Wildlife Crossings Toolkit GlossaryThis Glossary is a compilation of common terms used by engineers and biologists on highway issues. Numerous hydrological terms are included as well, because many of the places where wildlife can most effectively cross in structures are near watercourses. The Glossary’s purpose is to create a common understanding between
disciplines, so professionals can spend more time on innovative solutions and less time wondering what the other person is talking about.
Two simple summaries of terms used in highway applications are in the Summary of Crossing Structure Types , and the Typical Highway Cross-section Diagram. These two tools cover many of the structural terms used in the Wildlife Crossings Toolkit. Both are readily printable on 8 ½ “ x 11” printer paper for easy reference.
Numbers in parenthesis are references.
AASHTO
American Association of State Highway and Transportation Officials.Abutment
A substructure supporting the end of a single span or the extreme end of a multispan superstructure retaining or supporting an approach embankment. (5)
Also, a solid wall that counteracts the lateral thrust of an arch. (8) See Span.
Adaptive Management
The iterative process of designing and implementing management activities in a manner that allows the scientific basis for management plans to be rigorously tested. The primary objective of adaptive management is to develop a better understanding of the systems being managed and to apply that knowledge in a way that allows the manager to continue to learn and develop better management practices. (1)Amphibian
Frogs, toads, salamanders and newts. These animals require water to complete their reproductive life cycles. Amphibians are sometimes lumped with reptiles in a common slang term, ‘herps’. See Reptile, Herp.Angle of Repose
Angle to the horizontal at which construction material will no longer slide downward of its own accord. (8)Approach
Combination of natural and/or man-made features that comprise the entryway to an overpass, underpass, bridge or similar structure.Arch
A culvert section forming an arc of a circle (usually less than 180?) and having a natural substrate for its base, that is, a bottomless culvert (3). Types of arches include squash, elliptical, half-round and plate, and they can be high or low profile. See Culvert, Bottomless Culvert, Arch Pipe and contrast with Pipe-Arch.Arch Pipe
Open-bottomed pipe that usually has footings to anchor it and usually is assembled on site. See Bottomless Culvert. Contrast with Pipe-Arch.Auxiliary Lane
The portion of the roadway adjoining the traveled way for weaving, truck climbing, speed changing, or for other purposes supplementary to through-traffic movement. (4). Generally, those unfamiliar with highway terminology would consider this “four lanes” or a passing lane.Average Daily Traffic
The number of vehicles that pass a particular point on a roadway during a period of 24 consecutive hours averaged over a period of 365 days. ADT is a fundamental measurement of traffic that is used for the determination of the vehicle-kilometers (or vehicle-miles) of travel on the various categories of highway systems. (10)Average Highway Speed
The weighted average of the design speeds within a highway section when each subsection within the section is considered to have an individual design speed. (4)Backfill
Soil or rock placed behind and within the abutment and wingwalls to fill the unoccupied portion of a foundation excavation. (2)Back Slope
See Cut Bank. See Highway Cross Section diagramBankfull Stage
The point at which a stream first overflows its natural banks during floodstage. (4)Barrier
Barriers are natural or man-made diversion structures that prevent a plant or animal from moving across an otherwise permeable area. Barriers can be physical obstructions that physically prevent movement (such as walls or fences), or they can be behavioral obstructions that prevent movement due to a perception of danger or risk (for example, areas with substantial human activity or habitat transitions such as a forest edge). (1)Physical barriers include:
Fence-- Material strung between support structures at intervals. May be constructed from a variety of material including wire (smooth or barbed), woven wire, chain link, rails or plastic mesh.
Jersey Barrier– Solid concrete barrier used to influence traffic direction .
Wall - A solid wall made of concrete, brick or wood.
Lipped Wall – A wall with a flanged top edge acting as a barrier or diversion to small animals such as amphibians. Wall-ends may extend underground.
Sound Wall – A solid wall used to absorb or deflect highway noise. Made of brick, concrete, wood or sheet piling.
Electric—High tensile or braided rope carrying an electrical charge.
In-roadway Barrier—Support structures for vehicles built over a pit; similar to a cattle guard, used to prevent wildlife access across a break in fencing or other barrier. Also called deer guard.
