Wildlife and Roads: Decision Guide Step 1.2

Progress Bar Decision Guide Overview Step 1: Resource Evaluation Step 2: Identify Solutions Step 3: Select & Create Plan Step 4: Construction Step 5: Monitor & Evaluate

Step 1 Step 1.1 Step 1.2 Step 1.3

Identify Wildlife & Fisheries Issues

1.2 Identify Wildlife & Fisheries Issues: We direct the users to a series of steps which first provide a literature base on the effects of roads, and the need for permeability for wildlife. The guide then instructs the user in identifying the species, natural areas, and natural processes that may be affected by the plan/project. At the end of this step, the user will decide if there is a need for mitigation and whether to proceed with the decision guide.

1.2.1: Literature on Effects of Roads & Need for Permeability

1.2.2: Literature on Animal-Vehicle Collisions and Their Ecological and Societal Costs

1.2.3: Determine Ecologically Important Areas Within and Near Plan/Project

1.2.4: Determine Species Potentially Affected by Plan/Project

1.2.5: Determine If There Are Any Animal-Vehicle Collisions Safety Concerns in the Plan/Project

1.2.6: Investigate If Landscape Linkages Have Been Identified in The Area

1.2.7: Review Regulatory Reasons For Being Concerned About Wildlife

1.2.8: Summarize Results

Back to Top


1.2.1 Literature on the Effects of Roads and the Need for Permeability Introduction to Road Effects and Permeability

Transportation, Ecological Services, and the Virtual Footprint

Historically, linking transportation and ecological services may have seemed inherently in conflict but they need not be so. One can envision roads as having a physical as well as a virtual footprint. The physical footprint is easy to see and includes the actual dimensions of the road (length and width), as well as the dimensions of associated structures, e.g., the right-of-way. The virtual footprint is much larger and includes the area where the indirect effects of roads are manifested. The roaded landscape has both direct and indirect effects on wildlife species, community biodiversity, and ecosystem health and integrity. The most prevalent direct effect is road kill. Indirect effects include reduced habitat quality, barrier effects, and loss of connectivity resulting in restricted or changed animal movement patterns. The virtual footprint, therefore, can be understood only when put into a landscape, context-sensitive perspective. Here the 'Cinderella Principle' needs to be applied; namely establishing mitigation that effectively 'shrinks' the virtual footprint to more closely resemble the physical footprint. For surface transportation, this means that highway planners and engineers need to continue to incorporate mitigation measures that restore ecological integrity and landscape connectivity, while at the same time insuring safe state-of-the-art transportation services in a cost effective manner. This is not an inherently difficult job, but it does require purposeful activity guided by informed, synthetic analyses that reflect true benefits and costs. We define transportation services to mean, among other things, safe, efficient, reliable roads, inexpensive transportation, properly constructed intersections, safe and quiet road surfaces, good visibility, safe bridges, and good signage. By ecosystem services, we mean clean water, clean air, uncontaminated soil, natural landscape processes, recreational opportunities, abundant wildlife, normal noise levels, and a connected landscape that leads to restoration and maintenance of life-sustaining ecological processes.

Currently across North America, a mismatch exists. Ecosystem services have been compromised by road construction. The virtual road footprint is too large. We suggest that the overarching principle that needs to guide future road construction, renovation, and maintenance needs to link both transportation and ecological services. That is accomplished by reestablishing connectivity across the landscape. But restoration of connectivity is the desired end. The mechanism by which connectivity is established involves moving from roaded landscapes that are nearly impermeable, to landscapes that are semi-permeable and finally, fully permeable; when accomplished, the landscape is connected, and ecological services are restored. Nearly normal hydrologic flow, facilitated animal movement, reconnection of isolated populations and gene flow are made possible. In other words, the Cinderella Principle of 'shrinking the virtual footprint' has been applied effectively, restoring landscape permeability. Ecological objectives have been met coincident with a continually effective roadway network.

Permeability: The Ultimate Goal of Smart Roads

The concept and practical application of permeability might best be understood by an example. Imagine a middle-aged couple who live in a small town or suburb. They work close to their home, and shop in the neighborhood. They have walking access to a grocery store, a church, a pharmacy, a movie theater, a medical clinic; in short, all of the amenities they need for a happy and comfortable life. Then suppose that a major road that runs through the suburb is enhanced and made into a 4 lane divided interstate highway with its accompanying fences and barriers, to accommodate the increased traffic and to provide the requisite and expected transportation services. Because of the location of the road, it now separates our imaginary couple from their work, and from the amenities that they depended on and could access easily before. The couple, who always walked to access these amenities and resources, is now blocked by the highway. The highway does, however, provide connectivity in the form of crosswalks spaced approximately 6 to 8 blocks apart. The couple has a choice. They can either use their car and bear with the heavy traffic, or walk many more blocks to access the crosswalks that would allow them to cross the road. It is unsafe for them to cross the highway in any place other then the crosswalks provided. Their cohesive neighborhood is still connected, but much less permeable. This is the critical difference between connectivity and permeability. Regardless of the choice they make, accessing the resources the couple needs for everyday life is now much more difficult and entails much longer distances and a greater time commitment. Although fanciful, this imaginary situation is analogous to what happens to ecosystem resources for wildlife when highways are built across natural landscapes. Connectivity can be maintained by crossings, but the placement, type, and configuration of the crossing will determine whether permeability is impacted. Think of crossings as a funnel that guides animals under or over roads. Then imagine a context-sensitive road design that incorporates different types and designs of crossings in appropriate locations. The result can be thought of as a 'sieve' that facilitates animal movement, rather than a 'funnel'. Connectivity evolves to permeability.

