Base tunnel

A base tunnel is a type of tunnel, mainly a railway tunnel, that is built through the base of a mountain pass. This type of tunnel typically connects two valleys at about the same altitudes.^[1]

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.

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

• Gotthard Base Tunnel (57.1 km, 35.5 mi, 2016), Switzerland
• Lötschberg Base Tunnel (34.6 km, 21.5 mi, 2007), Switzerland
• Koralm Tunnel (32.9 km, 20.4 mi, 2025), Austria^[2]
• Pajares Base Tunnel (24.7 km, 15.3 mi, 2023), Spain
• Zimmerberg Base Tunnel (20 km, 12 mi, planned), Switzerland
• Túnel del Simplón ( 19,8 kilómetros (12,3 millas) , 1906/1921), Suiza 
• Túnel de base de los Apeninos ( 18,5 km, 11,5 millas , 1934), Italia  
• Túnel de base de Ceneri ( 15,4 km, 9,6 mi , 2020), Suiza  
• Túnel de base de Furka ( 15,4 km, 9,6 mi , 1982), Suiza  

• Túnel de base de Mont d'Ambin ( 57,5 km, 35,7 mi , proyecto 2032 ), Francia e Italia  
• Túnel de base del Brenner ( 55 km, 34 millas , proyecto 2032 ), Austria e Italia  
• Túnel de base de Semmering ( 27,3 km, 17,0 mi , proyecto 2030 ), Austria  
• Túnel Valico ( 27 km, 17 mi , proyecto 2026 ), Italia  
• Túnel de base del Monte Metálico en la línea ferroviaria de alta velocidad Dresde - Praga , Alemania/República Checa ( 30,4 km (18,9 millas) ) ^{[ 3 ] [ 4 ]}