cts of CLIMATE CHANGE on U.S. Transportation 

Potential Impacts of CLIMATE CHANGE on U.S. Transportation Potential Impacts of CLIMATE CHANGE on U.S. Transportation 

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Committee on Climate Change and U.S. Transportation

Transportation Research Board

Division on Earth and Life Studies

Transportation Research Board

Washington, D.C.

2008

www.TRB.org

Potential Impacts of 

CLIMATE CHANGE

on U.S. Transportation

TRANSPORTATION RESEARCH BOARD SPECIAL REPORT 290
Transportation Research Board Special Report 290

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This report has been reviewed by a group other than the authors according to the procedures

approved by a Report Review Committee consisting of members of the National Academy of

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This report was sponsored by the Transportation Research Board, the National Cooperative

Highway Research Program, the U.S. Department of Transportation, the Transit Cooperative

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Cover and inside design by Tony Olivis, Studio 2

Library of Congress Cataloging-in-Publication Data

National Research Council (U.S.). Committee on Climate Change and U.S. Transportation.

Potential impacts of climate change on U.S. transportation / Committee on Climate Change

and U.S. Transportation, Transportation Research Board and Division on Earth and Life

Studies, National Research Council of the National Academies.

p. cm.—(Transportation Research Board special report ; 290)

Includes bibliographical references.

1. Transportation—Climatic factors—United States. 2. Transportation engineering—United

States. 3. Climatic changes—Government policy—United States. 4. Global warming—

Environmental aspects. I. National Research Council (U.S.). Division on Earth and Life Studies.

II. Title.

TA1023.N38 2008

388.0973—dc22

2008008264

ISBN 978-0-309-11306-9
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

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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 the Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and

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www.national-academies.org
TRANSPORTATION RESEARCH BOARD

2008 EXECUTIVE COMMITTEE*

Chair: Debra L. Miller, Secretary, Kansas Department of Transportation, Topeka

Vice Chair: Adib K. Kanafani, Cahill Professor of Civil Engineering, University of

California, Berkeley

Executive Director: Robert E. Skinner, Jr., Transportation Research Board

J. Barry Barker, Executive Director, Transit Authority of River City, Louisville,

Kentucky

Allen D. Biehler, Secretary, Pennsylvania Department of Transportation, Harrisburg

John D. Bowe, President, Americas Region, APL Limited, Oakland, California

Larry L. Brown, Sr., Executive Director, Mississippi Department of Transportation,

Jackson

Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern

Corporation, Norfolk, Virginia

William A. V. Clark, Professor, Department of Geography, University of California,

Los Angeles

David S. Ekern, Commissioner, Virginia Department of Transportation, Richmond

Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering,

University of Virginia, Charlottesville

Jeffrey W. Hamiel, Executive Director, Metropolitan Airports Commission,

Minneapolis, Minnesota

Edward A. (Ned) Helme, President, Center for Clean Air Policy, Washington, D.C.

Will Kempton, Director, California Department of Transportation, Sacramento

Susan Martinovich, Director, Nevada Department of Transportation, Carson City

Michael D. Meyer, Professor, School of Civil and Environmental Engineering,

Georgia Institute of Technology, Atlanta (Past Chair, 2006)

Michael R. Morris, Director of Transportation, North Central Texas Council of

Governments, Arlington

Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore

Pete K. Rahn, Director, Missouri Department of Transportation, Jefferson City

Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson

Tracy L. Rosser, Vice President, Corporate Traffic, Wal-Mart Stores, Inc., Bentonville,

Arkansas

Rosa Clausell Rountree, Executive Director, Georgia State Road and Tollway

Authority, Atlanta

Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc.,

St. Louis, Missouri

C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of

Texas, Austin (Past Chair, 1991)

*Membership as of June 2008.
Linda S. Watson, CEO, LYNX–Central Florida Regional Transportation Authority,

Orlando (Past Chair, 2007)

Steve Williams, Chairman and CEO, Maverick Transportation, Inc., Little Rock,

Arkansas

Thad Allen (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington,

D.C. (ex officio)

Joseph H. Boardman, Administrator, Federal Railroad Administration,

U.S. Department of Transportation (ex officio)

Rebecca M. Brewster, President and COO, American Transportation Research

Institute, Smyrna, Georgia (ex officio)

Paul R. Brubaker, Administrator, Research and Innovative Technology

Administration, U.S. Department of Transportation (ex officio)

George Bugliarello, Chancellor, Polytechnic University of New York, Brooklyn;

Foreign Secretary, National Academy of Engineering, Washington, D.C. (ex officio)

Sean T. Connaughton, Administrator, Maritime Administration, U.S. Department 

of Transportation (ex officio)

LeRoy Gishi, Chief, Division of Transportation, Bureau of Indian Affairs,

U.S. Department of the Interior, Washington, D.C. (ex officio)

Edward R. Hamberger, President and CEO, Association of American Railroads,

Washington, D.C. (ex officio)

John H. Hill, Administrator, Federal Motor Carrier Safety Administration,

U.S. Department of Transportation (ex officio)

John C. Horsley, Executive Director, American Association of State Highway and

Transportation Officials, Washington, D.C. (ex officio)

Carl T. Johnson, Administrator, Pipeline and Hazardous Materials Safety

Administration, U.S. Department of Transportation, Washington, D.C. (ex officio)

J. Edward Johnson, Director, Applied Science Directorate, National Aeronautics and

Space Administration, John C. Stennis Space Center, Mississippi (ex officio)

William W. Millar, President, American Public Transportation Association,

Washington, D.C. (ex officio) (Past Chair, 1992)

Nicole R. Nason, Administrator, National Highway Traffic Safety Administration,

U.S. Department of Transportation (ex officio)

James Ray, Acting Administrator, Federal Highway Administration, U.S. Department 

of Transportation (ex officio)

James S. Simpson, Administrator, Federal Transit Administration, U.S. Department 

of Transportation (ex officio)

Robert A. Sturgell, Acting Administrator, Federal Aviation Administration,

U.S. Department of Transportation (ex officio)

Robert L. Van Antwerp (Lt. General, U.S. Army), Chief of Engineers and

Commanding General, U.S. Army Corps of Engineers, Washington, D.C. (ex officio)
Division on Earth and Life Studies 

Climate Research Committee

Antonio J. Busalacchi, Jr., University of Maryland, College Park, Chair

Ana P. Barros, Duke University, Durham, North Carolina

Cecilia Bitz, University of Washington, Seattle

James A. Coakley, Jr., Oregon State University, Corvallis

Gabriele Hegerl, University of Edinburgh, Edinburgh, United Kingdom

Henry D. Jacoby, Massachusetts Institute of Technology, Cambridge

Anthony C. Janetos, Pacific Northwest National Laboratory/University

of Maryland, College Park

Robert J. Lempert, Rand Corporation, Santa Monica, California 

Roger B. Lukas, University of Hawaii, Honolulu 

Linda O. Mearns, National Center for Atmospheric Research, Boulder,

Colorado 

Gerald A. Meehl, National Center for Atmospheric Research, Boulder,

Colorado 

Joyce E. Penner, University of Michigan, Ann Arbor 

Richard Richels, Electric Power Research Institute, Washington, D.C.

Taro Takahashi, Lamont–Doherty Earth Observatory, Palisades, New

York 

Lonnie G. Thompson, Ohio State University, Columbus 
Committee on Climate Change and U.S. Transportation

Henry G. Schwartz, Jr., Sverdrup/Jacobs Civil, Inc. (retired), St. Louis,

Missouri, Chair

Alan C. Clark, Houston–Galveston Area Council, Houston, Texas

G. Edward Dickey, Loyola College in Maryland, Baltimore

George C. Eads, CRA International, Washington, D.C.

Robert E. Gallamore, Gallamore Group, Rehoboth Beach, Delaware

Genevieve Giuliano, University of Southern California, Los Angeles

William J. Gutowski, Jr., Iowa State University, Ames

Randell H. Iwasaki, California Department of Transportation,

Sacramento

Klaus H. Jacob, Columbia University, Palisades, New York

Thomas R. Karl, National Oceanic and Atmospheric Administration,

Asheville, North Carolina

Robert J. Lempert, Rand Corporation, Santa Monica, California

Luisa M. Paiewonsky, Massachusetts Highway Department, Boston

S. George H. Philander, Princeton University, Princeton, New Jersey 

(through December 2006)

Christopher R. Zeppie, Port Authority of New York and New Jersey,

New York City

National Research Council Staff

Nancy P. Humphrey, Study Director, Transportation Research Board

Amanda C. Staudt, Senior Program Officer, Division on Earth and Life

Studies (through February 28, 2007)

Preface

Leading scientists on the Intergovernmental Panel for Climate

Change published their fourth assessment of the state of knowledge

about climate change and its impacts in spring 2007. They reached consensus that human activity is responsible for many observed climate

changes, particularly the warming temperatures of the last several

decades, and concluded that there is a need for far more extensive adaptation than is currently occurring to reduce vulnerability to future

climate changes. In September 2007, the National Research Council

(NRC) released a report examining the U.S. Climate Change Science

Program, which oversees federal research on climate change in the United

States. The report noted that understanding of the physical climate system has progressed rapidly but that the use of this knowledge to support

decision making, manage risks, and engage stakeholders is inadequate.

The transportation sector is a good case in point. Little consensus

exists among transportation professionals that climate change is occurring or warrants action now. Addressing climate change requires an

examination of plausible future scenarios, a long-term perspective, the

capacity to deal with uncertain and changing information, and

responses that may extend beyond jurisdictional boundaries and transportation modal responsibilities. These are significant challenges for

transportation professionals. This report is intended to help illuminate

the nature of the potential impacts of climate change of greatest relevance for U.S. transportation and to suggest appropriate adaptation

strategies and organizational responses.

ix
x Potential Impacts of Climate Change on U.S. Transportation

This study was requested by the Executive Committee of the

Transportation Research Board (TRB) and was conducted with the

Division on Earth and Life Studies (DELS). It was funded by a broad range

of organizations, including TRB, the National Cooperative Highway

Research Program, the U.S. Department of Transportation (USDOT), the

Transit Cooperative Research Program, the U.S. Environmental

Protection Agency, and the U.S. Army Corps of Engineers. TRB and

DELS formed a committee of 13 members comprising experts in climate

science, meteorology, transportation planning and engineering, transportation operations and maintenance, risk analysis, and economics to

conduct the study.1 The committee was chaired by Henry G. Schwartz, Jr.,

retired president and chairman of Sverdrup/Jacobs Civil, Inc., and member of the National Academy of Engineering.

To carry out its charge, the committee reviewed the literature in the

field, requested numerous briefings, commissioned five papers to explore

various aspects of the potential impacts of climate change on U.S. transportation, and held a 1-day conference to explore these issues with a

broader audience. The commissioned papers provided the committee

with important information on various aspects of the impacts of climate

change on transportation. The first paper, by Thomas C. Peterson,

Marjorie McGuirk, Andrew H. Horvitz, and Tamara Houston of the

National Oceanic and Atmospheric Administration and Michael F.

Wehner of the Lawrence Berkeley National Laboratory, helped set the

stage by identifying the climate factors of greatest relevance for transportation, summarizing current understanding of projected climate

changes for various U.S. regions, and describing potential impacts on

transportation. A paper by Michael D. Meyer of the School of Civil and

Environmental Engineering at the Georgia Institute of Technology examines the role of transportation design standards in light of potential

impacts from climate change. A third paper, by Stephen C. Lockwood of

Parsons Brinckerhoff, reviews operational strategies for addressing climate change. A fourth paper, by Lance R. Grenzeback of Cambridge

Systematics, Inc., and Andrew Lukmann of the Massachusetts Institute of

Technology—a case study of the transportation sector’s response to and

recovery from Hurricanes Katrina and Rita—examines the vulnerabili1George Philander, a member of the National Academy of Sciences, participated as a member

of the committee through 2006, when he resigned because of extended foreign travel and new

commitments.
xi

ties and strengths of various transportation modes in the event of a shock

to the system. A final paper, by James A. Dewar and Martin Wachs of the

Rand Corporation,2 provides a survey of approaches to decision making

under uncertainty, drawing on examples from other sectors and suggesting possible new approaches for transportation planning and decision

making.

The papers were reviewed by the committee and discussants at a 1-day

conference (see next paragraph) and revised by the authors. They are listed

in Appendix C. Because of their length and printing costs, the papers are

available only in electronic form. The reader is cautioned that the interpretations and conclusions contained in the papers are those of the

authors. The key findings endorsed by the committee appear in the body

of the report.

The committee recognizes that five papers cannot cover the full

range of issues facing the transportation sector as it begins to consider

the potential impacts of climate change. Thus, a conference was held

midway through the study to examine the papers with a broader audience of climate scientists and academicians and practitioners from all

transportation modes and to engage the transportation community in

particular in considering the potential impacts of climate change. Each

paper was presented and critiqued by a commentator, followed by discussion by the authors and invited participants. The conference concluded

with a summary by two rapporteurs—one from the climate science and

one from the transportation community. Of the 144 individuals invited

to the conference, 51 attended. Their names and affiliations, along with

the conference agenda, can be found in Appendix D. The commentary

and critiques of conference participants were considered in both finalizing the authored papers and preparing this final report.

The committee also supplemented its expertise with briefings at its

meetings from a wide range of experts. In particular, the committee

thanks Eric J. Barron, Distinguished Professor of Geosciences and Dean

of the College of Earth and Mineral Sciences, Pennsylvania State

University (now at the University of Texas at Austin), who provided the

committee with an overview of the scientific consensus on climate

change, continuing uncertainties, and implications for transportation.

The committee also thanks Michael Savonis, Team Leader for Air Quality,

Preface

2 The authors both work for the Rand Corporation, but the paper was prepared by the authors as

individuals.
xii Potential Impacts of Climate Change on U.S. Transportation

Federal Highway Administration (FHWA), and Joanne Potter, Senior

Associate, Cambridge Systematics, Inc., for their briefing on the Gulf

Coast Study sponsored by USDOT and the U.S. Geological Survey—an

in-depth look at the potential impacts of climate change in this vulnerable region; Paul Pisano, Team Leader, FHWA, for his presentation on the

U.S. Surface Weather Research Program; Ian Buckle, Director of the

Center for Civil Engineering Earthquake Research, University of Nevada

at Reno, for his briefing on the development of earthquake standards and

the relevance of this effort to the revision of transportation design standards to address the potential impacts of climate change; Mark Hinsdale,

Assistant Vice President, Capacity Management and Network Planning,

CSX Corporation, for his overview of the impacts of Hurricane Katrina

on rail infrastructure; and Lourdes Maurice, Chief Scientific and

Technical Advisor for Environment, and Mohan Gupta, Operations

Research Analyst, Federal Aviation Administration, for their overview of

potential impacts of climate change on the aviation system.

This report has been reviewed in draft form by individuals chosen for

their diverse perspectives and technical expertise, in accordance with procedures approved by NRC’s Report Review Committee. The purpose of

this independent review is to provide candid and critical comments that

assist the authors and NRC in making the published report as sound as

possible and to ensure that the report meets institutional standards for

objectivity, evidence, and responsiveness to the study charge. The content

of the review comments and draft manuscript remain confidential to

protect the integrity of the deliberative process. The committee thanks

the following individuals for their participation in the review of this

report: John J. Boland, Johns Hopkins University (retired), Baltimore,

Maryland; William R. Black, Indiana University, Bloomington; Virginia

Burkett, U.S. Geological Survey, Many, Louisiana; Isaac M. Held,

Princeton University, Princeton, New Jersey; George M. Hornberger,

University of Virginia, Charlottesville; Roger E. Kasperson, Clark

University, Worcester, Massachusetts; Margaret A. LeMone, National

Center for Atmospheric Research, Boulder, Colorado; Ananth Prasad,

Florida Department of Transportation, Tallahassee; and Michael J. Scott,

Pacific Northwest National Laboratory, Richland, Washington.

Although the reviewers listed above provided many constructive

comments and suggestions, they were not asked to endorse the committee’s conclusions or recommendations, nor did they see the final draft
xiii

of the report before its release. The review of this report was overseen

by Susan Hanson, Clark University, Worcester, Massachusetts, and 

C. Michael Walton, University of Texas at Austin. Appointed by NRC,

they were responsible for making certain that an independent examination of the report was carried out in accordance with institutional

procedures and that all review comments were carefully considered.

Responsibility for the final content of this report rests entirely with the

authoring committee and the institution.

Nancy P. Humphrey of TRB, together with Amanda C. Staudt of

DELS, managed the study.3 Ms. Humphrey drafted major portions of the

final report under the guidance of the committee and the supervision of

Stephen R. Godwin, Director of Studies and Special Programs at TRB, and

Chris Elfring, Program Director at DELS. Ms. Staudt drafted Chapter 2,

which provides an overview of the current state of knowledge about climate change and its potential impacts; committee members Thomas R.

Karl and William J. Gutowski, Jr., made substantial revisions. Committee

member George C. Eads wrote Appendix B, which summarizes the contribution of transport-related greenhouse gas emissions to climate change

and reviews potential strategies for mitigating these impacts. Suzanne

Schneider, Associate Executive Director of TRB, managed the report

review process. Special appreciation is expressed to Rona Briere, who

edited the report. Jennifer Weeks prepared the final manuscript and the

commissioned papers for posting; Norman Solomon provided final

editorial guidance; and Juanita Green managed the book design and

production under the supervision of Javy Awan, Director of Publications.

Amelia Mathis assisted with meeting arrangements and communications

with committee members, Laura Toth helped with conference arrangements, and Alisa Decatur provided word processing support for

preparation of the final manuscript.

Preface

3Ms. Staudt left DELS in February 2007 to join the World Wildlife Federation. Thereafter, Ian

Kraucunas and Curtis Marshall of DELS provided assistance with the study.

Contents

Summary ......................................................................1

1 Introduction ................................................................21

Study Charge, Scope, and Audience..........................................23

Why Climate Change Matters ...................................................28

Study Approach and Key Issues ................................................29

Organization of the Report .......................................................33

2 Understanding Climate Change ....................................36

Overview of Global Climate Change ........................................36

Climate Changes Relevant to U.S. Transportation...................49

Findings ......................................................................................72

3 Impacts of Climate Change on Transportation...............79

Vulnerability of the Transportation System to 

Climate Change.......................................................................79

Potential Impacts by Transportation Mode .............................83

Review of Assessments for Particular Areas or Regions ..........92

Findings ....................................................................................112

Annex 3-1: Potential Climate Changes and 

Impacts on Transportation...................................................117

4 Challenges to Response ............................................124

Decision Making in the Transportation Sector......................124

Challenges Posed by Climate Change.....................................131
A Decision Framework for Addressing Climate Change.......135

Findings ....................................................................................141

Annex 4-1: Applying Probabilistic Risk Assessment to 

Climate Change and Transportation ...................................143

5 Meeting the Challenges.............................................148

Adaptation Strategies ...............................................................149

Crosscutting Issues...................................................................163

Findings ....................................................................................170

Annex 5-1A: Potential Climate Changes, Impacts on Land

Transportation, and Adaptation Options............................175

Annex 5-1B: Potential Climate Changes, Impacts on 

Marine Transportation, and Adaptation Options...............181

Annex 5-1C: Potential Climate Changes, Impacts on Air 

Transportation, and Adaptation Options............................185

6 Summing Up .............................................................189

Which Climate Changes Are Most Relevant for

U.S. Transportation? .............................................................189

How Will Climate Change Affect U.S. Transportation?.........190

How Should Transportation Decision Makers Respond?......193

What Data and Decision Support Tools Are Needed?...........195

Which Adaptation Strategies Make Sense? .............................197

What Actions and Research Are Needed to Prepare for 

Climate Change? ...................................................................207

Appendices

A Detailed Statement of Task........................................209

B Contribution of U.S. Transportation Sector 

to Greenhouse Gas Emissions and Assessment 

of Mitigation Strategies.............................................210

C Commissioned Papers and Authors ............................267

D Conference Agenda and Participants..........................268

Study Committee Biographical Information ...........................273
1

Summary

The world’s leading climate scientists have reached consensus that

human activity in the form of greenhouse gas (GHG) emissions is

warming the planet in ways that will have profound and unsettling

impacts on natural resources, energy use, ecosystems, economic activity,

and potentially quality of life. The earth’s climate is always in a state of

flux, but what is of concern today is the rapid rate of change and the

unabated contribution of human activity to its occurrence. Many studies

have already examined the potential impacts of climate change on broad

sectors of the economy, such as agriculture and forestry, but few have

studied the impacts on transportation.

The primary focus of this report is on the consequences of climate

change1 for the infrastructure and operations of U.S. transportation.2 The

report provides transportation professionals with an overview of the scientific consensus on those current and future climate changes of particular

relevance to U.S. transportation, including the limitations of present scientific understanding as to their precise timing, magnitude, and geographic

location; identifies potential impacts on U.S. transportation and adaptation

options; and offers recommendations for both research and actions that

can be taken to prepare for climate change. The report also summarizes

1 Climate change refers to a statistically significant variation in either the mean state of the climate

or its variability over an extended period, typically decades or longer, that can be attributed to

either natural causes or human activity. Weather refers to the familiar hour-by-hour, day-by-day

changes in temperature, cloudiness, precipitation, and other atmospheric phenomena.

2 In this report, infrastructure refers to both transportation networks (e.g., road and rail systems)

and facilities (e.g., bridges, tunnels, ports). All modes of transportation are covered—highways

(including bridges and tunnels), rail (including private rail lines and public transportation), marine

and air transportation, and pipelines.
2 Potential Impacts of Climate Change on U.S. Transportation

previous work on strategies for reducing transportation-related emissions

of carbon dioxide (CO2)—the primary GHG—that contribute to climate

change, a relatively well-researched area (see Appendix B).

Climate change will have significant impacts on transportation, affecting the way U.S. transportation professionals plan, design, construct,

operate, and maintain infrastructure. Decisions taken today, particularly

those related to the redesign and retrofitting of existing or the location and

design of new transportation infrastructure, will affect how well the system

adapts to climate change far into the future. Focusing on the problem now

should help avoid costly future investments and disruptions to operations.

The primary objective of this report is to provide guidance for transportation decision makers on how best to proceed.

CLIMATE CHANGES OF GREATEST RELEVANCE 

FOR U.S. TRANSPORTATION

Climate change is not just a problem for the future. Recent global climate

changes, such as warming temperatures and rising sea levels, likely reflect

the effects of GHG emissions into the atmosphere over the past century.

Even if drastic measures were taken today to stabilize or eliminate GHG

emissions, the effects of climate change would continue to be experienced, and U.S. transportation professionals would have to adapt to their

consequences.

On the basis of current knowledge, climate scientists have identified

five climate changes of particular importance to transportation and estimated the probability of their occurrence during the 21st century (detailed

in Box S-1):

• Increases in very hot days and heat waves,

• Increases in Arctic temperatures,

• Rising sea levels,

• Increases in intense precipitation events, and

• Increases in hurricane intensity.

Climate scientists have the greatest confidence in projected changes in

mean temperature and other climate factors at the global or continental

scale; confidence in these projections diminishes as the geographic scale is
Summary 3

BOX S-1

Climate Change Impacts of Greatest Relevance

for U.S. Transportation

Increases in very hot days and heat waves. It is highly likely (greater than 

90 percent probability of occurrence) that heat extremes and heat waves

will continue to become more intense, longer lasting, and more frequent in

most regions during the 21st century. In 2007, for example, the probability of having five summer days at or above 43.3°C (110°F) in Dallas was about

2 percent. In 25 years, this probability increases to 5 percent; in 50 years,

to 25 percent; and by 2099, to 90 percent.

Increases in Arctic temperatures. Arctic warming is virtually certain (greater

than 99 percent probability of occurrence), as temperature increases are

expected to be greatest over land and at most high northern latitudes. As

much as 90 percent of the upper layer of permafrost could thaw under more

pessimistic emission scenarios. The greatest temperature increases in North

America are projected to occur in the winter in northern parts of Alaska and

Canada as a result of feedback effects of shortened periods of snow cover.

By the end of the 21st century, projected warming could range from as

much as 10.0°C (18.0°F) in the winter to as little as 2.0°C (3.6°F) in the

summer in the northernmost areas. On an annual mean temperature basis

for the rest of North America, projected warming ranges from 3.0°C to

5.0°C (5.4°F to 9.0°F), with smaller values near the coasts.

Rising sea levels. It is virtually certain (greater than 99 percent probability of

occurrence) that sea levels will continue to rise in the 21st century as a result

of thermal expansion and loss of mass from ice sheets. The projected global

range in sea level rise is from 0.18 m (7.1 in.) to 0.59 m (23.2 in.) by 2099,

but the rise will not be geographically uniform. The Atlantic and Gulf Coasts

should experience a rise near the global mean, the West Coast a slightly lower

rise, and the Arctic Coast a rise of only 0.1 m (3.9 in.). These estimates do

not include subsidence in the Gulf and uplift along the New England Coast.

Nor do the global projections include the full effects of increased melting of the Greenland and Antarctic ice masses because current understanding

of these effects is too limited to permit projection of an upper bound on

sea level rise.

Increases in intense precipitation events. It is highly likely (greater than 90 percent probability of occurrence) that intense precipitation events will continue

to become more frequent in widespread areas of the United States.

(continued)
reduced. Nevertheless, climate scientists are now able to project climate

changes for large subcontinental regions, such as the eastern United

States—a scale better suited to transportation infrastructure, which is

regional and local. Projections of future climate are often shown as gradual changes, such as the rise in global temperatures projected over this

century. However, these changes are unlikely to be experienced in such a

smooth manner because those induced by human activity will be amplified in some years by naturally fluctuating conditions, reflected in

potentially sudden and dramatic changes at the regional or local level. For

example, many climate scientists caution that warming temperatures may

trigger weather extremes and surprises, such as more rapid melting of the

Arctic sea ice or more rapid rises in sea levels than are projected by current models.

Finding: The past several decades of historical regional climate

patterns commonly used by transportation planners to guide their

operations and investments may no longer be a reliable guide for

future plans. In particular, future climate will include new classes

(in terms of magnitude and frequency) of weather and climate

4 Potential Impacts of Climate Change on U.S. Transportation

BOX S-1 (continued)

Increases in hurricane intensity. Increased tropical storm intensities, with

larger peak wind speeds and more intense precipitation, are projected as

likely (greater than 66 percent probability of occurrence). No robust projections concerning the annual global number of tropical storms have yet

emerged from modeling studies, but more detailed analyses focused on the

Atlantic Ocean suggest no significant increases in the annual number of

Atlantic tropical storms.

Note: The primary sources for these data are the 2007 Intergovernmental Panel for Climate

Change Summary for Policymakers on the Physical Science Basis (Contribution of Working

Group I to the Fourth Assessment Report); the Peterson et al. 2006 paper commissioned

for this study (see Appendix C); numerous other sources that can be found in Chapter 2

(see Table 2-1 and the text discussing each of these impacts); and the committee’s own

assessments about the certainty of some impacts, based on the literature.

Climate Change Impacts of Greatest Relevance

for U.S. Transportation
Summary 5

extremes,3 such as record rainfall and record heat waves, not

experienced in modern times as human-induced changes are

superimposed on the climate’s natural variability.

POTENTIAL IMPACTS ON TRANSPORTATION

Transportation professionals are keenly aware of the effects of weather

on system performance. Transportation infrastructure was designed

for typical weather patterns, reflecting local climate and incorporating

assumptions about a reasonable range of temperatures and precipitation

levels.

Finding: Climate change will affect transportation primarily

through increases in several types of weather and climate extremes,

such as very hot days; intense precipitation events; intense hurricanes; drought; and rising sea levels, coupled with storm surges

and land subsidence. The impacts will vary by mode of transportation and region of the country, but they will be widespread and

costly in both human and economic terms and will require significant changes in the planning, design, construction, operation, and

maintenance of transportation systems.

The infrastructure will be affected most by those climate changes that cause

environmental conditions to extend outside the range for which the system

was designed (see Table S-1 for illustrative impacts of key climate changes).

Finding: Potentially, the greatest impact of climate change for

North America’s transportation systems will be flooding of coastal

roads, railways, transit systems, and runways because of global

rising sea levels, coupled with storm surges and exacerbated in

some locations by land subsidence.

Fully 53 percent of the U.S. population now lives in counties with coastal

regions, many among the most densely populated in the nation. As retirement magnets and tourist destinations with rapidly growing economies,

coastal communities will continue to experience development pressures,

3 The exact threshold for what is classified as an extreme varies from one analysis to another, but

an extreme event would normally be as rare as or rarer than the top or bottom 10 percent of all

occurrences. For the purposes of this report, all tornadoes and hurricanes are considered extreme.
TABLE S-1 Potential Climate Changes and Illustrative Impacts on Transportation

Potential Climate Change Examples of Impacts on Operations Examples of Impacts on InfrastructureIncreases in very hot days 

and heat waves

Increases in Arctic 

temperatures

Rising sea levels, 

combined with storm surges

Impact on lift-off load limits at high-altitude or hotweather airports with insufficient runway lengths,

resulting in flight cancellations or limits on payload(i.e., weight restrictions), or both

Limits on periods of construction activity due to

health and safety concerns

Longer ocean transport season and more ice-free

ports in northern regions

Possible availability of a northern sea route or a

northwest passage

More frequent interruptions to coastal and low-lying

roadway travel and rail service due to storm surges

More severe storm surges, requiring evacuation or

changes in development patterns

Thermal expansion on bridge expansion joints and

paved surfaces

Concerns regarding pavement integrity (e.g., softening), traffic-related rutting, migration of liquid

asphalt

Rail-track deformitiesThawing of permafrost, causing subsidence of roads,

rail beds, bridge supports (cave-in), pipelines, andrunway foundations

Shorter season for ice roadsInundation of roads, rail lines, and airport runways in

coastal areas

More frequent or severe flooding of underground tunnels and low-lying infrastructure
Increases in intense 

precipitation events

More frequent strong 

hurricanes (Category 4–5)

Potential for closure or restrictions at several of the

top 50 airports that lie in coastal zones, affectingservice to the highest-density populations in theUnited States

Increases in weather-related delays and traffic 

disruptions

Increased flooding of evacuation routesIncreases in airline delays due to convective weatherMore frequent interruptions in air serviceMore frequent and potentially more extensive 

emergency evacuations

More debris on roads and rail lines, interrupting travel

and shipping

Erosion of road base and bridge supportsReduced clearance under bridgesChanges in harbor and port facilities to accommodate

higher tides and storm surges

Increases in flooding of roadways, rail lines, subterranean tunnels, and runwaysIncreases in road washout, damages to rail-bed support structures, and landslides and mudslides that

damage roadways and tracks

Increases in scouring of pipeline roadbeds and damage to pipelinesGreater probability of infrastructure failuresIncreased threat to stability of bridge decksImpacts on harbor infrastructure from wave damage

and storm surges
8 Potential Impacts of Climate Change on U.S. Transportation

increasing the exposure of people and businesses to harm from extreme

weather. The Atlantic and Gulf Coasts are particularly vulnerable because

they have already experienced high levels of erosion, land subsidence, and

loss of wetlands. Seven of the 10 largest U.S. ports (by tons of traffic), as

well as significant oil and gas production facilities, are located on the Gulf

Coast, an area whose vulnerability to disruption and damage was amply

demonstrated during the 2005 tropical storm season. Sea level rise and

coastal flooding also pose risks for the East Coast, as well as the Pacific

Northwest and parts of the California Coast.

The vulnerability of transportation infrastructure to climate change

will extend beyond coastal areas. For example, watersheds supplying water

to the St. Lawrence Seaway and the Great Lakes, as well as the Upper

Midwest river system, are likely to experience drier conditions, resulting in

lower water levels and reduced capacity to ship agricultural and other bulk

commodities, although a longer shipping season could offset some of the

adverse economic effects. Thawing permafrost in Alaska is already creating

settlement and land subsidence problems for roads, rail lines, runways, and

pipelines. Higher temperature extremes (mainly heat waves) in some U.S.

regions could lead to more frequent buckling of pavements and misalignment of rail lines. More severe weather events with intense precipitation

could increase the severity of extensive flooding events, such as the storms

that plagued the Midwest during the 1993 flooding of the Mississippi and

Missouri River system, the Chicago area in 1996, and the Houston region

during Tropical Storm Allison in 2001. Flooding of a waterway system can

knock out barge operations on the river itself, rail operations on rights-ofway adjacent to the river, and even highway approaches to bridges crossing

flooded rivers.

Not all climate change impacts will be negative. For example, the

marine transportation sector could benefit from more open seas in the

Arctic, creating new and shorter shipping routes and reducing transport

time and costs. In cold regions, expected temperature rises, particularly

decreases in very cold days and later onset of seasonal freezes and earlier

onset of seasonal thaws, could mean reduced costs of snow and ice control

for departments of transportation and safer travel conditions for passenger vehicles and freight.

Recommendation 1: Federal, state, and local governments, in

collaboration with owners and operators of infrastructure,
Summary 9

such as ports and airports and private railroad and pipeline

companies, should inventory critical transportation infrastructure in light of climate change projections to determine

whether, when, and where projected climate changes in their

regions might be consequential.

These inventories would need to be updated periodically as new scientific

knowledge about climate change becomes available. This would be a

relatively low-cost activity because a large portion of the necessary

information and tools [e.g., geographic information systems (GIS)] is

likely to be available. The inventorying process itself should also help

identify with greater precision the data needed from climate scientists on

transportation-relevant climate changes.

DECISION FRAMEWORK

Transportation decision makers have an opportunity now to prepare for

projected climate changes.

Finding: Public authorities and officials at various governmental

levels and executives of private companies are continually making

short- and long-term investment decisions that have implications

for how the transportation system will respond to climate change

in the near and long terms.

Recommendation 2: State and local governments and private

infrastructure providers should incorporate climate change

into their long-term capital improvement plans, facility

designs, maintenance practices, operations, and emergency

response plans.

