Creating Dark, Quiet Paths for Wildlife to Approach Highway Crossing Structures

Transportation and other agencies and organizations are increasingly planning and building under- and over-crossing structures to allow wildlife to traverse busy highways. Research has shown that traffic noise and light can impede wildlife species from using these structures. However, existing guidance in the field of wildlife crossing design inadequately addresses how structural and vegetation elements can be used to reduce such disturbance. If wildlife is hesitant to or refuses to approach structures due to noise, light, and other factors, then the structures may have a much lower benefit-to-cost ratio than expected. To help address this gap in guidance for design, a research team led by UC Davis used field measurements and modeling of light and noise from traffic to inform and test wildlife crossing designs. The researchers developed wildlife-responsive designs using berms, barriers, and new paths for two crossings being considered by the California Department of Transportation: 1) the proposed Wallis Annenberg wildlife over-crossing (WAOC) across US 101 in the city of Agoura Hills, and 2) a potential over-crossing across Interstate 15, south of the City of Temecula (TOC). The researchers identified key limitations and opportunities for each design approach and concluded that creating “dark and quiet paths” could increase the wildlife-responsiveness of the designs.