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Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.4. Designing to Accommodate Wildlife, Habitat Connectivity, and Safe Crossings

Wildlife issues are on the rise for state DOTs. Wildlife related concerns include habitat fragmentation and connectivity for wildlife, loss of habitat, increasing numbers of threatened and endangered species, and secondary and cumulative impacts.

The federal Endangered Species Act prohibits harm to or take of any listed species or adverse modification of designated critical habitat. Some of the existing regulations can be reviewed at the Overview of the U.S. Fish and Wildlife Service and recent developments at AASHTO's Center for Environmental Excellence website. Other sites which provide regulatory information include the USFWS' Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service , Executive Orders, FHWA's Summary of Environmental Legislation Affecting Transportation, December 1998 and the Center for Wildlife Law' Federal Wildlife and Related Laws Handbook, Statute Summaries . Maintenance and construction staff are responsible for ensuring that no threatened or endangered species within areas they are working are injured or destroyed or their habitat impacted without proper permits. DOTs are implementing stewardship practices specific to certain threatened and endangered species as well as practices designed to benefit wider groups of species and ecosystems more proactively. This sections specifically focuses on what DOTs are doing to improve habitat connectivity and the ability of wildlife to safely cross roads.

State transportation agencies currently employ a mix of underpasses, bridge extensions, culvert installations, and culvert modifications, and associated fencing and ecowalls to facilitate wildlife movement. Effective wildlife fencing and crossing structures can significantly reduce many harmful impacts of roads on wildlife populations, though such measures can contribute to habitat fragmentation. More and more DOTs are exploring wildlife passages and culvert retrofits as means to enhance wildlife passage. In a few cases overpasses are being built. From a wildlife conservation perspective, the impacts addressed by these stewardship measures include habitat loss, habitat fragmentation, degradation of habitat quality, road avoidance zones, increased human activities, direct mortality, reduced biodiversity, genetic isolation, chemical contamination, changed hydrology for fisheries, reduced access to vital habitat, disruption of processes important to animal life cycles, and disruption of the food chain. Rigorous evaluation of the success of these measures has been implemented more slowly as funding for such work after the conclusion of construction is harder to find and frequently involves partnerships with others. In a 2002 survey by the author, 17 of 50 state DOTs said they were beginning to systematically incorporate wildlife crossings into roadway designs, but only a couple state DOTs had wildlife crossing policies, and only two states reported they had prioritized barriers for correction based on benefit evaluation. [N]

NCHRP 25-27, starting in 2004 and concluding in 2007, will investigate what guidelines are currently used by DOTs to determine wildlife crossing dimensions or design, the decision process, and any tools or aids that are used in that process. As of early 2002, only five state DOTs reported providing some direction to designers in this regard. In dissecting existing decision processes, NCHRP 25-27 will seek to understand the various factors used to decide what type of crossing will be employed as well as the extent to which long-term maintenance costs (annuities) of a highway structure guide selection (e.g. steel arch culvert vs. precast concrete girders with concrete deck). Ultimately the project will produce design guidance and a decision support tool for DOTs, as well as measures of cost and effectiveness. [N]


3.4.1 Identifying Locations for Wildlife Crossings
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The locations of wildlife crossings and/or problem areas are critical for effective mitigation of the barrier effect caused by highways; however, few methodological approaches to identify and prioritize these key areas have been explored. Researchers from Madrid University found that 70 percent of collisions occurred on just 7.7 percent of the roads in the area they studied. [N] Collisions tended to occur where animals found it easier to cross roads in the absence of human habitation; fences or large, steep embankments deter animals from crossing roads and funnel animals to easy crossing points. Habitat availability on either side of the road is another factor in where animals choose to cross.

Only three state DOTs in the U.S. reported using modelling tools to identify habitat linkages as of 2002, and only one state did so for a large number of species on a statewide basis. [N] Six states had embarked on or participated in statewide efforts to determine connectivity needs as of early 2002. [N] Several more have begun to do so over the past two years.

Planning for wildlife crossings can be very involved; however, much can be accomplished using rapid assessment techniques, available information, and expert panels. The Forest Service's national expert on wildlife crossings advocates a simple rapid assessment approach that has proven effective in a variety of circumstances, is fast, and affordable: [N]

  • Select highways to be examined.
  • Select species for analysis
  • Use available, spatially specific information, especially that available digitally in geographic information systems (GIS).
  • Use a team of local biologists. Teams can often examine 100 miles/day.

DOTs, resource agencies, universities and non-governmental organizations such as The Nature Conservancy, American Wildlands, and the Rocky Mountain Elk Foundation have attempted to fill this gap by conducting workshops, often with DOT sponsorship. Biologists, researchers, and regulatory specialists come together in a workshop setting to make decisions on conservation and connectivity needs based on analysis of best available environmental data. With recent requirements of all states to identify priority conservation areas, new opportunities for interagency identification and prioritization of wildlife crossing needs are emerging.

NCHRP 25-27 will survey state transportation agencies to determine what information is used to determine location and number of wildlife crossings on planned sections of highway-improvement project, whether models are developed around political, project, or ecological boundaries, and whether connectivity needs are assessed at the project level, political/statewide level, or the level of ecoregions surpassing political boundaries.


