Wildlife and Roads: Glossary

American Association of State Highway and Transportation Officials.
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)
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)
Combination of natural and/or man-made features that comprise the entryway to an overpass, underpass, bridge or similar structure.
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)
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 diagram
Bankfull Stage
The point at which a stream first overflows its natural banks during floodstage. (4)
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 diagram
Baseline 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)
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)
A support element transferring loads from superstructure to substructure while permitting limited movement capability. (5)
The shoulder of a paved road or ditch. (8) See diagram
Best 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)
A term sometimes used for wildlife overcrossings. See Crossing Structure (Wildlife), Overcrossing.
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.
A system of tension and/or compression compoments that provides strength, support, or stability to beam, truss, or frame structures. (2)
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)
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)
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)
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'.
Same as a viaduct; often constructed over wetlands. See Viaduct.
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)
A dam that divides a drainage course into two or more sections with reduced slopes. (8)
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)
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)
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)
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)
A natural or artificial channel usually carrying fluids, such as a water pipe, canal, or aqueduct. (3)
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)
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)
A measure of the carrying capacity of a stream or channel. (4) See Water Conveyance Structure.
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).
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 Metal
A form of mitigation applied to a specific problem.
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)
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.
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.
The highest point of the surface of a tangent traveled way in cross-section. (4)
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)
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.
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)
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)
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)
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 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.
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 Fence
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.
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.html
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)
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.
The vertical distance of a point above mean sea level or relative to another datum. (4)
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)
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.
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)
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)
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.
The human-caused or natural process whereby a species or population ceases to exist. (1) See Endangered Species, Threatened Species.
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)
See Barrier
As in "cut and fill"; any material that is moved or added to the existing terrain to raise its elevation. (8)
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)
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.
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.
Geometric Design
The arrangement of the visible elements of a road such as alignment, grades, sight distance, widths, slopes, etc. (4)
Geotechnical Engineering
The application of scientific methods and engineering principles in the acquisition, interpretation and evaluation of subsurface data to predict the behavior of the materials in the earth's crust. It encompasses the fields of soil mechanics, rock mechanics, geological engineering, geophysics and related fields such as pavement design. (4)
Main horizontal support beam, usually supporting other beams. (8)
(a) The profile of the center of the roadway or its rate of ascent or descent. (b) To shape or reshape an earth road by means of cutting or filling. (c) Arrange according to size. (d) Elevation. (4)
Grade Separation
Crossing of two highways, or a highway and a railroad, at different levels. (8)
(a) Construction of the earthwork portion of a highway. (b) Planing or smoothing the surface of various parts of a roadbed. (4)
Gravity Abutment Wall
A heavy abutment wall which resists horizontal earth pressure through its own dead weight. (5)
Green Bridge
A term sometimes used for wildlife overcrossings, particularly in Europe. See Crossing Structure (Wildlife), Overcrossing.
Gross Vehicle Weight (GVW)
The maximum total weight of a traffic vehicle. (2)
Ground Line
Natural grade level from which measurements for excavations are taken. The level around a structure to which fill will be placed to form a finished grade. (8)
A safety feature element intended to redirect an errant vehicle away form the approach embankment (guiderail). (5)
Guide Fence
See Diversion Fence
A group of related or unrelated wildlife or plant species that can be managed as a group because of similar habitat requirements.
The area a species needs for its basic life requirements, such as food, water, escape from predators, and reproduction.
Habitat Effectiveness
The degree to which a patch of habitat is able to support an animal or group of animals. Habitat effectiveness in an otherwise "good" patch of habitat can be reduced by high levels of human disturbance, long distances to other habitat patches or any other factors in the surrounding landscape that detract from the patch's ability to function as habitat. (1)
Habitat Fragmentation
The process by which habitats are increasingly divided into smaller units. Habitat fragmentation results in increased isolation of habitat patches, a loss of total habitat area and a more substantial loss of core habitat conditions. (1)
Habitat Modeling
The representation of animal habitat quality as related to animal presence or reproductive success. Habitat modeling is most often conducted using computerized Geographic Information Systems (GIS) and can provide maps of estimated habitat quality based on selected environmental parameters.
