5 Longest Undersea Tunnels

1. Seikan Tunnel  -Japan

The Seikan Tunnel is a 53.85 km (33.46 mi) railway tunnel in Japan, with a 23.3-kilometre (14.5 mi) long portion under the seabed. Track level is about 140-metre (460 ft) below seabed and 240-metre (790 ft) below sea level. It travels beneath the Tsugaru Strait—connecting Aomori Prefecture on the Japanese island of Honshū and the island of Hokkaidō—as part of the Kaikyo Line of Hokkaido Railway Company. The name Seikan comes from combining the on'yomi readings of the first characters of Aomori and Hakodate, the nearest major city on the Hokkaido side.

It is the longest undersea tunnel in the world, although the Channel Tunnel between the United Kingdom and France has a longer undersea portion, and also the deepest rail tunnel in the world. It is the longest rail tunnel in the world, although the longer Gotthard Base Tunnel in Switzerland is under construction and scheduled to open to traffic in 2017.

2. Channel Tunnel - England/France

The Channel Tunnel is a 50.5-km (31.4 mi) undersea rail tunnel linking Folkestone, Kent near Dover in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is 75 metres (250 ft) deep. At 37.9 kilometres (23.5 mi), the Channel Tunnel possesses the longest undersea portion of any tunnel in the world, although the Seikan Tunnel in Japan is both longer overall at 53.85 kilometres (33.46 mi), and deeper at 240 metres (790 ft) below sea level.

3. Shin-Kanmon Tunnel - Japan

^{Shin-Kanmon Tunnel is 18,713 m long and carries the Sanyō Shinkansen under the Kanmon Straits.}

^{4. Tokyo Bay Aqua-Line - Japan}

^{The Tokyo Bay Aqua-Line, also known as the Trans-Tokyo Bay Highway, is a bridge-tunnel combination across Tokyo Bay in Japan. It connects the city of Kawasaki in Kanagawa Prefecture with the city of Kisarazu in Chiba Prefecture, and forms part of National Route 409. With an overall length of 14 km, it includes a 4.4 km bridge and 9.6 km tunnel underneath the bay—the fourth-longest underwater tunnel in the world.}

^{5. Great Belt Fixed Link - Danmark}

^{The Great Belt Fixed Link is the fixed link between the Danish islands of Zealand and Funen across the Great Belt. It consists of a road suspension bridge and railway tunnel (East tunnel) between Zealand and the island Sprogø, as well as a box girder bridge between Sprogø and Funen.The twin bored tunnel tubes of the East Tunnel are 8,024 metres (4.986 mi) long each. Between the two main tunnels, 31 connecting tunnels were placed at 250 metres (820 ft) intervals. The equipment that is necessary for train operation in the tunnels[clarification needed] is installed in the connecting tunnels. The connecting tunnels also serve as emergency escape routes.}