Modified pipe or box culvert that allows a watercourse and/or drainage to flow underneath the infrastructure and includes adaptations to facilitate terrestrial wildlife crossing. These often include dry ledges or shelves to provide dry passage, which are connected to adjacent habitat. The design and landscaping at the entrances is particularly designed for the needs of wildlife, not only erosion control.
A viaduct that is designed or modified to maintain continuous riparian and aquatic habitats or other types of habitats, thereby facilitating wildlife movement. Usually combined with road perimeter fencing that funnels the animals to the structure. Viaducts constructed to allow crossing of paved roads with high traffic intensity or other uses that are not compatible with wildlife use do not qualify as wildlife crossings. See also ‘Viaduct’.
Agricultural (underpass or overpass)
Passageway across transport infrastructure to provide access to agricultural or forestry land, which may also be used by wildlife. See also ‘Forestry road’, ‘Cattle passage’.
Animals and plants introduced accidentally or deliberately into a natural environment where they are not normally found. Such species can become invasive in their new environment if they start spreading and causing serious damage to native species and ecosystems. See also ‘Invasive Alien Species’.
A passage constructed under an infrastructure specifically for the movement of amphibians. Often consisting of multiple small pipes or purpose-built tunnels in close proximity to each other. They require effective opaque fencing to intercept the amphibians and funnel them to the crossing structure. Synonym: ‘Amphibian tunnel’.
A continuous structure erected alongside infrastructure, designed to prevent amphibians from crossing and directing them to a specific crossing point. See also Amphibian crossing.
See ‘Amphibian crossing’.
Animal Detection System (ADS)
Measure to alert drivers that a large animal is approaching the road. The system involves signs that emit flashing warnings, activated by large animal detection sensors. When an animal is detected, signs are activated warning drivers that animals may be on or near the road at that time.
Animal Vehicle Collision (AVC)
When an animal is hit by a moving vehicle. If the animal is a wildlife species also called ‘Wildlife Vehicle Collision’ (WVC). Synonym: Roadkill.
Generated and maintained, or at least strongly influenced by human activities.
Arboreal crossing structure
Wildlife crossing composed of rope, net or pole suspended above a road or railway from vertical poles or trees, for arboreal and scansorial species. While fencing would improve rates of use, fence designs have yet to be developed due to the climbing ability of the target species. Synonyms: ‘Tree top overpass’, ‘Canopy bridge’.
Measures such as project abandonment or infrastructure re-routing employed to avoid environmental impacts. See also 'Mitigation'.
Artificial water body fed by storm drains and surface runoff, where pollutants from the road can settle out or filter through reeds before being released into the wider drainage system.
Any structure that restricts or prevents the movement of flora or fauna.
The extent to which linear infrastructure features prevent, or filter animal movement. It is a combined effect of traffic mortality, physical barriers and avoidance, which together reduce the likelihood and success of species crossing infrastructure.
Study concept design in which data is gathered before and after infrastructure or infrastructure mitigation measures are constructed. This data from areas with infrastructure or mitigation measures (impact) is compared with data obtained from areas without infrastructures or mitigation measures (control).
Horizontal ledge in an earth bank or cutting constructed to ensure the stability of a steep slope. See also ‘Earth berm’.
Best practice (BP)
A superior or innovative method, process or technique that contributes to the improved performance of an asset, activity or organization and is usually recognised as ‘best’ by peer organizations. See also ‘Good Practice’.
The richness among living organisms including terrestrial, marine and freshwater ecosystems and the ecological complexes of which they are a part. It includes diversity within and between species and within and between ecosystems as well as the processes linking ecosystems and species. Synonym: ‘Biological diversity’.
All organisms in a community or area.
Area which has a characteristic set of environmental conditions and is inhabited by a specific community of living organisms.
Defined area (e.g. habitat corridor or patch) which, due to the presence of linear transport infrastructure or other land use, has become a limiting factor to animal migration or dispersal.
Cuttings of woody vegetation (often left in a pile, or randomly scattered across infrastructure verges).
Vegetated strip of land intended to protect sensitive habitats, e.g. protected sites, from impacts such as pollution or disturbance from infrastructure.
Highway route that passes around a congested town, village or other sensitive/vulnerable area.
See ‘Arboreal crossing structure’.
