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

NATIONAL RESEARCH COUNCIL
OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS
Washington, D.C.
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Assessing and Managing the Ecological Impacts of Paved Roads 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 NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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Assessing and Managing the Ecological Impacts of Paved Roads 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 Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This project was supported by Contract No. DTFH61-01-C-00036 between the National Academy of Sciences and the Department of Transportation. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project. Cover design by Liza R. Hamilton, National Research Council. Front photo by Anthony P. Clevenger, Montana State University. Back photos used with permission from Lance H. Gunderson, Emory University (double yellow line), Emory University Facilities Management (campus), and USGS (southeastern United States). International Standard Book Number 0-309-10088-7 (Book) International Standard Book Number 0-309-65631-1 (PDF) Library of Congress Control Number 2005937774 Additional copies of this report are available from The National Academies Press 500 Fifth Street, NW Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington metropolitan area) http://www.nap.edu Copyright 2005 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Assessing and Managing the Ecological Impacts of Paved Roads THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating 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 Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages 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 given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology 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 Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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Assessing and Managing the Ecological Impacts of Paved Roads COMMITTEE ON ECOLOGICAL IMPACTS OF ROAD DENSITY Members LANCE H. GUNDERSON (Chair), Emory University, Atlanta, GA ANTHONY P. CLEVENGER, Western Transportation Institute, Montana State University, Bozeman ADRIENNE T. COOPER, Temple University, Philadelphia, PA VIRGINIA H. DALE, Oak Ridge National Laboratory, Oak Ridge, TN LEONARD EVANS, Science Serving Society, Bloomfield Hills, MI GARY L. EVINK, Florida Department of Transportation (Retired), Tallahassee LENORE FAHRIG, Carleton University, Ottawa, Ontario, Canada KINGSLEY E. HAYNES, George Mason University, Fairfax, VA WAYNE W. KOBER, Transportation and Environmental Consulting, Dillsburg, PA STEPHEN B. LESTER, Urban Engineers, Inc., Philadelphia, PA KENT H. REDFORD, Wildlife Conservation Society, Bronx, NY MARGARET N. STRAND, Venable, LLP, Washington, DC PAUL WAGNER, Washington State Department of Transportation, Olympia J.M. (MAC) YOWELL, Kentucky Transportation Cabinet (Retired), Frankfort Staff SUZANNE VAN DRUNICK, Project Director DAVID POLICANSKY, Scholar RUTH CROSSGROVE, Senior Editor MIRSADA KARALIC-LONCAREVIC, Research Associate BRYAN P. SHIPLEY, Research Associate JOHN BROWN, Program Associate LIZA R. HAMILTON, Senior Program Assistant ALEXANDRA STUPPLE, Senior Editorial Assistant SAMMY BARDLEY, Librarian Sponsor FEDERAL HIGHWAY ADMINISTRATION