A wall or structure built at the end of a culvert to prevent earth from spilling into the channel. (4)
Headwater Depth
The total flow depth from the inlet invert of the culvert to the water surface at the inlet. Culverts may constrict the natural stream flow and cause a rise in the water surface at the culvert entrance. (4)
Vegetation that is nonwoody, such as leaves or moss. (4)
A slang term used to describe species of reptiles and amphibians. Herpetology is the study of reptiles and amphibians.
Hiding Cover
See Cover.
High Profile Arch
See Bottomless Culvert, Culvert
Horizontal Arch
A compressed circular culvert. Also called elliptical. See Continuous Culvert, Culvert.
(1) (Engineering) As applied to a bridge design, a dynamic increment of stress equivalent in magnitude to the difference between the stresses produced by a static load and those produced by the same loads applied dynamically. (2) (Biology) Adverse effects to species or habitat caused by management actions, such as highway construction removing important habitat.
In-roadway Barrier
A structure built flush with the travelway surface to prevent animals from crossing, primarily built on the same design as a cattle guard with sturdy bars over an excavated pit. Animal in-roadway barriers use design species' behavior and jumping abilities to design size of barrier, as cattle guards may be too small to be effective for many species. Also called cattle guard, deer guard
Inlet Control
A culvert operating under inlet control when the flow capacity is controlled by headwater depth, culvert cross section, and inlet edge configuration. (4)
An animal (bird, mammal or fish) that eats insects, or a member of the order of mammals that includes shrews and moles.
A system of interconnecting roadway in conjunction with one or more grade separations, providing for the movement of traffic between two or more roadways on different levels. (4)
Intermodal Transportation System
All forms of transportation, considered in a unified, interconnected manner. Includes the National Highway System, principal arterial roads, and facilities for transferring from one mode of transportation to another. Also includes public transportation, access to ports and airports, and programs that improve mobility for elderly persons, persons with disabilities and economically disadvantaged persons. (12)
The area common to two or more highways that come together at an angle. (4)
The lowest point of the internal cross-section of a closed conduit or channel. (4)
Island Biogeography
The study of the distribution of living things on fragments of habitat or islands. Much of the scientific theory relating to animal population dynamics in fragmented habitats was influenced by early studies of animal communities on oceanic islands. The primary concepts of island biogeography that have been applied to animal ecology in fragmented landscapes include species-area relationships (predicting that larger islands will support more species) and distance-colonization relationships (predicting that islands that are closer to other islands will be colonized by species from the nearby islands more often than islands that are far away). (1)
The degree to which animals are prevented from moving into a patch of habitat due to the landscape characteristics surrounding the patch. Habitat patches can be isolated because they are far from other similar patches or because barriers or strong filters to animal movement surround them. (1)
Jersey Barrier
A protective concrete barrier used as a highway divider or as a means of preventing access to a prohibited area. (7) Jersey barriers were first designed in New Jersey and the most common type resembles these originals. Since then most states have modified them to suit their specific purposes. A common type referred to in wildlife issues is the "Texas" barrier which is higher than the typical Jersey barrier and more difficult for wildlife to cross. See Barrier.
Land Bridge
A term sometimes used for wildlife overcrossings. See Crossing Structure (Wildlife), Overcrossing.
A relatively large area where the mix of local ecosystems and land uses is repeated in similar form. Landscapes are often referred to as forested, agricultural, urban or suburban landscapes. (1)
Landscape Connector
A term sometimes used for large wildlife overcrossings. See Crossing Structure (Wildlife), Overcrossing
Landscape Diversity
The variety of habitats, species and patterns of patches present within a landscape. (1)
Enhancing the natural features of the land through the design and use of vegetation and other materials. (4)
Level of Service
Levels of design or maintenance that correlates with the expected and desired speed and use of the road.
Linkage or Linkage Zone
A large segment of land that provides a suitable transit route for plants and animals as they cross from one inhabited area to another. See Connectivity, Corridor.
Lipped Wall
Wall with an extended top acting as a barrier or diversion, usually to small animals such as amphibians. See Barrier.
Live Load
A dynamic load that is applied to a structure suddenly or that is accompanied by vibration, oscillation, or other physical condition affecting its intensity. (2)
Live Stream
A streambed with flowing water. (3)
Low Profile Arch
See Bottomless Culvert, Culvert
The portion of a divided highway separating the traveled ways for traffic in opposite directions. (4)
Median Barrier
A longitudinal system used to prevent an errant vehicle from crossing the median of a divided highway. (4) See Jersey Barrier.