Taking measures now to evaluate and protect the most vulnerable

infrastructure should pay off by diminishing near-term maintenance

expenditures and reducing the risk of catastrophic failure, with its toll on

human life and economic activity (see Box S-2, which presents a six-step

approach for determining appropriate investment priorities). Such measures might include strengthening or elevating some coastal roads, rail lines,

and bridges, particularly those that serve as evacuation routes, or upgrading parallel routes where they are available. In the longer term, relocation
BOX S-2

Decision Framework for Transportation Professionals

to Use in Addressing Impacts of Climate Change

on U.S. Transportation Infrastructure

1. Assess how climate changes are likely to affect various regions of the

country and modes of transportation.

2. Inventory transportation infrastructure essential to maintaining network

performance in light of climate change projections to determine whether,

when, and where the impacts could be consequential.

3. Analyze adaptation options to assess the trade-offs between making the

infrastructure more robust and the costs involved. Consider monitoring

as an option.

4. Determine investment priorities, taking into consideration the criticality

of infrastructure components as well as opportunities for multiple benefits

(e.g., congestion relief, removal of evacuation route bottlenecks).

5. Develop and implement a program of adaptation strategies for the near

and long terms.

6. Periodically assess the effectiveness of adaptation strategies and repeat

Steps 1 through 5.

10 Potential Impacts of Climate Change on U.S. Transportation

of rights-of-way farther inland or installation of costly storm barrier systems to protect selected areas (e.g., parts of New York City or Miami) might

be considered. Prudent choices today could avoid some of these costs.

Finding: The significant costs of redesigning and retrofitting

transportation infrastructure to adapt to potential impacts of

climate change suggest the need for more strategic, risk-based

approaches to investment decisions.

Traditionally, transportation decision makers have not taken full advantage of quantitative, risk-based approaches that incorporate uncertainty

and probabilistic assessments in making investment and design decisions. Nor will past trends provide a reliable guide for future plans and

designs as they relate to climate.

Recommendation 3: Transportation planners and engineers

should use more probabilistic investment analyses and design
Summary 11

approaches that incorporate techniques for trading off the

costs of making the infrastructure more robust against the

economic costs of failure. At a more general level, these techniques could also be used to communicate these trade-offs to

policy makers who make investment decisions and authorize

funding.

One model is the California Seismic Retrofit Program, which uses a riskbased approach for analyzing vulnerability to earthquakes and the criticality

of highway bridges to determine priorities for retrofitting and replacement.

Adapting such techniques to address climate change will require continuing

education of current planners and engineers and training of future professionals. It will also require educating policy makers to gain their support and

may well necessitate new eligibility criteria in funding programs and new

funding sources so the investments identified by the application of these

techniques can be made.

DATA AND DECISION SUPPORT TOOLS

Transportation decision makers note that one of the most difficult

aspects of addressing climate change is obtaining the relevant information in the form needed for planning and design purposes. Specifically,

as noted earlier, climate change is understood with greatest confidence

as a global phenomenon, while transportation planners need local and

regional climate projections. They also need a better understanding of

how projected climate changes, such as changes in temperature and

precipitation, will affect the environment (e.g., soil moisture, runoff)

in which the infrastructure is situated, which will vary from region to

region.

Finding: Transportation professionals often lack sufficiently detailed

information about expected climate changes and their timing to take

appropriate action.

Simply put, transportation professionals, climate scientists, hydrologists,

and others have not communicated well.

Recommendation 4: The National Oceanic and Atmospheric

Administration, the U.S. Department of Transportation
12 Potential Impacts of Climate Change on U.S. Transportation

(USDOT), the U.S. Geological Survey, and other relevant

agencies should work together to institute a process for better

communication among transportation professionals, climate

scientists, and other relevant scientific disciplines, and establish a clearinghouse for transportation-relevant climate change

information.

All professions should benefit from the collaboration. Transportation professionals would be encouraged to define with greater precision the

climate data needed to make better transportation decisions, such as temperature and precipitation thresholds at finer-grained geographic scales or

climate conditions that would create unacceptable performance outcomes.

Climate scientists would be challenged to elaborate on the possibilities and

limitations of projecting the impacts of climate change at the levels of geographic specificity that are most useful for transportation planners. And

hydrologists and others would be challenged to consider how the environment would influence these effects and their impacts on transportation

infrastructure.

Finding: Better decision support tools are also needed to assist

transportation decision makers.

Recommendation 5: Ongoing and planned research at federal and state agencies and universities that provide climate

data and decision support tools should include the needs of

transportation decision makers.

For example, the research program of the USDOT Center for Climate

Change and Environmental Forecasting could be charged with expanding

its existing research program in this area and provided the necessary funding. Needed tools include highly accurate digital elevation maps in coastal

areas for forecasting the effects of flooding and storm surge heights; GIS

that can be used to map the locations of critical infrastructure, overlaid

with information on climate change effects (e.g., sea level rise, permafrost

melt); greater use of scenarios that include climate change in the development of long-range regional transportation plans to pinpoint likely

vulnerabilities and ways to address them; and better network models for

examining the systemwide effects of the loss of critical transportation

infrastructure links.
Summary 13

ADAPTATION OPTIONS

Numerous studies have examined ways of mitigating the transportation

sector’s contribution to global warming from GHG emissions. Far less

attention has been paid to the potential impacts of climate change on U.S.

transportation and how transportation professionals can best adapt to climate changes that are already occurring and will continue to occur into the

foreseeable future, even if drastic mitigation measures were taken today.

Operational Responses

Climate extremes and abrupt changes, such as storms and precipitation

of increased intensity, will require near-term operational responses from

transportation providers. U.S. transportation providers already address

the impacts of weather on transportation system operations in a diverse

range of climatic conditions. For example, snow and ice control accounts

for about 40 percent of annual highway operating budgets in the northern states. Likewise, hurricane planning has become a major focus of

transportation operations in the Gulf Coast states, where transportation

providers are forging close relationships with emergency responders to

handle severe weather events.

As climate changes induce new extremes, operational responses are

likely to become more routine and proactive than today’s approach of

treating severe weather on an ad hoc, emergency basis. For example, if

hurricanes increase in intensity, as is likely to be the case, establishment of

evacuation routes and use of contraflow operations may become as commonplace as the current use of snow emergency routes in the Northeast

and Midwest. More accurate and timely weather prediction and communication of storm warnings in real time to those potentially in harm’s way

will become more important.

Finding: Projected increases in extreme weather and climate

underscore the importance of emergency response plans in vulnerable locations and require that transportation providers work

more closely with weather forecasters and emergency planners

and assume a greater role in evacuation planning and emergency

response.

Recommendation 6: Transportation agencies and service

providers should build on the experience in those locations
14 Potential Impacts of Climate Change on U.S. Transportation

where transportation is well integrated into emergency

response and evacuation plans.

Monitoring and Use of Technology

Monitoring infrastructure conditions, particularly the impacts of extreme

climate changes, offers an alternative to preventive retrofitting or reconstruction of some facilities. In Alaska, for example, the Alyeska Pipeline

Company constantly monitors the right-of-way of the Trans-Alaska

Pipeline System to spot land subsidence problems, particularly along the

800 miles of pipeline elevated on vertical supports. Alaskan engineers also

closely monitor bridge supports that are experiencing damage from earlier

winter runoff and increased stream flow. In the future, sensors and other

smart technologies could be embedded in the infrastructure to monitor climate conditions and impacts.

Finding: Greater use of technology would enable infrastructure

providers to monitor climate changes and receive advance warning of potential failures due to water levels and currents, wave

action, winds, and temperatures exceeding what the infrastructure was designed to withstand.

Recommendation 7: Federal and academic research programs

should encourage the development and implementation of

monitoring technologies that could provide advance warning

of pending failures due to the effects of weather and climate

extremes on major transportation facilities.

Sharing of Best Practices

As the climate changes, many U.S. locations will experience new climateinduced weather patterns.

Finding: The geographic extent of the United States—from Alaska

to Florida and from Maine to Hawaii—and its diversity of weather

and climate conditions can provide a laboratory for identifying best

practices and sharing information as the climate changes.

Recommendation 8: The American Association of State

Highway and Transportation Officials (AASHTO), the Federal
Summary 15

Highway Administration, the Association of American

Railroads, the American Public Transportation Association,

the American Association of Port Authorities, the Airport

Operators Council, associations for oil and gas pipelines, and

other relevant transportation professional and research

organizations should develop a mechanism to encourage

sharing of best practices for addressing the potential impacts

of climate change.

This effort should build on existing technology transfer mechanisms,

such as AASHTO’s technology-sharing program. Technology should be

defined broadly to include probabilistic decision-making tools, as well as

monitoring technologies, new materials, and operating and maintenance

strategies.

Design Changes

Environmental factors are integral to the design of transportation infrastructure. Conditions such as temperature, freeze–thaw cycles, and

duration and intensity of precipitation determine subsurface and foundation design, choice of materials, and drainage capacity. Engineers, however,

have given little thought to whether current design standards are sufficient

to accommodate climate change. For example, will drainage capacity be

adequate for expected increases in intense precipitation events? Many infrastructure components are currently designed for the 100-year storm—an

event of such severity that it occurs, on average, once in 100 years. But projections indicate that what is today’s 100-year precipitation event is likely to

occur every 50 or perhaps even every 20 years by the end of the current

century. What new materials might be needed when very hot temperatures

and heat waves become more frequent? Are infrastructure components

sufficiently strong to withstand the forces of larger and more frequent

storm surges and more powerful wave action, the effects of which were

vividly demonstrated when Hurricane Katrina simply lifted bridge decks

off their supporting structures?

Finding: Reevaluating, developing, and regularly updating design

standards for transportation infrastructure to address the impacts

of climate change will require a broad-based research and testing

program and a substantial implementation effort.
Developing consensus standards is a time-consuming process. Changes

in design practices tend to be incremental, and building to higher standards

must be weighed against the cost involved. Thus there is a need for a selective, risk-based approach to making changes in standards that focuses first

on long-lived facilities, such as bridges and large culverts. A good model is

the congressionally mandated National Earthquake Hazard Reduction

Program, begun in 1977, which established a research effort and a coordination mechanism designed to reduce the risks to life and property from

earthquakes through standards that would afford different levels of protection for different levels of risk. If a similar program is to be launched to

address climate change in a timely manner, it should be initiated soon.

Recommendation 9: USDOT should take a leadership role,

along with those professional organizations in the forefront of

civil engineering practice across all modes, to initiate immediately a federally funded, multiagency research program for

ongoing reevaluation of existing and development of new

design standards as progress is made in understanding future

climate conditions and the options available for addressing

them. A research plan and cost proposal should be developed

for submission to Congress for authorization and funding of

this program.

The initial focus should be on essential links in transportation networks,

particularly those vulnerable to climate change in coastal or other lowlying areas in riverside locations.

Recommendation 10: In the short term, state and federally

funded transportation infrastructure rehabilitation projects

in highly vulnerable locations should be rebuilt to higher standards, and greater attention should be paid to the provision

of redundant power and communications systems to ensure

rapid restoration of transportation services in the event of

failure.

The development of appropriate design standards to accommodate

climate change is only one of several possible adaptation strategies.

Finding: Federal agencies have not focused generally on adaptation in addressing climate change.

16 Potential Impacts of Climate Change on U.S. Transportation
Summary 17

Recommendation 11: USDOT should take the lead in developing an interagency working group focused on adaptation.

This initiative would not necessarily require new funding beyond that recommended above. Better collaboration among agencies could help focus

attention on adaptation issues and shape existing research programs.

Transportation Planning and Land Use Controls

One of the most effective strategies for reducing the risks of climate change

is to avoid placing people and infrastructure in vulnerable locations.

Transportation planners currently consider expected land use patterns

when forecasting future travel demand and infrastructure needs. However,

they rarely question whether such development is desirable, much less

what effects climate change might have on the provision and development

of infrastructure in vulnerable locations. In part, this situation stems from

governance arrangements. States, regional authorities, and the private sector are responsible for large-scale transportation investment decisions, but

local governments and a few states control land use decisions through

comprehensive plans, zoning ordinances, permitting, and building codes.

Finding: Transportation planners are not currently required to

consider climate change impacts and their effects on infrastructure investments, particularly in vulnerable locations.

Recommendation 12: Federal planning regulations should

require that climate change be included as a factor in the development of public-sector long-range transportation plans;

eliminate any perception that such plans should be limited to

20 to 30 years; and require collaboration in plan development

with agencies responsible for land use, environmental protection, and natural resource management to foster more

integrated transportation–land use decision making.

Current surface transportation legislation encourages such collaboration. During reauthorization, requiring transportation planners to both

consider climate change and collaborate with land use planners in the

preparation of public-sector long-range plans could go a long way toward

putting these issues on the table. At the same time, any strategy employing

land use controls to address climate change would need to build consen-
18 Potential Impacts of Climate Change on U.S. Transportation

sus among key decision makers in transportation and land use, probably

at the regional level—a challenging proposition.

Finding: Locally controlled land use planning, which is typical

throughout the country, has too limited a perspective to account

for the broadly shared risks of climate change.

Insurance

Private insurers may be able to accomplish what government cannot in

terms of land use control. Some major insurers, for example, are refusing

to write new or renew existing homeowners’ policies in areas already vulnerable to hurricanes and other severe storms, which could intensify in a

warming climate. Florida, Texas, Louisiana, Mississippi, Hawaii, New York

City, and Long Island are among the areas affected thus far. Some states

have stepped up to become insurers of last resort for coastal homes and

businesses, but the high costs of providing coverage are unlikely to be sustainable. Moreover, the provision of insurance in hazard-prone areas that

is not actuarially based is bad public policy.

The federal government is the insurer of last resort for homeowners in

specially designated flood hazard areas. The National Flood Insurance

Program of the Federal Emergency Management Agency (FEMA) provides

homeowners with below-cost insurance. In return, the local community

must adopt and enforce floodplain management measures, including

building code ordinances for new construction and rebuilding after a disaster, to reduce flood damage. Critics contend that in practice, the program

has resulted in more development than would otherwise have occurred in

these areas. Moreover, the accuracy of flood insurance rate maps (FIRMs)

used to determine program eligibility is woefully inadequate, despite a

mapping modernization program. Flood hazard area boundaries are keyed

to the 100-year storm, and base elevation data are inadequate.

Finding: The National Flood Insurance Program and the FIRMs

used to determine program eligibility do not take climate change

into account.

Recommendation 13: FEMA should reevaluate the risk reduction effectiveness of the National Flood Insurance Program

and the FIRMs, particularly in view of projected increases in
Summary 19

intense precipitation and storms. At a minimum, updated

flood zone maps that account for sea level rise (incorporating

land subsidence) should be a priority in coastal areas.

New Organizational Arrangements

The impacts of climate change do not follow modal, corporate, or jurisdictional boundaries, yet decision making in the transportation sector is

structured around these boundaries. Transportation planning is conducted

primarily at the regional level, often through a bottom-up process that starts

with local jurisdictions. Railroads, trucking, and waterborne commerce are

largely private enterprises with varying levels of federal participation. Thus,

existing institutional arrangements are not well suited to addressing climate change. Some models of cross-jurisdictional cooperation exist, such

as regional authorities for specific facilities (e.g., the Alameda Corridor) and

multistate emergency response agreements. In addition, there are models of

state-mandated regional authorities, as is the case for regional air quality

improvement authorities. Organizational arrangements suited to addressing the impacts of climate change may require state or federal action.

Finding: Current institutional arrangements for transportation

planning and operations were not organized to address climate

change and may not be adequate for the purpose.

Recommendation 14: Incentives incorporated in federal and

state legislation should be considered as a means of addressing and mitigating the impacts of climate change through

regional and multistate efforts.

For example, states could use updated FIRMs or their own state maps to

identify geographic areas vulnerable to climate change and craft policies

for restricting transportation investments and limiting insurance in these

locations.

CONCLUDING THOUGHTS

The committee finds compelling scientific evidence that climate change

is occurring and that it will trigger new, extreme weather events and

could possibly lead to surprises, such as more rapid than expected rises in
sea levels or temperature changes. Every mode of transportation will be

affected as climate change poses new and often unfamiliar challenges to

infrastructure providers. The committee urges that the transportation

community start now to confront these challenges.

A strong federal role is needed to implement many of the committee’s

recommendations that require broad-based action or regulation, such as

creation of a clearinghouse for information on transportation and climate

change, the research program to reevaluate existing and develop new

design standards for addressing climate change, creation of an interagency

working group on adaptation, changes in federal regulations regarding

long-range planning guidelines and infrastructure rehabilitation requirements, and reevaluation of the National Flood Insurance Program.

Many of the committee’s recommendations, however, need not await

federal action. Local governments and private infrastructure providers can

begin to identify critical infrastructure that is particularly vulnerable to climate change. Professional organizations can begin to amass examples of

best practice, and planners and climate scientists at local universities and

research institutes can begin to collaborate on the development of regional

scenarios of likely transportation-related climate changes and the data

needed to analyze their impacts. The most important step, however, is for

transportation professionals to acknowledge that the time has come to

confront the challenges posed by climate change and to incorporate the

most current scientific knowledge into the planning, design, construction,

operation, and maintenance of transportation systems.

20 Potential Impacts of Climate Change on U.S. Transportation
21

1

Introduction

Climate scientists are projecting changes in the global climate with

potentially profound impacts on agriculture and forest productivity,

ecosystems, water resources, and energy, as well as related socioeconomic

effects.1 Increases in annual globally averaged mean temperatures, in the

number of warm days and nights over mid- and high-latitude land areas,

and in temperature and precipitation extremes all are projected to occur

with a high degree of confidence2 during the 21st century. These changes

will bring about the retreat of sea ice and the thawing of glaciers and ice

caps, particularly at high northern latitudes; rising sea levels; and greater

flooding and higher storm surges along vulnerable coastal and riverine

areas. The finer the geographic resolution and the longer the temporal projections, the greater are the uncertainties surrounding estimates of future

climate change. The respective roles of human and natural causes in these

changes have now been well established (IPCC 2007b).

Numerous studies have examined the link between climate change and

the transportation sector. These studies have been conducted primarily

1 Climate change refers to a statistically significant variation in either the mean state of the climate

or its variability over an extended period, typically decades or longer, that can be attributed to

either natural causes or human activity (IPCC 2007a). This definition is drawn from the

Intergovernmental Panel on Climate Change (IPCC), which was jointly established by the World

Meteorological Organization and the United Nations Environment Programme in 1988 to assess

the available scientific and socioeconomic information on climate change and its impacts and on

options for mitigating those impacts and developing adaptive responses.

2 Climate scientists express uncertainty in a variety of ways. To encourage greater uniformity in

communicating uncertainty, lead authors of the IPCC Fourth Assessment Report were provided

guidance on how to treat issues of uncertainty and statistical confidence in a consistent manner

(IPCC 2005). The term “high degree of confidence” means consistency across model projections

and/or consistency with theory and/or changes in the mean. See Chapter 2 for a more detailed 

discussion of uncertainty.
22 Potential Impacts of Climate Change on U.S. Transportation

from the perspective of transportation’s contribution to global warming

through the burning of fossil fuels, which releases carbon dioxide (CO2)

and other greenhouse gases (GHGs) into the atmosphere.3 CO2 from combustion of fossil fuels is the largest source of U.S. GHG emissions. In 2005,

the most recent year for which data are available, the transportation sector

accounted for 33 percent of U.S. CO2 emissions from fossil fuel combustion,4 exceeded only by electricity generation by the electric power industry

at 41 percent (USEPA 2007, Table 3-7).5 CO2 emissions from U.S. transportation activities are expected to increase over the next several decades,

primarily as a result of growth in road travel, fueled by population and economic growth (World Business Council for Sustainable Development

2004). However, these emissions are likely to be regulated. In a landmark

decision in April 2007 (Massachusetts et al., Petitioners, v. Environmental

Protection Agency et al.), the U.S. Supreme Court ruled that the U.S.

Environmental Protection Agency has the authority under the Clean Air

Act to regulate GHG emissions and that CO2 can be construed as an air

pollutant under the statute.

Far less attention has been paid to the consequences of potential climate

changes for U.S. transportation infrastructure and operations.6, 7 For example, projected rising sea levels, flooding, and storm surges could swamp

marine terminal facilities, airport runways near coastlines, subway and railroad tunnel entrances, and roads and bridges in low-lying coastal areas.

3 CO2 and other GHGs allow sunlight to enter and prevent heat from leaving the earth’s atmosphere—

the so-called greenhouse effect, loosely analogous to the operation of a greenhouse window. Higher

concentrations of CO2 and other GHGs than occur naturally trap excess heat in the atmosphere and

warm the earth’s surface (Staudt et al. 2005).

4 Emissions from combustion of both aviation and marine international bunker fuels (i.e., fuel

loaded on transport vehicles in the United States but consumed in international operations) are

excluded from this total. See Appendix B for a more detailed discussion of the transportation 

sector’s contribution in general, and the U.S. contribution in particular, to worldwide GHG

emissions, particularly emissions of CO2 from fuel combustion.

5 The total is larger if emissions from the extraction, production, and distribution of transport fuels

and from the manufacture, distribution, and disposal of transportation vehicles are summed to

produce a total life-cycle emissions estimate (see the discussion in Appendix B).

6 In this report, infrastructure refers to both transportation networks (e.g., road and rail systems)

and facilities (e.g., bridges, tunnels, ports).

7 In fact, a recent assessment of the U.S. Climate Change Science Program (CCSP) found that the

scientific community is not well structured to develop information that would enable adaptive

response for any sector in the United States (NRC 2007). The CCSP integrates federal research on

climate and global change, as sponsored by 13 federal agencies.
Across the northern portions of the contiguous United States, warmer temperatures and reduced lake ice will likely lead to increased evaporation

from bodies of water and their surrounding watersheds, potentially lowering lake and river levels and reducing vessel-carrying capacity. Shipping

across the Great Lakes and the Upper Midwest river system would thereby

be impaired, although a longer shipping season would offset some of the

adverse economic effects. Thawing permafrost in Alaska is already creating

settlement and land subsidence problems for roads, rail lines, runways,

and pipelines. Greater temperature extremes (mainly heat waves) in some

U.S. regions could lead to buckling of pavements and misalignment of rail

lines. More intense precipitation could increase the severity of flooding

events, such as the storms that plagued the Midwest during the flooding

of the Mississippi River in 1993 and the Chicago area in 1996. More

intense tropical storms, like Hurricanes Katrina and Rita, which ravaged

the Gulf Coast in 2005, are likely to become more frequent. However, no

significant increases in the annual number of Atlantic tropical storms are

projected.

The vulnerability8 of the transportation sector to these impacts has not

been thoroughly studied, nor has it been widely considered by transportation planners and decision makers in planning, designing, constructing,

retrofitting, and operating the transportation infrastructure. Many transportation professionals are unaware of the problems climate change could

create. Others are hesitant to take action in view of the uncertain outcomes

and long time frames involved and the lack of clear guidelines and standards for addressing the effects of climate change and related hazards.

STUDY CHARGE, SCOPE, AND AUDIENCE

The Executive Committee of the Transportation Research Board (TRB)

requested and provided funding for this study, which was undertaken

jointly with the Division on Earth and Life Studies of the National

Introduction 23

8 One in-depth assessment of impacts in the Gulf Coast region, entitled Impacts of Climate Change

and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, was ongoing during

the course of this study. It became available for public comment only after the committee had

completed its deliberations. The public review version of the Gulf Coast study can be accessed at

www.climatescience.gov/Library/sap/sap4-7/public-review-draft/default.htm.
Academies. The expert committee formed to conduct the study was

charged9 to

• Provide federal, state, and local transportation officials in the

United States with an overview of the scientific consensus regarding

climate change, including uncertainty about its nature and extent;

• Summarize previous work on strategies for reducing transportation’s impact on climate change;

• Summarize possible impacts on transportation, such as those due

to rising sea levels, higher mean temperatures with less extreme

low temperatures and more heat extremes, and more frequent

intense precipitation events;

• Analyze options for adapting to these impacts, including the possible need to alter assumptions about infrastructure design and

operations, the ability to incorporate uncertainty into long-range

decision making, and the capability of institutions to plan and act

on mitigation and adaptation strategies at the state and regional

levels;

• Identify critical areas for research; and

• Suggest policies and actions for preparing for the potential

impacts of climate change.

The committee’s charge can be viewed more broadly as a risk management problem with hazards to address (potential impacts of climate

change) and vulnerable10 assets to protect (transportation infrastructure).

Seen in this framework, the objective is to minimize risk by reducing the

hazards (i.e., identify mitigation measures to reduce the potential effects of

climate change) and protecting the assets (i.e., identify adaptation mea24 Potential Impacts of Climate Change on U.S. Transportation

9 A more detailed statement of task is included as Appendix A.

10 In this report, the term “vulnerability” is defined as “the degree to which a system is susceptible

to, and unable to cope with, adverse effects of climate change, including climate variability and

extremes. Vulnerability is a function of the character, magnitude, and rate of climate change and

variation to which a system is exposed, its sensitivity, and its adaptive capacity” (IPCC 2007a, 21).

The committee notes that there is a large literature on vulnerability as it relates to many hazards

and cites Turner et al. (2003) as an example of a broad vulnerability framework and its application

to several different types of hazards and affected communities in case studies.
sures11 to strengthen the infrastructure and increase its resilience to

changing climate conditions through more stringent design standards

and construction codes and retrofitting or relocation of at-risk facilities).12

The primary focus of this report is on adaptation strategies rather than

on strategies to mitigate transportation-related GHG emissions. The topic

of adaptation, particularly as it relates to transportation, has not received

the attention or research effort devoted to the issue of mitigation. Investigating both topics fully was beyond the resources available for this

study. In fact, at the time of this writing, TRB had initiated a new study

focused entirely on mitigation.13 Nevertheless, in response to its charge

and drawing heavily on existing studies, committee member George Eads,

with the consensus of the full committee, summarized current and projected contributions of the transportation sector to GHG emissions and

examined numerous technological and nontechnological mitigation

strategies (see Appendix B). The analysis did not attempt to pick winners

and losers by comparing the costs and benefits of alternative mitigation

approaches. Indeed, the data for doing so were not available. That level of

analysis would require a separate study or even a series of studies.

The committee was mindful of the potential interaction between mitigation and adaptation strategies as shown in Figure 1-1. For example, if the

fuel consumption and CO2 emissions and concentrations of transportation

vehicles could be substantially reduced by the introduction of new technologies, this would lessen the human-caused contribution to climate

change and its impacts on transportation infrastructure. Reductions in

travel demand or shifts to less GHG-emitting travel modes (e.g., public

transit for personal travel and rail for freight travel) would operate in a similar fashion. The summary of Appendix B notes, however, that a common

Introduction 25

11 Adaptation strategies refer to human attempts to protect or adapt systems so as to reduce the

risks and moderate the potential harm from and exploit the beneficial opportunities of the impacts

of climate change. Mitigation strategies refer to human intervention to reduce the sources of GHGs

that contribute to climate change.

12 Until researchers can quantify both the severity of expected outcomes and their probabilities,

however, a full risk assessment is not possible.

13 The study on potential energy savings and GHG reductions will review policies and strategies to

affect behavior and improve fuel economy for passenger and freight vehicles across all modes;

develop scenarios to illustrate potential savings over a 25- to 50-year time horizon for the United

States; and analyze the safety, economic, transportation finance, and environmental consequences

of energy-saving measures.
characteristic of these mitigation measures is the considerable time they

would take to be fully effective14 and the fact that they would affect only

future GHG emissions and concentration levels. Complementary adaptation strategies are thus essential if the transportation sector is to address the

consequences of GHG emissions and concentration levels that have already

occurred.

The report begins with an overview of the current state of knowledge

about climate change and its potential impacts, with a particular focus on

North America, to set the stage for assessing the consequences for the

transportation sector and identifying prudent adaptation strategies. The

objective of this review is not to advance the state of climate science but

26 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 1-1 Role of mitigation measures and adaptation strategies in addressing

climate change impacts on U.S. transportation infrastructure. (Bolded areas denote

the primary focus of this study.)

Greenhouse Gas 

Emissions and 

Concentrations 

Impacts on U.S. 

Transportation 

Infrastructure 

Policies/ 

Actions 

Adaptation 

Strategies 

Mitigation 

Measures Reduce Impacts 

Reduce greenhouse gas emissions and concentrations 

Climate 

Changes 

Mediating 

Environmental 

Effects 

14 The appendix notes that the time required to develop, commercialize, and disseminate new

vehicle technologies is probably shorter than the time required to alter the fundamental drivers of

demand for personal and freight transport—growth in real income, population growth, urbanization,

and changes in urban form. Nevertheless, both new technology and shifts in demand are needed if

future levels of transportation-related GHG emissions—a major source of total GHG emissions—

are to be significantly reduced.
to inform transportation professionals about climate change—including

uncertainty as to its precise timing and geographic locations—so they

can begin to consider appropriate responses.

The report encompasses all modes of transportation—highways

(including bridges and tunnels), rail (including private rail lines and

public transportation), marine and air transportation, and pipelines. Its

primary focus is on the direct impacts of climate change on transportation infrastructure and system operating performance, although indirect

impacts are noted (e.g., potential shifts in the location of economic activities and use of transportation modes, pollution impacts). These indirect

impacts are highly uncertain because they depend on assumptions about

population and economic growth, the rate of technological innovation,

and policy decisions (e.g., government regulations and controls on coastal

land use and development, private-sector decisions about business operations and logistics).

The geographic scope of the study is confined to the United States but

extends beyond the contiguous 48 states to include Alaska, Hawaii, and the

U.S. territories.15 The range of weather and climate conditions16 embraced

by this area is broad—from the permafrost conditions of Alaska to the

tropical conditions of Puerto Rico and Hawaii. Thus, the United States can

expect a wide range of climate changes and their impacts. International

studies were reviewed for techniques and approaches that might be appropriate to the United States. However, the committee found few studies that

address the impact of climate change on transportation and adaptation

strategies.

The audience for this report is the transportation community broadly

defined. The overall goal of the report is to demonstrate to decision

makers responsible for transportation infrastructure—both public and

private—why they should plan for climate change. At the same time, an

attempt is made to moderate expectations about the level of precision

with which the report can provide guidance on specific impacts of climate change and their time frames.

Introduction 27

15 Information on climate change effects and impacts, however, is not always available for smaller

geographic areas.

16 Climate change refers to a statistically significant variation in either the mean state of the climate

or its variability over an extended period, typically decades or longer, that can be attributed to

either natural causes or human activity. Weather refers to the familiar hour-by-hour, day-by-day

changes in temperature, cloudiness, precipitation, and other atmospheric phenomena.
WHY CLIMATE CHANGE MATTERS

When asked to consider climate change, transportation professionals frequently protest that dealing with a problem whose time horizon is decades

and centuries and whose effects are uncertain is impractical. Moreover,

they maintain, resources are insufficient to address day-to-day maintenance problems, much less to make investments on the basis of changes

that may or may not occur years or even generations into the future.

So why should transportation professionals take note of climate

change? First, it is not just a problem for the future. Recent changes, such

as global warming and resulting sea level rises, reflect the effects of GHG

emissions that were released into the atmosphere over the past century.

What appears to be new is the greater certainty of scientists that human

activity is already warming the climate and that the rate of change is likely

to be greater than at any time in modern history (IPCC 2007b).

Second, climate change will not necessarily occur gradually. Climate

scientists expect that higher temperatures will be amplified by normal variability in climate, leading to new extremes far outside current experience

[e.g., the heat wave in Europe in 2003 (Stott et al. 2004) and the near record

heat of 2006 in the United States (Hoerling et al. 2007)]. Higher temperatures are also likely to trigger surprises, such as more rapid than expected

melting of Arctic sea ice and rising sea levels.

Third, although transportation professionals typically plan 20 to

30 years into the future, many decisions taken today, particularly about

the location of infrastructure, help shape development patterns and markets that endure far beyond these planning horizons. Similarly, decisions

about land use, zoning, and development often create demand for longlived transportation infrastructure investments. Thus, it is important for

transportation decision makers to consider potential impacts of climate

change now in making these investment choices because those impacts

will affect how well the infrastructure adapts to climate change.

Fourth, professionals in many fields—among them finance, building

(where protecting against earthquakes, wildfires, or wind risk is a concern),

nuclear power, and water resources (in the design of dams and canals)—

are continually making decisions in the face of uncertain information

about risks and outcomes. In fact, the highway and bridge engineering

community, through the auspices of the American Association of State

Highway and Transportation Officials, has developed design guidelines and

28 Potential Impacts of Climate Change on U.S. Transportation
standards for earthquake resistance on the basis of probabilistic seismic hazard assessments that take many uncertainties into account. Similarly,

addressing climate change requires more quantitative assessments, such as

the development of probabilistic climate change scenarios at the level of

geographic and modal specificity needed by transportation planners and

engineers, which can be incorporated into planning forecasts and engineering design guidelines and standards.

Finally, transportation professionals already consider weather- and

climate-related factors in designing and operating the transportation

infrastructure. For example, many transportation networks and facilities

are designed with adequate drainage and pumping capacity to handle a

100-year storm.17 Materials and maintenance cycles are geared to assumptions about temperature and precipitation levels. Evacuation plans and

routes have been identified in hurricane- and other storm-prone locations

on the basis of current elevations and assumptions about storm surges

and wave action. But what if the 100-year storm were to become the 50-

or 30-year storm, or design thresholds were frequently to be exceeded, or

evacuation routes themselves were to become vulnerable (see Box 1-1)?

Such changes could necessitate different design criteria, asset management

policies, maintenance cycles, and operating strategies. Recent severe weather

events—such as the Mississippi River floods of 1993, Category 3 or greater

hurricanes (e.g., Ivan, Katrina, Rita), the California wildfires of 2003—

provide ample opportunities for transportation professionals to observe

the vulnerabilities of the infrastructure to shocks to the system that could

become more commonplace in the future. They also illustrate the

dilemma facing transportation decision makers of whether to rebuild,

rebuild differently, or relocate critical transportation infrastructure.

STUDY APPROACH AND KEY ISSUES

A wide range of climate changes could affect transportation infrastructure and result in changes in the way U.S. transportation professionals

plan, design, operate, and maintain the infrastructure. The committee

adapted a figure from a workshop conducted by the U.S. Department of

Introduction 29

17 A 100-year storm is defined as the amount of rainfall during a specified length of time that has

a 1 percent chance of being equaled or exceeded in any given year or, put another way, has a

recurrence interval of 100 years.
BOX 1-1

What If?

