Animals may also be attracted to the road surface. Reptiles like snakes and turtles sometimes bask on the warm asphalt of the road to regulate their body temperatures. These kinds of behavior increase the risk of mortality as they cause animals to spend more time around the road. Rates of mortality are closely linked with movement patterns, as more movement generally incurs a greater chance of coming into contact with a road.
Animals with large home ranges, such as Florida panthers with ranges of up to km 2 , have a high chance of encountering roads as they traverse such large distances. These patterns are often associated with reproduction, as when gravid turtles undergo migrations to seek out a site to nest.
Many reptiles begin dispersing immediately after hatching, which also results in mortality peaks. These specific factors that influence mortality can also result in demographic shifts in the population when particular segments of the population are killed. For example, aquatic female turtles make egg-laying migrations that males do not make, which puts them at a greater risk for mortality.
As a result, turtle populations near roads can become male-biased as females are differentially killed. In addition to causing direct mortality, roads can have a number of indirect impacts such as habitat fragmentation. This can result from either animals not being able to cross the road without being killed or through avoidance of the road.
For example, some snakes have been shown to turn around and not cross the road when they encounter it. Birds that typically fly short distances from one tree to the next may also be hesitant to fly across a large open space, which restricts their movements across roads. When roads create barriers to movement they can impact animal populations in many ways. One of these is through prohibiting gene flow. For example, in timber rattlesnakes, a study of genetics at hibernacula showed that in hibernacula that were blocked off by roads, genetic diversity was lower than in those that occurred across contiguous habitats.
Roads can disrupt the pheromone trail and make it difficult for males to follow the trails and find a mate. Animals may also suffer by not being able to access particular habitats. In times of drought, roads can prohibit animals from reaching water. As a result, they were relegated to suboptimal habitats where predation on their eggs was higher, which decreased reproductive success.
In addition to fragmenting habitat, constructing a road alters the habitat. When a road runs through a forest, it creates an edge habitat along the portion of the forest that fringes the road. This can have consequences for birds, as predation rates on bird nests are sometimes higher in edge habitats. This is because predators can prey on nests better in the edge, where the forest canopy offers less protection to nests.
In highly degraded wetlands, the edge of roads may be the only viable nesting habitat left available to these turtles. Frogs have also been shown to experience higher predation rates closer to roads. Hierarchical levels can be identified by a stronger set of interactions within a hierarchical level than among levels. These hierarchical levels correlate to scales, and each level has characteristic spatial and temporal domains; that is, each level see leaf, tree, or forest level in Figure has a characteristic turnover time and spatial domain.
Hierarchical levels can be identified in ecological systems, but how do they interact? The nature of ecological interactions at various scales has been the subject of much scientific debate.
The focus has been on the interaction between processes and their associated structures that operate for long periods and over large spatial scales and processes that are faster and smaller.
Because roads affect variables that change slowly, such as geological formations, soil composition, and topography, they often produce top-down effects. Examples of such interactions include disturbance dynamics, such as forest fires or forest-pest outbreaks Gunderson and Holling Peterson demonstrated how a road network can disrupt spatial patterns and succession in southern U. Other types of surprising ecological behavior appear to arise from such panarchical interactions.
The physical structure of the U. The replacement time of roads is on the order of multiple decades, although this value can vary as a function of road type. The presence of roads across the landscape generates a variety of effects and interactions with ecological systems.
The effects fall into three categories: 1 effects that are fixed in scale; that is, the domain of the change is fixed in space and time with sharp boundaries; 2 effects that generate or initiate cross-scale interactions; and 3 effects that constrain or limit cross-scale interactions.
In this context, cross-scale interactions are those that traverse hierarchical levels. Each of the categories is described in the following paragraphs. Many ecological effects of roads are spatially small. Most of the documented effects occur at the road-segment level, which includes the road, roadside, and a zone described as the effective road-impact zone Forman et al. Generally, the zone ranges from a few meters to a few kilometers, depending upon the type of impact.