Metal Plate
Hot-rolled sheets or plate, corrugated, custom hot-dipped galvanized, curved to radius, assembled and bolted together to form pipe, pipe-arches and other shapes.
Preparatory work, such as movement of personnel, equipment, supplies and incidentals to the project site, which must be performed prior to beginning actual construction of a project. (12)
Some management or land use activities can cause an animal's death directly or indirectly. In relation to roads and highways, direct animal mortalities are usually associated with collisions with vehicles, whereas secondary (indirect) animal mortalities can be the result of increased levels of disturbance or exclusion from required habitat areas. (1) See Wildlife/Vehicle Collisions. (12)
Metropolitan Planning Organization - A policy/planning body in designated urbanized area (population 50,000 or more). Composed of local elected officials, appropriate state officials, and officials (or representatives of agencies that administer major modes of transportation in the area). All enhancement projects within MPO jurisdictions must be approved by that MPO.
Multibeam Girder
A precast, prestressed concrete member where the concrete deck is precast as an integral part of the member. (3)
Multiple Chamber Culvert
Box culverts arranged in a horizontal series.
(n.) A species that has not been introduced from somewhere else by humans. (adj.) Not introduced by humans. (1)
Neat Line
A line defining the proposed or specified limits of an excavation or structure. (3)
Nominal Dimensions or Weights
The numerical values shown on the drawings or in the specification as measurements of material to be used in the construction. (3)
One-Way Gate
A gate (or ramp) designed to allow passage for the design species in only one direction, so that it can leave a highway but have difficulty accessing it. See Escape Structure.
The characteristic of a passage structure related to the ability of an animal to see through the structure and not feel confined while within the structure. The Openness Ratio is calculated as height X width/length. (1)
Open Bottom Culvert
Same as Bottomless Culvert
Open Channel Flow
Open channel flow may be uniform or non-uniform, steady or unsteady and critical or sub-critical. Of these, non-uniform, unsteady, and sub-critical flow is the most common type of low in open channels. However, to facilitate hydraulic computations, steady, uniform or gradually varied flow is generally assumed. (4)
Operating Speed
The highest overall speed, exclusive of stops, at which a driver can travel on a given highway under prevailing conditions without at any time exceeding the design speed. (4)
Material beyond the neat line of an excavation that is removed in the process of excavation, usually by blasting. (4)
Overcrossing (Wildlife)
A grade separation structure designed to allow wildlife to cross over an intersecting highway or railroad. It is usually covered with vegetation. In the Wildlife Crossings Toolkit, wildlife overcrossing is the standardized term for any structure (except a highway tunnel) designed to allow animals to cross over traffic. Also called ecoduct, green bridge, land bridge, biobridge, wildlife bridge or overpass. The largest overcrossings may be called landscape connectors. Sometimes called an ecoduct, land bridge, green bridge, biobridge or wildlife overpass. See Crossing Structure (Wildlife), Tunnel.
In general, any load that is in excess of the design load. (2)
A term sometimes used for wildlife overcrossings. See Crossing Structure (Wildlife), Overcrossing.
a) A low wall protecting a sudden change in elevation. b) A low wall along the top of a dam or at the edge of a bridge deck. (8)
Passage Structure
See Crossing Structure (Wildlife).
Passing Lane
See Auxiliary Lane.
