Go inside Brenner Basis Tunnel – The world’s largest railway tunnel under construction

Far below the Brenner Pass, the longest underground railway connection in the world is being built. The 64 km long Brenner Basis Tunnel (BBT) is a railway tunnel connecting Austria and Italy. The BBT tunnel system includes about 230 km of tunnels. 101 km have already been excavated. Four construction sites are currently in operation, two in Austria and two in Italy. I have had the possibility to document the ongoing work and to photograph the impressive construction site.

The BBT consists of two tubes, each 8.1 m wide, running 40-70 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.


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