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 (57.1km, 2016), Switzerland
- Mont d'Ambin Base Tunnel (57km, planned), France and Italy
- Brenner Base Tunnel (55km, proj. 2025), Austria and Italy
- Lötschberg Base Tunnel (34.6km, 2007), Switzerland
- Koralm Tunnel (32.9km, proj. 2022), Austria
- Semmering Base Tunnel (27.3km, proj. 2025), Austria
- Pajares Base Tunnel (24.7km, proj. 2012, but currently not usable), Spain
- Zimmerberg Base Tunnel (20km, planned), Switzerland
- Apennine Base Tunnel (18.5km, 1934), Italy
- Ceneri Base Tunnel (15.4km, proj. 2020), Switzerland
- Furka Base Tunnel (15.4km, 1982), Switzerland
- "LZMK: tunel" (in Croatian). enciklopedija.hr. Archived from the original on June 2, 2016. Retrieved June 2, 2016.
... prema dubini u terenu: niskoležeći (bazni) tuneli, tuneli koji spajaju dvije doline približno iste nadmorske visine, visokoležeći kratki vododijelni tuneli s usponima s obiju strana i prijelomom nivelete u sredini tunela te niskoležeći dugi vododijelni tuneli s jednim nagibom.
- Latest plan for California’s high-speed rail calls for tunnel into San Fernando Valley, Los Angeles Daily News, 2016-4-11