Bouygues Construction has helped deliver one of the world’s first post-tensioned timber bridges, marking a major milestone in low-carbon infrastructure and biodiversity protection. Built through its subsidiary VSL International, the wildlife crossing is located in Switzerland between Zurich and Bern and was commissioned by the Federal Roads Office (ASTRA).
Spanning both a motorway and the Koppigen cantonal highway, the bridge reconnects two previously divided natural habitats, allowing wildlife to cross safely while reducing vehicle collisions and ecosystem fragmentation.
Reconnecting Nature Across Major Transport Routes
Until now, the road corridor between Zurich and Bern formed a significant barrier to wildlife movement. The new structure restores ecological continuity by creating a continuous green corridor over the roadway.
Covered with around one metre of soil and native vegetation, the bridge blends into the surrounding landscape, encouraging animals to use it naturally while improving road safety and protecting biodiversity.
Timber Meets Advanced Engineering
From an engineering perspective, the project presented an unprecedented challenge: constructing a post-tensioned structure using timber, a bio-based material known for its low carbon footprint but rarely used for heavily loaded infrastructure.
The timber superstructure consists of two spans, including a 37-metre main span, supporting a concrete slab, backfill, and vegetated covering. The weight of these layers required the use of post-tensioning technology—an approach traditionally reserved for concrete bridges.
Adapting Concrete Technology for Wood
VSL International adapted post-tensioning systems originally designed for concrete to suit timber construction. Engineers developed a custom solution using a large steel plate fitted with multiple small anchorages, allowing high post-tensioning forces to be distributed evenly without damaging the wood.
This innovation made it possible to combine timber’s environmental benefits with the structural performance required for major transport infrastructure.
Backed by Years of Research
The bridge is the result of several years of research and testing conducted in Switzerland in collaboration with the Higher Technical School of Wood in Biel and ETH Zurich. Studies confirmed that post-tensioning significantly improves timber’s load-bearing capacity, reduces deformation, and simplifies long-term maintenance.
A New Path for Low-Carbon Infrastructure
By proving that timber can be used in complex, highly stressed infrastructure projects, Bouygues Construction is opening the door to new low-carbon construction methods that balance engineering performance with environmental responsibility.
The company has previously delivered landmark projects worldwide, including the Hong Kong–Zhuhai–Macau Bridge in China and the Simone Veil Bridge in Bordeaux, France.
