A base tunnel is a type of

tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...

, mainly a

railway Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...

tunnel, that is built through the base of a

mountain pass A mountain pass is a navigable route through a mountain range or over a ridge. Since many of the world's mountain ranges have presented formidable barriers to travel, passes have played a key role in trade, war, and both Human migration, human a ...

. This type of tunnel typically connects two

valley A valley is an elongated low area often running between Hill, hills or Mountain, mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers ...

s at about the same

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

s. When originally constructed, classical railway lines through mountainous terrain tried to minimize tunneling, due to technical limitations and expense, and therefore required long and steep gradients and many curves, or even spirals. Tunnels were generally short and much higher up the mountain. Such tunnels are sometimes also called ''culmination tunnels'', especially in the presence of a base tunnel through the same mountain massif. The base tunnels take the opposite approach, minimizing or eliminating gradients and curves with the consequence of having longer tunnels but shorter total distances to travel. This allows for higher speeds and lower energy costs. GBT-ESS

Some of the best-known base tunnels are (with length, opening and location): *

Mont d'Ambin Base Tunnel The Mont d'Ambin Base Tunnel, also known as the Mont Cenis Base Tunnel, is the largest engineering work of the Lyon–Turin rail link project. Once completed, it will facilitate the principal high speed rail link between Italy and France, conve ...

(, ''proj. 2032''), France and Italy *

Gotthard Base Tunnel , rm, Tunnel da basa dal Sogn Gottard , image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg , image_size = 250 , caption = Turnout at Faido multifunction station , line = Gotthard Line , location = Switzerland (Uri, Grisons and ...

(, 2016), Switzerland *

Brenner Base Tunnel The Brenner Base Tunnel (german: Brennerbasistunnel; it, Galleria di base del Brennero) is a railway tunnel under construction through the base of the Eastern Alps beneath the Brenner Pass. Upon completion, it will be the second or third longe ...

(, ''proj. 2025''), Austria and Italy *

Lötschberg Base Tunnel , line = Lötschberg Line , location = Traversing the Bernese Alps in Switzerland , coordinates = – , system = BLS, SBB CFF FFS , status = , start = Frutigen, canton of Bern, , end = Raro ...

(, 2007), Switzerland *

Koralm Tunnel The Koralm Tunnel is a railway tunnel that is under construction in Austria under the Koralpe mountain range. It forms one section of the -long Koralm Railway which will link Graz with Klagenfurt. Once complete, the Koralm Tunnel shall be Austri ...

(, ''proj. 2026''), Austria *

Semmering Base Tunnel The Semmering Base Tunnel is a railway tunnel under construction between Gloggnitz and Mürzzuschlag in Austria underneath the Semmering Pass. The existing route is 41 km in length and the Semmering Base Tunnel will be 27.3 km in length ...

(, ''proj. 2027''), Austria * Valico Tunnel (, ''proj. 2025''), Italy *

Pajares Base Tunnel The Pajares Base Tunnel is a twin pair of railway tunnels beneath the Puerto de Pajares pass in the Cantabrian Mountains, Spain. Once completed, the length tunnel will form a key portion of the high-speed rail line between Valladolid and Gijón, ...

(, ''proj. 2012, but currently not usable''), Spain *

Zimmerberg Base Tunnel The Zimmerberg Base Tunnel (ZBT) is a railway tunnel under the Zimmerberg mountains in Switzerland. Phase I of the tunnel was opened to traffic during April 2003. The ZBT has been divided into two phases of work; as of 2020, only Phase I is ope ...

(, ''planned''), Switzerland *

Simplon Tunnel , it, Galleria del Sempione , line = Simplon line, (Lötschberg railway line) , location = Traversing the Lepontine Alps between Switzerland and Italy , coordinates = – , system = Swiss Federal Railways (SBB CFF FF ...

(, 1906/1921), Switzerland *

Apennine Base Tunnel The Apennine Base Tunnel, alternatively known as the Grand Apennine Tunnel, is a railway base tunnel long on the Bologna-Florence Direttissima line in central Italy. At the time of its completion, the Apennine Base Tunnel was the world's second ...

(, 1934), Italy *

Ceneri Base Tunnel The Ceneri Base Tunnel (CBT, it, Galleria di base del Monte Ceneri) is a Swiss railway base tunnel in the canton of Ticino. It passes under Monte Ceneri between Camorino in the Magadino Flat and Vezia near Lugano; it bypasses the former high-a ...

(, 2020), Switzerland *

Furka Base Tunnel The Furka Base Tunnel is a Swiss railway base tunnel on the Matterhorn Gotthard Bahn's Furka–Oberalp line, an east-west railway connecting the cantons of Valais and Uri. Its west portal lies east of Oberwald (VS), at above sea level and its ...

(, 1982), Switzerland * Ore Mountain Base Tunnel as part of the Dresden Prague High Speed Railway Line (Czech Republic and Germany)

References

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