The missing gaps across the urban areas of Daejeon and Daegu were in construction for an expected opening in 2014, separate tracks into Seoul Station were also planned.

On 1 August 2015, construction on urban areas of Daejeon and Daegu were completed; all the sections of HSR line were connected.

After 2016, the privately owned SRT service started operations on the railway from Suseo station in Seoul.

[1] During the next years, several feasibility studies were prepared for a high-speed line with a Seoul–Busan travel time of 1 hour 30 minutes, which gave positive results.

[1] In 1989, following the go-ahead for the project, the institutions to manage its preparation were established: the Gyeongbu High Speed Electric Railway & New International Airport Committee, and the High Speed Electric Railway Planning Department (later renamed HSR Project Planning Board).

[6] Once planning progressed, in March 1992, the Korea High Speed Rail Construction Authority (KHSRCA) was established as a separate body with own budget responsible for the project.

[4] KHSRCA announced that the GEC-Alsthom-led consortium was the preferred bidder on 20 August 1993, and the contract was signed on 14 June 1994.

[10] Track-related design specifications included a design speed of 350 km/h (215 mph), standard gauge, continuously welded rails with UIC 60 profile (60 kg/m (120 lb/yd)), 2.6 m (8 ft 6 in) wide concrete sleepers, 35 cm (14 in) high ballast bed, swing-nose switches for high-speed passage, 25 kV/60 Hz electrification, standard French TVM 430[11] automatic cab signalling and centralised train control.

[5][7] Following the 1997 Asian Financial Crisis, the government decided to realise the Gyeongbu HSR in two phases.

[3] Well ahead of the opening of the Gyeongbu HSR for regular service, in December 1999, 34.4 km (21.4 mi) of the test section was finished to enable trials with trains.

[9] Other foreign contributors included SNCF (training and supervision of infrastructure and operations),[18] Pandrol[10] and Vossloh (rail fastenings),[18] and Cegelec (catenary).

[17] The original plans foresaw a second-phase opening in 2008, with new trains cruising at a top speed of 350 km/h (217 mph) cutting Seoul-Busan travel times to just 1 hours 56 minutes.

The main cause of delay was a long dispute over the environmental impact assessment of the Wonhyo Tunnel, which passes under a wetland area.

[26][27] The dispute gained nationwide and international attention due to the repeated hunger strikes of a Buddhist nun, led to a suspension of works in 2005,[28] and only ended with a supreme court ruling in June 2006.

[8] In February 2009, cracks were found on 332 newly laid concrete sleepers on the 96.9 km (60.2 mi) long section between Daegu and Ulsan, the cause of which was improper water insulation.

[38] On 1 September 2010, the government released a new strategic plan, with the aim to reduce travel times for 95% of Korea to under 2 hours by 2020.

The first incident on the high-speed line happened on 11 February 2011, when a KTX-Sancheon train[42] bound for Seoul from Busan derailed on a switch in the Iljik Tunnel, 500 m (1,600 ft) before Gwangmyeong station,[43] when travelling at around 90 km/h (56 mph).

[44] No casualties were reported, only one passenger suffered slight injury, but KTX traffic was blocked until repairs for 29 hours.

[42] Preliminary investigation indicated that the accident resulted from a series of human errors,[43] Workers had improperly repaired a point along the tracks.

[45] Investigators found that the derailment was caused by a switch malfunction triggered by a loose nut from track, and suspected that a repairman failed to tighten it during maintenance the previous night.

[43] The switch's detectors signalled a problem earlier, however, a second maintenance crew failed to find the loose nut and didn't properly communicate the fact to the control center, which then allowed the train on the track.

[46] From 1 December 2010, Korail added a pair of non-stop trains[49] with a travel time of 2 hours 8 minutes.

[50] With the completion of the sections across urban Daejeon and Daegu, a further improvement of the four-stop travel time to 2 hour and 10 minutes between Seoul and Busan is expected.

[52] In the first estimate after the separation of the project into phases, the prediction for the first-year average daily ridership of the Gyeongbu KTX Line was 141,497, which reduced to 115,828 in the final August 2003 forecast.

Services using the Gyeongbu HSR between Seoul and Dongdaegu, and diverging to the Gyeongbu Line to reach the Gyeongjeon Line, are operated as the Gyeongjeon KTX service, which started on 15 December 2010,[63] initially reaching Masan with a minimum travel time of 2 hours 54 minutes.

[66] The section from Cheonan to Daejeon, with Osong depot as operations base, was used for the commissioning of the KTX-I trains before the start of regular service.

At 1:24 am on 16 December 2004, the experimental train HSR-350x achieved the South Korean rail speed record of 352.4 km/h (219.0 mph) on the line.