Wallis Annenberg Wildlife Crossing

The Wallis Annenberg Wildlife Crossing, located near the 101 Freeway in Agoura Hills, California, is a new 210-foot-long vegetated bridge set to make history and be the world’s largest wildlife crossing. The bridge will span 10 lanes of U.S. Highway 101 serving over 300,000 vehicles daily and be composed of 82 individual precast concrete bridge girders. The wildlife crossing is a major conservation project made possible by the collaboration of many government agencies and environmental organizations.

A 1990 study conducted for the Santa Monica Mountains Conservancy highlighted the urgent need for a wildlife bridge at this location as the U.S. Highway 101 is seen to be one of the greatest barriers to wildlife connectivity in Southern California. The study identified this area as a critical bottleneck, preventing mountain lions and other wildlife from moving freely between the Santa Monica Mountains and the Simi Hills. This isolation threatened the survival of the local mountain lion population and posed substantial danger to people and vehicles by crossing animals.

For decades, government agencies worked to acquire the necessary land for the project. This involved purchasing private property and securing funding through public support. The primary goal of the wildlife crossing is to create a safe passage for animals to move across the busy freeway. This will allow them to find food, mates, and new territories, ensuring the long-term health of the mountain lion population. Construction began in 2022, and the work is scheduled to be completed in 2026. This project represents a significant step towards wildlife conservation and habitat connectivity in the region, and D.H. Charles Engineering, Inc. is grateful for the opportunity to collaborate with bridge contractor C.A. Rasmussen, Inc. to overcome the structural and construction engineering challenges presented in building this wildlife crossing.

D.H. Charles Engineering, Inc. was involved with multiple lines of work through this project’s construction sequence. From the ground up, our engineers were tasked to design rebar cage stability bracing for the new column reinforcement, concrete wall formwork and wind bracing for bridge abutment structures, and falsework/formwork design for new pier cap, bridge overhang, and other concrete support structures. One of the greatest challenges this project presented was the temporary shoring required to carry new precast bridge girders over the U.S. Highway 101.

Californians in the Agoura Hills area have seen this project come to life as all work has been visible from the U.S. Highway 101 and taking place directly over the highway. The temporary bridge girder shoring was not only a critical piece to the construction sequence, but it was also the primary means of providing a safe passageway for highway traffic as bridge girders were craned in and set over the U.S. Highway 101. The engineering that went into the temporary bridge shoring design was under the microscope as the heightened sensitivity for public safety was felt as the days edged closer to setting the girders and finally building the superstructure of the bridge. D.H. Charles Engineering, Inc. worked intimately with Caltrans officials to provide a design that was safe and tested by many years of both private and public falsework experience.

The temporary bridge girder shoring was constructed using structural steel beams to provide direct support for the new precast girders and timber columns and cross bracing to provide vertical support and stability. A challenge during the design phase of the temporary shoring was the limited space that was offered to the bridge contractor. Tucked neatly between the new abutment walls and the U.S. Highway 101, the limited width created the need for slender falsework towers only 4-feet wide and up to 25-feet tall at the North end of the bridge. Timber cross bracing and foundation structures needed to be designed to not only resist lateral seismic and wind demands per Caltrans standards, but also overturning effects from these same loads to ensure stability during the construction sequence in the event of a natural disaster.

A design process spanning over 2 years combined for a truly memorable experience in collaborating with Caltrans District 7 and bridge contractor C.A. Rasmussen, Inc. to accomplish the many construction challenges presented by the world’s largest wildlife crossing. D.H. Charles Engineering, Inc. grew immensely from this experience and cannot wait for another opportunity to partner with a great contractor to build infrastructure that helps both us and the surrounding natural habitats.