Geographical area from which all precipitation flows to a single stream or set of streams (may also be termed as drainage basin, or watershed). In this handbook this may also refer to the area from which animals come to use a particular fauna passage.
Ditch transversal to the road covered by metal bars which allows cars to pass over but prevent cattle and also some other species of wildlife to cross it. Usually installed when roads create openings in fences to avoid animal access into the fenced area.
See ‘Drove road’.
The strip running down the centre of a dual carriageway or motorway (sometimes vegetated), which separates traffic flowing in opposite directions.
Cuttings from herbaceous vegetation.
Cluster (roadkill cluster)
Road stretches with aggregations of animal vehicle collisions or road kills, stretches with a greater number of occurrences than would be expected by chance. Synonym: ‘Hotspot’. See also ‘Animal vehicle collisions’.
Assemblage of interacting species living in a given location at a given time.
Measure or action taken to compensate for a residual adverse ecological effect which cannot be satisfactorily mitigated. See also 'Mitigation'.
See ‘Ecological connectivity’.
See ‘Ecological corridor’, ‘Transport Corridor’.
Designated or recognised place for people or fauna to cross from one side of a linear infrastructure to the other.
The intersection of two or more roads. Synonym: ‘Junction’.
Buried pipe or channel structure, that allows a watercourse and/or a transport infrastructure drainage feature to pass under infrastructure.
The increasing impacts resulting from the combination of effects from several projects or activities over a period of time. Their assessment is called cumulative effect assessment (CEA).
V-shaped excavation of the land enabling transport infrastructure to be placed below the surrounding land surface.
Actions aimed at recovering or increasing ecological connectivity in territories affected by existing transport infrastructure. It is also used to refer to actions to mitigate any of the effects that cause habitat fragmentation (road mortality, habitats disturbances, etc.).
A wall built to prevent the sea or a river from flooding an area, or a channel dug to take water away from an area. Synonym: ‘Dyke’.
Ecological process that involves the movement of an individual or multiple individuals away from the population in which they were born to another location, or population, where they will settle and reproduce.
The system of drains, pipes and channels devised to remove excess water (surface or subsurface) from an infrastructure surface.
Traditional path for the movement of livestock that form reticular networks across regions. In some countries (i.e., Spain, Italy) they are legally regulated and protected. Synonym: ‘Stock route’, ‘Drover track’.
Road with two lanes of traffic moving in opposite directions on either side of a central reservation.
A constructed mound of earth, usually along a road or railway, to provide a visual screen or absorb sound. See also ‘Berm’.
See ‘Landscape bridge’.
Items of the infrastructure that have an ecological value. It includes wildlife mitigation measures preventing impacts on wildlife and enhancing traffic safety such as fencing, fauna passages, screens, adapted illumination and wildlife traffic signs. Drainage systems, road verges and other green areas associated with the infrastructure, managed in a way that supports wildlife conservation are also included.
Parameter of landscape function which measures the processes by which sub-populations or organisms are interconnected into a functional demographic unit. The concept can also encompass other processes such as flow of water or nutrients. It is based on the state of structural landscape features being connected, enabling access between places via a continuous route of passage. Synonym: ‘Connectivity’.
Landscape structures of various size, shape and vegetation cover, differing from the adjacent areas, that maintain, establish or enhance landscape connectivity. They allow movements of animals, seeds, nutrients and other elements between discrete habitat patches. Hedgerows or verges are examples of ecological corridors (natural and artificial) that can act as interconnecting routes permitting the movement of species across a landscape and increasing the overall extent of habitat available to individuals. Synonym: ‘Corridor’. See also ‘Transport corridor’.
System of ecological corridors, habitat core areas and their buffer zones which provide the network of habitats needed for the successful conservation of biological diversity at the landscape level.
Dynamic complex of plant, animal and micro-organism communities and their non-living environment, interacting as a functional unit.
Involves the ecological and evolutionary processes, including gene flow, disturbance, pollination and nutrient cycling.
Benefits provided to society by ecosystems. They are usually classified as provisioning (for example the production of food and water), regulation or maintenance (such as the control of climate, nutrient cycles…), and cultural, which includes the non-material characteristics of ecosystems that affect the physical and mental states of people.
Transitional zone between two habitats.
Distinct area with a recognisable set of characteristics relating to the soil, vegetation or water conditions. The ecotope represents the smallest land unit that makes up the landscape mosaic.
