Bouygues Construction delivers timber bridge innovation for wildlife protection
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Infrastructure is often associated with fragmentation, carving landscapes into disconnected zones that prioritise mobility over ecosystems. In Switzerland, a new wildlife bridge constructed by Bouygues Construction is attempting to reverse that logic, combining structural innovation with environmental restoration. Built between Zurich and Bern, the crossing represents one of the world’s first bridges to use post tensioned timber at this scale, a milestone that highlights how engineering techniques can be adapted to support biodiversity as well as transport.
Commissioned by the Swiss Federal Roads Office, the structure spans both a motorway and the Koppigen cantonal highway, reconnecting two previously separated natural areas. For years, the road corridor formed an effective barrier for wildlife, increasing habitat fragmentation and the risk of vehicle collisions. By restoring ecological continuity, the bridge aims to improve biodiversity outcomes while also enhancing road safety.
Covered by around one metre of soil and vegetation, the structure is designed to function as a natural extension of the surrounding landscape rather than a visible piece of transport infrastructure. From above, it forms a continuous green corridor that allows animals to cross without exposure to traffic noise or light, reflecting a growing emphasis on nature inclusive design in major infrastructure projects.
Timber engineering meets heavy load requirements
The most significant innovation lies beneath the vegetation. The bridge uses a post tensioned timber superstructure, a solution rarely applied in timber construction due to the challenges of managing heavy loads. In this case, the structure consists of two spans, including a main span of thirty seven metres, supporting not only the timber deck but also a concrete slab, backfill and a thick layer of earth and planting.
Such loads would typically push designers toward concrete or steel. Timber, while valued for its low carbon properties, has traditionally been limited in long span and high load applications. Post tensioning changes that equation by introducing compressive forces that enhance load bearing capacity and control deformation over time.
Bouygues Construction subsidiary VSL International adapted post tensioning techniques originally developed for concrete structures for use with timber. This required a customised anchoring system capable of distributing very high forces without damaging the wood. Engineers designed a large steel plate fitted with multiple small anchorages, allowing stresses to be spread evenly across the timber elements.
The result is a hybrid structure that combines the environmental benefits of a bio based material with the structural performance typically associated with more carbon intensive solutions. It demonstrates how established engineering methods can be reinterpreted to expand the role of timber in infrastructure.
Biodiversity protection through infrastructure design
Wildlife crossings have become an increasingly important tool in reducing the ecological impact of roads and railways. By allowing animals to move freely between habitats, they help maintain genetic diversity and reduce mortality caused by vehicle collisions. The Koppigen bridge addresses both concerns by restoring a key migration route between two natural areas.
The decision to cover the bridge with soil and vegetation is central to its function. Animals are more likely to use crossings that resemble their natural environment, avoiding exposed structures that feel artificial or unsafe. The depth of planting also supports a wider range of species, from small mammals to larger wildlife, increasing the ecological value of the corridor.
From a safety perspective, reducing wildlife collisions benefits motorists as well as ecosystems. In Switzerland, as in many European countries, such incidents carry significant economic and human costs. Integrating biodiversity measures into road infrastructure therefore delivers both environmental and societal returns.
Research driven innovation in sustainable construction
The bridge is the outcome of several years of research and testing carried out in Switzerland, involving collaboration with the Higher Technical School of Wood in Biel and ETH Zurich. These studies explored how post tensioning could improve the performance of timber structures, focusing on strength, deformation control and long term maintenance.
Research confirmed that post tensioned timber can offer enhanced durability and reduced lifecycle costs compared with conventional timber designs. By limiting deflection and cracking, the technique improves serviceability and extends structural life, addressing one of the common concerns associated with wood in large scale applications.
For Bouygues Construction and VSL International, the project serves as a demonstration of how low carbon materials can be integrated into demanding infrastructure contexts without compromising performance. As governments and clients place greater emphasis on embodied carbon and environmental impact, such solutions are likely to gain traction.
The Koppigen bridge suggests that future infrastructure does not have to choose between engineering performance and ecological responsibility. By combining advanced structural techniques with biodiversity led design, the project offers a model for how transport networks can be built to reconnect landscapes rather than divide them.
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