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Brenner Base Tunnel – Breakthrough at the Brenner Pass
Historic Moment – Austria and Italy United Underground
Since December 2023, construction lot H53 has been excavating the final section of the exploratory tunnel (EKS). With the breakthrough on September 18, 2025, underneath the Brenner Pass, the last 1.6 km of tunnel between km 30.4 and the national border at km 32.0 have now been completed. This connects lots H53 “Pfons–Brenner” and H61 “Mauls” – creating, for the first time, a continuous underground link between Innsbruck and Franzensfeste. The Brenner Base Tunnel is becoming reality!
The so-called exploratory tunnel (EKS) runs centered in between and slightly below the two future main rail tunnel tubes.
During the construction phase, the EKS is used for preliminary geological investigation of the subsurface and is therefore always excavated ahead of the main tunnels (rail tubes). In addition, the EKS collects all groundwater from the tunnel drainage systems during both construction and operation phases and discharges it from the tunnel using gravity flow – without the need for any pumping during regular operation.
Construction of the EKS on the Austrian side began at the end of 2009. The total length from the Sill Gorge south of Innsbruck to the national border underneath the Brenner Pass is approximately 30 km. Along this northern ramp, the longitudinal gradient varies between 4.0 ‰ and 8.0 ‰. On the Italian side, another approximately 27 km of tunnel follow with a gradient of about 4.0 ‰ leading to the Aicha portal north of Brixen. This shorter section was fully excavated by the end of 2021.
During the operational phase, the EKS is planned to serve as a permanently accessible route for maintenance personnel and to house various technical systems. As a service and drainage tunnel, the former exploratory tunnel will allow large portions of routine maintenance and servicing work to be carried out without disrupting train operations. Access to the crosslinks of the main tunnels will also be possible via shaft structures with staircases.
The breakthrough of the two main rail tunnel tubes at the national border is expected around mid-2026, which will connect all three tubes on both the Austrian and Italian sides. Excavation work will be completed by the end of 2026 with additional tunnel boring machine breakthroughs on the Austrian side – marking the start of the final construction phase comprising secondary lining and subsequent railway system installation on both sides of the Brenner Pass.
