The Seikan Tunnel is a 53.85 km (33.49 mile) railway tunnel in Japan, with a 23.3 km (14.5 mile) portion under the seabed. It is the longest undersea tunnel in the world, although the Channel Tunnel between England and France has a longer under-sea portion. 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. Although it is the longest traffic (railway or road) tunnel in the world, faster and cheaper air travel has left the Seikan Tunnel comparatively underused. Its claim to the record will be taken when the Gotthard Base Tunnel, another railroad tunnel, is completed around 2018. It is also the deepest rail tunnel in the world.