Restoring connectivity is a land-based concept and easy to understand. As can be seen by the example given above, it is not necessarily equivalent with the idea of landscape permeability, which is an animal-centered concept. The difference between the two concepts involves the idea of scale sensitive (allometric), animal-based movement. Permeability implies the ability of the animal to move across its home range or territory, (its ecological neighborhood) in a relatively unhindered manner, i.e., movement ease can be indexed by essentially a straight-line distance to resources. To put this into scientific terms, the fractal measure of the pathway less-tortuous and is of lower dimension. Anything that hinders movement or increases distance moves the landscape in the direction of impermeability. Scale-sensitivity considerations enter the picture because different animals have different movement capabilities and respond to the same landscape in very different ways. A mouse does not use or move across its home range or scale to the landscape in the same way a moose does. Hence an assessment of the local animal community that exists in the landscape that the road crosses is essential and will suggest different crossing types, configurations, and locations in order to achieve permeability in roaded landscapes. Understanding animal behavior is critical in achieving permeability.

Providing guidance on the use and effectiveness of wildlife crossings to mitigate habitat fragmentation and reduce the number of animal vehicle collisions involves thinking in a context sensitive framework that is based on sound ecological principles. Connectivity is intimately linked to permeability. Permeability is the goal of smart roads and intelligent mitigation. Our goal for this decision guide is to develop effective guidelines based on this premise: understanding and establishing landscape permeability guidelines that lead to effective landscape connectivity and the restoration of ecosystem integrity—while continuing to provide efficient and effective transportation infrastructure in a cost-effective economic manner.

Back to Top Ecological Effects of Roads Selected Literature

Click on a citation to view annotated notes

Back to Top Additional Literature of Road Effects and Permeability

Click on a title to view annotated notes

Back to Top Related Websites

Wildlands CPR Services for Citizens to Understand Road Effects

Banff National Park of Canada Highway Mitigation Research

Back to Top


1.2.2 Literature on Animal-Vehicle Collisions and Their Ecological and Societal Costs

Wildlife-vehicle collisions are the most significant part of the overall animal-vehicle collision problem. It is estimated that there are 1.5 million wildlife-vehicle collisions and an average of 200 human deaths from those collisions annually in the United States. The following articles and website further detail this problem and the potential alternatives.

Back to Top Literature Review

Click on a title to view annotated notes

Back to Top Related Links

Overview of Wildlife Vehicle Collisions in British Columbia and Recommendations for the Future

Deer-Vehicle Crash Information Clearinghouse

AAA Tips to Avoid Deer-Vehicle Collisions

Article on State Farm Insurance Estimates of Top Ten States for Deer-Vehicle Collisions

Back to Top


1.2.3 Determining Ecologically Important Areas Within or Near the Plan /Project Area

Considering ecological resources in the planning stages of transportation projects involves identifying data sources, information inputs from local ecological professionals, and possibly conducting field research on target species. Ecological considerations are best incorporated during the initial stages of long range planning (20 to 30 years prior to projects) because ecological resources may be heavily impacted by potential transportation projects. Late consideration may heavily impact permitting schedules, mitigation costs, and time constraints associated with project progress. If the scoping process determines that a potential project will proceed through the planning process, then the initial step in planning for wildlife needs would entail accessing several data resources. For an initial "Fast Track" approach, accessing databases such as the following will be most helpful in finding critical information:

Wildlife Action Plans

Each state has a State Wildlife Action Plan, which identifies the species at risk and threats to wildlife within the state. While these plans are uneven in treatment of the issues, each plan is required to have certain elements that can be useful in transportation planning. For an excellent treatment of the purpose of these plans, and information on each of the state's plans, see the Teaming With Wildlife website.

Numerous other resources exist to identify the wildlife and fish communities in the project area. Each state's resource agencies will have different Geographic Information Systems (GIS) data sources, maps, aerial photos, etc. It will be necessary to work with resource professionals locally to determine the communities affected.

At this point in the process it is desirable to have a general idea of the affected species so that all involved agencies understand the situation. Specific species affected will be identified in the next step.

Additional Related Links

Banff National Park Highway Mitigation Project Reasons to Consider Mitigation

Conservation Across the Landscape: A Review of State Wildlife Actions Plans

Back to Top


1.2.4 Determine Species Potentially Affected by Plan/Project

Incorporating wildlife concerns in the early stages of the planning process is critical to successful mitigation and was the number one priority in our North American survey of transportation and wildlife priorities.

Back to Top Fast Track Checklist for Determining Potentially Affected Species

Once information on transportation plans has been gathered, the work outlined below can help determine the species and other environmental effects that need consideration. The expert opinion of local biologists/ecologists is crucial in this process and incorporating local professionals into the entire transportation planning, design, construction, and maintenance process helps to insure the success of the mitigation. If any of the following investigations indicate that wildlife needs to move across the transportation corridor, the consideration process continues to the more "In Depth" approach.