Many effects are confined to the road and shoulder zone. Altered physical and chemical soil conditions from construction, management fertilization or salt applications , or vehicle exhausts are found primarily in a narrow zone around roads. Some of the effects on biota, such as changes to populations increased mortality or community composition, occur primarily within this zone or within an area of a few hundred meters perpendicular to the road segment.
Some road effects cross scales of space and time. These effects include the abiotic and the biotic components of ecological systems. One example is the set of effects on hydrological systems, where sediments, nutrients, and heavy metals are introduced into riparian systems. Changes in inputs have created shifts in biogeochemical cycles, resulting in changes in species distribution and abundance.
Another cross-scale effect occurs when roads serve as ecological corridors and increase dispersion. One example attributed to roads is the spread of exotic organisms, both plants, such as kudzu, and animals, such as armadillos Taulman and Robbins Many ecological effects of roads eventually influence structures and processes at longer and broader scales than first imagined.
The spread of kudzu or any other invasive organism is a good example of an unintended, broader scale effect. Originally intended as an ornamental vegetation cover for stabilizing steep roadsides, the vine has spread. Similar arguments could be made for the nutrients, such as nitrogen from automobile exhausts, that have been observed to spread via atmospheric transport and accumulate in wetland and estuarine areas.
Cumulative effects have been described in two ways. One type of cumulative effect is the cross-scale effect described in the previous paragraph. These effects accumulate over time, space, or both. They can manifest as a cumulative change in an ecosystem structure or function, such as the increase in the amount of heavy metals in soils adjacent to roadways or the increase in species or populations, such as scavengers that eat organisms killed on the roadway.
Spatial accretions occur as structures increase in distribution, such as the spread of kudzu. The other type of cumulative effect involves synergistic interaction among key structures or functions associated with a road.
For example, caribou migration in Alaska was differentially affected by the combination of roads and oil pipelines NRC The implications of the latter type of effect for assessment and environmental review are discussed in the next section on cumulative effects. The final set of effects occurs when roads decrease the scale of ecological structures or processes.
Often, they are barriers to landscape-scale phenomena. The restriction of wildlife migration or dispersion has long been recognized as a road effect. Fragmentation of populations due to roads is another such effect. Broad-scale disturbances, such as fire, that are critical to many types of ecosystems prairies in the Midwest and pine forests in the eastern and western United States are limited in spatial extent by roads that act as fire breaks.
In some fire-adapted ecosystems where fire is heavily managed, rules of smoke management restrict when and how prescribed fires may be set because of the need to prevent visual hazards on roads caused by the smoke.
Shifts in the timing and extent of fires can generate large-scale changes in ecosystems. Even though the awareness of the ecological effects of roads has grown steadily over the past few decades, only a small body of literature addresses cumulative effects associated with roads.
These factors accumulated to affect the habitat and behavior of animals, physically changed the environment next to the road, and increased access and social contacts among human communities. Caribou migration on and near roads, although they are gravel, is one example of a cumulative effect; roads with a parallel pipeline and those without a parallel pipeline had different migration patterns Forman et al.
In addition, new roads often are associated with development of residential, commercial, and industrial activities. In some cases, the roads are built to support the new activities and, in other cases, the roads lead to the additional development. Historically, most studies of road effects have been carried out at the project level, with local studies focusing on specific transportation effects. Collaborative research among multiple government agencies has been lacking.
States or provinces have had little coordinated formal data sharing to allow for information syntheses and analyses of effects at larger and perhaps more meaningful scales of evaluation. Defining the appropriate scale of research will depend on the ecological condition of interest. A watershed is one example of an appropriate spatial scale to assess water-quality issues. Transportation projects sponsored by the Federal Highway Administration FHWA and the Transportation Research Board TRB have stimulated and encouraged collaborative studies involving multiple state agencies with similar transportation problems that might be solved through large-scale ecological assessments and pooled-funding approaches TPF Pooled-funding projects often focus on specific information needs defined by the collaborative state transportation agencies, which frequently represent diverse environments across the continent.
