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Research Approach: Methods and Data where several individuals were interviewed, often information
was not available within central headquarters of the state
The Telephone Survey DOT; hence biologists-planners within each district or region
The research team administered a telephone survey to pro- were contacted for their knowledge of crossings. The profes-
fessionals in transportation and ecology in all 50 United States sional titles of respondents included engineers, planners,
and all Canadian provinces and territories. The survey consisted biologists/ecologists, geographic information systems (GIS)
of 25 questions centered on three areas of interest: wildliferoad analysts, and research personnel. Respondents included rep-
mitigation measures, WVC data, and transportation planning. resentatives from every state DOT, most Canadian MoTs,
Candidates for interviews were selected from contact informa- most state wildlife agencies, the FHWA, the U.S. Fish and
tion on individual state project entries on the U.S. Federal High- Wildlife Service, the U.S. Forest Service, the National Park Ser-
way Administration (FHWA) "Keeping It Simple" website, vice, Parks Canada, Native American tribes, several non-profit
through consultation with FHWA representatives, from lists of natural resource organizations, and consulting companies and
attendees of the Transportation Association of Canada (TAC) research personnel from universities.
meetings, and from personal contacts of team members. These
individuals were given approximately five opportunities to re-
Total Crossings
spond to requests for interviews through emails and phone calls
before a new contact was pursued. Once the contact person was The total number of wildlife crossings in North America is
introduced to the survey, she or he was given the opportunity difficult to assess accurately. The number depends on who is
to refer the survey or specific questions to someone more asked, when the question is asked, how crossings are defined,
knowledgeable. A goal was to interview a minimum of two in- and whether both aquatic and terrestrial crossings are consid-
dividuals within every state and province in an effort to best rep- ered. There are a minimum of 559 terrestrial underpasses and
resent state Departments of Transportation (DOTs), provincial four overpasses in the United States. In Canada there are a
Ministries of Transportation (MoTs), and the state or federal minimum of 118 terrestrial underpasses and three overpasses.
wildlife agency. Interviewees were encouraged to provide Aquatic passages are less likely to be recorded than terrestrial
answers to the survey questions, but many also provided re- passages and hence are more difficult to record accurately.
ports, articles, and photos of mitigation measures and DOT- There are a minimum of 692 aquatic passages (installed solely
sponsored research projects that focused on how wildlife move or in part for aquatic fauna) in the United States and roughly
with respect to roads. The survey was conducted from July 2004 10,000 aquatic passages placed throughout Canada. When
through March 2006. combined, there are a minimum of 684 terrestrial passages
and 10,692 aquatic passages in North America (Figure 3).
Crossing Structure Definition
An important component of this research was in defining a Interpretation, Appraisal, and Applications
crossing structure. For this survey, a crossing structure was de- Trends in Practice
fined as a new or retrofit passage over or below a roadway or
railroad that was designed specifically or in part, to assist in A number of trends in the development and practice of
wildlife movement. Culverts and bridges already in place when wildlife passages over the past 4 decades became apparent in
fencing was installed to lead animals to these pre-existing struc- the analyses of the data: Over time, the trends in the practice
tures were not considered crossings. These structures were only have been:
defined as crossings if they were altered by adding weirs for fish
passage, adding shelves for terrestrial wildlife, removing riprap · An increased number of target species considered in
to allow wildlife movement, or other such actions. mitigation projects,
· Increasing numbers of endangered species as target species
for mitigation,
Findings and Results · A continued increase of involvement of many agencies and
organizations in the planning and placement of crossings,
Survey Participants
· An increase in the placement of multiple structures, and
Four hundred and ten individuals participated in this · A continent-wide neglect of maintenance of these
survey. The number of participants per state/province varied structures.
from 1 to 44 (Figure 2). States or provinces with small repre-
sentation (less than five interviewees) were usually able to pro- The earliest wildlife crossings, which were installed in the
vide data from central resource personnel, while in states 1970s, were for white-tailed deer (Odocoileus virginianus) and
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Figure 2. Number of survey participants per state, province, and territory.