  • Determine if protected areas are involved (federal, state, provincial, local, native tribes, private, or a conservation easement). Check with USGS Landcover Database for all of North America Federal Lands, Amphibian Research and Monitoring Initiative (ARMI), Landcover, GAP analysis resources, water resources such as aquifers, rivers, topographic maps, and many more data layers and links. Check individual state and provincial resources for protected area information.
  • Determine the presence or potential presence of state/provincial or federally listed endangered and threatened species, or species that are sensitive or of special concern. At the NatureServe website for Natural Heritage Programs for each state and Canadian province, you can find species lists and interactive maps of species distributions
  • Review State Wildlife Action Plans which provide information on the most critical and some of the most common but important species in a state
  • Assess for the presence of wetlands with reptile, amphibian, mammal, bird, or aquatic species' populations that need to move across the landscape and would be affected by a road or railway across their home ranges. For a start, check the U.S. Fish and Wildlife Service National Wetlands Inventory
  • Check state/provincial wildlife agency for fish and aquatic organism situations; e.g., Oregon Fish & Wildlife Department Guidelines and Criteria for Stream-Road Crossings and the Maine DOT Fish Passage Policy and Design Guide
  • Check regulatory requirements of state/province in terms of transportation planning. Example includes the Ontario Environmental Protection Requirements for Transportation Planning and Highway Design, Construction, Operation and Maintenance
  • Evaluate project for existing fish barriers. The US Fish and Wildlife Service Fish Passage Decision Support System helps to identify existing barriers to fish movement across the United States
  • Identify the presence of wildlife movement corridors or landscape linkages that may be bisected or near enough to be influenced by the transportation project. Check potential resources in Step 1.2.6, Investigating Landscape Linkages
  • Contact local wildlife professionals for information on the presence of herds of ungulates (e.g., deer, elk, moose) or populations of nearby larger carnivores and/or their movement pathways
  • Contact local state and federal wildlife professionals and local citizens and conservation groups to determine if local species that are also involved in wildlife-vehicle collisions have declined
  • Examine current infrastructure for the lack of existing permeable connections for common wildlife to move under the transportation corridor, e.g., lack of existing culverts and bridges
  • Locate research studies that may provide genetic and other scientific evidence that local wildlife populations are becoming isolated from one another in the presence of the roadway. See below for examples of literature
  • Consult with wildlife professionals and land managers about the need for wildlife to move from one side of the roadway to another because of potential large scale changes in their current home ranges, such as flooding, fire, timber and mining activities, and large scale human development

Back to Top Continue a More In-Depth Process

If the situation warrants more information, there are several additional actions that can be taken. They include:

  • Further identify species at risk of transportation impacts
  • Conduct field site visits
  • Establish a wildlife monitoring study
  • Incorporate local stakeholder knowledge in this stage of evaluation
  • Determine species at risk and potential for wildlife crossing
  • Assess traffic volume effects on wildlife

Back to Top Further Identify Species at Risk from Transportation Project Impacts

Identify any terrestrial or aquatic species with policy or legal status known to occur in the project area, or that may have project impacts due to life history attributes such as long dispersal distances. Include species listed under the Endangered Species Act, globally insecure species, state listed species, or federal land management agency emphasis species (such as Forest Service sensitive species protected by agency policy).
Species with policy or legal status will take precedence over species without such protection.

Impacts to species are not limited to the highway corridor. Wide-ranging species or those that disperse long distances may be greatly affected by highway projects or existing highway conditions. Many if not most projects will require consultation under Section 7 of the Endangered Species Act, and some states have special transportation liaisons with the US Fish and Wildlife Service. These liaisons are a great resource in identifying species outside the project area boundaries that may be affected by the project.

The terrestrial and aquatic species that are not federally or state protected could also be at risk from road effects. These species can be identified in part by referring to the species types at risk in Step below. Also refer to Foreman et al's Road Ecology (2003) for a list of species groups at risk. These species are vulnerable often because they do not have as much protection (and therefore human notice) as species with legal status. At least one objective of identifying these species is to ensure that the project will not cause greater harm than a given species can tolerate and still maintain viability. Some formerly common species can be greatly affected by highways, with greatly reduced populations. Examples include formally locally abundant salamander, frog, and turtle populations that are severely reduced or eliminated near road corridors.

Back to Top Determine Types of Species at Risk and Potential for Wildlife Crossing Structures

Roads and railways cause several types of effects on wildlife, but the most pervasive of these are direct mortality from vehicle collisions and the barrier effect caused by intimidating and dangerous amount of vehicle traffic. The barrier effect of roads includes the loss of habitat connectivity or permeability of the landscape. Other impacts include pollution from exhaust fumes, oil and deicing agents, noise, loss of habitat from the footprint of the highway, and the disturbance during highway construction and operations. More information on impacts from highways can be found in Forman et al. (2003, see below for full citation).

Although roads cause effects other than mortality and loss of permeability, all species will tend to show these two effects if they are impacted by other less direct effects. Therefore, in this section we analyze types of species at risk in terms of mortality from collisions, including safety issues to humans, and barrier impacts. It is important to note that if mortality is an issue to a group of species, then the highway will most probably become a barrier as traffic volume increases (Mueller and Berthoud 1994, Van Langevelde and Jaarsma 2000).

Table is intended to assist in identifying the species in a project area potentially at risk from road / railway effects, and to determine if wildlife crossing structures (WCS) would be an appropriate mitigation measure based on the type of risk (mortality, barrier, or safety).

Species Group at Risk * Affected by Traffic Volume (TV) or Habitat Issues (H)? Type of Risk? Mortality (M),
Barrier (B),
Safety (S)
Are WCS Appropriate Mitigation? Example Species
Movement Issues
Slow, meandering, stopping TV M, B, S Yes Butterflies, reptiles, amphibians, rabbits, badgers, skunks
Immobilizing in response to danger TV M,B Yes Armadillos, opossum, snakes, turtles
Highly mobile TV M, B, S Yes Ungulates, carnivores, birds
Wide-ranging TV, H M, B, S  Yes Ungulates, carnivores, birds
Low mobility TV, H B If appropriate habitat is included in design Mollusks, invertebrates, birds with limited flight capability
Needing seasonal/daily complementary habitat TV, H M, B, S Yes Ungulates, quail, frogs, turtles, birds
Habitat Issues
Attracted to clear zone or road surface TV, H M, B, S Maybe (fences) Snakes, deer, raptors, scavengers, bats, waterfowl, pheasants, amphibians, reptiles
Species with small, isolated habitats H B Probably not Local populations of reptiles, amphibians, low mobility species like mollusks, butterflies
Area-sensitive species H B No Songbirds
Forest interior specialists H B No Tanagers, thrushes, winter wren
Species requiring dense cover H B Maybe Small mammals, snakes
Biological Issues
Wary of humans or noise TV B No Grizzly bears, raptors
Sensitive to lights TV B No Godwits, nesting sea turtles
Low reproductive potential TV M, B Yes Turtles, large carnivores
Low density or population size TV M, B Yes Threatened & Endangered species, large carnivores
Sensitive to road surface or edge H B Maybe Frogs, toads, small mammals
Sensitive to roadside pollutants H M, B No Frogs, toads

* References: Jackson 1999, Van Langevelde and Jaarsma 2000, Forman et al. 2003, Rich and Longcore 2005 see below for full citations.

