Wildlife-vehicle collisions : An evaluation of the mitigation effect by ecoducts and fauna bridges in Sweden

Abstract: The occurrence of wildlife vehicle collisions (WVCs) is an increasing problem in Sweden with a calculated increase of 45 percent from 2015 to 2022. The highest measured number of WVCs occurred in 2021 with over 67,000 reported incidents, where only the payment for the search of wounded animals were approximately 60 million Swedish crowns. The Swedish transport agency works actively with the problem by constructing several types of wildlife passages to mitigate the increasing problem, inter alia, ecoducts and fauna bridges.   The aim of this study was to evaluate the mitigation effect of wildlife passages, in this case ecoducts and fauna bridges. In addition, were also the spatial extent of the mitigation effect together with the relationship between mitigation effect and the annual daily traffic (ADT) evaluated.   The evaluation of mitigation effect was conducted by the usage of several types of geographical information systems (GIS) tools in the software ArcGIS Pro. A selection of seven passages was made, based on several requirements and each passage was assigned a study area with an area of 100 square kilometers. The mitigation effect was initially determined by conducting an Emerging hot spot analysis, categorizing the result into showing trend of decrease or showing no trend of decrease. The spatial extent of the mitigating effect was evaluated through the Emerging hot spot results while the relation between ADT and WVCs was evaluated in an overlay analysis.   Two of the passages were concluded as to having a mitigating effect, three passages were concluded as to showing no mitigating effect and two passages were excluded from further evaluation due to high uncertainty in the results. At the passages with stated mitigating effect were the spatial extent of effect shown in the whole study area. The result showed no evident correlation between ADT and mitigating effects which led to further reflections on the degree of influence that ADT has on the occurrence of WVCs.