[1] The proposed 73 km[2] tunnel is projected to take 11 years to complete [3] at an estimated cost of 14.6 trillion South Korean won (11.2 billion US Dollars).
The underwater tunnel would allow the KTX bullet train to connect the port city of Mokpo and Jeju island.
The provincial government predicts that by the time the project reaches completion, as many as 15 million passengers (for comparison over 14 million passengers flew between Jeju and Seoul alone in 2018 making it the world's busiest air route) will take advantage of the service in a year, with an annual savings of 42,000 won[dubious – discuss] in social cost[clarification needed] and 140,000 newly created jobs.
Residents of Jeju have raised concerns that the construction of the tunnel may impact the island's indigenous culture.
[4] The proposal was shelved because of the high cost and technological challenge of building the world's longest underwater tunnel.