Nicoll Highway station also meant it can no longer serve as a terminus for the Bukit Timah Line, partially influencing the creation of the current Downtown Line.

Other incidents during construction

On 16 August 2007, the Building and Construction Authority (BCA) issued a stop-work order and revoked the contractor's tunnelling permit after a 7 m stretch of two lanes close to the junction of Telok Blangah Road and Alexandra Road sank about 20 cm that evening.

A section of the road above a construction site near Holland Road caved in on the morning of 24 May 2008, creating a hole. The hole, directly in front of two private houses along Cornwall Gardens, measured 8 by 7 metres and was 3 metres deep. No one was injured, but the road was temporarily closed to traffic.

Major disruptions

From 17 January 2026 to 19 April 2026, a three-month scheduled service disruption is taking place on sections of the Circle Line for tunnel strengthening works. During this period, trains are to run on a single platform on the eastern stretch between three stations – Mountbatten, Dakota and Paya Lebar. This disruption was deemed necessary for longer engineering hours due to a phenomenon called "tunnel squatting". This is because portions of the Circle Line were constructed in soft marine clay, a material that naturally compresses over time. This ongoing soil settlement subjects the tunnels to external pressure, leading to the circular structure gradually deforming into an elliptical or oval shape that needs to be reinforced with steel plates.

Network and operations

Network

The Circle Line is the second line in Singapore to be completely automated and driverless, following the North East Line, and is among the world's longest driverless rapid transit lines. It is also the first medium capacity line in Singapore.

Capacity and overcrowding

In 2011, the Circle Line was projected to reach a final ridership of 400,000 passengers per day upon full completion. However, the line quickly surpassed expectations due to population growth and rising commuter demand, with reports of overcrowding emerging as early as October 2011 when Stages 4 and 5 opened. By May 2015, daily ridership had reached 398,000, and by 2023, the line averaged over 450,000 passengers per day.

Key interchanges such as in Serangoon and Bishan in particular have frequently experienced overcrowding especially during peak hours due to the stations' narrow platforms and the operational constraint of running only three-car trains. Commuters have reported waiting times of up to 30 minutes during peak hours to board a train. In response, the LTA has announced that 23 new trains will be added to the line in 2026 to further reduce headway.

Route

The 35.5 km 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 2026. 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 Line and North East Line, going eastwards and paralleling Bras Basah Road and Raffles Boulevard, before joining the Circle Line extension at Promenade station, which also interchanges with the Downtown Line. From Promenade station, the line goes northwards and towards the east, passing beneath the Kallang Basin. Between the Stadium and Dakota stations, 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 the Paya Lebar (which interchanges with the East–West Line) and Tai Seng stations.

The line curves and continues westwards between the Bartley and Marymount stations, also interchanging with the North East and North–South lines at Serangoon and Bishan stations respectively, and then it continues in a general southwest direction between Caldecott and Kent Ridge, the former having an interchange with the Thomson–East Coast Line, passing through Bukit Brown Cemetery between the Caldecott and Botanic Gardens stations. The line also interchanges with the Downtown Line at Botanic Gardens station and the East–West Line at Buona Vista station. After Kent Ridge station, the line curves eastwards, paralleling the West Coast Highway and then terminating at HarbourFront station, where it interchanges with the North East Line.

From 2026, upon the completion of Stage 6, the Circle Line will continue eastwards from HarbourFront, paralleling Keppel Road and Ayer Rajah Expressway, and joins the Circle Line extension at Marina Bay station. The Circle Line extension from Marina Bay to Promenade station generally parallels the Downtown Line and Bayfront Avenue, also passing underneath Marina Bay Sands at Bayfront station, which it serves and has cross-platform interchange with the Downtown Line. Also, end-destination number 8 and 9 will be replaced by clockwise and counter-clockwise loops.

Stations

Station codes for the line are orange, corresponding to the line's colour on the system map. All stations have island platforms, with the exception of Promenade and future infill station Bukit Brown.

Legend

List

The Circle Line's numbering scheme reserves station code "CC18" for future use.

Depots

Rolling stock

The rolling stock for the Circle Line uses electric multiple unit (EMU) trains operating in a three-car configuration, with four doors per side on each carriage and can accommodate of up to 931 passengers in each trainsets. It consists of 40 first-generation Alstom Metropolis trains were supplied under contract C830. They are built in France by Alstom between 2006 and 2008. They are stabled at Kim Chuan Depot, which was the world's largest underground depot when it opened in 2009. To increase the capacity of the Circle Line, an additional 24 second-generation Alstom Metropolis trains were supplied under contract C830C, a similar in design to the first-generation trains, were delivered to Singapore from July 2014. They are also built in Shanghai, China by Alstom between 2014 and 2016. To facilitate the extension of the line with the construction of Stage 6, a tender for additional trains for the line was published on 31 March 2017. To increase the capacity of the Circle Line for Circle Line Stage 6, an additional 23 third-generation Alstom Metropolis trains were supplied under contract C851E with the first train set arrived in Singapore on 11 March 2022.

The automated CBTC system on board relies on "continuous two-way digital communication" between each controlled train and the control centre.

Train control

The Circle Line is equipped with Alstom Urbalis 300 Communications-based train control (CBTC) moving block signalling system on the MASTRIA system with Automatic train control (ATC) under Automatic train operation (ATO) GoA 4 (UTO). The subsystems consist of Automatic train protection (ATP) to govern train speed, Iconis Automatic Train Supervision (ATS) to track and schedule trains and Smartlock Computer-based interlocking (CBI) system that prevents incorrect signal and track points to be set.

Train Data Management System (TDMS) which concentrate and dispatch the rolling stock information with fixed equipment. The IAGO Waveguide communications network has the capability to transmit video and is almost maintenance-free. Base stations are located within the signalling equipment room.

Automatic platform screen doors supplied by Westinghouse provide safety for commuters, offering protection from arriving and departing trains.

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