The Brenner Base Tunnel :The BBT consists of two tubes, each 8.1 m wide, running 70 m apart from one another. These tubes are each equipped with a single track, meaning that train traffic through the tubes is one-way. The two tubes are linked every 333 m by connecting side tunnels. These can be used in emergencies as escape routes. This configuration conforms to the highest security standards for tunnels.
A peculiar feature of the Brenner Base Tunnel (BBT) is the exploratory tunnel running from one end to the other. This tunnel lies between the two main tunnels and about 12 m below them and with a diameter of 5 m is noticeably smaller than the main tubes. The excavations currently underway on the exploratory tunnel should provide information on the rock mass and thereby reduce construction costs and times to a minimum. The exploratory tunnel will be essential for drainage when the BBT becomes operational.
The BBT runs for 64 km between Tulfes/Innsbruck and Fortezza, making it the longest underground railway stretch in the word. The BBT ends in Innsbruck in the existing railway bypass tunnel, which ends in Tulfes. A new rescue tunnel is being built running parallel to the bypass. The two-tube tunnel system between Innsbruck and Fortezza is 55 km long.
The slope in the base tunnel is 6,7 ‰ on the northern side and 4 ‰ on the southern flank of the Brenner. The apex height is 790 above sea level, lying 580 m below the Brenner Pass itself (1,371 m).