Back to Top Conduct Field Site Visits

There is no substitute for getting on the ground in an area and assessing the situation for topography, land cover, land use, riparian (stream) areas, land ownership, road geometrics, and how wildlife may be using the area. We recommend a multi-disciplinary team site visit.

Back to Top Establish a Wildlife Monitoring Study

The results of these analyses provide a range of options for proceeding. If there is an interest in learning more about the species that may be affected by the transportation project, it is prudent to conduct a study of the species and the area. These studies could help determine how and where species need to move, how stable their populations are, and if they are likely to be seriously affected by the proposed transportation project, even with mitigation. Directed studies would help ensure potential mitigation measures are scientifically based and may provide data for future projects. Collected data can then be used to help determine the next course of action. These include decisions about the proposed location of roadbed and predicted traffic flows. For example, if the road is predicted to have low traffic flows (average daily traffic measured in the hundreds), there may be sufficient opportunity for some species to cross the roadway unimpeded, thus minimizing the need for mitigation for these specific species. This may not be the situation, however, for all species in the area. This step necessitates working with local wildlife and highway engineering professionals.

Back to Top Assess Traffic Volume Effects on Wildlife

Traffic volume is one of the good predictors of road-railway impacts to wildlife. Traffic volume affects species differently. As traffic volume increases, small and slow animals are increasingly affected by mortality, whereas larger animals may be more affected by loss of permeability. Predicting these effects is highly dependent on the species and the situation. Waller and Servheen (2005) found grizzly bear were so sensitive to traffic volume that they restricted the majority of their road crossings to night time when there were only an average of 10 vehicles per hour (which would equate to 240 vehicles per day). For the majority of large and medium-sized mammals, it is when average daily traffic volume is measured in the thousands that we begin to see major effects on populations, from mortality to almost complete avoidance of the road area. For example, Ng et al. (2005) found an inverse relationship between traffic volume and wildlife-vehicle mortality. They analyzed traffic volume on freeways in Los Angeles, California and found that a road with monthly traffic volumes of 50,000 to 100,000 vehicles (1,666 to 3,333 vehicles per day) had higher road mortalities for large and medium-sized mammals than freeways with volumes ranging from 100,000 to 200,000 vehicles per month (3,333 to 6,666 vehicles per day). The authors surmised the higher volume highways posed such impenetrable barriers to wildlife that few attempted to cross them, while the lower volume road appeared to be less hazardous to the large and medium-sized animals that attempted to cross it. This example suggests a threshold for traffic volume, above which the roadway becomes much more dangerous for wildlife.

It is prudent to assess the effects of traffic volume effects on local wildlife populations. One can begin by determining how average annual daily traffic volume (and future projections) may impact the wildlife in the area. Below we present how to determine the traffic volumes, and we list literature pertaining to studies of how traffic volume has been shown to affect wildlife. We do not give specific recommendations for thresholds of traffic volume and their effects of specific species because the relationships of volume to effects tend to site and species specific.

Generally, traffic volume effects are as follows:

  • Roads with average daily volume measured in the hundreds of vehicles most greatly affect slow moving wildlife such as invertebrates, amphibians, and reptiles, and highly wary species such as grizzly bears. Other species may not find this volume a barrier, especially at night, or on specific days or seasons.
  • Road with average daily volumes from 1,000 to 3,000 vehicles tend to affect most wildlife species attempting to cross and pose a barrier to movement attempts by some.
  • Roads with average daily volume > 3,000 vehicles have been shown to be a barrier to some species, and cause high mortality to animals that attempt to cross the road. At some traffic level, the road becomes completely impenetrable. See references below for more formal treatments of this subject.

To address the traffic volume issue, one can determine the AADT and Functional Class of the highway(s) within the project area. Average Annual Daily Traffic (AADT), or traffic volume, is a basic metric used for many purposes by transportation departments. Traffic volume data is regularly collected and maintained at the national and state levels. It is available for larger volume roads through the national Highway Performance Monitoring System (HPMS). State Departments of Transportation and provincial Ministries of Transportation also collect traffic volume data for additional highways. It is possible to collect traffic volume data if none is available for the project in question.

The Functional Class of a highway is a shorthand way to determine the likelihood of its level of impacts to wildlife because highways are categorized according to the class of service they are intended to provide. The three major classes are arterial, collector and local. More information can be found on the Federal Highways Functional Classes website.

Once it is determined whether or not there are existing effects based on the AADT, it is useful to determine the projections of traffic volume trends and the amount of time expected to meet those projections. Many if not most highways are increasing in traffic volume but the rate over the entire U.S. is not constant. Knowledge of how many years before a critical traffic volume threshold is reached for the species of concern in a project area will help planners to know whether to include mitigation in the current project for conditions projected to occur in the near future.

Back to Top Incorporate Local Stakeholder Knowledge

Local stakeholders can be a valuable source of information on wildlife in the project area, and they are often very interested in the outcome of a planning effort. Aside from the basic responsibility of public agencies to incorporate the public in planning projects affecting them, local stakeholders can assist in garnering public or political support for mitigation.

The Interstate 90 Wildlife Bridges Coalition was a powerful force in marshalling public support and awareness for wildlife crossing structures on the Snoqualmie Pass expansion project in Washington State. Their mission was to advocate for high quality wildlife passages along the Interstate 90 Expansion. Their efforts in cooperation with the transportation and natural resource agencies can be found at the I-90 Wildlife Bridges Coalition website.

