Connecting Habitats Across Roads and Highways: The Swiss Experience

Raymond Sauvajot
National Park Service
(805)370-2339

Deer Warning Sign

Switzerland has developed some of the most sophisticated techniques for reducing transportation infrastructure impacts on wildlife. The Swiss approach addresses both the direct effects of roads resulting in wildlife mortality as well as proactive measures to ensure safe passage of animals across roads. Many of the methods and techniques utilized in Switzerland have been coupled with extensive research that documents the value of specific measures and provides on-the-ground information for improving crossing point designs.

To reduce wildlife mortality on roadways, the Swiss have developed animal crossing warning signs that are triggered by animals near the roads. When animals (e.g., roe deer, red deer, etc.) cross motion detectors along highway right-of-ways, the signs light up and warn motorists to slow down. The Swiss have documented that these signs have been very effective at influencing driver behavior and reducing wildlife mortality. The signs have been strategically placed on roads with routine drivers.

Like other European countries (e.g., France, Germany, the Netherlands, etc.), Switzerland also incorporates "green bridges" or vegetated overpasses in their highway designs. Such overpasses connect habitats on either side of major transportation routes and are vegetated to encourage their use by various types of animal species. Wildlife monitoring on green bridges (usually from tracks left in "sand traps") is used to establish use patterns and determine which species actually utilize the crossing structures.

Green Bridge in Switzerland

In some areas, the Swiss also provide smaller animal crossing structures, including tunnels, underpasses, and even narrow tubes. Depending on the species of interest, these structures can vary greatly in size and dimension. An interesting example is the one-way amphibian viaducts that funnel frogs and toads from upland habitats to breeding sites in the spring. The amphibians drop into small concrete channels and must travel through one-way tunnels to reach the opposite side of the roadway. This ensures safe dispersal across busy roads, substantially reducing road kills and helping to protect the already rare and sensitive amphibian species of Switzerland. To disperse from breeding sites, the animals follow similar one-way structures back from breeding areas to upland habitats. Although Swiss researchers acknowledge that such structures may be overly complex, they have proved effective in areas where amphibian-breeding sites are separated from upland areas by roads.

Another approach used by Swiss transportation and environmental planners is to couple landscape-level assessments into regional efforts at planning, designing, and constructing roadway crossing structures. In many areas, broad landscape plans were precursors to the actual development of green bridges, tunnels, or other crossing structures. Swiss biologists, planners, and landscape architects work closely together to develop region wide approaches for addressing fragmentation issues, with crossing structures included as only one component in the overall strategy. Landscape considerations include protecting important habitats in areas nearby but not necessarily adjacent to roads, providing hedgerows across agricultural landscapes to enhance regional connectivity, and planting vegetative cover or constructing habitat features (e.g. ponds) to encourage use by wildlife. In some cases, specific host plants or cover species are provided to encourage use by particular types of animals, from insects to larger mammals.

Finally, among the most important contributions provided by the Swiss is their wealth of research information that documents the use of crossing points by wildlife. An extensive research program has been underway in Switzerland for some time that has provided critical data to design and construct wildlife-crossing points across highways. By analyzing the relationship between structure dimensions and wildlife use, the Swiss have produced guidelines for overpass widths and lengths that are being used across Europe. Through innovative use of remote photography, Swiss researchers have compelling evidence of the types, frequencies, and behaviors of animals crossing roads on green bridges and wildlife underpasses. This information provides a critically important baseline that could be applied to similar efforts in the United States.