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Publication Number: FHWA-HRT-08-034
Date: August 2008

Wildlife-Vehicle Collision Reduction Study: Report To Congress

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Chapter 8. Mitigation Methods that Seek to Physically separate Animals from the Roadway

This broad category of WVC mitigation strategies includes those that attempt to physically separate animals from the roadway. The specific mitigation measures reported on in this chapter, by broad category based on their intent, consist of the following:

  • Wildlife fencing.

  • Boulders in the right of way.

  • Long tunnels and bridges over landscape.

  • Wildlife underpasses and overpasses.

Wildlife Fencing

Fencing is one of the most commonly applied measures to separate wildlife from motorists.(3) Wildlife fences in North America typically consist of 2.0–2.4-m (6.5–8-ft)-high wire mesh fence material (figure 42). Several types of fence material are used, but page wire or cyclone fence material is most common. The Utah Department of Transportation has painted wire mesh dark brown, which effectively camouflages the wire mesh. Wooden or metal fence posts are typically used, and the latter are particularly important when fencing over rock substrates.

Photograph showing two Montana Department of Transportation employees erecting a 2.4 m (8 ft) fence along Interstate 90 near   Bozeman,  Montana. The men are on each side of the fence tying two ends together. In order to reach the top of the fence, one man is on a stepladder and the other is standing in the open bed of a pickup truck, which is backed up to the fence. The highway is not visible in this picture.

Figure 42. Photo. Wildlife fence along Interstate 90 near Bozeman, MT (copyright: Marcel Huijser, WTI).

Woods reported 94–97 percent reduction in ungulate-vehicle collisions along a fenced section of the Trans-Canada Highway.(350) Along the same road, Clevenger and others showed that fences were effective in reducing vehicle collisions with ungulates by 80 percent.(351) Clevenger and others also identified that WVCs were closer to fence ends than expected by chance; however, access points (gaps in the fence) were not hotspots for WVCs along the Trans-Canada Highway in Banff National Park, Alberta.(351) Dodd and others found that wildlife fencing in combination with underpasses reduced elk-vehicle collisions by 86.8 percent.(352) Reed and others reported an average reduction of 78.5 percent for deer vehicle accidents in Colorado, and Ward reported a reduction of greater than 90 percent for mule deer in Wyoming.(353,354) In Sweden, fencing reduced moose-vehicle collisions by 80 percent.(76) Boarman and Sazaki found that new or properly maintained fences significantly reduced mortality for several wildlife species, including the desert tortoise.(355) They found 93 percent fewer tortoise carcasses and 88 percent fewer vertebrate carcasses along a fenced section compared to an unfenced section of highway. In British Columbia, exclusion fencing (2.4 m (8 ft) high on both sides) was 97–99 percent effective at reducing accidents with large wildlife.(356) In Pennsylvania, Feldhamer and others determined that 2.7-m (8.9-ft)-high fence was more effective than the 2.2-m (7.2-ft)-high fence but that deer permeated both types of fences, and overall DVCs were not reduced.(294) They suggested that fencing may be effective if properly maintained to fix holes that people cut into it and to repair gaps that develop under the fence. They also suggest that the size of the openings in the woven wire mesh be decreased.

The effectiveness of electric fencing (ElectroBraid™) in keeping deer off runways at airports was studied by Seamans and VerCauteren, and their results could be applicable to preventing deer from accessing short segments of highway.(357) The authors found that fencing as low as 1.3 m (4.3 ft) was sufficient to exclude deer unless deer were pressured across it. Fences were highly effective (90 percent) when turned on and maintained.

In a theoretical study investigating how full fencing (no wildlife crossings) with the intent of keeping wildlife off of roadways and reducing wildlife mortality might affect the long-term viability of animal populations, Jaeger and Fahrig modeled population responses to a range of scenarios.(358) Their models showed that when no fencing was in place, traffic mortality had a stronger effect on population viability than the effect of animals avoiding the road. The authors concluded that fencing could improve viability in populations with high road mortality. They discouraged the use of fencing (without crossing structures) when the population size was stable.

Case Studies and Contacts

For more information about wildlife fencing in combination with wildlife overpasses and wildlife underpasses on the Trans-Canada Highway in Banff National Park, Canada, contact Anthony Clevenger, Western Transportation Institute, Montana State University, P.O. Box 174250, Bozeman, MT 59717-4250, (403) 609-2127, Tony.Clevenger@pc.gc.ca.

For more information about wildlife fencing and underpasses along State Route 260 in Arizona, contact Norris Dodd, Wildlife Research Biologist, Arizona Game and Fish Department, Research Branch, P.O. Box 2326, Pinetop, AZ 85935, (928) 368-5675, doddnbenda@cybertails.com.

For information about wildlife fencing along U.S. Highway 93, Flathead Indian Reservation, Montana, contact Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

For an evaluation of ElectroBraid™ fencing, contact Thomas Seamans; Wildlife Service, USDA, National Wildlife Resource Center, Ohio Field Station, Sandusky, OH 44870, thomas.w.seamans@usda.gov.

Direct Benefits

Depending on the species concerned, the type of fencing, and whether safe crossing opportunities are provided, wildlife fencing may reduce the number of WVCs 80–99 percent. It is important to note, however, that these reductions were obtained where wildlife fencing was used in combination with wildlife overpasses and/or wildlife underpasses. If safe crossing opportunities are not provided for, or if they are too few, too small or too far apart, animals are more likely to break through the wildlife fence, reducing the effectiveness of the wildlife fencing.

Indirect Benefits

Wildlife fences help keep pedestrians away from the travel lanes with fast-moving traffic.

Undesirable Effects

Wildlife fences, when installed correctly, form a nearly impermeable barrier to large mammals. While this can nearly eliminate collisions with large mammals or at least reduce the number of collisions substantially, wildlife fences result in several unintended side effects, for example:

Animal movements across the road are blocked or nearly completely blocked, which increases the barrier effect of the road, disrupting daily, seasonal, and dispersal movements and potentially reducing the population survival probability of the species concerned. The species affected may include species that are not a safety threat or that may not have a population in the immediate vicinity of the transportation corridor. Therefore, absolute barriers, such as wildlife fencing, should always be accompanied with safe crossing opportunities.

