The Seikan Submarine Tunnel was opened in March 1988 and runs beneath the seabed of the Tsugaru Strait, which separates the southern edge of Hokkaido from Aomori Prefecture on the northern edge of the mainland. This tunnel is a part of a railway that runs between Aomori City and Hakodate City in just two and a half hours, and was named by combining the two characters and pronunciations of Aomori City's "Ao (Sei)" and Hakodate City's "Hako (Kan)". The length of 53.85 kilometers (33.5 miles) makes it world's longest, though its 23.3 kilometers (14.5 miles) of submarine portion was outdistanced by the 37.5-kilometer (23.3-mile) Euro Tunnel which opened in 1994. The railway track runs 240 meters (787 feet) below the sea surface, and is the deepest railway line in the world. The advanced civil engineering technologies have been rated highly that made it possible for the tunnel to run below 140-meter-deep (459-foot-deep) water as well as 100 meters (328 feet) below the seabed.