A stewardship team process can be used to incorporate local knowledge and passion. An example is the Sierraville (CA) Highway 89 Stewardship Team, which has been able to obtain one wildlife crossing underpass and is working on a long-term process to install several more. Click here to view the article (A GIS-Based Identification of Potentially Significant Wildlife Habitats Associated With Roads in Vermont (PDF, page 198).

Back to Top Combine Data and Knowledge for a Final Evaluation

With the assistance of the above guidelines, users of this decision guide can establish a general understanding of the wildlife and road issues in the area of concern and the potentials for mitigating the situation. The actions described here also help the user to build a contact list of people able to help evaluate wildlife movement, support a mitigation project, and who could be drawn upon for assistance during different development stages of a proposed project. Once at this point, the user(s) need to decide to proceed with mitigation ideas or if mitigation would not be appropriate. This is not a one-person decision. Wildlife professionals in state, as well as highway engineers and federal agencies are part of this decision as well. The steps we outline suggest an effective process to follow.

Back to Top Pertinent Internet Sites

Banff National Park of Canada Highway Mitigation Research, What We Know and Don't Know

Rockies Wildlife Crossing Structures Field Course, with Presentations on overall wildlife crossings, how to evaluate, successful projects

Why is Connectivity Important for Wildlife?

Geodata Services Wildlife Habitat Registry to Use a GIS tool to identify wildlife habitat improvement projects in the U.S.

Highway Median Barrier Impacts on Wildlife Movement and Mortality - State of the Practice Review and Gap Analysis

Using Wildlife Behaviors to Design Effective Crossing Structures

Wildlife, Fisheries, and Transportation Database, Search Engine

Federal Highways Keeping It Simple: Easy Ways to Help Wildlife Along Roads

Federal Highways Critter Crossings: Linking Habitats and Reducing Roadkill, Case Histories of a Variety of Wildlife Crossings

Wildlife Habitat Connectivity Literature and Maps for U.S. Northern Rockies

California's South Coast Missing Linkages - Beier Manuscript on Identifying Linkages (PDF)

Back to Top Literature

Literature Cited

Forman, R. T., D. Sperling, J. A. Bissonette, A. P. Clevenger, C. D. Cutshall, V. H. Dale, L. Fahrig, R. France, C. R. Goldman, K. Heanue, J. A. Jones, F. J. Swanson, T. Turrentine, T. C. Winter. 2003. Road Ecology: Science and Solutions. Island Press, Washington, D.C., USA.

Jackson 1999

Ng, S. J., R. M. Sauvajot, S. P. D. Riley, and J. W. Dole. 2005. Inverse relationship between wildlife vehicle mortality and traffic volume. In preparation.

Rich and Longcore 2005

Van Langevelde, F. and C.F. Jaarsma. 2004. Using traffic flow theory to model traffic mortality in mammals. Landscape Ecology 19:895-907.

Waller, J. S. and C. Servheen. 2005. Effects of transportation infrastructures on grizzly bears in northwestern Montana. Journal of Wildlife Management 69:985-1000.

Traffic Volume Literature

Alexander, S.M., N.M. Waters, and P.C. Paquet. 2005. Traffic volume and highway permeability for a mammalian community in the Canadian Rocky Mountains. The Canadian Geographer 49:321-331.

Bautista, L.M, J.T. Garcia, R. G. Calmaestra, C. Palacin, C.A. Martin, M.B. Morales, R. Bonal and J. Vinuela. 2004. Effect of weekend road traffic on the use of space by raptors. Conservation Biology. 18:726-733.

Clevenger, A. P., B. Chruszcz, and K. Gunson. 2001. Drainage culverts as habitat linkages and factors affecting passage by mammals. Journal of Applied Ecology 38:1340-1349.

Jaeger, J., J. Bowman, J. Brennan, L. Fahrig, D. Bert, J. Bouchard, N. Charbonneau, K. Frank, B. Gruber, and K. Tluk,von Toschanowitz. 2005. Predicting when animal populations are at risk from roads: an interactive model of road avoidance behavior. Ecological Modeling 185:329-348.

Langevelde, F. and C. F. Jaarsma. 2004. Using traffic flow theory to model traffic mortality in mammals. Landscape Ecology. 19: 895-907.

Ng, S. J., R. M. Sauvajot, S. P. D. Riley, and J. W. Dole. 2005. Inverse relationship between wildlife vehicle mortality and traffic volume. In preparation.

Waller, J. S. and C. Servheen. 2005. Effects of transportation infrastructures on grizzly bears in northwestern Montana. Journal of Wildlife Management 69:985-1000.

Van Langevelde, F. and C.F. Jaarsma. 2004. Using traffic flow theory to model traffic mortality in mammals. Landscape Ecology 19:895-907.

Genetic Literature

Bhattacharya, M., R. B. Primack, and J. Gerwein. 2003. Are roads and railroads barriers to bumblebee movement in a temperate suburban conservation area? Biological Conservation 109:37-45.

Epps, C. W., P. J. Palsboll, J. D. Wehausen, G. K. Roderick, R. R. Ramey III, and D. R. McCullough. 2005. Highways block gene flow and cause rapid decline in genetic diversity of desert bighorn sheep. Ecology Letters 8:1029-1038.

Gerlach, G. and K. Musolf. 2000. Fragmentation of landscape as a cause for genetic subdivision in bank voles. Conservation Biology 14:1066-1074.

Mills, S. L. and R. Y. Conrey. 2003. Highways as potential barriers to movement and genetic exchange in small mammals. Final Report to Montana Department of Transportation. University of Montana, School of Forestry.

Proctor, M.F., McLellan, B.N., and C. Strobeck. 2002. Population fragmentation of grizzly bears in southeastern British Columbia, Canada. Ursus 13:153-160.

