Assessing and Managing the Ecological Impacts of Paved Roads (Free Executive Summary) http://www.nap.edu/catalog/11535.html Free Executive Summary ISBN: 978-0-309-10088-5, 324 pages, 6 x 9, paperback (2005) This executive summary plus thousands more available at www.nap.edu. Assessing and Managing the Ecological Impacts of Paved Roads Committee on Ecological Impacts of Road Density, National Research Council This free executive summary is provided by the National Academies as part of our mission to educate the world on issues of science, engineering, and health. If you are interested in reading the full book, please visit us online at http://www.nap.edu/catalog/11535.html . You may browse and search the full, authoritative version for free; you may also purchase a print or electronic version of the book. If you have questions or just want more information about the books published by the National Academies Press, please contact our customer service department toll-free at 888-624-8373. 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. Copyright © National Academy of Sciences. All rights reserved. Unless otherwise indicated, all materials in this PDF file are copyrighted by the National Academy of Sciences. Distribution or copying is strictly prohibited without permission of the National Academies Press http://www.nap.edu/permissions/ Permission is granted for this material to be posted on a secure password-protected Web site. The content may not be posted on a public Web site. Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 1 Summary There are 4 million miles of roads in the United States. One hun- dred years ago, roads were primarily unpaved and had half the number of miles of the present U.S. road system. As the system grew, roads be- came wider and more complex structurally to provide for more and heav- ier traffic. New construction technology and greater structural stability were needed to improve the road system. All phases of road development—from construction and use by ve- hicles to maintenance—affect physical and chemical soil conditions, wa- ter flow, and air and water quality. Roads alter habitats, increase wildlife mortality, and disperse nonnative pest species of plants and animals. At larger scales, roads affect wildlife migration patterns. In some cases, roads can also enhance roadside habitats for native species. The importance of integrating environmental considerations into all phases of transportation is emphasized in legislation. The Transportation Equity Act for the Twenty-First Century (TEA-21) of 1998 called for protection of the environment by initiating transportation projects that would improve environmental quality and support fuel efficiency, cleaner fuels, and alternative transportation. The act called for streamlin- ing procedures to reduce red tape and paperwork in transportation project reviews without compromising environmental protection. Consideration of environmental issues in road development has been an evolving process. The increasing awareness of environmental issues, regulatory changes, and new solutions have made road develop- ment more complex and controversial. Many believe that environmental protection can be compatible with streamlining the project approval process through effective planning and coordination. Suggestions on Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 2 Assessing and Managing the Impacts of Paved Roads how environmental and transportation goals can be better integrated have been developed by government agencies and nongovernmental organiza- tions. Approaches include more integrated planning and interagency coordination, consideration of alternative designs earlier in the planning process, and consideration of mitigation strategies, such as installation of wildlife crossings and native vegetation management. As the road sys- tem expands and construction and management require additional re- sources, more is understood about the impact of roads on the environ- ment, but much remains to be learned. To address these matters, better understanding of road ecology and improved methods of integrating that understanding into all aspects of road development are needed. Over the past two decades, the Federal Highway Administration and state transportation agencies have increasingly recognized the impor- tance of the effects of transportation facilities on the natural environ- ment. The importance of this issue was reflected by congressional action in Section 5107(b)(4) of TEA-21, which required the secretary of trans- portation to “study the relationship between highway density and ecosys- tem integrity, including the impacts of highway density on habitat integ- rity and overall ecosystem health, and to develop a rapid assessment methodology for use by transportation and regulatory agencies in deter- mining the relationship between highway density and ecosystem integ- rity.” Section 5107(d) of TEA-21 authorized the secretary to arrange for a study of this relationship by the National Research Council (NRC). In response, at the request of the Federal Highway Administration, the NRC established the Committee on Ecological Impacts of Road Density (see Statement of Task in Box S-1). This committee’s report attempts to pro- vide guidance on ways to reconcile the different goals of road develop- ment and environmental conservation. The term “road density” is frequently used to mean the average to- tal road length per unit area of landscape. However, roads also have widely varying widths; therefore, lane miles per square mile (or lane length per unit area) is a better measure of density because it takes into account the differences between, for example, multilane expressways and two-lane rural roads. The concept of road density was developed as a way of quantifying one aspect of a road network and is applicable at scales larger than a road segment. Road density may be appropriate for measuring the structure of some existing road networks (especially those few urban or rural systems in a rectilinear grid), but it is not the only measurable term that can be used to describe road pattern and structure. Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Summary 3 BOX S-1 Statement of Task A multidisciplinary committee will be established to review the sci- entific information on the ecological effects of road density, including the impacts of roads and highway density on ecosystem structure and functioning and on the provision of ecosystem goods and ser- vices. The committee will focus on hard-surfaced roads and will as- sess data and ecological indicators needed to measure those im- pacts. Cumulative effects will be considered. The proposed study will also provide a conceptual framework and approach for the de- velopment of a rapid assessment methodology that transportation and regulatory agencies can use to assess and measure ecological impacts of road density. To the degree that the committee can iden- tify documentation of their effectiveness, it will consider the potential ameliorating effects of measures that might avoid, reduce, or com- pensate for the effects of highways and highway density on the structure and processes of ecosystems. The committee will consider such questions as the following: 1. What are appropriate spatial scales for different ecological processes that might be affected by roads? 2. The importance of various ecological models and their appro- priateness to the analysis. 3. The applicability of various ecological indicators, such as those recently recommended by the National Research Council. 4. The degree to which the national, regional, and local environ- mental concerns expressed in such laws as the Endangered Species Act and the Clean Water Act are relevant to the ecological effects of roads. The study will focus on all classes of hard-surfaced roads. The committee will consider and describe as possible the various attrib- utes of roads that have ecological significance, such as how the right-of-way is managed, surface composition, and the presence or absence of structures such as overpasses and underpasses. It will consider the importance of the pattern of road layout on ecological systems. It will not address global or regional climate effects, since they are being studied under other initiatives. However, local climate effects are appropriate in the scale of individual project design, con- struction, and use, and are directly related to ecosystem perform- ance in both long- and short-term contexts. Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 4 Assessing and Managing the Impacts of Paved Roads There are cases in which the meaning of the term “road density” is clear, but often it may be difficult to make useful comparisons between the ecological effects of different types of road networks. For example, several two-lane roads that have little traffic versus fewer, eight-lane roads that are heavily traveled. Therefore, the committee focused on variables that contribute to density, such as highway length and portion of land covered, rather than strictly on density, and used the broader con- cept of “scale” for evaluating environmental effects. The committee focused on the ecological effects of federally funded paved highways in urban and rural locations. The committee did not focus on urban street networks, and no consideration was given to the ecological effects of unpaved roads, such as those found in federal for- ests, wilderness areas, wetlands, parks, and farms, or the ecological ef- fects of state and local roads. The committee did not address global or regional climate effects, such as how potential climate changes might affect the interactions of organisms and the environment associated with roads and vehicles or how roads and traffic might influence climate. However, local climate interactions with road ecology are considered in this report. Developing policy choices to balance mobility, economic growth, and environmental protection goals has been important and challenging for more than 50 years. Although the committee was not charged to evaluate such policy choices, it identified the ecological effects of roads that can be evaluated in the planning, design, construction, and mainte- nance of roads. The committee did not address human ecological fac- tors; nonecological factors, such as safety; efficient movement of vehi- cles; or protection of farmlands, publicly owned recreation lands, and scenic, historic, and cultural areas. The committee also did not address such factors as urban sprawl or suburban growth; project costs; state- wide, regional, and local planning goals; and the economic viability of the communities of users. ECOLOGICAL EFFECTS OF ROADS Perhaps the most noticeable ecological effect of roads is direct, ve- hicle-related