Animals are more likely to break through the wildlife fencing if safe crossing opportunities are not provided or if they are too few, too small, or too far apart. Even if safe crossing opportunities have been provided for, animals may still end up in between the fences, caught in the transportation corridor, and these animals may pose a safety risk and expose the species concerned to road mortality after all. Animals may end up in between the fences around fence ends, digging under the fence (coyotes slipped beneath the fence along the Trans-Canada Highway in Banff National Park), through gaps in the fence, or they may be able to climb the fence. Therefore, absolute barriers, such as wildlife fencing, should always be accompanied with escape opportunities for animals that end up in between the fences.

Animals can and do cross the road where fences end. In some cases it can result in a concentration of AVCs at fence ends (Norris Dodd, Arizona Game and Fish Department, personal communication).(351) Therefore, consideration should be given to measures that mitigate a potential concentration of WVCs at fence ends.

Wildlife fencing can have a negative impact on landscape aesthetics; many people perceive tall wildlife fences as ugly.

Wildlife fencing may pose a direct or indirect mortality risk for certain species. Large mammals may get tangled up in the fence, or fences may injure them, potentially resulting in a slow death. In addition, wildlife fences may also be exploited by predators when pursuing prey. After the addition of two lanes on the Trans-Canada Highway and installation of fencing that cut off escape terrain for bighorn sheep, coyotes learned to stampede sheep into the fence. More than 30 sheep were killed this way until a mitigation measure was put in place (discussed later). In addition, wolves, bears, and other predators have also occasionally been seen running prey species into the wildlife fences.(359) Finally, birds may collide with fences and die.(360,361)

  • Access roads to the main road require a disruption of the wildlife fencing, resulting in an opening that has to be mitigated in order to avoid animals getting caught inside the fences along the transportation corridor.

  • Access for people (hiking, biking, fishing) may be blocked by wildlife fencing.

Wildlife underpasses and overpasses are tunnels and vegetated bridges designed for wildlife to allow them to cross the road. In addition, wildlife jump-outs are usually integrated with wildlife fencing. These features allow animals that do manage to cross the fence to escape from the fenced road and right of way. Other potential solutions for the unintended side effects described above are described in the next section "Addressing Undesirable Effects of Wildlife Fencing."

Costs

Wildlife fencing (2.4 m (8 ft) high) in Banff National Park, Alberta cost Can$30 per meter (Can$9 per ft) (one side of highway) during the phase 3A Trans-Canada Highway expansion in 1997 (Terry McGuire, Parks Canada, personal communication). For the entire 18-km section of highway, fencing both sides cost roughly Can$1,000,000. ElectroBraid™ fencing used in the study by Seamans and VerCauteren consisted of five-rope strands at 25 cm (9.7 inches) and cost $9 per meter ($2.7 per ft).(357) 1.2-m (4-ft)-high 5‑Braid™ ElectroBraid™ Deer Exclusion Fence is advertised at $4,300 per km ($7,000 per mi), while 1.5-m (5-ft)-high, 5-Braid™ ElectroBraid™ Moose Exclusion Fence is advertised at $4,750 per km ($7,500 per mi).(362)_

Sielecki compared the benefits to costs of fencing over different time spans (20–30 years) and given different levels of potential damage prevented. He determined that benefits of the wildlife fencing outweighed potential costs in 12 of 16 cases.(356) Fencing in his study ranged from Can$40,000–80,000 per km.

The cost of wildlife fencing along U.S. Highway 93 on the Flathead Reservation in Montana varied depending on the road section concerned: $26, $38, or $41 per m ($7.9, $11.6, or $12.5 per ft) (Pat Basting, Montana Department of Transportation, personal communication). A finer mesh fence was dug into the soil and attached to the wildlife fence for some fence sections at a cost of $12 per m ($6.7 per ft) (Pat Basting, Montana Department of Transportation, personal communication).

Fencing could be impractical in dense vegetation areas, where there is little or no public roadside right of way.

Guidelines

For large mammals and particularly ungulate species, the standard height of wildlife fencing is currently 2.4 m (8 ft). When targeting specific fauna of smaller size, lower fence heights and more customized designs are generally used.(355,363,364) To keep some climbing species (cougars, bears) from scaling, wildlife fences can be made higher, the mesh size can be made smaller, and outriggers or overhangs can be incorporated into the design.(365,366) Some testing of these fences has taken place in captive settings, but they have not been objectively tested in the field. Fencing should also be tied to the ground or buried into the ground, depending on the target species and soil characteristics. If properly installed, fence material (wire and posts) should last 20 years or more without integral replacement (Terry McGuire, Parks Canada, personal communication).(367) However, regular inspection for gaps and other problems is required.(368)

Regular fence maintenance is critical in order to keep the fence functioning properly. Earth slumping on hill slopes, inadequate installation techniques resulting in gaps between ground and fence bottom, and breaches of the fence by the public (e.g., hunters, snowmobile operators) allow animals to gain entry to the right of way. Fence maintenance is a major concern because priorities and budgets change over time. Fence maintenance is usually neglected shortly after construction; meanwhile fence damage and gaps are a recurrent problem.

Addressing Undesirable Effects of Wildlife Fencing

Absolute barriers such as wildlife fences increase the barrier effects of a road, disrupting daily, seasonal, and dispersal movements and potentially reducing the population survival probability of the species concerned. The species affected may include species that are not a safety threat or that may not even have a population in the immediate vicinity of the transportation corridor. Therefore absolute barriers, such as wildlife fencing, should always be accompanied by safe crossing or escape opportunities for wildlife. The specific mitigation measures reported on in this section, by broad category based on their intent, consist of the following:

  • Create gaps in fencing.

  • Install wildlife underpasses and overpasses.

  • Provide escape opportunities for wildlife stuck in the right of way using:

  • Jump-outs or escape ramps.

  • One-way gates.

  • Mitigate WVCs at fence ends using:

  • Boulders between fence and roadway.

  • Animal detection systems.

  • Improve landscape aesthetics of wildlife fencing.

  • Reduce wildlife mortality risk of fencing.

  • Mitigate gaps in fencing at access roads using:

  • Gates.

  • Cattle or wildlife guards.

Despite the fact that the primary intention of the various measures described in this section is to mitigate undesirable side effects of absolute barriers, some of the measures can also help further reduce WVCs while others may lead to an increase in WVCs. This is noted in the "direct benefits" and "undesirable effects" sections of the individual measures.