3.4.2 Monitoring Wildlife Crossings
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Performance evaluation of crossing structure depends upon adequate monitoring. Future design benefits from such information as well. Most monitoring efforts to evaluate wildlife crossings have been short-term and focused on discerning whether target species are using the crossings. Monitoring programs have largely been aimed at single-species or have been confined to certain taxonomic groups; consequently, such programs may fail to recognize the requirements of other non-target species and ecological processes. Further, studies have generally failed to address the need for wildlife adaptation to environmental change. How well crossings ultimately perform depends on how well they accommodate changes in wildlife species distributions, abundance and behavioral profiles. Wildlife crossings are expensive measures, but a large void exists in devising cost-effective designs based on ecological and engineering criteria. Also, the current information base on wildlife crossing performance is geographically limited.

While nine of 50 state transportation had modified culverts for enhancement of connectivity across roads as of 2002, only four of these monitored such crossings with feedback to DOT designers and/or the state or federal wildlife agency. [N] Eight of 50 state DOTs reported monitoring specially constructed wildlife underpasses, with feedback to design and wildlife agencies. [N] Though DOTs more commonly employed bridge extensions to facilitate wildlife passage, usage by wildlife was much less frequently monitored than with other crossing technologies. [N]

According to research by the Western Transportation Institute, evaluation of a wildlife crossing structure installation may involve consideration of the following issues: [N]

  • Motorist safety and animal-vehicle collisions
  • Ecological impacts of mortalities and the "barrier effect" due to roads and traffic on individual animals, on a specific species, on populations of animals, on ecological communities and biodiversity, or on ecosystem processes and functional landscape integrity.

NCHRP 25-27 will add to this knowledge base by collecting details about types and methods of wildlife crossing monitoring in use, how often monitoring occurs, and the length of time for which it has occurred. The project will seek to detail the ecological criteria currently used to judge whether wildlife crossings are functional or effective, whether targets are established in advance, criteria are based on single target species, observed frequency of use by target or multiple species, population- or ecosystem-level data collection and analysis, or accident reduction.


3.4.3 Wildlife Crossing Research, Resources, and Techniques
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This section reviews environmental stewardship practices and features that are being incorporated in many transportation projects across the country, including the restoration or preservation of habitat as mitigation and the addition of wildlife underpasses, overpasses, bridge extensions, enlarged culverts, and fencing by many states dealing with the realities of wildlife conservation and motorist safety. These practices were initially presented in NCHRP Report 305 on Interaction Between Roadways and Wildlife Ecology and are summarized herein. Habitat-related mitigation and conservation measures are some of the most effective measures and are used to address the broader ecological concerns associated with reductions in habitat and wildlife connectivity. Model stewardship practices in this area will also be briefly reviewed.

Existing crossing techniques can also be view at the Wildlife Crossing Toolkit developed by the U.S. Forest Service. Their website offers a searchable database of case histories from a wide variety of locations, time periods and wildlife species where people have attempted to solve issues resulting from wildlife/highway interactions. [N]

Research by the Western Transportation Institute found that the physical dimensions of the underpasses had little effect on passage because animals in the Banff National Park in Canada may have adapted to the 12-year old underpasses; however, structural attributes were more important on newer structures. Furthermore, the level of human activity in the vicinity was an important factor suggesting that mitigation strategies need to be proactive at the site and landscape level to ensure that crossing structures remain functional over time, including human use management. [N] The Western Transportation Institute is developing a vehicle-animal collision "toolbox" of countermeasures, which will provide detailed information to support application choices and decisions, and performance measurement. [N]

The remainder of this section consists of summary excerpts from NCHRP Synthesis Report 305 on Interaction Between Roadways and Wildlife Ecology and practices adapted from that discussion with regard to wildlife crossings, except where otherwise noted. [N]