Base Course
The layer, or layers of material of designed thickness placed on a subbase or a subgrade to support a surface course. (4) See diagramBaseline Monitoring
The initial set of measurements taken in ongoing monitoring, usually taken before a system is altered by some management activity. Baseline monitoring is often an important component of adaptive management. (1)Beam
Structural member supported at two or more points, but not throughout its full length, transversely supporting a load, subjected to axial load and flexure but primarily flexure. (8)Bearing
A support element transferring loads from superstructure to substructure while permitting limited movement capability. (5)Berm
The shoulder of a paved road or ditch. (8) See diagramBest Management Practice
A series of water quality protection practices and procedures approved or certified by the State water quality agency under the provisions of sections 319 and 402 of the federal Clean Water Act, as amended. (3)Biobridge
A term sometimes used for wildlife overcrossings. See Crossing Structure (Wildlife), Overcrossing.Biodiversity
The variety of life and its processes. Biodiversity includes the variety of organisms and processes at a continental or local scale, genetic differences within and between recognized groups of organisms, and the ecological and evolutionary processes which keep ecological communities functioning and allow them to adapt to new conditions. (1)Bottomless Culvert
A culvert that is discontinuous in profile and having a natural surface bottom. Profiles may be square, rectangular or a high/low profile arch. Materials include corrugated metal pipe, metal plate, precast concrete, cast-in-place concrete, wood and clay. Also called open-bottom culvert. See Arch, Box Culvert, Culvert.Box Culvert
A culvert with a square or rectangular cross-sectional profile having 4 sides, including a bottom. Sometimes a 3-sided culvert with an open bottom is considered a Box Culvert, however in this Wildlife Crossings Toolkit these are referred to as Bottomless Culverts. Made of precast concrete, cast-in-place concrete, corrugated metal, metal plate and wood. See Bottomless Culvert.Bracing
A system of tension and/or compression compoments that provides strength, support, or stability to beam, truss, or frame structures. (2)Bridge
A structure (usually over 20 feet), including supports, erected over a depression or an obstruction, such as water, a road, trail, or a railway, and having a floor for carrying traffic or other moving loads. (3) In the Wildlife Crossings Toolkit, a bridge is one of two basic types of underpasses for wildlife to cross under moving traffic; the other basic type is a culvert.Bridge Length
The overall length measured along the centerline of road to the back of abutment backwalls, if present. Otherwise, the end to end length of the bridge floor, but in no case less than the total clear opening of the structure. (3)Bridge Traveled Way Width
The clear width measured at right angles to the longitudinal centerline of the bridge between the bottom of curbs or, if curbs are not used, between the inner faces of parapet or railing. (3)Bulkhead
A retaining wall-like structure commonly composed of driven piles supporting a wall or a barrier of wooden timbers or reinforced concrete members. (5)Buttressed Wall
A retaining wall designed with projecting buttresses to provide strength and stability. (5)Camber
Slight convexity above the horizontal plane; in a beam, truss, or deck, to allow for self weight plus imposed load. Also, the amount of rise between the crown and one perimeter on a road or traveled surface. (8)Cast-in-place
The act of placing and curing concrete within formwork to construct a concrete element in its final position. (5) See Precast concrete.Cattle Guard, “Deer Guard”
Linear bars flush with the roadway surface built over an excavated pit, designed to use an animal’s fear of being caught in a pit to keep them off the road. While Cattle Guard is a commonly understood term, ‘Deer Guard’ seems to be almost universally in need of explanation, so in the Wildlife Crossings Toolkit it is called an ‘In-Roadway Barrier’.Causeway
Same as a viaduct; often constructed over wetlands. See Viaduct.Centerline
For a two-lane highway the centerline is the middle of the traveled way, and for a divided highway the centerline may be the center of the median. For divided highway with independent roadways, each roadway has its own centerline. (4)Chain Link Fence
Woven fence, normally made of steel wire and attached to posts and rails. (8)Channel (Watercourse)
An open conduit either naturally or artificially created which periodically or continuously contains moving water or which forms a connecting link between two bodies of water. River, creek, run, branch, anabranch, and tributary are some of the terms used to describe natural channels. Natural channels may be single or braided. Canal and floodway are some of the terms used to describe artificial channels. (4)Channel Stabilization
The protections of open channels from excessive erosion and scour by channel lining. Linings may be flexible, such as rock riprap and vegetation or of rigid concrete. (4)Check-Dam
A dam that divides a drainage course into two or more sections with reduced slopes. (8)Chord
In a truss, the upper and lower longitudinal members, extending the full length and carrying the tensile and compressive forces that form the internal resisting moment. (2)Chute
A steep, inclined open channel. (4) See Flume.Circular Culvert
See Continuous Culvert.
