Wildlife Crossings, Colorado USA

Wildlife crossings in the Rockies

In 2010 the state of Colorado, USA, started a competition to find a design for a system of wildlife crossings. The architectural studio ZJA was part of a combination of partners (with OKRA Landscape architects, IV-Infra and Sjef Jansen Planecologie) that belonged to the five finalists.

Read more about the design process

The location that the competition focussed on was the Vail Pass, where a highway crosses the wilderness in the southern flanks of the Rocky Mountains. This design chose to achieve an optimized combination of the specific functions of a wildlife crossing together with an integration of the structure into the landscape . Construction and landscape were to merge completely, as if the surrounding slopes themselves had decided to grow over and across the man-made highway to restore the ecological connection for plants and animals.

Ideal would be a free span that forms itself following the local, irregular and far from geometrical and symmetric shapes in the landscape. The question was how to combine these irregular curves with the engineering requirements that determine free concrete spans. This concept, aiming for a merging of natural and architectural shapes and qualities was dubbed ‘landshape’.

The construction method

Usually concrete is poured into formwork consisting of straight surfaces or cylinders. To be able to pour concrete into a freely formed shell at this scale required a new approach. The presented design relied on the application of shotcrete in formwork that consisted of a textile membrane supported by a network of steel cables. This allows for a free and unique shape to be produced. This type a flexible formwork can be re-used in its entirety, whereas traditional formwork is treated as waste.


A visitor’s centre, integrated into the slope is part of the design. It allows visitors to climb to a lookout, well hidden in the green, that offers the opportunity to watch the crossing fauna.


Parametric design

The look of the landshape-design can best be described as a double curved arch, with the two curves at a straight angle, much like in the case of a Pringle potato crisp. Why is this such an ideal shape? First of all it allows for a free span that mimics the gradient of the surrounding slopes in the landscape, while secondly producing a kind of bowl on top with curled up sides, giving the wildlife a sense of safety, because they shield off the visual and acoustic presence of the highway. This shape is both beautiful and functional and fits very well into the landscape, but it also produced quite a few technical challenges.

How does one find out how to accurately describe such a thin concrete shell for this specific asymmetrical location? And how does one produce the formwork to pour the concrete in this unique shape? The Vail wildlife crossing was designed using a parametric model, which is a description of the shape and structural qualities of the material in mathematic functions. Together they form a logical and coherent model. Changes in the parameters produce different shapes, new problems and new possibilities. This way the designer can ask questions and receive feedback from the parametric model, that, much like a script, dishes out a series of consequences as a result of assumed values.

Designing and form-finding merge in the application of this method. This is the way the resulting shape for this particular location was found. A parametric model makes it easy to produce adapted versions of the basic design for other locations.

The Colorado competition referred to a system of wildlife crossings. The ZJA design is particularly well suited to adapt itself to the morphology of other locations, without losing its characteristic look. The formwork, consisting of the textile membrane and the network of steel cables can be used to construct the other versions, as it is flexible. This reduces waste and the amount of energy used.

ZJA’s design philosophy

This design is a striking example of ZJA’s design philosophy. First it shows the drive to turn the inquiry into the required functions and the location into a logical, coherent and clear intervention, so that design and context reinforce each other. Secondly, it shows the search to use in-house research to translate new constructional methods, new technology and materials into realistic designs. These two aspects of ZJA’s design philosophy meet in an ideal way in the design for the Vail Wildlife Crossing.

Architect: ZJA
Combination of partners: ZJA, OKRA Landscape architects, IV-Infra and Sjef Jansen Planecologie
In collaboration with: Diederik Veenendaal ETH Zürich
Competition: 2010

Project: #628





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