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An objective road risk assessment method for multiple species: ranking 166 reptiles and amphibians in California

June 1, 2018


Transportation and wildlife agencies may consider the need for barrier structures and safe wildlife road-crossings to maintain the long-term viability of wildlife populations. In order to prioritize these efforts, it is important to identify species that are most at risk of extirpation from road-related impacts.


Our goal was to identify reptiles and amphibians in California most susceptible to road mortality and fragmentation. With over 160 species and a lack of species-specific research data, we developed an objective risk assessment method based upon road ecology science.


Risk scoring was based upon a suite of life history and space-use characteristics associated with negative road effects applied in a hierarchical manner from individuals to species. We evaluated risk to both aquatic and terrestrial connectivity and calculated buffer distances to encompass 95% of population-level movements. We ranked species into five relative categories of road-related risk (very-high to very-low) based upon 20% increments of all species scores.


All chelonids, 72% of snakes, 50% of anurans, 18% of lizards and 17% of salamander species in California were ranked at high or very-high risk from negative road impacts. Results were largely consistent with local and global scientific literature in identifying high risk species and groups.


This comparative risk assessment method provides a science-based framework to identify species most susceptible to negative road impacts. The results can inform regional-scale road mitigation planning and prioritization efforts and threat assessments for special-status species. We believe this approach is applicable to numerous landscapes and taxonomic groups.

Citation Information

Publication Year 2018
Title An objective road risk assessment method for multiple species: ranking 166 reptiles and amphibians in California
DOI 10.1007/s10980-018-0640-1
Authors Cheryl S. Brehme, Stacie A. Hathaway, Robert N. Fisher
Publication Type Article
Publication Subtype Journal Article
Series Title Landscape Ecology
Index ID 70198525
Record Source USGS Publications Warehouse
USGS Organization Western Ecological Research Center