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Summer 2002

Greener Roadsides

Greener Roadsides archive

Germany: Where Roads and Wildlife Coexist

Susan Hagood
The Humane Society (301)258-3149

German roadway with green bridges
Passages give safe passage to wildlife, local farm vehicles, and pedestrians.

It wasn't until we'd seen about a half dozen German wildlife overpasses over the course of three or four hours that our translator, Herr Fischer (from whom one got the impression that roadkill was not an issue that kept him awake at night), commented dryly as we pulled up to yet another: "Oh, another overpass. How exciting. Hold me back." He might have seen enough by that point, but the rest of the Scan participants couldn't see too many.

There are now 32 overpasses, or green bridges, in Germany. Eight more are under construction, and another 20 are planned. The majority serve dual functions - as safe passage for wildlife and for local farm vehicles and residents. "All creatures great and small" might best characterize Germany's approach to protecting wildlife from the negative impacts of highways. Insects are given consideration along with much larger animals.

Legal Requirements

The Nature Conservation Act requires action on behalf of environmental protection, as well. Similar to our National Environmental Protection Act, the Nature Conservation Act first requires officials to determine whether an impact can be avoided. An early warning system is built into the planning process to identify, through GIS analysis, critical projects requiring an environmental risk assessment. This process examines impacts on soil, air quality, hydrology, noise, fauna and flora. The final classification of risks which results is conducted by a party outside the transportation agency. A cost-benefit analysis is also conducted at the federal level.

In addition, European Union directives include the preparation of an Environmental Impact Assessment if a project may have considerable environmental impacts. Both federal and European approaches are characterized by strict requirements which, if not followed, carry legal consequences. Importantly, habitat alterations require compensation, whether on the basis of property protection or nature preservation. Finally, there is a nature conservation act, modeled after the federal act, in each of the 16 German states; protected areas within each state also are managed in accordance with legislation specific to that area. Both road construction and improvement projects are subject to the full range of law and review. Avoidance of impact is a primary means of coping with the consequences of building and improving German motorways; the construction of green bridges is a key component of that avoidance strategy, as these structures help to avoid landscape fragmentation.

The rigor and complexity of German law reflects in part the fact that this country, like so many in Western Europe, has little habitat wildlife left. Their protected species list is lengthy, beginning with lynx and the reintroduced wolf. There may be no coincidence between this long list of species on the brink, and the fact that Germany has the second densest road network in the world.

Research Efforts

A vibrant research effort in Germany and throughout much of Europe is beginning to provide answers to satisfy both the law and wildlife needs. Now, with every new project, engineers and biologists ask what information they need about the local habitat before construction. Where do bats fly? Where do birds cross? How can we offset habitat impacts? How can this particular structure contribute to maintaining ecosystem function? Emphasis is placed on ensuring that wild habitats remain connected or are reconnected.

Habitats that will be negatively impacted by, for instance, road noise (to which invertebrates are extremely sensitive), are recreated elsewhere. The design of habitat around green bridges is given as much consideration as the design of the bridges themselves. New roads are constructed not with culverts, but with bridges that span about the same width of land as water, thereby providing room for terrestrial animals to pass as well as minimizing changes in water flow. The zone in which impacts are assessed extends at least 500 meters on each side of the highway, and may be a kilometer or more depending on the species involved.

The depth of soil on green bridges depends on the vegetation it supports. One foot of soil is provided for grasses and forbs. Two feet of soil is placed atop bridges supporting shrubs, and six to seven feet if trees are planted. Most bridges are 30 to 50 meters wide, though one is less than 10 and two others, containing tunnels, are more than 500. Monitoring of dual purpose bridges has revealed that wild boar and deer tend to use the vegetated portion, while fox use the road itself. Bridges built solely for wildlife but used by humans are modified with the placement of boulders at the end that restrict access of vehicles.

small box tunnel, top flush with road surface
An Amphibian Crossing

On the Ground

Apart perhaps from our translator, the Scan team was particularly impressed with German efforts to assist amphibians in crossing motorways safely. We toured an extensive system of steel barriers along a motorway. These barriers are about a foot high with a lip at the top to discourage vertical assaults by amphibians, and are connected to a large underpass. Mesh fences are placed at the base of many higher fences for the same purpose. One amphibian crossing was built at the request of an eleven-year old girl who contacted the transportation minister after seeing so many salamanders killed in the motorway. The resulting crossing, while built to allow light and water to enter, is believed to be too noisy, as noise levels exceed 100 decibels within the passage when a vehicle passes overhead. More recent designs have used wider and deeper tubes in an effort to combat this problem. As with all wildlife crossing structures, monitoring of amphibian tunnel use is critical to analyzing its effectiveness, but funding for this purpose is difficult to obtain.

German motorists drive 800 billion kilometers per year without a speed limit. Clearly, green bridges, wildlife underpasses, and the ever present highway fences are critical in protecting public safety as well as wildlife. Though most wildlife structures are incorporated in new motorways, the Germans are increasing efforts to build green bridges where needed on existing roads.

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Questions and feedback should be directed to Marlys Osterhues (marlys.osterhues@dot.gov, 202-366-2052).

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