A dual gauge railroad track has three or four rails, allowing vehicles of two track gauges to run on it.
Signalling and sidings are more expensive to install on dual gauge tracks than on two single gauge tracks. Dual gauge is used when there is not enough room for two single tracks or when tracks of two different gauges meet in marshalling yards or train stations.
The Seikan Tunnel (Japanese: 青函トンネル, Seikan Tonneru or 青函隧道, Seikan Zuidō) is a 53.85-kilometre (33.5-mile) dual-gauge railway tunnel in Japan, with a 23.3-kilometre (14.5-mile) segment running beneath the seabed of the Tsugaru Strait, which separates Aomori Prefecture on Honshu, Japan's main island, from the northern island of Hokkaido. The tunnel's track level lies approximately 100 metres (330 ft) below the seabed and 240 metres (790 ft) below sea level. Following several decades of planning and construction, the tunnel opened on 13 March 1988.
The Seikan Tunnel forms part of the standard-gauge Hokkaido Shinkansen as well as the narrow-gauge Kaikyō Line operated by the Hokkaido Railway Company (JR Hokkaido). Its name, "Seikan," is derived from the on'yomi readings of the first characters of Aomori (青森), the nearest major city in Honshu, and Hakodate (函館), the nearest major city in Hokkaido.
The Hokkaido Railway Company (北海道旅客鉄道株式会社, Hokkaidō Ryokaku Tetsudō kabushiki gaisha) is one of the constituent companies of the Japan Railways Group (JR Group), and is often referred to by its official abbreviation: JR Hokkaido (JR北海道, Jeiāru Hokkaidō). It operates intercity and local rail services in Hokkaido, Japan. The company introduced Kitaca, a smart card ticketing system, in autumn 2008.
At the time of its privatization in 1987, JR Hokkaido operated 21 railway lines totalling 3,176.6 kilometres (1,973.8 mi) of narrow-gauge (1,067 mm (3 ft 6 in)) track, as well as a ferry service to Aomori. Since then, that figure has dwindled to just below 2,500 kilometres (1,600 mi), as unprofitable lines have been shut down or spun off (in the case of the Hokkaidō Chihoku Kōgen Railway). The ferry service has also been replaced by the 53.85-km long dual-gauge Seikan Tunnel for railways.
The Birmingham Snow Hill to Wolverhampton Low Level Line was part of the Great Western Railway's London Paddington to Birkenhead Woodside route. As the name suggests, it ran between Birmingham Snow Hill and Wolverhampton Low Level in England. The line was dual-gauged, both 7 ft 1⁄4 in (2,140 mm) and 4 ft 8+1⁄2 in (1,435 mm) standard gauge.
The line opened in 1854 and the final section was closed in August 1992, following the closure of other sections during the 1970s and 1980s. The opening was delayed for two months because a bridge collapsed near Winson Green, which caused chief engineer Isambard Kingdom Brunel to order strengthening on several other bridges. Passenger services had been discontinued in 1972, although parts of the line continued to be used by goods trains.