It is the first rail connection for the city of Siheung, and serves areas of Gyeonggi Province which were previously without rail. The Seohae Line (literally West Sea Line) has 12 stations and shortens what was previously a 1.5 hour trip by car to 33 minutes by train. Services will operate every 13 minutes during peak times and every 20 minutes off-peak.

The line connects with Seoul's Line 1 at Sosa and Line 4 at Choji. Siheung City Hall will also become a transfer station with enhanced lines to Seoul when the future Sinansan and Wolgot-Pangyo lines open.

In addition, the Seohae Line will eventually connect to the planned Daegok - Sosa and Hongseong - Wonsi lines, opening a direct link between the Gyeongui Line and Janghang Line and enabling commuter, high-speed, and freight trains to use the new corridor.