The Yulhyeon Tunnel ( Korean 율현 터널 Yulhyeon-teoneol ) opened in December 2016 in South Korea is one of the longest railway tunnels in the world at 50.3 kilometers . The tunnel, which consists of a tube with two tracks, is part of the 61.1-kilometer high-speed Suseo – Pyeongtaek line , which connects Suseo station in the southeast of the South Korean capital Seoul with the high-speed line from Seoul Central Station to Daegu , which opened in 2004 . The threading into the older high-speed line takes place in the south of the city of Pyeongtaek . The tunnel itself takes up approx. 82% of the entire new line. The Yulhyeon Tunnel was built using the New Austrian Tunneling Method (NÖT) and is structurally designed for a maximum speed of 300 km / h. The mean travel speed is around 240 km / h due to the stop at the Dongtan underground station in the southern part of the tunnel.
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