mule deer (Odocoileus hemionus). These installations include arroyo toad (Bufo californicus) in California, reptiles such as
the first documented underpass/culvert crossings in Colorado the desert tortoise (Gopherus agassizii)31 in California and
for mule deer (1970)195 and New York (1970) for white-tailed Arizona, birds such as the pygmy owl (Glaucidium brasil-
deer. The first overpass in North America was created for mule ianum cactorum) in Arizona, and invertebrates such as the
deer and elk (Cervus elaphus) in Utah in 1975. During the Karner Blue butterfly (Lycaeides melissa samuelis) in New
1980s, Florida became the continental leader in the number York have all been targets of mitigation measures across and
and variety of types of wildlife passages, and began the trend under roads. Future crossings will continue to be influenced
of multiple species crossings with the installation of 24 under- by the presence or potential presence of species in some sta-
passes and 12 culverts for wildlife during the expansion of tus of protection, from kit fox (Vulpes macrotis mutica) in
Interstate 75 from Naples to Fort Lauderdale.99,100 California; lynx (Lynx canadensis) in Colorado, Oregon,
Florida also began the trend in creating passages for Montana, Minnesota, and Idaho; ocelot (Felis pardalis) in
endangered species of wildlife with its focus on passing wide- Texas; grizzly bear (Ursus arctos) in Montana and Alberta;
ranging federally listed carnivores, such as the Florida pan- Blanding's turtle (Emydoidea blandingii) in Minnesota, the
ther (Puma concolor coryii)150 and Florida black bear (Ursus diamondback terrapin (Malaclemys terrapin) in Delaware
americanus floridus),202 under roads that carry an increasing and Georgia, Salt Creek tiger beetles (Cicindela nevadica lin-
number of motorists. Carnivores are not the only type of colniana) in Nebraska; and the Grizzled Skipper butterfly
endangered species that are targets for wildlife crossings. (Pyrgus malvae) in Ohio to the salmonid species of fish in
Endangered ungulates such as the Key deer (Odocoileus vir- Washington, Oregon, and California. These and other
ginianus clavium) in Florida, endangered small mammals species' needs to move throughout roaded landscapes, the
such as Preble's meadow jumping mouse (Zapus hudsonius laws that protect them, and the oversight and involvement in
preblei) in Colorado, endangered amphibians such as the transportation projects by the U.S. Fish and Wildlife Service
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Figure 3. Number of terrestrial and aquatic wildlife crossings
in North America.
contribute greatly to increase the number of crossings exist- Members of First Nations and Native American tribes
ing and planned for North America. across the continent are involved in mitigating roads for
There is also an increase in the number of agencies involved wildlife. Examples of how Native peoples have insisted on
in the planning and placement of wildlife crossings. The more protecting and helping wildlife pass under and over roads in-
traditional model was for a state or provincial DOT/MoT to clude the grassroots efforts of the Tohono O'Odham tribe in
work with the state/provincial wildlife agency in determining Arizona to bring the community together to install fencing to
the species present and the necessary mitigation measures. In- help desert tortoises pass through existing culverts. The Salish-
creasingly, the U.S. Fish and Wildlife Service in the United Kootenai tribe has worked with the U.S. government and
States is involved in planning and placing wildlife crossings as Montana DOT to help design more than 50 passages on U.S.
the awareness of the needs of federally listed endangered and Highway 93 that passes through the Flathead Reservation in
sensitive species of wildlife and plants grows. The FHWA has Montana. If this trend continues, an increase will occur in
also become more involved in the creation of mitigation meas- grassroots efforts to tackle the problems of roads and wildlife.
ures and urges their design early in the planning process. The research team also found a trend of increasing efforts
As roads were widened and otherwise upgraded in rural land- to include multiple associated structures along with under-
scapes, federal natural resource agencies, e.g., the U.S. Forest passes to help guide wildlife. Fences still are used to encour-
Service, became involved in determining the need for and age wildlife to use structures. Innovative measures today also
placement of wildlife crossings. This increased federal involve- include placing large boulders near the approach to passages
ment has happened in Canada as well, with Parks Canada to help guide larger wildlife to the crossing. The problem of
largely responsible for the installation of 24 wildlife crossings animals entering the roadway at the end of the fence, or find-
under and over the Trans-Canada Highway. As cities grow into ing or creating holes in the fence to enter the roadway quickly
areas that were until recently largely rural and wild, the plan- became apparent and created a need for mitigation that
ning and placement of wildlife passage begins to be done in allowed wildlife to escape the road right-of-way (ROW). In
concert with city and county entities. The Pima County the 1970s, escape gates were designed, probably originating in
(Arizona) experience with wildlife crossings is an example of Colorado,194 where deer or elk could escape the fenced road-
how a county entity has helped in researching, designing, and way by pushing their weight against tines in a specific gap in
placing wildlife crossings for suites of species near Saguaro the fence. In the 1980s and 1990s, escape, or jump-out, ramps
National Park; they have also placed what may be the first bird began being built in several western states to help deer and elk
crossing in North America for the pygmy owl. escape the road.28 These ramps are continually being refined
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and tested across western North America and are used by they are working for the intended species.93,94 In Arizona, the
deer, elk, and bighorn sheep (Ovis canadensis). Efforts are also same U.S. Highway 93 has dozens of crossings for species
underway to "coax" animals to passages; for example, water ranging from desert tortoise to bighorn sheep, with dozens
guzzlers, which collect water in dry climates, have been used more planned. In Florida, the first series of crossings were
to encourage wildlife to passages in California and Arizona.74 built in 1982 along Florida's Alligator Alley for the Florida
Passages are also baited during the first post-construction panther and the accompanying suite of wildlife from the
years. Wildlife shelves are placed in existing culverts and pas- ecosystem such as Florida black bear, bobcat (Lynx rufus),
sages to encourage small and medium animal use when the deer, alligators (Alligator mississippiensis), wading birds, fox
passages are wet.93,94 Shrubs, logs, woody debris, and tubes (Vulpes vulpes, Urocyon cinereoargenteus), raccoon (Procyon
have been placed for small animal passage. Shrubs and trees lotor), opossum (Didelphis virginiana), fish, and other species.