Often, projects are not defined by appropriate scales or ecologically defined areas, such as specific eco-regions for example, the northern Rocky Mountains. Reports have called for nationwide assessments and national syntheses on how wildlife respond to highway barriers, for mapping habitat linkages and landscape connectivity at regional and national scales, and for means of standardizing roadkill data collection and analyses Evink Two reports Evink , TRB a highlight the need for more systems-level studies addressing long-term issues regarding re-.
As discussed above, these efforts have produced a substantial body of literature that documents the effects of roads and traffic on ecological conditions. However, almost no studies of ecological effects of roads have been conducted over long time periods multiple decades or at large spatial scales spatial windows above tens of kilometers.
Such studies should be a priority for research. Few, if any, studies directly address ecological effects of road density. The appropriate scale for research is not always known beforehand, and the ecological impacts of roads can go undetected if an arbitrary scale is chosen for the research.
Some multiscale studies have shown that roads affect ecological condition at much larger scales than previously thought. Therefore, multiscale studies can uncover the ecological effects of roads and the scale at which roads affect ecological condition. Finally, much of the research on the ecological effects of roads can be found in reports that may not have been peer-reviewed or commercially published. For example, committee members are aware of studies documenting the effects of roads on sediment production in reports from the state departments of transportation, the Army Corps of Engineers, and the World Bank.
Although included in some searchable databases, such as the Transportation Research Information Service, these reports are not included in scientific abstracting services for example, Cambridge Abstracts and, therefore, are generally less accessible to the academic research community. Future studies on the ecological impacts of roads should be published in the peer-reviewed venues.
Roads influence ecological conditions across a range of organizational levels and scales. A large part of the scientific knowledge of ecological effects of roads has been based on short-term studies focused on narrowly defined objectives and has generally been related to specific construction or planning needs.
As a result, more research is needed on ecological effects that occur over large areas or long periods. The ecological effects of roads are much larger than the roads themselves, and the effects can extend far beyond ordinary planning domains.
Few studies address the complex nature of the ecological effects of roads. For example, little is known about how roads impede access to foraging areas or key prey species, potentially resulting in cascading or other trophic effects.
Studies assessing ecological effects are often based on small sampling periods and, therefore, do not adequately sample the range of variability in ecological systems. More research should be directed at identifying the appropriate scale at which roads affect ecological conditions.
Information on the resiliency of biodiversity components to road-related disturbances is needed to better understand the effects of roads on ecological systems. Research on the local scale should continue, however, because the context of many transportation decisions is at the local scale with direct application, and studies that address the context are likely to be the most frequently used and have the largest influence.
All phases of road development—from construction and use by vehicles to maintenance—affect physical and chemical soil conditions, water flow, and air and water quality, as well as plants and animals.
Roads and traffic can alter wildlife habitat, cause vehicle-related mortality, impede animal migration, and disperse nonnative pest species of plants and animals. Integrating environmental considerations into all phases of transportation is an important, evolving process. The increasing awareness of environmental issues has made road development more complex and controversial.
Over the past two decades, the Federal Highway Administration and state transportation agencies have increasingly recognized the importance of the effects of transportation on the natural environment. This report provides guidance on ways to reconcile the different goals of road development and environmental conservation. It identifies the ecological effects of roads that can be evaluated in the planning, design, construction, and maintenance of roads and offers several recommendations to help better understand and manage ecological impacts of paved roads.
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Click here to buy this book in print or download it as a free PDF, if available. Do you enjoy reading reports from the Academies online for free? Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released. Get This Book. Visit NAP. Looking for other ways to read this? No thanks. Road System Page 62 Share Cite. Page 63 Share Cite. Page 64 Share Cite. Abbreviation: NA, not available.
Page 65 Share Cite. Page 66 Share Cite. Ecological Conditions and Scale. Page 67 Share Cite. Ecological Significance of Road Attributes.
Page 68 Share Cite. Page 69 Share Cite. Page 70 Share Cite. Road and Traffic Density. Page 71 Share Cite. Engineering Structures. Page 72 Share Cite. Hydrological and Geomorphological Changes. Page 73 Share Cite.
