Jeolla Line

The upgrade of the Iksan-Suncheon section started with the construction of a bypass around Jeonju with wider curves, opened in 1981.

From 1989, the first phase of the project to re-lay and double-track the line, mostly in a new alignment with wider curves, longer tunnels and bridges, was launched on three sections between Sin-ri, at the end of the Jeonju realignment, and Suncheon. The two longest new structures were the 5,671 m (18,606 ft) long[5] Byeongpung Tunnel, north of Suncheon, and the 6,128 m (20,105 ft) long Seulchi Tunnel, south of Jeonju, which became South Korea's longest rail tunnel,[5] surpassing Jeongam Tunnel on the Taebaek Line.[6] The three sections of the first phase with altogether 64.3 km (40.0 mi), shortening the original route by 16.7 km (10.4 mi), were finished by 1999 and entered service on 18 May 1999.[5] The two gaps between those sections were plugged in a second phase in 2002 and August 2004, the altogether 58.3 km (36.2 mi) long new sections shortened the line by another 11.4 km (7.1 mi).[5]

The third phase of the upgrading project, started in 2002, involved the double-tracking of the remaining 35.2 km (21.9 mi) long single-track section from Iksan to Sin-ri, until the end of the Jeonju realignment, and electrification of the entire double-tracked and re-aligned section from Iksan to Suncheon, altogether 154.2 km (95.8 mi),[7] to allow speeds of 180 km/h (110 mph).[8] By March 2010, progress on the 154.2 km (95.8 mi) section from Iksan to Suncheon reached 63.0%.[7] This phase of the project is implemented as a public private partnership of the Build-Transfer-Lease (BTL) method, with a government contribution of 510.852 billion won and a BTL share of 470.699 billion won.[7] The upgrade and re-alignment of the final Suncheon-Yeosu section was launched as a separate project in 2001,[9] with work starting in December 2003.[10] As of March 2010, progress on the 40.0 km (24.9 mi) long alignment stood at 88.0% out of a total budget of 732.002 billion won.[11] The entire upgrading project is to be completed in 2011.[7][11]

On September 1, 2010, the South Korean government announced a strategic plan to reduce travel times from Seoul to 95% of the country to under 2 hours by 2020. As part of the plan, the Jeolla Line is to be further upgraded for 230 km/h (140 mph).[12]

Yeosu hosted the Expo 2012, and Korail timed the introduction of Korea Train Express services on the line ahead of the event.[10] Original plans foresaw the start of Jeolla KTX services in April 2011, reducing the Seoul–Yeosu travel time to 2 hours 55 minutes, using KTX-II (KTX-Sancheon) high-speed trains.[14] In February 2011, when the necessary electrification works were 96% complete, the start of services was postponed to September 2011, and the Yongsan–Yeosu travel time was planned to be 3 hours 7 minutes.[15] After the completion of the first stage of the Honam High Speed Railway, the travel time is planned to reduce to 2 hours 25 minutes.[14]