Safe Crossing Opportunities: Gaps in Fence

Gaps in fences on opposite sides of the road allow animals to cross the road. In most cases such gaps are accompanied with wildlife warning signs, crosswalks for wildlife, wildlife warning signs in combination with mandatory or advisory speed limit reductions, or animal detection systems. Along SR 260 near Payson, AZ, a gap in an electric fence has been combined with an animal detection system (David Bryson, Electrobraid Fence Ltd., personal communication; Norris Dodd, Arizona Game and Fish Department, personal communication).

A system of wildlife fences and gaps was installed to reduce vehicle collisions with mule deer (Odocoileus hemionus) along a two-lane and divided four-lane highway in northeastern Utah.(41) The gap had warning signs for motorists, and a crosswalk was painted on the road surface as an additional sign for motorists. Road mortality was reduced by 42.3 percent (four-lane highway) and 36.8 percent (two-lane highway) compared to the expected road mortality. However, statistical significance of this reduction could not be demonstrated.

Similar to wildlife fences, median barriers can be an absolute or partial barrier to certain species.(310) In some cases gaps have been created in the median barrier to allow animals to cross the road. However, the effectiveness of these gaps has largely been untested.(310)

Case Studies and Contacts

For information on gaps in wildlife fencing with warning signs and crosswalk, contact John Bissonette, Utah Cooperative Fish Wildlife Research Unit, Utah State University, Logan, UT, 84322-5290, (435) 797-2511, john.bissonette@usu.edu.

An example of a gap in a wildlife fence accompanied by wildlife warning signs and an advisory speed limit reduction in The Netherlands is shown in figure 43.

An example of a gap in a wildlife fence combined with an animal detection system and accompanying wildlife warning signs and an advisory speed limit reduction in The Netherlands is shown in figure 44.

This is a picture of a roadway with two lanes. A large bus and a car drive toward each other. On either side of the roadway is an identical sign. The top portion of the sign is a yellow rectangle with a white triangle with a red border printed on it. Inside the white area of the triangle is a silhouette of a deer. The bottom portion of the sign is a 60 km/h speed limit sign (blue with white lettering). The fencing is not clearly visible in this picture.

Figure 43. Photo. Gap in a wildlife fence accompanied by wildlife warning signs and advisory speed limit reduction, The Netherlands (copyright: Marcel Huijser).

This picture shows the end of a fence line paralleling the roadway. At the end of the fence is a metal box that either transmits or receives an infrared, break-the-beam animal detection sensor. In the background the roadway can be seen with a speed limit sign for 50 km/h.

Figure 44. Photo. Gap in a wildlife fence combined with an animal detection system, wildlife warning signs and advisory speed limit reduction, The Netherlands (copyright: Marcel Huijser).

Direct Benefits

Wildlife fences may reduce road mortality by 80–99 percent but may increase the barrier effect of the road. Gaps in the wildlife fence allow animals to cross the road, but since they cross at grade, mortality occurs, reducing the effectiveness of the wildlife fence. Data are not available on the roadkill that occurs at a gap with or without warning signs, but a gap in a wildlife fence that is combined with wildlife warning signs and a crosswalk reduced the effectiveness of the wildlife fence from 80–99 percent to 42.3 percent (four-lane highway) and 36.8 percent (two-lane highway).(41) Animal detection systems have been used at gaps in wildlife fences, but there are no data on the effectiveness of this measure in combination with a gap in a fence. As a standalone mitigation measure, however, animal detection systems may reduce collisions with ungulates by 82 percent on average.(197)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

At gaps in fences, animals cross the road at grade, exposing the drivers and wildlife to potential collisions. This may reduce the effectiveness of the wildlife fence, but this depends on what type of warning signals are presented to drivers at the gap in the fence. No data have been located about the risk of gaps that have static warning signs, but the available data for animal detection systems suggest that a gap with an animal detection system may reduce the effectiveness of the wildlife fencing from 87 percent (on average) to 82 percent. In addition, once through a gap, animals may wander along the road or in the right of way, becoming trapped in between the wildlife fences, exposing the drivers and wildlife to other potential collisions. Measures that allow animals to escape from the road and right of way should be implemented (see further information later in this section).

Costs

The costs of crosswalks across a two-lane road and a four-lane road (excluding wildlife fencing and escape from right of way measures) were reported at $15,000 and $28,000, respectively.(41)

The estimated cost of animal detection systems at a gap in the fence is $50,000 (including installation and fence).(197)

Guidelines

See Lehnert and Bissonette for guidelines.(41)

Safe Crossing Opportunities: Wildlife Underpasses and Overpasses

Wildlife underpasses and overpasses are used extensively by a wide array of species to get from one side of the road to the other side (figure 45 through figure 47). (See references 294, 368, 369, and 370.) The performance of these structures in reducing WVCs and creating crossing opportunities is linked to associated wildlife fencing that keeps animals off the road and funnels them toward the wildlife overpasses and underpasses.(368) In some cases wildlife fencing is only installed over relatively short distances funneling wildlife towards a crossing structure.(371) The use of wildlife fencing was found to increase the use of underpasses by elk (Cervus elaphus) and increase the permeability of a road substantially.(352) In other cases wildlife underpasses and overpasses have no or very limited wildlife fencing, making them the primary measure to reduce WVCs on short road sections.

The location, type, and dimensions of wildlife crossing structures must be carefully planned with regard to the species and surrounding landscape. For example, grizzly bears, deer and elk tend to use wildlife overpasses to a greater extent than wildlife underpasses, while black bears and mountain lions use underpasses more frequently than overpasses.(368) In addition, different species use different habitats, influencing their movements and where they want to cross the road. Other factors that should be considered are the vegetation in the direct vicinity of the crossing structure (cover), co-use by humans, and the time it takes for animals to learn the location of the structures and to learn that they are safe to use.

In North America, wildlife overpasses are far less common than in Europe. Therefore there are few experiences with tunnels and wildlife overpasses, as only six of the latter are found in North America and only two in Banff have been studied with regard to their effectiveness in terms of reducing road mortality and allowing for safe crossing opportunities.

This is a picture of a large (roughly 2.4 m (8 ft) high) arch culvert going under a roadway. The culvert is corrugated metal with a sand and gravel layer in the bottom. Eight-foot deer-proof fencing that parallels the road can be seen ending on either side of the culvert.

Figure 45. Photo. Wildlife underpass along U.S. Highway 93 on the Flathead Indian Reservation, MT (copyright: Marcel Huijser, WTI).

