Engineering Feasibility Study of Alternative Wildlife Crossings over I-15 in Temecula, Southern California

Wen Cheng

Large multi-lane highways can be detrimental to wildlife habitat connectivity. These highways can act as barriers between habitats and make it difficult for mammalian carnivores such as mountain lions to cross, resulting in fatalities due to animal-vehicle collisions as well as inbreeding. Over the course of the last 15 years, the I-15 freeway located south of Temecula in southern California has seen multiple vehicle strikes on mountain lions, and severe genetic restriction of the mountain lion population west of I-15 in the Santa Ana Mountains due to I-15’s barrier effect.  Both phenomena have led to a significant threat of extinction of the mountain lions in the Santa Ana’s.  This project sought to find a solution to increase wildlife connectivity and demonstrate how such fatalities can be prevented by presenting key recommendations for safe passageways of mountain lions and other wildlife in order to promote habitat connectivity along the I-15. Fatality, genetic, camera, and mountain lion movement data in the area were gathered by researchers from the Wildlife Health Center, University of California, Davis, and collaborators at The Nature Conservancy and other institutions.   This data was considered when proposing passageway locations and designs, and Caltrans standards and specifications were utilized since the I-15 freeway is maintained by Caltrans. With assistance from a collection of multidisciplinary professionals involved in wildlife conservation, the team was able to develop effective and feasible solutions to create safe wildlife crossings. Three types of passageways were explored – overpass, underpass, and culvert. Each type of passageway had several alternative designs, and through cost-benefit analysis in terms of site location, structural design, cost, and effectiveness, we selected the most optimal design for each type of passageway. Ideally, all three selected passageways should be constructed at the determined locations so that there are multiple crossings for the mountain lions and other wildlife along the I-15 and to prevent further mountain lion fatalities.