• What if design lives for infrastructure and return periods were to be

exceeded routinely? Many facilities are built to withstand a 100-year

storm. The design of other facilities, such as bridges, assumes a 50-year

storm and does not take into account the effect of wave action, vividly

illustrated by Hurricane Katrina (Meyer 2006). What if the 50-year storm,

or even the 100-year storm, were to be exceeded routinely, reducing projected recurrence periods to much below one in 50 or one in 100 years?

• What if multiple severe weather events were to occur? Each year, Florida

and the Gulf Coast brace for hurricanes, and California prepares for wildfires or heavy rains. Emergency personnel are generally able to handle

these events, and transportation managers find alternative routes to keep

freight moving, largely because the events occur sequentially and at relatively infrequent intervals. But consider the impact of a Category 4 or

5 hurricane directed at Houston and its critical petrochemical infrastructure at the same time that torrential rains and mudslides prevent access

to the Port of Los Angeles. How would emergency responders and the

economy fare in the face of multiple and simultaneous intense storms

that climate change could bring with greater frequency?

• What if critical evacuation routes were themselves to become submerged by rising seas and storm surge? Population increases in coastal

areas are projected to more than double in the next 20 years. Many seaside communities count on coastal highways for evacuation in a major

storm. Some of these highways also act as flood barriers. What if the

current accelerating rate of sea level rise were to continue into the foreseeable future? Highways in low-lying areas that provide a vital lifeline

could themselves become compromised by encroaching seas and storm

surge. Some communities could be cut off in a severe storm or would be

forced to evacuate well in advance of the storm’s known trajectory to

avoid that risk. In the longer term, it may be possible to relocate some

coastal highways farther inland and still provide a means of egress for

vulnerable communities.

30 Potential Impacts of Climate Change on U.S. Transportation
Transportation (USDOT 2003) on the potential impacts of climate

change on transportation (Potter and Savonis 2003) to provide a conceptual framework for this study (Figure 1-2). The first task is to identify

potential climate change effects, focusing on those of greatest relevance

for transportation (see Column 1). This task also includes indicating

what is known from climate scientists about the certainty of these effects,

particularly at the regional and local levels, and the time frame over

which they are likely to unfold.

The second task (see Column 2) involves describing the impacts of the

effects of climate change on transportation. These impacts can be considered in several different ways—by type of climate change effect (e.g., sea

level rise, temperature extremes), by transportation mode, by geographic

area, and by type of impact. With regard to the latter, impacts on transportation can be direct (i.e., affecting the physical infrastructure as well as

Introduction 31

1. Potential Climate 

Change Effects 

• Effects of greatest 

relevance for 

transportation 

• Geographic scale at 

which effect can be 

projected with 

confidence 

• Degree of certainty 

with which effect is 

known 

• Time frame over 

which effect is likely 

to unfold 

2. Impacts on U.S. 

Transportation

• By climate change 

effect 

• By transportation 

mode 

• By geographic area 

where the 

infrastructure is 

located 

• By type of impact 

– Direct, indirect 

– Infrastructure, 

operations 

3. Possible 

Adaptation 

Strategies 

• Identification of 

critical infrastructure 

potentially at risk 

• Monitoring of 

changing climate 

conditions and 

impacts on 

infrastructure 

• Changes in 

operating and 

maintenance 

practices 

• Changes in 

infrastructure design 

and redesign 

• Relocation of 

vulnerable 

infrastructure

FIGURE 1-2 Potential impacts of climate change on transportation infrastructure.

[Note in Column 2 that the impacts of climate change on U.S. transportation

infrastructure will be influenced by the environment in which the infrastructure

is located (e.g., soil moisture, stream flow), which will vary from region to

region.] (Source: Adapted from Potter and Savonis 2003, 29.)
the operating performance of the system) or indirect (e.g., affecting the

location of economic activities or levels of pollution). Finally, these impacts

will be influenced by changes in the environment in which the infrastructure is situated. For example, changes in temperature and precipitation will

affect soil moisture and runoff, which in turn will affect peak stream flows,

sediment delivery to coasts, and the sustainability of the landforms upon

which the infrastructure is built, with considerable regional variability. The

tasks listed in Columns 1 and 2 require good communication among climate scientists, transportation professionals, and other relevant scientific

disciplines.

The final task (see Column 3) requires developing possible adaptation

strategies. A range of approaches is suggested—from the identification of

at-risk critical infrastructure, to the monitoring of conditions (both climate

and infrastructure), to changes in operating and maintenance practices, to

changes in infrastructure design and redesign, to relocation of vulnerable

infrastructure. The strategies listed in this column require action primarily by transportation decision makers—planners, designers, engineers, and

operating and maintenance personnel.

Figure 1-2 links together potential climate change effects, impacts on

U.S. transportation infrastructure, and possible adaptation strategies, but

it does not fully address several key points. First, issues of scale affect the

certainty with which the effects of climate change on transportation infrastructure can be examined at present. Climate change projections are most

accurate at the global level, but transportation infrastructure is largely

local and regional. Nevertheless, the ability to predict climate change at the

local and regional levels is improving. Furthermore, the effects of climate

change are not point specific; their impacts may differ even within a region,

depending on location. For example, sea level rise will affect coastal regions,

but the seriousness of the impact will depend on the elevation, the amount

of land subsidence, and the extent of protection (e.g., levees) provided and

the redundancy of vulnerable infrastructure in the affected areas.

The network character of transportation infrastructure adds another

layer of complexity. Adverse impacts of climate change on transportation

facilities in one region, for example, may shift activity to another location

or route, either temporarily, as was the case for freight movement in the

wake of Hurricane Katrina, or in the longer term (e.g., shifts in port activity resulting from new shipping routes opening as a result of warming

and deepening seas), with net effects that may be positive or negative.

32 Potential Impacts of Climate Change on U.S. Transportation
Differences in time frames are another complicating factor. Some climate changes will unfold over decades and centuries, ostensibly allowing

time for transportation decision makers to plan and respond. Others are

likely to increase the sensitivity of the climate system and could bring

surprises and abrupt changes that would make planning difficult.18 The

lifetime of transportation infrastructure can be as little as 10 to 20 years

(e.g., some pavement surfaces), allowing engineers to adapt to some climate changes as they unfold. Many other transportation networks and

facilities are longer-lived. Major bridges and pipelines, for example, have

lifetimes of 50 to 100 years, while the right-of-way of major transportation

networks (e.g., rail lines, roads) is easily that long-lived. Thus, many of the

investment decisions made by transportation professionals today will have

a significant effect on how well the infrastructure adapts to climate change.

Finally, like so many other problems, climate change will not be

experienced in isolation. It will manifest itself in the context of other

demographic, social, and economic trends, often aggravating existing conditions. For example, many coastal areas are likely to experience increased

development pressures as a result of population growth, greater affluence,

and tourist demands. Many of these areas are already vulnerable to erosion

and storm damage. As sea levels rise with global warming, coastal storms

with higher tides and storm surges are likely to create the conditions for

more severe coastal flooding and erosion, placing more people in harm’s

way and increasing the difficulty of evacuating in an emergency.

ORGANIZATION OF THE REPORT

The remainder of this report addresses the committee’s charge. Chapter 2

reviews the current state of knowledge about climate change, including

projected changes over the next century, and those factors of particular

relevance to U.S. transportation. Chapter 3 is focused on the potential

impacts of climate changes on transportation infrastructure. The chapter

begins with an overview of the vulnerability of the infrastructure to these

changes; it then examines the likely impacts of the most critical climate

changes by transportation mode, reviews the handful of studies that have

examined the impacts of climate change on transportation, and draws a

Introduction 33

18 Evidence exists for abrupt climate changes that can occur within a decade. The Dust Bowl

drought of the 1930s is a good example (NRC 2002).
series of findings. Chapter 4 describes how the transportation sector is

organized and explains why climate change poses a difficult challenge to

decision makers. It concludes with some suggestions for a more strategic,

risk-based approach to investment decisions. Chapter 5 considers adaptation strategies—both engineering and operational measures, as well as

changes in transportation planning and land use controls, development

of new technologies, improved data and analysis tools, and organizational changes. In the sixth and final chapter, the committee offers its

recommendations for policies and actions to address the impacts of climate change on transportation and for needed research.

REFERENCES

Abbreviations

IPCC Intergovernmental Panel on Climate Change

NRC National Research Council

USDOT U.S. Department of Transportation

USEPA U.S. Environmental Protection Agency

Hoerling, M., J. Eischeid, X. Quan, and T. Xu. 2007. Explaining the Record U.S.

Warmth of 2006. Geophysical Research Letters, Vol. 34, No. 17, L17704.

IPCC. 2005. Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on

Addressing Uncertainties, July. ipcc-wg1.ucar.edu/wg1/Report/AR4_Uncertainty

GuidanceNote.pdf. Accessed Jan. 30, 2008.

IPCC. 2007a. Summary for Policymakers. In Climate Change 2007: Impacts,

Adaptation, and Vulnerability. Contribution of Working Group II to the Fourth

Assessment Report of the Intergovernmental Panel on Climate Change (M. L. Parry,

O. F. Canziani, J. P. Palutikof, P. J. van der Linden, and C. E. Hanson, eds.),

Cambridge University Press, Cambridge, United Kingdom.

IPCC. 2007b. Summary for Policymakers. In Climate Change 2007: The Physical

Science Basis. Contribution of Working Group I to the Fourth Assessment Report of

the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning,

Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.), Cambridge

University Press, Cambridge, United Kingdom, and New York.

Meyer, M. D. 2006. Design Standards for U.S. Transportation Infrastructure: The

Implications of Climate Change. Georgia Institute of Technology, Dec. 18.

NRC. 2002. Abrupt Climate Change: Inevitable Surprises. National Academies Press,

Washington, D.C.

NRC. 2007. Evaluating Progress of the U.S. Climate Change Science Program: Methods

and Preliminary Results. National Academies Press, Washington, D.C.

Potter, J. R., and M. J. Savonis. 2003. Transportation in an Age of Climate Change:

What Are the Research Priorities? TR News, Vol. 227, July–Aug., pp. 26–31.

34 Potential Impacts of Climate Change on U.S. Transportation
Introduction 35

Staudt, A., N. Huddleston, and S. Rudenstein. 2005. Understanding and Responding to

Climate Change: Highlights of National Academies Reports. National Academies

Press, Washington, D.C., Oct.

Stott, P. A., D. A. Stone, and M. R. Allen. 2004. Human Contribution to the European

Heatwave of 2003. Nature, Vol. 432, pp. 610–614. doi: 10.1038/nature03089.

Turner, B. L., P. A. Matson, J. J. McCarthy, R. W. Corell, L. Christensen, N. Eckley, G. K.

Hovelsrud-Broda, J. X. Kasperson, R. E. Kasperson, A. Luers, M. L. Martello,

S. Mathiesen, R. Naylor, C. Polsky, A. Pulsipher, A. Schiller, H. Selin, and N. Tyler.

2003. Illustrating the Coupled Human–Environment System for Vulnerability

Analysis: Three Case Studies. Proceedings of the National Academy of Sciences,

Vol. 100, No. 14, July 8, pp. 8080–8085.

USDOT. 2003. The Potential Impacts of Climate Change on Transportation, Summary

and Discussion Papers. Federal Research Partnership Workshop, Brookings

Institution, Washington, D.C., Oct. 1–2, 2002.

USEPA. 2007. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2005. EPA

430-R-07-002. Washington, D.C., Apr. 15.

World Business Council for Sustainable Development. 2004. Mobility 2030: Meeting

the Challenges to Sustainability. Sustainable Mobility Project. National Academies

Press, Washington, D.C.
36

2

Understanding Climate Change

This chapter begins with an overview of current understanding of therole greenhouse gases (GHGs) play in the atmosphere and evidence

for how they are already influencing the earth’s climate in both general

and specific ways. The discussion includes a review of the climate change

projections of global climate models and some of the evidence that has

led recent national and international scientific assessments—including

those of the Intergovernmental Panel on Climate Change (IPCC)

(2007), the National Research Council (2001), and the Climate Change

Science Program (CCSP) Synthesis and Assessment Report 1.1 (Karl et al.

2006)—to link the rise in temperature, particularly since the 1970s, to

increases in GHGs. Next is a discussion of the projected climate changes for

North America most relevant for U.S. transportation. For each climate

variable, past projections and key uncertainties are also discussed. The

chapter ends with a series of findings.

OVERVIEW OF GLOBAL CLIMATE CHANGE

The Greenhouse Effect and Atmospheric Composition

The natural “greenhouse” effect is real and is an essential component of the

planet’s climatic processes. A small proportion (roughly 2 percent) of the

atmosphere is, and long has been, composed of GHGs (water vapor, carbon dioxide, ozone, and methane). These gases effectively prevent part of

the heat radiated by the earth’s surface from otherwise escaping to space.

The response of the global system to this trapped heat is a climate that

is warmer than it would be without the presence of these gases; in their
absence, the earth’s temperature would be too low to support life as we

know it. Among the GHGs, water vapor is by far the most dominant, but

other gases augment its effect through greater trapping of heat in certain

portions of the electromagnetic (light) spectrum.

In addition to the natural greenhouse effect outlined above, a change is

under way in the greenhouse radiation balance. Some GHGs are proliferating in the atmosphere because of human activities and increasingly

trapping more heat. Direct atmospheric measurements made over the past

50 years have documented steady growth in the atmospheric abundance of

carbon dioxide (CO2). In addition to these direct, real-time measurements,

ice cores have revealed the atmospheric CO2 concentrations of the distant

past. Measurements using air bubbles trapped within layers of accumulating snow show that atmospheric CO2 has increased by nearly 35 percent

over the Industrial Era (since 1750), compared with its relatively constant

abundance over at least the preceding 10,000 years (see Figure 2-1). The

predominant causes of this increase in CO2 are the combustion of fossil

fuels and deforestation. Further, the abundance of methane has doubled

over the Industrial Era, although its increase has slowed during the past

decade for reasons not clearly understood. Other heat-trapping gases are

also increasing as a result of human activities. Scientists are unable to state

with certainty the rate at which these GHGs will continue to increase

because of uncertainties in future emissions, as well as in how these emissions will be taken up by the atmosphere, land, and oceans. They are

certain, however, that once in the atmosphere, these gases have a relatively

long residence time, on the order of a century (IPCC 2001). This means

they become well mixed across the globe.

There is no doubt that the composition of the atmosphere is affected

by human activities. Today GHGs are the largest human influence on

atmospheric composition. The increase in GHG concentrations in the

atmosphere implies a positive radiative forcing (i.e., a tendency to warm

the climate system).

Increases in heat-trapping GHGs are projected to be amplified by feedback effects, such as changes in water vapor, snow cover, and sea ice. As

atmospheric concentrations of CO2 and other GHGs increase, the resulting

rise in surface temperature leads to less sea ice and snow cover, causing the

planet to absorb more of the sun’s energy rather than reflecting it back

to space, thereby raising temperatures even further. Present evidence

also suggests that as GHGs lead to rising temperatures, evaporation

Understanding Climate Change 37
38 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-1 Atmospheric concentrations of carbon dioxide, methane, and

nitrous oxide over the past 10,000 years (large panels) and since 1750 (inset

panels). Measurements are from a combination of ice cores (going back

10,000 years) and atmospheric samples in the 20th century. (Source: IPCC

2007, Figure SPM-1, p. 15. Reprinted with permission of the IPCC

Secretariat, Geneva, Switzerland.)
increases, leading to more atmospheric water vapor (Soden et al. 2005;

Trenberth et al. 2005). Additional water vapor, the dominant GHG, acts as a

very important feedback to increase temperature further. The most uncertain feedback is related to clouds, specifically changes in cloud frequency,

location, and height. The range of uncertainty spans from a significant positive feedback to no feedback, or even a slightly negative feedback. Present

understanding suggests that these feedback effects account for at least half

of the climate’s warming (IPCC 2001; Karl and Trenberth 2003). The exact

magnitude of these effects remains a significant source of uncertainty in

understanding the impact of increasing GHGs. Increases in evaporation

and water vapor affect global climate in other ways besides causing rising

temperatures, such as increasing rainfall and snowfall rates and accelerating

drying during droughts.

Particles suspended in the atmosphere (aerosols) resulting from human

activities can also affect climate. Aerosols vary considerably by region. Some

aerosol types (e.g., sulfate) act in a way opposite to the GHGs by reflecting

more solar radiation back to space than the heat they absorb, and thereby

causing a negative radiative forcing or cooling of the climate system. Other

aerosols (e.g., soot) act in the same way as GHGs and warm the climate. In

contrast to the long-lived nature of CO2, aerosols are short-lived and

removed from the lower atmosphere within a few days. Therefore, humangenerated aerosols exert a long-term forcing on climate only because their

emissions continue each day of the year. The effects of aerosols on climate

can be manifested directly by their ability to reflect and trap heat, but also

indirectly by changes in the lifetime of clouds and in the clouds’ reflectivity to sunshine. The magnitude of the negative forcing of the indirect

effects of aerosols is highly uncertain, but it may be larger than that of their

direct effects (IPCC 2001).

Emissions of GHGs and aerosols continue to alter the atmosphere by

influencing the planet’s natural energy flows (see Box 2-1), which can cause

changes in temperature and precipitation extremes, reductions in snow

cover and sea ice, changes in storm tracks, and increased intensity of hurricanes (IPCC 2007). There are also natural factors that exert a forcing

effect on climate [e.g., changes in the sun’s energy output and short-lived

(a few years) aerosols in the stratosphere following episodic and explosive

volcanic eruptions]. If all the possible influences of natural and human climate forcings over the past several decades are considered, increases in

GHGs have had a larger influence on the planet’s radiation flow than all the

Understanding Climate Change 39
40 Potential Impacts of Climate Change on U.S. Transportation

BOX 2-1

What Warms and Cools the Earth?

The sun is the earth’s main energy source. Its output appears nearly constant,

but small changes during an extended period of time can lead to climate

changes. In addition, slow changes in the earth’s orbit affect how the sun’s

energy is distributed across the earth, creating another variable that must be

considered.

Greenhouse gases warm the earth:

Water vapor (H2O), supplied from oceans and the natural biosphere,

accounts for two-thirds of the total greenhouse effect but acts primarily as

a feedback. In contrast to other greenhouse gases, the amount of water

vapor in the atmosphere generally cannot be controlled by humans. Water

vapor introduced directly into the atmosphere from agricultural or other

activities does not remain there very long and is overwhelmed by natural

sources; thus it has little warming effect.

Carbon dioxide (CO2) has natural and human sources. CO2 levels are

increasing as a result of the burning of fossil fuels.

Methane (CH4) has both human and natural sources and has risen significantly since preindustrial times as the result of an increase in several

human activities, including raising of livestock; growing of rice; use of

landfills; and extraction, handling, and transport of natural gas.

Ozone (O3) has natural sources, especially in the stratosphere, where

changes caused by ozone-depleting chemicals have been important;

ozone also is produced in the troposphere (the lower part of the atmosphere) when hydrocarbons and nitrogen oxide pollutants react.

Nitrous oxide (N2O) has been increasing from agricultural and industrial

sources.

Halocarbons continue to be used as substitutes for chlorofluorocarbons

(CFCs) as refrigerant fluids, and CFCs from pre–Montreal Protocol usage as

refrigerants and as aerosol-package propellants remain in the atmosphere.

Scientists have a high level of understanding of the human contributions

to climate forcing by carbon dioxide, methane, nitrous oxide, and CFCs and

a medium level of understanding of the human contributions to climate

forcing by ozone (Forster et al. 2007).

(continued)
Some aerosols (airborne particles and droplets) warm the earth:

Black carbon particles, or “soot,” produced when fossil fuels or vegetation

is burned, generally have a warming effect by absorbing solar radiation.

Some aerosols cool the earth:

Sulfate (SO4) aerosols from burning of fossil fuels reflect sunlight back

to space.

Volcanic eruptions emit gaseous sulfur dioxide (SO2), which, once in the atmosphere, forms SO4 aerosols and ash. Both reflect sunlight back to space.

Scientists currently have a low level of understanding of the human contributions to climate forcing by aerosols (Forster et al. 2007).

Changes in land cover, ice extent, and cloud cover can warm or cool the earth:

Deforestation produces land areas that reflect more sunlight back to space;

replacement of tundra by coniferous trees that create dark patches in the

snow cover may increase absorption of sunlight.

Sea ice reflects sunlight back to space; reduction in the extent of sea

ice allows more sunlight to be absorbed into the dark ocean, causing

warming.

Clouds reflect sunlight back to space but can also act like a greenhouse

gas by absorbing heat leaving the earth’s surface; the net effect depends

on how the cloud cover changes.

Source: Adapted from Staudt et al. 2006, p. 7.

Understanding Climate Change 41

other forcings, one that continues to grow disproportionately larger (IPCC

2007; Karl and Trenberth 2003).

Human activities also have a large-scale impact on the earth’s land surface. Changes in land use due to urbanization and agricultural practices,

although not global, are often most pronounced where people live, work,

and grow food and are part of the human impact on climate. Land use

changes affect, for example, how much of the sun’s energy is absorbed or

reflected and how much precipitation evaporates back into the atmosphere. Large-scale deforestation and desertification in Amazonia and the

Sahel, respectively, are two instances in which evidence suggests the likeli-
hood of a human influence on regional climate (Andreae et al. 2004;

Chagnon and Bras 2005). In general, city climates differ from those in surrounding rural green areas, causing an “urban heat island” due to greater

heat retention of urban surfaces, such as concrete and asphalt, as well as the

waste generated from anthropogenic activities1 (Bornstein and Lin 2000;

Changnon et al. 1981; Jones et al. 1990; Karl et al. 1988; Landsberg 1983;

Peterson 2003).

What Is a Climate Model and Why Is It Useful?

Many of the scientific laws governing climate change and the processes

involved can be quantified and linked by mathematical equations. Figure 2-2 shows schematically the kinds of processes that can be included

in climate models. Among them are many earth system components,

such as atmospheric chemistry, ocean circulation, sea ice, land surface

hydrology, biogeochemistry,2 and atmospheric circulation. The physics of

many, though not all, of the processes governing climate change are well

understood and may be described by mathematical equations. Linking

these equations creates mathematical models of climate that may be run

on computers or supercomputers. Coupled climate models can include

mathematical equations describing physical, chemical, and biogeochemical processes and are used because the climate system is composed of

different interacting components.

Coupled climate models are the preferred approach to climate modeling,

but they cannot at present include all details of the climate system. One reason is that not all details of the climate system are understood, even though

the major governing processes are known well enough to allow models to

reproduce observed features, including trends, of global climate. Another

reason is the prohibitive complexity and run-time requirements of models

that might incorporate all known information about the climate system.

Decisions on how to build any given climate model include trade-offs among

the complexity of the model and the number of earth system components

included, the model’s horizontal and spatial resolution, and the number of

42 Potential Impacts of Climate Change on U.S. Transportation

1 The global effects of these urban heat islands have been analyzed extensively and assessed to

ensure that they do not bias measurements of global temperature.

2 Biogeochemistry refers to the biological chemistry of the earth system, such as the uptake of

atmospheric carbon by land and ocean vegetation.
Understanding Climate Change 43

FIGURE 2-2 Components of the climate system and their interactions, including

the human component. All these components must be modeled as a coupled

system that includes the oceans, atmosphere, land, cryosphere, and biosphere.

GCM = General Circulation Model. (Source: Karl and Trenberth 2003, Figure 3.

Reprinted from Science, Vol. 302, No. 5651, with permission.)
years of simulations the model can produce per day of computer time.

Consequently, there is a hierarchy of models of varying complexity, often

based on the degree to which approximations are required for each model or

component processes omitted.

Approximations in climate models represent aspects of the models that

require parameter choices and “tuning.” As a simple example, imagine representing a single cumulus cloud in a global climate model. The cloud may

encompass only a few hundred meters in vertical and horizontal space—a

much finer resolution than can be run on today’s coupled atmosphere and

ocean climate models. As a result, if such clouds are to be incorporated into

the climate model, some approximations must be made regarding the

clouds’ statistical properties within, say, an area 100 or 1,000 times larger

than the cloud itself. This is referred to as model parameterization, and the

process of selecting the most appropriate parameters to best simulate

observed conditions is called model tuning. Similar methods are also

required in today’s state-of-the-science weather forecasting models.

An important difference between weather forecasting models and

climate models is that the former are initialized with a specific set of

observations representing today’s weather to predict the weather precisely

x days or hours into the future. By contrast, the initial conditions of climate

models are much less important. Also, climate models are not intended to

predict specific future weather events. Rather, they are used to simulate

many years of “weather” into the future with the intent of understanding the change in the collection of weather events at some point in 

the future compared with some point in the past (often the climate of

the past 30 years or so). Scientists are thus interested in properties of

climate, such as average rainfall and temperature and the degree of fluctuation about that average. This comparison enables scientists to study the

output of climate model simulations to understand the effect of various

modifications of those aspects of the climate system that might cause the

climate to change. A key challenge in climate modeling is to isolate and

identify cause and effect. Doing so requires knowledge about the changes

and variations in the external forcings controlling climate and a comprehensive understanding of climate feedbacks (such as a change in the earth’s

reflectivity because of a change in the amount of sea ice or clouds) and natural climate variability. A related key challenge in climate modeling is the

representation of sub-grid-scale processes, such as in some storms, and

land-terrain effects.

44 Potential Impacts of Climate Change on U.S. Transportation
Model simulations of climate over specified periods can be verified

and validated against the observational record. Likewise, model parameterization schemes for particular processes of interest can be tested by

comparison with observations and with higher-resolution, smaller-scale

models. Models that describe climate variability and change well can be

used as a tool to increase understanding of the climate system. Once evaluated and validated, climate models can then be used for predictive

purposes. Given specific forcing scenarios, the models can provide viable

projections of future climate. In fact, climate models have become the primary means of projecting climate change, although ultimately, future

projections are likely to be determined through a variety of means, including the observed rate of global climate change.

How Do We Know the Global Air Temperature Is Increasing?

A comprehensive analysis of changes in temperatures near the earth’s surface and throughout much of the atmosphere is presented in the April 2006

CCSP Synthesis and Assessment Report 1.1 (Karl et al. 2006). This report

addresses the nagging issue of differences in the rate of warming between

measurements derived near the surface (typically 2 m above the surface)

and those taken from higher in the atmosphere (i.e., the lower troposphere,

or the atmosphere below roughly 12 km). The surface air temperatures are

derived from several different analysis teams, using various combinations

of ocean ships and buoys, land observations from weather reporting stations, and satellite data. Atmospheric data sets have been derived by using

satellites, weather balloons, and a combination of the two.

Considering all the latest satellite, balloon, and surface records, the

CCSP report concludes that there is no significant discrepancy between

the rates of global temperature change over the past several decades at the

surface compared with those higher in the atmosphere. The report does

acknowledge, however, that there are still uncertainties in the tropics,

related primarily to the data obtained from weather balloons. Many developing countries are struggling to launch weather balloons routinely and

process their measurements, and it is unclear whether scientists have been

able to adjust adequately for known biases and errors in the data.

Globally, data indicate that rates of temperature change have been

similar throughout the atmosphere since 1979, when satellite data were

first available, and that the rates of change have been slightly greater in the

Understanding Climate Change 45
troposphere than on the earth’s surface since 1958 (when weather balloons

first had adequate spatial coverage for global calculations). The global surface temperature time series shown in Figure 2-3 indicates warming on

even longer time scales, with acceleration since 1976.

Instrumental temperature measurements are not the only evidence for

increasing global temperatures. The observed increased melting of glaciers

can be used to estimate the rate of temperature increase since the late 19th

century. Estimates of near-surface temperature based on glacial melting are

very similar to estimates based on instrumental temperature data. A 15 to

20 percent reduction in Arctic sea ice since the 1970s, a 10 percent decrease

in snow cover since the 1970s, and shortened periods of lake and river ice

cover (about 2 weeks shorter since the 19th century) have been observed.

Also, ocean heat content has significantly increased over the past several

decades (IPCC 2007).

46 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-3 Globally averaged surface air temperature and carbon dioxide (CO2)

concentration [parts per million by volume (ppmv)] since 1880. Note that the

shaded bars refer to global temperature anomalies and the solid line to CO2

concentrations. (Source: Updated from Karl and Trenberth 2003.) Global Temperature Anomaly (oC) (bars)

CO2 Concentration (ppmv) (curve)

0.6 400

380

360

340

320

300

280

260

0.4

0.2

0.0

–0.2

–0.4

–0.6

1880 1900 1920 1940 1960 1980 2000
Why Do Scientists Think Humans Are Influencing 

the Earth’s Climate?

Since the 1980s, the scientific community has been actively working on

detecting climate change and determining how much of the change is

attributable to human activities. As described above, one set of tools often

used for detection and attribution is mathematical computer models of the

climate. Outstanding issues in modeling include specifying forcing mechanisms (e.g., the causes of climate variability and change) within the climate

system; addressing complex GHG feedback processes (e.g., methane and

carbon) and properly dealing with indirect aerosol forcings and complex

physical feedback processes (e.g., energy and water sources); and improving simulations of regional weather, especially extreme events. Today’s

inadequate or incomplete measurements of the various forcing mechanisms, with the exception of well-mixed GHGs, add uncertainty when one

is trying to simulate past and present climate. Confidence in predicting

future climate depends on using climate models to attribute past and present climate changes to specific causes. Despite these issues, a substantial

and growing body of evidence (IPCC 2007) shows that climate models are

useful tools for understanding the factors leading to climate change.

Recent CO2 emission trends are upward, with increases of 0.5 to 1 percent per year over the past few decades. Concentrations of both reflective

and nonreflective aerosols are also estimated to be increasing. Net positive

radiative forcings3 from GHGs dominate the net cooling forcings from

aerosols, and the global temperature change over the past 25 to 30 years has

exceeded the bounds of natural variability estimated from climate simulations with no human-caused changes. This has been the case since about

1980. As an example of how models are used to detect human influence on

the climate system, Figure 2-4 shows that, without including all the known

forcing mechanisms (natural and human or anthropogenic), the models

cannot replicate observed global temperature changes. Moreover, many

aspects of the climate system other than global surface temperatures have

been tested for human influences.

Understanding Climate Change 47

3 Radiative forcing can be thought of as the change in heat flow [expressed in watts per square

meter (W/m2)] at the tropopause due to an internal change or a change in the external forcing of

the climate system, such as a change in the concentration of CO2 or the output of the sun. The

tropopause is the boundary between the troposphere and the stratosphere, represented by a rather

abrupt change from decreasing to increasing temperature with height.
Today there is convincing evidence from a variety of climate change

detection and attribution studies pointing to human influences on climate.

These studies include continental and subcontinental analyses of changes

in temperature; the paleoclimatic4 temperature record; three-dimensional

analyses of changes in atmospheric temperature, in free atmospheric tem48 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-4 Comparison of observed global change in surface temperature

with simulations by climate models using natural and anthropogenic forcings.

Decadal averages of observations are shown for 1906 to 2005 (black line) 

plotted against the center of the decade and relative to the corresponding 

average for 1901–1950. Solid shading shows the 5 to 95 percent range for 

19 simulations from five climate models using only the natural forcings due to

solar activity and volcanoes. Banded shading shows the 5 to 95 percent range

for 58 simulations from 14 climate models using both natural and anthropogenic

forcings. (Source: IPCC 2007, Figure SPM-4, p. 18. Reprinted with permission

of the IPCC Secretariat, Geneva, Switzerland.) Temperature Anomaly (oC)

Models using only natural forcings

Observations

Models using both natural and

anthropogenic forcings

1900

1.0

0.5

0.0

1950 2000

Year

4 Climate during periods prior to the development of measuring instruments includes historical

and geological time for which only proxy climate indicators are available. A proxy climate indicator

is a local record that is interpreted, on the basis of physical and biophysical principles, to represent

some combination of climate-related variations back in time. Climate-related data derived in this

way are referred to as proxy data. Examples of proxies are tree ring records, characteristics of

corals, and various data derived from ice cores.
perature, in sea ice extent and other components of the cryosphere, and in

ocean heat content; and new studies on extreme weather and climate

events. Thus, there is high confidence that the observed warming, especially during the period since the 1970s, is due mainly to human-caused

increases in GHGs (Allen 2005; Gillett et al. 2002; Hegerl et al. 2001; IPCC

2007; Karl et al. 2006; Karoly and Wu 2005; Stone and Allen 2005; Stott 

et al. 2001; Tett et al. 2002; Zhang et al. 2006; Zwiers and Zhang 2003). How

climate warming will be manifested over the next 50 to 100 years and

which factors will have the greatest potential impact on transportation are

discussed in the following section.

CLIMATE CHANGES RELEVANT TO U.S. TRANSPORTATION

Climate variability and change impact transportation mainly through

changes in weather extremes, such as very hot days, very cold days, or severe

storms; changes in climate extremes,5 such as increases in the probability of

intense precipitation events and extended droughts; and sea level rise. The

U.S. transportation system was built for the typical weather and climate

experienced locally, including a reasonable range of extremes, such as flooding events occurring as rarely as once in 100 years. Moderate changes in the

mean climate have little impact on transportation infrastructure or operations because the system is designed to accommodate changing weather

conditions. However, changes in weather and climate extremes can have a

considerable impact on transportation, especially if they push environmental conditions outside the range for which the system was designed.

Weather and climate extremes of relevance to transportation have been

changing over the past several decades and are projected to continue to

change in the future, with both negative and positive effects on the transportation system.

Table 2-1 lists the potential climate changes of greatest relevance for

transportation, including the level of uncertainty associated with each.