The use of wildlife underpasses and overpasses depends on many parameters, including their location in the landscape, their dimensions, the habitat surrounding the structures, human co-use, and the time since installation (learning curve for the animals).(368) Furthermore, different species have different preferences.

This picture shows a vegetated and fenced overpass extending over a four-lane roadway with a median.

Figure 46. Photo. Wildlife overpass in Banff National Park, Alberta, Canada (copyright: Marcel Huijser, WTI).

This picture shows a bridge of a currently dry (but seasonally wet) drainage.

Figure 47. Photo. Underpass in southern Florida that allows for ecosystem process (hydrology) as well as wildlife use, including the Florida panther (copyright: Marcel Huijser).

Case Studies and Contacts

For information on crossing structures in Banff National Park, contact Tony Clevenger, Western Transportation Institute, (403) 609-2127, tony.clevenger@pc.gc.ca.

For information on Florida crossing structures, contact Melissa Foster, University of Florida, Gainesville, FL.

For more information on wildlife underpasses and one wildlife overpass along U.S. Highway 93 on the Flathead Indian Reservation in Montana and on one wildlife overpass across Montana Highway 83 near Salmon Lake (in planning, under construction and completed), contact Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

For more information about wildlife fencing and underpasses along State Route 260 in Arizona, contact Norris Dodd, Wildlife Research Biologist, Arizona Game and Fish Department, Research Branch, P.O. Box 2326, Pinetop, AZ 85935, (928) 368-5675, doddnbenda@cybertails.com.

Direct Benefits

Wildlife overpasses and underpasses increase the effectiveness of wildlife fencing or other barriers alongside the road in reducing WVCs. If no safe crossing structures are provided, animals are more likely to break through the wildlife fencing (or other barrier) and thereby reduce the effectiveness of the wildlife fencing.

Indirect Benefits

Wildlife overpasses and underpasses provide crossing opportunities for wildlife, which are needed to mitigate habitat fragmentation effects of roads and maintain viable populations over the long term.

Undesirable Effects

If overpasses are not designed properly, wildlife that are reluctant to use the structure may try to breach the fence and cross the highway.

Costs

Costs vary widely depending on dimensions of underpass structures. Some estimated costs for different underpass structures are box culverts (3.0 m (9.8 ft) high by 2.5 m (8.2 ft) wide) = $Can2,800 per m ($854 per ft) length, elliptical culverts (4 m (13 ft) high by 7 m (23 ft) wide) = $Can5,400 per m ($Can1,646 per ft) length, open span bridge underpass (13 m (43 ft) wide by 5 m (16 ft) high) = $Can55,000 per m length (Terry McGuire, Parks Canada, unpublished data).

In The Netherlands, large underpasses (7–10 m (23–33 ft) wide) are estimated to cost €30,000–50,000 per m.(372)

Tunneling and overpass structures can cost approximately $Can33,650 per m ($Can10,259 per ft) for a 50-m (164-ft)-wide overpass to $Can119,300 for a 27-m (88-ft)-wide and 200-m (656‑ft)-long tunnel (Terry McGuire, Parks Canada, unpublished data). Actual overpasses were estimated at Can$1,750,000 (Anthony P. Clevenger, Western Transportation Institute, Montana State University, personal communication).

A proposed overpass across Montana Highway 83 near Salmon Lake (two-lane road) is estimated to cost $1,500,000–2,400,000.

The costs for seven wildlife overpasses in The Netherlands ranged between €1,400.000 and €5,600,000.(372)

Guidelines

Recommended minimum dimensions for underpasses and overpasses have been suggested for some ungulate species, but the needs of wide-ranging species are vague at best.(166) The most comprehensive guidelines for designing wildlife crossing structures, including most below-grade crossing structures, can be found in Iuell.(373) This European handbook draws from the wealth of European experience building a variety of wildlife crossings. Guidelines for different wildlife taxa in Europe and North America can be found in Iuell, Foster and Humphrey, Clevenger and Waltho, Clevenger and Waltho, and Kruidering and others. (See references 166, 372, 373, 374, and 375.) The last publication includes cost estimates for a range of types of crossing structures. Guidelines for wildlife crossings are being developed from NCHRP 25 to 27 and will available in 2008.

If large species are involved that are sensitive to human disturbance, or if multiple habitats have to be provided for on an overpass, wildlife overpass structures are generally recommended to be at least 50–70 m (164–230 ft) wide. Further rationale for this width is provided by Pfister and others, who showed that the increase in use of wildlife overpasses increases linearly until a width of about 50 m (164 ft) at which point the increase in wildlife use starts to taper off.(376)

Escape Opportunities From Right of Way

Animals may end up in between fences or other barriers placed along the transportation corridor, posing a safety risk and exposing the species concerned to road mortality. Therefore, absolute barriers, such as wildlife fencing, should always be accompanied with escape opportunities for animals that have ended up in between the fences. (See references 82, 294, 370, and 377.)

Escape Opportunities From Right of Way: Jump-Outs or Escape Ramps

Jump-outs or "escape ramps" are sloping mounds of soil placed against a backing material approximately 1.5 m ( 5 ft) in height and constructed on the right-of-way side of the fence (figure 48 ). The highway fence ( 2.4 m ( 8 ft)) is lowered at the ramp site and forms an integral part of the jump-out that allows deer or other species to jump to the safe side of the fence. The vertical drop off on the back side of escape ramps is designed to preclude deer from gaining access to the right of way from the nonhighway side of the fence. Deer and elk are the most common users of jump-outs along the Trans-Canada Highway in Banff National Park, but moose and bighorn sheep have also used these structures (Bruce Leeson, personal communication).

This is a picture of what is commonly referred to as a jump-out. There is eight-foot deer proof fencing that parallels the roadway. On the road side of the fence is an earthen mound built up such that an animal trapped on this side of the fence could walk up the mound and jump down to the other side of the fence. Holding up the mound at the fence line is a retaining wall made up of railroad ties creating a wall on the highway-side of the fence.

Figure 48. Photo. Jump-out or escape ramp along U.S. Highway 93 on the Flathead Indian Reservation, MT (copyright: Marcel Huijser, WTI).

