A tunnel through the Alps in Switzerland that has taken 17 years to build officially opens today. The Gotthard Base Tunnel stretches for 57 km (35 mi), making it the longest rail tunnel in the world. In addition, at 2,300 m (7,546 ft) below the surface of the mountain in places, it is also the world's deepest rail tunnel.

London's Crossrail is regarded as the largest construction project in Europe, but includes only 42 km (26 mi) of new tunnels. The Gotthard Base Tunnel is also just over 3-km (1.9-mi) longer than the Seikan Tunnel in Japan and just under 7-km (4.3-mi) longer than the Channel Tunnel between the UK and France, both of which provide rail passage. It is the ninth longest tunnel of any type in use in the world.

If you take into account the two main tubes that comprise the Gotthard Base Tunnel and its various shafts, cross passages and access tunnels, it actually has 152 km (94 mi) of tunnels in total. It is also said to have virtually no gradients.

The initial idea for the tunnel was conceived 68 years ago, but the plans were redrawn on a number of occasions. Once construction finally commenced, there were 2,400 workers on site at peak times. Nine workers also lost their lives during the build.

There were a wide variety of different rock types through which it was necessary to bore, including granite and sedimentary rock. Around 80 percent of the work was carried out by tunnel boring machines, with the final 20 percent undertaken using blast methods. In total, 28.2 million tonnes (31.1 million tons) of material was excavated.

When work began on laying the slab track, the task took 125 workers working three shifts around the clock over three years to complete. The process used 131,000 cu m (4,626,200 cu ft) of concrete, 290 km (180 mi) of track and 380,000 sleepers.

The tunnel connects Erstfeld with Bodio and will see 325 trains per day run through it, of which 260 will be 160-km/h (99-mph) freight trains and 65 will be 200-km/h (124-mph) passenger trains. The speed of those passenger trains is expected to rise over time to a potential 250 km/h (155 mph) and the journey-time between Zurich and Lugano, which are north and south of Erstfeld and Bodio respectively, is expected to be cut by around 45 minutes.

The Gotthard Base Tunnel is being opened with a special ceremony today, with additional opening events at the weekend expected to attract around 50,000 to 100,000 visitors. Commercial services are scheduled to begin in December 2016.

The video below is an introduction to the tunnel.

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