Seoul Subway Line 1 (dubbed The Dark Blue Line) of the Seoul Metropolitan Subway is a rapid transit and commuter rail line which links central Seoul, South Korea to Yeoncheon in the northeast, Incheon in the southwest, and Sinchang via Suwon and Cheonan in the south. The central underground portion of Line 1, running underneath Sejongno, Jongno, and Wangsan-ro avenues along Seoul's traditional downtown area, is the oldest subway-operated section in the Seoul Metropolitan Subway system. Its branches and services cover a large part of the Seoul Metropolitan Area; totaling in route length. In its above-ground stations, Line 1's station signs are a lighter blue and hang from the roof, but it uses dark blue, oblong signs with rounded ends (like lines 2 and 3 except with a different colour) in the underground stations.
The underground section between Seoul station and Cheongnyangni station, which is referred to as Seoul Metro Line 1 () after its operator, is currently operated by Seoul Metro, and is electrified at the subway standard of 1.5 kV DC. The line first opened in 1974 as the Korean National Railroad of Seoul with through services to newly-electrified (at the mainline KNR standard of 25 kV AC 60 Hz) national mainline railways from Seongbuk station (now: Kwangwoon University station) to Incheon and Suwon stations. This was the first electrified rapid transit line and service in South Korea and the second in the Korean Peninsula after the Pyongyang Metro in North Korea opened the year before.
Frequent service is provided between Soyosan, Dongducheon, Uijeongbu, Cheongnyangni, Seoul, Yongsan, and Guro, where trains split between Incheon in the west and Byeongjeom and Cheonan in the south. Express trains operate from Yongsan and Seoul stations to Dongincheon and Sinchang stations. Trains run every 3-6 min in the central route between Seoul Station and Cheongnyangni, every 6-9 min between Seoul and Guro, every 8-10 min between Guro and Incheon and between Guro and Byeongjeom, every 10-15 min from Byeongjeom to Cheonan, and every 35 min between Cheonan and Sinchang and service up to the Dongducheon area and Soyosan station.
Service to Yeoncheon is approximately once per hour, limited due to the single track section approaching Soyosan station. This service is meant to be the replacement for the Gyeongwon line commuter trains, which began at Dongducheon station prior to its closure.
Trains travel along Gyeongbu (Seoul-Cheonan), Gyeongin (Guro-Incheon), Janghang (Cheonan-Sinchang), and Gyeongwon (Hoegi-Yeoncheon) railway lines. The line runs on the left-hand side of the track, as opposed to the right-hand side of the track like all other Seoul Metropolitan Subway lines (another exception to this is Seoul Subway Line 4 although it runs on the right-hand side until Namtaeryeong station, and operates on the left-hand side for the parts afterwards) <오후여담>좌측통행, Munhwailbo since railways in Korea generally run on the left side.
Rapid (Express) trains Korail operates a variety of express "rapid" (Korean: 급행 geup-haeng, Hanja: 急行) trains for long distance commuter services on Line 1. These services include: Gyeongin line express services from Yongsan to Dongincheon, operating express between Guro and Dongincheon, introduced on January 29, 1999, following quadruple-tracking of the Gyeongin Line. Gyeongbu line "A" express services from Cheongnyangni to Cheonan or Sinchang, operating express between Gasan Digital Complex and Cheonan and running local elsewhere. Gyeongbu line "B" express service from Seoul Station to Cheonan or Sinchang, originating at a platform adjacent to Seoul Station, skipping all stations between Seoul station and Geumcheon-gu Office station, making intermediate stops at Anyang, Gunpo, Uiwang, and Sungkyunkwan University, and then following the Gyeongbu line "A" express service pattern south of Suwon. Northbound services (departing from Cheonan/Sinchang and terminating at Seoul Station) stop at Yeongdeungpo station, but southbound services are unable to due to the lack of a raised platform. This service was introduced on September 25, 1982. Gyeongwon line express services from Dongducheon to Incheon, operating express between Dongducheon and Kwangwoon University and running local between Incheon and Kwangwoon University.
Former express services include: One late night Gyeongin line express service that originated at Soyosan, made all stops to Guro, then made express stops until Incheon. Yeongdeungpo-Byeongjeom Gyeongbu line express service, skipping all stations between Yeongdeungpo and Anyang and then following the Yeongsan-Cheonan/Sinchang express service pattern south of Anyang until Byeongjeom. This service was introduced on August 25, 2014 and was discontinued on December 9, 2016. Two faster Yongsan-Sinchang limited express trains (one in each direction), introduced in 2013. This train only operated on weekends and holidays. It was discontinued on July 1, 2018. Faster Yongsan-Dongincheon limited express (Korean: 특급 teuk-geup, Hanja: 特急) trains, introduced on July 7, 2017. These were discontinued on May 26, 2026.https://www.newspim.com/news/view/20260520000969
Electrification Seoul Subway Line 1 is powered by 1500 V direct current on the underground tunnel segment between Cheongnyangni station and Seoul station, and by 25000 V alternating current (60 Hertz frequency) on the rest of the line. Underground DC system was implemented in order to prevent possible telecommunication malfunction by AC current on telephone lines, following the opposition from the Ministry of Postal Service (currently Ministry of Science and ICT). Because of this different manner of offering electric current, there are neutral sections between Cheongnyangni station and Hoegi station, as well as between Seoul Station and Namyeong station. All Line 1 rolling stock are similarly required to be multi-system compatible with both electrification systems.
Stations
Until 2000, the underground city-center portion run by Seoul Metro Corporation—one of Seoul Metro's predecessors—was the only section properly referred to as Line 1 and labeled red on maps. On the other hand, the remaining sections of the rail line run by Korail were referred to as Korean National Railroad of Seoul and the local all-stop services labeled either blue or gray on maps, while the express services were labelled thin red. Since 2000, all adjacent through-running Korail services from the Gyeongbu, Gyeongin and Gyeongwon Lines, as well as later Korail-operated extensions and branches, are officially bundled together with the aforementioned underground portion as part of a greater Line 1, and the labeling on maps was changed and standardized to the current dark blue color (as illustrated in the map below); also to avoid confusion with Line 4's light blue color. (A slightly different shade of red is now used to label the Shinbundang Line which opened in 2011.)
Main Lines Local lines: Yeoncheon, Soyosan, Dongducheon, Yangju, Uijeongbu, Dongmyo or Guro — Incheon Uijeongbu (3 times only on weekdays), Kwangwoon Univ., Cheongnyangni or Guro — Cheonan, Sinchang, or Seodongtan Yeongdeungpo — Gwangmyeong (shuttle)
Express lines: GW: Gyeongwon Express (Dongducheon - Incheon) GI: Gyeongin Express (Yongsan – Dongincheon) GB A: Gyeongbu Express (Cheongnyangni – Cheonan or Sinchang) GB B: Gyeongbu Express (Seoul – Cheonan or Sinchang) ※ Only Korail trains are used for express trains. Key: ● Stops at the station｜ Does not stop at the station○ Limited service
Stationnumber Station name Station name GW GI GB A GB B Transfer Line name Distance Totaldistance Location100-3Yeoncheon No serviceNo serviceNo serviceNo serviceGyeongwon Line0.0Gyeonggi-doYeoncheon-gun100-2Jeongok 8.78.7100-1Cheongsan 3.312.0Dongducheon-si 100 Soyosan 5.8 17.8