 The line was originally two spur lines, which were built across difficult mountainous terrain in stages, before a connection was built.The line includes the steepest section of the South Korean network, a short parallel line that is operated as a second track on the section includes South Korea's longest spiral tunnel.The centerpiece of the last-built section west of Taebaek, is a tunnel that was the longest in South Korea at the time of its construction, and Chujeon Station at the eastern end of the tunnel is the highest altitude in South Korea at .