Integrating Stakeholders and Connectivity Data in Wildlife Crossing Infrastructure Planning for Highway 58 in the Tehachapi Linkage in Central California

The Tehachapi Mountains are a hypothetical landscape-scale wildlife corridor that forms the only wildland link between two mountain ranges – the Sierra Nevada to the east and the Coast and Transverse Ranges to the west. This region of California is notable for the convergence of several major geomorphic and biogeographic provinces. Given the importance of this linkage to state-wide wildlife connectivity, significant land conservation efforts by The Nature Conservancy (TNC) and Tejon Ranch in this area over the last two decades, and the known barrier effects of State Route (SR) 58 to wildlife movement, Caltrans has engaged several stakeholders in ongoing efforts to exchange data and expertise on wildlife connectivity enhancement measures for SR 58. Stakeholders include California Department of Fish and Wildlife (CDFW), UC Davis Wildlife Health Center (UCD WHC), UC Davis Road Ecology Center (UCD REC), Tejon Ranch Conservancy, and TNC.
California Department of Transportation (Caltrans District 9) is currently planning two transportation projects for State Route 58 bisecting the Tehachapi Mountains: the Keene Pavement and State Route 58 Truck Climbing Lane (SR 58 TCL) projects. The 11.3-mile Keene Pavement project, currently in the design phase, will upgrade existing pavement, guardrail, bridge rail, median barrier, drainage, and lighting. The SR 58 TCL project will improve traffic flow by constructing a 14-foot truck climbing lane with a 10-foot-wide shoulder. A wildlife undercrossing and/or culvert modifications will be constructed within the limits of Keene Pavement project in advance of the SR 58 TCL project. Construction of this mitigation structure in advance would serve to address potential impacts to wildlife habitat connectivity and movement as a result of the construction and operation of the SR 58 TCL project by promoting safe movement of wildlife under the existing highway.
Caltrans, CDFW and TNC have been collaborating on a wildlife camera trap monitoring study along a 11-mile segment of the highway to identify wildlife use of existing drainage culverts. Caltrans is also working with UCD REC to analyze available roadkill data to identify hotspots for further analysis. Additionally, UCD WHC has initiated a mountain lion GPS collaring study in the area, while CDFW will be conducting black bear and mule deer GPS collaring studies starting in early 2023. These data are being used by Caltrans and stakeholders to 1) identify existing culverts that are currently functioning for wildlife passage; 2) identify stretches of the highway that lack functional crossing structures for possible construction of new structure; and 3) identify low cost upgrades to existing culvert structures to enhance their function for wildlife passage; and 4) identify locations for installation of directional fencing to funnel wildlife to planned new or existing functional crossing structures. While these data are critical to informing mitigation measures for the Keene Pavement and Truck Climbing Lane projects, Caltrans and stakeholders are also hoping to use the data to inform long-term wildlife crossing infrastructure needs for SR 58 in this critical landscape-scale linkage area.