Clear Area
An area that is cleared of vegetation or obstructions to the clearing limits. See Clearing Limits.Clearing Limits
The limits of clearing as designated on the ground or on the drawings. (3)Clear Span
The unobstructed space or distance between support elements of a bridge or bridge member. (5)
Cofferdam
A cofferdam is an enclosed single or double wall-braced structure with walls sheeted with timber, concrete, or steel, and extending well below the bottom of excavation, when practical. Earthen or rockfill dikes, dams, or embankments are not considered cribs or cofferdams for this purpose. (3)Column
A general term applying to a vertical member resisting compressive stresses and having, in general, a considerable length in comparison with its transverse dimensions. (5)Conduit
A natural or artificial channel usually carrying fluids, such as a water pipe, canal, or aqueduct. (3)Connectivity
The degree to which an organism can move between habitat patches having similar characteristics. Connectivity is most affected by how far apart habitat patches are and if there are barriers or filters to movement between them. (1) See Corridor, Linkage Zone.Construction Survey
A survey executed to locate or layout engineering works. In highway construction application, this survey is used to set grading elevation stakes, reference points, slope stakes and other such control. (4)Continuous Culvert
An approximately round culvert unbroken (entire) in cross-section, and sometimes called a circular culvert. The lower portion may be covered with substrate so that it appears ‘bottomless’. Continuous culverts may be made of corrugated metal pipe, concrete, plastic and clay. Sometimes called ecopipes in Europe when used for badgers, or simply pipes. Continuous culvert types include:
Slotted drain culvert: Corrugated metal pipe with reinforced longitudinal slots at the crown (top) that allows sunlight or moisture to enter. Used for interception of sheet flow and can be used for amphibian passage. The system provides inlet, runoff pipe and grate in a single unit. Pipe can be perforated for use as an underdrain.
Pipe-Arch (squash pipe) culvert: A pipe that has been factory deformed from a circular shape such that the width (or span) is larger that the vertical dimension (or rise).
Elliptical (horizontal) culvert: A compressed circular culvert.Continuous Spans
A beam or truss-type superstructure designed to extend continuously over one or more intermediate supports. (2)Contour Grading Plan
A drawing showing an arrangement of contours intended to integrate construction and topography, improve appearance, reduce erosion, and improve drainage. (4)Contraction
The reduction in the cross-sectional area of a stream channel. (4)Control Survey
A survey made to establish the horizontal and vertical positions of a series of control points. In highway applications, a control survey is generally the first survey performed on a project. Other aspects of the surveying process base their measurements on the control points established during the control survey. (4)Conveyance
A measure of the carrying capacity of a stream or channel. (4) See Water Conveyance Structure.Corridor
a) (Engineering) A strip of land within which traffic, topography, environment and other characteristics are evaluated for transportation purposes. (4)
b) (Biology) A route that allows movement of organisms across an otherwise inhospitable landscape. Corridors may or may not provide all of the habitat characteristics required to support an individual over time, but do provide the habitat characteristics that allow an individual to move between suitable patches of habitat. For smaller, less mobile species, corridors may function as strips of habitat that provide for the flow of genetic material between larger patches of habitat over more than one generation. (1) See Linkage (Linkage Zone).Corrugated
