Originally consisting of seven stations from National Stadium to Saphan Taksin when the BTS first opened 5 December 1999. A planned station at S4 was not built but is under construction as of 2019.. Its formal name is The Elevated Train in Commemoration of HM the King's 6th Cycle Birthday 2nd line.
Extensions and current construction
A 2.2 km extension across the river to Wongwian Yai opened 15 May 2009 after many years of delay. Originally, this extension was due to open in 2007. A further 5.3 km, 4 station extension from Wongwian Yai to Bang Wa in Phasi Charoen District was delayed for many months by the Bangkok floods of late 2011. The first station of extension, Pho Nimit opened on 12 January 2013. The second station of the extension, Talat Phlu opened on 14 February 2013. The extension was initially operated by a separate 6 car shuttle service due to the absence of a turnout between Wongwian Yai and Talat Phlu. The remaining two stations Wutthakat and Bang Wa were opened on 5 December 2013.
Future extension plans
South: After the opening of Wutthakat and Bang Wa stations 5 December 2013, the BMA announced a new proposal to further extended the Silom line by 7 km from Bang Wa station, by six stations to Taling Chan. Here, it would connect with the SRT Light Red line. A public hearing was held in 2015. Three route options were considered, with construction planned to start in 2017. However, as of August 2018, no plan has been finalised. Part of the basis for this further extension by the BMA is that it would provide proximate access to the Southern Bus Terminal. This proposal in currently under preliminary study by the BMA.
West: The Silom line is planned to be extended by two stations west from National Stadium to link with the SRT Dark Red line at Yot Se station. However, no time frame for this extension has been announced and this section of the Dark Red line will not be built until after 2022. Originally, the plan was to extend the Silom line west from National Stadium into Chinatown, then north to Democracy Monument where it would then run west to Rattanakosin Island and Sanum Luang, tunnel under the river to the Thonburi side before terminating at Phrannok. However, this plan was shelved back in 2009 and much of this route has been replaced by routing changes to the planned MRT Orange line.