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Assessing and Managing the Ecological Impacts of Paved Roads BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY Members JONATHAN M. SAMET (Chair), Johns Hopkins University, Baltimore, MD RAMÓN ALVAREZ, Environmental Defense, Austin, TX JOHN M. BALBUS, Environmental Defense, Washington, DC THOMAS BURKE, Johns Hopkins University, Baltimore, MD DALLAS BURTRAW, Resources for the Future, Washington, DC JAMES S. BUS, Dow Chemical Company, Midland, MI COSTEL D. DENSON, University of Delaware, Newark E. DONALD ELLIOTT, Willkie Farr & Gallagher LLP, Washington, DC J. PAUL GILMAN, Oak Ridge National Laboratory, Oak Ridge, TN SHERRI W. GOODMAN, Center for Naval Analyses, Alexandria, VA JUDITH A. GRAHAM, American Chemistry Council, Arlington, VA DANIEL S. GREENBAUM, Health Effects Institute, Cambridge, MA WILLIAM P. HORN, Birch, Horton, Bittner and Cherot, Washington, DC ROBERT HUGGETT, Michigan State University (emeritus), East Lansing JAMES H. JOHNSON JR., Howard University, Washington, DC JUDITH L. MEYER, University of Georgia, Athens PATRICK Y. O’BRIEN, ChevronTexaco Energy Technology Company, Richmond, CA DOROTHY E. PATTON, International Life Sciences Institute, Washington, DC STEWARD T.A. PICKETT, Institute of Ecosystem Studies, Millbrook, NY DANNY D. REIBLE, University of Texas, Austin JOSEPH V. RODRICKS, ENVIRON International Corporation, Arlington, VA ARMISTEAD G. RUSSELL, Georgia Institute of Technology, Atlanta ROBERT F. SAWYER, University of California, Berkeley LISA SPEER, Natural Resources Defense Council, New York, NY KIMBERLY M. THOMPSON, Massachusetts Institute of Technology, Cambridge MONICA G. TURNER, University of Wisconsin, Madison MARK J. UTELL, University of Rochester Medical Center, Rochester, NY CHRIS G. WHIPPLE, ENVIRON International Corporation, Emeryville, CA LAUREN ZEISE, California Environmental Protection Agency, Oakland Senior Staff JAMES J. REISA, Director DAVID J. POLICANSKY, Scholar RAYMOND A. WASSEL, Senior Program Officer for Environmental Sciences and Engineering KULBIR BAKSHI, Senior Program Officer for Toxicology EILEEN N. ABT, Senior Program Officer for Risk Analysis K. JOHN HOLMES, Senior Program Officer SUSAN N.J. MARTEL, Senior Program Officer SUZANNE VAN DRUNICK, Senior Program Officer ELLEN K. MANTUS, Senior Program Officer RUTH E. CROSSGROVE, Senior Editor

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Assessing and Managing the Ecological Impacts of Paved Roads TRANSPORTATION RESEARCH BOARD 2005 EXECUTIVE COMMITTEE1 JOHN R. NJORD (Chair), Utah Department of Transportation, Salt Lake City MICHAEL D. MEYER (Vice Chair), Georgia Institute of Technology, Atlanta ROBERT E. SKINNER (Executive Director), Transportation Research Board, Washington, DC MICHAEL W. BEHRENS, Texas Department of Transportation, Austin ALLEN D. BIEHLER, Pennsylvania Department of Transportation, Harrisburg LARRY L. BROWN, Mississippi Department of Transportation, Jackson DEBORAH H. BUTLER, Norfolk Southern Corporation and Subsidiaries, Atlanta, GA ANNE P. CANBY, Surface Transportation Policy Project, Washington, DC JOHN L. CRAIG, Nebraska Department of Roads, Lincoln DOUGLAS G. DUNCAN, FedEx Freight, Memphis, TN NICHOLAS J. GARBER, University of Virginia, Charlottesville ANGELA GITTENS, HNTB Corporation, Miami, FL GENEVIEVE GIULIANO (Past Chair, 2003), University of Southern California, Los Angeles BERNARD S. GROSECLOSE, JR., South Carolina State Ports Authority, Charleston SUSAN HANSON, Clark University, Worcester, MA JAMES R. HERTWIG, CSX Intermodal, Jacksonville, FL GLORIA J. JEFF, Michigan Department of Transportation, Lansing ADIB K. KANAFANI, University of California, Berkeley HERBERT S. LEVINSON, Herbert S. Levinson Transportation Consultant, New Haven, CT SUE MCNEIL, University of Delaware, Newark MICHAEL MORRIS, North Central Texas Council of Governments, Arlington CAROL A. MURRAY, New Hampshire Department of Transportation, Concord MICHAEL S. TOWNES (Past Chair, 2004), Hampton Roads Transit, VA C. MICHAEL WALTON, University of Texas, Austin LINDA S. WATSON, LYNX–Central Florida Regional Transportation Authority, Orlando MARION C. BLAKEY (ex officio), Federal Aviation Administration, U.S. Department of Transportation, Washington, DC JOSEPH H. BOARDMAN (ex officio), Federal Railroad Administration, U.S. Department of Transportation, Washington, DC REBECCA M. BREWSTER (ex officio), American Transportation Research Institute, Smyrna, GA GEORGE BUGLIARELLO (ex officio), Polytechnic University, Brooklyn, NY; Foreign Secretary, National Academy of Engineering, Washington, DC J. RICHARD CAPKA (ex officio), Federal Highway Administration, U.S. Department of Transportation, Washington, DC THOMAS H. COLLINS (ex officio), Commandant, U.S. Coast Guard, Washington, DC JAMES J. EBERHARDT (ex officio), U.S. Department of Energy, Washington, DC JACQUELINE GLASSMAN, (ex officio), National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, DC EDWARD R. HAMBERGER (ex officio), Association of American Railroads, Washington, DC 1   As of March 2005.

