Looking down a subway train tube.
The Seoul Metropolitan Subway is one of the most heavily used subway systems in the world, with well over 8 million trips daily on the system's nine lines (total figures for Seoul Metropolitan Subway Corporation, Seoul Metropolitan Rapid Transit Corporation & Korean National Railroad commuter lines). The system serves Seoul and surrounding Gyeonggi province and Incheon city, with a connection to the Incheon subway system. It began to serve Cheonan, Chungnam province in 2005. Ticket prices start at 900 won for a trip up to 12 km, with 100 won added for each 6 km after that. Riders may also enter the system using a pre-paid debit card called T-Money for a discounted price.
Current total length of the subway system is about 287 km except KNR lines).
Subways are operated by three different organisations:
- Korean National Railroad (KNR) (Bundang Line, most of Line 1, and parts of Lines 3 and 4);
- Seoul Metropolitan Subway Corporation (SMSC) (Line 2, underground part of Line 1, and most of Lines 3 and 4). The corporation runs a total of 199 trains at 115 stations on lines 1-4. Generally, operation intervals are 2.5 -3 minutes during rush hours and 4-6 minutes during non-rush hours. An average of 3,879,000 passengers use subway lines 1-4 everyday. and
- Seoul Metropolitan Rapid Transit Corporation (SMRTC) (Lines 5, 6, 7, and 8).
The KNR, the forerunner of the SMSC, began operating Line 1 in 1974. Lines 2, 3, and 4 followed in the late 1970s and 1980s. The SMRTC was formed in 1994 to take over operation of lines 5 to 8.
The subway lines and their operators and colours are as follows:
Two new subway lines are currently under construction and have yet to open:
- Line 9 will run east from Gimpo Airport along the south bank of the Han River. Construction of the first phase began in April 2002 and is due for completion in 2008.
- New Bundang Line will be a new line from Gangnam in Seoul to Jeongja in Bundang, Seongnam. Construction is due to be completed in 2010.
Several existing lines are also currently undergoing extension:
- Line 3 will be extended south from Suseo to Garak Market and Ogeum, interchanging with lines 8 and 5 respectively, by 2009.
- By 2008, the Bundang line will be extended north from Seolleung to Wangsimni and south to Yongin and Suwon, with eventual plans for it to run all the way to Incheon, completing a southern outer semicircle.
- Line 7 will be extended west 9.8 km from Onsu to meet Incheon Subway line 1 at Bupyeong-gu Office. Nine new stations will be added by 2010.
There are several major works still in the planning stage:
- A 10 km extension to the New Bundang Line (see above) northward from Gangnam station to Yongsan is under consideration. If approved, the project is estimated to cost at least 400 billion won.
- By the end of 2011, Seoul City plans to build a 10.72 km 'light' subway line from Ui-dong to Sinseol-dong in northern Seoul. The line is expected to carry 110,000 passengers a day and will have 12 stations. It will connect to Line 4 at Sungshin Women's University Station, Line 6 at Bomun Station and Sinseol-dong Station (Line 1 & 2).
- EverLine Rapid Transit System will be a new line branching off the Bundang line extension and running east into Yongin and then to the theme park Everland.
- An extension of the Jungang Line from Deokso is also planned. This should eventually terminate in Wonju, Gangwon Province.
For more details on new projects, see  (in Korean)