Wildlife Undercrossing Design
Wildlife crossings or habitat connectivity structures can be located in upland forests, wooded and herbaceous wetland systems, and along riparian stream crossings. The overall purpose and need for the crossing is to maintain habitat connectivity within natural landscape linkages bisected by the roadway, avoid habitat loss and degradation, reduce wildlife roadway mortalitiy, promote genetic connectivity for the target wildlife species, and to maintain public safety. The long-term conservation goals are to maintain the productivity of the natural system and increase the long-term survival potential of the target wildlife species. Acquisition of public conservation land which increases the size of the core habitat area for the target species is also an extremely important and essential consideration, together with the strategic placement of wildlife crossings, in order to adequately minimize and mitigate highway impacts.
There are numerous wildlife crossing designs which are suitable for target mammals, amphibians, and reptile species, including bridges and designs that provide for both aquatic and terrestrial species movement as well as habitat and hydrological connectivity. Structure types may include upland and wetland bridges, box culverts, and large drainage pipes which can be designed and constructed at suitable locations. Appropriately designed fencing erected along the outside right-of-way is also needed to exclude animals from the roadway and funnel and encourage them to use the structure. Fine wire mesh attached along the lower one-third of the fence will deter smaller species such as amphibians, reptiles, and small mammals and reduce roadway mortality. Signage for wildlife underpasses may also be useful in the area of heavy animal use near undercross structures.
Wildlife crossings are primarily designed for major federal, state and some county roadways where there are known wildlife issues. The National Wildlife Crossing Decision Guide Protocol provides step-by-step guidance to planning wildlife crossings on a national level. The Florida Department of Transportation has produced Wildlife Crossing Guidelines, and the U.S. Department of Transportation, Federal Highway Administration has developed a Best Practices Manual to wildlife crossing design and planning. These resources can be applied to any transportation corridor, multiple-lane interstate highways, county roads, and small residential roads.