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Assessing and Managing the Ecological Impacts of Paved Roads DAVID B. HORNER (ex officio), Federal Transit Administration, U.S. Department of Transportation, Washington, DC JOHN C. HORSLEY (ex officio), American Association of State Highway and Transportation Officials, Washington, DC JOHN E. JAMIAN (ex officio), Maritime Administration, U.S. Department of Transportation, Washington, DC EDWARD JOHNSON (ex officio), Applied Science Directorate, National Aeronautics and Space Administration, John C. Stennis Space Center, MS ASHOK G. KAVEESHWAR (ex officio), Research and Innovative Technology Administration, U.S. Department of Transportation, Washington, DC BRIGHAM MCCOWN (ex officio), Pipeline and Hazardous Materials Safety Administration, U.S. Department of Transportation, Washington DC WILLIAM W. MILLAR (ex officio) (Past Chair, 1992), American Public Transportation Association, Washington, DC SUZANNE RUDZINSKI (ex officio), U.S. Environmental Protection Agency, Washington, DC ANNETTE M. SANDBERG (ex officio), Federal Motor Carrier Safety Administration, U.S. Department of Transportation, Washington, DC JEFFREY N. SHANE (ex officio), U.S. Department of Transportation, Washington, DC CARL A. STROCK (ex officio), U.S. Army Corps of Engineers, Washington, DC

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Assessing and Managing the Ecological Impacts of Paved Roads OTHER REPORTS OF THE BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY Superfund and Mining Megasites—Lessons from the Coeur d’Alene River Basin (2005) Health Implications of Perchlorate Ingestion (2005) Air Quality Management in the United States (2004) Endangered and Threatened Species of the Platte River (2004) Atlantic Salmon in Maine (2004) Endangered and Threatened Fishes in the Klamath River Basin (2004) Cumulative Environmental Effects of Alaska North Slope Oil and Gas Development (2003) Estimating the Public Health Benefits of Proposed Air Pollution Regulations (2002) Biosolids Applied to Land: Advancing Standards and Practices (2002) The Airliner Cabin Environment and Health of Passengers and Crew (2002) Arsenic in Drinking Water: 2001 Update (2001) Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001) Compensating for Wetland Losses Under the Clean Water Act (2001) A Risk-Management Strategy for PCB-Contaminated Sediments (2001) Acute Exposure Guideline Levels for Selected Airborne Chemicals (4 volumes, 2000-2004) Toxicological Effects of Methylmercury (2000) Strengthening Science at the U.S. Environmental Protection Agency (2000) Scientific Frontiers in Developmental Toxicology and Risk Assessment (2000) Ecological Indicators for the Nation (2000) Waste Incineration and Public Health (1999) Hormonally Active Agents in the Environment (1999) Research Priorities for Airborne Particulate Matter (4 volumes, 1998-2004) The National Research Council’s Committee on Toxicology: The First 50 Years (1997) Carcinogens and Anticarcinogens in the Human Diet (1996) Upstream: Salmon and Society in the Pacific Northwest (1996) Science and the Endangered Species Act (1995) Wetlands: Characteristics and Boundaries (1995) Biologic Markers (5 volumes, 1989-1995) Review of EPA's Environmental Monitoring and Assessment Program (3 volumes, 1994-1995) Science and Judgment in Risk Assessment (1994) Pesticides in the Diets of Infants and Children (1993) Dolphins and the Tuna Industry (1992) Science and the National Parks (1992) Human Exposure Assessment for Airborne Pollutants (1991) Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) Decline of the Sea Turtles (1990) Copies of these reports may be ordered from the National Academies Press (800) 624-6242 or (202) 334-3313 www.nap.edu