Bissonette and Hammer studied the effectiveness of earthen escape ramps (jump-outs) and one-way gates along a fenced section of U.S. 91 and U.S. 40 in northern Utah.(82) The 2.4-m (8‑ft) fence was not 100 percent effective, due to human vandalism and gaps under the fence, so additional measures were necessary to help get deer off the highway. The authors noted peaks in DVCs in spring and fall, and noted that DVCs declined after installation of jump-outs. Jump-outs were eight to eleven times more effective than one-way gates. The authors calculated that if the ramps offset even 2 percent of deer mortality, they would be considered cost effective within 1 to 2 years. They recommended jump-outs instead of one-way gates and determined that (with fencing) these are effective mitigation measures at removing deer from highway rights of way and minimizing accidents with motorists. Clevenger and others documented use of jump-outs by deer, elk, and coyote on the Trans-Canada Highway.(378)

Case Studies and Contacts

For information on jump-outs along U.S. Highway 93, Flathead Indian Reservation, Montana, contact Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

For more information on field tests with escape ramps in Utah, contact John Bissonette and Mary Hammer, USGS Utah cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, College of Natural Resources, Utah State University, Logan, UT 84322-5290, (435) 797-2511, john.bissonette@usu.edu; and hammer@wra-ca.com.

For information on field observations from jump-out use along the Trans-Canada Highway, Canada, contact Tony Clevenger, Western Transportation Institute, Montana State University, P.O. Box 174250, Bozeman, MT 59717-4250, (403) 609-2127, Tony.Clevenger@pc.gc.ca.

Direct Benefits

Using jump-outs or escape ramps along two fenced road sections reduced collisions by 28.6 percent on average.(82)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

If the jump-outs are not high enough, animals may jump up and end up in the right of way in between the fences. On the other hand, if jump-outs are too high, animals will not use them to escape from the transportation corridor. Furthermore, jump-outs need to be well away from the travel lanes and recovery zone to avoid cars running into them.

Costs

Reported costs for one jump-out include $11,000 and $6,250 (Pat Basting, Montana Department of Transportation, personal communication).(82)

Guidelines

The wall of a jump-out must be just high enough to discourage wildlife from trying to jump up into the right of way, but not so high that they discourage wildlife from jumping off. This is a delicate balance, and the optimal height of the jump-out is likely to be influenced by the species that is expected to breach the fence most often and the nature of the terrain surrounding the jump-outs (e.g., up slope or down slope). To prevent injury to the animals that jump out, the landing spot at the bottom of the jump-out should consist of loose soil or other soft material (Bruce Leeson, personal communication). Where bears are present, the walls must be smooth to prevent them from climbing into the right of way (Bruce Leeson, personal communication). Furthermore, it is thought to be best for jump-outs to be positioned in a set-back in the fence, in an area protected with tree cover, where animals may calm down and have time to decide whether to jump off the jump-out (Bruce Leeson, personal communication). A short fence on the jump-out itself, perpendicular to the road and the right-of-way fence, may also help guide animals to the jump-outs. For additional guidelines see Bissonette and Hammer.(82)

Escape Opportunities From Right of Way: One-Way Gates

One-way gates allow animals to enter from the road side and go through the fence, providing a possible opportunity for escape from the transportation corridor. Gates (figure 49 and figure 50) have been built for different species, including elk, deer, and the Eurasian badger.(82,370,372) Reed and others found one-way gates relatively effective for deer, whereas Lehnert found that only 17 percent of the deer that approached the gates ended up using them.(377,379) In general one-way gates are no longer recommended as wildlife can learn how to use them to get into the right of way, sometimes aided by hikers, fisherman, equestrians, and bikers who propped and tied the gates open (Bruce Leeson, personal communication).(368) In Banff National Park, Canada, an elk herd not only learned how to go through the gate the "wrong way," but they also destroyed the gate within a week after they learned how to enter the gate from the wrong side (Bruce Leeson, personal communication). In the same area, coyotes learned to crawl through the tines to feed on mice that became more abundant in the right of way now that it was no longer grazed by ungulates (Bruce Leeson, personal communication). At another location, at least one elk has been observed taking a gate "out" as the gate was too small for its body size (Monique DiGiorgio, Southern Rockies Ecosystem Project, personal communication), and at least one moose has been observed getting stuck with its antlers and damaging its velvet (Rick Sinnott, Alaska Fish and Game, personal communication). Finally, jump-outs appear more effective than one-way gates in allowing ungulates to escape from the right of way.(82)

In this picture of a one-way elk gate, there is a jog in the fence that is about 0.915 m (3 ft) wide. The jog has no wire mesh or fence material between the posts, but a series of metal tines on either side that bend inward, allowing animals to squeeze through in only one direction away from the highway.

Figure 49. Photo. One-way elk gate in British Columbia, Canada (copyright: Marcel Huijser).

This picture shows a man crouching hear an apparatus at the bottom of a deer proof fence. A roughly 0.61-m (2-ft) square piece of wire mesh is placed perpendicular to the fence, creating a corner. In the bottom of the deer-proof fence at this corner is an opening about 0.305-m (1-ft) square. This opening is covered by a gate that swings one way.

Figure 50. Photo. One-way Eurasian badger gate, The Netherlands (copyright: Marcel Huijser).

Case Studies and Contacts

For more information on one-way gates for deer in Utah, contact John A. Bissonette, Utah Cooperative Fish Wildlife Research Unit, Utah State University, Logan, UT, 84322-5290, (435) 797-2511, john.bissonette@usu.edu.(82)

Direct Benefits

No direct benefits were identified in the literature review.

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

There are undocumented reports that animals tried to back up in elk gates, got stuck, wounded themselves, and died.

Costs

Estimated costs were reported at $8,000 per one-way gate.(82)

Guidelines

See Bissonette and Hammer for guidelines.(8)

Mitigation for Fence Ends: Boulders Between Fence and Roadway

To discourage ungulate species from entering the fenced sections of the Trans-Canada Highway in Alberta, Canada, rock impediments or boulder fields were placed at the ends of the fence between the roadway and the fence, as shown in figure 51 .(378) Boulders roughly the size of bowling balls were laid out uniformly to create a boulder field. The boulders are thought to discourage animals, especially ungulates, from walking on them.

