Wildlife Road-Crossing Structures: Green Bridge vs Underpass

What Are Wildlife Road-Crossing Structures?

Wildlife road-crossing structures, such as green bridges and underpasses, are designed to provide safe passage for animals across or beneath highways. These structures aim to reduce the frequency of wildlife-vehicle collisions (WVCs) and maintain habitat connectivity, allowing species to move freely between fragmented habitats.

Green bridges are elevated walkways that span over roads, offering a natural path for animals to cross safely. Underpasses are tunnels built below the road surface, providing an alternative route beneath the highway.

Why Do We Need These Structures?

Highways can fragment wildlife habitats into isolated patches, limiting animal movement and genetic exchange. This fragmentation can lead to population isolation, reduced biodiversity, and increased vulnerability to environmental changes. Wildlife road-crossing structures help mitigate these issues by providing safe routes for animals to navigate around roads.

The effectiveness of these structures depends on various factors such as the type of wildlife using them, the design features (e.g., width, vegetation cover), and traffic volume. By reducing WVCs, these structures can improve both animal welfare and road safety.

How Do Green Bridges and Underpasses Work?

Green bridges are typically designed to mimic natural habitats, with appropriate vegetation and structural features that encourage animals to use them. These structures often include ramps or walkways leading from the forest edge to the bridge itself, ensuring a smooth transition for wildlife.

Underpasses, on the other hand, are usually constructed in areas where animal crossings are known to occur frequently. They are designed with appropriate dimensions and lighting conditions that make them attractive to animals. Vegetation cover within underpasses can also enhance their effectiveness by providing shelter and camouflage.

Real-World Examples and Case Studies

Numerous case studies have demonstrated the success of wildlife road-crossing structures in reducing WVCs and enhancing animal movement. For instance, the Mont St-Hilaire Wildlife Overpass in Quebec, Canada, has significantly reduced deer collisions with vehicles since its installation.

In Europe, green bridges over highways have been shown to facilitate safe crossings for a variety of species, including roe deer, wild boar, and even large carnivores like wolves. These structures not only protect wildlife but also contribute to the overall ecological health of fragmented landscapes.

Frequently asked questions

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