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Public Roads - November/December 2002

The Scan of The Wild

by Fred Bank

01gamal1As development and urban expansion increase in many areas around the globe, the transportation systems built to serve this growth can adversely affect existing wildlife populations and the natural habitats they occupy. Increasingly, transportation agencies must address impacts to wildlife and habitat resources when planning and implementing transportation improvements.

Since the issues involved in addressing these impacts are international in nature, the Federal Highway Administration's (FHWA) Offices of International Programs and Natural Environment, the American Association of State Highway and Transportation Officials (AASHTO), and the National Cooperative Highway Research Program (NCHRP) recently sponsored an international technology scan to learn what actions are being taken abroad to address transportation and wildlife issues.

These organizations chose to examine activities in five European countries that have successful programs for dealing with transportation and wildlife issues. Specifically, the scan objectives were to observe and document policies, technologies, and practices in Europe that are:

  • Reducing wildlife mortality
  • Maintaining wildlife habitat connectivity across transportation facilities
  • Protecting threatened populations of wildlife species
  • Improving highway safety by reducing collisions with wildlife

In October 2001, an interdisciplinary delegation of Federal, State, and conservation group representatives visited Slovenia, Switzerland, Germany, France, and the Netherlands. Although each country uses different approaches to address wildlife issues, they have formed an international network to share information. The Infra Eco Network Europe (IENE) brings together state-of-the-art information on wildlife and transportation. Through comprehensive research on wildlife and habitat-related issues, IENE ultimately will benefit all of Europe as well as the rest of the world.


A Swiss scientist sets up an infrared video camera on a overpass to monitor wildlife.


Slovenia is a young country, a fact that is reflected in the number and type of actions that it has undertaken to address habitat fragmentation by highways. Because of the connectivity of its forests with those of Croatia and Italy, Slovenia has the opportunity to affect the future of European wildlife significantly.

Although the Slovenians have the necessary environmental laws and documentation processes to address wildlife-transportation issues, various environmental issues remain unresolved. The Eurasian brown bear, for example, is both a protected and a legally hunted species.

An infrared still camera with a protective case is mounted on a Slovenian bridge.

As was the case in several of the European countries visited, hunting is an important factor in wildlife management. University and forestry personnel studying wildlife behavior (the Eurasian brown bear in particular) use information from hunters in their research. They also use public opinion to influence the transportation ministry to provide connectivity across highways. The survey indicated the Slovenian public's desire to accommodate habitat and wildlife considerations.

In concert with public action, the researchers also provide the transportation agency with specific information on habitat connectivity needs on Slovenian highways. One result was a viaduct that was constructed for multiple purposes—habitat connectivity, hydrology, and human access. Subsequent studies of the structure have indicated that a variety of wildlife cross under the structure.

Fencing, including electrical fence, is used on Slovenian highways to keep wildlife off the roads, thereby increasing motorists' safety. The scan team believes that the situation in Slovenia is similar to that in the United States because the impact of transportation on wildlife is an emerging issue, and it often takes diverse interests joining together to influence the actions of transportation agencies.


In contrast to Slovenia, Switzerland's transportation and environmental programs have a long history of research and actions related to wildlife. Swiss actions are scientifically based, supplemented by hunter information as in Slovenia. Swiss scientists have completed geographic information system- (GIS-) based identification of wildlife habitat and corridors nationwide, pinpointing bottlenecks and voids in connectivity. They characterize the wildlife corridors as impacted, impaired, or interrupted, with only one-third categorized as intact. The main corridors are forested, and riparian corridors are highly impacted.

Landscape planning plays an important role in Switzerland, as do habitat restoration and purchases for connectivity. Expert groups use scientific research to develop standards for assessing habitat, as well as designing and implementing restoration and other mitigation actions. In this process, the Swiss use scientific information from other European countries extensively, including adopting measures employed by their neighbors.

The Swiss use a variety of structural and nonstructural measures. Vegetated overpasses, called "green bridges" or "ecoducts," are a preferred structure for maintaining habitat connectivity. Swiss research demonstrates that the diverse habitats on green bridges provide important connectivity for a broad spectrum of species—from invertebrates to ungulates. "We compared observations of butterflies crossing highways between forest segments connected by a green bridge with segments having no overpass," Verena Keller of the Swiss Ornithological Institute told the scan team. "Few crossed without, many crossed with the overpass."

