Improving Connectivity: Innovative Fiber-Reinforced Polymer Structures for Wildlife, Bicyclists, and/or Pedestrians

Abstract

Engineers and ecologists continue to explore new methods and adapt existing techniques to improve highway mitigation measures that increase motorist safety and conserve wildlife species. Crossing structures, overpasses and underpasses, combined with fences, are some of the most highly effective mitigation measures employed around the world to reduce wildlife-vehicle collisions (WVCs) with large animals, increase motorist safety, and maintain habitat connectivity across transportation networks for many other types and sizes of wildlife. Published research on structural designs and materials for wildlife crossings is limited and suggests relatively little innovation has occurred. Wildlife crossing structures for large mammals are crucial for many highway mitigation strategies, so there is a need for new, resourceful, and innovative techniques to construct these structures. This report explored the promising application of fiber-reinforced polymers (FRPs) to a wildlife crossing using an overpass. The use of FRP composites has increased due to their high strength and light weight characteristics, long service life, and low maintenance costs. They are highly customizable in shape and geometry and the materials used (e.g., resins and fibers) in their manufacture. This project explored what is known about FRP bridge structures and what commercial materials are available in North America that can be adapted for use in a wildlife crossing using an overpass structure. A 12-mile section of US Highway 97 (US-97) in Siskiyou County, California was selected as the design location. Working with the California Department of Transportation (Caltrans) and California Department of Fish and Wildlife (CDFW), a site was selected for the FRP overpass design where it would help reduce WVCs and provide habitat connectivity. The benefits of a variety of FRP materials have been incorporated into the US-97 crossing design, including in the superstructure, concrete reinforcement, fencing, and light/sound barriers on the overpass. Working with Caltrans helped identify the challenges and limitations of using FRP materials for bridge construction in California. The design was used to evaluate the life cycle costs (LCCs) of using FRP materials for wildlife infrastructure compared to traditional materials (e.g., concrete, steel, and wood). The preliminary design of an FRP wildlife overpass at the US-97 site provides an example of a feasible, efficient, and constructible alternative to the use of conventional steel and concrete materials. The LCC analysis indicated the preliminary design using FRP materials could be more cost effective over a 100-year service life than ones using traditional materials.