Cost benefit analysis to identify the best type and location for a wildlife crossing structure

Wildlife-vehicle collisions cause damages and loss for people and animals alike and are a reason of human wildlife conflict. Collisions are considered a consequence of the landscape fragmentation which is also a major cause of biodiversity loss world- wide. In Europe the most of the recorded accidents involves ungulates, and in Trentino (N Italy) a similar trend is observed. Since 2010, an average of 700 collisions per year have been reported between wildlife and vehicles (99% ungulates of which 77% roe deer) and a total of 6 collisions involved the brown bear (Ursus arctos arctos). Even if the number of accidents with bears is small, the size of the species poses a risk for the drivers and the loss of a bear individual can have a big impact on the small and isolated population of the South Eastern Alps. Wildlife crossing structures increase habitat connectivity and reduce up to 86% the number of accidents when appropriately designed and strategically placed. This work aims to identify the best type of structure and its location to reduce bear-vehicle collisions in the Province of Trento (PAT). The data used to perform the analysis includes: habitat suitability models and connectivity models for the brown bear available from literature, the wildlife vehicle collision geo database form the PAT, GIS layers about topography, land use, road network and human settlements. The analysis included a GIS assessment to overlap the main movement corridors, the hotspots of wildlife-vehicle collisions and the terrain features that allow the building of a crossing structure. After a field survey of three possible locations, Environmental Impact Assessment (EIA) and Cost-Benefit Analysis (CBA) were used to identify the best type of structure and its final location. The cost-benefit analysis was performed using prices and other economic values available from in literature for other countries. The GIS assessment identified the road SS45bis in “Valle dei Laghi” as an hotspot with some tract with more than 10 collisions per km in 9 years. This road has a high volume of traffic and cuts two large areas with high habitat suitability for the bear. The potential sites have been selected in function of their proximity to the wildlife corridors, the permeability for the species and concordant slope on both road sides. The latter is important from building perspective. The most appropriate crossing structures in this study case was an overpass: brown bear and ungulates are known to prefer overpasses to underpasses and the site geo morphological conformation is more suited for an overpass, thus facilitates the construction phase. The location identified as the best to build an overpass would connect two forest patches and is within 400 m of two potential corridors. The final mitigation system consists in the two-lanes overpass, two km of fences and eight Jump-outs (2 per km, per roadside). The total cost is estimated in 4730750 euro and it would require 50 years to amortize the costs (life span of the structure is 75 years) and would avoid more then 700 accidents. This work identified the most effective engineering solutions and spatial locations to build wildlife crossings in Valle dei laghi, Trentino and complies the local Mobility Plan. The final estimation of the cost and its depreciation are the most critical part, because the costs of collisions and structures are based on prices derived from other countries and are probably under estimate. The availability of several type of data, especially the locations of collisions highlights the importance of continuous monitoring for suggesting detailed options for conservation and accident reductions