title: How Effective Is Road Mitigation at Reducing Road-Kill? A Meta-Analysis.
abstract: Road traffic kills hundreds of millions of animals every year, posing a critical threat to the populations of many species. To address this problem there are more than forty types of road mitigation measures available that aim to reduce wildlife mortality on roads (road-kill). For road planners, deciding on what mitigation method to use has been problematic because there is little good information about the relative effectiveness of these measures in reducing road-kill, and the costs of these measures vary greatly. We conducted a meta-analysis using data from 50 studies that quantified the relationship between road-kill and a mitigation measure designed to reduce road-kill. Overall, mitigation measures reduce road-kill by 40% compared to controls. Fences, with or without crossing structures, reduce road-kill by 54%. We found no detectable effect on road-kill of crossing structures without fencing. We found that comparatively expensive mitigation measures reduce large mammal road-kill much more than inexpensive measures. For example, the combination of fencing and crossing structures led to an 83% reduction in road-kill of large mammals, compared to a 57% reduction for animal detection systems, and only a 1% for wildlife reflectors. We suggest that inexpensive measures such as reflectors should not be used until and unless their effectiveness is tested using a high-quality experimental approach. Our meta-analysis also highlights the fact that there are insufficient data to answer many of the most pressing questions that road planners ask about the effectiveness of road mitigation measures, such as whether other less common mitigation measures (e.g., measures to reduce traffic volume and/or speed) reduce road mortality, or to what extent the attributes of crossing structures and fences influence their effectiveness. To improve evaluations of mitigation effectiveness, studies should incorporate data collection before the mitigation is applied, and we recommend a minimum study duration of four years for Before-After, and a minimum of either four years or four sites for Before-After-Control-Impact designs.
authors.affiliation: Geomatics and Landscape Ecology Research Laboratory, Department of Biology, Carleton University, Ontario, Canada.
authors.forename: Trina
authors.initials: T
authors.lastname: Rytwinski
authors.affiliation: Australian Research Centre for Urban Ecology, Royal Botanic Gardens Victoria, C/- School of BioSciences, University of Melbourne, 3010, Victoria, Australia.
authors.forename: Kylie
authors.initials: K
authors.lastname: Soanes
authors.affiliation: Department of Geography, Planning and Environment, Concordia University Montreal, 1455 Montreal, Quebec, Canada.
authors.forename: Jochen A G
authors.initials: JA
authors.lastname: Jaeger
authors.affiliation: Geomatics and Landscape Ecology Research Laboratory, Department of Biology, Carleton University, Ontario, Canada.
authors.forename: Lenore
authors.initials: L
authors.lastname: Fahrig
authors.affiliation: Institute of the Environment & Ottawa-Carleton Institute of Biology, Ottawa, Ontario, Canada.
authors.forename: C Scott
authors.initials: CS
authors.lastname: Findlay
authors.affiliation: Department of Biology, University of New Brunswick at Saint John, Saint John, 550, New Brunswick, Canada.
authors.forename: Jeff
authors.initials: J
authors.lastname: Houlahan
authors.affiliation: Australian Research Centre for Urban Ecology, Royal Botanic Gardens Victoria, C/- School of BioSciences, University of Melbourne, 3010, Victoria, Australia.
authors.forename: Rodney
authors.initials: R
authors.lastname: van der Ree
authors.affiliation: Alterra, Wageningen University and Research Centre, Wageningen, The Netherlands.
authors.forename: Edgar A
authors.initials: EA
authors.lastname: van der Grift
mesh_terms: D000063:Accidents, Traffic / Q000517:prevention & control*; D000818:Animals; D006801:Humans; D018986:Motor Vehicles