The portion of an ecosystem near its perimeter, where influences of the surroundings prevent the development of interior environmental conditions.
Effective mesh density
Metrics for quantifying the effective number of meshes per square kilometre, that is the density of the meshes. The effective mesh density value rises when fragmentation increases. See also ‘Effective mesh size’.
Effective mesh size
Metrics for quantifying the degree of landscape fragmentation, based on the probability that two randomly located points (or animals) in an area are connected and are not separated by a barrier (e.g. roads, urban area). The smaller the effective mesh size, the more fragmented the landscape. See also ‘Effective mesh density’.
Effective population size
The number of interbreeding adults in a population (smaller than the total population because it excludes juveniles, non‐reproductive and post‐reproductive individuals).
Artificial bank (made of packed earth or gravel) such as a mound or dike, constructed above the natural ground surface in a linear form and designed to carry a roadway or railway across a lower lying area.
A species confined to a particular region and thought to have originated there.
Procedure that ensures that the environmental implications of transport infrastructure development are taken into account before the decisions are made. Environmental assessment can be undertaken for public plans or programmes ('Strategic Environmental Assessment', SEA) or for individual projects, such as a motorway, an airport or a channel ('Environmental Impact Assessment' EIA).
Measure installed to prevent animals from becoming trapped by fences along infrastructure, e.g. badger gate, or built in the edge of a canal to enable animals to exit, e.g. escape-ramps. Synonym: ‘Fauna exit’.
Structure designed to facilitate the safe movement of wildlife across linear transport infrastructure, located over or under the infrastructure. It can be specifically designed for wildlife use or modified to combine wildlife crossing with other uses such as drainage and other. Synonym: ‘Wildlife crossing’.
A structure made of wire or other materials supported with posts that is put along linear transport infrastructure to keep animals out and eventually guide them to crossing structures. It is also installed on areas of land as a boundary to keep animals in.
Referred to the effect caused by the infrastructure which inhibits the movement of certain species or individuals. The scale of the effect varies between species and may even vary between sexes or age categories.
Modified pipe or box culvert that allows a watercourse and/or drainage to flow underneath the infrastructure and includes adaptations to provide particular conditions that allow fish to swim through.
Plant or bacterial life.
(Narrow) road built mainly for forestry purposes which may or may not have public access.
The breaking up of a habitat, ecosystem or landuse unit into smaller parcels.
Animals hunted for sport and food.
Fencing specifically for game species such as wild boar and deer. See also ‘Fencing’.
The transfer of alleles or genes from one population to another.
The level of variability of genetic data within a sample or population, commonly measured through metrics such as heterozygosity and allelic richness.
A methodology, process or technique that represents an effective way of achieving a specific objective, one that has been proven to work well and produce expected results, and is therefore recommended as a model or as a useful example. See also ‘Best Practice’.
The (rate of) change of a parameter between one area or region and another.
Green Infrastructure (GI)
A strategically planned network of natural and semi-natural areas with other environmental features designed and managed to deliver a wide range of ecosystem services. It incorporates green spaces (or blue if aquatic ecosystems are concerned) and other physical features in terrestrial (including coastal) and marine areas (European Commission, 2003). It is also defined as ‘an interconnected network of protected land and water that supports native species, maintains natural ecological processes, sustains air and water resources and contributes to the health and quality of life for communities and people’.
See 'Safety fence'.
Fencing built to lead wild animals to a dedicated crossing point. See also ‘Amphibian fencing’, ‘Fencing’.
Paved channel designed to carry runoff from the edge of infrastructure into the drainage system.
The type of site (vegetation, soils, etc.) where an organism or population naturally occurs - including a mosaic of components required for the survival of a species.
Habitat destruction due to progressive damage, loss or decline in quality.
Dissection and reduction of the habitat area available to a given species - caused directly by habitat loss (e.g. land-take) or indirectly by habitat isolation (e.g. by barriers preventing movement between neighbouring habitat patches).
The relocation of a habitat from one place to another usually to avoid destruction of the habitat by infrastructure development.
Habitats related to Transport Infrastructures (HTI)
Green areas associated with transport infrastructure and usually managed by transport authorities and stakeholders. These areas include verges, resting sites, water retention ponds and other drainage elements, as well as fauna passages. These areas are inhabited by many animals, plants and other organisms which find refuge, food or other resources and can potentially have either negative or positive effects on natural ecosystems and landscape surrounding the infrastructure.