The following subsections address these changes in turn, largely summarizing the findings of a paper commissioned for this study (by Peterson

Understanding Climate Change 49

5 The exact threshold for what is classified as an extreme varies from one analysis to another, but

an extreme event would normally be as rare as, or rarer than, the top or bottom 10 percent of all

occurrences (CCSP 2007). For the purposes of this report, all tornadoes and hurricanes are 

considered extreme.
50 Potential Impacts of Climate Change on U.S. Transportation

TABLE 2-1 Level of Uncertainty Associated with Potential Climate Changes 

of Greatest Relevance to Transportation

Potential Climate Change of Relevance to U.S. Transportation Level of Uncertainty

Temperature

Increases in very hot days and heat waves Very likely

Decreases in very cold days Virtually certain

Increases in Arctic temperatures Virtually certain

Later onset of seasonal freeze and earlier onset of seasonal thaw Virtually certain

Sea level rise Virtually certain

Precipitation

Increases in intense precipitation events Very likely

Increases in drought conditions for some regions Likely

Changes in seasonal precipitation and flooding patterns Likely

Storms

Increases in hurricane intensity Likely

Increased intensity of cold-season storms, with increases in Likely

winds and in waves and storm surges

Note: Italicized uncertainty designations are those identified by IPCC (2007). Others reflect the committee’s judgment,

based on the available literature. IPCC (2007, 3) Working Group I established the following terminology to describe 

uncertainty, that is, probability of occurrence: virtually certain, ≥99 percent; extremely likely, ≥95 percent; very likely, ≥90

percent; likely, ≥66 percent; more likely than not, ≥50 percent; unlikely, ≤33 percent; very unlikely, ≤10 percent; extremely

unlikely, ≤5 percent.

et al. 2006; see Appendix C). Each subsection highlights past trends,

future projections, and key uncertainties. (The reader is referred to the

paper by Peterson et al. 2006 for more detail and additional figures to

support the discussion.) Note that the discussion generally progresses

from those climate changes about which there is most certainty to those

about which there is less.

Changes in Temperature

An increase in air temperature allows more water vapor in the atmosphere,

which defines the upper bounds of the amount of precipitation that can

occur during short-term (e.g., hourly to 1-day) extreme precipitation events.

Surface moisture, if available (as it always is over the oceans), effectively acts

as the “air conditioner” of the surface, as heat used for evaporation moistens

rather than warms the air. Therefore, another consequence of global heating of the lower troposphere is accelerated land-surface drying and more
atmospheric water vapor (the dominant GHG). Human-induced warming

has been linked to the water vapor increases in both surface observations

(Willett et al. 2007) and satellite observations over the oceans (Santer et al.

2007). Without an increase in precipitation, accelerated drying increases the

incidence and severity of droughts (Dai et al. 2004), whereas additional

atmospheric water vapor increases the risk of heavy precipitation events

(Trenberth et al. 2003). Increases in global temperature also cause sea

surface temperatures to rise, one of several important factors affecting

hurricane intensity.

Changes in Temperature Including Extremes

U.S. temperatures have been rising over the past century, with more rapid

increases since 1970 than earlier, as shown in Figure 2-5. It is unlikely that

North American temperature changes since 1950 are due to natural climate variability alone (Karoly et al. 2003). The warming has not been

uniform across the continent. In general, the western portion of the

Understanding Climate Change 51

FIGURE 2-5 Area-averaged mean temperature time series for the contiguous

United States. (Source: National Oceanic and Atmospheric Administration,

National Climatic Data Center.) oF

oC

56.0

13.0

12.0

11.0

10.0

Yearly Values

Filtered Values

Long-Term Mean

55.0

54.0

53.0

52.0

51.0

50.0

49.0

1900 1920 1940 1960

Year

1980 2000
contiguous United States has warmed more than the eastern portion.

Alaska has warmed the most rapidly, with temperatures in some regions

increasing by more than 0.6°C (1.1°F) per decade since 1970.

These warming trends are projected to continue over the next century on the basis of reasonable scenarios for future GHG emissions.

Figure 2-6 shows the temperatures projected for the eastern United

States for three different scenarios, each scenario having been run by

multiple models. Other areas of the United States show similar warming trends [see Figure 6 in the commissioned paper by Peterson et al. 2006

(Appendix C)]. It is interesting to note that for the next 30 years, the

uncertainties are primarily model related and not due to different emissions scenarios. Even if atmospheric concentrations remained at

current levels, the models would still project similar warming over the

next couple of decades (IPCC 2007).

52 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-6 Annual surface air temperature anomaly, from the 1990–1999 

average, for the eastern United States and for three different emissions scenarios

(SRES = Special Report on Emission Scenarios). (Source: Peterson et al.

2006, Figure 5.) oC

oC

Year
Increases in Very Hot Days and Heat Waves

The next century is likely to bring more very hot days and heat waves [see

Figure 9 in the paper by Peterson et al. 2006 (Appendix C)]. The number

of days with temperature above 32.2°C (90°F) and 37.7°C (100°F) has

been increasing since 1970, but it is not quite as high today as during the

early 1950s, when several areas, particularly the south-central United States,

had severe droughts. By 2090–2099, it is expected that the average temperature on the hottest day of the year will be 2.5°C to 4.5°C (4.5°F to 8.1°F)

warmer than the hottest day of the year in the 1990s. Not only will there

be hotter and more very hot days, but it is likely that the continental

United States will have significantly more heat waves with sustained high

temperatures for 5 consecutive days or longer.

There are several ways to conceptualize the change in very hot days.

For example, the 20-year return value for the hottest day of the year in

2090–2099 can be compared with the same value for the 1990s. The 

20-year return value is the temperature that is reached or exceeded on

average once every 20 years over a long period of time. Such temperatures

are truly rare events because they are expected to be reached only three or

four times during the course of a human lifetime. Over most of the continental United States, the present-day 20-year return value temperatures

would be reached or exceeded seven times or more in a 20-year interval by

the end of the 21st century. Hence, the rare high-temperature event becomes commonplace in this scenario. Figure 2-7 depicts another way of

considering the change in very hot days expected in the next century, with

Dallas, Texas, as an example. The figure shows the probability of having 

1 to 20 days during the summer when the temperature exceeds 43.3°C

(110°F). The probability increases substantially 25, 50, and 90 years in the

future. Similar plots are presented for Minneapolis, Minnesota, and

Honolulu in the paper by Peterson et al. 2006 (see Appendix C).

Decreases in Very Cold Days

The number of very cold days has been decreasing in the United States

since about 1970 (see Figure 2-8). This trend is also expected to continue

into the future across the continent. For example, in the Washington, D.C.,

area, there is currently a 75 percent chance that 3 days each winter will

have maximum temperatures at or below freezing. By the end of the century, this probability is projected to drop to 20 percent.

Understanding Climate Change 53
54 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-7 Current and future probability of having 1 to 20 days during the

summer at or above 43.3C (110F) in Dallas, Texas. (Source: Peterson et al. 2006,

Figure 10b.)

Number of Days

0

0 2 4 6 8 10 12 14 16 18 20

 + 90 Years: 2097

+ 50 Years: 2057

+ 25 Years: 2032

Current Year: 2007

20

40

60

80

100

Probability

Later Onset of Seasonal Freeze and Earlier Onset of Seasonal Thaw

It is not just extremes of temperature that can have an impact on transportation. In particular, the number of days from the last freeze in the

spring to the first freeze in the fall is expected to increase. Figure 2-9 shows

a corresponding period—the length of time between the first day in the

year that the maximum daily temperature reaches 21.1°C (70°F) and the

last day of the year when this occurs. This interval has been increasing

since 1970 and can be expected to increase further in the future. While

there is considerable year-to-year variability in the number of freeze–thaw

days (i.e., days when an observation station’s maximum temperature is

above freezing and its minimum temperature below freezing), no distinct

trend has been observed in this quantity.

Changes in Sea Level

Sea level is projected to rise over the next century, but there is significant

uncertainty as to how much and how fast. The IPCC Third Assessment

Report includes a range of estimates that sea levels will rise 0.1 to 0.9 m

above 1990 levels by 2100 (IPCC 2001). To put this in context, the IPCC
FIGURE 2-8 U.S. nationally averaged anomaly of the number of days at or 

below the coldest 10 percent of January maximum and minimum temperatures 

at each station (percentiles were calculated on a 1961–1990 base period).

(Source: Peterson et al. 2006, Figure 14.)

Anomaly of Number of Very Cold Days

Year

1950

-8

-6

-4

-2

0

2

4

6

8

10 Maximum Temperature

Minimum Temperature

1960 1970 1980 1990 2000

FIGURE 2-9 U.S. area-averaged anomaly of the length of time between the first

day above 21.1C (70F) in the spring and the last day above 21.1C in the fall.

(Source: Peterson et al. 2006, Figure 19.)

Number of Days

Year

1950

-20

-10

0

10

20

30

1960 1970 1980 1990 2000
56 Potential Impacts of Climate Change on U.S. Transportation

estimates that during the past 6,000 years, global average sea level variations on time scales of a few hundred years and longer are likely to have

been less than 0.3 to 0.5 m. Observed sea level changes from tide gauges

and satellite altimeters indicate that the 1993–2005 rate of sea level rise

was 3 mm per year (Church and White 2006). If this linear trend continues, sea level will rise by about 0.3 m by the end of the 21st century.

Several analyses have identified a number of factors that as yet have

uncertain likelihoods but could easily contribute to nonlinear and abrupt

rises in sea level (IPCC 2007; Schoof 2007; Vaughan et al. 2007). Such

extrapolations are tentative, however, because the extent to which the

trends of the past decade are due to natural variability in the climate system is unknown.

Global warming affects sea level through two mechanisms: thermal

expansion of seawater and melting of ice present on land surfaces.

Other factors also play a role in sea level, such as the amount of water

held back by human-made land reservoirs, leading to sea level falls, but

these factors are less important. There are still problems in reconciling

the observed changes of the past century with the estimated contributions from these different sources (Munk 2002). Most of the projected

sea level rise is due to thermal expansion, but should the melting of the

polar ice caps accelerate, sea level would rise much higher. The rapid

melting of Greenland, which would have a very large impact, is possible, but too little is known to assess its likelihood (IPCC 2007). Current

model projections of sea level rise are based on the observed rate of

melting during 1993–2003, but these rates could increase or decrease

in the future.

More important to transportation than the global change in sea level

is the local apparent change in sea level (Burkett 2002; Titus 2002).

Estimates of local apparent sea level rise take into account the vertical

movement of land and coastal erosion. Coastal erosion, in turn, is driven

by sea level rise. To estimate local sea level rise, land subsidence in the Gulf

Coast and uplift along the New England coast are important factors (NRC

1987). Figure 2-10 illustrates that because of these factors, different

regions can have quite different local sea level rise.

Impacts of Sea Level Rise on Shoreline Location

Predicting rates of shoreline retreat and land loss is critical to planning

future coastal infrastructure. According to the Bruun rule, shorelines
Understanding Climate Change 57

FIGURE 2-10 Trends in sea level from global changes in seawater volume 

and local changes in land surface elevation for representative locations in the

United States. (Source: NOAA 2001, p. 4.)

Year

Scale (cm)

40

20

0

1900 1920 1940 1960 1980 2000

Galveston, TX

New York, NY

Baltimore, MD

Key West, FL

San Francisco, CA

Sitka, AK
retreat so as to maintain a constant slope, and by some estimates, move

inland roughly 150 m for every meter rise in sea level (Bruun 1962;

Leatherman et al. 2000). Thus, for a 0.5-m worldwide sea level rise,

sandy shores could retreat 75 m. Although the Bruun rule is useful as a

conceptual model, rigorous application of coastal geology and climatology models is necessary for risk analysis at specific locations.

Exacerbation of Storm Surge by Sea Level Rise

Storm surge is the abnormal rise in sea level accompanying a hurricane

or other intense storm, above the level of the normal or astronomic tide.

Storm surge can be exacerbated by tidal piling, a phenomenon of abnormally high water levels from successive incoming tides that do not

completely drain because of strong winds or waves persisting through

successive tide cycles. Flooding due to coastal storms results from a combination of storm surge and intense precipitation. Storm surge is of great

concern to port operations, mooring facilities, and moored vessels, as

well as to coastal infrastructure that is vulnerable to flooding.

Storm surge has been estimated or modeled by using the United States

Army Corps of Engineers’ Waterways Experiment Station model; the

National Weather Service’s Sea, Lake, and Overland Surge from Hurricanes model; and more recently the Advanced Circulation Model

(ADCIRC) (Westerink et al. 1994). These models use wind fields from

past storms as input; these historical input data are updated infrequently.

When updated, these models show wider areas of 100-year floodplains.

For example, a recent analysis with the ADCIRC model using input data

through the 2005 hurricane season showed greater storm surge and higher

flooding. The magnitude of the 100-year storm surge flood (previously

established using data for 1900–1956) would now recur at an interval of

75 years on the basis of data for 1900–2005 (Levinson 2006).

Changes in Precipitation

Changes in the Intensity of Heavy and Extreme Precipitation

Basic theory and climate model simulations as well as empirical evidence

(see Figure 2-11) confirm that warmer climates, owing to increased water

vapor, lead to more intense precipitation events even when total precipitation remains constant, with prospects for even stronger events when

precipitation amounts increase. Figure 2-12 depicts the aggregate land58 Potential Impacts of Climate Change on U.S. Transportation
surface worldwide changes in intense precipitation events over the last half

of the 20th century, with an associated geographic depiction of where

changes in intense precipitation have occurred; most areas show increases.

Worldwide, an increase of a few percent in intense precipitation events is

evident since the middle of the 20th century, particularly in the middle and

Understanding Climate Change 59

FIGURE 2-11 Diagram showing that warmer climates have a higher percentage 

of total rainfall coming from heavy and very heavy events. The data are based on

a worldwide distribution of observing stations, each with the same seasonal

mean precipitation amount of 230 (±5) mm. In cool climates, there are more

daily precipitation events than in warmer climates (adapted from Karl and

Trenberth 2003). The various cloud and rain symbols reflect the different daily

precipitation rates and are categorized in the top panel of the figure to reflect

the approximate proportion of the different rates for cool, moderate, and warm

climates across the globe.
60 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-12 Trends in the contribution to total annual precipitation from 

very wet days (95th percentile) in percent per decade: (a) regional changes, with

stippled areas not reporting; and (b) worldwide changes in areas with adequate

data. Percentiles were calculated on the basis of 1961–1990 data. [Source:

Alexander et al. 2006. (Copyright 2006 by American Geophysical Union.

Reproduced with permission of American Geophysical Union in the format

Other book via Copyright Clearance Center.)]

(a)

(b)

Percent Change per Decade

Percent –2

1950 1960 1970 1980 1990 2000

–2 0 2 4

90W

45S

45N

90N

0

0 90E 180

–4

–1

0

1

2

3
high latitudes. This leads to more frequent events that are currently rare.

For example, by the end of the 21st century, a conservative projection of

climate change has the recurrence period (or average expected waiting

time) for the current 1-in-20-year, heaviest daily precipitation event reducing to every 6 to 8 years over much of North America (Kharin et al. 2007;

Wehner 2005).

The practical implications of addressing these changes are seen in the

National Oceanic and Atmospheric Administration’s (NOAA’s) recent

update of the Ohio River Basin’s 100-year daily precipitation return

period. These data are used to help set engineering design standards

related to excessive rainfall. Over the past several decades, increases in the

amount of precipitation occurring during the heaviest daily precipitation

events have been observed in many areas of the central and eastern United

States (Groisman et al. 2004; Groisman et al. 2005; Karl and Knight 1998).

In fact, over the 20th century, annual precipitation averaged across the

United States increased by about 7 percent, but very intense precipitation

events (above the 95th percentile) increased by nearly three times that

rate (20 percent). The observed behavior supports one of the most confident projections that scientists can make about future precipitation.

Considerable analysis has shown that because water vapor has increased

in the atmosphere and will continue to do so with added anthropogenic

GHG emissions, the intensity of precipitation will continue to increase in

much of the United States (and elsewhere). In many regions of the world,

increases in extreme precipitation are occurring even when total precipitation is relatively constant (Alpert et al. 2002; Groisman et al. 2003;

Groisman et al. 2005). In areas where overall precipitation increases, the

increase in the intensity of very heavy precipitation events will be even

greater.

There are several different ways to think about how the increase in the

intensity of heavy and extreme precipitation events might be manifested.

One option is to consider changes in a 20-year return event. In the A1b

emissions scenario, the present-day 20-year precipitation event would take

place 2 to 4 times as frequently by the end of the 21st century [see Figure 27c

and text in Peterson et al. 2006 (Appendix C) for an explanation of the emissions scenarios]. Another useful measure is the Simple Daily Intensity Index,

which equals the total annual precipitation divided by the number of days

with precipitation in that year. Figure 2-13a shows that this quantity has

increased over the United States, indicating that on days that precipitation

Understanding Climate Change 61
62 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-13 (a) Upward trend in the Simple Daily Intensity Index (i.e., total 

precipitation per year divided by the number of days with precipitation) indicating

that, on a U.S. area-averaged basis, when precipitation does occur, it tends to be

heavier. (b) Median model-projected changes in the Simple Daily Intensity Index for

the continental United States. (Source: Peterson et al. 2006, Figures 28a, 28b.)

Year

Year

1950

SRES A1B

SRES A2

SRES B1

-0.4

-0.2

0

0.2

0.2

0.3

0.4

0.5

0.1

0

0.4

0.6

1960 1970 1980 1990 2000

2000 2020 2040 2060 2080 21000

0.1

0.2

0.3

0.4

0.5

Anomaly in mm mm/day

(a)

(b)
does occur, the amount is becoming greater. Median model projections

for the future over the continental United States (Figure 2-13b) indicate

that the Simple Daily Intensity Index is expected to continue to increase

over the next century.

Changes in the Severity and Frequency of Drought

Drought is a recurring feature of the climate system; major droughts have

occurred in the past and are expected in the future. At any given time, at

least part of the United States is in drought, with proportions ranging from

5 to 80 percent of the nation’s total land area. U.S. droughts show pronounced multiyear to multidecadal variability, but there is no convincing

evidence for systematic long-term trends toward more or fewer events.

Drought calculations have shown that over the United States, the increase

in temperatures that may have led to increased evaporation has been compensated by a general increase in precipitation during the past few decades

(Dai et al. 2004), with the result that there has been no general trend in

drought intensity nationwide (Figure 2-14). Over the United States, climate

model projections of precipitation change by the end of the 21st century

show a tendency for increasing winter precipitation and decreasing summer precipitation as global temperatures increase. Locations that do

experience decreased precipitation in addition to the continuing increase

in temperatures, such as the recently observed record-high January–June of

2006 (NOAA 2006), could have greater drought severity and frequency,

especially during periods of dry weather due to increases in evaporation.

Long-term warming trends have already led to changes in the timing of

snowmelt and stream flows, especially in the West, resulting in earlier peak

stream flows and diminished summertime flows.

For the continental United States, the most extensive drought in the

modern observational record occurred from 1933 to 1938. In July 1934,

80 percent of the United States was gripped by moderate or greater drought

(see Figure 2-14), and 63 percent was experiencing severe to extreme

drought. During 1953–1957, severe drought covered up to 50 percent of the

country. Paleoclimatic data (e.g., tree ring measurements) have been used to

reconstruct drought patterns for the period prior to the modern instrumental record (Cook et al. 1999; Cook et al. 2004). These reconstructions

show that during most of the past two millennia, the climate of the western United States has been more arid than at present. The recent intense

western drought from 1999 to 2004 that strongly affected the Colorado

Understanding Climate Change 63
Year

Percent Area Dry

1930s Dust Bowl 1950s Mini-Dust Bowl

Moderate - Extreme Drought

1900 1920 1940 1960 1980 2000

0

20

40

60

River basin was exceeded in severity as recently as the 19th century. Within

the past millennium, severe droughts in both the western United States and

the Midwest have occurred that have lasted for multiple decades.

One of the more robust findings of the IPCC (2007) relates to recent

agreement among virtually all climate model simulations of the 21st century that a drying of the southwestern United States is evident. Seager 

et al. (2007) provide the details and indicate that this drying is attributable to both an increase in evapotranspiration and reduced precipitation.

Droughts in this part of the country that occur naturally, such as those of

the past two millennia, would be expected to be enhanced as a result of

greenhouse forcing of the climate. Increased temperatures will lead to

increased drying during periods of dry weather, leading to more intense

droughts in much of the United States. For the southwestern United

States, reduced precipitation will add to this effect.

64 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 2-14 Percentage of the contiguous U.S. land area in moderate to

severe drought, January 1900–March 2006, based on the Palmer Drought Index.

(Source: NOAA, National Climatic Data Center.)
Changes in Storms

Changes in Hurricane Intensity and Frequency

Tropical storms, particularly hurricanes, are an important issue of concern

for the United States. The record-breaking hurricane season of 2005, especially the havoc created by Katrina, raised public awareness of the dangers

of hurricanes to new heights. Hurricanes respond to a number of environmental factors, including ocean temperatures, atmospheric stability, wind

changes, El Niño, and others. One important question is whether hurricane

activity has changed over the past 100 years. Since 1995, Atlantic hurricane

activity has increased substantially, with more and more intense hurricanes, compared with the previous two decades, and this increased level

of activity is also reflected in those hurricanes striking the United States

(see Figure 2-15). Earlier periods, however, such as 1945–1970, were

nearly as active.

Understanding Climate Change 65

FIGURE 2-15 Number of hurricanes striking the United States, 1901–2005,

summed by 5-year periods (e.g., 1901–1905, 1906–1910). The black bars 

represent the number of major hurricanes (Category 3–5) and the gray bars 

the number of weaker Category 1 and 2 hurricanes per 5-year period 

(pentad). (Source: NOAA, National Climatic Data Center.)

Number of Landfalling Hurricanes

Pentad
An important consideration with regard to hurricane intensity is the

trend toward warmer sea surface temperatures, particularly in the tropical

Atlantic and the Gulf of Mexico, indicating that climate change may play

some role in increased hurricane intensity (Emanuel 2005; Webster et al.

2005). Another factor is a slow cycle of natural fluctuations in atmospheric conditions and ocean temperatures in the North Atlantic, referred

to as the Atlantic Multidecadal Oscillation, which is currently in a warm

ocean temperature phase.

What does the future hold for hurricane activity? In the near term, it is

expected that favorable conditions for Atlantic hurricanes will persist for

the next decade or so on the basis of previously active periods. For the

longer term, climate models project an increase in the intensity of strong

hurricanes in the 21st century (Bengtsson et al. 2007; McDonald et al. 2005;

Oouchi et al. 2006; Sugi et al. 2002). Specifically, this translates to increases

in wind speed and about a half-category increase in intensity on the commonly used Saffir-Simpson Hurricane Intensity Scale as tropical sea surface

temperatures increase by nearly 2°C. Given these conditions (stronger

hurricanes and warmer tropical sea surface temperatures), climate models also predict an increase in storm rainfall rates of about 20 percent

(T. R. Knutson, personal communication, 2006). No robust projections

concerning the annual global number of tropical storms have yet emerged

from modeling studies, but more detailed analyses focused on the Atlantic

Ocean suggest no significant increases in the annual number of Atlantic

tropical storms (CCSP 2007). Many relevant factors, such as future changes

in wind field patterns, remain very difficult to predict.

Extratropical Storms

The IPCC AR4 models projected a reduction in the total number of midlatitude cyclones and an increase in the number of intense storms. This is

a robust result, yielded by essentially all the models (Lambert and Fyfe

2006). Associated with these changes is an increase in ocean wave height

in the northeastern Atlantic and the northern Pacific (Wang et al. 2004).

Analysis of the conditions that cause thunderstorm systems in the United

States to produce hail results in a time series fairly similar to the U.S. temperature time series shown in Figure 2-5, decreasing from 1950 to the

1970s and then increasing (Brooks and Dotzek 2008). Projecting these

conditions into the future is difficult because contemporary climate models lack sufficient resolution to simulate these storms directly.

66 Potential Impacts of Climate Change on U.S. Transportation
Visibility

Some of the climate changes discussed earlier in this chapter may have secondary effects. Visibility is one such effect. For example, if the number of

intense extratropical storms increases, they may be accompanied by more

time with low visibility during heavy snowfall events (Rasmussen et al.

1999). Projections of drying in the interior of continents would imply the

possibility of increases in blowing dust. The risk of forest wildfires in the

American West is strongly associated with increased spring and summer

temperatures and an earlier spring melt (Westerling et al. 2006) as well as

possible biomass increases from increased precipitation (e.g., Bachelet et al.

2001; Lenihan et al. 2003). These are exactly the conditions being projected

by models for the future. Therefore, wildfire-induced decreases in visibility

are likely to become more frequent. It is uncertain from a theoretical standpoint how the occurrence of fog might change in a warming climate.

Therefore, while the number of low-visibility events associated with intense

storms and fires might be projected to increase, it is uncertain whether the

total number of occurrences of low visibility would increase, decrease, or

remain the same in the projected climate of the future.

Transportation is significantly affected when visibility drops to less

than about 400 m (0.25 mi). Times with such low visibility are associated

primarily with fog, heavy precipitation, blowing sand or snow, or smoke

from wildfires. Observations of past trends in visibility and models of

changes projected for the future are not currently available. While visibility is observed at airports throughout the United States, changes in

observing practices over the past decades make it inappropriate to examine long-term changes in low visibility without a major effort to assess the

data’s homogeneity.

Climate Considerations Related to Alaska

The Alaskan Arctic and sub-Arctic are recognized as the area of the world

where changes to the climate are likely to be among the greatest, leading to

significant impacts. In addition, the area has always experienced great natural climatic variability. Because the climate changes in Alaska are so distinct

from those in the rest of the United States, this section is devoted to an

examination of these expected changes as they relate to transportation.

Climate variables of particular relevance to the transportation sector in

Alaska include (a) the extent of sea ice, snow cover, and permafrost, all

Understanding Climate Change 67
directly driven by temperature change and to some extent by atmospheric

and oceanic circulation; (b) storminess as related to wave height and storm

surges; (c) precipitation and related snow and ice cover; and (d) sea level as

related to land ice, ocean temperature, and movement of the land relative

to the ocean due to geologic features and glacial rebound of the land as

land ice melts.

Generally, the extent of sea ice is important because the ice dampens

the energy of ocean waves. Wave energy is dependent on the distance

traveled by the wind over open water. Less extensive sea ice exposes the

coastline to more frequent and potentially higher ocean waves and swells.

Temperature drives the extent of sea ice, but changes in atmospheric and

ocean circulation also play an important role in multiyear variations in the

extent and location of sea ice. Changes in the type, amount, and intensity

of precipitation, as well as the extent of snow and ice cover, can also contribute to coastal erosion from stream flow and overland runoff to the sea.

Loss of permafrost along coasts can lead to subsidence of the land, which

occurs when ice beneath the sea and along the shoreline melts. Alaska has

considerable permafrost along its northern and western coasts. The height

of the sea relative to the land is the ultimate long-term driver of coastal erosion, but Alaskan sea level rise is complicated by both climatic factors and

geologic forces, affecting local and regional changes in the height of the

land relative to the ocean.

Atmospheric Temperature

Temperatures in Alaska have increased. Observational data indicate that

Alaskan spring and summer surface temperatures have increased by about

2°C to 3°C (about 4°F to 5°F) in the past few decades. However, there are

no discernible trends in temperature during autumn, and changes in winter temperature are more complex. There were two 5-year periods in the

first half of the 20th century when temperatures were nearly as warm as

today, but record-breaking high temperatures have become more common

during recent decades.

Most climate model projections for temperature change during the

21st century suggest that Alaska, and the Arctic as a whole, will warm at

least twice as much as the rest of the world. The warming is expected to be

greatest during the cold half of the year. The observed lack of warming during the autumn and the relatively large increases during other times of the

year are not entirely consistent with model projections; they do not depict

this asymmetry.

68 Potential Impacts of Climate Change on U.S. Transportation
As temperatures increase and sea ice continues to melt, a natural climate feedback occurs as a result of less reflection of sunlight by the ocean

formerly covered by sea ice. This feedback can lead to accelerated warming and additional sea ice melting. At present, the rate of loss of Northern

Hemisphere sea ice is exceeding climate model projections, and at the

present rate of loss, summer sea ice will be absent before the middle of

this century. Climate models do project an acceleration of sea ice retreat

over the 21st century, with periods of extensive melting lasting progressively further into spring and fall. All climate models project this trend

to continue regardless of the emission scenario used and the sensitivity

of the model.

Large portions of Northern Hemisphere sea ice form during the

cold seasons and melt during the warm seasons. Considerable sea ice

persists through the melt season, but because of ocean circulation and

the resultant ice movement, multiyear sea ice makes up only a fraction

of the total ice extent. Records indicate that the formation of new sea

ice each year cannot keep pace with the rate of melting, which is consistent with observed surface warming. Northern Hemisphere sea ice

has been decreasing steadily since the 1950s, measured largely through

continuous coverage provided by NOAA polar orbiting satellites beginning in the 1970s. Prior to that time, assessment of the extent of Northern

Hemisphere sea ice during the first half of the 20th century was limited

to reports from land stations and ocean surface observations. Scientists

have less confidence in the data for the first part of the century, but

independent anecdotal evidence, such as interviews with native peoples

of Alaska, also suggests substantially greater extent of sea ice earlier in

the century.

It is important to understand trends in the extent of coastal sea ice

because it is an important determinant of wave energy affecting coastlines.

As the storms that create wave energy also exhibit strong seasonal variation, it is important to know how sea ice is changing by season. Since the

1950s, the extent of sea ice during winter and autumn has decreased from

15 million square kilometers (km2) to 14 million km2 and from 12 million

km2 to 11 million km2

, respectively. Since the 1950s, decreases in spring and

summer have been substantially greater, down from an average of 15 million km2 to 12 million km2 and 11 million km2 to 8 million km2

, respectively.

This is equivalent to more than 10 percent of the North American land mass

and is an area larger than the state of Alaska.

Understanding Climate Change 69
Extratropical Storms

The climatology of Pacific Ocean storms favors the development of the

strongest storms (extratropical cyclones) from autumn to spring. Although

there are remaining uncertainties about the quality of the data, analyses of

Pacific Ocean extratropical cyclones over the past 50 years indicate little

change in the total number but a significant increase in the number of

intense storms (those with low central pressure and resultant high winds

and waves). The increase in extratropical storms is punctuated by considerable year-to-year variability. Both observational evidence and modeling

projections support the notion that as the world warms, the intensity of

cyclones in the northern Pacific (and the northern Atlantic) will increase

(e.g., Lambert and Fyfe 2006; Wang et al. 2006).

Even without an increase in storm intensity, the greater expanse of open

water due to less extensive sea ice means that ocean waves, with resultant

coastal erosion, can occur more frequently and with greater impact.

Precipitation and Extent of Snow Cover

One of the most difficult quantities to measure across the state of Alaska is

precipitation. This is the case because of the variable nature of precipitation in general, the relatively low number of observing stations across the

state, and the difficulty of providing high-quality data in the harsh Arctic

environment. The large uncertainty in estimated precipitation trends is

also due to the difficulty of measuring wind-blown solid precipitation.

On the basis of existing records, however, there is evidence to indicate

that during the past 40 years, as temperatures have warmed, more precipitation has been falling in liquid form (rain) as opposed to solid

form (snow, ice). The quantity of precipitation also increased during

the 20th century, with much of that increase occurring during the recent

period of warming over the past 40 years. The increase is estimated to be

between 10 and 20 percent, with most of it occurring during the summer

and winter rather than during the transition seasons. Because of greater

overall precipitation in the summer,the percent increase in summer equates

to a greater quantity of precipitation compared with winter.

Analyses of changes in intense precipitation events have been conducted

for areas south of 62°N latitude. They show that the frequency of intense

precipitation events has increased substantially (30 to 40 percent) during

the past several decades. Thus, a disproportionate amount of the precipitation increase is attributable to the most intense precipitation events.

70 Potential Impacts of Climate Change on U.S. Transportation
Climate models project that precipitation will increase by a greater

proportion in the high latitudes compared with the rest of the world. This

result is consistent from model to model, as is the fact that this increase is

expected to be disproportionately larger in the more intense precipitation

events. Both of these phenomena can lead to increased erosion.

NOAA’s polar-orbiting environmental satellite data and surface-based

observations have also revealed major changes in the extent of snow cover.

The extent of North American snow cover has decreased by about 1 million km2, and this trend is expected to continue or accelerate. Surface

observers also report a 1- to 2-week reduction in the number of days with

snow on the ground across the state. In addition, in the Arctic, the lake and

river ice season is now estimated to be 12 days shorter than in the 19th

century.

The increase in total and liquid precipitation, especially when falling

on less extensive snow cover, can affect soil erosion. However, the complex

effects of changes in precipitation type and intensity, earlier breakup of

winter ice, and less extensive snow cover have not been well evaluated with

respect to potential impacts on coastal erosion and flooding. It will be necessary to know which factor dominates in order to understand whether

coastal erosion and flooding will be enhanced or ameliorated as a result of

changes in the extent of precipitation and snow cover.

Permafrost

Thawing of the permafrost, especially along the northern coasts, is expected

to continue. Long-term measurements of temperatures within the permafrost are rare, but it is clear that as air and ocean temperatures have

warmed, permafrost has been melting. As permafrost melts along the

coastlines, the effect on coastal erosion can be compounded by the retreat

of sea ice. The thaw causes the land to subside along the shore, exposing more land to the action of the waves. The thaw also causes slumping

and landslides in the interior, undermining structures built on or near

permafrost.

Sea Level

A general increase in sea level would expose more land to coastal erosion

through wave energy and storm surges. However, it is important to recognize that there are many local and regional variations in sea level rise,

and Alaska is no exception in this regard. Complications arise because of

Understanding Climate Change 71
geologic forces; the rebound of the land as glaciers melt; and in some

areas, local engineering projects. For certain areas in Alaska (e.g., parts of

southeast Alaska), sea level is actually falling as a result of natural geologic

and glacial rebound effects, but this is generally not the case in much of

the state. It is clear, however, that changes in Alaskan climate are among

the greatest in the world. They have likely played an important role in

determining the extent of coastal erosion and flooding in the state and are

likely to continue to do so in the future. Accelerated coastal erosion and

flooding linked to sea level rise in Alaska cannot be ruled out.

FINDINGS

The state of the science continues to indicate that modern climate change

is affected by human influences, primarily human-induced changes in

atmospheric composition that are warming the climate. These changes

result mainly from emissions of GHGs associated with energy use, but on

local and regional scales, urbanization and land use changes are also

important contributors to climate change. Once in the atmosphere, GHG

concentrations have a long residence time—on the order of a century.

