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The Channel Tunnel (known to the French as Le tunnel sous la Manche), often referred to as the Chunnel, is a 31.35 mile railway tunnel beneath the English Channel at the Strait of Dover, that connects Folkestone in England with Coquelles in France. At its lowest point, it runs 250 ft below the sea bed and 380 ft below sea level. The tunnel has the longest underwater section of any tunnel in the world -- 23.5 miles. [Geological profile]

Construction began in 1988 and the tunnel opened in 1994. Valued at 5.5 billion GBP in 1985, it was at the time the most expensive construction project ever proposed. The cost finally amounted to 9 billion GBP (equivalent to 16 billion in 2016).

Working from both the English and the French sides of the Channel, eleven tunnel boring machines cut through chalk marl to construct two rail tunnels and a service tunnel. The two tunnelling efforts met each other with an offset of only 14 inches (36 cm).

The tunnel carries high-speed Eurostar passenger trains, the Eurotunnel Shuttle for road vehicles (the largest such transport in the world) and international freight trains, and connects end-to-end with the high-speed railway lines of the LGV Nord in France and High Speed 1 in England. In 2017, through rail services carried 10.3 million passengers and 1.22 million tonnes of freight, and the Shuttle carried 10.4 million passengers, 2.6 million cars, 51,000 coaches, and 1.6 million lorries (equivalent to 21.3 million tonnes of freight).

In 1994, the American Society of Civil Engineers elected the tunnel as one of the seven modern Wonders of the World.