Passing Opportunity
A section of two-lane highway where the clear passing sight distance allows safe passing. (4)
Passing Sight Distance
Minimum sight distance on 2-lane highways that must be available to enable the driver of one vehicle to pass another safely and comfortably, without interfering with the speed of an oncoming vehicle traveling at the design speed should it come into view after the overtaking maneuver is started. (4)
A contiguous area with similar characteristics relative to the issues of concern. Patches may be defined differently depending on the questions being addressed, however a patch will be the contiguous unit of area within a landscape with similar conditions based on the problem being considered. (1)
Permeability (Landscape or Highway)
The ability of an animal to move through an area, including those with man-made structures such as highways. Areas with low permeability are difficult for an animal to move across and may be the result of inhospitable habitat conditions or the presence of barriers or filters. (1)
A substructure built to support the ends of the spans of a multiple-span superstructure at intermediate points between the abutments. (2)
A shaft like linear member driven into the earth through weak material to provide a secure foundation for structures built on soft, wet, or submerged sites. A bearing pile receives its support in bearing through the tip or lower end. A friction pile receives its support through friction resistance along its lateral surface. (2)
Pipe, Arch
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) (3), and forms a continuous circumference pipe that is not bottomless. Contrast with Arch Pipe, and see Circular Culvert, Culvert
Pipe, Clay
Pipe made of shale and fired clay; unglazed or glazed and vitrified, with or without bell. Used for field drains, edge drains, culverts, sewers, etc. (4)
Pipe, Concrete
Pipe made of concrete with or without steel reinforcement; used for culverts, sewers, etc. (4)
Pipe, Corrugated Metal (CMP)
Pipe fabricated from corrugated metal sheets, generally steel or aluminum alloy stock; used for culverts. (4)
Pipe, Corrugated Plastic
Pipe fabricated from corrugated plastic, generally Polyethylene (PE) or polyvinylchloride (PVC), and used for culverts. (4)
Pipe, Perforated
Pipe fabricated from metal plastic, or concrete with holes or slots on approximately ½ of the periphery and used as underdrains to drain off water trapped in the soil. (4)
Pipe, Slotted Drain
Corrugated metal pipe with reinforced longitudinal slots at the crown. Used for interception of sheet flow. The system provides an inlet, runoff pipe and grate in a single unit. Pipe can be perforated for use as an underdrain. (11)
Contract drawings that show the location, character, and dimensions of the prescribed work, including layouts, profiles, cross-sections, and details. (8)
Plastics are materials composed of long, chainlike molecules called high polymers. (9) These include but are not limited to polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS) and polyethylene (PE). Pipe made from corrugated plastic and used for culverts is generally polyethylene (PE) or polyvinylchloride (PVC). Smooth pipe without corrugations used for underdrains and downdrains is generally polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS).
In biology, any group of organisms belonging to the same species at the same time and place. (1)
Population Sink
Portions of a species geographic range where death rates exceed birth rates for local populations. (1) Sink populations are usually in poor habitat or have other impacts such as disturbance or high mortality. Populations of many species along highways are sink populations because of high mortality.
Precast Concrete
Concrete members which are cast and cured before being placed into their final position on a construction site.(5) See Cast in Place.
Profile Grade
The trace of a vertical plane as shown on the drawings and intersecting the top surface at the centerline of the proposed facility construction. (3)
Preliminary Engineering
All work necessary to advance a project from concept stage to award of contract. Includes scooping, planning studies, developing alternatives, environmental documentation, project design and preparation of all project plans and contract documents. (12)
Reasonably Close Conformity
Compliance with reasonable and customary manufacturing and construction tolerances, performing all work and furnishing all materials in "reasonably close conformity" with lines, grades, cross-sections, dimensions, and material requirements shown on the drawings, indicated in the specifications, or designated on the ground. (3)
Reinforced Concrete
Concrete where steel reinforcement is embedded so that the steel and concrete act together in resisting stress. (3)
Loss of species in a given location after the area has been cut off from exchange with neighboring areas. (1)
Snakes, lizards, alligators and turtles. See Herp.
Retaining Wall
A structure designed to restrain and hold back a mass of earth. (5)
Reverse Curve
A curve consisting of two arcs of the same or different radii curving in opposite directions and having a common tangent or transition curve at their point of junction. (4)
Right of Way
(1) Generally publicly owned land acquired for and devoted to transportation purpose, (4) under and adjacent to the highway.
Right of Way Line
Line marking the limit between land secured for public use and adjacent private property. (8)
Riparian Area
Riparian areas are plant communities contiguous to and affected by surface and subsurface hydrologic features of perennial or intermittent water bodies (rivers, streams, lakes, or drainage ways). Riparian areas have one or both of the following characteristics: 1) distinctively different vegetative species than adjacent areas, and 2) species similar to adjacent areas but exhibiting more vigorous or robust growth forms. Riparian areas are usually transitional between wetland and upland. (6)
Gabions, stones, blocks of concrete or other protective covering material of like nature deposited upon river and stream beds and banks, lake, tidal or other shores to prevent erosion and scour by water flow, wave or other movement. (5)
Road Template
The shape and cross-sectional dimensions of the roadway to be constructed as defined by the construction staking notes and the characteristics of the typical sections. (3)
The graded portion of a road between the intersection of subgrade and side slopes excluding that portion of the ditch below subgrade. (3)
Slang term used to indicate either the deceased product of animal/vehicle collisions, or the process of killing them. Other slang includes road pizzas or flattened fauna.
