Existing highways act as barriers to wildlife movement, and as a result, have caused habitat loss/fragmentation and reduced population size, population persistence, and genetic diversity for various wildlife species. To remedy these negative effects, the California Department of Transportation (Caltrans District 7) has constructed/is in the process of constructing multiple “wildlife crossing” projects and is performing wildlife studies on multiple routes within the district (in partnership with NPS).
State Route 118 (SR-118) Undercrossing Improvement Project includes the improvement of five undercrossings (four culverts and one bridge) located between postmiles (PM) 9.7 and 14.5 along SR-118 within the unincorporated community of Somis (Ventura County), and the city of Moorpark. Improvements consist of wildlife fencing installation and construction of ramps which allow wildlife to scale the high ledges under culverts which have proved to be barriers for wildlife crossing. This road is currently one of the largest obstacles affecting wildlife movement within the Santa Monica-Sierra Madre wildlife corridor.
The Skirball Bridge (PM 36.71) was completed as mitigation for the 405 HOV Lane Project, and consists of a small narrow walkway, parallel to the Skirball Center Drive overpass, which was made with comprised granite bottom. “Stepping-stones” (swaths of vegetation) were also placed to facilitate the safe movement of wildlife across I-405. Further improvements are being considered at Skirball Bridge, as well as LA 405 PM 34.794 (Sepulveda Blvd.) and LA 405 PM 35.83 (Bel Air Crest Underpass). In a separate but related project (same area), one escape ramp (with a timber retaining wall) was constructed on the southbound side of the 405, and 8’ chain-link wildlife fencing was installed.
Caltrans is currently constructing a wildlife crossing over U.S.101 just west of Liberty Canyon Road at post mile 33.0 in the City of Agoura Hills in Los Angeles County. The linkage between the Santa Monica Mountains and the Sierra Madre Mountains is one of the few potential coastal-inland connections remaining in the South Coast Ecoregion, and Liberty Canyon has been identified as a critical linkage in this broader, regional connection (Penrod, et al., 2006). The project includes construction of an approximately 180-foot wide by 200-foot-long bridge across U.S.101, as well as an extension of the overcrossing over Agoura Road. The overcrossing over Agoura Road consists of a 54-foot-wide tunnel and associated retaining wall system along Agoura Road to keep the road operational and to accommodate the fill material needed to construct the wildlife crossing. The project also includes wildlife fencing along US-101, the enhancement of native vegetation and habitat adjacent to the overcrossing structure, and the construction of sound walls and gabion walls.
These are only a few examples out of many projects in which Caltrans has increased wildlife connectivity within the region.