have been planted to lead black bears to the entrances of pas- Thirty-eight crossings, from large underpasses to culverts,
sages in Florida.202 Wildlife walls less than 2 m high have been were established over 64 kilometers,100 allowing for a greater
placed to funnel smaller species such as reptiles and amphib- degree of permeability than most established crossings.
ians to crossings, e.g., at Paynes Prairie in Florida.71 Turtle, Vermont is an example of how several simultaneous projects
tortoise, and amphibian fences have been designed to direct have helped to create a permeable landscape in several dif-
these smaller species to crossings.31,131 The future of wildlife ferent regions. Road projects currently underway include
crossings will no doubt include continued innovative meth- Route 78 along the viaduct over Missisquoi National Wildlife
ods, such as vegetation and median berms to direct airflow up Refuge, and the Bennington Bypass on US Highway 7 and
over the road and traffic, helping insects and birds fly over the State Route 9.
roadway dangers.
Although there are many positive examples of mitigation
Trends in Science
efforts, there are also efforts that have not proven successful.
The two most often cited reasons for passage failures are The research team assessed the state of the science of
incorrect location and lack of maintenance for passages and wildlife passages from reports submitted by telephone survey
accompanying fences. The latter reason is preventable as a participants and a concurrent review of the literature, which
simple planning and staffing effort. Wildlife crossings are amassed over 370 reports and papers. Trends in the science of
placed in dynamic landscapes; rivers and ephemeral water roads and wildlife indicate:
sources bring debris into structures, snow pulls down fences,
and wildlife and human activity create holes in fences or de- · A tendency for a greater percentage of new passages to be
grade crossings. Additionally, human activities make passage monitored for efficacy,
by wildlife difficult or impossible because of vehicle use and · A broadening of the number of species monitored for use
parking in passages, camping in passages, domestic dog usage of passages,
and marking of passages, or shelter for homeless people. · Increases in the length of time for monitoring,
Although passages require maintenance, a common theme · Increased numbers of participants in research projects, and
across the continent is that passages, fences, and accompany- · Increasingly sophisticated research technology.
ing structures are inadequately maintained.
Monitoring of wildlife passages began in 1970 with one of
the first underpasses for wildlife in North America. This un-
Examples of Multiple Crossings
derpass was placed near Vail Pass along Interstate 70 in
that Promote Permeability
Colorado and was monitored for mule deer use.195 This level
The overall trend of increasing numbers of target species of monitoring was rare for passages placed during the fol-
for wildlife crossings is illustrated by several projects that con- lowing 2 decades. Since 2000, there has been an increase in
tain or will contain series of crossings for suites of species. the pre-construction monitoring of new passages. During the
These projects include the Trans-Canada Highway in Banff past 15 years, an increasing number of studies have consid-
National Park, Alberta, which has 24 crossings in place and ered multiple species near roads, thus broadening the knowl-
8 more planned over 45 kilometers. These crossings include edge base and mitigation efforts. Research projects today tend
overpasses, underpasses, and culverts for species ranging to monitor species use of passages for greater lengths of time
from small mammals to grizzly bear and elk.52,57 In Montana, than in 1980s and 1990s studies, with monitoring efforts ex-
U.S. Highway 93 has 20 current crossings of various size tending to several years post-construction. Finally, the study
south of Missoula, and over 60 more crossings planned from of wildlife crossings has included more scientific partners
Sula north to Polson. These crossings are intended for suites than in past decades, including state wildlife agencies, federal
of species and several have already been studied to find that natural resource agencies such as the U.S. Forest Service, the
