Sukhumvit Line

The Elevated Train in Commemoration of HM the King's 6th Cycle Birthday 1st line, also known as Sukhumvit Line, is one of the rapid transit lines of the BTS Skytrain System in Bangkok, Thailand. The line runs from Siam Station, where it interchanges with the Silom Line, and continues both northwards along Phaya Thai and Phahon Yothin Roads to Khu Khot in Lam Luk Ka District, Pathum Thani, and eastwards along Rama I, Phloen Chit and Sukhumvit Roads, through Bang Na District to Kheha Station in Samut Prakan.
The line was first opened on 5 December 1999, along with the Silom Line. Both lines are operated by the Bangkok Mass Transit System Public Company Limited under a 30-year concession from the Bangkok Metropolitan Administration. When it opened, the line ran from Mo Chit to On Nut covering a total distance of with 17 stations. Sukhumvit Line is one of the main arteries of the Bangkok Mass Rapid Transit System with 900,000 daily passengers per day. The line rapidly expanded from 2011 until 2021, tripling its distance through three extension projects and reaching a total length of with 47 stations.

History

Original plan

The Sukhumvit Line's initial proposal was for route running from N4 station to E9 station with the depot located at Lumphini Park near the Silom Line. However, this location for the depot faced backlash from the public opinion, which argued that it violated King Vajiravudh's intention in donating his land to establish Lumphini Park for the public. Additionally, there were protests demanding that the construction of both Skytrain lines be built underground instead of being fully elevated. Therefore, several alternative locations for the depot were considered, such as a vacant land plot in Soi Rangnam owned by the Crowned Property Bureau or the Phra Khanong pumping station in Sukhumvit 50. Ultimately, the Bangkok Metropolitan Administration decided to relocate the depot to the former site of the Northern Bus Terminal. With the decision made, the Sukhumvit Line route was extended from N4 station to N8 station. Several changes were made during the construction, as follows:

N3, N4, E8, and E9 stations were changed from an island platform to side platforms.
The fully operational year was pushed from the end of 1996 to the end of 1999.
Station designs were drastically changed from the EIA reports.
CEN station was moved from the east side of Chaloem Phao junction to the west side.
E1 station was moved from the east side of the Chit Lom junction to the west side, in front of Mater Dei School, with the two entrances in front of the school being canceled due to protests from school staffs and students concerned about privacy, landscape, and air pollution issues.
E2 station was originally located between Sukhumvit 2 and Soi Nana but was later moved to the west side of the Chaloem Maha Nakhon Expressway.
E4 station was moved from the east side of the Asok junction to the west side.
Extensions

Bearing Extension

Construction started in August 2006 on a four-billion baht, extension from On Nut to Bearing which included 5 new stations The extension was funded by the BMA. The original scheduled opening date was mid-2009. However, a delay in tendering the contract for the electrical and signaling works resulted in a two-year delay.
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 on this extension until the end of 2011 as compensation.

Samut Prakan Extension

Construction started in April 2012 on a, nine station extension from Bearing station to Kheha station. The extension was 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.
In 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. Track works were 98% completed by November 2016. The total cost of the extension was estimated at 21.4 billion baht. In January 2017, it was announced that the opening of the extension could be further delayed to 2018-2019 due to budgetary concerns and ongoing disputes between the MRTA and BMA.
The first section of the extension to Samrong station opened on 3 April 2017. The full extension to Kheha opened on 6 December 2018.

Khu Khot Extension

An 11.4 km, 11 station northern extension from Mo Chit station to Saphan Mai in Don Mueang District had 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 was continually delayed. A further, nine station extension from Saphan Mai to Khu Khot was also planned once the extension to Saphan Mai had been completed.
After multiple delays, in mid-2013 a decision was made to tender extensions and 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 with an April deadline before being delayed until late May 2014 due to concerns from bidders. 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 that the tender would proceed before the end of 2014. In August 2014, the MRTA announced that the new tender deadline was 30 September 2014. Five bidders qualified and the successful bids were announced in December 2014. The tender specified a construction period of 1,350 days.
On 3 April 2015, MRTA signed four contracts for this extension:

Contract	Notes	Contractors	Length	Costs
1	Mo Chit to Saphan Mai	Italian-Thai Development		฿15,269 million
2	Saphan Mai to Khu Khot	UN-SH-CH joint-venture		฿6,657 million
3	Khu Khot Depot and Park & Ride buildings at Yaek Kor Por Aor and Khu Khot stations	STEC-AS joint-venture		฿4,019 million
4	Track laying and system design	STEC-AS joint-venture		฿2,841 million

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 was demolished, which commenced on 12 September 2015.
At 31 December 2017, the progress of civil works construction was at 53.31% according to the MRTA. the MRTA stated that civil works progress had advanced to 63.27%. overall construction had progressed to 78.79%. By the end of March 2019, civil construction had nearly been completed having progressed to 99.42%.
Testing of the final 9.8 km, seven-station-section from Wat Phra Sri Mahathat to Khu Khot began on 5 October. The final section was officially opened on 16 December 2020 by the Prime Minister.

Tamru Extension ''(future)''

There is a plan to extend Sukhumvit Line from Kheha to Tamru for, including 5 additional stations: Sawangkhaniwat, Mueang Boran, Si Chan Pradit, Bang Pu, and Tamru. This extension has been suspended indefinitely until clarity is reached regarding passenger guarantees.

Lam Luk Ka Extension ''(future)''

There is a plan to extend Sukhumvit Line from Khu Khot Station eastwards for, including four additional stations: Khlong Sam, Khlong Si, Khlong Ha, and Eastern Ring Road-Lam Luk Ka. This extension has been suspended indefinitely until clarity is reached regarding passenger guarantees.

Opening timeline

Stations

Infrastructure

Depot

The Sukhumvit Line has three depots: Mo Chit Depot, Khu Khot Depot, and Kheha Depot.
Mo Chit Depot serves as the central operations center for the BTS Skytrain network. It is located near Mo Chit Station, opposite Chatuchak Park, and was built as part of the original phase of the BTS Skytrain System, completed in 1999.
Khu Khot Depot, situated in the Sai Mai District of Bangkok near Khu Khot Station, was constructed as part of the Khu Khot Extension and was completed in 2019.
The third facility, Kheha Depot, is located in Mueang Samut Prakan District, Samut Prakan Province. It was built alongside the Samut Prakan Extension and completed in 2018.
Both Mo Chit and Khu Khot Depots are also shared with the Silom Line. Trains from these depots operate regular service on the Sukhumvit Line before switching to the Silom Line at Siam Station, continuing until they terminate at Bang Wa Station.

Park & Ride

Sukhumvit Line offers five parking lots located at Mo Chit, Victory Monument, Asok, and Samrong stations. In addition, Park & Ride buildings owned and operated by the Mass Rapid Transit Authority of Thailand are available at Khu Khot, Yaek Kor Por Aor, and Kheha stations.

Station

There are 55 stations on the Sukhumvit Line, all of which are elevated. Most stations feature a side platform layout, with the exceptions of Ha Yaek Lat Phrao and Samrong stations, which have island platforms. Siam Station is unique with a stacked island platform layout, allowing for a cross-platform interchange with the Silom Line.
Stations on the Sukhumvit Line are generally 150 meters in length and are equipped with half-height platform screen doors at most locations. However, some stations—such as Mo Chit, Saphan Khwai, Ari, Sanam Pao, Ratchathewi, Phloen Chit, Nana, Ekkamai, Phra Khanong, Bang Chak, Punnawithi, Udom Suk, Bang Na, and Bearing—do not have platform screen doors.