Reh, W., and A. Seitz. 1990. The influence of land use on the genetic structure of populations of the common frog (Rana temporaria). Biological Conservation 54:239-249.

Riley, S. P. D., J. Pollinger, R. M. Sauvajot, E. C. York, C. Bromley, T. K. Fuller, and R. K. Wayne. 2006. Southern California freeway is a physical and social barrier to gene flow in carnivores. Molecular Ecology 15:1733-1741.

Back to Top


1.2.5. Determine If There Are Any Animal-Vehicle Collisions Safety Concerns in the Plan/Project
  • GIS Mapping and Analyses
  • Database spreadsheet Analyses
  • Cluster Analyses
  • Discussions with Local Agency Personnel
  • Use of Safety Performance Functions
  • Website Resources

In some situations, there is a need for safety purposes to identify areas of higher than average wildlife-vehicle collisions. This can be done through analysis of available data for specific segments of existing roadway or a road with similar characteristics to a proposed road. While we emphasize the term wildlife-vehicle collision data, the common recording of such information is classified as animal-vehicle collisions, which may also include livestock collisions. If animal-vehicle collision data or road associated carcass data is available, several analyses can be conducted including:

  • GIS Mapping and Analyses
  • Database Spreadsheet Analyses
  • Cluster Analyses
  • Discussions with Local Agency Personnel
  • Use of Safety Performance Functions.

Back to Top GIS Mapping and Analyses

Wildlife-vehicle collision and wildlife carcass data can be mapped separately or in combination in a GIS to determine hotspots of collisions. Accurately mapping such data is dependent on the methods used to record collision locations. If Global Positioning Systems (GPS) units are not used for site locations then they are sometimes noted to the nearest intersection or mile/kilometer post. If this is the case, then the resulting map would yield more generalized information in an area of potential conflict zones, rather than precise locations. In our NCHRP 25-27 research the magnitude and patterns of location-based wildlife-vehicle collision reports and deer carcass removal datasets from Iowa were compared qualitatively through visual GIS plots and quantitatively (e.g., frequency per mile) (See Section 3.1 in our report: Evaluation of the Use and Effectiveness of Wildlife Crossings). Police-reported wildlife-vehicle collision information, deer carcass removals, and deer salvage data were evaluated. Results showed that the number of deer carcasses removed by was approximately 1.09 times greater than the number of wildlife-vehicle collision reported to the police. The number of salvaged and un-salvaged deer carcasses, on the other hand, was approximately 1.66 times greater. Clearly, the choice of the data used impacts whether a particular roadway segment might be identified for closer consideration. The message here is that the choice of the database used to define and evaluate the wildlife-vehicle collision problem and its potential countermeasures should be considered carefully. Recommendations are provided in the NCHRP final report about how the databases might be used appropriately and how the data should be collected

Back to Top Database spreadsheet Analyses

If the collision or carcass data was not collected with a Global Positioning System (GPS) unit and therefore not fully geo-referenced for a straight forward GIS analysis, then a database spreadsheet analysis could be applied. Data sources for such analyses include: the Highway Safety Information System (HSIS) database for animal-vehicle collisions for certain states, state and provincial DOTs/MoTs' websites of collision data, or data available within DOT/MoTs' safety divisions. Spreadsheet analysis would entail classing specific road ways into segments (typically one-mile segments) to analyze animal-vehicle-collision or carcass data such as Kassar (2005) did for Utah. Collision hotspots could then be identified. In Utah, Page (2006) and the Utah DOT determined a stretch of road was a wildlife-vehicle hotspot if there were an average of five or more wildlife-vehicle collisions per mile (1.61 kilometers) annually. These analyses could help to determine and prioritize general areas of necessary mitigative actions.

Back to Top Cluster Analyses

Studies of wildlife-vehicle collisions have demonstrated that they are not random occurrences but are spatially clustered. Modeling or analytical techniques permit a more detailed assessment of where wildlife-vehicle collisions occur, their intensity, and the means to begin prioritizing highway segments for potential mitigation applications. The identification and delineation of WVC clusters, which often vary widely in length depending on distribution and intensity of collisions, facilitates between-year or multi-year analyses of the stability or dynamics of wildlife-vehicle collisions hotspot locations. The wildlife-vehicle collisions data that transportation departments currently possess are suitable for meeting the primary objective of identifying hotspot locations at a range of geographic scales, from project-level (<50 km of highway) to larger district-level or state-wide assessments on larger highway network systems. The spatial accuracy of WVCs is not of critical importance for the relatively coarse-scale analysis of where hotspots are located. Any of the analytical clustering techniques can be used when more detailed information is needed. Our research analyzed several clustering methods including: Linear Nearest Neighbor Index (a simple plotting technique) to assess whether the location of dead animals found on roads as a result of wildlife-vehicle collisions were random; Ripley's K-statistic of road-kills; Nearest-Neighbor measurements (using Crimestat® software); and Density measures (See NCHRP 25-27 reports). We found that the Nearest Neighbor (Crimestat®) approach was useful for identifying key hotspot areas on highways with many road-kills because it, in essence, filters through the road-kill data to extract where the most problematic areas lay. The Density analysis approach identified more hotspot clusters on longer sections of highway. Although the Density analysis approach appears to be less useful to management, it may be a preferred option where managers are interested in taking a broader, more comprehensive view of wildlife-vehicle conflicts within a given area. Please see our final report for a more detailed description of using cluster analyses.

Back to Top Discussions with Local Agency Personnel

Accessing department of transportation or ministry of transportation data is not the only method of identifying areas with animal-vehicle collision concerns. Local wildlife agency personnel often keep records of wildlife carcasses removed from the road. A call to the area conservation officer or other wildlife agency representatives can quickly reveal potential wildlife conflict zones in an area. A visit to the local department of transportation/ ministry of transportation maintenance facility for a discussion with road maintenance workers could also be helpful.