Thus, they would continue to affect climate conditions even if GHG emissions were eliminated today, and they demand a response.

Substantial progress has been made in monitoring and understanding

the causes of climate change, but scientific, technical, and institutional

challenges to improving projections of future climate change remain.

For example, considerable uncertainty persists about the rates of climate

change that can be expected during the 21st century. Nevertheless, it is clear

that climate change will be increasingly manifested in important and tangible ways, such as changes in extremes of temperature and precipitation,

decreases in seasonal and perennial snow and ice extent, and rising sea levels. In addition, climate models project an increase in the intensity of

strong hurricanes, with an increase in related storm rainfall rates, in the

21st century. Thus, as human-induced climate changes are superimposed

on the natural variability of the climate, the future will include new classes

of weather and climate extremes not experienced in modern times.

Climate changes will affect transportation largely through these

extremes. The U.S. transportation system was built for the typical weather

and climate experienced locally, including a reasonable range of extremes.

If projected climate changes push environmental conditions outside the

range for which the system was designed—and the scientific evidence sug72 Potential Impacts of Climate Change on U.S. Transportation
gests that this will be the case—the impacts will be significant. They will

vary by mode of transportation and region of the country, and some will

be positive; in general, however, the impacts will be widespread and costly

in both human and economic terms and require significant changes in the

planning, design, construction, operation, and maintenance of transportation systems. In the next chapter, the likely impacts of projected climate

changes on transportation are examined in detail.

REFERENCES

Abbreviations

CCSP U.S. Climate Change Science Program

IPCC Intergovernmental Panel on Climate Change

NOAA National Oceanic and Atmospheric Administration

NRC National Research Council

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78 Potential Impacts of Climate Change on U.S. Transportation
79

3

Impacts of Climate Change 

on Transportation

This chapter explores what is known about the potential impacts of

climate change on transportation. First, the vulnerability of the transportation system to climate change is considered, recognizing, however, that

not all changes will have negative impacts. Then, the potential impacts of

the major climate change factors of relevance for U.S. transportation identified in the previous chapter are described for each transportation mode.

Next, the few studies that have actually assessed the impacts of climate

change on transportation in a particular region or metropolitan area are

reviewed; these studies provide a good illustration of regional differences in

both expected climate changes and impacts. The chapter ends with the committee’s findings on the impacts of climate change on transportation.

VULNERABILITY OF THE TRANSPORTATION SYSTEM 

TO CLIMATE CHANGE

No comprehensive inventory exists of U.S. transportation infrastructure

vulnerable to climate change impacts, the potential extent of that exposure,

or the potential damage costs. Nevertheless, some salient data can be pieced

together from various sources. For example, 53 percent of the U.S. population lives in counties with coastal areas, although such areas make up only

17 percent of the nation’s contiguous land area (Crossett et al. 2004; U.S.

Census Bureau 2005, 28).1 Population density in coastal counties (exclud1 Coastal areas are defined by the U.S. National Oceanic and Atmospheric Administration as counties

and equivalent areas with at least 15 percent of their land area either in a coastal watershed or in

a coastal area between watersheds.
80 Potential Impacts of Climate Change on U.S. Transportation

ing Alaska) is significantly higher than the national average—300 versus

98 persons per square mile—reflecting the limited land area involved

(Crossett et al. 2004). This population swells in the summer months, as

beaches are the top tourist destination (Douglass et al. 2005). Coastal areas

are projected to experience continued development pressures as both

retirement magnets and tourist destinations. For example, many of the

most populous coastal counties located in California, south Florida, and

Texas (Harris County), which already experience the effects of hurricanes

and other tropical storms, are expected to grow rapidly in the coming

decades (Crossett et al. 2004). This growth will generate demand for more

transportation infrastructure and increase the difficulty of evacuation in

an emergency.

Sea level rise, which climate scientists now believe to be virtually certain, in combination with expected population growth, will aggravate the

situation, making housing and infrastructure in low-lying coastal areas

even more vulnerable to extensive flooding and higher storm surges. An

estimated 60,000 miles of coastal highways is already exposed to periodic

coastal storm flooding and wave action (Douglass et al. 2005).2 Those highways that currently serve as evacuation routes during hurricanes and other

coastal storms could be compromised in the future. Although coastal highway mileage is a small fraction of the nearly 4 million miles of public roads

in the United States, the vulnerability of these highways is concentrated in

a few states, and some of these routes also serve as barriers to sea intrusion

and as evacuation routes (Titus 2002).

Coastal areas are also major centers of economic activity. Six of the

nation’s top 10 U.S. freight gateways (by value of shipments) (BTS 2007)

will be at risk from sea level rise (see Table 3-1). Seven of the 10 largest

ports (by tons of traffic) (BTS 2007, 30) are located in the Gulf Coast,

whose vulnerability was amply demonstrated during the 2005 tropical

storm season.3 The Gulf Coast is also home to the U.S. oil and gas industries, providing nearly 30 percent of the nation’s crude oil production and

2 These estimates were made by using geographic information systems to measure the length of

roads in coastal counties, superimposing data from the Flood Insurance Rate Maps of the Federal

Emergency Management Agency to indicate those roads along the coast or tidal rivers likely to be

inundated by storm surge in a 100-year storm, and finally adjusting the estimate to eliminate

flooding from rainfall runoff.

3 The Port of South Louisiana is the nation’s largest port by tonnage and the largest agricultural

export facility in the United States (Mineta 2005). Fortunately, it suffered only minor structural

damage from Hurricane Katrina.
approximately 20 percent of its natural gas production (Felmy 2005).

Several thousand off-shore drilling platforms, dozens of refineries, and

thousands of miles of pipelines are vulnerable to disruption and damage from storm surge and high winds of tropical storms, as was recently

demonstrated by Hurricanes Katrina and Rita. Those hurricanes halted all

oil and gas production from the Gulf, disrupted nearly 20 percent of the

nation’s refinery capacity, and closed oil and gas pipelines (CBO 2006).4

Climate scientists believe that global warming is likely to increase the intensity of strong hurricanes making landfall, increasing the risk of damage to

or lengthening the disruption in the operation of these vital facilities.

Inland areas are also likely to experience the effects of climate change.

Increased intense precipitation predicted by climate scientists for the continental United States could increase the severity of such events as the great

flood of 1993. That event caused catastrophic flooding along 500 miles of

the Mississippi and Missouri River system, paralyzing surface transportation systems, including rail, truck, and marine traffic. Major east–west

traffic was halted for roughly 6 weeks in an area stretching from St. Louis

Impacts of Climate Change on Transportation 81

TABLE 3-1 Top 10 U.S. Foreign Trade Freight Gateways by Value 

of Shipments, 2005

Shipment Value 

Rank Port Mode ($ billions)

1 John F. Kennedy International Airport, New York Air 134.9

2 Los Angeles, California Vessel 134.3

3 Detroit, Michigan Land 130.5

4 New York, New York, and New Jersey Vessel 130.4

5 Long Beach, California Vessel 124.6

6 Laredo, Texas Land 93.7

7 Houston, Texas Vessel 86.1

8 Chicago, Illinois Air 73.4

9 Los Angeles International Airport, California Air 72.9

10 Buffalo–Niagara Falls, New York Land 70.5

Source: BTS 2007, 39.

4By the end of 2005—4 months after Hurricane Katrina and a little more than 3 months after

Hurricane Rita—roughly one-quarter of crude oil production and one-fifth of natural gas production

from the Gulf remained shut down (CBO 2006). Two percent of the nation’s refinery capacity still

was not operating.
west to Kansas City and north to Chicago, affecting one-quarter of all U.S.

freight that either originated or terminated in the flood-affected region

(Changnon 1996). Drier conditions are likely to prevail in the summer in

midcontinental regions, such as the Saint Lawrence Seaway. Weather and

vessel incidents cause most of the lock downtime on the seaway, but in

2000 and 2001, water levels were at their lowest point in 35 years, reducing

vessel carrying capacity to about 90 percent of normal (BTS 2005, 140). If

low water levels become more common because of dryer conditions due to

climate change, freight movements in the region could be seriously

impaired, and extensive dredging could be required to keep shipping channels open (Great Lakes Regional Assessment Team 2000; Quinn 2002). A

longer shipping season afforded by a warmer climate, however, could offset some of the resulting adverse economic effects.

The vulnerability of transportation infrastructure to climate change is

in part a function of its robustness and degree of protection from exposure

to climate change effects (as is the case, for example, with seawalls and levees). It also depends on the amount of redundancy in the system. Box 3-1

illustrates how system redundancies proved critical to the rapid restoration of partial rail service during both Hurricane Katrina and the 1993

Mississippi River flood.5 Yet the predominant trend has been for the railroads (as well as other owners of infrastructure) to shed uneconomical

unused capacity by consolidating operations and abandoning underused

lines. Likewise, major businesses, both manufacturing and retail, have

reduced operating costs through just-in-time delivery strategies, but with

the effect of increasing their vulnerability to disruptions or failures of the

transportation system from either natural or human causes.

The network character of the transportation system can help mitigate

the negative economic consequences of a shock to the system, particularly

in the longer term, as shipments can be shifted to alternative modes or

other regions can pick up the interrupted service. To illustrate, the Port of

Gulfport, Mississippi, which was competing with New Orleans to be the

second-largest container port in the Gulf, was 95 percent destroyed by the

30-foot storm surge from Hurricane Katrina (Plume 2005). Subsequently,

much of the traffic shifted to other ports while Gulfport undertook major

reconstruction of its facilities. On the other hand, the network character

82 Potential Impacts of Climate Change on U.S. Transportation

5 See also the discussion later in this chapter of the results of a case study of Hurricanes Katrina

and Rita commissioned for this study.
of the transportation system can work to magnify the effects of a shock to

the system, particularly when critical links are damaged or destroyed. This

situation was well illustrated during Hurricane Katrina with the loss of

critical highway and rail bridges.

POTENTIAL IMPACTS BY TRANSPORTATION MODE

The impacts of climate change on transportation infrastructure will differ

depending on the particular mode of transportation, its geographic locaImpacts of Climate Change on Transportation 83

BOX 3-1

Examples of the Role of System Redundancies

in the Restoration of Critical Infrastructure

Following Natural Disasters

Hurricane Katrina significantly damaged rail transport in the Gulf Coast

region, particularly east–west traffic through the New Orleans interchange

rail gateway—one of only four major rail crossings of the Mississippi River.

CSX was the rail carrier most affected, sustaining significant damage to

two-thirds of its track mileage between Mobile and New Orleans and to five

railroad bridges between Biloxi and New Orleans (M. Hinsdale, presentation to the committee, Jan. 5, 2006). Estimated reconstruction costs were

approximately $300 million, or about one-quarter of CSX’s annual operating revenues available for capital investment. Nevertheless, CSX coped with

the situation by using “borrowed” track of other, less hard-hit railroads in

the region and by rerouting freight as far north as the St. Louis Mississippi

River crossing. CSX has committed to rebuilding its coastal track in the

short term but is evaluating less vulnerable alternative routes using existing rail corridors or constructing farther inland.

At the time, the flood of 1993 was hailed as the worst natural disaster

ever experienced by the U.S. railroad industry. Total physical damages

amounted to more than $282 million in 2005 dollars—23 percent of

which included costs to operate detoured trains (Changnon 2006). In addition, because of the delays, the railroads lost revenues of $198 million.

Nevertheless, nearly 3,000 long-distance trains were rerouted onto other

railroad lines and some little-used lines bordering on abandonment. System

redundancies and operating arrangements with other carriers enabled the

affected railroads to continue operating—more slowly and at increased cost—

but operating nonetheless.
tion, and its condition. This section is focused on those climate changes

and weather parameters identified in the previous chapter (see Table 2-1)

that climate scientists agree are most likely to occur over the course of this

century and are of greatest relevance to transportation. Potential impacts

on all modes of transport—land, marine, and aviation—are considered.

However, the discussion is intended to be illustrative rather than comprehensive in coverage, highlighting major impacts, similarities and

differences among modes, and implications for adaptation strategies.

Annex 3-1 gives the relevant climate and weather parameters along

with potential impacts by transportation mode. In preparing this table,

the committee drew on past efforts to identify transportation-sensitive

weather conditions, as well as the collective expertise of the committee

members. Some notable past reports include the Weather Information for

Surface Transportation National Needs Assessment Report (OFCM 2002),

the Metropolitan East Coast Assessment (Gornitz and Couch 2000; see

detail in the next section), the U.S. Department of Transportation

Workshop on Transportation and Climate Change (USDOT 2002), and an

article by Black (1990). In addition, the discussion in this section draws

heavily on a paper commissioned for this study (Peterson et al. 2006; see

Appendix C) that provides a more detailed discussion of the potential

impacts of climate change on transportation on the basis of recent global

climate simulations.

The primary focus here is on the direct impacts of potential climate

changes on transportation infrastructure. Nevertheless, many of these

effects will be influenced by the environment in which the infrastructure

is located. For example, increased precipitation levels in some regions will

affect moisture levels in the soil and hydrostatic buildup behind retaining

walls and abutments and the stability of pavement subgrades. Runoff

from increased precipitation levels will also affect stream flow and sediment delivery in some locations, with potentially adverse effects on bridge

foundations. Permafrost decline will affect Arctic land forms and hydrology, with potentially adverse effects on the stability of road- and rail beds.

And sea level rise will affect coastal land forms, exposing many coastal

areas to storm surge as barrier islands and other natural barriers disappear. Such changes are noted here, but their variability from region to

region prohibits further elaboration.

There are also likely to be many indirect effects of potential climate

changes on transportation. For example, possible climate-caused shifts in

84 Potential Impacts of Climate Change on U.S. Transportation
demographics or in the distribution of agricultural production, forests, and

fisheries would have implications for road usage and other transport patterns between emerging economic centers and urban areas. Transportation

patterns could also shift as the tourism industry responds to changes in ecologically or recreationally interesting destinations. Similarly, climate changes

elsewhere in the world that shift markets or demographics could affect the

U.S. transportation system.

Other indirect effects may be manifested at the interface between mitigation and adaptation. Likely U.S. regulation of greenhouse gas emissions

by the Environmental Protection Agency will affect transportation

activities, potentially shifting travel to more energy-efficient modes (see

Appendix B). Furthermore, climate changes may present additional

challenges to meeting air and water quality standards. For example,

warmer summertime temperatures will exacerbate air pollution, particularly ground-level ozone, likely requiring further action to mitigate

transportation-related emissions of pollutants. Similarly, changes in

runoff resulting from modified precipitation regimes could affect water

quality, with implications for roadway treatments.

Impacts of Warming Temperatures and Temperature Extremes

Land Transportation Modes

Land transportation modes comprise highways (including bridges and

tunnels); rail (including private rail lines and public transportation); the

vehicles that use these facilities—passenger cars, trucks, buses, rail and rail

transit cars—and pipelines (recognizing that the latter are buried underground in many areas).

Projected warming temperatures and more heat extremes will affect

all of these modes (see Annex 3-1). The effects of temperature warming

are already being experienced in Alaska in the form of continued retreat

of permafrost regions (see the discussion of Alaska below), creating land

subsidence issues for some sections of the road and rail systems and for

some of the elevated supports for aboveground sections of the TransAlaska pipeline. Warming winter temperatures have also shortened the

season for ice roads that provide vital access to communities and industrial activities in remote areas.

Alaska’s situation is quite different from that of many of the lower

48 states, however, where warming temperatures should have less draImpacts of Climate Change on Transportation 85
86 Potential Impacts of Climate Change on U.S. Transportation

matic, and in some cases beneficial, effects. In many northern states, for

example, warming winter temperatures will bring about reductions in

snow and ice removal costs, lessen adverse environmental impacts from

the use of salt and chemicals on roads and bridges, extend the construction season, and improve the mobility and safety of passenger and freight

travel through reduced winter hazards. Expected increases in temperature

extremes, however, will have less positive impacts. More freeze–thaw conditions may occur, creating frost heaves and potholes on road and bridge

surfaces and resulting in load restrictions on certain roads to minimize the

damage. With the expected earlier onset of seasonal warming, the period

of springtime load restrictions may be reduced in some areas but is likely

to expand in others with shorter winters but longer thaw seasons.

Periods of excessive summer heat are likely to increase wildfires, threatening communities and infrastructure directly and bringing about road

and rail closures in affected areas. Longer periods of extreme heat may

compromise pavement integrity (e.g., softening asphalt and increasing rutting from traffic); cause deformation of rail lines and derailments or, at a

minimum, speed restrictions (Rossetti 2002);6 and cause thermal expansion of bridge joints, adversely affecting bridge operation and increasing

maintenance costs. Pipelines in the lower 48 states are not likely to experience adverse effects from heat extremes.

Marine Transportation

Marine transportation infrastructure includes ports and harbors and

supporting intermodal terminals and the ships and barges that use these

facilities. Expected climate change impacts differ for coastal and inland

waterways.

Warming winter temperatures, particularly in northern coastal areas,

could be a boon for marine transportation. Fewer days below freezing

would reduce problems with ice accumulation on vessels, decks, riggings,

and docks; the occurrence of dangerous ice fog; and the likelihood of ice

jams in ports. The striking thinning (Rothrock and Zhang 2005) and overall downward trend in the extent (Stroeve et al. 2005) of Arctic sea ice are

regarded as a major opportunity for shippers (Annex 3-1). In the short

6 Proper installation of continuous welded rail usually prevents kinks from occurring, but not

always (Changnon 2006).
term, continued reduction in Arctic sea ice should result in more ice-free

ports, improved access to both ports and natural resources in remote

areas, and longer shipping seasons. In the longer term, shippers are looking forward to new Arctic shipping routes that could provide significant

cost savings in shipping times and distances (see the discussion of Alaska

below). For the next several decades, however, warming temperatures and

melting sea ice are likely to result in increased variability in year-to-year

shipping conditions and higher costs due to requirements for stronger

ships and support systems (e.g., ice-capable ship designs, icebreaker

escorts, search and rescue support) (ACIA 2004). In addition, improved

access to remote areas may increase the risk of environmental degradation

to fragile ecosystems.

Warming temperatures are also likely to provide longer shipping seasons for the St. Lawrence Seaway and the Great Lakes (Annex 3-1). Because

of the complex interaction among warmer temperatures, reduced lake ice,

and increased evaporation, however, all nine climate model simulations

suggest lower lake levels as the climate warms (Great Lakes Regional

Assessment Team 2000).7 With lower lake levels, ships will be unable to

carry as much cargo, and hence shipping costs will increase, although some

of the adverse economic impacts could be offset by a longer shipping season.8 A recent study of the economic impact of climate change on

Canadian commercial navigation on the Great Lakes, for example, found

that predicted lowering of Great Lakes water levels would result in an estimated increase in shipping costs for Canadian commercial navigation of

between 13 and 29 percent by 2050, all else remaining equal (Millard

2005).9 Lower water levels could also create periodic problems for river

traffic, reminiscent of the stranded barges on the Mississippi River during

the drought of 1988 (du Vair et al. 2002). In the longer run, of course, less

Impacts of Climate Change on Transportation 87

7 See in particular Chapter 4 on climate change and shipping/boating.

8 According to the Lake Carriers’ Association, a 1,000-foot-long vessel typically used for intralake

transport loses 270 tons of capacity for each inch of draft loss. (Draft is the distance between

the water line and the bottom of the vessel.) Oceangoing vessels, sized for passage through the

St. Lawrence Seaway, are approximately 740 feet long and lose 100 tons of capacity for each inch

of draft lost (Great Lakes Regional Assessment Team 2000).

9 Impacts were estimated on the basis of three climate scenarios: one that assumes a doubling of

the atmospheric concentration of CO2 by midcentury and two that assume a more gradual increase

in greenhouse gases and include the cooling effects of sulfate aerosols. The study found that 

economic impacts varied widely by commodity and route.
efficient waterborne commodity movement would likely result in shifts to

other transportation modes, such as truck and rail. Increased dredging

could offset some of the impacts of climate change, but at a high cost and

with potentially negative environmental consequences.

Air Transportation

Air transportation comprises airports and ground facilities, as well as the

airplanes that carry both passengers and freight and the air traffic control

system.

Warming temperatures and possible increases in temperature

extremes will affect airport ground facilities—runways in particular—in

much the same way that they will affect roads. In Alaska, where use of air

transport is atypically high relative to land transportation modes and

many airstrips are built on permafrost, continued retreat and thawing of

permafrost could undermine runway foundations, necessitating major

repairs or even relocation of some landing strips (Annex 3-1; U.S. Arctic

Research Commission Permafrost Task Force 2003). In contrast, airports

in many of the lower 48 northern states are likely to benefit from reductions in the cost of snow and ice removal and in the environmental

impacts of salt and chemical use. Airlines could benefit as well from

reduced need for deicing of airplanes. The amount of any reduction, however, will depend on the balance between expected warming and increased

precipitation.

More heat extremes, however, are likely to be problematic. They could

cause heat buckling of runways. Extreme heat can also affect aircraft lift;

hotter air is less dense, reducing mass flowing over the wing to create lift.

The problem is exacerbated at high-altitude airports. If runways are not

sufficiently long for large aircraft to build up enough speed to generate lift,

aircraft weight must be reduced or some flights canceled altogether. Thus,

increases in extreme heat are likely to result in payload restrictions, flight

cancellations, and service disruptions at affected airports, and could

require some airports to extend runway lengths, if feasible. An analysis by

the National Oceanic and Atmospheric Administration for the Denver

and Phoenix airports estimated summer cargo loss (June through August)

for a single Boeing 747 of about 17 and 9 percent, respectively, by 2030

because of the effects of increased temperature and water vapor (T. R. Karl

and D. M. Anderson, Emerging Issues in Abrupt Climate Change, briefing, March 12, 2007).

88 Potential Impacts of Climate Change on U.S. Transportation
Impacts of Increased Heavy Precipitation and Sea Level Rise

Land Transportation Modes

The frequency, intensity, and duration of intense precipitation events are

important factors in design specifications for transportation infrastructure. Probabilistic estimates of rainfall intensities for a range of durations

(5 minutes to 24 hours) for return periods, or recurrence intervals, of 20,

50, and 100 years have been used by civil engineers for designs of road culverts, storm water drainage systems, and road- and rail beds. Projected

increases in intense precipitation events will necessitate updating design

specifications to provide for greater capacity and shorter recurrence intervals, increasing system costs.

The most immediate impact of more intense precipitation will be

increased flooding of coastal roads and rail lines (Annex 3-1). Expected sea

level rise will aggravate the flooding because storm surges will build on a

higher base, reaching farther inland (Titus 2002). In fact, the chapter in the

Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment

Report on North America identifies coastal flooding from expected sea

level rise and storm surge, especially along the Gulf and Atlantic coasts, as

one of the most serious effects of climate change (Burkett 2002 in Field 

et al. 2007). Indeed, several studies of sea level rise project that transportation infrastructure in some coastal areas along the Gulf of Mexico and the

Atlantic will be permanently inundated sometime in the next century

(Dingerson 2005; Gornitz and Couch 2000; Leatherman et al 2000; Titus

2002). Low-lying bridge and tunnel entrances for roads, rail, and rail transit will also be more susceptible to flooding, and thousands of culverts

could be undersized for flows. Engineers must be prepared to deal with the

resulting erosion and subsidence of road bases and rail beds, as well as erosion and scouring of bridge supports.10 Interruption of road and rail traffic

is likely to become more common with more frequent flooding.

The impact of sea level rise is limited to coastal areas, but the effect of

intense precipitation on land transportation infrastructure and operations is not. For example, a record-breaking 24-hour rainstorm in July

Impacts of Climate Change on Transportation 89

10 Scour is the hole left behind when sediment (sand and rocks) is washed away from the bottom 

of a river. Although scour may occur at any time, scour action is especially strong during floods.

Swiftly flowing water has more energy than calm water to lift and carry sediment downriver.

Removal of sediment from around bridge piers or abutments (piers are the pillars supporting a

bridge and abutments the supports at each end of a bridge) can weaken and ultimately undermine

the integrity of bridges (Warren 1993).
1996 resulted in flash flooding in Chicago and its suburbs, with major

impacts on the urban area. Extensive travel delays occurred on metropolitan highways and railroads, and streets and bridges were damaged.

Commuters were unable to reach Chicago for up to 3 days, and more than

300 freight trains were delayed or rerouted (Changnon 1999).

Pipelines may also be affected by increased intense precipitation. For

example, federal regulations require that pipelines carrying hazardous

materials in the lower 48 states be buried with a minimum of 3 feet of

cover—up to 5 feet near heavily populated areas. Intense precipitation can

erode soil cover and cause subsidence (i.e., sinking of the earth underneath the pipeline). Scour and shifting of pipelines are a major problem

in shallow riverbeds, where pipelines are more exposed to the elements

(B. Cooper, Association of Oil Pipe Lines, personal communication,

Dec. 7, 2006). Ultrashallow seabed waters can also be a problem if the

pipeline becomes exposed and subject to potential movement and even

fracture from continuing storm wave action.

Changes in seasonal precipitation levels, with more precipitation falling

as rain than snow, can be beneficial but can also create problems in certain

areas. For example, California’s transportation infrastructure could be sensitive to even modest changes from frozen to liquid precipitation. When

precipitation falls as rain rather than snow, it leads to immediate runoff and

increases the risk of floods, landslides, slope failures, and consequent damage to roadways, especially rural roadways in the winter and spring months

(du Vair et al. 2002). Navigable rivers with both rainfall and snowmelt

responses would probably see greater winter volume flows associated with a

greater risk of flooding (U.S. Global Change Research Program 1999).

Marine Transportation

Coastal ports and harbor facilities will be affected by increased intense

precipitation and sea level rise. Landside facilities will be particularly vulnerable to flooding from an increase in intense precipitation events and to

the impacts of higher tides and storm surges from rising seas (Annex 3-1).

Sea level with respect to dock level is an important consideration at both

wet and dry docks, general cargo docks, and container berths for clearance

of dock cranes and other structures. Changes due to increased intense precipitation and sea level rise could require some retrofitting of facilities. At

a minimum, they are likely to result in increased weather-related delays

and periodic interruption of shipping services.

90 Potential Impacts of Climate Change on U.S. Transportation
The navigability of shipping channels is also likely to change. Some

channels may be more accessible to shipping farther inland because of sea

level rise. The navigability of others, however, could be adversely affected

by changes in sedimentation rates and the location of shoals. In other areas,

a combination of sea level rise and storm surge could eliminate waterway

systems entirely. For example, the Gulf Coast portion of the intercoastal

waterway will likely disappear with continued land subsidence and the disappearance of barrier islands. This will bring an end to coastal barge traffic,

which helps offset rail and highway congestion; all ships will have to navigate the open seas. According to the U.S. Geological Survey, Hurricanes

Katrina and Rita alone destroyed 217 square miles of coastal wetlands. This

loss represents slightly more than two-fifths of that which scientists had

previously predicted would take place over the 50-year period from 2000 to

2050 (Barras 2006).

The increased intense precipitation and periodic droughts predicted

for the midcontinental United States will affect shipping on the Mississippi

and Missouri River system. Increased precipitation could bring a repetition

of the floods that devastated travel on the Upper Mississippi River in 1993.

Droughts have a greater influence on commercial navigation on the lower

portion of the river—from St. Louis to the Gulf—where there are no locks

and dams and channel depths are entirely dependent on river flows. The

1988 drought, for example, stranded more than 4,000 barges, shifting

freight to the railroads, which experienced increased business in hauling

grains and other bulk commodities (Changnon 2006; du Vair et al. 2002).

In a recent study of climate change impacts on the lock and dam system on

the Middle Mississippi, between the Missouri and Ohio Rivers, the U.S.

Army Corps of Engineers concluded that the uncertainty associated with

predicting future river flows called for a “wait and see,” monitoring

approach rather than for expensive infrastructure improvements (Institute

for Water Resources 2005). Nevertheless, feasibility studies for navigation

projects have a 50-year planning horizon, thus requiring at least some consideration of the impacts of climate change and identification of the most

robust strategies under a range of different possible scenarios.

Air Transportation

Several of the nation’s largest airports lie in coastal zones, built along tidal

waters, sometimes on fill (Titus 2002). Their runways are particularly

vulnerable to flooding and erosion from increased intense precipitation

Impacts of Climate Change on Transportation 91
and, in the longer term, from sea level rise. Some airports, such as New

York’s LaGuardia, are protected by dikes (see the discussion below of the

Metropolitan East Coast Assessment), but others may require protection.

At a minimum, increased intense precipitation is likely to cause increased

disruptions and delays in air service and periodic airport closures.

Impacts of More Intense Tropical Storms

Climate scientists believe that more intense tropical storms are a likely

effect of climate change. Three aspects of tropical storms are relevant to

transportation: precipitation, winds, and wind-induced storm surge. All

three tend to be much greater during strong storms. Such storms tend to

have longer periods of intense precipitation; wind damage increases with

wind speed; and wind-induced storm surge and wave action can have devastating effects.

All modes of infrastructure are affected by more intense tropical

storms. Sustained storm surge and damaging wave action displaced highway and rail bridge decks during the recent hurricanes along the Gulf

Coast, not to mention the loss of thousands of sign and signal supports.

Shipping was disrupted, and barges that were unable to get out of harm’s

way in time were destroyed. Airports were closed and sustained wind

damage. Refineries were damaged, and barge traffic between offshore drill

sites and coastal pumping facilities was suspended. The vulnerability of

different transportation modes, as well as their resilience to intense tropical storms, is well documented by the case study of the transportation

sector’s response to and recovery from Hurricanes Katrina and Rita discussed later in this chapter.

REVIEW OF ASSESSMENTS FOR PARTICULAR AREAS OR REGIONS

Few studies have attempted to examine the potential impacts of climate

change on transportation in a particular area or region. Those the committee found are briefly reviewed in this section.

The Metropolitan East Coast Assessment

This study of the impacts of climate change in the tristate area of New York,

New Jersey, and Connecticut focused on transportation infrastructure

92 Potential Impacts of Climate Change on U.S. Transportation
because of the enormous value of the Metropolitan East Coast’s (MEC’s)

highly developed infrastructure to the region’s nearly $1 trillion economy

(Jacob et al. 2007).11 With more than 2,000 km of shoreline and extensive

areas of vulnerable residential development and business centers and supporting infrastructure, the focus was on the effects of sea level rise.

The study used two global climate models, tailored to the MEC area, to

describe possible future climate scenarios over the 21st century.12 The projections showed a potential rise in sea level of 0.24 to 1.08 m (nearly 0.8 to

3.5 ft) between the reference year, 1980, and 2080. More important, the

combined effect of sea level rise and storm surge could result in flood

heights for the 100-year coastal storm of 3.2 to 4.2 m (10.5 to nearly 14 ft)

above the current reference height of 2.96 m (nearly 10 ft) for New York

City. Thus, projected increases in sea level could raise the frequency of

coastal storm surges and related flooding by a factor of 3, on average.

Moreover, the return interval of the 100-year storm could shorten to as little as 4 to 60 years, depending on the climate scenario.

Elevation maps of areas within the 3-m (10-ft) reference height above

current sea level reveal that roughly 10 percent of the total MEC land

area—portions of lower Manhattan; coastal areas of Brooklyn, Queens,

Staten Island, and Nassau County; and the New Jersey Meadowlands—

could experience a marked increase in flooding frequency (see Figure 3-1).

Many critical transportation infrastructure facilities lie at elevations 2 to 

6 m (6 to 20 ft) above present sea level—well within the range of current

and projected coastal storm surges of hurricanes and more frequent

nor’easters (see Figure 3-2). Most area rail and tunnel entrance points, for

example, as well as three major airports, lie at elevations of 3 m or less.13

Impacts of Climate Change on Transportation 93

11 The study, one of 18 regional components of the U.S. National Assessment of the Potential

Consequences of Climate Variability and Change organized by the U.S. Global Change Research

program under the Clinton administration, was one of the only assessments that examined

transportation infrastructure.

12 The two models used were the United Kingdom Hadley Centre model and the model from the

Canadian Centre for Climate Modeling and Analysis. For a more detailed discussion, see Jacob 

et al. 2000.

13 Some of these facilities are protected but may need modification. For example, the Port

Authority of New York and New Jersey (PANYNJ), an active participant in the MEC study, built a

dike and levee system to protect LaGuardia Airport. After the severe nor’easter in 1992, PANYNJ

built floodgates to protect the Port Authority Trans-Hudson tunnel under the Hudson River, which

had flooded and put commuter trains out of operation for 10 days (Jacob et al. 2007).
The New York metropolitan area is no stranger to the devastating

impacts of flooding. For example, the nor’easter of December 1992 produced some of the worst flooding in the area in 40 years, resulting in an

almost complete shutdown of the regional transportation system and evacuation of many seaside communities (Jacob et al. 2007). More recently,

heavy rainstorms in September 2004 and in August 2007 crippled the

New York City transit system. Torrential rainfall (nearly 3 inches of rain

in a 1-hour period in the 2007 event) overwhelmed the drainage system,

designed to handle only about half that amount of rainfall, sending water

into the subway tunnels (Chan 2007). Recent emergency planning for

94 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 3-1 Central portion of the MEC study area. Gray shading shows the

areas at elevations below 3 m (10 ft) above present mean sea level. [Source:

Jacob et al. 2007. (Copyright Elsevier 2007. Reprinted with permission of

Elsevier Limited, Oxford, United Kingdom.)]
New York has focused on a worst-case scenario evacuation of approximately

2.3 million New Yorkers, many by transit, in the event of a Category 3+

hurricane.

Flooding and storm surge will only be exacerbated by sea level rise.

