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Effectiveness of Crossing Structures for Wildlife on Two Roads Associated with Biological Corridors in Costa Rica
IADB
2026.05.28
After implementing mitigation measures on road projects, it is critical to assess whether they effectively address the targeted impactsnamely, restrict wildlife movement and mortality from wildlife-vehicle collisions. In this study, we used a control-impact design to answer two key questions: (1) Is the probability of use by terrestrial and arboreal animals similar in crossing structures compared to surrounding forest sites? (2) Is wildlife mortality lower on road sections with mitigation measures than on those without? Our study was conducted on two roads in Costa Rica National Route 160 and National Route 1 focusing on underpasses and canopy bridges. We applied single-season occupancy models to camera trap data for ground-dwelling and arboreal mammals and reptiles, collected at crossing structures and surrounding forest, and compared roadkill data from vehicle surveys between road segments with and without crossing structures. Multiple taxa, including ground-dwelling and arboreal species, used structures such as underpasses, box culverts, bridges adapted with dry ledges, and canopy bridges. The probability of use suggests some species are relatively well adapted to these structures, although confidence intervals remain broad. However, certain species were never recorded using any crossing structures, and, on Route 1, roadkill was higher for road segments with crossing structures. While wildlife crossing structures show promise in facilitating animal movement across roads, they are insufficient on their own to prevent wildlife mortality, showing that the mitigation system needs improvement. Based on existing best practices, we recommend extending and upgrading the exclusion fence for the underpasses, retrofitting box culverts with dry ledges and exclusion fence and maintenance activities to improve the effectiveness of this mitigation system.