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U.S. Department of the Interior National Park Service, Parks and road-associated mortality data.72,74,102 Colorado's Moun-
Canada, university researchers, consulting companies, mu- tain Corridor project for I-70 through the Rocky Moun-
nicipal biologists, and the indirect input of many more scien- tains140 with a possible overpass, and Washington's I-90 Sno-
tists who help to develop state-wide connectivity analyses. qualmie Pass project,238 will involve as many as a dozen new
These analyses are becoming increasingly important in the crossings per project. In the east, Vermont has at least nine
placement of crossings. The advancing sophistication of tech- existing crossings, and at least a half dozen more scheduled
nologies such as GIS, infra-red video cameras, and global for the next 5 years. Many of these new crossings will be for
positioning system (GPS) collars have greatly facilitated as- multiple species. Finally, Florida is continuing to construct
pects of scientific research of wildlife in relation to roads and crossings, with 30 more planned for the next 10 years, in-
have helped to make mitigation structures more accurate in cluding an overpass near Orlando.
placement, dimensions, and overall design.
As an extension of an evaluation of wildlife crossing
General Recommendations for Crossings
science, a review has begun of studies evaluating the use of
wildlife passages. Approximately 25 scientific studies assess- As part of research for this project, the research team has
ing the efficacy of 70 terrestrial wildlife passages across North examined the general recommendations for installing wildlife
America found that all passages passed wildlife, and 68 of the crossings. The following list reviews the consistent trends that
passages passed the target wildlife species appear in the literature, in scientific presentations, and in the
telephone interviews, with reference to what the state of the
science reveals about wildlife crossings:
Conclusions and Suggested Research
· Bigger is (usually) better, especially for large animals.
Ongoing Projects
· Cover is important at the ends of passages for some species,
While every state and province in North America is working while others need cover inside the passage.
to create more permeable roads for wildlife, there are several · Elk appear to require a larger openness ratio than most
notable efforts under way. Currently (2007), the most exten- other mammals.
sive mitigation efforts in the United States occur on U.S. High- · Some deer in urbansuburban situations use pre-existing
way 93, which runs from just northwest of Phoenix, Arizona, structures that are far smaller than those used by their
through Nevada, Idaho, and Montana and into British counterparts in more natural landscapes.
Columbia and Alberta. Dozens of crossings are already placed · Ungulates and carnivores may prefer different types of
on this roadway to facilitate movement by desert tortoises and passages; for example, ungulates may prefer overpasses
ungulates in Arizona, and for fish, and small and large mam- while certain carnivores prefer underpasses.57
mals in Montana. In Montana alone, 40 crossings specifically · Light in the middle of the tunnel/passage is helpful for
for large mammals are in place. This highway will have an passage of many species from salamanders to deer, but may
estimated 50 more crossings in Montana, including one over- not be welcome by certain carnivores.
pass, and dozens of crossings in Arizona, for a total of over 125 · Noise reduction is generally beneficial.
crossings along its length. · In general, reduced human use in the vicinity of crossings
Perhaps the most frequently written about mitigation is important, especially at night.
measures in the media and the most published in the scien- · Pathways or shelves for wildlife to pass through riparian
tific literature are those measures employed in Banff National underpasses are working for large (deer and elk) and small
Park on the Trans-Canada Highway: two overpasses and animals (mice and voles) alike.
22 underpasses along 45 kilometers of road, with 8 more · Special considerations concerning conditions for target
planned along the next stage of construction.163 Another care- species or suites of species are often necessary, for example:
fully designed project is that of State Road 260 in Payson, Amphibians need tunnels that are wet and cool;
Arizona, on the Tonto National Forest. This mitigation proj- Small mammals may need cover in the form of logs,
ect was designed, constructed, and monitored in joint collab- rocks, and bushes;
oration with the Arizona DOT, Arizona Game and Fish Pronghorn need open, natural conditions to the extent
Department, and the U.S. Forest Service, among others. possible; and
Seventeen bridges have been or will be placed along the high- Fish, especially juveniles, need culverts that do not rise
way so that elk, mule deer, and other wildlife can cross safely more than two body lengths above natural water levels.
underneath. The biologists working on this project have done They need low natural volume in culverts, with culvert
an exemplary job of monitoring wildlife use of these passages bottoms approximating natural riverine conditions.
through utilization of GPS collars, video surveillance systems, Weirs may need to be provided temporarily.