The New York metropolitan area is constantly rehabilitating and modernizing its aging capital stock, providing opportunities to build in new

protections against potential increased flooding. The MEC study proposes

several measures, including incorporating sea level rise into the design, siting, and construction of new infrastructure facilities or renovation of

existing facilities; recognizing sea level rise in federal Flood Insurance Rate

Maps used by many local jurisdictions for land use planning and construction regulations; instituting land use measures to prevent new or

further development in highly vulnerable coastal areas; and constructing

strategically placed storm surge barriers, similar to those in operation in

Impacts of Climate Change on Transportation 95

FIGURE 3-2 Current lowest critical elevations of facilities operated by the Port

Authority of New York and New Jersey compared with changing storm elevations at

these locations for surge recurrence periods of 10, 50, and 500 years between

2000 (baseline) and the 2090s. Note that 10 ft equals approximately 3 m.

[Source: Jacob et al. 2007. (Copyright Elsevier 2007. Reprinted with 

permission of Elsevier Limited, Oxford, United Kingdom.)]

Lowest elevation

5–10 year/baseline

5–10 year/2090

50 year/2090

500 year/baseline

500 year/2090

50 year/baseline

Newark

Airport

Feet

Holland

Tunnel

Lincoln

Tunnel

Passenger

Ship Terminal

JFK

Airport

LGA

Airport
the Netherlands and across the Thames River near London, to protect

highly vulnerable and valuable areas.

Climate’s Long-Term Impacts on Metro Boston Study

The Environmental Protection Agency funded a 3-year project to study the

potential impacts of climate change on infrastructure systems, including

transportation, in the metropolitan Boston area and to recommend strategies for preventing, reducing, or managing the risk (Kirshen n.d.). The

long-term economic success and quality of life of the region depend heavily on reliable infrastructure systems, which could be adversely affected by

climate change. The concern is that global warming may result in sea level

rise and increased flooding, higher peak summer temperatures, and more

frequent and intense winter and summer storms with higher storm surges.

At the same time, continued population and economic growth will result

in increased development pressure on already vulnerable coastal and riverine areas, increasing not only the amount of infrastructure at risk but also

the amount of runoff that must be handled by area rivers, streams, and

storm water systems (Suarez et al. 2005).

The human and economic costs of disruption to infrastructure systems from flooding and storm surge in the area were dramatically

illustrated by the devastating storm of October 1996. Drainage systems

were inadequate to handle the 100-year storm. Backups and overflows

affected several sections of the city, causing $70 million in property

damage in addition to disrupting business and personal travel (Kirshen

et al. 2004, 71). Portions of the Boston Museum of Fine Arts and

Northeastern University were flooded, as were a Green Line tunnel and

four rapid transit stations, causing major damage and interrupted service for several weeks.

The study analyzed climate change impacts on seven sectors, including transportation.14 The impact analysis for land transportation systems

focused on flooding and impacts on the road system, emphasizing the

effect on system performance rather than on infrastructure damage

(Suarez et al. 2005). The methodology involved integrating projected

changes in land use, demographics, economic activity, and climatic condi96 Potential Impacts of Climate Change on U.S. Transportation

14 The sectors were energy use, sea level rise, river flooding, water supply, public health (heatstress mortality), localized systems (water quality, tall buildings, bridge scour), and transportation.
tions into the urban transportation modeling system of the Boston

Metropolitan Area Planning Council (MAPC).15 The model was then used

to simulate traffic flows for a range of different flooding scenarios for a

base case year (2003) and a future year (2025), incorporating anticipated

socioeconomic changes, as well as projected new links or increased capacity in the road network.16 Finally, the models were rerun to take into

account the aggregate effect of increased flooding on delays and lost trips

over the period 2000 to 2100.17

The results show that delays and trips lost between the baseline year

2000 and 2100 would increase by 80 and 82 percent, respectively, as a result

of increased flooding attributable to climate change (Suarez et al. 2005,

240). Nevertheless, because of the large number of daily baseline trips in

the Boston metropolitan area—approximately 14.6 million in 2000—these

percentage increases represent relatively modest effects. The results also

reflect the redundancy of the transportation network that is typical of a

mature metropolitan area, which lessens but does not eliminate vulnerability. For example, although coastal areas are more densely populated, the

road network is less redundant, so that residents are unable to make trips

when the roads become inundated. In contrast, riverine floods result in

increased vehicle miles and vehicle hours traveled. Travelers have more

alternative routes available, but many are major commuter routes, thereby

increasing congestion and time traveled (Suarez et al. 2005).

The report concludes that even if one uses high monetized values for

lost trips and incremental delays, the impacts are “significant, but probably not large enough to justify a major effort for adapting the physical

Impacts of Climate Change on Transportation 97

15MAPC forecasts population and employment growth to 2025 at the town level, providing the

best available estimates of the spatial evolution of people and economic growth in the region. The

study assumed that similar growth trends would persist up to 2050 and then remain constant. The

Canadian Climate Centre and Hadley Centre climate scenarios used in the New England Regional

Assessment—another regional component of the U.S. National Assessment—were superimposed

over time series data on local weather conditions to provide the climate change predictions for

2001 to 2100 (Kirshen et al. 2004).

16 Twelve flooding scenarios were developed to reflect different years of simulation, areas flooded

(none, 100-year, and 500-year floodplains), and type of flooding (coastal, riverine, or both). Flood

Insurance Rate Maps were used to identify coastal and riverine floodplains, and these were overlaid

on maps showing land use and the road networks within the boundary of each traffic analysis zone

used in the model (Kirshen et al. 2004).

17 Two climate states were modeled—one assuming no climate change, projecting past trends into

the future by bootstrapping from 50 years of rainfall and sea level data for the Boston area, and

the second assuming climate changes in line with available climate model predictions. The 

difference in network performance between the two scenarios was attributed to climate change

(Kirshen et al. 2004).
infrastructure to expected climatic conditions, except for some key links”

(Suarez et al. 2005, 231). The study, however, did not take into consideration the potential physical damage to transportation infrastructure and

repair costs due to climate change that also must be part of any investment

decision.

Seattle Audit of Climate Change Impacts

Since the early 1990s, Seattle has been a leader in its efforts to reduce

greenhouse gas emissions that contribute to climate change (Soo Hoo and

Sumitani 2005). Because the impacts of climate change are likely to persist

well into the 21st century, however, policy makers have also recognized the

need to develop appropriate adaptation strategies. Seattle’s Office of City

Auditor initiated a series of reviews of how changes in the climate of the

Pacific Northwest region would affect the operations and infrastructure of

various city departments. The first review was focused on the Seattle

Department of Transportation (SDOT), which is responsible for the city’s

$8 billion transportation infrastructure, including its roadways, most

bridges, and bike paths (Soo Hoo and Simitani 2005).

The primary changes predicted by climate scientists for the Pacific

Northwest in the 21st century are warmer temperatures, rising sea levels,

and increased winter precipitation. The study identified five potential types

of impact.

First, increased winter precipitation could lead to more flooding and

landslides, which could damage the city’s transportation infrastructure and

underlying utilities and hamper the mobility and safety of travel.18 More

flooding, for example, could overwhelm the existing storm water drainage

system, causing soil saturation and surface erosion. It could also exacerbate

erosion of soil around roads, bridge footings, and retaining walls.

Second, rising sea levels could affect the adequacy of seawall heights

and bridge clearances. SDOT had considered sea level rise in developing

design standards for a major Alaskan Way Seawall replacement project, but

questions were raised regarding whether the projected sea level rise was

underestimated.

98 Potential Impacts of Climate Change on U.S. Transportation

18 Seattle Public Utilities has primary responsibility for responding to emergencies, such as

landslides and surface flooding. However, SDOT is primarily responsible when the structural

integrity of public streets, bridges, and retaining walls is threatened (Soo Hoo and Sumitani 2005).
Third, increased precipitation and temperatures and sea level rise

would adversely affect bridge operations. More than one-third of Seattle’s

105 bridges are currently rated as being in poor condition.19 Warmer temperatures could cause greater thermal expansion at bridge expansion joints,

affecting bridge operations and adding to maintenance costs. Increased

winter precipitation could exacerbate erosion around bridge footings, and

rising sea levels could affect bridge clearances (see Figure 3-3).

Fourth, warmer temperatures and increased precipitation could cause

roadways to deteriorate. SDOT is responsible for approximately 1,500 lane

miles of arterial streets and 2,700 lane miles of nonarterial streets. The city’s

arterial streets are in good condition, but there is a backlog of repair

and resurfacing projects. Climate changes could shorten street lives

(Figure 3-3). Hotter summers could result in pavement softening and

buckling and the appearance of heat bumps, although use of warmertemperature asphalt mix could mitigate some of these effects. Increased

precipitation would increase street flooding and tax drainage systems.

Finally, warmer and longer summers and reduced summer precipitation would place stress on trees and landscaped areas in the city’s rightsof-way, requiring increased maintenance.20 SDOT’s Urban Forestry unit is

already considering the use of drought-resistant plants and other strategies

to offset the negative effects of climate change.

In response to the report, SDOT noted that it is including climate

change as a factor in the scoping of new projects. It is also undertaking a

new asset management effort that will focus on replacement cycles for all

transportation infrastructure; climate change impacts will be considered as

one factor in determining the adequacy of proposed replacement and rehabilitation projects (E. Paschke, SDOT, personal communication, April 14,

2006). That being said, SDOT noted that the long time frames and uncertainties of expected climate changes, coupled with maintenance backlogs

and short-term planning horizons for operating budgets, justify “a prudent

approach: one that combines watchfulness in following trends in climate

Impacts of Climate Change on Transportation 99

19 According to the 2004 Report of the Citizens’ Transportation Advisory Committee, 37 percent of

the city’s bridges are in “poor condition or worse,” and 4 percent already face weight restrictions

because of critical deficiencies (Soo Hoo and Sumitani 2005, 20).

20 SDOT’s Urban Forestry unit maintains an inventory of 130 acres of land in city rights-of-way.

Approximately 30,000 trees are located on city-owned land, with an estimated value of $100 million.

Approximately half of the city’s landscaped areas are currently rated as being in good condition

(Soo Hoo and Sumitani 2005, 24).
100 Potential Impacts of Climate Change on U.S. Transportation

FIGURE 3-3 Potential impacts of climate change on Seattle’s transportation 

infrastructure. (a) SDOT already monitors some bridges, such as the Admiral Way

Bridge, because of erosion concerns. (Photo courtesy of SDOT.) (b) Increased

rainfall could cause more rapid deterioration of pavements in city streets. (Photo

courtesy of Seattle Municipal Archives.) (Source: Soo Hoo and Sumitani 2005.)

(a)

(b)
change, including anticipating how climate change may increase our

resource needs, while we continue with our efforts to mitigate the causes”

(Soo Hoo and Sumitani 2005, 46). Finally, SDOT officials recommended

an interdepartmental team to coordinate a comprehensive assessment of

projections for sea level rise, as well as data on other issues related to climate change, that could be used to revise existing or establish new and

consistent standards reflecting climate change across all city infrastructure

investment projects (Soo Hoo and Sumitani 2005).

Alaska

Alaska is already experiencing some of the effects of climate change, such as

warming temperatures and continued shrinkage of permafrost regions—

areas of permanently frozen ground below the surface layer—with consequences for all modes of land transportation.21 Warming temperatures are

also affecting marine transportation. Decreased concentrations and extent

of sea ice in the Arctic Ocean have lengthened the ice-free shipping season,

expanded shipping along the Northern Sea Route, and opened the possibility of a Northwest Passage for shipping.22 At the same time, however,

more open seas have exposed coastal villages along northern and western

Alaska to increased storms and wave action, with attendant erosion. Coastal

villages, along with their infrastructure, will need greater protection or may

have to be relocated (G. Wendler, Geophysical Institute Climate Center, personal communication, March 2, 2006).

As noted earlier, Alaska’s transportation infrastructure differs from

that of the lower 48 states. Although Alaska is twice the size of Texas, both

its population and road mileage are more like Vermont’s. Of its 12,700

Impacts of Climate Change on Transportation 101

21 Permafrost refers to soil, rock, or sediment that has remained below 32°F for 2 or more consecutive

years (ACIA 2004). The 2-year designation is intended to exclude the overlying ground surface

layer that freezes each winter and thaws each summer. Regions are classified into continuous 

permafrost zones, in which the permafrost occupies the entire area, and sporadic or discontinuous

permafrost zones, in which the permafrost underlies from 10 to 90 percent of the land and may

be only a few meters thick in places. Permafrost is further classified into two types: (a) cold 

permafrost, where temperatures remain below at least 30°F, and the introduction of considerable

heat can be tolerated without thawing; and (b) warm permafrost, where temperatures remain just

below freezing, and very little additional heat may induce thawing.

22 The Northern Sea Route encompasses all routes across the Russian Arctic coastal seas to the

Bering Strait. The Northwest Passage is the name given to the marine routes between the Atlantic

and Pacific Oceans along the northern coast of North America that span the straits and the

sounds of the Canadian Arctic Archipelago.
miles of roads, for example, only about 30 percent are paved (U.S. Arctic

Research Commission Permafrost Task Force 2003, 28). The road and rail

networks are concentrated largely in the south-central part of the state,

near major population centers. Transport by air is much more common

than in most states. Alaska has 84 commercial airports and more than

3,000 airstrips, many of which serve as the only means of transport for

rural communities. The state also is home to the Trans-Alaska Pipeline

System (TAPS).

Two recent studies (ACIA 2004; U.S. Arctic Research Commission

Permafrost Task Force 2003) considered the impacts of a warming Arctic on

both Alaska and its infrastructure, particularly the effects on permafrost.

The band of discontinuous, warm permafrost has been moving northward

for some years. For highways, thawing of the permafrost causes settling of

the roadbed and frost heaves that adversely affect roadway performance,

such as load-carrying capacity. The majority of the state’s highways are

located in areas where permafrost is discontinuous, and dealing with thaw

settlement problems already claims a significant portion of highway

maintenance dollars [M. Miles, Alaska Department of Transportation

and Public Facilities (DOT&PF), personal communication, March 3, 2006].

Nevertheless, a road rehabilitation cycle of about 15 years is sufficiently

short to enable engineers to adapt to changing climate conditions. Thus,

they are able to anticipate some problems created by thawing prior to construction and have developed a number of mitigation techniques.23 In

addition, the Cold Regions Research and Engineering Laboratory

(CRREL),24 in partnership with DOT&PF and the University of Alaska, has

developed a web-based geographic information system tool—the Alaska

Engineering Design Information System (AEDIS)—for use in monitoring

and design. AEDIS provides geographic-specific data on climate factors,

such as precipitation levels, permafrost, and snow depth, that can be used to

derive engineering design parameters (e.g., load-bearing capacity), schedule

maintenance, and select optimum transportation routes (T. Douglas,

CRREL, personal communication, March 9, 2006).

102 Potential Impacts of Climate Change on U.S. Transportation

23For example, insulation can be placed in the road prism (area of road containing the road surface,

cut slope and fill slope), and different types of passive refrigeration schemes can be used, 

including thermosiphons, rock galleries, and “cold culverts” (M. Miles, Alaska DOT&PF 

personal communication, March 3, 2006).

24The Civil and Infrastructure Engineering Branch of CRREL, part of the U.S. Army Corps of

Engineers, conducts applied research and develops innovative engineering solutions for facilities

and infrastructure that operate under freezing, thawing, and extreme temperature differences.
Less flexible and longer-lived bridges and large culverts are sensitive to

movement caused by thawing permafrost and are more difficult than roads

to repair and modify for changing site conditions. Thus, designing these

facilities to take climate change into account is more critical than is the case

for roads (O. Smith, University of Alaska, Anchorage, personal communication, March 1, 2006). Another impact of climate change on bridges is

increased scour. Hotter, dryer summers have led to increased glacial melting and longer periods of high streamflows, leading to both increased

sediment transport on rivers and scour at bridge crossings. A network of

sonars has been installed on several scour-critical bridges around the state,

and the monitoring data are regularly sent to Alaska DOT&PF (J. Conaway,

United States Geological Survey, personal communication, March 8, 2006).

Temporary ice roads and bridges are commonly used in many parts of

Alaska to access northern communities and provide support for the mining and oil and gas industries. Rising temperatures have already shortened

the season during which these critical facilities can be used (ACIA 2004).

Like the highway system, the Alaska Railroad crosses permafrost terrain, but the railroad does not extend northward into the zone of

continuous permafrost. While frost heave and settlement from thawing

affect some portions of the track, increasing maintenance costs, major relocations of existing track will not likely be required (U.S. Arctic Research

Commission Permafrost Task Force 2003).

Alaska’s airports and airstrips are located throughout the state. A significant number of airstrips in the southwest, the northwest, and the interior are

built on permafrost and thus will require major repairs or relocation if their

foundations are compromised by thawing (U.S.Arctic Research Commission

Permafrost Task Force 2003).

TAPS, which stretches from Prudhoe Bay in northern Alaska to the icefree port of Valdez in the south, crosses a wide range of permafrost types

and varying temperature conditions. More than half of the 800-mile

pipeline is elevated on vertical supports over thaw-unstable permafrost to

avoid problems of permafrost degradation, soil liquefaction, and land

subsidence (U.S. Arctic Research Commission Permafrost Task Force

2003). Because the system was designed in the early 1970s on the basis of

permafrost and climate conditions of the 1950–1970 period, it requires

continuous monitoring, and some supporting members have had to be

replaced. The Federal–State Joint Pipeline Office, which regulates TAPS,

and the Alyeska Pipeline Company, which operates it, do not regard

Impacts of Climate Change on Transportation 103
permafrost degradation as a problem, but this assessment does not take

into account the Arctic Climate Impact Assessment predictions for the

next 30 years (U.S. Arctic Research Commission Permafrost Task Force

2003).

Arctic marine transport will benefit from climate changes. Observations over the past 50 years show a decline in the extent of Arctic sea ice

in all seasons, with the most prominent retreat in the summer (ACIA

2004). Climate models project an acceleration of this trend, opening new

shipping routes and extending shipping seasons along Arctic coastlines,

including Alaska. Improved accessibility, however, will not be uniformly

distributed. For example, the navigation season25 for the Northern Sea

Route is projected to increase from 20 to 30 days per year to about 90 to

100 days by 2080 (ACIA 2004, 83). For trans-Arctic voyages, this route represents up to a 40 percent savings in distance from northern Europe to

northeastern Asia and the northwest coast of North American compared

with southerly routes via the Suez or Panama Canal. In contrast, reduction

in the extent of sea ice may create highly variable conditions in the

Northwest Passage, reflecting the complex geography of the Canadian

Arctic that could not be captured by the regional climate models used for

the Arctic Climate Impact Assessment.

In sum, recent climate change assessments show that Alaska is already

experiencing the effects of climate change, particularly warming of the

Arctic climate and thawing of permafrost. The effects are projected to

accelerate during this century (ACIA 2004), and Alaska’s experience with

adaptation may be instructive for some other cold-weather regions of the

United States. Most of the state’s transportation infrastructure was designed

for permafrost, and those systems with relatively short rehabilitation

cycles relative to projected climate changes will have time to adapt to the

changes. Nevertheless, projected changes are likely to require at best

increased monitoring of climate conditions and higher maintenance

costs, and at worst more major retrofits or even relocation of some facilities. According to one transportation professional, the greatest challenge

lies not in dealing with the impacts of climate change but in not knowing

exactly what changes to expect or when (B. Connor, Alaska University

Transportation Center, personal communication, March 9, 2006).

104 Potential Impacts of Climate Change on U.S. Transportation

25 The navigation season is generally defined as the number of days per year when there is less

than 50 percent sea-ice concentration.
Impacts of Climate Change on Transportation 105

Gulf Coast

The committee commissioned a special case study of the transportation

sector’s response to and recovery from Hurricanes Katrina and Rita.26 One

of the primary objectives of this study was to examine the vulnerability of

the transportation system to a major disruption, with a particular focus

on the impact of an interruption on national-level movement of freight.

The Gulf Coast is one of the key economic and population centers of

the United States, home to more than 15 million Americans located in five

states (Texas, Louisiana, Mississippi, Alabama, and Florida) and three

major metropolitan areas. The low-lying flat land along the Gulf Coast,

skirting the subtropical waters of the Gulf of Mexico, makes the region vulnerable to major hurricanes, more so than any other region in the United

States. However, the geography that makes the coastal area dangerous during hurricanes also makes it attractive for industrial and commercial

development. Several of the nation’s most heavily used ports are located

along the Gulf Coast. The Ports of South Louisiana and Houston—among

the world’s 10 most heavily used ports—are particularly attractive to international shippers because of the area’s centralized location with respect to

the rest of the nation and its wealth of transportation connections by

pipeline, highway, rail, and river. The Gulf of Mexico also contains some

of the largest U.S. oilfields and, with its large share of domestic natural gas

and petroleum production, combined with its status as a major energy

importer, is the epicenter of the U.S. petrochemical industry.

Hurricane Katrina was the most destructive and costliest natural disaster in U.S. history, claiming more than 1,800 lives and causing an estimated

$75 billion in damage. Hurricane Rita, exceeding Katrina in both intensity

and maximum wind speed, claimed 120 lives and caused approximately

$10 billion in damage. The significantly lower casualty and damage levels

of Rita can be attributed to its easterly track, which spared the Houston

metropolitan area from the worst of the storm. The unusually large losses

of life and physical destruction of Hurricane Katrina resulted from a levee

failure and the inability of the floodwaters to recede because so much of

New Orleans lies below sea level. A failed evacuation plan for the car-less

exacerbated the human toll. Both storms seriously disrupted transportation systems. Key highway and railroad bridges were heavily damaged or

26 This section draws heavily on the commissioned paper, by Grenzeback and Lukmann (2007).
destroyed, necessitating rerouting of traffic and placing increased strain on

other routes, particularly other rail lines. Barge shipping was halted, as was

export grain traffic out of the Port of New Orleans, the nation’s largest

export grain port. The pipeline network was shut down, producing shortages of natural gas and petroleum products.

Despite predictions of long-lasting transportation stoppages, however,

the majority of the Gulf Coast highways, rail lines, pipelines, ports, and airports were back in service within weeks to a month (see Table 3-2). The

worst-damaged bridges took 3 to 6 months to repair. Just three bridges that

carry highway US-90 along the edge of the Gulf Coast failed to reopen until

mid- to late 2007, approximately 2 years after they were destroyed.

The fact that Hurricanes Katrina and Rita had only a modest impact on

national-level freight flows can be attributed primarily to redundancies

in the transportation system, the timing of the storms, and the track of

Hurricane Rita. For example, truck traffic was diverted from the collapsed

bridge that carries highway I-10 over Lake Pontchartrain to highway I-12,

which parallels I-10 well north of the Gulf Coast. The primary north–south

highways that connect the Gulf Coast with the major inland transportation

hubs were not damaged and were open for nearly full commercial freight

movement within days. The railroads were able to reroute intermodal and

carload traffic not bound directly for New Orleans through Memphis and

other Midwest rail hubs. Although New Orleans is a major rail freight

interchange point for east–west rail traffic, it is not itself a major origin or

destination for rail freight. Had Hurricane Rita struck a larger industrial

and transportation hub such as Houston, the effects on rail transportation

and freight movement would have been greater and more costly. Timing

also played a role. The hurricanes struck before the peak of the corn and

soybean export season. Most of the Mississippi River ports and the inland

waterway were back in service to handle peak export demand later in fall

2005. Finally, the major pipelines suffered relatively little damage and were

able to open within days, as electrical power was restored.

The hurricanes’ impacts on national freight flows may have been modest, but they were certainly not without cost. A full accounting of the direct

costs to repair transportation facilities damaged by Hurricanes Katrina and

Rita has not yet been compiled. Reported costs of individual projects

shown in Table 3-2 total more than $1.1 billion. Replacement of the I-10

Twin Span Bridge between New Orleans and Slidell, Louisiana, will add

nearly another $1 billion, and the repair and replacement of rail lines,

106 Potential Impacts of Climate Change on U.S. Transportation
pipelines, ports, waterways, and airports will likely add several billion more

to the total. Moreover, the numbers do not include the costs of unreported

emergency operating expenditures, lengthy detours, the opportunity costs

of lost shipments, and the long-term costs of displaced business and trade.

What lessons were learned about the vulnerability of the transportation system from the experience with these two hurricanes? First, with few

exceptions, the physical redundancies of a mature transportation system

provided sufficient alternative routes to keep freight flows moving without major disruption. Where the infrastructure was privately owned (e.g.,

CSX Railroad), arrangements with other carriers enabled operations to

continue. Of course, this outcome might be quite different if multiple catastrophic storms were to strike major industrial and transportation hubs

in close succession—a plausible scenario in a climate-changed world.

Second, restoration of transportation services depended heavily on the

availability of electrical power and manpower. Electricity is critical for the

highway system to operate traffic lights and signs, for railroads to operate

signal systems and crossing gates, for ports to operate cranes and elevators,

for airports to power air traffic control facilities and operate nighttime runway lights, and for pipelines to power pumping stations. Thus, redundancy

of power and communications systems is also necessary for the rapid

restoration and functioning of freight transportation networks. Similarly,

adequate manpower is critical to timely efforts to restore transportation

services and staff restoration projects. Because of the devastation wreaked

by Hurricane Katrina, many public- and private-sector employees lost

family and homes in the storm, and many others evacuated the region;

New Orleans itself was closed for more than a month. Thus, major transportation companies such as CSX were forced to bring in workers from

other locations to staff reconstruction projects.

Finally, the storms have resulted in plans for relocating at least one

facility and redesigning others in anticipation of future hurricanes. The

Port of New Orleans is considering relocating companies and facilities to

the main port area on the Mississippi riverfront from the deep-water channel connecting the port’s Inner Harbor navigation canal to the Gulf, where

they are more vulnerable to future storms. The cost of the relocation is estimated at $350 million. CSX has considered moving its vulnerable rail line

inland—less as a response to hurricane threats than as a response to

Mississippi politicians who are interested in the land for casino and housing development (M. Hinsdale, CSX, personal communication, Sept. 12,

Impacts of Climate Change on Transportation 107
108 Potential Impacts of Climate Change on U.S. Transportation

TABLE 3-2 Major Transportation Facilities Damaged and Closed 

by Hurricanes Katrina and Rita

Cost to 

Repair

Element of Infrastructure Issue ($ millions) Closed On Closed Until

Highways

I-10 (Louisiana and Mississippi)

Twin Span Bridge (New Orleans, 35.0

Louisiana–Slidell, Louisiana)

Eastbound span Heavily damaged Aug. 29, 2005 Oct. 14, 2005

(collapsed spans)

Westbound span Heavily damaged Aug. 29, 2005 Jan. 6, 2005

(collapsed spans)

I-10 to US-90 ramp bridges Damaged 0.4 Aug. 29, 2005

(Mobile Bay, Alabama)

Pascagoula River Bridge Eastbound 312-ft section 5.2 Aug. 29, 2005 Oct. 1, 2005

(Jackson County, Mississippi) damaged

US-90 (Louisiana, Mississippi, 

and Alabama)

Chef Menteur Pass Bridge Damaged 2.9 Aug. 29, 2005 Aug. 2007

(East New Orleans, Louisiana)

Rigolets Bridge (East New Electrical/mechanical 44.0 Aug. 29, 2005 Dec. 7, 2005

Orleans, Louisiana) damage

Bay St. Louis Bridge (Bay Destroyed 266.8 Aug. 29, 2005 May 2007

St. Louis, Mississippi–Pass 

Christian, Mississippi)

Roadway (Pass Christian, Missis- Heavily damaged 100.0 Aug. 29, 2005 Oct. 29, 2005

sippi–Ocean Springs, Mississippi)

Biloxi–Ocean Springs Bridge Destroyed 338.6 Aug. 29, 2005 Nov. 2007

(Biloxi, Mississippi–Ocean 

Springs, Mississippi)

Cochrane–Africatown Bridge Damaged (oil rig) 1.7 Aug. 29, 2005 Sept. 1, 2005

(Mobile, Alabama)

Mobile Causeway/Tensaw Damaged Aug. 29, 2005 Sept. 2, 2005

Bridge (Mobile Co./Baldwin

Co., Alabama)

Lake Pontchartrain Causeway 

(Louisiana)

Northbound span Undamaged Aug. 29, 2005 Not closed

Southbound span Damaged Aug. 29, 2005 Sept. 24, 2005

I-110 (Biloxi, Mississippi) Damaged 5.0 Aug. 29, 2005 Sept. 1, 2005

LA-1 Damaged Aug. 29, 2005
Impacts of Climate Change on Transportation 109

Aug. 29Sept. 5Sept. 12Sept. 19Sept. 26Oct. 3Oct. 10Oct. 17Oct. 24Oct. 31Nov. 7Nov. 14Nov. 21Nov. 28Dec. 5Dec. 12Dec. 19Dec. 26Jan. 2Jan. 9Jan. 16Jan. 23Jan. 30Feb. 6Feb. 13Feb. 20Feb. 27

(continued on next page)
110 Potential Impacts of Climate Change on U.S. Transportation

Rail Corridors

CSX: Gulf Coast Mainline Heavily damaged 250.0 Aug. 29, 2005 Jan. 31, 2006

(New Orleans, Louisiana–

Pascagoula, Mississippi)

Norfolk Southern: Lake Washed out Aug. 27, 2005 Sept. 12, 2005

Pontchartrain Bridge

Union Pacific Minor damage Aug. 29, 2005 Aug. 31, 2005

Burlington Northern Santa Fe: Minor damage Aug. 29, 2005 Sept. 1, 2005

Bayou Boeuf Bridge

Canadian National Minor damage Aug. 29, 2005 Sept. 30, 2005

Kansas City Southern Undamaged Aug. 29, 2005 Aug. 31, 2005

Pipelines

Louisiana Offshore Oil Port Minor damage Aug. 28, 2005 Sept. 2, 2005

Capline Mostly affected by Aug. 28, 2005 Sept. 1, 2005

power outages

Colonial Pipeline Mostly affected by Aug. 28, 2005 Aug. 31, 2005

power outages

Plantation Pipeline Mostly affected by Aug. 28, 2005 Sept. 1, 2005

power outages

Ports

Port of New Orleans Significant damage Aug. 28, 2005 Sept. 12, 2005

175 barges stranded in Out of commission 7.6

New Orleans

Port of South Louisiana Damaged Aug. 28, 2005

Port Fourchon Damaged Aug. 28, 2005

Port of Gulfport Mostly destroyed Aug. 28, 2005 Sept. 30, 2005

Port of Lake Charles Minor damage Sept. 22, 2005a Oct. 1, 2005

Port of Houston Undamaged Sept. 22, 2005a Sept. 27, 2005

Aviation

Louis Armstrong New Orleans Heavily damaged 15.2 Aug. 28, 2005 Sept. 13, 2005

International Airport

Lakefront Airport Heavily damaged 2.0 Aug. 28, 2005 Oct. 19, 2005

Gulfport–Biloxi International Airport Heavily damaged 44.0 Aug. 28, 2005 Sept. 8, 2005

Lake Charles Regional Airport Heavily damaged 8.0 Sept. 22, 2005a Sept. 28, 2005

Southeast Texas Regional Airport Damaged 6.0 Sept. 22, 2005a Oct. 8, 2005

Duration of facility closure; now reopened. Duration of facility closure; still closed for repair or replacement.

Partially closed. aClosures caused by Hurricane Rita; all others caused by Hurricane Katrina.

Source: Grenzeback and Lukmann 2007, 40.

TABLE 3-2 (continued) Major Transportation Facilities Damaged and Closed 

by Hurricanes Katrina and Rita 

Cost to 

Repair

Element of Infrastructure Issue ($ millions) Closed On Closed Until
Impacts of Climate Change on Transportation 111

Aug. 29Sept. 5Sept. 12Sept. 19Sept. 26Oct. 3Oct. 10Oct. 17Oct. 24Oct. 31Nov. 7Nov. 14Nov. 21Nov. 28Dec. 5Dec. 12Dec. 19Dec. 26Jan. 2Jan. 9Jan. 16Jan. 23Jan. 30Feb. 6Feb. 13Feb. 20Feb. 27
112 Potential Impacts of Climate Change on U.S. Transportation

2006). And at the initiative and recommendation of the Federal Highway

Administration (FHWA), almost all of the major river and bay bridges

destroyed by the hurricane’s surge waters will be rebuilt at higher elevations, above the maximum forecast surge levels.27

FINDINGS

All modes of transportation are vulnerable to climate change. Just as infrastructure is local and regional, however, so, too, are the impacts of climate

change. They will vary depending on the location, mode, and condition of

the transportation infrastructure. For example, coastal areas and their

infrastructure will be subject to the impacts of sea level rise, while the 

St. Lawrence Seaway and the Great Lakes may experience lower water levels. The infrastructure will experience impacts unique to each mode (e.g.,

scour on bridge supports), but many impacts, such as flooding and erosion, will be common across all modes. The condition of the infrastructure

itself will affect the impacts experienced. Increased intense precipitation,

for example, could cause accelerated degradation of the surfaces of roads

in poor condition. As the examples in this chapter have illustrated, the

impacts of climate change on U.S. transportation will be widespread and

costly.

According to the most recent scientific assessment, the IPCC Fourth

Assessment Report, the greatest impact of climate change on North

America’s transportation system will be coastal flooding, especially along

the Gulf and Atlantic Coasts, because of sea level rise, aggravated in some

locations by land subsidence and storm surge (Burkett 2002). However, the

rate at which these changes are likely to occur remains uncertain. The current IPCC projections do not include melting of the Greenland ice mass,

for example, which could accelerate sea level rise.

Projected climate extremes are likely to have a particularly severe impact

on transportation infrastructure because the U.S. transportation system was

built to typical weather conditions at the time and local weather and climate

27Hurricane damage to the Gulf Coast bridges resulted primarily from a combination of storm

surge and wave crests that simply lifted bridge decks off their supports. Thus, FHWA recommended

that a 100-year rather than a 50-year design frequency be used for Interstates, major structures,

and critical bridges and that design guidelines take into consideration a combination of wave and

surge effects. It was also recommended that risk and cost assessments be conducted (FHWA

2005 in Meyer 2006). New standards have not yet been agreed upon, so it is unclear whether

they will take forecasts of sea level rise into consideration.
experience. Expected changes in climate extremes, such as more extreme

temperatures, more intense precipitation, and more intense storms, could

push environmental conditions outside the range for which the system was

designed. This in turn could necessitate changes in design, materials,

construction, and operating and maintenance practices. For example,

increased flooding from more intense storms could require a combination

of physical improvements (e.g., greater pumping capacity, more elevated

bridges) and operational measures (e.g., better flood warning and evacuation plans, better real-time micro-level weather forecasts).