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Assessing and Managing the Ecological Impacts of Paved Roads OTHER REPORTS OF THE TRANSPORTATION RESEARCH BOARD Predicting Air Quality Effects of Traffic-Flow Improvements: Final Report and User's Guide (2005) Energy and Environment Concerns 2004 (2004) Short-Term Monitoring for Compliance with Air Quality Standards (2004) Travel Matters: Mitigating Climate Change with Sustainable Surface Transportation (2003) Environmental Law and Transportation (2003) Sustainability and Environmental Concerns in Transportation 2003 (2003) Energy, Air Quality, and Fuels 2003 (2003) Environmental Information Management and Decision Support System—Implementation Handbook (2003) Strategies for Increasing the Effectiveness of Commuter Benefits (2003) Guideline for Selecting Compensatory Wetlands Mitigation Options (2003) Interactions Between Roadways and Wildlife Ecology (2002) Assessing the Impact of Bridge Deck Runoff Contaminates in Receiving Waters (2002) Mitigating Transportation’s Ecological Impacts (2002) Surface Transportation Environmental Research: A Long-Term Strategy (2002) A Process for Setting, Managing, and Monitoring Environmental Windows for Dredging Projects (2002) Congestion Mitigation and Air Quality Improvement Program: Assessing 10 Years of Experience (2002) Energy, Air Quality, and Fuels 2002 (2002) Environmental Research Needs in Transportation: Report of a Conference, Washington, D.C., March 21-23, 2002 (2002) Sustainability and Environmental Concerns in Transportation 2003 (2002) Environmental Performance of Tanker Designs in Collision and Grounding: Method for Comparison (2001) Toward A Sustainable Future: Addressing the Long-Term Effects of Motor Vehicle Transportation on Climate and Ecology (1997) Expanding Metropolitan Highways: Implications for Air Quality and Energy Use—Special Report 245 (1995) Copies of these and other TRB reports may be ordered from the Transportation Research Board (202) 334-3213 TRB Bookstore (www.TRB.org/bookstore) TRBSales@nas.edu

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Assessing and Managing the Ecological Impacts of Paved Roads ACKNOWLEDGMENTS We are grateful for the generous support provided by U.S. Department of Transportation and are especially grateful for the outstanding assistance provided by Dr. Paul Garrett. Many people assisted the committee and National Research Council by providing data and reports. We are grateful for the information and support provided by the following: Marina Alberti, University of Washington David Andersen, Washington State Office of Community Trade and Economic Development Fred Bank, Federal Highway Administration Paul Barten, University of Massachusetts William I. Boarman, U.S. Geological Survey Ray Bransfield, U.S. Fish and Wildlife Service Todd D. Carlson, Washington State Department of Transportation Laurie W. Carr, TerraSystems Research Kristan Majors Chilcoat, Emory University Scott Dawson, California Department of Fish and Game Robert Fuerstenberg, King County Department of Natural Resources and Parks Margot J. Griswold, Earthworks Construction & Design Howard Haemmerle, King County Department of Transportation Eugene S. Helfman, University of Georgia Art Homrighausen, LSA Associates, Inc. Geary Hund, California State Parks Robert A. James, California Department of Transportation John Kusler, Association of State Wetland Managers Gino Lucchetti, King County Department of Natural Resources Gary McVoy, New York State Department of Transportation Ivan Miller, Puget Sound Regional Council William Ruediger, U.S. Forest Service Mark Shaffer, Doris Duke Foundation Emily Tibbott, The Nature Conservancy Benjamin Tuggle, U.S. Fish and Wildlife Service Sylvia Vega, California Department of Transportation Paul A. Waddel, University of Washington Michael White, Conservation Biology Institute