Having a cross-section or profile comprising a regular series of repeated geometric shapes, most commonly semi-circular. (8)Corrugated Metal Pipe
See Pipe, Corrugated MetalCountermeasure
A form of mitigation applied to a specific problem.Cover
Any of several types of cover that wildlife require to stay alive and reproduce, including to stay warm or cool (thermal cover), to escape from enemies (escape cover), or to hide from perceived danger (hiding cover). Many animals will more readily cross an open area if hiding cover is available nearby to enable them to survey for danger before crossing. Cover is usually vegetation, but it can be structural such as boulders or other topographical features.Crest Vertical Curve
A vertical curve having a convex shape in profile. (4)Crib
A structure consisting of a foundation grillage combined with a superimposed framework providing compartments that are filled with gravel, stones, or other material satisfactory for supporting the structure placed on top of it. (2)Critical Length of Grade
That combination of gradient and length of grade that will cause a designated vehicle to operate at some predetermined minimum speed. (4)Critter Crossing
Slang for Wildlife Crossing Structure. A critter is a generalized term for animal. More specifically, the brochure created by the FHWA on wildlife crossing structures.Cross-Section
The transverse profile of a road showing horizontal and vertical dimensions. (4)Crossing Structure (Wildlife)
Any of several types of structures designed to allow safe passage of wildlife species across a road or highway. Passage structures can reduce direct animal mortality, improve highway safety and improve landscape permeability for the species of concern. (1)
These structures usually can be categorized as an overcrossing or an underpass.
Overcrossing: A grade separation structure designed to allow wildlife to cross over an intersecting highway or railroad. It is usually covered with vegetation. Overpasses primarily designed to serve wildlife species are denoted as Wildlife Overcrossings in this toolkit. Also called ecoduct, green bridge, land bridge, biobridge, wildlife bridge or overpass. The largest overcrossings may be called landscape connectors.Underpass: Animals pass under vehicles through a Bridge or Culvert.
Wildlife Underpass--Bridge: A bridge forms part of the roadway and is usually more than 20 feet long. Bridge types include:
Single Span Bridge – No intermediate support columns.
Multiple Span Bridge – One or more intermediate support columns.
Viaduct – A long multi-span bridge.
Causeway – Same as viaduct, often built over wetlands.Wildlife Underpass--Culvert: A culvert is covered with embankment around its entire perimeter. Small conduits for amphibians are sometimes called tunnels. The following are types of culverts based on cross-sectional profile:
Box Culvert:--Square or rectangular culverts with fabricated bottom.
Bottomless Culvert--Arch, square and rectangular culverts with natural substrate bottom. Sometimes called open-bottom culvert.
Continuous Culvert--Round, slotted drain, pipe-arch and elliptical culverts. Sometimes called ecopipe or simply pipe.
Crown
The highest point of the surface of a tangent traveled way in cross-section. (4)Culvert
A conduit or passageway under a road, trail, or other obstruction that may or may not be designed to convey water. (3) A culvert is generally used to divert a stream or rainfall runoff to prevent erosion or flooding on highways. In the Wildlife Crossings Toolkit, a culvert is one of two basic types of underpasses for wildlife to cross under moving traffic; the other basic type is a bridge. See Crossing Structure or specific type of culvert (Box, Continuous, Bottomless).