Climate change will create both winners and losers. For example, the

marine transportation sector could benefit from more open seas in the

Arctic, reducing shipping routes, times, and costs in the long run. In cold

regions, expected temperature warming, particularly decreases in very cold

days and later onset of seasonal freeze and earlier onset of seasonal thaw,

could mean less snow and ice control for departments of transportation

and safer travel conditions for passenger vehicles and freight.

In all cases, transportation professionals will have to confront and

adapt to climate change without knowing the full magnitude of expected

changes. The greatest challenge is the uncertainty as to exactly what changes

to expect and when. Thus, transportation decision makers will need to

adopt a more probabilistic risk management approach to infrastructure

planning, design, and operations to accommodate uncertainties about

the nature and timing of expected climate changes—a major focus of the

next chapter.

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Abbreviations

ACIA Arctic Climate Impact Assessment

BTS Bureau of Transportation Statistics

CBO Congressional Budget Office

FHWA Federal Highway Administration

NOAA National Oceanic and Atmospheric Administration

OFCM Office of the Federal Coordinator for Meteorological 

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USDOT U.S. Department of Transportation

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116 Potential Impacts of Climate Change on U.S. Transportation
ANNEX 3-1 Potential Climate Changes and Impacts on Transportation

Impacts on Land Transportation (Highways, Rail, Pipeline) Impacts on Marine Transportation Impacts on Air Transportation

Potential Climate Operations and Operations and Operations and 

Change Interruptions Infrastructure Interruptions Infrastructure Interruptions InfrastructureTemperature: 

increases in very hot days and heat waves

Limitations on 

periods of constructionactivity due tohealth andsafety concerns;restrictions typically begin at29.5°C (85°F);heat exhaustionpossible at40.5°C (105°F)

Vehicle overheating

and tire deterioration

Impacts on 

pavement andconcrete constructionpractices

Thermal expansion

on bridge expansion joints andpaved surfaces

Impacts on landscaping in

highway andstreet rightsof-way

Concerns regarding pavement

integrity, e.g.,softening, traffic-relatedrutting, migration of liquidasphalt; 

Impacts on shipping due to

warmer water inrivers and lakes

Delays due to

excessive heat

Impact on lift-off

load limits athigh-altitude orhot-weather airports withinsufficient runway lengths,resulting inflight cancellations and/orlimits on payload (i.e., weightrestrictions)

More energy consumption on the

ground

Heat-related

weathering andbuckling ofpavements andconcretefacilities

Heat-related

weathering ofvehicle stock

(continued)
Temperature: 

decreases in very cold days

Impacts on Land Transportation (Highways, Rail, Pipeline) Impacts on Marine Transportation Impacts on Air Transportation

Potential Climate Operations and Operations and Operations and Change Interruptions Infrastructure Interruptions Infrastructure Interruptions Infrastructure

Regional changes

in snow and iceremoval costsand environmental impactsfrom salt andchemical use(reduction overall, butincreases insome regions)

sustained airtemperature over32°C (90°F) is a significantthreshold

Rail-track deformities; air temperature above

43°C (110°F)can lead toequipment failure

Decreased utility of

unimprovedroads that relyon frozen groundfor passage

Less ice accumulation on vessels,

decks, riggings,and docks; lessice fog; fewerice jams in ports

Changes in snow

and ice removalcosts and environmentalimpacts fromsalt and chemical use

Reduction in need

for deicing

Fewer limitations

on ground crew

ANNEX 3-1 (continued) Potential Climate Changes and Impacts on Transportation
Temperature: 

increases in Arctic temperatures

Temperature: later 

onset of seasonal freeze and earlier onset of seasonal thaw

Fewer cold-related

restrictions formaintenanceworkers

Changes in 

seasonal weightrestrictions

Changes in 

seasonal fuelrequirements

Improved mobility

and safety associated witha reduction inwinter weather

Longer construction

season

Thawing of permafrost, causing

subsidence ofroads, rail beds,bridge supports(cave-in), andpipelines

Shorter season for

ice roads

Reduced pavement

deteriorationresulting fromless exposure tofreezing, snow,and ice, butpossibility ofmore freeze–thaw conditionsin some locations

Longer ocean

transport seasonand more icefree ports innorthern regions

Possible availability of a Northern

Sea Route or aNorthwestPassage

Extended shipping

season forinland waterways (especiallythe St. LawrenceSeaway and theGreat Lakes) dueto reduced icecoverage

work at airports,typicallyrestricted atwind chillsbelow −29°C 

(−20°F)

Thawing of 

permafrost,underminingrunway foundations

(continued)
Sea level rise, added

to storm surge

Impacts on Land Transportation (Highways, Rail, Pipeline) Impacts on Marine Transportation Impacts on Air Transportation

Potential Climate Operations and Operations and Operations and Change Interruptions Infrastructure Interruptions Infrastructure Interruptions Infrastructure

More frequent

interruptions intravel on coastaland low-lyingroadways andrail service dueto storm surges

More severe storm

surges, requiring evacuation

Inundation of

roads and raillines in coastalareas

More frequent or

severe floodingof undergroundtunnels and lowlying infrastructure

Erosion of road

base and bridgesupports

Bridge scourReduced clearance

under bridges

Loss of coastal

wetlands andbarrier shoreline

Land subsidence

More severe storm

surges, requiring evacuation

Changes in harbor

and port facilities toaccommodatehigher tides andstorm surges

Reduced clearance

under waterwaybridges

Changes in 

navigability ofchannels; somewill be moreaccessible (andfarther inland)because ofdeeper waters,while others willbe restrictedbecause ofchanges in sedimentationrates and shoallocations

Potential for 

closure orrestrictions forseveral of thetop 50 airportsthat lie incoastal zones,affecting serviceto the highestdensitypopulations inthe UnitedStates

Inundation of 

airport runwayslocated incoastal areas

ANNEX 3-1 (continued) Potential Climate Changes and Impacts on Transportation
Precipitation: 

increase in intense precipitation events

Increases in

weather-relateddelays

Increases in traffic

disruptions

Increased flooding

of evacuationroutes

Disruption of 

constructionactivities

Changes in rain,

snowfall, andseasonal flooding that affectsafety andmaintenanceoperations

Increases in flooding of roadways,

rail lines, andsubterraneantunnels

Overloading of

drainage systems, causingbackups andstreet flooding

Increases in road

washout, damages to rail bedsupport structures, andlandslides andmudslides thatdamage roadways and tracks

Impacts on soil

moisture levels,affecting structural integrity ofroads, bridges,and tunnels

Adverse impacts of

standing wateron the road base

Increases in

weather-relateddelays

Impacts on harbor

infrastructurefrom wave damage and stormsurges

Changes in underwater surface

and silt anddebris buildup,which can affectchannel depth

Increases in delays

due to convective weather

Storm water runoff

that exceeds thecapacity of collection systems,causing flooding, delays, andairport closings

Implications for

emergency evacuation planning, facilitymaintenance,and safety management

Impacts on structural integrity of

airport facilities

Destruction or disabling of

navigation aidinstruments

Runway and other

infrastructuredamage due toflooding

Inadequate or

damaged pavement drainagesystems

(continued)
Precipitation: 

increases in droughtconditions for some regions

Precipitation: 

changes in seasonal precipitation and river flow patterns

Impacts on Land Transportation (Highways, Rail, Pipeline) Impacts on Marine Transportation Impacts on Air Transportation

Potential Climate Operations and Operations and Operations and Change Interruptions Infrastructure Interruptions Infrastructure Interruptions Infrastructure

Increased 

susceptibility to wildfires, causing roadclosures due tofire threat orreduced visibility

Increases in scouring of pipeline

roadbeds anddamages topipelines

Increased 

susceptibility towildfires thatthreaten transportationinfrastructuredirectly

Increased susceptibility to mudslides in areas

deforested bywildfires

Increased risk of

floods fromrunoff, landslides, slopefailures, and

Impacts on river

transportationroutes and seasons

Periodic channel

closings orrestrictions iffloodingincreases

Changes in silt

deposition leading to reduceddepth of someinland waterways and

Decreased visibility

for airportslocated indroughtsusceptibleareas withpotential forincreased wildfires

Benefits for safety

and reducedinterruptions iffrozen precipitation shifts torainfall

Inadequate or

damaged pavement drainagesystems

Benefits for safety

and reducedinterruptions iffrozen precipitation shifts to

ANNEX 3-1 (continued) Potential Climate Changes and Impacts on Transportation
Storms: more 

frequent strong hurricanes (Category 4–5)

rainfall, depending on terrain

More debris on

roads and raillines, interrupting travel andshipping

More frequent and

potentially moreextensive emergency evacuations

damage to roadsif precipitationchanges fromsnow to rain inwinter andspring thaws

Greater probability

of infrastructurefailures

Increased threat to

stability ofbridge decks

Increased damage

to signs, lighting fixtures, andsupports

Decreased expected

lifetime of highways exposed tostorm surge

Benefits for safety

and reducedinterruptions iffrozen precipitation shifts torainfall

Implications for

emergency evacuationplanning, facility maintenance,and safety management

impacts onlong-term viability of someinland navigation routes

Greater challenge

to robustness ofinfrastructure

Damage to harbor

infrastructurefrom waves andstorm surges

Damage to cranes

and other dockand terminalfacilities

More frequent

interruptions inair service

Damage to 

landside facilities (e.g.,terminals, navigation aids,fencing around perimeters,signs)
1 Highways and bridges on federal lands are an exception, as are privately owned toll roads. In

addition, the vehicles that use the highway system are privately owned, except for transit buses

(see Table 4-1).

124

4

Challenges to Response

This chapter explores the challenges and constraints faced by transportation professionals as they begin to confront projected impacts

of climate change. The chapter begins with an overview of how the U.S.

transportation system is organized and how investment and operating

decisions are made. These organizational arrangements and planning

approaches influence how transportation decision makers consider the

issue of climate change and help explain why responding poses difficult

challenges—the next topic of discussion. A framework for addressing the

uncertainties and analyzing the trade-offs associated with adaptation to

climate change is then introduced. The chapter ends with the committee’s

findings, suggesting opportunities for meeting the challenges to response.

DECISION MAKING IN THE TRANSPORTATION SECTOR

Organization and Funding

Responsibility for transportation infrastructure is decentralized and

shared between the public and private sectors (see Table 4-1). Highways,

bridges, and public transportation infrastructure are owned and operated

by state and local governments.1 Major funding for capital improvements—

and in the case of public transportation, rolling stock (e.g., transit

buses, railcars)—is provided by the federal government, with matching
Challenges to Response 125

TABLE 4-1 Transportation System Responsibility

System Owner–Operators Capital Improvements

Land Transportation

Highways and bridges

Infrastructure

Vehicles

Public transportation

Infrastructure

Rolling stock

Railroads

Infrastructure

Rolling stock

Pipelines

Marine Transportation

Inland and coastal 

navigation channels, 

St. Lawrence Seaway, 

and associated 

navigation aid (all 

infrastructure)

Ports and terminals

Infrastructure

Vessels

Air Transportation

Infrastructure

Vehicle fleet

Note: NA = not applicable. a The exceptions are highways on federal lands and private toll roads. States are responsible for highways and bridges on

major roads. Cities are responsible for major arterial streets in some metropolitan areas.

b Some public transportation services are contracted out to private providers.

State and local governmentsa

Privately owned and operated

Local governments and 

independent authoritiesb

Publicly owned and operated

Privately owned and operated

Privately owned and operated

Privately owned and operated

Federal government through the 

U.S. Army Corps of Engineers 

and U.S. Coast Guard

State and local governments, 

independent authorities, and 

private entities

Privately owned and operated

Local governments and 

independent authorities

Privately owned and operated

Federal funding for major 

highways with required local 

match

NA

Federal funding with required 

local match

NA

Private funding

NA

Private funding

Joint federal and nonfederal 

public funding, user fees

Public and private funding

NA

Federal funding, supplemented 

with state and local grants 

and passenger facility 

charges

NA
126 Potential Impacts of Climate Change on U.S. Transportation

requirements from other governmental levels. Railroads and pipelines are

privately owned and operated, although the federal government has regulatory oversight over railroad and pipeline safety.2 Ports are joint

public–private operations. Typically, an independent authority or public

entity owns the land and sometimes the landside facilities, which are then

leased to private operators, generally on a long-term basis. Major improvements, such as dredging of harbors and channels, are federally funded

through the U.S. Army Corps of Engineers, with required cost sharing.3

The St. Lawrence Seaway system is jointly operated by the U.S. government

and Canada through management corporations established expressly for

this purpose, while the inland waterway system, including upkeep of the

lock system, is operated by the U.S. government through the U.S. Army

Corps of Engineers, also with cost-sharing arrangements. Airports are publicly owned and operated by local governments or independent authorities.

At the major hub airports, the airlines often operate their own hangars and

maintenance facilities. Many airport capital improvements are federally

funded, supplemented with state and local grants and passenger facility

charges. In sum, decision making in the transportation sector is a shared

responsibility among many governmental owner–operators and the private sector, largely decentralized, and modally focused.

Infrastructure Service Lives

Transportation infrastructure is designed to perform for a wide range of

service lives (see Table 4-2).4 Roads are among the shortest-lived facilities, with surfaces that must be repaved every 10 to 20 years.5 Bridges,

locks, and pipelines are among the longest-lived—designed for a 50- to

100-year service life—although many of their components (e.g., bridge

decks) must be rehabilitated more frequently. Transportation facilities

2 The Federal Energy Regulatory Commission regulates the siting of new natural gas pipelines, and

the U.S. Department of Transportation requires 3 feet of cover at initial construction of an oil

pipeline.

3 There is some privately constructed and maintained infrastructure (e.g., channels to private

terminals, private berthing areas).

4 Service life can be defined as the length of time a facility will remain in use to serve its intended

function. This will often exceed the facility’s design life or the period of time used for economic

analysis of project benefits and costs.

5 Typically, the road base is far more durable, unless it is compromised by poor drainage or other

adverse conditions.
with shorter design lives provide numerous opportunities for engineers

to adapt to the impacts of climate change, such as by use of more heatresistant paving materials to withstand the more extreme temperatures

projected for some U.S. regions. Opportunities for adaptation—for example, elevating a bridge to accommodate expected sea level rise—are fewer

for longer-lived facilities, which are rehabilitated or retrofitted at much

longer intervals.

In practice, many transportation facilities perform well beyond their

design lives. Moreover, the most critical decision is where to locate a facility

initially. Once the right-of-way and alignment for a facility have been established, such as for a highway or rail line, relocating the right-of-way, as

might be required in coastal areas experiencing sea level rise, would be enormously expensive. Thus, investment choices made today about the location,

retrofitting, and rehabilitation of transportation infrastructure will have farreaching consequences for the ability of transportation infrastructure to

accommodate climate change and for the costs of any necessary adaptation.

Challenges to Response 127

TABLE 4-2 Transportation Infrastructure Design Lives

Expected Infrastructure 

Transportation Mode Design Life (years)

Highways, bridges, and tunnels

Pavement 10–20

Bridges/culverts 50–100/30–45

Tunnels 50–100

Public transportation

Rail track Up to 50

Rail

Track Up to 50

Marine transportation

Locks and dams 50 

Docks and port terminals 40–50 

Air transportation

Runway pavements 10 

Terminals 40–50 

Pipeline 100 

Note: Design lives are averages. Much of the infrastructure operates far beyond its

design life.

Source: Meyer 2006.
Long-Range Planning and Investment Decisions

For each mode, transportation professionals engage in planning for

long-term capital improvements to infrastructure assets. Below is a brief

summary of the planning process for publicly and privately owned

infrastructure and the implications for addressing climate change.

Publicly Owned Infrastructure

Planning and investment decisions for publicly owned land transportation infrastructure are made within the framework and requirements

defined by the planning provisions contained in legislation; codified in

Title 23, U.S.C.; and most recently amended in August 2005 by the Safe,

Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for

Users, known as SAFETEA-LU. State departments of transportation and

metropolitan planning organizations (MPOs), working in coordination

with local governments, have lead responsibilities for planning.6 The

transportation planning process has two principal products: a long-range

transportation plan and a short-term transportation improvement program. Because the infrastructure is largely in place, the vast majority of

capital improvement projects involve retrofitting or upgrading the existing transportation system or providing new capacity at the margin.

Each state and metropolitan area with an MPO prepares a long-range

plan, looking ahead 20 to 30 years. The plans incorporate forecasts of

population, economic growth, and land use patterns to help determine

the locus and extent of demand for passenger and freight travel and supporting transportation infrastructure needs. The second product—a

transportation improvement program—provides a list of short-term capital improvement projects, reflecting available funding, which is updated

on a 4-year cycle.

Joint Public–Private and Privately Owned Infrastructure

Ports generally have a short planning horizon—5 to 10 years—because of

the highly competitive nature of port business operations.Analyses of major

capital improvements, however, such as landside facilities—warehouses,

128 Potential Impacts of Climate Change on U.S. Transportation

6 The Highway Act of 1973 required the establishment of MPOs in urbanized areas with a population

of more than 50,000 and dedicated a small portion of each state’s funding from the Highway Trust

Fund for this purpose. MPOs are composed primarily of local elected officials whose purpose is to

facilitate decision making on regional transportation issues.
terminals, berths, rail links, and truck access roads—many of which have

40- to 50-year design lives, require forecasting of costs and expected

returns over a much longer planning period. Similarly, the planning horizon for capital improvements to long-lived locks and dams along inland

waterways is about 50 years.

Airports have 20- to 30-year capital improvement plans for landside

investments. Because many of these improvements are federally financed,

the Federal Aviation Administration, as well as local airport authorities

and local planners, is involved in the development of long-range plans for

airport infrastructure.

The planning cycle for privately owned infrastructure—railroads and

pipelines—is handled by individual companies through their capital

budgeting process. Railroads are characterized by their capital intensity

and large fixed investments. Even when a fully functional network is in

place, large annual capital investments must be made to provide operating equipment (e.g., locomotives, freight cars, maintenance vehicles,

computer and signaling equipment) and maintain the physical right-ofway.7 Capital budgets are part of strategic plans that look 5 years out and

annual financial plans that identify the available budget for capital outlays each year. Analyses of individual capital projects forecast costs and

returns over 20- to more than 30-year lifetimes for major facilities, such

as a double-tracking project or a new marshaling yard.8

Pipelines involve a large initial investment; assets are designed to be

very long-lived (about 100 years); and there are few new entrants. Pipeline

companies conduct market forecasts looking ahead 5 years at most.

Planning for capital improvements follows the normal private-sector

capital budgeting process (i.e., project analysis using present value calculations over asset lifetimes, minimum expected rates of return for project

selection, and annual capital budgets).

In sum, public and private transportation infrastructure providers

are making short- and long-term investment decisions every day that

have implications for how well the transportation system will respond to

climate change in both the near and long terms.

Challenges to Response 129

7 These investments tend to be uneven or “lumpy,” however, because equipment, such as railcars,

is purchased in batches.

8 Note, however, that discounting of future benefits at typical discount rates means that for financial

purposes, benefits beyond, say, 20 years will be of diminishing importance.
Operational and Emergency Planning

Transportation professionals in both the public and private sectors also

engage in operational planning to respond to short-term congestion,

delays, and disruptions to system operations. Transportation professionals are keenly aware of the effects of weather on system performance and

already address the impacts of weather on operations for a diverse range

of climate conditions. For example, many departments of transportation

have well-organized snow and ice control operations that can consume

up to 40 percent of annual highway operating budgets in some northern

U.S. states. Others are organizing to achieve better management of traffic

congestion and incident control by establishing transportation management centers.9

Climate changes are expected to affect transportation primarily through

climate extremes, such as more severe tropical storms and flooding from

intense rainfall. One of the probable outcomes is the growing importance

of transportation to emergency response and evacuation. The organizational arrangements necessary to support this interaction are generally

not well developed, although some regions have been more proactive in

this regard. For example, Florida has a well-organized multigovernmental approach to emergency planning and evacuation for hurricanes

that includes transportation. Hurricanes Katrina and Rita provided a

wake-up call to many governments in the Gulf Coast region, which have

since improved emergency plans and evacuation strategies. The events of

September 11, 2001, were instrumental in focusing attention on the need

for emergency plans and evacuation strategies and in underscoring the

critical support transportation can provide. In practice, however, transportation is not always well integrated into these plans. Emergencies that

involve multistate geographic areas and require a regional response are

particularly difficult, as Hurricane Katrina illustrated (Deen 2006).

In the longer term, critical infrastructure that serves as evacuation

routes or egress points may itself be threatened by climate change. For

example, highways in low-lying coastal areas could become endangered

as encroaching sea level rise combines with storm surge to make these

routes impassable.

130 Potential Impacts of Climate Change on U.S. Transportation

9 For more detail, see the paper by Lockwood (2006) commissioned for this study. See also the

discussion about transportation management centers in Chapter 5 (Box 5-1).
CHALLENGES POSED BY CLIMATE CHANGE

Climate change poses a complex set of challenges that in many ways are

new and different for transportation planners and decision makers, and

this may help explain why there is little consensus on the issue or how to

address it.10 The lack of a consistent response may also stem from resource

constraints and an absence of adequate information and guidance.

Differences in Planning Horizons

Climate scientists describe the future in terms of outcomes that unfold

over decades to centuries. One of the reasons for these long time frames

is that the inherent variability of the climate makes it difficult to separate

the “signal from the noise” in making short-term (i.e., less than 25 years)

projections. For many public-sector transportation planners, long-term

planning horizons rarely exceed more than 30 years; 20 to 25 years is

the norm. Port, rail, and pipeline providers have much shorter planning

horizons—5 years at most for strategic plans—although many of their

assets are designed to be much longer-lived, and capital project analyses

reflect these longer time frames. Thus, many transportation planners perceive that impacts of climate change will be experienced well beyond the

time frame of their longest-term plans, not realizing that climate changes

are already occurring and that investment decisions made today will affect

how well the infrastructure accommodates these and future changes.

Treatment of Uncertainty

The issue of climate change introduces uncertainties with which transportation planners are unfamiliar and uncomfortable. Climate scientists

describe the future in probabilistic terms with a portfolio of plausible

scenarios and outcomes that are constantly refined and revised as new

knowledge accumulates. Uncertainties exist with regard to the rate of climate change and the extent of its impacts, even for those changes about

which climate scientists have the greatest confidence, such as warming

temperatures and sea level rise. These uncertainties make it difficult to

Challenges to Response 131

10 See the paper by Dewar and Wachs (2006) commissioned for this study for a more complete

discussion of many points made in this section.
plan and design infrastructure that can accommodate these impacts. The

likelihood of climate extremes and surprises only exacerbates the problem. Moreover, knowledge about climate change impacts is likely to

change over time, requiring a dynamic decision process that can adapt to

new information and accommodate feedback.

In contrast to climate scientists, transportation professionals tend to

focus on “knowns.” Metropolitan transportation planners, for example,

typically provide a single vision of the future on the basis of “best available” forecasts of population, employment, housing, and development

that drive transportation infrastructure needs. Infrastructure is built to

meet the forecast demand, often without fully incorporating uncertainties associated with the predictions. Unexpected, unplanned events, such

as earthquakes, hurricanes, and floods, challenge the system, but a combination of traveler adaptability and system redundancy has enabled

transportation infrastructure providers thus far to maintain operations

with surprisingly little disruption.

Perhaps for these reasons, regional transportation planners appear to

be satisfied with their performance. A national survey of regional planning

agencies, for example, revealed that the majority rated their performance as

acceptable and their models as adequate or better. Only a few, however,

had simulated the effects of removing key links from their systems or

assuming large and irregular fluctuations in traffic flows in some corridors,

such as might occur if tropical storms become more severe or intense precipitation and flooding become more frequent in some regions (Dewar

and Wachs 2006).

Poor Alignment Between Climate Change Impacts 

and Transportation Organizational Arrangements

The decentralized and modally focused organizational structure of the

transportation sector may not align well with climate change impacts,

which do not always follow modal, jurisdictional, or corporate boundaries.

Sea level rise and flooding from intense precipitation, for example, can

affect individual transportation facilities, but they are also likely to have

widespread impacts requiring the response of multiple infrastructure

providers. Some climate changes, such as more frequent intense tropical

storms (Category 4–5 hurricanes), will require regional or even multistate

responses that transportation institutions are poorly configured to address.

132 Potential Impacts of Climate Change on U.S. Transportation
Regional planning organizations exist, but regional government does not.

Multistate action is difficult, as Hurricane Katrina illustrated.

Resource Constraints

Climate change poses the possibility of significant, long-lasting impacts

on transportation infrastructure and system performance that are likely

to be widespread and costly in human and economic terms. Most other

challenges confronted by the transportation sector, even extreme weather

events such as Hurricane Katrina or earthquakes, cause significant damage,

but the effects tend to be local and temporary. By contrast, climate changes

in some U.S. regions may necessitate permanent changes. Over time, for

example, roads, rail lines, and airport runways in low-lying coastal areas

may become casualties of sea level rise, ultimately requiring relocation or

expensive protective measures (e.g., levees, which themselves would be subject to catastrophic failure, as was experienced during Hurricane Katrina).

Resistance to Change

Transportation planners and engineers typically extrapolate from historical trends to forecast future trends and conditions that influence their

investment choices and operating plans. However, the past will not be a

reliable guide for future plans and designs as they relate to climate. Climate

scientists caution that climate change will usher in a new regime of weather

and climate extremes, likely falling outside the range for which many

existing transportation facilities were designed.

Faced with a new problem such as this predicted break in trend, transportation professionals typically adopt incremental rather than radical

solutions. This tendency to favor proven methods and practices is understandable, particularly for engineers, who are designing infrastructure

expected to provide reliable service for decades, and in view of the uncertainties about the rate of climate change and the magnitude of its effects.

Nevertheless, reinforced by conservative institutions, regulatory requirements, and limited funding, this way of thinking can hamper timely

responses to issues such as climate change that involve risk and uncertainty.

Interviews with transportation planning officials conducted for the

U.S. Department of Transportation’s (USDOT’s) Gulf Coast study by

Cambridge Systematics, Inc. (2006) are illustrative of prevailing attitudes.

Challenges to Response 133
The interviews were conducted in spring 2006, when the impacts of

Hurricanes Katrina and Rita were very much on the minds of local planners. Understandably, local officials were concerned with the immediate

problems of rebuilding and recovery from the hurricanes. When questioned about the possibility that climate change could bring about more

storms of the intensity of Katrina or Rita in the future, however, many

local officials expressed skepticism or pleaded ignorance. Others opted

for a literal interpretation of SAFETEA-LU’s planning guidance, which

does not require consideration of climate change, or pointed to federal

policies that allow replacement of facilities only as they are currently

designed, preventing consideration of design modifications that could

provide for adaptation to potential climate change impacts (e.g., elevated

bridges to accommodate sea level rise, storm surge, and wave action).11

Some officials interviewed believed that Federal Highway Administration

regulations prevented them from considering any changes that would

extend beyond the time horizon of their long-range plans.12 Still others

identified limited current funding that, in combination with uncertainties about the rate and timing of projected climate changes, disinclines

planners to give more attention to the issue.

Lack of Relevant Information

Even those transportation professionals who are aware of the importance

of climate change and are already addressing its impacts, such as the planners and engineers in Alaska who are managing the effects of melting

permafrost, indicate that they often lack sufficiently detailed information

on which to take appropriate action. Climate scientists tend to describe

projected climate changes in terms of global averages and confidence levels for global, continental, or large subcontinental regions because climate

models have the greatest fidelity at these levels of analysis. In addition,

studies of the impacts of climate change—with the exception of the handful of studies reviewed in the previous chapter—have not focused on

134 Potential Impacts of Climate Change on U.S. Transportation

11 The Federal Highway Administration, however, has granted exceptions and is rethinking its

regulations and guidance for design of bridges in a coastal environment (Meyer 2006).

12 Section 6001 of SAFETEA-LU references a 20-year forecast period for long-range transportation

plans. Many states and MPOs, however, are using a 20- to 30-year time horizon.
transportation specifically, but on other critical sectors, such as agriculture,

forestry, energy, and water resources.

Transportation professionals need data at the finest-grained level of

geographic detail possible because infrastructure is regional and local.

Fortunately, the most recent assessment of the Intergovernmental Panel

on Climate Change (IPCC 2007) noted the improved capability of climate

scientists to simulate regional climates and make robust statements about

projected climate changes for many regions—a level of geographic specificity that is more useful to transportation planners and designers. Climate

scientists should be encouraged to develop information on transportationrelevant climate changes that is as detailed as possible. Transportation

professionals also have a role to play in helping to define what information about climate change they need, such as temperature and precipitation

thresholds, climate conditions that create unacceptable performance outcomes, and the like.

A DECISION FRAMEWORK FOR ADDRESSING CLIMATE CHANGE

How should transportation planners and engineers proceed in view of the

challenges just outlined? A decision-making framework is needed that

more adequately accommodates uncertainty and incorporates more probabilistic approaches to assessing risk and making investment choices. The

basic concepts in such a probabilistic assessment include hazards, assets, and

consequences, each of which is subject to uncertainties (see Annex 4-1). In

the context of climate change, the hazards represent the potential threats

from changing climate conditions, such as more extreme temperatures or

more intense tropical storms. The assets represent the infrastructure and

its value—both its economic value to the performance of the transportation system and its physical replacement value. The consequences represent

the susceptibility of the infrastructure to damage from the hazards, which

in turn depends on the infrastructure’s design and state of repair, among

other factors. Estimating future risk involves solving for the probability of

occurrence of the hazards times the probable consequences if the hazards

occurred, summed over all the transportation assets in a region. The objective is to minimize future risks.

Transportation professionals already take risk into account, particularly

in designing facilities, and in recent years more probabilistic approaches

have been incorporated (Meyer 2006). For example, engineers design

Challenges to Response 135
structures to withstand certain wind speeds on the basis of a probabilistic assessment of wind speed occurrence as measured by historical wind

speed frequency. The 100-year storm is another example. Engineers often

size the drainage capacity of a transportation facility to handle a storm so

severe that it occurs, on average, just once in 100 years. Adapting riskbased approaches to account for climate change poses new challenges.

First, historical experience will not be a reliable predictor of future climate

conditions. Second, the hazards themselves are likely to change over time,

but in ways that are not currently understood with any precision. Finally,

attempting to hedge by simply designing to a more robust standard—say,

a higher wind speed tolerance or a 500-year storm—will produce much

more costly designs, likely to be unacceptable given limited budgets.13 A

more strategic and selective risk-based approach that explicitly trades off

the costs of designing for greater resilience against the costs associated

with failure could help in setting realistic design standards and investment priorities.

California’s seismic retrofit program for bridges is an example of one

way to proceed (see Box 4-1). Following the Loma Prieta earthquake in

1989, the state was faced with the daunting task of how best to retrofit its

stock of some 25,000 bridges. Earthquakes are a recurring problem, but

there is considerable uncertainty about when or where a seismic event

will occur. Moreover, the resources needed to retrofit every bridge to the

highest standard or to conduct a physical inventory of all structures to

determine which need to be retrofit are not available. The California

Department of Transportation decided to proceed in the following manner. First, departmental engineers determined an acceptable performance

standard or level of risk, reducing one of the uncertainties. For most

bridges, that standard was “no collapse” under a maximum seismic event,

consistent with the geographic location of the bridge. The objective was

to avoid loss of life. However, some damage to the structure was acceptable as long as the structure itself remained intact and could be reopened

136 Potential Impacts of Climate Change on U.S. Transportation

13 The committee is aware of the precautionary principle, which holds that “where there are

threats of serious or irreversible damage, the lack of full scientific certainty shall not be used as a

reason for postponing cost-effective measures to prevent environmental degradation” (UNEP 1992

in Whiteside 2006). The committee recommends that cost-effective measures to protect the more

vulnerable transportation infrastructure be taken. However, the significant costs of redesigning and

retrofitting much of the infrastructure to adapt to potential climate change impacts underscore the

need for more strategic and selective risk-based analyses.
Challenges to Response 137

BOX 4-1

California Seismic Retrofit Program for Bridges

Following the Loma Prieta earthquake in 1989, the California Department of

Transportation (Caltrans) faced the enormous task of prioritizing its inventory

of structures throughout the state for seismic retrofit. Approximately 25,000

bridges on state and local highways required evaluation. Because of this

large number of bridges, a simple and computationally manageable prioritization methodology had to be devised. The goal was to identify and rank the

most seismically vulnerable bridges in the state so the available resources

could be used in the most efficient manner possible.

The process began with establishing a required performance standard. For

most bridges, the minimum standard was “no collapse” during a major

seismic event to prevent loss of life. However, damage to the structure was

acceptable provided that the structure itself remained intact and could be

reopened for service soon after the event. The exceptions to the “no collapse” requirement were 750 structures for which the highest level of

performance was desirable to protect the substantial investment in these

major structures and ensure that they would remain in service after a major

seismic event to provide access for emergency responders. The 11 major toll

bridges, including the San Francisco–Oakland Bay Bridge, were handled separately because their complexity necessitated a time-consuming dynamic

analysis.

A risk algorithm was developed for screening of the nontoll bridges. This

algorithm was based on four major evaluation criteria: seismic activity, seismic hazard, impact, and vulnerability. Seismic activity was determined by

locating structures in one of four fault activity zones, ranked from highly to

minimally active. Seismic hazard was determined on the basis of specific

conditions (e.g., soil) at the bridge site. Impact was based on such attributes as average daily traffic, route type, and detour length. Vulnerability

was assessed on the basis of structural characteristics (e.g., structure type,

structure age, presence of expansion joints) to assess the risk to the structure itself. The score on each criterion was multiplied by a weighting

factor—seismic activity and hazard were weighted more heavily—and

summed with those on the other criteria to arrive at a final score.