Terrestrial plant living in a salty environment.
A close row of woody species (bushes or trees) serving as a boundary feature between open areas (often used in combination with or as an alternative to a fence).
A chemical application which kills weeds.
Major road, usually with two or more lanes in each direction. See also ‘Road’.
Hotspot (AVC hotspot/Roadkill hotspot)
The effect of an external factor on an organism, species or community which may result in wider consequences at the population level. Synonyms: ‘Effect’.
Measures of simple environmental variables used to denote some aspect of the state of the environment, e.g. the degree of habitat fragmentation.
Species indicative of (a) some current or historical environmental or historical influence (e.g. lichens can be atmospheric pollution indicators, and woodland ground-flora can be indicative of ancient woodland), or (b) a community or habitat type (e.g. some species can be used to classify invertebrate communities, or are indicative of particular habitats).
The system of communications and transport services within an area.
Infrastructure life cycle
The stages that an infrastructure asset passes through during its life cycle. These phases are: 1) Strategic Planning, including Transport Policy, Strategic Transport Plan and Project Plan (Transport Area or Corridor Delimitation); 2) Design, including Area or Route Selection, Concept Design, Procurement and Detailed design (also called Constructive Project); 3) Construction; 4) Operation and Maintenance and 5) Decommissioning.
Invasive Alien Species (IAS)
Animals and plants that are introduced accidentally or deliberately into a natural environment where they are not normally found, with serious negative consequences for their new environment. These species are subject to common action at a European Union level under the European regulation and included on the ‘List of invasive alien species of Union concern’. See also ‘Alien Species’.
Animals lacking a vertebral column, or backbone.
Edging (usually concrete) built along linear transport infrastructure to form part of the gutter. Synonym: ‘Curb’.
A species that plays a pivotal role in an ecosystem and upon which a large part of the community depends for survival.
Combination of landuse and vegetation cover.
The smallest functional element of the landscape.
Natural feature on the surface of the earth.
The total spatial and visual entity of human living space integrating the geological, biological and human-made environment. A heterogeneous land area composed of a cluster of interacting ecosystems that create a specific, recognisable pattern.
Large overpass, usually > 50 m wide (min. recommended width in Europe 80 m), constructed to provide connectivity between habitats on both sides of the infrastructure. Due to their width, a diversity of habitat types (e.g. vegetation or soil types) can be included. Usually combined with perimeter fencing that funnels the animals to the structure. The main difference to wildlife overpasses is width and vegetation cover. Synonym: ‘Ecoduct’. See also ‘Wildlife overpass’.
The variation and richness of landscapes in a region.
Each of the relatively homogeneous units, or spatial elements, recognised at the scale of a landscape mosaic.
To modify the original landscape by altering the topography and/or plant cover - this may include building earthworks to form new landscape structures.
Activity aimed at predetermining the future spatial usage of land and water by society. Synonym: ‘Spatial planning’.
Linear transport infrastructure
Road, railway or navigable inland waterway. Powerlines and pipelines are also included as they are designed for the transport of materials.
Road which is assigned permanent traffic priority over other roads.
In landscape ecology, the background habitat or land use type in a mosaic, characterised by extensive cover and high connectivity. See also ‘Mosaic’.
The strip of land separating the lanes of a divided road. Often vegetated with grass, shrubs and/or trees.
A set of local populations within an area, where typically migration from one local population to at least some others is necessary to sustain local population numbers. The metapopulation may have a higher persistence than the single local populations.
Small‐scale differences in habitat.
The regular, usually seasonal, movement of all or part of an animal population to and from a given area. Usually undertaken by some species in response to changing seasons or climatic events, such as rainfall.
Action to reduce the severity of, or eliminate, an adverse impact.
Form of transport (e.g. road, rail, air, shipping, pipeline, bicycle, etc.).
Combination of repeated observations and measurements taken over time, usually to assess the temporal change in a parameter or in response to a disturbance/intervention or to quantify the performance of a plan, measure or action against a set of predetermined indicators, criteria or policy objectives.
The pattern of patches and corridors embedded in a matrix (in this case, within a landscape). See also ‘Matrix’.
Major arterial road that features two or more traffic lanes of traffic moving in each direction, separated by a central reservation called ‘median’ and controlled entries and exits.