Many of the overpasses are multiple use, accommodating forestry roads and wildlife. The structures are monitored using standard approaches such as animal tracks and photography, and evolving technologies including infrared video. The video makes it possible to record the behavior of the animals while using the structures. The Swiss research indicates that overpasses with a width of 50 meters (164 feet) or greater are used by the widest variety of species, and the animals exhibit natural behavioral characteristics when using the structures.


German transportation projects identified at the cabinet and parliament levels are sent to the transportation ministry for implementation. The Federal Environment Ministry is consulted and enforces environmental actions using Germany's Nature Conservation Act and what is known as the "Red List" (threatened and endangered species). All actions must follow strict measures for using land in a sustainable manner. Germany has an early warning system of environmental risk assessment to help avoid environmentally sensitive projects.

Landscape planning plays an important role in identifying protected flora and fauna and mitigating impacts to the natural environment. The scan team observed that the Germans apply landscape ecology principles to highway planning in areas where adjacent land use and distribution can be expected to change because of highway development. All proposed detrimental changes to natural areas require compensation measures. Three kinds of compensation are possible: in-kind, off-site, and compensation fees (in-lieu-fees), in that order of preference.


This German highway features a culvert for habitat connectivity, with a rail barrier for amphibians and a fence for larger wildlife.

Legal requirements in Germany necessitate wildlife fencing (needed because many highway stretches have no speed limits), signing, underpasses, green bridges, and land conservation as mitigation for transportation facilities. Germany has the largest number of green bridges (32) of the countries visited. The overpasses vary in width from 8.5 to 870 meters (27.9 to 2,854 feet). Eight more are under construction, and another 20 are planned. Forest and agricultural roads cross about half of Germany's green bridges. In other cases, large rocks are used to keep vehicles out of wildlife underpasses and off overpasses.

The team observed extensive projects to keep amphibians and other small animals away from roads by constructing fences and crossing structures. More than 100 such projects for small animals were completed nationwide. The Germans also report that 130 bridges over rivers were designed to accommodate wildlife passage and keep the animals away from the traffic lanes.

"Where do the bats fly? Where do the birds cross?" said an unidentified member of the German team hosting the scan tour. "We consider even these small details when deciding where to construct a green bridge."


France's transportation plan is derived from a land-use plan whose goal is to have all residents live within 5 kilometers (3.1 miles) or 45 minutes from a limited-access highway or high-speed rail. Using the French Law of Protection of Nature as guidance, both the environmental and the transportation ministries must approve highway projects. No separate permits are needed for the various aspects of a project—one approval does it all. An extensive public involvement process is used, and legal challenge is frequent. Many projects can take as long as 10 years to develop. Environmental factors receive equal consideration with social and economic factors.

The French transportation ministry's primary objective when looking at transportation and wildlife issues is to increase motorist safety. Approximately 30 deaths per year result from collisions with animals. "Unfortunately, we drive too fast," said Michel Galet of Cofiroute, the French tollroad company. "We must consider safety as a major reason for measures to keep animals off our highways."

The French have taken numerous measures to reduce wildlife collisions. Fencing for wildlife is required on all federal highways. The French reported to the scan team that permanent signing does little to reduce wildlife mortality, and measures such as reflectors and vehicle-mounted whistles generally are ineffective. Culverts, underpasses, overpasses, and viaducts are used as structural alternatives.

Wildlife Connectivity Scan Team Members

  • Fred G. Banks, FHWA Coleader, FHWA, Headquarters
  • C. Leroy Irwin, AASHTO Coleader, Florida Department of Transportation (DOT)
  • Gary L. Evink, Ecologist, Scan Facilitator
  • Mary E. Gray, FHWA, Washington Division
  • Susan Hagood, The Humane Society of the United States
  • John R. Kinar, P.E. Wisconsin DOT
  • Alex Levy, FHWA, Southern Resource Center
  • Dale Paulson, HWA, Montana Division
  • Bill Ruediger, U.S. Forest Service
  • Raymond M. Sauvajot, Ph.D., National Park Service
  • David J. Scott, PE, State of Vermont Agency of Transportation
  • Patricia White, Defenders of Wildlife

France was the first European country to construct green bridges for wildlife and has an extensive network of such structures. The widest is 800 meters (2,624 feet). France also was the first European country to try the hourglass-shaped green bridge to reduce structural cost. The size of these bridges varies at the narrowest point from 8 to 15 meters wide (26 to 49 feet). The French have tried a number of designs for amphibian crossings, including a directional trench to guide the animals to one-way pipes that cross under the highway. They use plastic mesh attached to the regular wildlife fence to guide amphibians to culverts.

Structures generally are monitored for a 1-year period and then revisited 3 to 5 years later. The monitoring information is used in future projects and guidance documents.

