Simplon Tunnel

The Simplon Tunnel is a railway tunnel on the Simplon railway that connects Brig, Switzerland and Domodossola, Italy, through the Alps, providing a shortcut under the Simplon Pass route. It is straight except for short curves at either end. It actually consists of two single-track tunnels built nearly 15 years apart. The first to be opened is 19,803 m long; the second is 19,824 m long, making it the longest railway tunnel in the world for most of the twentieth century, from 1906 until 1982, when the Daishimizu Tunnel opened.

Culminating at a height of only 705 m above sea level, the Simplon Tunnel was also the lowest direct Alpine crossing for 110 years, until the opening of the Gotthard Base Tunnel in 2016. The tunnel has a maximum rock overlay of approximately 2,150 m , also a world record at the time. Temperatures up to 56 °C have been measured inside the tunnel.

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