Future Wild Life Crossings
Part of Florida Black Bear National Scenic Byway mission is to enhance the byway for both residents and wildlife for future generations. One way to accomplish this mission is through new road construction and placing wildlife crossing in strategic places along the byway.
In 2028 part of the byway from Silver Springs to 314 will become 4 lanes, wildlife crossings are in the construction plans. Florida Black Bear National Scenic Byway is at the forefront and very much involved with the planning phase.
Let us talk structural engineering for Wildlife overpasses; they are the reverse of most conventional bridges. Conventional bridges generally have longer spans than width, so they are narrow to accommodate 4 lanes of traffic but their span might be longer to cross a river, span a bay, or cross a highway.
Wildlife bridges are typically shorter in span and much wider, they have to accommodate a thick layer of soil, vegetation, landscape surface and local habitat. No one has really looked at how to make these structures lighter, more adaptable or even using recycled materials which could lower the cost. The construction could be more modular or even more dynamic. These innovations could result in a more sustainable and affordable construction. An adaptable modular structure could also expand, and be moved to respond to changing habitats.
Animal Road Crossing (ARC) came up with a new idea for the infrastructure of wildlife crossing; they hosted an international design completion for wildlife structures. The contest was dedicated to finding and implementing leading edge solutions to human and wildlife mobility and to long term landscape connectivity.
The 5 finalist came up with some interesting ideas:
The goal of this design is to create a modular and efficient “kit of parts” using sustainable materials. To achieve this, the design strategy specifies using locally manufactured, laminated timber girders made from timbers killed by the pine beetle. The resulting bridge is a sustainable free-form structure that stores more CO2 than was used in the manufacturing process. The topography of the local landscape is reflected in the underside contours of the structure, while the surface habitat, with its wide ramps, is designed to blend seamlessly into the surrounding landscape.
The goal of this design is to create a modular structure that can be locally assembled and adapted as habitats change. To achieve this, the design strategy creates a double-curved inverted arc structure, composed of a steel and Ductal grid overlaid with a rhomboid-shaped micro-grid lattice. The lattice is composed of pre-vegetated, lightweight, glass-reinforced plastic habitat modules—inserts that can be adapted, replanted, replaced or expanded as conditions dictate. Customized to local habitat conditions, the modules can be planted off-site and readily transported by flatbed trailer to the site for insertion or replacement.
The design goal for this concept is to build a lightweight, flexible structure that is at once iconic yet almost invisible. To achieve this, the design strategy involves using lightweight, resilient wood-core fiberglass for the bridge structure, which is designed in flexible, modular configurations, or “strands” in the landscape. This strategy makes use of the existing tree canopy as additional habitat between strands and proposes multiple connections into the site with varied possible routes across the bridge, based on the travel habits and preferences of each target species. Notably, the bright red bridge is intended to be an iconic structure for humans, signifying the crossing, the landscape and its non-human inhabitants, but is at once unremarkable to wildlife that cannot see the colour red.
The goal of this scheme is to create a cost-effective, lightweight, pillar-free structure that appears to float across the highway. To achieve this, the design strategy involves using concrete formwork to create a thin-shell, double-curved, pillar-less structure. The formwork can be reused many times, and results in a cost-effective structure due to the thin layer of concrete required and the intention of repetitive construction to create a series of bridges. The upper curve of the “landshape” contains the habitat for the crossing, including a system of ponds to serve as a draw for wildlife.
The Winner Is:
The design goal for the winning design in the ARC competition is to develop a sustainable, modular, flexible, cost-effective crossing system that appears to weave over and under the road, and that can be made locally and assembled on site. To achieve this, the design strategy employs thin-shell, precast, concrete forms based on a three-hinged arch. These hypar-forms allow for minimal site disturbance and relatively easy on-site assembly and deployment, given the widespread availability of local precasting facilities across North America. The hypar-forms can be readily expanded or adapted as wildlife movements and habitats change, or as site-specific conditions dictate. The scheme is a landscape and structural collaboration, bridging both under and over the road, effectively layering both the drivers’ experiences and animals’ preferences.