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Wildlife overpass structure size, distribution, effectiveness, and adherence to expert design recommendations
Liam Brennan1,2, Emily Chow1, Clayton Lamb3
1British Columbia Ministry of Forests, Lands, and Natural Resource Operations and Rural Development, Cranbrook, British Columbia, Canada.
Peerj
|December 19, 2022
Summary
Wildlife crossing structures help reduce animal-vehicle collisions and improve connectivity. Most overpasses are narrower than recommended, but wider structures show increased species use and crossing rates.
Area of Science:
- Conservation Biology
- Transportation Ecology
- Wildlife Management
Background:
- Wildlife crossing structures and exclusion fencing are vital for reducing wildlife-vehicle collisions and maintaining habitat connectivity.
- Effective species and landscape stewardship necessitates managing animal mortality and subpopulation connectivity.
- Highway mitigation projects represent significant, long-term financial investments requiring cost-effective solutions.
Purpose of the Study:
- To assess how expert recommendations for wildlife overpass dimensions are implemented in practice.
- To evaluate the conformity of existing wildlife overpasses to suggested design guidelines.
- To investigate the relationship between overpass dimensions, species usage, and crossing rates.
Main Methods:
- Analysis of dimensions of 120 wildlife overpasses globally using a novel measurement technique.
- Comparison of built structure dimensions against expert guidelines (e.g., ~50m width, 0.8 width-to-length ratio).
- Examination of crossing rates for large mammal species across 12 western North American overpasses.
Main Results:
- The average width of analyzed overpasses was 34m, with most in North America and Europe not meeting expert width guidelines.
- Wider North American overpasses (40-60m) exhibited more diverse species use and nearly double the crossing rates compared to narrower ones.
- Qualitative observations suggest wider overpasses are associated with increased ecological benefits.
Conclusions:
- Wide overpasses (~50m) are ecologically sound and cost-effective for mitigating road barriers, particularly for width-sensitive species and large mammal assemblages.
- Current overpass designs in many regions do not fully align with expert recommendations.
- Further research is needed to explore cost-effectiveness of narrower or underpass structures and their integration into comprehensive wildlife crossing systems.
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