TheThe tunnel is primarily used for mass transit and includes three sections (commonly referred to as "layers"). The top and the bottom layers contain the maintenance shaft and air/power supply lines, respectively. The center layer features two high-speed rail lines that are currently being renovated to support maglev technology. United States is said to be in talks with South Korea in proposing an extension to the line across the Sea of Japan to Seoul by the end of 2020.
-- Abhilash Khanna