Gotthard Tunnel, 57 km (35.4 miles).
• Seikan Tunnel, 54 km (33.5 miles) in Japan.
• The Yulhyeon Tunnel, 50.3 km (31.2 miles).
The Seoul metropolitan high-speed railway project broke ground in 2011 designed to build a 61.1 km-long (38 mile) high-speed railway connecting from Suseo in Seoul to Pyeongtaek in Gyeongi Province with a budget worth 3.06 trillion won (US$ 2.76 billion).
The total excavation period, including access adits and ventilation shafts, was a swift three years and five months from January 2012 to June 2015.
Hyundai Rotem has been awarded two contracts to supply 300 km/h (186 mph) high speed train-sets. A 324bn won (US$282.6 B)contract covers 10 KTX-Sancheon train-sets for the Suseo High Speed Railway subsidiary of Korail, which will operate the 60 km high speed line [44:48] now under construction.
Travel time through the Yulhyeon tunnel will be about ~15 minutes at 240km/hr (150 mph.)
Article aggregated from several South Korean resources.