The section between Songdo-Oido opened early by next year 2008-01-13 "서울경제 : 송도~오이도 내년말 조기개통". Archived from the original on 2011-10-04. Retrieved 2008-01-27.
The section between Songdo-Oido opened early by next year 2008-01-13 "서울경제 : 송도~오이도 내년말 조기개통". Archived from the original on 2011-10-04. Retrieved 2008-01-27.
wikipedia.org
ko.wikipedia.org
"수도권 전철 4호선". 위키백과, 우리 모두의 백과사전 (in Korean). 2018-03-28.