This impressive engineering feat is announced by new portal structures at both ends of the tunnel, to a competition-winning design by architect Peter Riepl. The highly architectonic approach taken is unusual for projects of this kind, suggesting a new building typology in celebration of transport infrastructure. But precedents can be found with the architectural treatments of 19th century railway tunnel entrances.
At Bosruck, the architecture is thoroughly modern and the design strategy almost theatrical. A series of screens – made up of perforated brass cassettes, profiled and arranged to reflect the verticality of the surroundings – partially conceal buildings and equipment essential to the tunnels operation and safety. They impose a visual order and consistency for these disparate elements but also offer transparency and airiness, symbolic of the now barrier-free connection between the two federal provinces. The rhythms of the vertical brass screens will highlight the experience of travellers as they approach and drive straight into the building, moving through the dramatic ‘flying roof’ entrance and exit galleries which act as transition spaces between inside and out.
This light touch approach belies the permanent nature of the structures and technical demands of such a challenging environment. Brass was chosen for its long-life and durability, including resistance to road salt, after running a corrosion trial simulating the exposure of the material for 30 years.