Fencing is a common practice used throughout the world to keep animals off highways. Twenty-eight states report using fencing to protect wildlife. The most frequent application is to keep deer off of roads. Deer are locally overabundant in a number of states, and fencing has proven to be an effective way to keep deer off the roads. Clevenger [N] reported an 80 percent reduction in ungulate-vehicle collisions on the Trans-Canada Highway in Banff National Park after fencing. [N]
  • Design fencing applications for target species. Typical fencing applications are rectangular mesh or chain link fence from 2.6 to 3.0 m (8.5-10 ft) high. Florida and some European countries use strands of barbed wire along the top of the fence to discourage animals from climbing over the fence. Also used is finer mesh wire of from 2 x 2 cm (0.78 in.) to 4 x 4 cm (1.57 in.) buried 20 to 40 cm (7.87-15.75 in.) with a height extending from the ground of from 0.5 to 1 m (1.64-3.28 ft).
  • Keep local wildlife interactions in mind when designing fences. For example, in California fencing application in areas with kit fox and coyotes provide a gap under the fence just large enough for the kit fox to negotiate at full run so that the latter can escape predators such as the coyote.
  • For reptiles and amphibians, bend the upper edge of the finer mesh at a 90-degree angle to provide a lip to prevent animals from climbing over the fence. In Waterton Park, Canada, a temporary silt barrier type fence was used to direct frogs into polyvinyl chloride (PVC) drop traps so that volunteers could move them across the highway to a pond during the few-week-long migration period. Europeans have used a PVC barrier with an angled lip to keep reptiles and amphibians off the highways as well as a fabricated galvanized steel rail with a barrier lip along the upper edge. Iowa DOT has placed finer mesh fence at the bottom of regular fence to prevent smaller wildlife such as turtles, snakes and other small animals from getting on the Eddyville Bypass and Highway 63 at the Bremer-Chicksaw county line. This fencing approach has been commonly used in Europe to keep smaller animals off highways.
  • Bury fine-meshed fencing at the bottom in use with pipe culverts for small animal connectivity or in association with other ROW fences. This practice has been successfully used under highways in Europe in culvert pipes with diameters approximately 0.4 m to 2.0 m (1.31-6.56 ft). California used a unique fencing application for desert tortoise approximately 6 km (3.7 mi) east of Kramer Junction on Highway 58 in San Bernardino County. A finer [1.27 cm (0.5 in.)] mesh section of wire fence, approximately 50.8 cm (20 in.) in height, was installed along the bottom of a typical 1.22-m (4-ft) right-of-way fence. The finer mesh fence was buried approximately 15 cm (5.9 in.) to prevent animals from going under. This portion of the fence was held in place using three strands of wire. The fencing application was done on an approximately 35.42- km (22-mi) section of four-lane highway. The fencing angled into the road at a series of culverts and bridges that were constructed for wildlife connectivity.
  • Fence installation decisions should account for the potential for wildlife to be trapped between the fences should they find a way to enter the rights-of-way under, over, or around the fence ends. Because fencing is not totally exclusionary, Bissonette and Hammer studied two highway sites in Utah to compare the use of one-way gates and earthen ramps. They found that earthen ramps were used from 8 to 11 times more than one-way gates. Irrespective of the species, fencing without provisions for movement across the road can cause disruption of connectivity resulting in isolation of populations. This can be especially problematic for species with low populations, where the possibility of extinction can result.
Properly designed culverts can enable wildlife to cross roadways by passing under an intersecting roadway through a culvert. A culvert is a conduit covered with embankment around the entire perimeter. It may or may not convey water. Small conduits for amphibians are sometimes called tunnels. The following table is from the U.S. Forest Service on-line Wildlife Crossing Toolkit . [N]

Table 8 : U.S. Forest Service Wildlife Crossing Toolkit Guide to Culverts



Typical Material

Box Culvert

Culvert has four sides, including bottom. Sometimes square or rectangular corrugated metal pipe culverts without bottoms are called box culverts, but in this toolkit they are referred to as bottomless culverts.

Box culverts may be arranged in a horizontal series of small culverts to form multiple chambers.

Precast concrete
Cast-in-place concrete

box culvert


Culvert is continuous in circumference. The lower portion may or may not be buried. Sometimes simply called pipe. European badger culverts are sometimes called ecopipes.

Slotted drain culverts are continuous except for a break
in the upper portion.

Corrugated metal pipe
Metal plate
Cast-in-place concrete
Precast concrete

continuous culvert

Bottomless Culvert

Culvert is discontinuous in circumference with rounded or square top and natural surface bottom. Also called open-bottom culvert.

Corrugated metal pipe
Metal plate
Precast concrete
Cast-in-place concrete

bottomless culvert

From Forest Service Wildlife Crossings Toolkit on-line at

Modified Drainage Culverts
Drainage culverts can be modified to accommodate wildlife, a practice increasingly implemented by state DOTs and for which the Netherlands is renowned. Small mammals and amphibians are able to move through the culverts on shelves and floating docks or through wildlife tunnels built parallel to the wet culvert. NCHRP Synthesis Report 305 identifies the following stewardship practices with regard to modified drainage culverts: [N]

  • Addition of a 0.46 m wide × 0.30 m high (18 in. × 12 in.) elevated concrete walkway can allow animals to move through a culvert even when water is present. Such modified culverts were successfully tried on US-98 in Texas for bobcats.
  • A central "sacrificial" culvert with other culverts placed on both sides but at a higher elevation for drainage and connectivity can diminish blockage by beavers, which attempt to block the lower culvert, and the adjacent culverts at higher elevation remain open. Beaver-exclusion devices, including fencing, perforated pipe, or a combination of the two have been successfully used throughout the United States to reduce impounding of water behind road fills and for wetland mitigation and habitat preservation.

Colorado DOT has addressed a number of safety issues with beaver damage to roadways by using a modified culvert such as that described above. Safety issues have included potential to damage to the roadbed from water saturation, loss of flood capacity that otherwise would have been provided in the area flooded by the beaver dams, potential for heaving of the road way from frost or ice, and concern for motorist safety should they skid into the deeper water caused by the beaver dams. CDOT also wanted to cooperate with residents of nearby neighborhoods who desired the beavers to remain. To allow beavers to remain, CDOT perforated the beaver dams with pipes long enough to defeat the beavers natural inclination to plug holes in their dams. The pipes were inserted at a level that would allow the beavers to have a pond but not at such a level that the water continued to be a serious threat to the highway. Wire cages were placed over the ends of the pipes to prevent the beavers from clogging the pipes. [N]

Drainage Culverts
NCHRP Synthesis Report 305 reports a number of states are using culverts in different applications for a variety of species. Florida, Montana, New Hampshire, Texas, and Wisconsin are using culverts for reptiles and amphibians. Nebraska and South Dakota are using them for turtles. [N]

Culverts with dual drainage and wildlife crossing purposes have proven successful in accommodating both terrestrial and aquatic organisms depending on water levels in the area of the culverts. When placed at the proper elevation, they can serve both types of organisms. Drainage culverts are typically used where highway causeways or fill sections transverse wetlands with fluctuating water levels such as wet prairies and marsh. They are also used on intermittent streams and floodplain areas that may inundate during wet periods. Aquatic species such amphibians and fish use them when they are wet and terrestrial species including reptiles and small mammals use them when they are dry.

