 At the time, the 7.8 km underground portion was run by Seoul Metro was called Line 1 and labeled red on maps.On the other hand, the remaining sections of the rail line run by Korail were labeled either blue or gray on maps, and the express lines were red.In 2000, the adjacent through-running Korail services from the Gyeongbu, Gyeongin and Gyeongwon Lines were officially bundled together as part of a greater Line 1, and the labeling on maps was changed to the current dark blue color.