Cumulative Effects
The combined effects of all human activities on a defined area. Cumulative effects assessments investigate the collective impacts of all historic, present, and predicted human activities in an area. (1)Curb
A short barrier paralleling the side limit of the roadway to guide the movement of vehicle wheels and safeguard constructions and pedestrian traffic existing outside the roadway limit from collision with vehicles and their loads. (5) See Berm.Cut
Depth in which material is to be excavated as in “cut and fill”. (8)Cut Bank
Excavated bank from the ditch line to the top of the undisturbed slope of a road. (8)Curve Widening
A design feature that widens a highway on sharp curves to compensate for the fact that the rear wheels of a motor vehicle do not follow exactly in the track of the front wheels. (4)Dead load
The static load imposed by the weight of the materials that make up a given structure. (2)Deck
That portion of a bridge offering direct support for vehicular and pedestrian traffic. (5)Deer Guard
See In-roadway Barrier.Deer/Vehicle Collision
A special category of wildlife/vehicle collision that involves deer of any species. The most commonly considered wildlife/vehicle collision is with deer because this group of species is large enough to cause injury or death to humans, and usually property damage. The typical deer/vehicle collision ultimately results in the animal’s death.Design Capacity
Maximum number of vehicles that can pass over a lane or a roadway during one hour without operating conditions falling below a preselected design load. (8)Design Load
The loading compromising magnitudes and distributions of all loads used in the determination of the stresses, stress distributions, and ultimately the cross-sectional areas and compositions of the various portions of a bridge structure. (2)Design Species
For wildlife crossing structures, the species that is intended to be the primary user. Different species require specific types, sizes and siting of structures to accommodate differences in behavior and habitat use. See Ecological Structure.Design Speed
A speed selected for purposes of design and correlation of the geometric features of a highway and a measure of the quality of service offered by the highway. It is the highest continuous speed where individual vehicles can travel with safety upon a highway when weather conditions are favorable, traffic density is low and the geometric design features of the highway are the governing conditions for safe speed. (4)Design Stress
The stress produced in a structural member by the design loading. (2)Design Thickness
The total thickness of the pavement structure determined from the thickness design charts as adequate for a given total 18-ton equivalent single-axle loads soil strength value. (4)Design Vehicle Turning Radius
The turning radius of a design vehicle used to determine the minimum radius used in the design of turning and intersecting roadways. (4)Design Volume
Volume determined for use in design, representing traffic expected to use a highway. Unless otherwise stated, it is an hourly volume. (8)Dike
An embankment used to confine or control water, especially one built along the banks of a river to prevent overflow of low lands or to deflect water away from a bank. Also called a levee. (4)Dike, Spur
Relatively short embankments constructed at the upstream side of a bridge or culvert for the purpose of aligning flow with the waterway opening, and to move scour away from the structure. (4)Dike, Toe
Embankments constructed to prevent lateral flow from scouring the corner of the downstream side of an abutment embankment. Sometimes referred to as training dikes. (4)Dip (Low Water Crossing)
A road stream crossing designed to accommodate occasional flooding. The road grade is lowered to streambed level from bank to bank. (4)Dispersal
The movement of an organism from the area where it was born and reared (its natal home range) to an area that may provide the necessary habitat conditions for establishing an adult home range. For many species of animals dispersal is the period in which it will undertake its longest distance movement and during which it is most likely to encounter a variety of risks and inhospitable habitat conditions, including crossing highways. (1)Disturbance
Disturbance to wildlife is anything that causes them to deviate from their normal activities such that it makes it difficult to complete their life cycles. An example would be highway noise that discourages wildlife from approaching and crossing the road to reach foraging habitat.Diversion Fence
A fence or wall that funnels animals towards or away from a designated area. Examples are fences that funnel migrating deer towards an underpass allowing them to cross under a highway. Diversion fencing may also work to simply keep animals off the highway instead of diverting them to a crossing structure. Sometimes called a drift or guide fence.Drawings
Documents providing concise instructions for the construction of a facility. Drawings may include plan and profile sheets, cross-sections, diagrams, layouts, schematics, descriptive literature, illustrations, schedules, performances and test data. (3)Drift Fence
See Diversion FenceEcoduct
A term sometimes used for wildlife overcrossings, particularly in Europe. See Crossing Structure (Wildlife), Overcrossing.Ecological Structure
A structure that allows the natural functioning of an ecosystem to occur while meeting the objectives of the infrastructure feature. An example would be a high bridge that allows native vegetation, unsubmerged land along a streamcourse, and all native wildlife to pass under a highway without constraint.Ecology