mortality (animals killed by collisions with vehicles). Al- though it is not the most threatening effect of roads for most species, mortality can reduce wildlife-population densities and ultimately affect Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Summary 5 the survival probability of local populations, including endangered or threatened species, such as the Florida panther and grizzly bear. In addi- tion to vehicle-related mortality, roads―acting as barriers to wildlife movement—may affect wildlife-population structure by disrupting breeding patterns or impairing reproductive success because they can fragment and isolate populations. In extreme cases, the resulting limita- tion of gene flow could result in local extirpation of a species. Properly designed mitigation measures, such as wildlife-crossing structures, can facilitate wildlife movement across roads and reconnect isolated popula- tions. Fish movement can also be blocked by road-crossing structures, such as culverts (usually a large pipe under a road where it crosses a stream) that are improperly designed or not present at all. Some fishes avoid moving through culverts, possibly because of the increased speed of the water flow, even if there are better habitat conditions on the oppo- site side. Reluctance to move, for example, downstream, could contrib- ute to isolating upstream populations and, in some cases, localized extir- pations. In evaluating the ecological effects of roads, it is important to con- sider the physical, socioeconomic, and legal context, as well as the eco- logical context. Each has spatial and temporal dimensions. The term “road-effect zone” means the distance from a stretch of road or road seg- ment that ecological effects can be detected. The road-effect zone is usually asymmetric extending outward on either side of the road, with varying zone boundaries. The effect of distance varies, depending on the species, location, and disturbance type. For example, animals avoid roads by a distance that increases with increasing traffic volume, and that distance varies by species. Noise from high-traffic-volume roads reduces the breeding densities and distribution of many bird species within a 40- to 1,500-m zone. Increased traffic and road density negatively affect aquatic habitats and the species that depend on them. For example, wet- land species diversity is negatively correlated with paved roads up to 2 km away. Other disturbances, such as heavy metals and chemical pollu- tion, can degrade habitat quality in the road-effect zone up to 100 m and 200 m, respectively. Vehicle-generated pollutants (such as nitrogen ox- ides, petroleum, lead, copper, chromium, zinc, and nickel) are the pri- mary pollutants associated with road use. Along with pollutants from spills, litter, and adjacent land uses, they accumulate on impervious roads and enter waterways via surface runoff or atmospheric deposition. Run- off contaminated with road salt can damage vegetation and potentially Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 6 Assessing and Managing the Impacts of Paved Roads cause a shift in plant community structure when salt-sensitive plant spe- cies are replaced by less-sensitive species, such as cattails and common reed grass. Salt-related vegetation changes can also affect wildlife by adversely altering habitat, inhibiting road crossing by amphibian species, and causing behavioral and toxicological impacts on birds and mammals. Similarly, air pollution from vehicle exhaust (volatile organic com- pounds, nitrogen oxides, carbon monoxide, and particulate matter) can alter the composition of roadside vegetation, promoting a few dominant plant species at the expense of more sensitive species, such as ferns, mosses, and lichens. This effect can extend up to 200 m from multilane highways and up to 35 m from two-lane highways. The underlying topography, aspect (the direction a site faces or its exposure), geology, soils, ecological conditions, and land cover all influ- ence how a road affects the environment. For example, the environ- mental effects of a road that does not cross a river are different from the effects of one that crosses a river several times in a few kilometers. New patterns of water runoff can develop as the local topography is altered. Aspect can influence how quickly snow and ice melt off the road and adjacent surfaces. Original topography, geology, and soils often dictate the road path and provide construction constraints or opportunities. The environmental effects of a road also depend on the prevailing land cover and use, such as wildlands, wetlands, agricultural lands, or a river valley versus a ridge. In fire-prone landscapes, a road can serve as a firebreak if the road is wide enough or as a source of fire initiation if access to the surrounding environment is increased. Ecological productivity is influenced by roads. The roadside be- tween the paved road and prevailing land cover often has lower produc- tivity and different composition than the surrounding landscape (espe- cially for roads through forests). The native habitat conditions of a road- side are frequently altered, but when the surrounding landscape is greatly altered by development, roadsides can include some of the last remaining habitats, especially for certain native plant species and some insects, birds, and small mammals. Roadside areas can also