On 1st July 2023, South Korean state railway Korail opened the 18.3 km extension of the Seohae Line from Sosa to Daegok for regular operation. The section serves the western side of the Seoul metropolitan region. The southern Wonsi – Siheung – Sosa section had already opened in June 2018. Construction of the northern section began in 2016 and was realised by a consortium consisting of Hyundai Engineering & Construction and Daewoo Engineering & Construction, with a total cost of €1.12 billion (KRW 1.6 trillion). The extension runs from Sosa to Gimpo Airport and then under the Han River to a junction with Seoul’s metro line 3 at Daegok, adding four intermediate stations. Connections to Korail's Gyeongui Jungang Line are available at both Neunggok and Daegok. Another extension from Daegok to Ilsan is expected before the end of August 2023.
