Oracle Road Wildlife Crossings
The Wildlife Bridge
The Oracle Road wildlife bridge is the first of its kind in the Sonoran Desert. The bridge measures 150 feet wide, the minimum width necessary to provide shielding from the sights, smells and sounds of the roadway below. The bridge was designed to accommodate the greatest number of species, and specifically for deer and bighorn sheep. Construction was completed in March 2016. New wildlife monitoring cameras captured a herd of mule deer using the bridge just a few weeks later. While it is not built to support full sized trees, the bridge has been seeded with native plants that will provide a natural environment and plant cover for smaller animals. Because wildlife will not use it while people are present, the bridge itself is closed to people, with an infrequent exception for official maintenance and research. (Return to top)
The Wildlife Underpass
The wildlife underpass is 50 feet wide, 12 feet high, and 190 feet long. Natural sunlight comes through a skylight in the median of the highway, so that the underpass is not too dark for deer to use. The natural dirt floor is attractive to wildlife, and makes it easy for researchers to document animal tracks. From the underpass, animals can see the Catalina Mountains to the east and can access Big Wash to the west. Dirt excavated during construction was re-purposed to create a bowl shaped entrance with high berms on the east side, which helps to reduce traffic noise and lights as animals approach. On the west end, a walking trail runs between two communities on either side. The underpass itself is closed to the public.
The original plan included two wildlife underpasses, but challenges with right-of-way access on the second one threatened to increase the budget to the point where the whole project – and all three crossings – were in peril. The solution was to remove the second underpass and instead modify the highway as it passed over the Ca. The river is a large sandy arroyo (an ephemeral desert wash that is dry on the surface for most of the year) that connects Catalina State Park and Sutherland Wash to the east, with Big Wash on the west. By ensuring enough height for deer to pass underneath, we used this crossing point to replace the second underpass. You can view this wildlife crossing as you pass over the river using the Cañada del Oro River Park bike path. When you go, you can see the fine-mesh continued along the bike railing to keep small animals headed in the right direction. (Return to top)
The Wildlife Fencing
Unfortunately for us, animals can’t read our wildlife crossings signs. And even though wildlife crossing structures are placed in the best possible location to provide safe passage for the greatest number of animals, funneling wildlife to the crossings is a critical part of every wildlife crossing project. The Oracle Road wildlife funnel-fence extends 1 mile to the north of the wildlife bridge, connects the bridge and the underpass, and extends XX miles south of the underpass, and was designed by biologists and engineers to be high enough (8 feet) so deer don’t jump over it, and deep enough (buried 6 inches) to keep animals from burrowing underneath. A fine-mesh panel along the bottom ensures that smaller critters, like toads, tortoises, and rabbits, can’t squeeze through the larger square openings. The view of the Catalina Mountains at sunset and sunrise is one of the highlights of living in this area, so engineers took that into consideration in the design, which had to be effective without being visually jarring. The fence is painted with a patina that helps it blend into its natural surroundings. Funnel-fencing is a critical component of wildlife crossings and is very effective at directing wildlife to these safe passageways.
Where some side streets meet Oracle Road, a carefully designed cattle guard was installed to discourage wildlife from getting onto the roadway. If an animal does get onto the road, several “jump-outs,” or one-way dirt escape ramps, allow wildlife to get off the road safely without being able to get back in. Residents have already observed coyotes using the jump-outs successfully.
See a broken fence? The Arizona Department of Transportation is responsible for maintaining the wildlife fence along Oracle Road, and the Pima County Regional Transportation Authority (RTA) has taken responsibility for maintaining the funnel-fence where it leaves the highway right-of-way near Catalina State Park on the east and Big Wash on the west (the fencing was move back away from the roadway in these areas to avoid blocking local communities and businesses). These agencies can make repairs when needed. If you see a breach or broken section of wildlife fence that needs repaired, please contact us here. (Return to top)
Restoring Natural Vegetation
The Arizona Department of Transportation spread a special mix of native seeds and mulch over the wildlife bridge and underpass after construction was complete, and straw berms were placed on the slopes to help reduce erosion until plant roots could grow and stablize the soil. In addition, a few cactus species were planted with temporary irrigation. Because of the Sonoran Desert’s unique rain patterns, most seed growth occurs after summer monsoons and winter rains. A Sky Island Alliance report of the vegetation growth in September 2016 documented a variety of plants successfully growing, including brittlebush, white-thorn acacia, and several species of native grass including needle grama and Rothrock grama. It takes time for plants to become established, and the Coalition, with our partners, are watching the progress of revegetation on the crossings to assess whether additional restoration planting will be needed. In addition, Pima County and the Santa Catalina Catholic Church worked with the Coalition for Sonoran Desert Protection, Sky Island Alliance, and Tucson Audubon Society to protect the wildlife bridge crossing adjacent to the church with a native vegetation screen. Work was completed in the fall of 2015 and involved volunteers from the community. Read the initial results of that project here. (Return to top)
NOW “CLOSED” FOR BUSINESS
The completion of the wildlife crossings was celebrated with a ribbon-cutting and “grand closing” event on May 10, 2016. As a special treat, the public was invited to see the bridge and overpass for themselves, before the crossings were closed to the public. Except for official research and maintenance purposes, people and bikes, horses, and vehicles should not use the wildlife crossings. When you are there, the wildlife are not!
See the Coalition’s Poster: Extensive Community Partnerships Lead to a Successful Wildlife Overpass and Wildlife Underpass on the Edge of the Highly Urbanized Tucson, Arizona Region presented at the 2017 International Conference on Ecology and Transportation in Salt Lake City, UT in May 2017.
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