Following the 1961 coup, the Supreme Council for National Reconstruction started South Korea's first five-year plan, which included a construction program to complete the railway network, to foster economic growth. One of the first lines completed under the plan was the Hwangji Branchline, which would later become the eastern end of the Taebaek Line. The long spur from Baeksan on the Cheoram Line (today the Yeongdong Line) to Hwangji (renamed Taebaek in 1984) opened on December 20, 1962. Another project under the five-year plan was a railway between Yemi on the Hambaek Line and Jeongseon. The section climbing the mountains around Hambaek to Jeongsan (renamed Mindungsan in 2009), which would later become part of the Taebaek Line, was completed on December 19, 1966, and the entire railway from Jecheon to Jeongseon was renamed the Jeongseon Line, with the short Yemi–Hambaek branch retaining the Hambaek Line name. A long track section on the climb after Yemi is the steepest on South Korea's network at 30.3‰. Also on December 19, 1966, a branch from Jeongsan to Gohan opened as the Gohan Line, which would also become part of the future Taebaek Line. The Jeongseon Line was completed to Jeongseon on January 20, 1967; this section and its later extensions form the present-day Jeongseon Line.