The branch of science concerned with the relationship of organisms and their environment. (4)Ecoregion (Bailey)
A consistent approach to ecosytem classification and mapping at multiple geographic scales developed by the USDA Forest Service. Maps and descriptions of each of the four levels of the ecological units can be found at http://www.fs.fed.us/land/ecosysmgmt/ecoreg1_home.htmlEcosystem
A dynamic complex of plant, animal, fungal, and microorganism communities and their associated nonliving environment interacting as an ecological unit. (1)Ecosystem Approach
A strategy or plan to manage ecosystems to provide for all associated organisms, as opposed to a strategy or plan for managing individual species. (1)Ecosystem Management
Any land-management system that seeks to protect viable populations of all native species, perpetuate or mimic natural-disturbance regimes on a regional scale, adopt a planning timeline of centuries, and allow human use at levels that do not result in long-term ecological degradation. (1)Effectiveness
A structure is effective when it meets the intended management objectives. In the Wildlife Crossings Toolkit, an effective structure is able to provide passage or reduce vehicle-caused mortality for the species it was designed to serve.Effectiveness Monitoring
Monitoring to determine if some human activity is having the desired effect. (1)Electric Fence
Electrified stands that give grounded animals an intense but not injurious shock when touched. Barrier fences can be two types: high tensile wire or braided rope.Elevation
The vertical distance of a point above mean sea level or relative to another datum. (4)Embankment
A barrier comprised of earth and constructed above the natural ground surface to carry a road or to prevent water from passing beyond desirable limits; also known as a bank. (5)Empirical
Developed from experience or observations without regard to science and theory. (4)Endangered Species
A species listed under the federal Endangered Species Act as being endangered with extinction throughout all or a significant part of its range. These species are rare and have certain legal protection for individuals and their habitats. See Threatened Species.Endrun
Animals crossing a highway at the ends of a barrier instead of by way of a crossing structure.Energy Dissipater
A riprap basin or concrete structure placed at the outlet end of a culvert to dissipate the stream energy and reduce scour and erosion. (4)Environment
The totality of man’s surroundings—social, physical, natural, and manmade. (4)Environmental Design
The location and design of a highway that includes consideration of the impact of the facility on the community or region based on aesthetic, ecological, cultural, sociological, economic, historical, conservation, and other factors. (4) See Context Sensitive Design.Equivalent Single-Axle Load (EAL)
The effect on pavement performance of any combination of axle loads of varying magnitude equated to the number of reference single-axle loads required to produce an equivalent number of repetitions of an 18-ton single axle. (4)Escape Cover
See Cover.Escape Structure
A structure (usually an escape ramp, funnel fence or one-way gate) designed to allow an animal trapped by a diversion fence to exit the roadway. They are designed to allow passage in only one direction so animals can escape the highway but have difficulty getting onto the highway.
Expansion Joint
A joint designed to provide for expansion and contraction movements produced by temperature changes, loadings or other forces. (5)Expressway
A multilane, divided highway designed to move large volumes of traffic at high speeds under free-flow conditions. Expressways have full control of access with grade-separated interchanges. (4) See Grade Separation.Extinction
The human-caused or natural process whereby a species or population ceases to exist. (1) See Endangered Species, Threatened Species.Extirpation
Local extinction; a species or subspecies disappearing from a locality or region without becoming extinct throughout its range. (1)Factor of Safety
A factor or allowance predicated by common engineering practice upon the failure stress or stresses assumed to exist in a structure or a member or part thereof. Its purpose is to provide a margin in the strength, rigidity, deformation, and endurance of a structure or its component parts compensating for irregularities existing in structural materials and workmanship or other unevaluated conditions. (2)Federal-aid Projects
Activities funded solely or partly through the Federal Highway Administration. Applicants must share in project costs by providing “matching funds”. (12)Fence
See BarrierFill
As in “cut and fill”; any material that is moved or added to the existing terrain to raise its elevation. (8)Filter
A landscape feature that reduces an animal’s ability to move across an area. Filters are partial barriers to the movement of animals or other organisms. (1)Footing
The enlarged, lower portion of a substructure which distributes the structure load either to the earth or to supporting piles; the most common footing is the concrete slab. “Footer” is a local term for footing. (5)Foraging Habitat
Habitat for the purpose of finding food.Foundation
The supporting material upon which the substructure portion of a bridge is placed. (2)
Functional Classification
The grouping of individual roads in a road system according to their purpose and the type of traffic they serve. (4)Funnel Fence
A type of escape structure that uses a narrow entrance to discourage large animals from entering the ends of barrier fencing, and allows escape several meters away from the ends through one-way gates or other structures.