The boulder field at Dead Man's Flats wildlife underpass along the Trans-Canada Highway east of Canmore, Alberta, is 100 m ( 328 ft) long with the width varying from about 8– 20 m (26–66 ft), depending on how close the fence is positioned to the roadway, with the boulders extending right from the edge of pavement up to the fence (Bruce Leeson, personal communication) (figure 51). In addition, a 19-m (62-ft)-wide strip of boulders was placed in the median. The boulders are subangular, quarried rock, ranging in size from 20 to 60 cm (7.8–23.6 inches) (about 75 percent are larger than 30 cm (11.8 inches)). The boulder apron, at a depth of about 40– 50 cm (15.7–19.7 inches), is installed on geofabric on subexcavated smoothed ground. The boulders project about 20– 30 cm (7.8–11.8 inches) above the local ground surface (Bruce Leeson, personal comment).

Case Studies and Contacts

For information on the use of boulders between the fence and roadway at fence ends along the Trans-Canada Highway in Banff National Park, contact: Bruce Leeson, Bruce F. Leeson Environmental Consulting Co., 10011 5th St. S.E., Calgary, Alberta, Canada T2J 1L4, (403) 271-7235 (desk), (403) 869-8180 (cell), bfleeson@shaw.ca; and Tony Clevenger, Western Transportation Institute, Montana State University, P.O. Box 174250, Bozeman, MT 59717-4250, (403) 609-2127, Tony.Clevenger@pc.gc.ca.

Direct Benefits

Clevenger and others found that the combination of the boulder field and wildlife fencing were effective in reducing WVCs. Six DVCs occurred prior to fencing (and boulder field installation), while only two occurred after fencing.(378) The boulders were believed to be an effective deterrent in keeping ungulates from wandering in between the fences.(378)

This is a picture of the end of a segment of deer-proof fencing. Between the fence end and the roadway, continuing beyond the fence end is a roughly 4.575-m (15-ft) wide swath of boulders (or rip-rap). The boulders average 0.305 m (1 ft) in diameter and go right up to the edge of the pavement. Most of the length of boulders are protected with guardrail that was probably already in place to protect a culvert seen in the lower left of the picture. The area of boulders beyond the guardrail had reflective delineators.

Figure 51. Photo. The boulder field at the fence end at Dead Man's Flats along the Trans-Canada Highway east of Canmore, Alberta, Canada (copyright: Bruce Leeson).

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

In areas of regular snowfall, the boulder fields become covered with snow, which allows ungulates to travel across them. There may be some motorist safety issues for some states by having an obstruction (and hazard) within the clear zone. In Alberta these safety issues were addressed by placing a guard rail at the road edge.

Costs

The material and labor for the installation of boulders at the fence end at Dead Man's Flats wildlife underpass along the Trans-Canada Highway east of Canmore, Alberta, was estimated to cost Can$65,000 (installed in 2005, cost estimate for 2007) (Bruce Leeson, personal communication).

Guidelines

The boulder field begins at the fence end, sits on the margin of the paved edge of the highway, and is approximately 15 m (49 ft) wide. The length of the field starting at the fence ends is approximately 20–25 m (66–82 ft).

Mitigation for Fence Ends: Animal Detection Systems

Animals may cross the road where fences end, which can in some cases result in a concentration of AVCs. In Arizona, an experiment is currently being conducted with animal detection systems at fence ends to mitigate a concentration of deer and elk vehicle collisions (Norris Dodd, Arizona Game and Fish Department, personal communication).

Case Studies and Contacts

For information on animal detection systems at fence ends, contact Norris Dodd, Wildlife Research Biologist, Arizona Game and Fish Department, Research Branch, P.O. Box 2326, Pinetop, AZ 85935, (928) 368-5675,doddnbenda@cybertails.com.

Direct Benefits

The benefits of using animal vehicle detection systems at fence ends are unknown, but as a standalone mitigation measure, animal detection systems can reduce collisions with large ungulates by 82 percent.(197) The application of animal detection systems at fence ends can be expected to result in a similar reduction in WVCs, but data on effectiveness are relatively scarce and may vary.

Indirect Benefits

No indirect benefitswere identified in the literature review.

Undesirable Effects

No undesirable effectswere identified in the literature review.

Costs

No costwere identified in the literature review.

Guidelines

See Huijser and others for general design considerations.(197)

Landscape Aesthetics of Wildlife Fencing

Wildlife fencing can have a negative impact on landscape aesthetics; many people perceive tall wildlife fences as ugly. A potential solution is to replace wildlife fencing with large boulders (see earlier) to discourage ungulates from entering the right of way. However, there are no data on how effective large boulders are at reducing WVCs. Other approaches have been tried or are in the process of being tried to make the fence less visible by installing fences behind trees and painting the fence brown or green so that it blends in better with the background (Terry McGuire, Parks Canada, personal communication).

Case Studies and Contacts

For details on installation of fences behind trees along Trans-Canada Highway, contact Terry McGuire, Parks Canada,terry.mcguire@pc.gc.ca.

For information on future experiments with green instead of metal-colored fencing along the Trans-Canada Highway, contact Terry McGuire, Parks Canada,terry.mcguire@pc.gc.ca.

Direct Benefits

Colored fencing has no known additional impact on WVCs beyond the standard colored wildlife fencing.

Indirect Benefits

Less visible fences have reduced impact on landscape aesthetics.

Undesirable Effects

As fencing becomes less visible, the risk of wildlife colliding with it may increase (see "Reduce Mortality Risk of Wildlife Fencing" below).

Costs

Fencing costs remain similar to standard wildlife fencing (see earlier) (Terry McGuire, Parks Canada, personal communication).

Guidelines

Similar to standard wildlife fencing (see earlier).

Reduce Mortality Risk of Wildlife Fencing

Wildlife fencing may pose a direct or indirect mortality risk for certain species through entangling or wounding animals, or because predators run prey species into the wildlife fence. Parks Canada installed a green "curtain" on the wildlife fence along a section of the Trans-Canada Highway, which enabled the sheep to see the fence and veer away from it (Terry McGuire, Parks Canada, personal communication). Chestnut paling has been used in deer exclusion fences to make them more visible to birds, especially capercaille (Tetrao urogallus).(361)

Case Studies and Contacts

For details on the green curtain on the wildlife fence used to increase visibility for bighorn sheep along the Trans-Canada Highway in Banff National Park, contact Terry McGuire, Parks Canada,terry.mcguire@pc.gc.ca.

For information on chestnut paling used in a deer exclusion fence to increase visibility for birds, especially capercaille, contact: John Dobson, The Croft, Balmoral, Ballater, Scotland, AB35 5TX,forestry@balmoralestate.co.uk.

Direct Benefits

There is no additional benefit from this alteration that further reduces WVCs as compared to the basic WVC mitigation measure.