facilitate the estab- lishment of nonnative plants transported by vehicles, among other mechanisms, including the clearing of land during road construction. Biodiversity along roads typically is different from that in the surround- ing landscape. Plants along roads must survive vehicular pollution, ex- posure to bright sunlight, dry soils, and regular mowing. Roadside plant- ings in the United States once consisted of grasses and herbs (often of European origin) known to thrive in stressful conditions. Now there is Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Summary 7 an effort to plant vegetation along many highways, some of which is se- lected because it is native to the United States (but not always from the local area). The linear pathways of continuous terrestrial or aquatic habi- tat adjacent to roads can serve as corridors for animal movement. Some animals are attracted to roadside vegetation, road kill (an animal that has been killed on a road by a motor vehicle), or the light and heat often as- sociated with roads, and other animals are deterred by disturbances in the road-effect zone. The ecological effects of building a road typically exhibit several time lags. Some effects of road construction are not realized until sev- eral months or even decades after a road is completed as nearby trees and other plants slowly die, although the most severe (condensed and sud- den) effects typically occur when construction begins. Vegetation rees- tablishment efforts may result in a quick pulse of plant growth after seed- ing and fertilization, but the new equilibrium of vegetation along road- sides usually takes some time to establish, particularly in locations with steep slopes, rocky or nonorganic substrate, or other conditions that en- courage roadside erosion. Although most of the current and foreseeable transportation pro- jects in the United States are along established roads, the increase in traf- fic volume on these roads and the selection of sites for new roads bring to the forefront the potential for new ecological impacts―and associated, often delayed responses of the environment. Understanding and Assessing Road Effects As described above, a great deal is known about the ecological ef- fects of roads, even though there is need for more and better information about cumulative, long-term, and large-scale effects. The available in- formation, much of it reviewed, summarized, and synthesized in this re- port, should be used in all stages of road building and maintenance, in- cluding planning. From planning through construction stages, ecological indicators are important in assessing road effects; however, determining the broader and cumulative effects of roads and their corridors also is important and often not captured by indicators. Ecological indicators are generally de- veloped to quantify ecological responses to a variety of factors. Several indicators have been proposed to measure or monitor ecological effects, and some of them are applicable to the effects of roads. Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 8 Assessing and Managing the Impacts of Paved Roads Ecological effects of roads at local scales (within a few kilometers of the roads) have been widely studied, documented, and understood, while effects at large scales are less documented and understood. More is known about the effects of bridges, overpasses, and culverts on flows of materials and organisms than about the effects of roads on larger pat- terns and processes, such as watersheds or migratory pathways. The lack of information at large scales is related to many factors, such as (1) legal and policy directives that guide what components of ecosystems must be considered; (2) planning and assessment practices that restrict scales; (3) limitations of data, indicators, and methods at broad scales; and (4) lim- ited financial and technical support for ecological investigations at large scales. CONCLUSIONS AND RECOMMENDATIONS CONCLUSION: Most road projects today involve modifications to existing roadways, and the planning, operation, and maintenance of such projects often are opportunities for improving ecological conditions. A growing body of information describes such practices for improving aquatic and terrestrial habitats. Recommendation: The many opportunities that arise for mitigat- ing or reducing adverse environmental impacts in modifications and re- pairs to existing roads should not be overlooked. Environmental consid- erations should be included when plans are made to repair or modify existing roads, as well as when plans are made to build new roads. CONCLUSION: Planning boundaries for roads and assessing as- sociated environmental effects are often based on socioeconomic consid- erations, resulting in a mismatch between planning scales and spatial scales at which ecological systems operate. In part, this mismatch results because there are few legal incentives or disincentives to consider envi- ronmental effects beyond political jurisdictions, and thus decision mak- ing remains primarily local. The ecological effects of roads are typically much larger than the road itself, and they often extend beyond regional planning domains. Scientific literature on ecological effects of roads generally ad- dresses local-to-intermediate scales, and many of those effects are well documented. However, there are few integrative or large-scale