wildlifecrossingstructuretypesbyfunctioniawhi.pdf

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Terrestrial Wildlife Crossing Structu re Types (By Function)

This table is for terminology only and is not in tended to be used for structure design. It can be used for generalized discussions early in planning procesintended to be prescriptive since each site requires site-specific planning by qualified biologists and engineers.

Note: Structures are viewed from animals perspective. Some structures constructed for transportation purposes alone may be retrofitted to meet these functional claGenerally, species that use small structures will use larger structures if appropriate cover and other features are provided, but most species can not use smaller class

CrossingStructure Class

FunctionApp rox imate Dim ensi on

Range(Span x Rise)

Structure Examples Species ExamplesWildlife B ehaviora

Att rib utes

Class 0: Nostructure or non-functionalstructure

No useable structureavailable where one isneeded.

No structure or small drainagepipes.

Fill slope blocking a drainage wherethere is no structure present or astructure with an aquatic componentonly.

Determined by target species. N/A

Class 1: SmallUnderpass

Provides enclosedprotection for small animalsthat require cover.

Metal pipe culverts or smallbox culverts 1.5 m (5) span orless

Small bridges, dry culverts, andephemerally flooded drainageculverts. Continually flooded drainagestructures have limited functionality forterrestrial species but may function forsome aquatics.

Amphibians, reptiles, smallmammals and some medium-sizedmammals (badger, fox, bobcat).Aquatic species include fish, aquaticamphibians, and invertebrates.

Small animals that precover or do not mindconfinement.

Class 2: MediumUnderpass

Provides some cover yetmore openness than Class1 structures for animalssmaller than deer. If water isconveyed, allows for streamsimulation includingunwetted natural banks.

Underpasses larger than 1.5 m(5) span, to 2.4 m (8) span x2.4 m (8) rise

Box culverts, arch pipes and otherculvert shapes, small bridges.

Coyote, bobcat, ocelot, lynx andsome large carnivores (black bear,puma); alligator.

Medium sized mammathat require some coveand some openness tothrough passage.

Class 3: LargeUnderpass

Provides an approximateminimum for ungulates,especially deer, and otherspecies that requirevisibility, maneuverability,and moderated noise. Mayallow some naturalprocesses includingvegetation growth andstream processes.

Underpasses with minimumdimensions: 6.1 m (20) span x2.4 m (8) rise, or 3.1 m (10)span x 3.1 m (10) rise, andopen span bridges

Box culverts, large arch pipes, bridgesincluding open span bridges. Multiplechambered structures are consideredas individual units.

Ungulates use structures inapproximate proportion to their size(ie, deer can use smaller structuresthan elk or moose) althoughpronghorn require larger structures(minimum 18.3 m span x 5.5 m rise).Large carnivores (wolf, grizzly bear,black bear, puma).

Larger mammals thatrequire structures of aminimum size for passa


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CrossingStructure Class

FunctionApp rox imate Dim ensi on

Range(Span x Rise)

Structure Examples Species ExamplesWildlife B ehaviora

Att rib utes

Class 4:Extensive Bridge(includesViaducts)

Allows ecosystemprocesses to permeatehighway such as wetlandwater flow, vegetationgrowth, and entirefloodplains. Provides

excellent horizontal visibilityfor animals requiringopenness.

Bridge extending over severalspans. Designed for each siteso dimensions vary. May allowmore sunlight under structurethan other types.

Viaducts are long bridges elevatedover the landscape in a series ofsmaller spans, often connecting pointsof equal height. Typically overwetlands, steep terrain.

Most species including wetlandspecies, birds, pronghorn.

Viaducts are particulargood for wary speciesincluding carnivores thmay not approach othestructures, or low mobspecies such as mollus

that require vegetationthroughout the structur

Class 5: WildlifeOverpass

Provides an open top andexpansive visibility of thehorizon for animalspreferring unenclosedspaces. Allows full sunlightand precipitation forvegetation growth. Mayallow small, sunlit waterfeatures.

Overpass structure for wildlifeto pass over roadway, as smallas 6.7 m (22) wide, butpreferably >50 m (164) wide.Large highway traffic tunnelscan be very long and providevast amounts of undisturbedhabitat.

Overpasses with soil and plantgrowth. A tunnel for highway trafficunder intact bedrock, soil andvegetation would function as a wildlifeoverpass regardless of the originalobjective of the structure.

All ungulates (pronghorn not provenyet), carnivores (bear, puma, forestcarnivores). Songbirds and insectsincluding butterflies.

Any species that requirnatural habitat, sunlighambient conditions formovement.

Class 6:SpecializedCulvert

Allows outsideenvironmental conditions tooccur within the entirestructure, including light,

temperature and moisture.

Current designs are smallculverts less than .5 m (24)span but could be largerstructures.

Trench drains and slotted culverts. Reptiles and amphibians Reptiles and amphibiathat require ambientoutside conditions tosurvive and disperse, o

orientate duringmovements.

Class 7: AerialBridge

Provides an aerial passagefor animals that typically donot descend below treecanopy to ground.

Adequate to cross all trafficlanes. May be connected totrees in the median.

Treetop rope bridges, or modified wireor metal structures. Towers mayfunction the same way for somespecies (such as flying squirrels).

Squirrels, arboreal rodents,opossum, monkeys. Potential forinsects and plants.

Species that move throthe canopy rather than the ground surface.

Wildlife Fence Functions to barrier accessto the roadway and to divertthe animals towards asuitable crossing location.

Dimensions vary by targetspecies from small concrete orpolymer curved structures afew centimeters in height, to 2m page wire mesh for high-

jumping mammals.

Types vary greatly but can bedistinguished from standard right-of-way fencing which is primarily onlyeffective for livestock. Concave orlipped concrete walls; buried smallmesh wire; 2 m page wire.

All animals, including some birds,can be effectively barriered from theroadway with fencing designed tomatch their physical and behavioralcharacteristics.

Wildlife tend to have 4types of fence avoidanbehaviors: Pushing,digging, climbing, or

jumping.

May 28, 2010 version-- Innovative Approaches to Wildlife and Highway Interactions. Table modified from NCHRP 25-27 Evaluating the Use and Effectiveness of Wildlife Crossing S


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and meso mammal species in the Park, from grizzly bear and elk to lynx (Clevenger and Waltho 2000, 2005, Clevenger et al. 2001). Wildlife use has been found to be dependent onan animal to see across the passage to where it connects to, vegetative cover, lack of human use, and fencing to guide the animals to the passage. Overpasses have also been useground pipelines, with anecdotal evidence of caribou, moose, black bear and coyote use.

Figure 1. Number of wildlife crossings within each one/tenth of a meter height class.

wildlifecrossingstructuretypesbyfunctioniawhi.pdf

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