It is important to also consider wildlife that may not necessarily be a safety risk to drivers. Local area wildlife professionals and the citizens of a community are usually aware of ongoing road associated mortality of local populations of smaller mammals, birds, amphibians, and reptiles. Contacts should be made with biologists working for the state wildlife agency, the U.S. Fish and Wildlife Service, and public land agencies near the project in order to better understand if there are potential problems with smaller species in the area of concern that need to be considered.

Back to Top Use of Safety Performance Functions

Safety Performance Functions are a more sophisticated statistical technique of identifying locations along roadways with a higher than average number of wildlife-vehicle collisions. Safety Performance Functions (SPFs) are predictive models for wildlife-vehicle collisions that typically relate the response variables (animal vehicle collision data and/or roadside carcass collection data) to the explanatory variables (physical roadway and roadside characteristics; often referred to as road geometrics). Other explanatory variables that animals respond to (e.g., topography, vegetative cover, and other off-road variables) are not among these variables that are readily available within the typical DOT safety databases. Hence, this approach will result in some unexplained variation, because the safety approach limits the explanatory variables to road geometrics. Regardless, this is a valuable approach because only these lower levels of data availability may exist in some jurisdictions.

The approach is statistically correct and accounts for "regression to the mean" problems. It makes use of three different levels of road data commonly available. The first level requires data on: 1) road length; and 2) annual average daily traffic volume (ADDT). The second level adds the requirement that road segments to be classified as flat, rolling, or mountainous terrain. The third level incorporates the data used in levels 1 and 2, but includes additional roadway variables such as average lane width. The safety approach has several applications and can be used to:

  1. Identify crash prone locations for existing or proposed roads for all crash types combined or for specific target crash types
  2. Aid in the evaluation, selection and prioritization of potential mitigation measures
  3. Evaluate the effectiveness of mitigation measures already implemented
    SPFs are introduced on the website www.safetyanalyst.org, and are reviewed in depth in our research by Persaud and Lyon in Section 3.1 of our report.

An important caveat is that the safety approach does not address any aspect of wildlife population response. As they stand, the primary application of the models is for the safety management of existing roads as opposed to design or planning applications for new or newly built roads.

Back to Top Website Resources

NCHRP website for NCHRP 25-27 Interim and Final reports detailing methods to analyze animal-vehicle collisions

Safety Analyst

Deer-Vehicle Crash Clearinghouse

Highway Safety Information System (HSIS) database for animal-vehicle collisions for select states

Literature Cited

Kassar, C. 2005. Wildlife-vehicle collisions in Utah: An analysis of wildlife mortality hotspots, economic impacts, and implications for mitigation and management. Thesis, Utah State University, Logan Utah.

Page, M. 2006. A toolkit for reducing wildlife and domestic animal-vehicle collisions in Utah. In Transportation Research Board 2006 Annual Meeting. CD-ROM. Transportation Research Board, National Research Council, Washington, D.C.

Back to Top


1.2.6 Investigate if Landscape Linkages Have Been Identified in the Area

If large scale habitat connectivity analyses exist for the project area, consider the priorities identified for protection or restoration of habitat linkage areas. States that have conducted large scale (state- or region-wide) interagency habitat connectivity analyses report that the analysis has facilitated identification and prioritization of linkage areas so that both transportation and natural resource agencies can agree on linkage areas.

Arizona, Colorado, New Mexico, Vermont, and Florida as well as other states have statewide habitat connectivity maps. See below for links to some known connectivity analysis results. Each state developed its system independently, and to date there is no mandate or standardized system to construct these maps. Nevertheless, these states now have a basis for agreeing on linkage areas as well as which linkage areas are highest priority, allowing transportation departments to have a degree of predictability in project planning, and allowing natural resource departments to choose priority areas for conservation efforts.

There are numerous ways to create a large scale connectivity map. Florida has an elaborate, detailed, and expensive system, called the 'Efficient Transportation Decision Making'. It is useful for far more than transportation planning and has been used in a number of other planning applications.

A shorter, less complex approach it a rapid assessment process that can be accomplished with relatively few resources in a short period of time. Rapid assessments have the benefit of low cost because few hours of agency personnel are used; however they still can provide a level of interagency agreement on the concepts of linkage area identification and prioritization that is useful. Once developed on a generalized basis, agencies can refine them over time as resources permit. Here is an example of a regional area in southwestern Montana rapid assessment.

If the project area does not already have an interagency team to create a habitat connectivity map, it is useful to consider creating one. Habitat connectivity analyses may exist at other scale extents (i.e., a highway segment or a portion of the state).

Back to Top

Linkages Websites:

Why is Connectivity Important for Wildlife?

Western States

Northern Rockies

Wildlife Habitat Connectivity Literature and Maps for U.S. Northern Rockies

American Wildlands Analysis of the Crown of the Continent Linkages in Montana, Idaho, Alberta, and British Columbia (PDF)

American Wildlands Corridors of Life Analysis of U.S. Northern Rockies


California's South Coast Missing Linkages - Beier Manuscript on Identifying Linkages (PDF)

California's South Coast Wildlands Missing Linkage Overview Website

California's Central Coast Wildlands Conservation Plan (PDF)


Update on Arizona's Missing Linkages Work, at Dr. Paul Beier's website

Arizona Game and Fish Update on Arizona Missing Linkages 12-2006

Sky Islands Alliance has some site specific maps for southern AZ

Other Western States

Colorado's Southern Rockies Ecosystem Project 'Linking Colorado's Landscapes' Report

New Mexico

Wildlands Project Sky Islands Network Design

Yellowstone to Yukon Initiative

Western and Southwestern Municipality and Non-Profit Initiatives

Midwestern States

Overview of Midwestern States Mapping Efforts

Natural Connections Map of Green Infrastructure in Illinois, Wisconsin and Indiana