That portion of the right-of-way outside the roadway. (4)
Roadside Hazards
Potential roadside hazards for out-of-control vehicles. These may include embankments,ditches,trees, boulders, poles, side road intersections and narrow medians. (4)
Round Culvert
See Circular Culvert, Culvert
The size of the area under consideration for a given plan or project. Land management can range from the very broad-scale (such as when considering whether a project occurs within the range of a species of concern) to the very fine-scale (such as when considering whether a project will impact a particular tree being used for nesting by a sensitive species). (1)
(Engineering) The use of trees, shrubs, fences or other materials to obscure an undesirable view or noise. (4) (Biology) The use of screening materials to provide hiding cover for wildlife and to reduce sight distance. See Cover.
Section (in a drawing)
See Cross-section
Section 4(f)
Section 4(f) of the U.S. Department of Transportation Act. Requires that transportation projects avoid the use of publicly owned parks, recreation areas, wildlife and waterfowl refuges and historic sites of national, state or local significance unless there is "no prudent and feasible alternative". Does not apply to historic transportation facilities if the proposed work will not adversely affect the historic qualities associated with the facility. (12)
Sensitive Species
(1) A USDA Forest Service designation given by a Regional Forester for a species needing special management because of limited habitat or small population numbers. These species do not have legal status such as those listed as endangered or threatened under the Endangered Species Act, but they have protected status under Forest Service Policy. (2) Sometimes used less precisely to indicate species easily impacted by human activities.
Service Load
The vehicle live load used for design, which represents the maximum load level that can use the structure on a continual basis. (2)
Sheet Piling
Pile in the form of a plank driven in close contact or interlocking with others to provide a tight wall to resist the lateral pressure of water, adjacent earth, or other materials. (8) See Pile.
The portion of the roadway contiguous to the traveled way for accommodation of stopped vehicles for emergency use and for lateral support of base and surface courses. (4)
Side Slopes
Slopes along the side of the roadway identified by their distance from the traveled way, their slope rate and their height. (4)
Sight Distance
(Engineering) The length of roadway visible to the driver. (4) (Biology) The distance at which a specified proportion of an animal is visible, usually through screening such as vegetation. Most wildlife tend to want to keep some screening between them and a human or vehicle, so some species may approach a disturbance such as a highway only up to the point where they remain partially or completely concealed.
Slab Bridge
A bridge having a superstructure composed of a glue laminated timber slab or a reinforced concrete slab constructed either as a single unit or as a series of narrow slabs placed parallel with the roadway alignment and spanning the space between the supporting abutments. (5)
Sound Wall
See Barrier.
Span, Multiple (Bridge)
One or more intermediate support columns. See Single Span, Open Span, Multiple Span (Bridge)
Span, Simple (Bridge)
The span of a bridge or a structural element that begins at one support and ends at an adjacent support. No intermediate support columns (5) See Single Span, Open Span, Multiple Span (Bridge)
Span, Single (Bridge)
The span of a bridge rests on abutments with no intermediate support columns. Also called open span bridge.
The basic unit of taxonomic organization, indicating an interbreeding group of individuals with very similar characteristics of behavior, structure and physiology that pass on these characteristics to their offspring. Examples of species are white-tailed deer, mule deer, moose and elk.
Species Richness
The number of species within a defined area. (1)
A description of the technical requirements for a material, product, or service that includes criteria for determining whether these requirements are met. (3)
Spring Line
A point of contact between arch and footing. (3)
Squash Pipe
See Circular Culvert, Culvert
(1) A measure of distance used for highways and railroads equal to 1 kilometer or 100 feet (2) A precise location along a survey line. (3)
Statewide Transportation Improvement Program - A five-year multimodal capital improvement program. The STIP is developed annually through coordinated efforts by state, federal and local governments, tribal governments and the public. All enhancements projects must be included in the STIP to be eligible for funding. (12)
Strip Map
A map used to illustrate a long linear feature, such as a highway, over several pages.
