The Channel Tunnel is a 50.45 km rail link under the Strait of Dover between Folkestone in Kent and Coquelles near Calais, opened on 6 May 1994. It is made up of three parallel bores, two for trains and one for service, and its 37.9 km undersea section is the longest of any tunnel in the world. Eurostar passenger trains and Eurotunnel's LeShuttle vehicle trains use it, with the shuttle taking about 35 minutes.
Two Centuries of Plans Britain Kept Burying
Engineering was never the main obstacle to a tunnel under the Channel. Politics was. The first serious plan came in 1802, when the French mining engineer Albert Mathieu-Favier proposed a tunnel lit by oil lamps, with horse-drawn coaches and an artificial island on the Varne sandbank midway across where the horses could be changed. War resumed in 1803, and for the rest of the century every British debate on a fixed link became an argument about invasion: a tunnel that could carry passengers to Dover could carry an army.
The Victorians came closest in the early 1880s, when the railway promoter Sir Edward Watkin backed a pilot tunnel using a compressed-air boring machine designed by Frederick Beaumont and improved by Thomas English. Working from Shakespeare Cliff near Dover and from Sangatte on the French coast, the crews drove roughly 1.8 km on the English side and about 1.7 km on the French side through the same chalk the modern tunnel would later use. The machine worked. What stopped it was a campaign led by General Sir Garnet Wolseley, who warned that a few hundred soldiers could seize the English portal. The dig was halted in 1882.
The idea returned after both world wars, and work finally started at both ends in 1974. In January 1975 Harold Wilson's government cancelled it, citing spiralling costs, leaving a lasting French suspicion that Britain would never commit.
From the Treaty of Canterbury to a Private Concession
In 1985 the two governments invited private proposals, including road bridges and a drive-through road tunnel. Margaret Thatcher insisted on no public money, so the winner had to be financeable. In January 1986 they chose the Channel Tunnel Group/France-Manche scheme: twin rail tunnels with vehicle shuttle trains, the least ambitious design but the most realistic.
On 12 February 1986 Thatcher and François Mitterrand signed the Treaty of Canterbury in the chapter house of Canterbury Cathedral. It set out the frontier, policing and joint safety arrangements, and a 1987 concession gave Eurotunnel the right to build and run the link. Construction went to Transmanche Link (TML), ten British and French contractors, funded by shares and a syndicate of more than 200 banks.
Boring Through the Chalk Marl
Most of the tunnel follows a single geological layer: the chalk marl, a soft, fairly impermeable mix of chalk and clay at the base of the Chalk sequence. It cuts easily and keeps water out better than the fissured chalk above, so the engineers set the tunnel's line to follow the layer as it dips and rises, which is why the route bends gently rather than running straight. On average the tunnels sit about 40 m below the seabed, and the lowest point is around 75 m below sea level.
Eleven tunnel boring machines did the work, six on the English side and five on the French. On the English side the chalk marl was dry enough for open-faced machines; near Sangatte the French crews met wetter, fractured rock and used closed machines that could hold back water under pressure. Spoil from the British drives at Shakespeare Cliff now forms Samphire Hoe, a country park of about 30 hectares.
The service tunnel went first, as a probe. On 1 December 1990 the British and French service tunnels met under the sea. Graham Fagg and Philippe Cozette shook hands through the gap, and laser guidance had brought the two bores together within about half a metre of each other. The rail tunnels broke through in 1991. Ten workers were killed during construction, eight of them British.
Three Tunnels, One System
The Channel Tunnel is really three parallel tunnels, each 50.45 km long. The two running tunnels, about 7.6 m in internal diameter, each carry a single track: trains heading for France use the northern bore and trains heading for England use the southern one. Between them runs a 4.8 m service tunnel, kept at higher air pressure so smoke from a fire cannot enter it.
- Cross-passages connect each rail tunnel to the service tunnel every 375 m.
- Piston relief ducts of about 2 m in diameter link the two rail tunnels every 250 m, relieving the air pressure pushed ahead of trains.
