A simple framework for large-scale road-related risk assessments
Written by Fernando Ascensão
Centre for Ecology, Evolution and Environmental Changes - FCUL, Portugal
April 29th 2025
Spatial distribution of susceptibility and exposure (road density) at global scale.
Summary
Roads are essential for human development, but they also pose significant threats to wildlife. From roadkill to habitat fragmentation and increased human encroachment, infrastructure development is a key driver of biodiversity loss. Understanding which species are most at risk and where conservation efforts should be focused is crucial for mitigating these impacts. Our recently published study describes a framework for assessing road-related risks to wildlife on a global scale. The study uses mustelids – a diverse group of carnivorous mammals including otters, weasels, martens, and badgers – as an example of the framework. These animals are particularly vulnerable to road impacts due to their large home ranges and susceptibility to habitat fragmentation. We developed a method to assess species’ susceptibility to road effects and their exposure to roads, helping to identify priority areas for conservation action.
Measuring exposure and susceptibility
To assess road-related risks, we combined two key factors:
Smooth-coated otter - a species at high risk due to declining populations and because it inhabits areas with high road density. © Stock images.
Susceptibility – This refers to how vulnerable a species is to road impacts, which was estimated using biological traits such as body mass and population trends. Larger animals with declining populations were considered more susceptible than smaller and more abundant species since they are more likely to encounter roads and suffer from population declines due to roadkill.
Exposure – This was measured as the road density within a species’ geographic range, based on global infrastructure data. Higher road density means a greater likelihood of negative interactions between roads and wildlife. Using a bivariate mapping approach, the study identified areas where high-susceptibility species coincide with high road exposure, creating a global risk assessment for mustelids.
This approach produced a matrix ranking each species by both susceptibility and exposure, allowing us to identify where these risk factors intersect and to map potential road-related threats across the mustelid family.
Species at the Highest Risk
Mustelid species facing the greatest threats from roads are primarily located in eastern Europe, southeast Asia, and parts of Africa. These regions have extensive road networks that overlap with highly susceptible species. Some of the most at-risk species include:
· Smooth-coated otter – A species experiencing population declines and found in areas with high road density.
· Asian small-clawed otter – Vulnerable to roadkill and habitat loss.
· Greater hog badger – A large-bodied mustelid that is heavily impacted by roads in Southeast Asia.
Priority Conservation Areas
The study also identified priority preservation areas—regions where mustelids are highly susceptible but currently have low road density. Protecting these areas from future road development is key to preventing biodiversity loss. The most important preservation zones include:
· South America, and specifically the Amazon Basin – Home to the giant otter, a species with high susceptibility but low exposure.
· North America and Siberia – Where several mustelid species inhabit road-free landscapes that should remain protected.
· Borneo and parts of Africa – Regions with low road density but high conservation value.
Wolverine - a species inhabiting largely road-free landscapes that should remain protected. © Heeres Wildlife Photography.
The Need for Proactive Conservation
With infrastructure rapidly expanding worldwide, especially in biodiversity hotspots, road-related impacts on wildlife will inevitably increase unless we avoid high risk areas. The study provides a tool for proactive conservation planning, allowing researchers, policymakers, and transportation planners to:
· Preserve road-free areas to maintain critical habitat for susceptible species.
· Guide future infrastructure development to minimize environmental impact.
· Identify priority mitigation zones on new and existing roads where wildlife crossing structures and fencing is urgently needed to reduce roadkill.
Better road planning and design is urgently needed
The findings of this study emphasize that conservation efforts must be integrated into road planning to reduce biodiversity loss. By identifying which species are at the highest risk and where conservation interventions should be prioritized, this framework provides a science-based approach to balancing development with environmental protection.
As global road networks continue to expand—especially in developing countries—this type of risk assessment can help ensure that new infrastructure projects do not come at the cost of irreversible biodiversity loss. For mustelids, and for many other species, adopting smart conservation strategies today could mean the difference between survival and extinction.
Author information
Fernando, Rafael, and Marcello are long-time collaborators in the field of road and railway ecology, with extensive experience studying the impacts of linear infrastructure on biodiversity and ecological processes. Their joint research spans topics such as road-kill patterns, barrier effects, species behaviour, and the effectiveness of mitigation measures.
fjascensao@edu.ulisboa.pt, rafabarr@ucm.es, damico@ebd.csic.es
Source citation
Ascensão, F., Barrientos, R., & D’Amico, M. (2024). A framework for large-scale risk assessment of road-related impacts, with application to mustelids. Global Ecology and Conservation, 56, e03329. https://doi.org/10.1016/j.gecco.2024.e03329
Editor:
Rodney van der Ree
Cite this summary:
Ascensão, F. (2025). A simple framework for large-scale road-related risk assessments. Edited by van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/road-related-risk-assessment