Construction began March 24, 1967. The initial segment between Gajwa in the Seo District of Incheon and Yangpyeong-dong in the Yeongdeungpo District of Seoul opened on December 21, 1968. In 1985, the easternmost segment between Yangpyeong and the Shinwol Interchange was transferred to Seoul, making Shinwol in the Yancheong District the new terminus.
It was assigned route number 2 in 1983. In 2001, South Korea re-rationalized its expressway numbering system, and it was redesignated route 120.
History
24 March 1967: Construction begins
21 December 1968: Yangpyeongdong~Gajwa segment open to traffic.
21 July 1969: Gajwa~Incheon Port segment open to traffic.
12 November 1985: Korea National Expressway Corporation passes control of the northernmost 5 km stretch of expressway (between Sinwol and Yangpyeong-dong) to the City of Seoul.
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