Pictures of Florida DOT drainage/wildlife culverts, Massachusetts amphibian tunnels, Dutch structures, and wildlife using the culverts mentioned above, as well as other projects around the world can be seen at FHWA's wildlife crossings website; however, Evink notes that few states have researched the effectiveness of these structures. [N] Nevertheless, it is known that

  • Culverts should be sized for use by multiple species, wherever possible.
Stream Culverts and Bridges
Like drainage culverts in upland areas, oversized culverts can be designed and placed at the proper elevation over waterways to provide passage for a large number of aquatic and terrestrial species. [N]
  • Use the natural stream bottom rather than a concrete or metal bottom.
  • Provide shallow water or even dry edges along the stream edge in the culvert or bridge to allow the greatest number of species to move through.
  • Allow extra height for larger mammals, such as deer, bear, and other species that ordinarily follow riparian corridors for movement and pass safely under roads. A wide variety of designs are possible depending on the site-specific construction environment - concrete box culverts, and round, oval, and elliptical pipe culverts.
  • Provide cover as well as substrate on the inside of the culvert, similar to that of the exposed stream, to expand utility of the culvert. Proper sizing of the culvert depends on site-specific considerations and hydraulics, but including the natural streambed and as much adjacent upland as possible proves most successful.
Wildlife Underpass Bridges and Dry Culverts
Upland culverts are one of the most frequently used structures for wildlife crossings and have proven successful for accommodating a wide variety of species. Pipe culverts and box culverts have proven effective for small animals. California is using culverts for San Joaquin kit fox. Illinois, Kansas, Montana, New Hampshire, New Jersey, Oregon, Texas, Utah, and Virginia are using culverts for other small mammals. Arkansas, Colorado, New Jersey, Wyoming, Utah, Michigan, Washington, and Kansas report using larger culverts for deer and other wildlife. [N]
  • A range of culvert sizes, from 1.22 m × 1.22 m (4 ft × 4 ft) in Arkansas up to 2.44 m × 7.32 m (8 ft × 24 ft) in Florida and from 1.5 to 10 m (4.92 - 32.81 ft) in New South Wales, Australia, have been successfully used for various species of terrestrial mammals and reptiles.
  • Use frequently placed culverts [150 - 300 m (492.13 - 984.25 ft)] of varying size in close proximity to shrub or tree cover. Clevenger and Waltho found that for a variety of culvert sizes for small and medium-sized mammals, passage was positively correlated with traffic density, road width, road clearance, and culvert length. They also found that all species with the exception of coyotes and shrews preferred small culverts with low openness ratios. There appeared to be some evidence of predation at crossings so the thought was that the smaller culverts provided comfort to the prey species. Weasels and shrews preferred culverts with nearby cover. The researchers felt that drainage culverts could be used to mitigate the harmful effects of high-speed roads. [N]

Wildlife underpasses are bridges and/or large culverts over dry land and sometimes land and water, constructed expressly to facilitate wildlife movement in important corridor areas. The length and height of these large culverts or bridges varies with the wildlife expected to use them. Twenty-three states report using underpasses for wildlife. The Western Transportation Institute is cataloging existing uses of and research on underpasses and culverts to provide further guidance to DOTs on stewardship practice in this area. [N]

Extended Bridges and Existing Structures
One of the most successful and cost-effective means of providing for wildlife movement down riparian corridors is the extended bridge. Twenty-four states report using extended bridges for wildlife movement and wetland protection. [N]
  • Provide adequate area for both water movement with associated organisms and dry habitat for terrestrial species movement.
  • Consider the characteristics of the area when trying to determine the appropriate length of the bridge. In cases where there is an important corridor for movement of rare or protected wildlife species, bridging the entire floodplain may be necessary. At the other end of the spectrum, where the floodplain is being used by habitat-limited species, a combination of smaller structures and fences may be possible.
  • When choosing a combination of bridge and fill, consider what reptile and amphibian species will likely move up the fill slope onto the road. Standard fencing will not stop this movement so that very expensive barrier walls and associated guard rails may be necessary to prevent significant kills of these species during periods of the year when they are moving around in large groups.
  • Consider the cost of mitigation for wetland takings by opting for a fill section. By the time the costs of shorter bridges or culverts, fill acquisition, barrier walls for reptiles and amphibians, guardrails, and fencing are factored in, along with the cost of wetland mitigation, the cost of a more substantial bridge, preferred for habitat connectivity, may already have been approached.

Viaducts are a potential solution for the entire spectrum of species moving through an area, as these long bridges can leave wetlands, rivers, and variable topography and geology below largely intact. Typically, this approach is most cost-effective where there is topographic relief, such as in mountainous areas, is sufficient to make bridging necessary for a significant span of a waterway, canyon, or valley; use of spanned lands by wildlife is typically a secondary benefit. [N] Design of viaducts for wildlife connectivity and habitat enhancement is increasing, especially in Europe.