Northeast and Mid-Atlantic Overview of Efforts

Eastern States

Massachusetts' BioMap

Maryland's GreenPrint Program Identifying Green Infrastructure or Lands

New Jersey's Garden State Greenways

Vermont Wildlife Habitat Linkage Analysis

Vermont Wildlife Linkages Report

Site for GIS data layers

Washington D.C.'s Green Infrastucture

Overview of Southeastern States Efforts

Florida's Efficient Transportation Decision Making Website for On-Line GIS Mapping

The Conservation Fund's Efforts to Build Green Infrastructure in Eastern and Midwestern States

The EPA's Southeastern Ecological Framework for Florida, Georgia, South Carolina, North Carolina, Mississippi, Alabama, Tennessee, and Kentucky


Carr, M., Hoctor, T., Goodison, C., Zwick, P., Green, J., Hernandez, P., McCain, C., Teisinger, J., Whitney, K., "Southeastern Ecological Framework." Final Report, Geoplan Center, Departments of Landscape Architecture, Urban and Regional Planning, and Wildlife Ecology and Conservation, University of Florida, Gainesville, FL (2002).

Penrod, K., Hunter, R. and Merrifield, M., "Missing Linkages: Restoring Connectivity to the California Landscape." Conference Co-Sponsored by California Wilderness Coalition, The Nature Conservancy, U.S. Geological Survey, Center for Reproduction of Endangered Species, and California State Parks, Proceedings (2001).
Ruediger, B., Basting, P., Becker, D., Bustick, J., Cavill, P., Claar, J., Foresman, K., Hieinz, G., Kaley, D., Kratville, S., Lloyd, J., Lucas, M., McDonald, S., Stockstad, G., Vore, J., Wall, K., Wall, R., "An Assessment of Wildlife and Fish Linkages on Highway 93 - Western Montana." Forest Service Publications #R1-04-81, USDA Forest Service, USDI Fish and Wildlife Service, confederated Salish and Kootenai Tribe, Rocky Mountain Elk Foundation, Montana Fish, Wildlife and Parks, Montana Department of Transportation, Geodata Services, The University of Montana, Missoula, MT (2004) 41 pp.
Ruediger, B. and J. Lloyd. 2003. A rapid assessment process for determining potential wildlife, fish and plant linkages for highways. In: Proceedings from the 2003 ICOET conference, Lake Placid, NY. Pp.205-222. (PDF)

Singleton, P., Gaines,W. and Lehmkuhl, J., "Landscape Permeability for Large Carnivores in Washington: A Geographic Information System Weighted-Distance and Least-Cost Corridor Assessment." USDA Research Paper PNW-RP-549, Pacific Northwest Research Station, U.S. Forest Service (2002).

Back to Top


1.2.7. Regulatory Reasons to Be Concerned About Wildlife

There are over one dozen federal laws in the U.S. and Canada that pertain to wildlife and transportation. In the U. S. the major laws include but are not limited to:

SAFETEA-LU the 2005 Transportation Act
Department of Transportation Act
National Environmental Protection Act
Endangered Species Act
Clean Water Act

In Canada the laws include but are not limited to:

Canada Wildlife Act
Species at Risk Act
Fisheries Act
Migratory Birds Convention Act
Ontario Endangered Species Act
Fish and Wildlife Conservation Act

The web-sites below explicitly describe the acts for both Canada and the U.S. and we leave it to the user to further explore these laws and pertinent regulations.

Back to Top

Pertinent Websites

Defenders of Wildlife: Guide to Transportation and Wildlife Law

U.S. Federal Highways Environmental Guidebook - use "Select Topics" function to search by type of act

U. S. National Marine Fisheries Service Anadromous Fish Conservation Act

Canada Fisheries Act

Transport Canada New Elements of the Fisheries Act

Ontario Environmental Protection Requirements for Transportation Planning and Highway Design, Construction, Operation and Maintenance

Back to Top


1.2.8 Summarize Results

At this final stage of evaluating whether the planned project may affect wildlife, the remaining step is the identification of potential future situations in the project area. Important considerations include assessment of changes over time that may increase the probability of highway effects to wildlife; e.g., within a 20-year planning timeframe. Traffic volume is one variable that is likely to change over time. Additionally, rapidly increasing development will affect transportation decisions not only on the affected road but adjacent roads as well. Transportation departments have the technical ability to project traffic increases. This information, particularly traffic volume increases, combined with local planning projections, can assist in determining if mitigation may be warranted in the current project rather than waiting for future expected growth. As a case in point, wildlife crossings are much less expensive to install in new construction than as a retrofit in an existing highway.

An important consideration is the project area's importance to large scale conservation goals. Even if an area is not pristine, its position on the landscape may mark it as important for future connectivity needs. Conversely, an area may be inevitably slated for subdivisions and commercial developments. These projections will help the project team to determine the amount and type of mitigation needed currently. If there is a high probability that an area will become useless for wildlife over the next 20-50 years, then it is possible that the appropriate choice may be to do no mitigation. This difficult decision is made in light of the understanding that priorities for habitat maintenance, protection, and restoration are best made in context with large scale ecosystem needs. If the project team decides that the project area will not be suitable for mitigation due to its probable future conditions, the remainder of the Decision Guide will have little use for the team.

At this final stage of step 1.2, users are in a position to decide if the present and projected conditions in a planned project area may affect wildlife in ways that can be mitigated with potential wildlife crossings. At this point, user(s) decide whether to proceed or not with mitigation. This is not a one-person decision. Ideally, all stakeholders are part of the decision. With this decision guide, we have provided steps to accomplish the process. If the decision is that wildlife will be affected by the proposed transportation plan and wildlife crossings may help ameliorate transportation effects, proceed to step 1.3. If Mitigation Needed: Identify Goals and Objectives.

Back to Top