 At the same time, the Taebaek Triangle Line, a connection built for trains from Jecheon to Donghae to run without reversal at Baeksan, was also put in service.To improve traffic on the steep climb from Yemi to Jodong, the Hambaek Line was extended to Jodong to provide a second track.The altitude difference was mastered with a spiral tunnel, the Hambaek 1 Tunnel, which was South Korea's longest spiral tunnel at .