Brenner Base Tunnel

The 55-kilometre (34 mi) long, twin-tube tunnel begins in the Innsbruck suburb of Wilten and penetrates the Alps reaching a height of about 840 metres (2,760 ft) above sea level (ASL). The tunnel will be up to 1,720 m (5,640 ft) below the surface at its deepest point in the gneiss section stretching south from the Italian border.[10] Since under the most recent plan the tunnel starts as a twin-tube tunnel, the junction already prepared in the Inntal tunnel on the Innsbruck bypass will not be used. Instead, a diversion with several branches is planned.

The volume of rock to be excavated during the construction of the tunnel is estimated at 21 million cubic metres (740 million cubic feet), of which approximately 60% will be incurred in Austria, as about 60% of the tunnel will be in Austria. A part of the spoil will be used as fill for the approach lines and another part of the spoil material is used to produce the concrete segment for the final lining of the tunnel. The main tunnels will have a circular cross section with a diameter of approx. 8.1 m (27 ft).

According to current planning the apex of the tunnel will be at the border at an altitude of about 810 m (2,660 ft) ASL, although an apex farther south would have been lower. The placing of the apex at the border is set out in the treaty between Austria and Italy. As justification for this choice it is stated that this will allow Austrian water to run in the tunnel to Austria and Italian water to Italy.

On its north end, the base tunnel (BBT) has two entrances, which must go underground a few kilometres before the junction with the main tunnels, and will also be built as part of the BBT. One route leads from the main Innsbruck station under Bergisel and the other connects with the Innsbruck bypass. This route adds about 8 kilometres (5.0 mi) more to the length of the tunnel than the Innsbruck station route; with it included, the BBT, at 62.7 kilometres (39.0 mi), would become the longest continuous railroad tunnel in the world. However, if the Axentunnel extension is added to the Gotthard Base Tunnel, its length would become 75 kilometres (47 mi), allowing it to reclaim the 'longest tunnel' title.

The northern approach from Munich within Germany is the 165 kilometres (103 mi) Grafing–Rosenheim–Kufstein route. The "Brenner Nordzulauf" (Brenner northern link) project aims to construct a high-speed line for speeds of up to 230 km/h (143 mph) between Grafing and Brannenburg in addition to the existing line, adapting the route's capacity to the projected increase as a result of the BBT. The project has reached in-depth planning stages but suffers from lacking support by locals.[11] A more direct route between Munich and Innsbruck, for example, via Garmisch-Partenkirchen, Mittenwald and Seefeld was not pursued, though it could have shortened the Munich Innsbruck line to 129 kilometres (80 mi).

In Austria, a new double-track high-speed line supplements the Lower Inn Valley railway between Wörgl and Baumkirchen. It manages to cut travel time between Munich and Innsbruck from 1:50 via the old tracks to merely 0:55 using the high-speed line.[12] About 32 kilometres (20 mi) of the 40-kilometre (25 mi) line through the Lower Inn Valley (Unterinntal) is built underground, in troughs, or under snow sheds. Noise and vibration mitigation is accomplished by the use of 80,000 square metres (860,000 sq ft) of elastomer in a mass-spring system. The segment's track superstructure is load class E5. It is capable of handling 260-300 trains per day.[1] This section was opened 2012-12-09.[13] Planning is under way on the continuation of this line to the German border at Brannenburg.

The southern approach for the BBT will be 189 kilometres (117 mi) long and reach from the southern portal of the tunnel in Franzensfeste/Fortezza to Verona. Planning has been completed for some sections.

Early in the preliminary planning, at a Brussels meeting in June 2005, BBT SE (Brenner Base Tunnel Societas Europae), presented an interim status report. Expectations following the meeting were that the project could be finalized and the pilot tunnel started by 2006. The target for the tunnel to start service was 2015.[15][16]

In 2007 a construction timeline with a 2022 finish date was specified in a memorandum signed by the Austrian and Italian ministers of transport.[17]

In December 2008 Antonio Tajani, the European commissioner for transport, approved funds totalling €1.7 billion to finance 11 railway projects that together should establish two major routes across the continent.[18][19]

In May 2009 it was confirmed that final go-ahead for the project had been given.[20]

The final estimated cost was put at €8.384bn at 2018 levels.[17]

In the summer of 2007 work started on a pilot tunnel to run along the line of the future tunnel and to be used for removing water and spoil during the major construction phase. Construction of the pilot tunnel between 2006 and 2009 was estimated to cost €430 million and would be 50% EU funded.

On 6 July 2019, two Austrian segments were connected, and an unbroken 36 kilometres (22 mi) long tunnel was formed – around 65% of the tunnel's 55 kilometres (34 mi) projected length.[21]