Saetgang Station is a railway station on Line 9 of the Seoul Subway. The Seoul Metropolitan Subway, in Seoul, South Korea, is one of the most heavily used rapid transit systems in the world, with well over 8 million trips daily on the system''s eleven lines (total figures for Seoul Metro, Seoul Metropolitan Rapid Transit Corporation & Korail commuter lines). The system serves Seoul, Incheon, Gyeonggi-do and northern Chungcheongnam-do. There is a connection (not a free transfer) to the Incheon International Airport Railroad (A''REX) at Gimpo Airport Station on Line 5 and a free transfer with the single-line Incheon Subway system at Bupyeong on Seoul Subway Line 1. Over 70% of the total metro track length is underground.