Wildlife Overpasses
Although wildlife overpasses are largely a European phenomenon, Florida, Hawaii, New Jersey, and Utah reported overpasses being used by wildlife and the Montana Department of Transportation and the Connecticut DOT are installing wildlife overpasses on Highway 93 and Route 6, respectively. The New Jersey overpasses, among the first in the United States, were completed in 1985 at a cost of $12 million. The overpasses were designed to provide connectivity across I-78 (a six-lane highway) at an approximately 2-mile stretch that crossed the Watchung Reservation in Union County. Specifically, one was constructed solely for wildlife use (especially deer). Another one was constructed for shared wildlife and vehicular use; however, it has since been closed to traffic. A third overpass was constructed as a shared use between wildlife, vehicular traffic, and a bridle path for horses. The Utah overpass was constructed principally for deer. The Florida overpass on I-75 in Marion County just north of County Road 484 is a multi-use overpass designed to accommodate a recreational and equestrian trail, as well as for wildlife use. Two overpasses were built over the Trans-Canada Highway in Banff National Park and are being used by a variety of wildlife. [N]

  • Allow the widest width possible. Wildlife overpasses can vary in width from 3.4 m (11.15 ft) to 870 m (2,853.6 ft). Wider passages are more effective at allowing animals to cross and animal behavior on wider structures is more normal than on narrower ones.
  • Establish or preserve suitable habitat at and leading to the overpasses. Where this has been accomplished, it has been found that the overpasses were effective for a wide variety of animals including invertebrates.
Other Structural and Non-Structural Measures for Wildlife
Signage and deer reflectors are common approaches to informing motorists when they are entering an area where the danger of wildlife collision is high, though the effectiveness of these methods has not been demonstrated. However, a few methods have been documented to work: [N]
  • Use a series of solar-powered, battery-operated, motion sensors to determine animal presence and trigger low-voltage, LED-illuminated warning signs that reduce the posted speed limit to 40 km/h (25mi/h) and alert motorists to the presence of approaching wildlife. This method has been successfully used in Switzerland, though the location on the road was also adjacent to a large wildlife overpass over a major nearby freeway.
  • Install vertical pipes perpendicular to bridge railings to keep bird flight patterns above the elevation of traffic. Florida reported installing PVC pipe approximately 3 m (9.84 ft) in height perpendicular to the railing on the San Sebastian Bridge. The poles were spaced approximately 3.7 m (12 ft) and kept birds hovering over the bridge from dropping down into traffic crossing the bridge, reducing bird kills.


3.4.4 State DOT Initiatives to Address Wildlife Habitat Connectivity Needs in Planning and Design
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Maine DOT Initiatives to Limit Disruption of Habitat and Transportation Related Wildlife Mortality

Maine DOT chairs a multi-agency task force looking into how to prevent collisions between vehicles and animals, predominantly moose and deer. This task force, initiated in 1999, comprises members from Maine Department of Inland Fisheries and Wildlife, Maine Secretary of State, Maine Turnpike Authority and Maine Department of Public Safety.

A focused, statewide campaign begun in 2001 to make the public aware that moose and deer crashes are likely to happen on any road in Maine and providing tips for drivers to avoid or lessen the severity of these crashes. This public information campaign was expanded in April 2004 to include a new brochure with safe driving tips distributed statewide to all towns, libraries, schools, state parks, tourism centers, and other distribution points. News media alerts are distributed to all radio and TV stations, and to newspapers throughout the state each spring, in time to alert the traveling public that May and June are the most dangerous months of the year for moose/vehicle collisions. In 2004, Maine DOT's efforts were publicized by statewide media outlets and picked up by other news outlets including the Washington Post and Chicago Tribune. Public outreach also includes a module on large animal collisions that continues to be part of driver education programs throughout the state. In addition, the task force produced a safety video in 2001 and distributed the video to all driver educators in Maine.

Maine is increasing the number of available moose hunting permits in areas with severe/high crash locations. Maine DOT is supplementing these efforts by examining and testing measures to prevent collisions by either warning motorists or warning/excluding animals from roadsides. Some of these measures include alternative striping, reflectors, signs (with and without additional warning lights), and fencing. The Department is also looking at increased roadside clearing widths, to make moose visible from greater distances, allowing drivers more time to react and therefore prevent or lessen consequences of collisions. Roadside vegetation management practices, such as the composition of seed mixes and preventing sprouting of roadside woody plants, are also being examined to eliminate choice food sources close to highways. Maine DOT is investigating habitat conditions, especially at historically high crash locations, to better predict likely cross locations and to choose and install appropriate prevention measures in the most effective locations.

On the planning end, Maine DOT has initiated meetings and invited representatives from resource agencies to join them in speaking with officials from New Brunswick and Quebec who are facing the same issues with wildlife and the traveling public. These meetings have helped Maine DOT understanding issues in a regional context, learn from the experience of experts in those fields, and further develop Maine DOT strategies that will benefit the traveling public while responsibly addressing wildlife issues related to transportation. Maine DOT is also actively participating in a "Beginning With Habitat" initiative for Habitat and Transportation with Maine Audubon, The Nature Conservancy, Maine State Planning Office, Maine Department of Environmental Protection, Maine Department of Conservation, and Maine Department of Inland Fisheries and Wildlife. The group is looking into comprehensive awareness and protection measures for all types of wildlife and identifying transportation related actions to benefit habitat statewide. Maine DOT is also developing a process to screen future projects for valuable wildlife habitat and has funded research into developing crossing measures for smaller animals, amphibians and other species. Maine DOT develops mitigation for projects specifically looking for opportunities to protect, improve or restore significant wildlife/fisheries corridors and habitats. Recently, as part of a cooperative assessment of the Sunday River watershed, a restoration plan was developed providing a number of projects that could be implemented by various partners. Maine DOT will construct a tributary restoration project during 2005 in the lower Sunday River watershed. Other agencies and groups are organizing to implement additional projects from the watershed plan.

