Wildlife and Roads: Decision Guide Step 2.1.6
2.1.6 Identify Appropriate Wildlife Crossing Type
Wildlife overpasses are among the most effective structures for allowing wildlife of many types to move relatively unimpeded across the road or railway. They have been successfully employed in Europe and North America.
Figure 2.1.1. Wildlife overpass (known as the Wolverine Overpass) across the Trans Canada Highway, in Banff National Park, Alberta, Canada. Picture taken approximately 2000, three years after passages were installed. As time progresses, the vegetation on the overpass will grow to resemble the nearby forest. Passage is 50 m wide, 70 m long. Photo credit: K. Gunson.
By early 2007 there were three overpasses in Canada (two in Alberta in Banff National Park, and one in British Columbia over the Okanagan Connector Freeway), and two in the United States that have been constructed exclusively for wildlife passage (one in Utah over Interstate 15 for mule deer, and one in New Jersey over Interstate 78 for white-tailed deer). There are several other overpasses built for mixed uses such as wildlife and human recreation or unpaved roads. In the United States these are found in New Jersey over Interstate 78 along with the exclusive wildlife overpass, and in Florida along the Florida Greenway Trail over Interstate 75. In Canada the two wildlife-exclusive overpasses in Banff National park have the best documentation of wildlife use data .They are 50 meters wide and have been designed to blend in with the natural surroundings with earth, bushes and trees on them (see picture). Since their construction in 1997, they have been monitored with track plates, cameras and wire snags for hair samples for genetic analysis. These crossings have facilitated wildlife movement, in part because the accompanying fences are regularly maintained. Thousands of animal crossings have been documented across these two overpasses, including elk, mule deer, moose, grizzly bear, black bear, and puma (see Clevenger and Waltho 2000, 2005). These are perhaps the best known and best documented overpasses in North America. It is possible that overpasses with less width would be used regularly if fencing was placed along the road right of way and was continually maintained. Bobcat use has been documented over the multi-use overpass along Florida's Greenway has documented bobcat use (see picture). This passage spans a 6 lane divided highway. The two overpasses in Banff and the multi-use passage in Florida are the only three North American overpasses seriously monitored for wildlife use. There is an overpass approximately 7 meters wide in British Columbia over the Okanagan Connector Freeway near Peachland which has anecdotal evidence of mule deer use. The predecessor to the British Columbia overpass is in Utah over Interstate 15 south of the town of Beaver. This is the first overpass built in North America (1975). It is approximately 7 meters wide and has sign of mule deer use (see picture). There is one overpass 15-22m wide over Interstate 78 near Berkley Heights, New Jersey which has anecdotal evidence of use by white-tailed deer and other species. More data is needed on the use of these structures. Specifically, measures of human presence or disturbance may be important determinants of their use. In selecting an appropriate size of overpass for future projects, perhaps a compromise between the wide (50 m) overpasses in Banff, and the narrow (7m-22m) overpasses in Utah and British Columbia may prove to be acceptable to target species while providing cost effectiveness, however it is not possible to determine minimum effective size with available data.
Wildlife overpass (7 m wide) Beaver, Utah. Note mule deer path in foreground. Photo credit: S. Rosa.
Entrance to Florida overpass spanning Interstate 75, near Ocala, Florida. Note overpass is for multiple use and part of a larger greenway. Picture taken within on year of completion (2001). Photo credit: P. Cramer.
Multi-use overpass in Florida, over Interstate 75, Ocala. . Note overpass is for hikers, equestrians, and cyclists, as well as wildlife and is part of a larger greenway. Picture taken within on year of completion (2001). Photo credit: P. Cramer.
Bobcat on Ocala overpass, Florida. Photo credit: D. Smith and Florida DOT.
At-Grade Crosswalks are designated areas for wildlife to pass across the roadway. The idea is that motorists will be cautious for wildlife where these at-grade crossings are located. Very few crosswalks have been employed and even fewer studied to see if they reduce the problem of wildlife-vehicle collisions. Lehnert and Bissonette (1997) studied the efficacy of a crosswalk for mule deer and elk in rural Utah on a 4 lane divided highway and on a 2 lane road where fencing led the animals to specific area of roadway to cross. The method used a series of 3 stationary deer warning signs to warn motorists to reduce speed. After installation, deer mortality declined~42% and ~37% along the roads, but they could not demonstrate statistically that the mortality reductions were a result of the crosswalk system, rather data led the researchers to surmise that the decrease in Wildlife-Vehicle Collisions was largely due to the decline in the deer population in the area. Additionally, given access to the ROW, deer came to the road-right-of way to graze, exacerbating the Wildlife-Vehicle Collision problem. It is possible that at-grade crossings can be effective on low traffic volume roads if used in conjunction with remotely sensed message board that report to the motorist when an animal is on the road. Currently (as of Summer 2007) there is a high technology crosswalk in place in Payson Arizona on State Highway 260. There are 11 wildlife underpasses in place along this roadway with 6 more planned. Fencing funnels wildlife to the passages but the fence ends in an area still prone to elk-vehicle collisions. At the end of the fence, there is monitoring equipment that senses if an animal enters the roadway; it triggers a driver message board and lights when an animal is on the road-right-of way. Drivers are expected to slow down to avoid a collision. Prior to the installation of these devices, the wildlife biologist heading the research on the project clocked 136 motorists driving over 100 mph in a two day period. Preliminary evidence suggests the system is working and motorists are slowing down considerably in this cross walk area.