Chemical Characteristics. Page 74 Share Cite. Page 75 Share Cite. Air Quality. Page 76 Share Cite. Other Disturbances. Page 77 Share Cite. Local Climate Effects. Page 78 Share Cite. Page 79 Share Cite. Roads as Enhancers of Dispersal. Page 80 Share Cite. Page 81 Share Cite. Page 82 Share Cite. Habitat Effects. Page 83 Share Cite.
Page 84 Share Cite. Road Access with Secondary Effects. Page 85 Share Cite. Page 86 Share Cite. Page 87 Share Cite. Range of Occurrence of Effects. Page 88 Share Cite. Page 89 Share Cite. Page 90 Share Cite. Page 91 Share Cite. Cross-Scale Effects. Page 92 Share Cite.
Page 93 Share Cite. Scales of the U. Road System and Ecological Effects. Page 94 Share Cite. Cumulative Effects. Page 95 Share Cite. Page 96 Share Cite. Page 97 Share Cite. Page 62 Share Cite. Login or Register to save! Stay Connected! Affected Ecosystem Service. Chemical input from roads to water bodies. Degradation of water quality, bioaccumulation.
Water purification, pollution abatement. Increased temperature and rainfall. Fluvial dynamics, sediment transport, floodplain ecology. Flood and drought mitigation, nutrient cycling. Plant species composition natives and nonnatives. Nutrient cycling, soil fertility, seed dispersal. Habitat quality, wildlife mortality.
Density and composition of animal species and populations. Crop pollination, aesthetics, ecotourism. Ecological Condition. National or Regional Scale. Few a. Nonnative plants in roadsides and adjacent landscapes.
None a. BOX Aquatic Culvert Design Effects Salmon have evolved to negotiate waterfalls during both upstream spawning migrations and downstream juvenile passage to the sea.
Road Effect. Heavy metals. The main sources of these dangerous goods are vehicles both road users and maintenance.
During road construction and maintenance all vehicles on the site need to be serviced appropriately to ensure that there are no leaks. The economic cost of waste is an important reason why waste should be avoided. Poor waste management costs time and money. Examples are:. This can give rise to high costs at a later stage. Such costs can be avoided if the waste is managed correctly right from the start. These costs, when taken together, clearly demonstrate that it is beneficial to have a thoroughly thought-out strategy for waste management.
Road materials and road furniture can also be source of pollutants. The environmental impacts and amount of pollutants created depend on the type of materials involved. In addition the type, condition and wear resistance of the surface layer, the influence of water and traffic and a range of other factors all have influences.
Recycled materials and industrial by-products can bring new environmental contamination risks. Recycled materials may contain a number of pollutants for example heavy metals, oil and organic micro-contaminants, and others.
The use of these materials has to be considered very carefully therefore, and all have to be appropriately tested to assure that they are suitable as road materials.
These define, for example, the quality, specification, chemical and technical requirements for the materials as well as instructions for their testing. The guidelines also give advice on how to perform an environmental assessment, where the waste material can be used and where it cannot.
Modern bitumens used in asphalt pavements are designed to release very low levels of pollutants. A modern hazard that does arise from pavements is the wear of the pavement surface with studded tyres where they are allowed. This should not be an issue however on lightly trafficked low volume roads.
Old pavements containing coal tar on the other hand will generally need special care due to the particular chemical constituents of coal tar. Not all national waste legislations and environment assessments classify coal tar as a hazardous waste. If the particular legislation classifies coal tar as a hazardous waste recycling of the material will be more difficult. Some authorities prefer coal tar to be recycled rather than removal and treatment. For example in Sweden, the Swedish Transport Administration has published special guidelines for dealing with coal tar.
These offer several alternative options depending on the concentration of the compound PAH. The practice that has been shown to be best is to leave the asphalt containing the tar in the road structure and not to touch it at all. If it does need to be excavated out, then the guidelines give advice on how it should be handled. Each case will need to be dealt with carefully in accordance with the environmental best-practice of the country involved.
In Norway asphalt very seldom contains coal tar. This is because the road network in Norway is younger than, say, Sweden or Scotland. Roads in Norway have mainly been built after the Second World War when coal tar was not in general use. The properties of natural aggregates are a consequence of their mineralogy and heavy metal content. A common problem with aggregates in low-volume roads is dust.