Caltrans Interchange Removal and Partnership to Identify and Address Habitat Connectivity Needs

Due to the rising importance of the wildlife connectivity issue and implications for future construction, Caltrans participated in a statewide symposium/workshop with scientists, activists, and planners from resource agencies and conservation organizations to identify "Missing Linkages" in fall 2000. The meeting report identifies 232 critical habitat linkages in the state, 59 percent of which are threatened. Connectivity areas identified in the report ranged from narrow choke points, like the Coal Canyon underpass, later removed by Caltrans, to long stretches of rivers and broad swaths of redwood forest. More than half of the linkages were deemed to be high priorities because of development threats and good opportunities for conservation.

The interchange Caltrans decided to remove was located where two intersecting state highways divided several protected natural areas, including greater diversity of vegetation types than any other area of comparable size in the United States . By closing the ramps, removing the pavement and lighting, rearranging fencing, and restricting access, Caltrans created a wildlife crossing with substantial height, width, ample natural lighting, and openness. In addition, Caltrans worked with State Parks to find funding to purchase approximately 685 additional acres of conservation lands adjacent to the freeway and interchange, ultimately linking the Tecate Cypress Reserve, the Cleveland National Forest and the Irvine Company's Gypsum Canyon Preserve and lowering development pressure in the area.

Caltrans determined that the site has great mitigation value for transportation impacts, but no agreements exist with other resource agencies to obtain credits at this point. Instead, Caltrans still considers the site an excellent example of leadership and interagency cooperation, which "indirectly facilitates other transportation efforts." Wildlife passage features were incorporated into current and future state highway improvements nearby, benefiting both federally listed species and non-federally listed species with large habitat ranges.

Caltrans plans to utilize the products of the state's collaborative "Missing Linkages" project to assess viable communities, habitats, and wildlife movement corridors throughout the state. This resource will be used to help environmental impacts wherever possible, and as a guide for addressing habitat and wildlife connectivity needs when the state implements conservation measures. Generation of the statewide conservation and connectivity maps is providing the foundation for interagency buy-in, acknowledgement, and utilization of a common set of environmental priorities. The mapped priorities are expected to streamline interagency coordination and negotiation on a project-by-project basis, reduce conflict, and facilitate achievement of mutual stewardship objectives among Caltrans, FHWA, federal and state resource and regulatory agencies, non-profit conservation organizations, and environmental advocates. The Nature Conservancy (TNC) is now assisting Caltrans in comparing the 20-year transportation plan to priority conservation areas, to minimize potential impacts and to identify opportunities where Caltrans mitigation projects could achieve the greatest environmental benefit and make a tangible contribution to achievement of interagency, public and private conservation objectives.

Florida DOT Partnership to Determine and Prioritize Connectivity Needs and Contribute to "Green Infrastructure"

The State of Florida issued a report in 1994 that identified the state's highest priority wildlife habitat, which is the basis for a successful current state-funded effort to protect priority habitat conservation areas. The Florida Game and Fresh Water Fish Commission completed a land cover map of Florida's 34 million acres and performed modeling to identify the long-term habitat needs of many focal species on public and private lands. Florida DOT helped support the development of the extensive wildlife occurrence and habitat geographic information system database, which is used in roadway alignment analysis and impact assessment. The database includes: 1) a statewide vegetation map with 22 land cover classes; 2) habitat maps for over 150 individual wildlife species, constructed by modeling habitat requirements, radio-telemetry range data, museum records, and other surveys, and 3) statewide maps of strategic habitat conservation areas, defined as lands which have a high priority for protection and acquisition, but are not in public ownership.

Because significant efficiencies and ecological gains can be made by coordinating wildlife crossing installation with statewide efforts to map conservation areas and large scale linkage needs, FDOT and the Florida Game and Fresh Water Fish Department developed a decision-based geographic information system (GIS) computer model for FDOT road improvement projects associated with road mortality of wildlife and other environmental impacts. This system is integrated with other state environmental initiatives such as the greenways and CARL (Conservation and Recreation Lands) programs. An interactive CD-ROM allows the user to perform multiple scenarios and develop their own priorities, and contains all necessary data and information to perform analyses. The computer model program enables FDOT to appropriately schedule future projects according to critical environmental and transportation improvement needs.

In 2000, the Florida Department of Transportation DOT initiated a cooperative effort with the Florida Fish & Game Commission to prioritize and begin to address black bear roadkill problem areas on a statewide basis, to focus and direct investments in habitat conservation and connectivity improvements, and to streamline project approvals. Bear roadkill data were re-analyzed to rank road segments by the percent of total statewide roadkills and percentage of kills in the past ten years. This ranking was then combined with habitat information, including percent of road buffer encompassed by conservation lands and strategic habitat conservation areas. The ranking is providing guidance in siting wildlife underpasses on a statewide basis. Fifteen black bear roadkill problem areas were identified, comprising 40 percent of the total transportation-related bear mortality in the state. The core habitat systems surrounding these problem areas also provide important habitat for many species of mammals, amphibians and reptiles. At least as important as the priority crossing and connectivity needs, the analysis revealed that land management and conservation are critical in enhancing the black bear's potential for long-term survival in Florida. The results were shared with the state's Conservation and Recreational Lands program to help justify the purchase of a 22,260-acre tract associated with the Aucilla River Project in the Big Bend area of north Florida, a top three conservation priority as a result of the study.