Pertaining to more than one 'mode' of transport.
Structure built over infrastructure with multiple functions or goals, including the movement of wildlife. Other uses include agricultural or forestry access, cattle passage, and recreational use. It may include modifications such as addition of strips covered by natural materials and vegetation, to encourage use by wildlife. Usually combined with perimeter fencing that funnels the animals to the structure.
Structure built below infrastructure with multiple functions or goals, including wildlife crossing. Other uses include drainage, agricultural or forestry access, cattle passage and recreational use. It may include modifications such as adaptation of the vegetation at the entrances or measures to avoid excessive pooling of water. Usually combined with perimeter fencing that funnels the animals to the structure.
Network of sites considered to have Community importance under the Habitats Directive 92/43/EEC or classified as special protection areas (SPAs) under the Birds Directive 79/409/EEC. Together, the SPAs designated by the Member States make up the European network of protected sites, Natura 2000.
Measure installed to reduce the dispersal of traffic noise in a certain sensitive area (e.g. wall, fence, screen).
Structure (including its approaches) which allows one linear transport infrastructure to pass above another.
A road which surface is made with asphalt, bitumen, concrete or tarmac. See also ‘Unpaved road’.
Tunnel under an infrastructure designed for use by pedestrians.
Any chemical application used to kill insects, rodents, weeds, fungi or other living organisms, which are harmful to plants, animals or foodstuffs.
Cylindrical water tight structure sunk into the ground to provide a passage (from one side of the infrastructure to another).
Functional group of individuals that interbreed within a given, often arbitrarily chosen, area.
Public-Private Partnership (PPP)
A cooperative system made up of two or more public and private organizations, typically involved in a long-term agreement.
The IUCN Red List of Threatened Species provides taxonomic, conservation status and distribution information on taxa that have been evaluated using a system designed to determine the relative risk of extinction. The main purpose of the IUCN Red List is to catalogue and highlight those taxa that are facing a higher risk of global extinction (i.e. those listed as Critically Endangered, Endangered and Vulnerable). Red lists of species also exist at the national level.
Re-establishment of forest by the planting of trees (may have commercial or ecological functions).
A geographical area (usually larger than 100 km2) embracing several landscapes or ecosystems that share some features, e.g. topography, fauna, vegetation, climate, etc. Examples include bio-geographic and socio-economic regions.
The process of converting an existing landscape surface into a designed form by undertaking earthworks, e.g. cutting, filling or smoothing operations.
The ability of an ecosystem to respond to a perturbation or disturbance by resisting damage and recovering quickly.
The process of returning something to an earlier condition or state. Ecological restoration involves a series of measures and activities undertaken to return a degraded ecosystem to its former state.
Forest situated by a riverbank or other body of water.
Concrete or tarmac public way for vehicles, humans and animals.
Linear surface used by vehicles plus any associated verges (usually vegetated). Includes the area of land immediately influenced by the road in terms of noise, visual, hydrological and atmospheric impact (normally within 50 to 100 m of the edge of the infrastructure).
See ‘Transport Ecology’.
The interconnected system of roads serving an area.
The vegetated area adjacent to roads, generally located outside the road shoulder.
Animals that have died as a result of collisions with vehicles on roads. See also ‘Animal vehicle collision’.
Area adjacent to the carriageway, generally includes the road shoulder and the road verge.
Junction where three or more roads join and traffic flows in one direction around a central island of land which is often vegetated.
A vehicle-resistant barrier installed alongside or on the central reserve of infrastructure, intended to prevent errant vehicles from leaving the designated corridor and thus limit consequential damage. 'Safety fence' (see below) is one example of a safety barrier.
Continuous structure (of varied material) erected alongside infrastructure designed to prevent errant vehicles from leaving the designated corridor and limit consequential damage. Synonym: 'Guard-rail'.
In landscape ecology, the spatial and temporal dimensions of patterns and processes.
Process for identifying content and extent of the information to be submitted to the competent authority under the EIA process. Scoping is mandatory for the SEA process.
Subsidiary road connecting a more major road with adjacent buildings or facing properties. Normally not a thoroughfare.
Waterway bank erosion protection (wooden, iron or concrete planks sunk vertically between the edge of the water and the embankment).