Dust is generated from the unbound surface layers of gravel roads. Examples of road furniture are road signs, crash barriers, sign-posts and lamp-posts. Usually these are made of galvanized steel but they are still subject to corrosion. Zinc can be released into the environment through the use of de-icing salts and in addition the older types of paints may contain heavy metals. However, compared to heavily trafficked roads, the environmental impacts of road furniture on rural road networks are relatively minor.
Every road produces some impact on the environment. The construction phase is potentially the most damaging phase in this respect and measures should be taken as necessary to mitigate any impacts caused. Before this can happen the sources and movement routes of pollutants should be identified.
These define the three major parameters in mitigation. Mitigation methods can be carried out both ex-situ and in-situ. The options for dealing with the source of pollution are: prevention, avoidance and reduction. Prevention aims to stop the emissions of pollutants into the environment. A practical example of prevention is to forbid the use of de-icing agents in groundwater areas. Avoidance covers the special design procedures, such as re-routing the road alignment to avoid crossing an environmentally sensitive area.
Reduction is the last resort and should only be considered when the emissions cannot be stopped or avoided. An example of this is the reduction in the number of dangerous goods transports passing through a sensitive area.
The mitigation options for pollution pathways are interception the in-situ method or reorientation ex-situ. Interception means that the movement of the pollutant is contained such as in a detention pond or by a reactive barrier.
Reorientation means that the pollution is redirected along a new pathway. An example of this could be a waterborne pollutant being redirected along a waterproof drainage system for collection and treatment.
If any pollutants reach the specified limit level the only possible mitigation measure is remediation in-situ or compensation ex-situ. Compensation means economic or replacement measures.
In practice compensation means, for example, that some form of payment is made to the landowner whose land has been polluted. Remediation is normally only used when deleterious or adverse effects impact an environmental area. In practice this means that the areas with contaminated materials are replaced with new, clean material. The road operations which cause the most significant environmental impacts in the ROADEX countries are a de-icing and snow clearing in winter, and b the use of dust binders on gravel roads in summer.
These operations both aim to reduce slipperiness on the road to maintain its functionality. The following paragraphs consider ways by which road administrations can mitigate any impacts through actions, principles and policies. Note: Special protection measures may require to be taken on roads passing through important groundwater areas to protect the quality of the water.
These may even be necessary on low volume roads if the pumping station is situated close to the road. Ice and snow removal can be carried out either mechanically or chemically. The most popular de-icing chemical is sodium chloride NaCl. A minute quantity of potassium ferrocyanide is usually added to NaCl as an anti-caking agent to stop the salt grains binding together. Other de-icing chemicals that can be used are urea, calcium chloride and calcium acetate.
In low volume roads in Nordic countries the most common way for snow removal is mechanical methods and salt is not used on these roads. The main disadvantages of de-icing chemicals are that they can contaminate soils, groundwater and surface water. De-icing salts can also increase the mobility of heavy metals which accumulate at the sides of roads.
Salts make the road surface wet, which enables pollutants on the road surface to leak through any cracks down into the road structure and along road shoulders.
Sodium chloride increases the solubility of many heavy metals. Dusting and dust binding are common features on low-volume gravel roads where the wearing course material does not have enough fines to create suction. Dust binding is usually done chemically with salts like calcium chloride CaCl2 and magnesium chloride MgCl2. These salts have the same disadvantages as de-icing salts. The amount of dust bind binding chemical can be reduced by using enough good quality fines in the wearing course.
For instance in Finland crushed glacial moraine has been found to be a suitable wearing course with good dust properties. The risk of finding previously polluted soil is not particularly high, although it is conceivable.
A number of warning signals are however possible. Oily water in a ditch for example is a clear warning sign. The reason for the oil may be spillage from road operations, but it may also be due to existing old pollutants. The nose, or rather the sense of smell, is an excellent instrument for detecting pollutants. Care should be taken if the smell of oil, sulphur, etc.
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