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Assessing and Managing the Ecological Impacts of Paved Roads ETAP environmental technical advisory team FHWA Federal Highway Administration FLH federal lands highway FPPA Farmland Protection Policy Act FTA Federal Transit Administration GIS geographic information system HEP habitat evaluation procedure HGM hydrogeomorphic method IRI international roughness index ISTEA Intermodal Surface Transportation Equity Act LARCH landscape ecological analysis and rules for the configuration of habitat model LOS level of service LRTP long-range transportation plan LWCFA Land and Water Conservation Fund Act MBTA Migratory Bird Treaty Act MOU memorandum of understanding MPO metropolitan planning organization NAAQS National Ambient Air Quality Standards NAS National Academy of Sciences NCHRP National Cooperative Highway Research Program NEPA National Environmental Policy Act NGO nongovernmental organization NHPA National Historic Preservation Act NHS national highway system NOAA National Oceanic and Atmospheric Administration NOX nitrogen oxides NPDES national pollutant discharge elimination system NPS National Park Service NRC National Research Council NWP nationwide permit PM10 particulate matter up to 10 micrometers in diameter ROD record of decision SAMP special area management plan SEA street edge alternatives SEF southeastern ecological framework SEMP Strategic Environmental Management Program SIP state implementation plan SPGP state program general permit STIP state transportation improvement plan

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Assessing and Managing the Ecological Impacts of Paved Roads STPP surface transportation policy project TE transportation enhancement TEA-21 Transportation Equity Act for the Twenty-First Century TIP transportation improvement program TMDL total maximum daily load TNC The Nature Conservancy TRB Transportation Research Board USFWS U.S. Fish and Wildlife Service V/SF volume to service flow ratio VMT vehicle miles of travel VOC volatile organic compound

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Assessing and Managing the Ecological Impacts of Paved Roads Contents     SUMMARY   1 1   INTRODUCTION   14      Committee Charge and Response,   17      What Is Different and New in This Report?   24      Organization of Report,   31 2   HISTORY AND STATUS OF THE U.S. ROAD SYSTEM   37      Introduction,   37      A Brief History of the U.S. Road System,   37      Definitions and Characteristics of Roads,   41      Ownership and Maintenance Responsibilities,   54      Current Status and Future Trends,   54      Summary,   60 3   EFFECTS OF ROADS ON ECOLOGICAL CONDITIONS   62      Introduction,   62      Definitions,   63      Ecological Condition—Ecosystem Goods and Services,   65      Literature Review,   66      Information Gaps,   95      Summary,   96

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Assessing and Managing the Ecological Impacts of Paved Roads 4   AMELIORATING THE EFFECTS OF ROADS   98      Introduction,   98      Scale-Based Considerations of Environmental Mitigation,   99      Opportunities for Environmental Stewardship,   113      Summary,   116 5   LEGAL CONTEXT FOR PLANNING AND POLICY   117      Introduction,   117      Transportation Processes: How Transportation Is Planned and Projects Are Developed,   118      Federally Structured Regional and Local Planning,   119      Major Federal Environmental Laws,   130      Other Types of Laws,   149      Discussion of Laws and Ecological Concerns,   151      Issues,   163      Summary,   168 6   PLANNING AND ASSESSMENT   170      Introduction,   170      State of Road Planning and Assessment Processes,   170      Types of Environmental Planning Activities,   175      Transportation Ecological Assessments,   180      Tools and Methods for Assessment,   181      Potential Solutions and Improvements for Assessment and Planning,   192      Summary,   202 7   INTEGRATING OBSTACLES AND OPPORTUNITIES   204      Introduction,   204      Issues of Integration Across Scales,   204      Integrating Ecological Concerns and Social Objectives,   207      Toward Integrative Solutions,   209      Summary,   219 8   CONCLUSIONS AND RECOMMENDATIONS   220     REFERENCES   226

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Assessing and Managing the Ecological Impacts of Paved Roads     APPENDIXES     A   Biographical Information on Committee Members   249 B   Spatial Scale of Road Effects on Ecological Conditions: Annotated Bibliography   255 C   Congressional Declaration of National Environmental Policy, National Environmental Policy Act of 1969   293 FIGURES 1-1   Photograph of double yellow line in the center of a road,   27 1-2   A larger segment of the road as seen in Figure 1-1,   28 1-3   A larger (longer segment) of road on Emory campus,   29 1-4   At this scale of photograph, most of the buildings that make up the central campus of Emory University can be seen embedded in a network of roads,   30 1-5   At an extent of 10 km × 10 km, the road patterns around Emory campus are evident, yet individual roads are scarcely visible,   31 1-6   At an extent of 100 km × 100 km, the urban imprint of Atlanta is visible,   32 1-7   At an extent of 1,000 km × 1,000 km, geological features dominate,   33 1-8   At an extent of approximately 10,000 km × 10,000 km, clouds and atmospheric structures appear as well as the entire continent of North America,   34 1-9   Ecological hierarchy indicated by the spatial and temporal scales of vegetation structures (needles, patches, and forests), disturbance processes (fire), and atmospheric structures (fronts),   35 2-1   Time course of number of vehicle miles traveled by year from 1960 to 2000, indicating travel on rural and urban portions of the highway system,   41 2-2   Map of National Highway System in the 50 states, the District of Columbia, and Puerto Rico,   46 2-3   Miles of road and use of roads in urban and rural portions of the National Highway System,   47 2-4   Total road mileage (summation of all road lengths) and travel by functional type in the year 2000,   48

