Seoul Subway Line 4 of the Seoul Metropolitan Subway (dubbed the blue line) is a long line crossing from the southwest to the northeast across the Seoul National Capital Area. The southern portion of the line is divided into the Gwacheon and Ansan Lines, but this does not affect the trains which run on it, most of which run all the way from one end of the line to the other. The southern terminus (Oido) is in Jeongwang 4-dong, Siheung City, and the northern terminus (Danggogae) is in Sanggye 4-dong, Nowon-gu, northern Seoul.
Line 4 was built 1980-94. Total length in Seoul: 31.7 km.