As part of Florida's DOT's updated environmental policy, approved in February 2002, FDOT committed to cooperate in the state's Greenways Program of land acquisition and management through identification and prioritization of important habitat connections. The objective of the statewide greenways program is to establish an ecological network of green infrastructure to reduce wildlife mortality and restore connectivity to the landscape by restoring natural processes as they originally occurred across the landscape (e.g., wildlife movement and migration, flood, and fire). Where alternative mitigation strategies permit, FDOT will support land acquisition activities to help achieve this ecological infrastructure, and will utilize methods to preserve, enhance, and protect trees and other vegetation as valuable natural resources consistent with ecosystem management principles. So far, over one million acres have been preserved through this program, which has garnered the support of a diverse array of citizens, land managers, and state policy-makers.

New Hampshire DOT's Pilot Project for Identifying Habitat Connectivity and Wildlife Crossing Needs

The New Hampshire Department of Transportation (NHDOT) is engaged in a pilot project effort with the New Hampshire Audubon Society, the New Hampshire Fish & Game Department, and others to develop a methodology for predicting wildlife movement in the state. The effort is an outcome of a discussion on how NHDOT and these partners could cooperatively address wildlife and transportation issues. The partners hope to develop a geographic information system (GIS) layer of important wildlife habitat areas and locations of frequent wildlife crossings to be used as a planning and design tool for future projects.

The pilot effort focuses on Route 4, one of the state's major east-west routes. When sections of Route 101 were widened to four lanes, NHDOT extended bridges to improve habitat linkages. NHDOT is now interested in further increasing the level of connectivity. To this end, NHDOT has contacted Fish & Game Conservation Officers, local road agents, conservation commission members, and NHDOT maintenance patrol foremen to collect anecdotal evidence of crossings and road kills and record that information in a database. In the future, roadkill data will be collected by maintenance staff. Concurrently, the New Hampshire Audubon Society is reviewing mapping of the corridor to identify prospective habitat units, for purposes of predicting where wildlife crossings are likely to occur. The partners will pool efforts to see how well the field data correlates with the mapping predictions. The goal is to develop a predictive model that can be used elsewhere in the State.

To further improve habitat linkages, NHDOT is also supporting efforts to develop an inventory of contiguous habitat areas, to be taken into consideration when siting new alignments, bridge extensions, and crossing locations. The New Hampshire Fish & Game Department has decided that investing in habitat preservation in key areas can be a higher priority than adding or enhancing crossing structures. The New Hampshire Ecological Reserve Project, a partnership between The Nature Conservancy and the University of New Hampshire, is working with the New Hampshire Department of Environmental Services and the Fish & Game Department to develop criteria for the identification of priority conservation parcels. This will generate information that NHDOT can use in planning and project development, and will also guide state investment through the New Hampshire Land and Community Heritage Investment Program.

Maryland SHA's Net Gain Wetland Mitigation Policy & Contribution to Regional Restoration/Connectivity Goals

The Maryland State Highway Administration (SHA) has made a commitment to mitigate for historical impacts to wetlands from transportation projects, with an overall "net gain" wetland mitigation policy. The MDSHA is working with local jurisdictions and watershed groups around the state to realize watershed goals and restore stream segments, and contribute to the state's green infrastructure at the same time.

Maryland has two million acres of ecologically significant land that has not been developed, of which almost three-quarters are unprotected. The state designated the GreenPrint program to preserve the state's remaining natural resources and to create an extensive, intertwined network of conservation lands. The purpose of the program is threefold:

  • Identify, using the most up-to-date computer mapping techniques, the most important unprotected natural lands in the state;
  • Link, or connect, these lands through a system of corridors or connectors; and
  • Save those lands through targeted acquisitions and easements.

GreenPrint databases and watershed plans are available to Maryland State Highways' planning, environmental, and design staff to reference in avoiding, minimizing, and mitigating for unavoidable impacts from transportation. The State Highway Administration is currently undertaking internal discussions to maximize use of this resource.

MDSHA is contributing to watershed restoration and regional habitat connectivity through 23 separate stream restoration projects across the state, with funding matched by local project sponsors. MDSHA has plans to restore approximately nine miles of streams and install a number of stormwater retrofits to improve water quality and stream habitat over the next three years.

VTrans Habitat Connectivity Training

The Vermont Agency of Transportation (VTrans) began offering Habitat Connectivity Training in 2002, which has been very popular. The training is offered to VTrans staff to help them understand the importance of habitat and consider it while doing their work as transportation professionals. In particular, the training fosters an awareness of habitat and encourages a lively dialog about how transportation can fit into the landscape while still considering habitat and connectivity and incorporating that into the planning and design of projects. Solutions that are discussed range from big-picture land use discussions to the details of engineering a bridge or culvert to allow wildlife passage to the merits of including warning signs to alert drivers of wildlife hazards and many things in between. Engineers, planners, environmental specialists, biologists, maintenance staff, landscape designers, project managers, have joined bridge and roadway designers in the training program. Consultants and DOT staff from neighboring states have also attended. Much of the discussion engages transportation professionals in discussions about the challenges they face when planning, designing, constructing, and maintaining a transportation infrastructure.

