OOS 25-6 - Comparison of cost-effectiveness of different types of wildlife crossing structures

There are more than 64 million kilometres of road that transect nearly every landscape on earth. These roads can have severe and detrimental impacts on wildlife. Two of the most prominent impacts include habitat fragmentation (i.e., loss of landscape connectivity) and road mortality. These impacts prevent wildlife from traversing the landscape successfully, and can restrict individuals from accessing necessary resources such as habitat, food, and mates. It may be possible to mitigate and reduce the negative impacts of habitat fragmentation and road mortality by fencing roads, and providing safe crossing points by means of ‘Crossing Structures’. Crossing Structures are typically over- or underpasses, providing safe crossing passage for wildlife over or under a road, respectively. Crossing structure designs vary depending on the target species and context in which they are installed. These factors include broad width, traffic volume, the adjacent landscape and vegetation, and the movement ecology and behaviour of the targeted species. This has resulted in a plethora of crossing structure styles, for example, large vegetated overpasses, small corrugated drainage culverts running under roadways, canopy bridges that connect the from the vegetation on one roadside verge to the other, and co-use structures intended to be used by people as well as wildlife. The costs and benefits of each type of crossing structure can vary considerably. In this presentation, we will present an overview of costs and benefits of different types of crossing structures, focussing on monetary costs for constructing new structures or retrofitting existing roads, the time to complete construction, and the demonstrated benefit where possible (e.g., use of crossing structures to cross the road and potential reductions in road mortality before and after structure installation). We will conclude with guidelines for where and when different crossing structures may be more – or less – cost-effective to install. The results from this presentation will be to provide concrete advice to planners and managers based on expert opinions and experience in the field and/or in constructing crossing structures.