The focus for the design for Passageway 3, is to redevelop the area in order to better support and encourage the Mountain Lions to travel to the other side of I-15 through the Temecula Creek Underpass. Initial site investigations revealed the large amount of human activity in this area, which is the biggest deterrent for Mountain Lion crossing. This design deters humans through the installation of signs, vegetation, and fencing. The layout of the fencing was created based on criteria focused mainly on human deterrence, as well as cost and maintenance. The design proposes the installation of two different types of fences for both wildlife and humans. The wildlife fence for this project is based on the fence used in the award-winning SR-241 Wildlife Protection Fence Project. Research was also done on vegetation. Native plants, such as California roses and stinging nettles, are proposed to be installed in order to make the area uncomfortable for humans. The research was performed to ensure that these plants would not be invasive to existing plants and that they would not be harmful to wildlife. Sound baffles are proposed due to the echoing discovered during a site investigation. It is a possibility that this noise is discouraging mountain lions from moving through the underpass. The sound baffles are made of a textured material, which will also assist in deterring humans since graffiti was found on the walls of the underpass during said site investigation. This passageway will be implemented in the following phases: signs, vegetation, fencing, and sound baffles. These phases will allow future wildlife crossing projects to know which phase works best in deterring humans.