Indirect Benefits

Wildlife mortality as a result of the presence of the fence is decreased.

Undesirable Effects

Increased visibility of the fence may negatively impact landscape aesthetics.

Costs

No costs were identified in the literature review.

Guidelines

No guidelines were identified in the literature review.

Gaps Caused by Access Roads

Access roads to the main road require a disruption of the wildlife fencing, resulting in an opening that has to be mitigated in order to avoid animals getting caught inside the fences along the transportation corridor. The following sections describe potential solutions to this problem.

Gaps Caused by Access Roads: Gates

Gates can be opened when leaving or accessing the main road. This approach is an inconvenience to drivers, as they have to stop and get in and out of their vehicle. Gates are normally only installed at access roads that have very low traffic volume.

Case Studies and Contacts

For information on gates along U.S. Highway 93, Flathead Indian Reservation, MT, contact: Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

Direct Benefits

The use of gates results in no further reduction in collisions compared to an undisrupted wildlife fence (presuming the gates are closed by users).

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

Gates are an inconvenience to drivers, and they may potentially increase WVCs if they are left open.

Costs

Costs for single- and double-panel gates along U.S. Highway 93 on the Flathead Indian Reservation, MT, were $300–360 and $350–550, respectively (Pat Basting, Montana Department of Transportation, personal communication).

Guidelines

No guidelines were identified in the literature review.

Gaps Caused by Access Roads: Cattle or Wildlife Guards

Cattle or wildlife guards are designed to discourage wildlife, especially ungulates, from walking through a gap in the fence (figure 52). However, standard cattle guards may be easily passable by Florida Key deer and mule deer and dangerous to pedestrians and cyclists, and special designs may be needed (for example, those developed for the Florida Key deer).(380,381) In some cases, such as along a side road of the Trans-Canada Highway in Banff National Park, Canada, a wildlife guard has also been put under electric current to discourage bears from walking across it. An electrified mat across an access road has also been used to discourage ungulates from using a gap in a fence for an access road to approach a larger road with higher traffic volume and vehicle speeds (David Bryson, Electrobraid Fence Ltd, personal communication).

This picture shows deer-proof fencing, paralleling a highway, that abuts an approach road. The surface of the approach road between these fence ends is a colored metal grate used to prevent animals from getting on the other side of the fence through this approach road.

Figure 52. Photo. Wildlife guard along U.S. Highway 93 on the Flathead Indian Reservation, MT (copyright: Marcel Huijser, WTI).

Case Studies and Contacts

For details on an electrified wildlife guard in Banff National Park, Canada, contact Terry McGuire, Parks Canada,terry.mcguire@pc.gc.ca.

For information on wildlife guards along U.S. Highway 93 on the Flathead Indian Reservation, MT, contact Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

Direct Benefits

Cattle or wildlife guards offer no additional benefits in reducing WVCs compared to undisrupted wildlife fencing. Depending on the type of cattle or wildlife guard, the guard may be ineffective at discouraging certain species, or it may be only partly effective (e.g., 75–99 percent for Florida Key deer), depending on the type of wildlife guard.(381) Intrusions result in wildlife ending up on the road or in between the fences along the right of way, posing a threat to traffic safety and putting the animal's life in danger.

Indirect Benefits

Wildlife guards are easy on drivers as they do not require them to stop or get out of their vehicle. In addition, in contrast to a gate, a wildlife guard cannot accidentally be left open.

Undesirable Effects

Depending on the design, cattle or wildlife guards may be dangerous to pedestrians and cyclists and unpleasant to drivers.

As mentioned above, depending on the design and target species, some cattle or wildlife guards may be fully or partially passable to certain wildlife species.

Costs

The reported cost of a specially designed wildlife guard was $30,000 (Pat Basting, Montana Department of Transportation, personal communication).

Guidelines

See Peterson and others for guidelines.(381)

Access for People such as Hikers, Skiers, Cyclers, and Fishers

Wildlife fencing presents people with a barrier. In some cases, access has been provided that allows people to cross the wildlife fence, for example to hike, cycle, or fish on the other side of the fence. Angled openings (figure 53) and swing gates, with or without steps to accommodate for deep snow (figure 54), have been implemented to allow access for people. In The Netherlands, gates for people have been installed that have angled doors that allow gravity to automatically close the gate (Marcel P. Huijser, Western Transportation Institute, Montana State University, personal communication).

This picture shows an angled opening in a 2.4-m (8-ft) fence that parallels U.S. Highway 93 (south). One end of the fence ends in a V shape and the other ends approximately 1 m (3 ft) away creating the opening. To show the opening and the height of the fence an MDT worker stands at the crux of the angle.

Figure 53. Photo. Angled opening in fence allowing access for people along U.S. Highway 93, MT (copyright: Marcel Huijser, WTI).

The 1-m (4-ft) spring loaded swing gate sits above a set of three stairs to allow access in deep snow. The stairs and swing gate interrupt a 2.4-m (8-ft) fence. The highway is not seen in this picture.

Figure 54. Photo. Swing gate in fence (spring loaded) allowing access for people, along the Trans-Canada Highway in Banff National Park, Alberta, Canada (copyright: Adam Ford, TCH research project/WTI-MSU).

Case Studies and Contacts

For details on an opening in a fence along U.S. Highway 93 (south), contact Pat Basting, Montana Department of Transportation, (406) 523-5872, pbasting@mt.gov.

Direct Benefits

No direct benefits were identified in the literature review.

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

Some access designs (e.g., the opening in a fence along U.S. Highway 93 (south) in Montana), have not been evaluated yet with regard to wildlife potentially using the structure to get into the right of way.

Not all access designs are accessible to handicapped individuals.

Costs

No costs were identified in the literature review.

Guidelines

No guidelines were identified in the literature review.

Boulders in the Right of Way

Large boulders have been placed in the right of way, outside of the clear zone, as an alternative to wildlife fencing. Large boulders are thought to make it hard for animals, especially ungulates, to walk across an area. Boulders have been used for this purpose along State Route 260 in Arizona (Terry Brennan, U.S. Forest Service, personal communication; Norris Dodd, Arizona Game and Fish Department, personal communication) (figure 55 and figure 56). The boulder barrier was not extended through areas with steep slopes, since it was thought that wildlife would not move through these steep areas. However, animals have traveled through these areas. The barrier is thought to be effective with exception of the gaps in the steep areas. (Norris Dodd, Arizona Game and Fish Department, personal communication).

