The BBT consists of two single-track tunnels at a distance of approx. 70 m. The Tunnels are connected by cross-passages at intervals of 333 m. The cross-passages serve as escape routes in case of an emergency.
A distinctive feature of the base tunnel is the exploratory tunnel; it lies at a depth of approx. 12 m below and between the two main tunnels with a diameter ranging from 6 to 8 m. The excavation of the exploratory tunnel will help determine the exact geological nature of the rock and therefore minimize the excavation cost and time of the main tunnels. After completion of the main tunnels, the exploratory tunnel will be used as a service and drainage tunnel.
Upon completion of the BBT, the tunnel will have a total length of 64 km and be the world’s longest underground railway connection. In Innsbruck, the tunnel connects to the current bypass, which leads into the Unterinntalstrasse in Tulfes. Parallel to the bypass there will be an emergency tunnel/gallery. The two main tunnels between Innsbruck and Franzenfeste are 55 km long.
The gradient of the base tunnel is 6.7‰ on the north side and 4.0‰ on the south side.
Lombardi Ltd., together with partners of the joint venture BBT north, was assigned the planning, tendering, design details and geotechnical supervision of the construction lots H21 (Sillschlucht), H41 (Sillschlucht-Pfons) and H51 (Pfons-Brenner). Lombardi Ltd. is responsible for the planning of the excavation.