- Two undersea crossover caverns, one on each side of the midpoint, let trains switch between tunnels, so a section can close for maintenance while traffic continues.
The terminals at Cheriton, outside Folkestone on the M20, and Coquelles, off the A16, each have a loop of track so shuttles turn without reversing. Both countries' border checks happen at the departure terminal under juxtaposed controls.
Crossing Today: LeShuttle and Eurostar
Queen Elizabeth II and President Mitterrand opened the tunnel on 6 May 1994. The Queen took a Eurostar from Waterloo to Coquelles, and the two heads of state then rode back to Folkestone together in the Queen's Rolls-Royce aboard a shuttle. Eurostar's public service began on 14 November 1994.
LeShuttle, run by Eurotunnel (now Getlink), loads cars and coaches onto enclosed carriages; passengers stay with their vehicles and the crossing takes about 35 minutes. Freight shuttles carry lorries while drivers ride in a club car. Eurostar runs through the tunnel without stopping. Since High Speed 1 was completed in 2007 and the London terminal moved to St Pancras, the fastest trains have reached Paris in about 2 hours 16 minutes and Brussels in about 2 hours. Speeds in the tunnel are limited to about 160 km/h.
The tunnel turned the narrowest part of the sea between England and France, described in our guide to the English Channel and the Strait of Dover, from a ferry crossing into a rail journey.
Fires, Migrants and Money: The Hard Years
The tunnel's finances were in trouble before it opened. Construction alone cost about £4.65 billion, roughly 80% more than forecast, and with financing costs the total investment is usually put at around £9 billion or more, depending on what is counted. Traffic lagged the forecasts, and after years of debt talks Eurotunnel went through a court-supervised restructuring in Paris in 2007 that cost early shareholders most of their money. It renamed itself Getlink in 2017.
Fire has been the main operational danger, and it has come from lorries, not passenger trains. On 18 November 1996 a fire on a freight shuttle badly damaged several hundred metres of tunnel lining. Everyone escaped through the service tunnel. A second serious fire on 11 September 2008, again on a lorry shuttle, damaged a longer stretch of the northern rail tunnel and kept it out of full use until February 2009. Eurotunnel then installed fixed fire-suppression stations, which spray water mist onto a burning train at set points inside the tunnel.
The tunnel has also been part of the long-running migration crisis around Calais. Between 1999 and 2002 the Red Cross ran a reception centre at Sangatte, close to the French portal, until the two governments agreed to close it. Attempts to board shuttles or walk through the tunnel rose sharply in summer 2015, and people were killed trying. The terminals are now ringed by fences and detection systems paid for largely by the UK.
Channel Tunnel vs Seikan Tunnel vs Gotthard Base Tunnel
The Channel Tunnel is often called the world's longest tunnel. It isn't: Japan's Seikan and Switzerland's Gotthard Base are both longer.
Seikan, opened on 13 March 1988, links Honshu and Hokkaido under the Tsugaru Strait. It goes much deeper than the Channel Tunnel: about 240 m below sea level and roughly 100 m below the seabed, because the strait is deeper and the geology is volcanic and badly faulted. Its construction cost 34 lives. Only about 23 km of Seikan is under water, though, while the Channel Tunnel's 37.9 km undersea section is still the longest in the world.
The Gotthard Base Tunnel, opened on 1 June 2016, is the longest rail tunnel overall at 57.1 km. It runs entirely under the Alps between Erstfeld and Bodio, with as much as 2,300 m of mountain above it. Its builders worried about rock temperatures of up to about 45°C and the pressure of the mountain, not seawater. Like the Channel Tunnel it has twin single-track tubes, but instead of a service bore it relies on two underground emergency stations.
Gotthard fought depth under mountains, Seikan depth under a rough strait, and the Channel Tunnel distance under the sea, plus a political obstacle the other two never faced. The full ranking is in our list of the ten longest tunnels in the world, and the Alpine road crossing between France and Italy is covered in the Mont Blanc Tunnel guide. For the two countries at either end, which spent centuries fearing each other before digging this link, see how they line up in our United Kingdom vs France comparison.