This picture shows a swath of large boulders running through a forested area.

Figure 55. Photo. Large boulders placed in the right of way as a barrier to elk and deer along State Route 260 in Arizona (copyright: Marcel Huijser).

This picture shows a swath of large boulders running through a forested area with the roadway, under construction, in the background.

Figure 56. Photo. Large boulders placed in the right of way as a barrier to elk and deer with a view of State Route 260 (under construction) in Arizona (copyright: Marcel Huijser).

Case Studies and Contacts

For information about the use of boulders as an alternative to wildlife fencing along State Route 260 in Arizona, contact Terry Brennan, Tonto National Forest, (602) 225-5375, tbrennan@fs.fed.us; and Norris Dodd, Arizona Game and Fish Department, Pinetop, AZ 85935, (928) 367-5657, doddnbenda@cybertrails.com.

Direct Benefits

The large boulders are believed to be an effective alternative to wildlife fencing if all the gaps are eliminated.

Indirect Benefits

In contrast to wildlife fences, large boulders are natural and, depending on the landscape, can address the landscape aesthetics concern associated with wildlife fences.

Undesirable Effects

If boulders are indeed an absolute barrier to ungulates and/or other species groups, safe passage may have to be provided for wildlife at selected locations. See the previous section on wildlife fencing on addressing undesirable effects of wildlife fencing.

Costs

Costs for the Arizona case study were less than $197 per m (less than $60 per linear ft) (Norris Dodd, Arizona Game and Fish Department, personal communication).

Guidelines

No guidelines were identified in the literature review.

Long Tunnels and Long Bridges Over Landscape

In this section, long tunnels (or landscape bridges) are defined as tunnels that are at least several hundreds of meters long, sometimes many kilometers. They may include "cut and cover" strategies, where a "roof" is constructed over the road rather than a tunnel, leaving the landscape above intact. Long bridges (or elevated road sections) are defined as bridges that are at least several hundreds of meters long, sometimes many kilometers. Long tunnels and bridges are primarily constructed because of the nature of the terrain (e.g., through a mountain, across a floodplain), but in some cases they are constructed to avoid areas that are ecologically very sensitive and where no alternatives are available. If the nature of the terrain permits, animals can move freely over long tunnels or under long bridges, and because the animals are physically separated from traffic, WVCs are eliminated. While long tunnels and long bridges may be among the most effective mitigation measures to reduce roadkill, they are rarely specifically designed to reduce WVCs.

Long tunnels and long bridges should not be confused with wildlife overpasses or wildlife underpasses. Wildlife overpasses and underpasses are typically combined with wildlife fencing, and it is the wildlife fencing that keeps the animals from entering the roadway, whereas the primary function of wildlife overpasses and wildlife underpasses is to mitigate the barrier effect of the wildlife fencing and to provide safe crossing opportunities. Long tunnels and long bridges are not necessarily combined with wildlife fencing. They allow for free animal movements over or under the road, as well as other ecosystem processes, including those related to soil and hydrology (figure 57).

This picture shows one end of a bridge spanning a valley. Even though this is new construction, the majority of the vegetation under the bridge is intact.

Figure 57. Photo. Long bridge on Arizona State Route 260 constructed in such a way as to minimize the impact to soil and vegetation (copyright: Marcel Huijser).

Case Studies and Contact

At one section of the U.S. 61 reconstruction project in Minnesota, Silver Creek Cliff, a tunnel was constructed. To meet the design standards for the reconstruction, the cliff top needed to be removed (estimated to be a million cubic yards of cut). Environmental and aesthetic concerns led to what was actually a less expensive solution. The Minnesota Department of Transportation was able to use the existing highway as a bypass during tunnel construction, which they would not have been able to do if a typical cut would have been used. This approach resulted in cost savings of earthwork (to remove the cliff top which was estimated to be one million cubic yards (765,000 cubic meters)) and no need for a construction of a bypass (estimated at $2 million due to the terrain restrictions). Additionally, this alternative was a much more environmentally friendly and aesthetically pleasing. The tunnel was constructed using the new Australian Tunneling Method (Scott Bradley, Minnesota Department of Transportation, personal communication). For further information, contact Scott Bradley, FASLA, Chief Landscape Architecture, MNDOT, (651) 284 3758,scott.bradley@dot.state.mn.us.

When State Route 40 in Florida was constructed, a long bridge over dry land was built in anticipation of a planned canal (figure 58). The canal was never built, but the bridge allows wildlife to pass unharmed underneath.

This picture shows a long bridge elevated over forested area.

Figure 58. Photo. Long bridges do not have to be excessively large to provide ample space for wildlife crossings. While not exceedingly long, this bridge provides plentiful space for both the stream and wildlife to cross.

There are numerous other examples of long bridges and tunnels. A cut and cover option was used for a long tunnel in the United Kingdom (A12 Hackney to M11 link). A long bridge was constructed on roadway A9, over an important wetland surrounding the Mino River near Galicia, Spain. Interstate 70 in Glenwood Canyon, CO, has several sections that are elevated viaducts.

Direct Benefits

No data are available, but since there is a physical separation of the vehicles and animals, WVCs should be reduced by 100 percent or close to 100 percent.

Indirect Benefits

Long tunnels and long bridges allow for connectivity at the landscape level for a wide array of species. In multifunctional and agricultural landscapes, they also allow for humans, forest products, crops and livestock to freely move from one side of the road to the other.

Undesirable Effects

No undesirable effects were identified in the literature review.

Costs

A 200-m (660-ft)-long tunnel was constructed for Can$24,000,000. A 200-m (660-ft)-long elevated roadway (long bridge) cost Can$12,500,000 (Anthony P. Clevenger, Western Transportation Institute, Montana State University, personal communication).

Guidelines

No guidelines were identified in the literature review.

Wildlife Underpasses and Overpasses

Wildlife underpasses and overpasses are not always installed in combination with wildlife fencing (see earlier section on wildlife fencing in this chapter).(382) In some cases, the landscape in the surroundings of the crossing structures may guide the animals to the crossing structures, reducing the need for wildlife fencing. In other cases, wildlife fencing may not be on option, for example because of landscape aesthetics. For a discussion on wildlife underpasses and overpasses see the earlier section on addressing the undesirable effects of wildlife fencing in this chapter.

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