Structural Frame
Load-bearing skeleton of a structure that resists all imposed and applied forces and loads. (8)
Structural Plate Corrugated Metal Pipe
Hot-rolled sheets or plate. Corrugated, custom hot-dipped galvanized, curved to radius, assembled, and bolted together to form pipes, pipe-arches, and other shapes. (11)
Soil prepared and compacted to support aggregate, paved surface, a concrete slab, or other construction. (8)
Substructure (Bridge)
All of the structure below the bearings of simple and continuous spans, skewbacks of arches, and tops of footings of rigid frames, together with the backwalls, wingwalls, and wing protection railings. (3)
Superstructure (Bridge)
The entire structure excluding the substructure. (3)
Surface Course
The top layer of a pavement structure, sometimes called the wearing course, usually designed to resist skidding, traffic abrasion, and the disintegrating effects of climate. (3)
Surface Transportation System
All elements of the Intermodal Transportation System excluding aviation. (12)
A binder for vegetative mulch. (3)
Transportation Equity Act for the 21st Century. The United States Highway Act for FY 1998-2003. (12)
Threatened Species
A species listed under the federal Endangered Species Act as being threatened with extinction throughout all or a significant part of its range. Threatened species are less endangered than species listed as 'endangered' and have a lower legal status. These species are rare and have certain legal protection for individuals and their habitats. See Endangered Species.
Transportation Planning (vs Transportation Project Planning)
Transportation planning is the large scale, long-term process that the FHWA uses to determine transportation needs. Transportation planning is not subject to NEPA. Transportation projects are the result of large-scale transportation planning and involve individual highway stretches with specific projects, such as a 15-mile realignment project. Transportation projects are subject to NEPA.
Traveled Way
The portion of the roadway for the movement of vehicles, exclusive of shoulders. (4)
A jointed structure having an open web construction so arranged that the frame is divided into a series of triangles with members primarily stressed axially. (2)
1) A small culvert of various types designed for amphibian passage. The term tunnel is not used in the Wildlife Crossings Toolkit because the term is not standardized. 2) A bored hole through a substantial amount of earth for a highway, allowing undisturbed soil and vegetation on top. See Circular Culvert, Crossing Structures (Wildlife), Overcrossings (Wildlife)
A short auxiliary lane on a one-lane road provided for the passage of meeting vehicles (3), or on highways used by slower vehicles to allow faster vehicles to pass.
Twinned highways have at least two lanes in each direction.
A crossing structure allowing animals to pass under traffic. Underpasses can be broadly categorized as either bridges or culverts. See Crossing Structure (Wildlife).
Vertical Curve
A curve on the longitudinal profile of a road providing for change of gradient. (4)
Viable Population
A population that contains an adequate number of individuals appropriately distributed to ensure a high probability of long-term survival without significant human intervention. (1)
Long multi-span bridge. See Causeway, Crossing Structure (Wildlife).
See Barrier.
The available width for the passage of water beneath a bridge. (5)
Wiggle or Wriggle Gates
Escape structures primarily for deer that consist of a narrow opening in a livestock fence that is blocked by a single post. Livestock can normally not wriggle through the tight corners, but smaller and more flexible deer can.
Unrestrained animals in their native habitat. Usually includes mammals and birds, and in the Wildlife Crossings Toolkit also includes reptiles and amphibians, but generally excludes fish.
Wildlife Bridge
See Crossing Structure (Wildlife)
Wildlife Crossing Structure
See Crossing Structure (Wildlife).
Wildlife Underpass/Overpass
See Crossing Structure (Wildlife).
Wildlife/Vehicle Collisions
Collisions between any wildlife species and vehicles, usually on highways. Normally this results in the animal's death as well as property damage and possible injury or death to people. A special category of wildlife/vehicle collisions are deer/vehicle collisions, often abbreviated DVC's.
Wing Wall
The retaining wall extension of an abutment intended to restrain and hold in place the side slope of an approach roadway embankment. (2)
Woven Wire
Woven with the wire reinforcement applied helically by means of a circular loom. (8)


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