The linear paved strip at the side of a 'motorway' which vehicles are allowed to use during emergencies, and which is used by maintenance vehicles to access works. Synonym: ‘Hard shoulder’.
Road in which a single lane of traffic is flowing in each direction, with no barrier or median strip dividing them.
Road that is only as wide as a single vehicle, and thus does not permit the flow of two-way traffic.
A defined place, point or locality in the landscape.
Activity or measure aimed at preventing soil erosion on slopes (e.g. by covering the ground with vegetation, stones, concrete or asphalt).
Source - sink habitats and populations
Source habitats are areas where populations of a given species can reach a positive balance between births and deaths and thus act as a source of emigrating individuals. Sink habitats, on the other hand, have a non-sustaining birth-death ratio and are dependent on immigration from source populations.
See 'Land use planning'.
Ecologically suitable patch where an organism temporarily stops while moving along a heterogeneous route.
See ‘Drover route’.
Strategic Environmental Assessment (SEA)
The application of the principles of Environmental Impact Assessment to policies, plans and programmes at a regional, national and international level. See also ‘Environmental Impact Assessment.
System devised to remove water from the surface of the ground (or infrastructure) (see also 'Drainage').
A species or group of species that is the subject of a conservation or mitigation action or the focus of a study.
Taxon (pl. taxa)
Category in the Linnean classification of living organisms, e.g. species.
Pertaining to land or earth.
The top layer of soil that supports vegetation.
Areas which concentrate linear transport infrastructure, such as roads, railways, waterways or powerlines, and which may impede or facilitate movement across the landscape. See also ‘Ecological corridor’.
Science that seeks an understanding of the interactions between roads/railways/utility easements etc. and the natural environment, including wildlife, natural resources, land use and climate change. Synonym ‘Road Ecology’.
See ‘Arboreal crossing structure’.
Structure (including its approaches) which allows one linear transport infrastructure to pass under another.
A road not covered by any artificial material such as asphalt or concrete. See also 'Paved road'.
Works to improve the condition of the infrastructure to raise quality, safety and efficiency.
The strip of land (often vegetated) beyond the infrastructure surface itself, but within the infrastructure corridor.
Any animal characterised by a vertebral column, or backbone.
Long elevated bridge, typically supported on pillars, which carries a transport infrastructure over a valley or other similar low-level landscape area. The landscape below these structures can be designed to conserve or maintain continuous riparian and aquatic habitats, thereby facilitating wildlife movement. See also ‘Adapted viaduct’.
A navigable body of water.
Construction in a river or canal designed to hold the water upstream at a certain level.
Land or area containing high levels of soil moisture or completely submerged in water for either part or the whole of the year.
All wild animals, plants, fungi and bacteria collectively.
Linear-shaped area or feature of value in facilitating wildlife movement across a landscape. See also ‘Ecological corridor’.
Wildlife crossing point
A structure for wildlife to cross transport infrastructure safely and also a place where animals cross frequently over the carriageway with the consequent risk of collisions with vehicles. See also ‘Wildlife crossing structure’, ‘Fauna passage’.
Wildlife crossing structure
See ‘Fauna passage’. See also ‘Wildlife crossing point.
Fencing designed and erected specifically to prevent animals from gaining access onto infrastructure and to lead them to safe crossing points.
Structure built over infrastructure specifically to provide a safe crossing point for wildlife and, when possible, to connect habitats on either side above transport infrastructure. The surface is covered with natural materials and soil allowing vegetation growth. Other refuges for fauna can also be installed. Usually combined with perimeter fencing that funnels the animals to the structure. While similar to landscape bridges, they are narrower, limiting the extent to which different habitats and vegetation can be included on the structure.
Construction built under infrastructure in order to connect the habitats on either side or to provide a safe crossing point for wildlife. The surface is, at least partly, covered with soil or other natural material that allows the establishment of vegetation. Depending on underpass size, it can be used by small to large animals. Underpass types are predominantly bridges, arches and box/pipe structures. Usually combined with fencing. (Complemented by: Van der Ree et al. 2015).
Wildlife Vehicle Collisions (WVC)
See ‘Animal Vehicle Collision’.
A term used in economics to quantify the maximum amount of consumption possibilities that an individual is prepared to sacrifice in order to consume a particular good. In many research projects, such as valuation of various environmental assets, the purpose is to estimate WTP in terms of money.