Sukhumvit Line

East

1st extension, in operation - Construction started in August 2006 on a four billion baht, 5.25 km extension from On Nut (E9) to Bearing.^[1] The extension was funded by the BMA.^[2] The original scheduled opening date was mid-2009. However, a delay in tendering of the contract for the electrical and signals resulted in a two-year delay. Deputy governor Teerachon Manomaiphibul commented: "The senior City Hall official responsible for making the purchase has apparently stalled the scheme over fears of being investigated if something went wrong with the purchase. The official in question is due to retire and does not want to take risks despite being told the scheme is strictly in line with regulations".^[3] The extension did not open until over two years later on 12 August 2011. The delay in opening prompted the BMA to offer free travel for this extension until the end of 2011 as compensation. An additional flat fee is charged additionally to the distance-based fare of the rest of the BTS network.

2nd extension, currently under construction with one open station - Construction started in April 2012 on a 12.6 km, nine station extension from Bearing station to Kheha station. The extension is funded by the MRTA as it is outside BMA city limits, Bangkok Province. Construction was contracted to take 1,350 days and the extension was originally scheduled to open by early 2017. In April 2013, the MRTA awarded Ch Karnchang the contract for track laying and electrical systems.^[4] As of June 2014, civil works were stated to be 28.3 percent complete. In August 2016 the BMA agreed to take over the operation of the extension from MRTA. Delays over the agreement of how much the BMA should pay MRTA caused a delay in the commencement of test runs on the extension. Trackwork was 98% complete by November 2016. The total cost of the extension was estimated at 21.4 billion baht.^[5]

In January 2017, it was announced that the opening of the extension could be further delayed to 2018-9 due to budgetary concerns and ongoing disputes between the MRTA and BMA. ^[6] However, the first 1.2km section of the extension to Samrong station (E15) opened in April 2017.^[7] However some services from Mo Chit terminate at Bearing and some at Samrong. Passengers for Samrong on trains terminating at Bearing are recommended to change at Bang Na Station to avoid changing platforms, as the termination platform for Bearing services at Bearing is platform 2 bound for Mo Chit.

As of 31 December 2017, civil works construction had been 100% completed according to the MRTA with signalling and electrical installation ongoing.^[8] As of the end of April 2018, the MRTA stated that the installation of signalling and electrical systems was at 60%. ^[9]

The full extension is currently due to open in December 2018. ^[10]

North

Map of North Extension at Thong Lo station. Station N9 will open in 2019 and stations N10 to N24 will open in 2020.

1st and 2nd extension, currently under construction

• 1) Mo Chit station to Saphan Mai: 11.4 km, 12 stations (N9–N20)
• 2) Saphan Mai to Khu Khot: 7.5 km, four stations (N21-N24)

A 11.4 km, 11 station northern extension from Mo Chit station to Saphan Mai in Don Mueang District has been planned since the Sukhumvit line opened. Originally, this extension was scheduled to be completed by 2008. However, due to a combination of changes in government, a prolonged environmental study, and problems with locating a suitable train depot the extension has been continually delayed. A further 16.5 km, nine station extension from Saphan Mai to Lam Lukka was also planned once the extension to Saphan Mai had been completed.

After many delays, in mid-2013 it was decided to tender extension (1) and (2) at the same time by the end of 2013. However, the dissolution of parliament in November 2013 delayed this yet again. A tender was finally released in January 2014 ^[11] with an April deadline before being delayed until late May 2014 due to concerns from bidders.^[12] A military coup in late-May 2014 suspended the bidding process whilst the military administration reviewed all major projects. In late June, the military administration affirmed the tender which will proceed before the end of 2014. In mid-August, the MRTA announced that the new tender deadline will be 30 September 2014.^[13] Five bidders qualified and successful bids were due to be announced by December 2014.^[14] The tender specifies a construction period of 1,350 days.

On 3 April 2015, MRTA signed four contracts for this extension:^[15]

• Contract 1: Civil works of 11.4 km from Mo Chit to Saphan Mai, will be constructed by Italian-Thai Development (15,269 million baht)
• Contract 2: Civil works of 7.5 km from Saphan Mai to Khu Khot, will be constructed by UN-SH-CH joint venture (6,657 million baht)
• Contract 3: Civil works of Depot and Park and Ride building, will be constructed by STEC-AS joint venture (4,019 million baht)
• Contract 4: Tracklaying and system design, will be constructed by STEC-AS joint venture (2,841 million baht)

The MRTA, contactors and Thai Traffic Police met on 2 September 2015 and confirmed construction would begin on 8 September 2015. A flyover at Kasetsart will need be demolished, which commenced on 12 September 2015.^[16]

As of 31 December 2017, the progress of civil works construction was at 53.31% according to the MRTA. ^[17] As of the end of April 2018, the MRTA stated that civil works progress had advanced to 63.27%. ^[18] As of 30 September, overall construction had progressed to 78.79% ^[19]

The first section to N9 station is planned to open in the first half of 2019, with the full extension currently due to open by July 2020.