VTrans Habitat Linkage Area Assessment

In a collaborative effort with the Vermont Department of Fish and Wildlife, VTrans has sponsored development of a GIS habitat database, called the Habitat Linkage Area Assessment. This tool will be used for making decisions for addressing habitat connectivity on VTrans projects and also help the two agencies identify priority areas for consideration for habitat connectivity investments. The project utilizes landscape features as its base and is augmented by years of existing data collected on wildlife crossing areas, recorded road kill locations, anecdotal reports of crossing areas, land ownership, conservation lands, and other data layers. The database identifies areas that range from high priority to low priority in terms of habitat linkage areas and relationship to the Vermont transportation infrastructure.

The Habitat Linkage Area Assessment efforts rests upon VTrans' Operations and Maintenance Division, which collaborated with the Environmental Section and the Vermont Department of Fish and Wildlife in developing a method for collecting roadkill information from District Maintenance Crews. The method utilizes an existing database called MATS that the Maintenance and Operation Division was already using to manage their resources. An existing but unused field was modified, with the guidance of VT DF&W, as a field for recording roadkill data. The Maintenance field crews keep a log in their trucks. When they identify a road kill that is included as a target species in the database they record it (species, location/mile marker, date, and route). These road kill data sheets are collected on a monthly basis and then entered into the database. This information is shared with the VT DF&W and is included as a field in the Habitat Linkage Assessment described above.


3.4.5 Maintenance and Management of Created, Modified, or Restored Habitat
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Most state DOTs try to find a land management agency to provide maintenance for mitigation/conservation habitats. A few have sought to perform mitigation (modification or restoration) on public lands that are already being managed by a resource agency. While some federal resource agencies encourage this approach, others disallow it. Universities, conservation groups, resource agencies, and even private groups where consistent with the objectives of the mitigation have become involved in maintenance of habitat by taking possession or easement of land from the state DOTs. Few transportation departments are maintaining habitat except for wetland mitigation sites, though creative conservation partnerships have been developed in a number of states through in lieu fee arrangements. Texas, Tennessee, Kentucky, North Carolina, and Florida are among the DOTs allowed to provide funding instead of mitigation. Habitat management is frequently the responsibility of the agency or partnering organization holding title to the land or conservation easement.

In most cases, when a state uses a habitat strategy as a conservation or mitigation measure, the maintenance plans for these habitats contain a monitoring requirement. These requirements vary in length and design, but states are often required to maintain sites to varying performance levels (such as a percent survival of desired species and exotic/invasives free) for some period of time (commonly 3 to 5 years). Specific management plans including funding can also be a requirement. Such a monitoring program is designed to:

  • Specify recommended mitigation and ensure that it is included in the final design process.
  • Monitor the implementation of the mitigation through design, construction, and operation.
  • Resolve issues that are contingent on the outcome of design as it progresses to more detailed stages.
  • Report on progress toward implementation of mitigation measures to responsible parties.

Biologists from resource and conservation agencies associated with CDOT's Shortgrass Prairie Initiative crafted recommended Baseline/Annual Reporting Requirements that would provide an effective yet practicable framework for adaptive management and annual reporting: [N]

  • Type of plant communities/habitats present:
  • Size/extent of each present plant community or habitat group.
  • Description of plant communities present and estimated percent cover.
  • General condition of each plant community/habitat type (estimated percent weed cover, estimated weed sp. relative abundance, estimated percent bare ground, etc.).
  • Juxtaposition of communities/habitats.
  • Brief description of land use on-site and in surrounding areas documented in initial baseline. Report changes over the past year.
  • Recommendations for management of parcel (i.e., grazing, controlled burns, plantings, etc.) to achieve conservation goals.
  • Success of recommendations from previous year and suggested modifications.
  • Observations on wildlife diversity, activity, and general trends. i.e. field notes. Surveys and quantitative data are not required.
  • Photo points at established permanent locations according to protocols to be developed in the management plan. The on-site managers and regulatory oversight agreed that new aerial photos would be acquired as they become available.
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Continue to Section 3.5»
Table of Contents
Chapter 3
Designing for Environmental Stewardship in Construction & Maintenance
3.1 Beyond Mitigation: Projects to Achieve Environmental Goals
3.2 Context Sensitive Design/Solutions
3.3 Avoiding Impacts to Historic Sites
3.4 Designing to Accommodate Wildlife, Habitat Connectivity, and Safe Crossings
3.5 Culverts and Fish Passage
3.6 Stream Restoration and Bioengineering
3.7 Design Guidance for Stormwater and Erosion & Sedimentation Control
3.8 Drainage Ditches, Berms, Dikes, and Swales
3.9 Design for Sustainable, Low Maintenance Roadsides
3.10 Designing to Reduce Snow, Ice, and Chemical Accumulation
3.11 Designing to Minimize Air Quality Problems
3.12 Design and Specification for Recycling
3.13 Designing to Minimize Noise
3.14 Lighting Control/Minimization
3.15 Design for Sustainability and Energy Conservation
3.16 Safety Rest Areas, Traveler Services, and Parking Area Design
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