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Assessing and Managing the Ecological Impacts of Paved Roads 2-5   Example of rectangular grid pattern of roads in Chicago,   50 2-6   Example of hub-and-spoke pattern of roads found in Washington, DC,   51 2-7   Traffic congestion map showing a concentration of congested highways in the southeastern and south-central regions of New Hampshire,   57 2-8   Percentage of vehicle miles traveled on urban freeways and principal arterials occurring under congested conditions from 1987 to 2000,   58 2-9   Pavement surface condition of the national and interstate highway systems,   58 3-1   Road affecting four aspects of stream connectivity,   72 3-2   Sources of 23 pollutant constituents in storm-water runoff,   74 3-3   Schematic representation of the primary ecological effects of roads on species and populations,   78 3-4   Wildlife crossings are designed to link critical habitats and provide safe movement of animals across busy roads,   81 3-5   Spatial and temporal dimensions of ecological effects of roads,   90 4-1   Illustration of a reduction in total road length reducing the ecological effect of roads and traffic,   101 4-2   Illustration of the effect of traffic volume on the road-avoidance zone or the distance maintained by those animals that avoid a road,   102 4-3   Illustration of reducing traffic near ecologically sensitive water bodies,   103 4-4   Conceptual illustration of the general relationship between the width of the road-effect zone and the volume of traffic on the road,   104 4-5   Illustration of how the ecological effects of a new road can be mitigated by consideration of surrounding land use,   105 4-6   Illustration of mitigation measures to reduce the ecological effects of roads when it is not possible to redirect traffic away from natural areas,   106 4-7   Examples of ecological restoration performed by ongoing road maintenance operations,   115 6-1   EPA ecological framework: essential ecological attributes,   189 6-2   The spectrum of environmental performance measures,   189

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Assessing and Managing the Ecological Impacts of Paved Roads 6-3   Diagram of committee’s proposed framework for a rapid assessment method,   195 6-4   A suite of indicators across scales is being adopted by the U.S. Department of Defense’s Strategic Environmental Management Project,   198 TABLES 2-1   Functional System Changes, 1990-2000,   43 2-2   Interstate Highway System—Key Statistics,   45 2-3   National Highway System Mileage and Travel in Rural and Urban Areas,   47 2-4   Ownership of U.S. Roads and Streets,   55 2-5   Level-of-Service Chart for Major State Highways in New Hampshire Based on 2002 Traffic Data,   56 2-6   Conditions of Highway Bridges,   59 2-7   Backlog of Bridge Investment Needs,   60 3-1   Comparison of Ecosystem Goods and Services and Ecosystem Structures and Processes Affected by Roads,   64 3-2   Summary of Number of Studies Addressing Different Types of Road Effects on Ecological Conditions,   68 3-3   Examples of the Extent to Which Road-Induced Effects Penetrate Adjacent Habitat,   88 5-1   Types of Considerations Required by Environmental Laws, Programs, and Executive Orders That Address Ecosystems and Components of Ecosystems with Regard to Roads,   154 5-2   Types of Considerations Required by Environmental Laws, Programs, and Executive Orders That Address Groups of Organisms (Species and Populations) with Regard to Roads,   156 5-3   Types of Considerations Required by Environmental Laws, Programs, and Executive Orders That Address Different Ecosystem Types with Regard to Roads,   158 5-4   Ecological Scale at Which Legislation Is Applied,   160 5-5   Political Scale at Which Environmental Legislation, Program, or Executive Orders Are Applied,   164

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