Inn bridge Terfens, A12 Inntal motorway

Around 60,000 vehicles use the A12 Inntal motorway near Terfens every day. Due to the increasing volume of traffic and the requirement for two lanes per directional carriageway, the Terfener Inn bridge had reached the limits of its load-bearing capacity. Replacement was urgently required.

In the beginning there were three. In order to keep traffic flowing as freely as possible during the construction period, PORR first built a 220-metre-long temporary bridge on the southern side. The existing northern bridge was then demolished and rebuilt. One year later, it was the turn of the existing southern bridge.

Bridge construction - always a challenge. The new Terfen Inn Bridge is a 3-span prestressed concrete structure with a box girder cross-section. There is a separate bridge structure for each directional carriageway.

The supporting structures were erected "in free cantilever" from the bridge piers, i.e. without any downward support, they are assembled section by section and pushed further and further forward. The existing river pier in the centre of the river was removed and replaced by two new river piers for each bridge support structure. The foundations of these newly constructed piers were laid using large bored piles. A watertight sheet pile box was erected for the construction of the foundation slab. Construction in the Inn could only be carried out from November to April due to the water level. In addition, the foundations (bored piles, foundations) and the piers had to be built on islands in the river area during periods of low water. Since 2021, traffic has been flowing freely again on two lanes in each direction plus a hard shoulder.