Visit the following website for more information on Arizona crosswalks:
See Huisjer et al (2006) for a review of similar driver warning technologies. url: http://trb.org/news/blurb_detail.asp?id=6690/. See Gordon et al. 2004 for evaluation of driver warning systems in an area deer move across a roadway in Wyoming.
Wildlife underpasses are typically bridges or culverts that allow wildlife to pass underneath a road. In an effort to standardize the many types of underpasses, we have created the table below to categorize the types of underpasses based on size, type of structure, and function. The table below can be used to identify different size classes and provides preliminary specifics on configurations: more detail on dimensions is given in Step 2.3. Below the table are the references that we used to determine the breaks between the classes, and pictures of examples.
Types of Underpasses and Their General Dimensions, Functions, and Target Species
|Underpass Size Class||Dimension Range||Function||Passage Examples||Species Examples|
|Class 1: Small Underpass||1.5 m (5') high or less||Provides enclosed protection for small terrestrial animals that require cover, and also covers typical aquatic passages. It is highly recommended that aquatic passages also provide some terrestrial passage on the outer edges.||Small bridges, dry culverts, ephemerally flooded drainage culverts, aquatic passages. Drainage or stream structures that are continually with water may function for aquatic species but have limited functionality for terrestrial species, unless upland or wildlife paths/shelves are provided.||Small animals that like cover or do not mind confinement: Amphibians, reptiles, small mammals and some meso-sized mammals (badger, coyote, bobcat). Aquatic species include fish, aquatic amphibians, and invertebrates.|
|Class 2: Medium Underpass||Box culverts larger than 1.5 m (5') high, to a 2.4 m x 2.4 m (8'x 8')||Dimensions allow medium to large sized animals yet still not most ungulates, provides some cover, and may additionally allow for stream passage. If water is conveyed, stream passage should also allow for natural banks that stay dry with minimal rocks.||Standard box culverts, arch pipes, possible bridge extensions. Does NOT count bridges 2.4 m high. There are different standards within different locales: speaking with local manufacturer helps to determine what is available. It is standard to upsize a passage and then sink it one foot in order to have natural floor, and to keep passage dry.||Animals that require some cover and some openness to see through passage. Meso mammals - coyote, bobcat, ocelot, lynx. Large carnivores: black bear, puma. Alligator, and all taxa that use smaller passages.|
|Class 3: Large Underpass||Box culverts w/ min. dimensions: 2.4 m h x 6.1 m wide (8' h x 20'w) or 3.1 m x 3.1 m (10' x 10'), and open span bridges||Provides passage for ungulates and other species that need visibility, maneuvering room, light, possible vegetative cover, and moderated noise from traffic. May allow some natural processes including plant growth and stream movement along passage.||Typical standard box culverts, arch pipes, and bridges. Bridges that are 2.4 m high and at least 10 m wide are included as the lower limits to this class. Bridges may sometimes have stream flow, with upland passage or wildlife shelves for terrestrial wildlife movement. Bridge width (aka length in terms of span autos travel) typically much longer than culvert width (greater than 13 m wide).||Most ungulates (deer, elk, moose, & potentially pronghorn which need minimum 5.5 m high, 18.3 m across) large carnivores: wolf, grizzly bear, black bear, puma. Most of species that use the smaller passages.|
Examples of small underpasses
Desert tortoise using bridge underpass, Utah. Photo credit: A. McLuckie.
Turtle using culvert passage in Oregon. Photo credit: Port of Portland, OR.
Coyote using culvert underpass, Montana. Photo credit: K. Foresman.
Examples of Medium Underpasses
Tennessee Bear Culvert. Photo credit: K. Brown
Vermont Agency of Transportation and Vermont Fish and Wildlife personnel on a field trip to examine wildlife use tracks in a box culvert. Photo credit: C. Slesar.
Bobcat using medium size box culvert underpass, Florida.
Examples of Large Underpasses
Arizona bridge underpass for elk, which have been documented using it thousands of times. Photo credit: P. Cramer.
Corrugated steel (multi-plate) culvert for mule deer and elk in Utah. Only mule deer documented using passage in first two years post-construction. Photo credit: S. Rosa.
Quebec underpass, accommodating both stream and upland for terrestrial wildlife movement. Photo credit N. Desbiens
Florida extended bridge over creek, to accommodate black bear, otter, white-tailed deer, and other wildlife movement. At the time of photograph, deer and otter tracks were detected. Photo credit: P. Cramer.
Wildlife bridge underpass in Chino Hills, California. The initial wildlife culvert passages did not pass the targeted bobcat and coyote, so in an adaptive management strategy, Caltrans (California's Transportation Agency) removed the original box culvert and installed a bridge in an attempt to create an effective passage. Monitoring began in 2007. Photo credit: K. Sacilotto.
Wildlife crossings in San Diego region of California. Photo credit: B. April.
Idaho box culvert underpass. In first two years of monitoring, documented use by bear, moose, mule deer, bobcat and other species, but not used by elk. Photo credit: P. Cramer.
Examples of Overpasses
First overpass in North America, Utah's overpass built in 1975. Mule deer tracks to the left of Silvia. Photo credit: P. Cramer.