As the human population in California increases, new transportation facilities are constructed and existing facilities are modified to accommodate increased traffic volumes and improve safety. Existing two-lane roads are being upgraded to divided four-lane or larger roads. In the absence of quantitative information, the California Department of Transportation (Caltrans), natural resource agencies such as the U.S. Fish and Wildlife Service (USFWS) and the California Department of Fish and Wildlife (CDFW), assume impacts to amphibians and reptiles from such highway modifications. This can result in costly Caltrans project delays and the implementation of mitigation measures of partly understood or unknown efficacy. Although amphibian and reptile passages and barriers have been constructed under and over roads in many countries, there is a need to critically compile the results of what designs and materials are effective or ineffective so that informed recommendations for road mitigation can be made. Although there are numerous amphibian and reptile underpasses in North America and Europe, there are few that have had adequate monitoring for effectiveness. Therefore, there is both a need for properly designed studies to evaluate the effectiveness of current underpasses to directly test and compare the effectiveness of underpass and barrier designs for species movement and population connectivity.

Through desk research, field inspection, and laboratory and field experimentation, this project will investigate the constraints and opportunities of existing and future available crossing structure designs and materials. The research team will address the range of aquatic and te1rnstrial topographies and road types for amphibian species and their habitats, to include the priority species dealt with by Caltrans. Data from a review of existing projects, monitoring reports and publications and material performance documentation will form the basis of specific design guides, advice or decision pathways and recommendations, while taking into consideration the needs of and potential constraints from, other wildlife species.