The Netherlands

The Netherlands is a leader in the European community on wildlife and transportation issues, despite the fact that the country has very little remaining habitat for wildlife. The Dutch have a strong philosophy of providing and improving habitat connectivity across the highway system. The country has a national habitat connectivity plan that is consulted when planning for improvements to the transportation system, as well as individual projects. On existing highways, maintenance crews refer to the plan when implementing retrofit projects to enhance habitat connections and protect species.

The plan uses viability analyses at the population level and information about locations of elevated wildlife mortality from collisions (individual level). Because loss of population viability is in many cases exclusively the result of road presence (a barrier), both policymakers and managers give high priority to restoring habitat connectivity across highways. "You can't do everything at once, but you can do something with each project," said Hans Bekker, program manager for defragmentation at the Netherlands Ministry of Transport.

The Dutch take extensive and innovative measures to protect some species. The most extensive measures are for badgers, the largest carnivore in the country. Many initiatives to save the badger result from cooperation between nongovernmental organizations (NGOs) and the Dutch environmental and transportation ministries. In fact, the transportation ministry made badger protection a national priority. An extensive system of approximately 600 culverts is provided for connecting badger habitats, and highway maintenance funds are used for retrofits, which are based on a system-wide transportation plan for the entire country.

A fence near a Dutch overpass includes a one-way door for small mammals.

In addition to measures for badgers, the Netherlands has 10 pipe-culvert systems designed specifically for amphibians and strategically located to provide for seasonal movements. Existing bridges and culverts for waterways were modified to provide dry passage on wooden or earthen shelves along the insides of the structures, primarily for small-mammal movement. Other measures for small animals include tree stumps placed on or under bridge structures to provide habitat for cover and passage across or under highway facilities.

The Dutch have constructed four ecoducts, as green bridges are called in the Netherlands. The ecoducts range from 17 to 50 meters (56 to 164 feet) wide, using either the hourglass-shape or straight-side design. All have fences and earthen berms along the edges for noise and light reduction.


The scan team developed recommendations in four topic areas: policy, communications, guidance manuals, and research. Concerning policy, the team believes that the FHWA and AASHTO strategic plans should contain objectives to address wildlife mortality and habitat connectivity issues. They also believe that a policy of ecosystem-level mitigation should be implemented. Another policy should ensure consistency of highway alignments and designs with the management objectives of adjacent public lands. Post-construction monitoring and maintenance of measures implemented for wildlife are essential as well.

Regarding communications, a central source of information on wildlife and transportation is important, including provisions for international exchange. The scan team believes that the publications produced by various wildlife societies and groups should be used to disperse wildlife and transportation information. Similarly, the universities and State wildlife agencies that conduct much of the wildlife research should disseminate information, and the streamlining and stewardship programs in the State transportation agencies should do so as well.

The scan team has identified a number of guidance manuals that could be developed, including a general one on the assessment of transportation impacts on wildlife. Guidance on coordination with resource agencies and nongovernmental organizations could be a component of that publication. A glossary of definitions of commonly used terms in the wildlife sciences and transportation should be developed, as well as a design manual for wildlife structures, in coordination with FHWA and AASHTO.

Finally, the team recommends interagency efforts to study connectivity needs for all types of wildlife in the United States, possibly including a connectivity study relating to the Nation's transportation system. Interagency cross-training would be desirable.

The Transportation Research Board (TRB) and AASHTO Standing Committee on the Environment could take leadership roles in implementing all of these recommendations.

Author's note: This article was excerpted from the scan team's final report, Wildlife Habitat Connectivity Across European Highways (FHWA-PL-02-011). The contents reflect the view of the authors and do not necessarily reflect the official policy of the U.S. Department of Transportation. The report summary is currently available on the Web at The full report will be available at the same address in the near future. Hard copies are available free of charge by contacting the FHWA Office of International Programs: or 202-366-2155.

The habitat overpass includes board fences to reduce road noise and lights. Rocks are placed at the ends of the overpass to prevent vehicular use.


Fred Bank is an ecologist and team leader with FHWA's Office of Natural Environment in Washington, DC. He leads a team of environmental scientists who develop agency policy, provide training and technical assistance, and manage research on a variety of natural science topics. Previous experience includes managing wildlife-related research and providing expert testimony on highway impacts to fish and wildlife habitat. He also has served on several technical panels of TRB's National Cooperative Highway Research Program. Bank is a graduate of the University of California at Davis, holding bachelor's and master's degrees in range management.