studies. Sometimes the appropriate spatial scale for ecological research is not Copyright © National Academy of Sciences. All rights reserved. This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Summary 9 known in advance, and in that case, some ecological effects of roads may go undetected if an inappropriate scale is chosen. Few studies have ad- dressed the complex nature of the ecological effects of roads, and the studies that have done so were often based on small sampling periods and insufficient sampling of the range of variability in ecological systems. Recommendation: Research on the ecological effects of roads should be multiscale and designed with reference to ecological condi- tions and appropriate levels of organization (such as genetics, species and populations, communities, and ecological systems.) Recommendation: Additional research is needed on the long-term and large-scale ecological effects of roads (such as watersheds, eco- regions, and species’ ranges). Research should focus on increasing the understanding of cross-scale interactions. Recommendation: More opportunities should be created to inte- grate research on road ecology into long-term ecological studies by us- ing long-term ecological research sites and considering the need for new ones. Recommendation: Ecological assessments for transportation pro- jects should be conducted at different time scales to address impacts on key ecological system processes and structures. A broader set of robust ecological indicators should be developed to evaluate long-term and broad-scale changes in ecological conditions. CONCLUSION: The assessment of the cumulative impacts of road construction and use is seldom adequate. Although many laws, regulations, and policies require some consideration of ecological effects of transportation activities, such as road construction, the legal structure leaves substantial gaps in the requirements. Impacts on certain resources are typically authorized through permits. Permitting programs usually consider only direct impacts of road construction and use on a protected resource, even though indirect or cumulative effects can be substantial (for example, effects on food web components). The incremental effects of many impacts over time could be significant to such resources as wet- lands or wildlife. Recommendation: More attention should be devoted to predict- ing, planning, monitoring, and assessing the cumulative impacts of [...]... thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Assessing and Managing the Ecological Impacts of Paved Roads Committee on Ecological Impacts of Road Density Board on Environmental Studies and Toxicology Division on Earth and Life Studies Transportation Research Board Copyright © National Academy of Sciences.. .Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 10 Assessing and Managing the Impacts of Paved Roads roads In some cases, the appropriate spatial scale for the assessment will cross state boundaries, and especially in those cases, collaboration and cooperation among state agencies would be helpful CONCLUSION: The methods and data used... volume and road capacity, mostly through widening of roads rather than construction of new corridors, have smaller but nevertheless important ecological effects compared with the creation of new, paved roads Copyright © National Academy of Sciences All rights reserved This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads. .. education and research, and recognizes the superior achievements of engineers Dr Wm A Wulf is president of the National Academy of Engineering The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public The Institute acts under the responsibility... This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html Copyright © National Academy of Sciences All rights reserved This executive summary plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html... with the Academy’s purposes of furthering knowledge and advising the federal government Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities The. .. understanding in a number of areas—how roads interact with different ecological structures and processes across scales of space and time; how the legal framework for evaluating ecological effects intersects with the scales of ecological features; and how ecological considerations can be integrated better into all phases of road development—from planning to use The compilation of current understanding of the. .. plus thousands more available at http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National... society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters Dr Ralph J Cicerone is president of the National... length As the road system changes, so does the relationship between roads and the environment With the increase in roads, more resources are going toward road construction and management More is also understood about the impact of roads on the environment To address these matters, a better understanding of road ecology and better methods of integrating that understanding into all aspects of road development . http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 2 Assessing and Managing the Impacts of Paved Roads. http://www.nap.edu Assessing and Managing the Ecological Impacts of Paved Roads http://books.nap.edu/catalog/11535.html 6 Assessing and Managing the Impacts of Paved Roads