Seoul Subway Line 4

Seoul Subway Line 4 (dubbed The Light Blue Line) of the Seoul Metropolitan Subway is a long line crossing from the southwest to the northeast across the Seoul National Capital Area. The central section in Seoul City is operated by Seoul Metro with some trains offering through service to Korail's Ansan and Gwacheon Lines. The southern terminus (Oido) is in Jeongwang 4-dong, Siheung City, and the northern terminus (Jinjeop) is in Jinjeop-eup, Namyangju-si, Gyeonggi-do; the newly built northern section (officially called the Jinjeop Line) is correspondingly owned by a company owned by Namyangju-si, with operations contracted to Seoul Metro. In 2022, the Seoul Metro operated section had an annual ridership of 219,587,000 or about 601,608 passengers per day.

Northbound trains that run on the Ansan and Gwacheon Lines terminate at Danggogae, except during night time where they short-turn at various stations. Southbound trains that run on the Ansan and Gwacheon Lines terminate at Oido or Ansan. All trains from Jinjeop short-turn at Sadang, though some short-turn trains to Sadang start at Danggogae or terminate one station south at Namtaeryeong.

Express train service stops at all stations between Danggogae and Sanbon, then at Sangnoksu, Jungang, Choji, Ansan, Jeongwang, and Oido. The express service only operates during rush hours on weekdays.