All 12,600 state highway bridges were processed by using this screening

procedure and were prioritized by score. (The 750 major structures were

flagged to be in the program.) Additional screening was required for 7,000

(continued)
138 Potential Impacts of Climate Change on U.S. Transportation

BOX 4-1 (continued)

California Seismic Retrofit Program for Bridges

bridges that failed to meet the minimum performance standard. These bridges

were reviewed for specific deficiencies through an examination of the as-built

plans for each. The second “paper” screening was used to determine whether

the bridge was in the program or retrofit could be deferred; the goal was to

make the program more manageable while still addressing the most urgent

needs given the available resources. As a result of this second screening,

2,194 bridges were found to be in need of retrofit and were programmed for

improvement. A final in-depth field inspection was performed, with the

result that some bridges were found to meet the “no collapse” requirement

and were removed from the list. A similar procedure was followed for the

12,400 local roadway bridges, resulting in 4,500 structures that required

further evaluation and analysis.

Since the program was initiated, 2,194 bridges on the state highway system have been retrofit at a cost of $3 billion, and the program is considered

99 percent complete. The remaining phase of the program consists of retrofitting 1,235 bridges on local roadways at an estimated cost of $1.7 billion;

the program for local bridges is about 60 percent complete. Funding is provided through a combination of local funds, state gas tax revenues, statewide

bond initiatives, and federal funds.

Caltrans has maintained ongoing assessment of the seismic retrofit

needs of its bridge inventory to identify structures with potential seismic

vulnerabilities based on lessons learned since the program’s inception.

The bridges identified through this process are prioritized and added to the

program as required.

State and local governments and private infrastructure providers could

adopt a similar approach for identifying and screening critical infrastructure

relative to projected climate changes. Key to adopting such an approach is

establishing a performance standard for a particular facility that reflects a

tolerable level of risk (a “no collapse” equivalent), along with a screening

process that takes into consideration such factors as the degree of risk (e.g.,

magnitude of the hazard), the vulnerability of the facility, and how essential

the facility is to the system so priorities for rehabilitation or retrofit can be

determined.

Source: Information provided by Craig Whitten, Robert Stott, Kevin Thompson, and Cynthia

MacLeay, Division of Engineering Services, Caltrans, October 2007.
for service soon after the event. The exceptions were 750 structures on

state highways and 11 major toll bridges, which were held to a higher

standard both to protect the substantial investment in these major structures and to ensure that these vital transportation lifelines would remain

in service following a major seismic event to provide access for emergency

responders. Second, the experts devised a layered screening system to rate

the structures most in need of retrofit; an in-depth physical inventory

was conducted only for those bridges that did not meet the performance

standard. Finally, elected officials were brought on board, and a combination of funds—federal grants, state gas tax and bond funds, and local

revenues—was employed to implement a long-term investment program

that continues to this day.

State and local transportation officials could adopt a similar approach

to assess how climate change may affect transportation assets and develop

appropriate adaptation responses and investment strategies. To begin, they

might ask the following questions:

• Which projected climate changes are most relevant for their region?

• How are climate change hazards likely to be manifested (e.g., flooding, storm surge coupled with sea level rise)?

• Which transportation assets may be affected?

• How severe must a hazard be before it becomes relevant and

action is required? Can thresholds be identified?

• How likely is it that a projected hazard will exceed the threshold,

when, and where?

• How much risk can be tolerated, or in other words, what infrastructure performance level is tolerable?

• What level of investment (capital and operating) is needed to

maintain different levels of service? Can acceptable performance

standards for all modes of transportation be established?

• Are there critical levels of service needed to protect health and

safety?

• Who is empowered to make these judgments and decisions?

• What are the risks of adverse impacts or consequences if no

action is taken?

Challenges to Response 139
BOX 4-2

Decision Framework to Address Impacts 

of Climate Change on U.S. Transportation Infrastructure

1. Assess how climate changes are likely to affect various regions of the

country and modes of transportation (assess hazards).

2. Inventory transportation infrastructure essential to maintaining network

performance in light of climate change projections to determine whether,

when, and where the impacts of projected changes could be consequential (assess the vulnerability of assets and the system’s resilience to loss

of assets).

3. Analyze adaptation options to assess the trade-offs between making the

infrastructure more robust and the costs involved. Consider monitoring

as an option.

4. Determine investment priorities, taking into consideration the criticality

of the infrastructure component as well as opportunities for multiple benefits (e.g., congestion relief, removal of evacuation route bottlenecks).

5. Develop and implement a program of adaptation strategies for the near

and long terms.

6. Periodically assess the effectiveness of adaptation strategies, and repeat

Steps 1 through 5.

140 Potential Impacts of Climate Change on U.S. Transportation

• If action is necessary, how will investment priorities be determined?

• Who will make the necessary investments, and how will they be

funded?

Answers to many of these questions can be found by following the six

steps set forth in Box 4-2. This approach provides guidance on how to

proceed in addressing many of the technical questions previously posed.

However, it does not cover relevant organizational and political issues.

Transportation officials must communicate the results of their technical

analyses to senior management and elected officials, who make the policy

decisions that guide funding choices. In the California situation, the Loma

Prieta earthquake focused attention on the need for seismic retrofit of

many of the bridges throughout the state to avoid catastrophic failure and

loss of life from such an event in the future.With climate changes, however,

the impacts will not always be as unambiguously attributable to those
changes or as dramatic, with the exception of extreme events (e.g., severe

tropical storms, intense precipitation events, heat waves). Thus, communicating the need for early attention to the impacts of climate change requires

leadership, supported by compelling analyses, on the part of the transportation community.

FINDINGS

Climate change poses a complex set of problems, associated risks, and

uncertainties with which transportation planners and decision makers

are unfamiliar. Among the characteristics of climate change that make it

particularly difficult to tackle are uncertainties about the rate and extent

of projected changes; the fact that climate change impacts may not follow

the modal, jurisdictional, or corporate boundaries of the transportation

sector; and the fact that impacts may require coordinated regional or

multistate responses that infrastructure providers are poorly configured

to address. The significant costs of designing infrastructure to allow for

adaptation to long-term climate change impacts in the face of resource

constraints, the tendency of transportation planners and engineers to

extrapolate from the past and adopt incremental solutions when approaching new problems, and the lack of relevant information and

guidance on which to base appropriate actions also affect how transportation planners and engineers view climate change.

A change in perspective is needed. First, transportation professionals

must recognize climate change as a credible and important problem so that

champions will emerge to bring attention to the issue and to make collaboration with climate scientists and meteorologists a priority. Second,

addressing climate change requires a longer-term perspective and recognition that investment decisions made today, particularly about the

location of transportation infrastructure, help shape long-term development patterns and markets well beyond the 30-year time frames of many

public-sector capital improvement plans and private-sector capital budgeting analyses. These decisions also affect how well the transportation system

will adapt to climate change in the near and long terms. Third, the significant costs of redesigning, retrofitting, and potentially having to relocate (or

protect at great expense) some transportation infrastructure to adapt to

potential impacts of climate change suggest the need for more strategic,

risk-based approaches to decision making and infrastructure design. Such

Challenges to Response 141
142 Potential Impacts of Climate Change on U.S. Transportation

approaches should be better oriented to assessing the trade-offs between

the costs of investments to make the infrastructure more robust and the

likelihood and costs of facility failures or major disruptions to the system.

The results of such assessments should be presented in a form that can be

communicated to senior management and elected officials as a prudent

action program, and provision should be made for adjustments as new

knowledge becomes available. Finally, addressing the impacts of climate

change that require regional and multistate responses is likely to entail

developing new coalitions and organizational arrangements. Many of these

changes will take time. Fortunately, transportation professionals have many

avenues through which to begin to develop adaptation strategies, the topic

of the next chapter.

REFERENCES

Abbreviations

IPCC Intergovernmental Panel on Climate Change

UNEP United Nations Environment Programme

Cambridge Systematics, Inc. 2006. Potential Impacts of Climate Variability and Change

to Transportation Systems and Infrastructure—Gulf Coast Study: Long-Range

Planning and Investment. Working Paper. Cambridge, Mass., June 30.

Deen, T. B. 2006. Preliminary Remarks Outline, Rapporteur. Conference on Climate

Change Impacts on U.S. Transportation. Transportation Research Board and

Division on Earth and Life Studies, Oct. 12.

Dewar, J. A., and M. Wachs. 2006. Transportation Planning, Climate Change, and

Decisionmaking Under Uncertainty. Dec. 13.

IPCC. 2007. Summary for Policymakers. In Climate Change 2007: The Physical Science

Basis. Contribution of Working Group I to the Fourth Assessment Report of the

Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning,

Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.), Cambridge

University Press, Cambridge, United Kingdom, and New York.

Lockwood, S. A. 2006. Operational Responses to Climate Change Impacts. PB Consult,

Dec. 29.

Meyer, M. D. 2006. Design Standards for U.S. Transportation Infrastructure: The

Implications of Climate Change. Georgia Institute of Technology, Dec. 18.

UNEP. 1992. Principle 15. Declaration made at the United Nations Conference on

Environment and Development, Rio de Janeiro, Brazil, June 14.

Whiteside, K. H. 2006. Precautionary Politics: Principle and Practice in Confronting

Environmental Risk. Massachusetts Institute of Technology Press, Cambridge,

Mass.
ANNEX 4-1

Applying Probabilistic Risk Assessment 

to Climate Change and Transportation

Probabilistic risk assessment (PRA) is a comprehensive, well-developed

methodology for evaluating risks so they can be prioritized and

managed more effectively. Properly applied, PRA will likely prove an

indispensable tool for transportation managers considering the potential

impacts of climate change.

CLASSIC RISK ASSESSMENT

The central idea behind PRA is to define risk as the product of the magnitude of adverse consequences and the probability that those consequences

will occur. For instance, the risk of the loss of a coastal road due to a storm

surge would be the likelihood of a storm surge rising high enough to inundate the road, multiplied by both the dollar cost of replacing the flooded

road and the costs of the economic disruption during the time the road was

unusable.

In principle, transportation managers could use this risk definition to

thoroughly assess the risks posed by climate change for their system. They

could list the full range of hazards associated with climate change for their

region (e.g., sea level rise, heat) and then estimate the consequences that

each hazard, if it occurred, would have for each transportation asset in

their region. Each component of this equation has an associated probability. Thus, for example, there is a certain annual probability of occurrence

for a 5-foot, 10-foot, or 20-foot storm surge; a certain probability that a

road would fail if confronted by a 5-foot, 10-foot, or 20-foot storm surge;

and a certain probability that the economic costs of such a failure would

be $1 million, $5 million, or $10 million.

143
In sum, the risk due to climate change for all the assets in a manager’s

system would be given by

where the first term represents the probability densities for each hazard

and the second term represents the probability densities for the costs of

each hazard (including the probability and the cost of failure) for each

asset in the transportation system.

Carrying out this analysis would provide transportation managers

with an estimate of their total risk and the most important sources of that

risk. (In practice, the probability of hazard is time dependent, and any

future consequences for long-lived infrastructure would be discounted.

However, this simplified expression is sufficient for the discussion below.)

Note that the same contribution to risk can be made by a hazard with a

relatively high probability of occurrence but moderate consequences and

a hazard with a relatively low probability of occurrence but relatively high

consequences. Such information provides a solid foundation for determining the most effective ways to manage the risk.

CHALLENGES OF ASSESSING THE RISKS OF CLIMATE CHANGE

FOR TRANSPORTATION ASSETS AND SYSTEMS

In practice, it is difficult to carry out this calculation in its complete form.

First, all the necessary data on the likelihood of the various hazards and

their economic consequences may not be available. Second, significant

uncertainty may be associated with the data that are available. Decision

and risk analysts often distinguish between risk and uncertainty. In the

former, knowledge of future events can be well characterized by probability distributions. In the latter, decision makers may not view the best

available probability distributions as very reliable. For instance, if transportation managers were completely confident that the climate is not

changing, they might have high confidence in estimates of the probability of moderate-probability hazards, that is, those expected to occur every

10 years or less as gleaned from weather records for their region extending back several decades or more. Managers might regard estimates of

low-probability hazards, that is, those expected to occur every century,

as less reliable. However, transportation managers have little basis for

Total risk Prob hazard) Prob consequence) al= × ( ( l assets,

all hazards

∑

144 Potential Impacts of Climate Change on U.S. Transportation
assuming that estimates of future climate-related hazards gleaned from

past weather records in their region can serve as good estimates of the

future likelihood of such events. They need to adjust their expectations

on the basis of the results of probabilistic projections from climate models. As discussed in Chapter 2, some hazard estimates from such models,

in particular, estimates of the likelihood of extreme events, may be less

reliable than others.

The final reason that a comprehensive probabilistic risk assessment

would prove difficult is that many transportation assets are long-lived,

many of the most important impacts of climate change are expected to

increase over time, and future transportation managers may take steps

that can reduce (or perhaps unintentionally increase) the consequences

of future climate changes. To address such changes over time, those who

study the impacts of climate change identify four key factors that characterize the ability of a system to adjust to climate change. Using a slightly

different language drawn from the ecological and biological literatures as

opposed to the engineering literature of formal probabilistic risk assessment, the Intergovernmental Panel on Climate Change defines these

factors as follows:

• Exposure, defined as the manner and degree to which a system is

exposed to significant climate variations;

• Vulnerability, defined as the potential for loss, or the degree to

which a system is susceptible to or unable to cope with adverse

effects of climate change;

• Resilience, which refers to the restorative or regenerative capacity

of a system when faced with change; and

• Adaptation, defined as the adjustment made to a system in

response to actual or expected climate change to mitigate harm or

exploit beneficial opportunities.

Exposure and vulnerability are similar to hazards and consequences.

System-level resilience is a particularly important concept in the transportation sector because individual assets function as components of a

network. The consequences of damage to any one asset will depend on the

ability of traffic to reroute by using other routes or modes. They will also

depend on the speed with which the affected private transportation

providers and public agencies (e.g., state and local governments) can react

Challenges to Response 145
and bring resources to bear to restore damaged systems to service. The

resilience, or lack thereof, of the system can thus reduce or increase the

consequences of damage to individual assets in the system.

Adaptation will also be an important component of transportation

managers’ ability to manage future risks associated with climate change.

Managers today do not need to address the full range of potential impacts

of future climate change because they can reasonably assume that future

managers will take prudent steps to reduce the vulnerability of their assets

and increase the resilience of their systems. However, some decisions made

today can have implications that might make adaptation actions by future

managers significantly more or less effective. For instance, some choices

regarding the design and location of new transportation infrastructure

may make it easier and less costly for future managers to adapt to climate

changes if those changes turn out to be larger than currently expected. If

there are two otherwise similar locations for a new road, for example,

locating it farther from the coast will make it less costly for future managers to address any vulnerabilities of the asset should sea level rise turn

out to be larger than currently expected.

CLIMATE RISK ASSESSMENT FOR TRANSPORTATION MANAGERS

IN PRACTICE

The above factors—lack of complete data, uncertainty about the reliability of projections of future climate change, and uncertainty about the

actions future managers will take to reduce the vulnerability and increase

the resilience of a transportation system—make it difficult to conduct a

comprehensive probabilistic risk analysis for a regional transportation

system. In future years, more comprehensive planning frameworks can be

expected to come into use that will help transportation managers integrate consideration of exposure, vulnerability, resilience, and adaptation

factors. In the near term, however, a number of convenient and relatively

simple methods can facilitate transportation managers’ incorporation of

these risk assessment concepts into their planning.

For instance, the California Seismic Retrofit Program (see Box 4-1)

provides an example of a simple screening analysis, based on the concepts

of probabilistic risk analysis, that allowed the California Department of

Transportation to prioritize seismic retrofit investments for approximately

25,000 bridges on state and local highways. The screening criteria focused

146 Potential Impacts of Climate Change on U.S. Transportation
on both the vulnerability of individual assets and the resilience of the system. For instance, the program prescribed a higher performance standard

for 11 major toll bridges, such as the San Francisco–Oakland Bay Bridge,

whose loss would cause major economic disruption and whose replacement would be extremely expensive.

Transportation planners can address the potential for future system

adaptation by time windows. For instance, operational decisions will be

focused on near-term changes in weather and climate conditions, such as

more frequent and more extreme events (e.g., intense precipitation and

flooding), with which transportation operators are already familiar. Retrofit

decisions will determine the performance of assets for several decades

and thus should use probabilistic climate forecasts that extend out for

several decades to estimate hazards. Finally, land use and location decisions for new infrastructure may influence transportation systems for a

century or more, so managers should use probabilistic climate projections for future climate conditions extending into the 22nd century. The

decision framework described in Box 4-2 provides one way to incorporate such considerations.

ROBUSTNESS AND SENSITIVITY ANALYSIS

Particularly when they use multidecadal and century-scale climate projections, transportation managers should pay heed to potentially significant

uncertainties in these estimates. In particular, when transportation managers use probabilistic risk assessments to compare alternative design

choices or even when they conduct a screening analysis, they should be

aware of choices or rankings that are especially sensitive to particular

probabilistic estimates. Engineers commonly incorporate safety factors into

designs or design standards to account for unforeseen events or abnormal

forces on structures. Similarly, transportation managers should recognize

that it may be difficult for climate change projections to distinguish a

future 100-year storm from a future 500-year storm, or that estimates of

the likelihood that sea level rise will exceed 1 m by 2100 may change significantly in the years ahead. To the extent that they can make location

decisions and design choices that account for such uncertainties in their

risk assessments, today’s transportation managers will help future stewards of their systems minimize avoidable surprises.

Challenges to Response 147
148

5

Meeting the Challenges

Adaptation to climate change would be necessary even if drastic

mitigation measures were taken immediately to stabilize or even

eliminate greenhouse gas (GHG) emissions (IPCC 2007). The effects of

such global climate changes as warming temperatures and sea level rise

occurring today reflect emissions of GHGs released into the atmosphere

over the past century. Because of these long-lasting effects, the actions taken

by transportation professionals today have implications for how the transportation system will respond to climate change in the near and long terms.

The first section of this chapter is organized on the basis of timescales

that transportation decision makers must consider in determining how

best to adapt to climate change. In the short term (i.e., the next several

decades), transportation professionals are likely to have operational

responses to changing climate conditions and climate extremes. Operators

of transportation systems already react to many climate changes, particularly extreme events (e.g., intense precipitation, intense tropical storms)

and can rapidly adapt operating and maintenance practices for those climate conditions projected to increase in frequency or intensity.

Rehabilitating or retrofitting infrastructure requires a longer time horizon because engineers design many infrastructure facilities with long service

lives in mind (see Chapter 4), thereby providing fewer opportunities for

adapting to changing climate conditions without incurring significant costs.

Adapting facilities for climate change may also involve the reevaluation and

development of design standards—a process that typically entails a

lengthy research and testing program.

Finally, constructing new transportation infrastructure or providing

major additions to existing transportation systems requires the longest

time horizon. Transportation systems shape land use and development
patterns, and in turn, population growth and economic development

stimulate demand for new infrastructure facilities to support growth. In

both cases, decisions made today about where to locate or expand transportation infrastructure establish development patterns that persist for

generations and are difficult to change. These decisions should be weighed

carefully to ensure that people and businesses are not placed in harm’s

way as projected climate changes unfold.

Following discussion of these topics, the chapter turns to many crosscutting issues—flood insurance; monitoring technologies and new

materials; data, models, and decision support tools; and new partnerships

and organizational arrangements—that can help facilitate adaptation to

climate change or bring climate change issues into the decision-making

process. The chapter ends with the committee’s findings.

ADAPTATION STRATEGIES

Annexes 5-1A through 5-1C summarize a wide range of adaptation measures that can be used to address many of the climate change impacts

discussed in Chapter 3 (see Annex 3-1). Potential adaptations are identified for land, marine, and air transportation, respectively, by response

category: (a) changes in operations, (b) changes in infrastructure design

and materials, and (c) other. No attempt is made to estimate the relative

costs or effectiveness of these measures, although such analyses would be

necessary to evaluate specific infrastructure investment alternatives. The

remainder of this section addresses the key issues and opportunities for

adaptation in each response category.

Operational Responses

The most rapid response to the impacts of climate change is likely to come

through changes in transportation operating and maintenance practices.1

Every U.S. transportation provider already experiences the adverse impacts

of weather on operations under a diverse range of climate conditions. For

example, approximately 75 percent of air travel delays in the National

Airspace System are weather related (L. Maurice and M. Gupta, presentation to the committee, Jan. 4, 2007). Slick pavement and adverse weather

1 This section draws heavily on the paper by Lockwood (2006) commissioned for this study.

Meeting the Challenges 149
150 Potential Impacts of Climate Change on U.S. Transportation

contribute to nearly one-quarter of all highway crashes and about 7,400

fatalities annually.2 In addition, snow, ice, rain, and fog cause about 15 percent of total delays on the nation’s highways (FHWA 2004; NRC 2004b).

Weather also causes delays and interruptions in service for railroad and

marine transportation.3

Transportation agencies expend considerable resources to address

these conditions. For example, snow and ice control accounts for about 

40 percent of annual highway operating budgets in snowbelt states (FHWA

2006a). Hurricane response is a major focus of transportation operations

in states bordering the Gulf Coast. Collaboration between departments of

transportation (DOTs) and emergency response personnel has improved,

particularly in those areas of the country subject to recurring natural

disasters—the Gulf Coast (hurricanes) and California (earthquakes and

wildfires)—but still has a long way to go. Climate change is altering the

frequency, intensity, and incidence of weather events.

Changes in Frequency of Extreme Weather Events

With changes in the frequency of extreme weather events, operational

responses treated today on an ad hoc, emergency basis are likely to become

part of mainstream operations. One could imagine, for example, that if

strong (Category 4 and 5) hurricanes increased in frequency as is likely,

widespread establishment of evacuation routes and use of contraflow

operations4 in affected areas might become as commonplace as snow

emergency routes in the Northeast and Midwest. Mainstreaming such

responses will require expanding the scope of the traditional operating

focus of DOTs on traffic and incident management to include weather

management, as well as improved training for operating personnel.

Increases in Intensity of Weather Events

Climate change is expected to trigger more extreme weather events, such as

more intense precipitation, which are likely to produce areawide emergen2 Based on averages from 1995–2004 data collected by the National Highway Traffic Safety

Administration and analyzed by Mitretek Systems.

3 See, for example, Changnon (2006) on the impacts of weather and climate on American railroading

and a report by the Office of the Federal Coordinator for Meteorological Services and Supporting

Research on the impacts of weather on surface transportation modes (OFCM 2002).

4 Contraflow involves the reversal of traffic flow on one or more of the inbound lanes and shoulders

of roads and highways for use in the outbound direction to increase evacuation capacity in an

emergency by using both sides of a roadway.
cies and may require evacuation of areas vulnerable to flooding and storm

surge. In the wake of September 11, 2001, and Hurricanes Katrina and Rita,

the U.S. Department of Homeland Security has mandated an all-hazards

approach to emergency planning and response and encouraged better

evacuation planning (DHS 2006). Coordination among state and local

emergency managers—the first responders in an emergency—has

improved, and emergency operations centers (EOCs) have been established in many metropolitan areas as command posts that can be activated

rapidly in an emergency. Typically, transportation is a support function,

but the critical role it plays in emergency response and especially in evacuation—a role that is likely to become more important as the climate

changes—should be strengthened through increased collaboration between

emergency managers and transportation providers and more representation of transportation agencies and private transportation providers at

EOCs. Operators of transportation systems also need to work more

closely with weather forecasters and emergency response planners to

convey their own lead-time requirements for providing the necessary

personnel and equipment in an evacuation and protecting their own

assets. Finally, a greater emphasis on emergency management as a separate

functional responsibility within DOTs and other transportation providers

is needed.

Regional transportation management centers (TMCs) provide one

location through which collaboration between transportation providers

and emergency managers can occur (see Box 5-1). TMCs are currently

focused on traffic monitoring and incident management through rapid

deployment of police, fire and rescue, and emergency medical services. In

some metropolitan areas, new functions are being added, such as better

weather information and greater use of real-time traffic advisories, as well

as links with emergency managers. Some TMCs are also serving as EOCs.

However, integration of weather and emergency management functions

in TMCs is still in its infancy according to a recent U.S. Department of

Transportation assessment (FHWA 2006b).

Changes in Incidence of Weather Patterns

Climate changes will bring new weather patterns to previously unaffected

areas of the United States. These changes, however, may not necessarily

require the development of new operating and maintenance strategies.

The United States has a diverse climate, ranging from subtropical to arctic

Meeting the Challenges 151
152 Potential Impacts of Climate Change on U.S. Transportation

and from arid to wet, with several regions being subject to temperature

extremes and such events as blizzards, hurricanes, tornadoes, floods, wildfires, avalanches, and mudslides. As climate patterns change, the transfer

of best practices from one location to another will be essential. A mechanism is needed to encourage such information exchange, involving all

BOX 5-1

Transportation Management Centers

Improving the efficiency of the existing highway network involves the application of technologies, such as intelligent transportation systems (ITS),

and control strategies, such as ramp metering, dynamic message signs,

and incident management. In many large metropolitan areas, these developments have been accompanied by establishment of regional transportation

management centers (TMCs), which are seen as the cockpit or nerve center

for monitoring traffic incidents and providing rapid police response, crash

clearance, and travel advisories. Many TMCs are manned by staff from multiple agencies and jurisdictions working as a team.

Some TMCs are focused primarily on traffic and incident management.

Others, such as Houston TranStar, have a broader scope. Opened in 1996,

Houston TranStar is a consortium partnership of transportation and emergency management agencies in the greater Houston area housing engineers,

law enforcement personnel, information technology specialists, and emergency managers. In addition to traffic monitoring and incident control,

emergency management personnel from the Harris County Office of Emergency Management monitor potential emergencies due to severe weather

using state-of-the-art technology, such as flood warning monitors, Doppler

radar, satellite imagery, and weather data from the National Weather Service,

to provide the public with real-time information.

The city of Chicago recently opened a new City Incident Center (CIC),

which integrates the city’s homeland security efforts with traffic services,

among other activities. CIC follows on the creation of a Traffic Management

Authority in 2005, dedicated to improving traffic flow through ITS technology and centralized control systems. The new facility will have positions

dedicated to traffic management but will also provide a central location for

communication among dispatch operators from all the relevant city departments so they can respond rapidly and effectively in the event of an

emergency (Inside ITS 2006).
transportation modes. This effort should build on existing technology

transfer mechanisms, such as the Technology Implementation Group of

the American Association of State Highway and Transportation Officials

(AASHTO).5

Design Strategies

Operational responses are geared to addressing near-term impacts of

climate change. To make decisions today about rehabilitating or retrofitting transportation facilities, especially those with long design lives

(see Table 4-2 in the previous chapter), transportation planners and

engineers must consider how climate changes will affect these facilities

50 years or more from now. Adapting to climate change will also require

reevaluation, development, and regular updating of design standards

that guide infrastructure design.

The purpose of design standards is to provide engineers with guidance

on how to construct infrastructure for safe and reliable performance.6

These standards represent the uniform application of the best engineering

knowledge, developed through years of experimental study and actual

experience. Often they become embedded in regulatory requirements and

funding programs.7 Design standards embody trade-offs between performance (e.g., safety, reliability) and cost. Faced with a myriad of factors

that can affect performance, engineers typically select the most demanding parameter—the 100-year storm, the heaviest truck, the most powerful

wind speed—as the basis for design, thereby building in a safety margin to

minimize the chances of failure.

Environmental factors are integral to the design of transportation

infrastructure. Conditions such as temperature, freeze–thaw cycles, and

duration and intensity of precipitation determine subsurface and founda5 The primary objective of AASHTO’s Technology Implementation Group, which grew out of an

AASHTO task force’s successful effort to implement products of the Strategic Highway Research

Program, is to provide leadership to state DOTs, local governments, and industry in the selection

and promotion of ready-to-implement technologies.

6 This section draws heavily on the paper by Meyer (2006) commissioned for this study.

7 To be eligible for federal funding, for example, state and local governments must comply with

federal standards with respect to lane and shoulder widths on highways and bridge clearances over

navigable waterways. If the infrastructure is damaged or destroyed, federal agencies and insurers

typically allow renovation or rebuilding only to replacement standards; upgrading is not a 

reimbursable cost.

Meeting the Challenges 153
tion designs, choices of materials, and drainage capacity. The issue is

whether current design standards are adequate to accommodate the climate changes projected by scientists. Table 5-1 provides an assessment by

Meyer (2006) of the principal climate-induced changes and their implications for infrastructure design in both the short and long terms. Looking

across all climate changes, the author notes that the most dominant impact

is on those design elements most associated with forces resulting from

water flows. This finding is not surprising in view of the extensive damage

to transportation infrastructure and buildings caused by flooding and

storm surge in Hurricanes Katrina and Rita. Climate changes, however,

will not affect the design of all infrastructure modes equally, a second

important observation. For example, wave action is more critical than

temperature changes for coastal bridge design. Finally, climate extremes,

such as stronger wind speeds, increased storm surges, and greater wave

heights, will place the greatest demands on infrastructure because they are

likely to push the limits of the performance range for which facilities were

designed.

How should engineering design decisions be modified to address climate change, particularly for longer-lived infrastructure for which the

uncertainties are greater regarding the magnitude and timing of climate

changes? One option is to build to a more robust standard, assuming a

greater frequency and magnitude of extreme events, without a full understanding of future risks and presumably at greater cost. This strategy could

be appropriate for major facilities in vulnerable locations (e.g., critical

bridges and evacuation routes), but its high costs necessitate a highly

selective approach. Another option is to upgrade parallel routes, but

this alternative depends on the availability of right-of-way and the cost

of upgrading. A third option is to build infrastructure with shorter design

lives, presumably at lower cost, to be retrofitted as more knowledge about

future climate conditions is gained. This alternative probably is not viable

in the United States because of the disruption and negative public reaction

resulting from more frequent retrofits of major facilities. Most states are

adopting a “fast in, fast out, and stay out” approach to major reconstruction projects. A final option is to hedge by building to current standards

or making marginal improvements, recognizing that the infrastructure

remains at risk and may require major improvements in the future. This

alternative poses many of the same problems as the previous one. All four

options involve important cost–risk reduction trade-offs that engineers

154 Potential Impacts of Climate Change on U.S. Transportation
TABLE 5-1 Climate-Induced Changes That Could Influence Transportation

Infrastructure Design

Climate-Change Changes in 

Phenomenon Environmental Condition Design Implications

Temperature 

change

Changing 

precipitation 

levels

Wind loads

Sea level rise

Greater storm 

surges and 

wave heights

a For purposes of this table, short term is defined as the next 30 to 40 years; long term is from 40 to 100 years.

Source: Meyer 2006, Table 1.

Rising maximum 

temperature; lower

minimum temperature; wider

temperature range;

possible significant

impact on permafrost

Worst-case scenario,

more precipitation;

higher water tables;

greater levels of

flooding; higher 

moisture content 

in soils

Stronger wind speeds

and thus loads on

bridge structures;

more turbulence

Rising water levels in

coastal areas and

rivers; increases in

severe coastal 

flooding

Larger and more frequent storm surges;

more powerful wave

action

Over the short term,a minimal impact on 

pavement or structural design; potential 

significant impact on road, bridge scour, and

culvert design in cold regions

Over the long term, possible significant impact on

pavement and structural design; need for new

materials and better maintenance strategies

Over the short term, could affect pavement and

drainage design; need for greater attention to

foundation conditions, more probabilistic

approaches to design floods, more targeted

maintenance

Over the long term, definite impact on foundation

design and design of drainage systems and

culverts; impact on design of pavement

subgrade and materials

Over the short term, design factors for design

wind speed might change; wind tunnel 

testing will have to consider more turbulent

wind conditions

Over the long term, need for materials of greater

strength; impact on design considerations for

suspended and cable-stayed bridges

Over the long term, greater inundation of coastal

areas; need for more stringent design standards for flooding and building in saturated

soils; greater protection of infrastructure

needed when higher sea levels combine with

storm surges

Over the short term, need for design changes to

bridge height in vulnerable areas; need for

more probabilistic approach to predicting

storm surges

Over the long term, need for changes to bridge

design, both superstructure and foundations; changes in materials specifications;

and more protective strategies for critical

components
156 Potential Impacts of Climate Change on U.S. Transportation

and planners can best address through a more strategic, risk-based

approach to design and investment decisions, such as that described in the

previous chapter. The approach taken by Transit New Zealand to determine the necessity and feasibility of taking action now to protect the state

highway network from the potential future impacts of climate change

could also be instructive (see Box 5-2).

More fundamentally, the scientific community and professional associations must reevaluate design standards for transportation infrastructure

that take climate change into account and begin the lengthy process of

developing new standards where appropriate. Reexamination of design

standards can be prompted by a single event, such as the damage to coastal

highway bridges from Hurricane Katrina, when it became evident that the

current state of practice—designing bridges for a riverine environment

and a 50-year storm—was inadequate. The Federal Highway Administration (FHWA) not only approved and shared in the cost of rebuilding

the damaged bridges to a higher design standard but also recommended

the development of more appropriate bridge design standards in general

for a coastal environment that would take into account the combined

effects of storm surge and wave action and assume a more severe storm

event (e.g., a 100-year or even 500-year storm) (FHWA 2005a).8

Typically, however, the development of design standards follows a

time-consuming and systematic process that involves professional organizations in an extensive research and testing program over a period of

decades. Once the standards are in place, engineers are understandably

reluctant to change them. A combination of the length of time required to

modify or develop new standards, the institutional procedures for approval

of standards (vetting any changes through professional committees of

practicing engineers), and the use of well-established standards as evidence of “good practice” in litigation leads to a conservative approach to

change. Developing standards to address climate change in a timely

manner thus will require leadership by the scientific community and

professional associations and, given the scope of potential impacts, a

broad-based, federally sponsored research program that must begin soon.

A good model is the congressionally mandated National Earthquake

8 AASHTO and state DOTs are leading this initiative, and research on wave forces and wave load

design practices is now being undertaken by universities and the U.S. Department of

Transportation’s Turner–Fairbank Highway Research Center, among others.
BOX 5-2

Climate Change and Asset Management: 

New Zealand Transit’s Approach to Addressing 

Impacts of Climate Change

Under the 2004 Resource Management (Energy and Climate Change)

Amendment Act—New Zealand’s principal legislation for environmental 

management—Transit New Zealand was required to take into account the

effects of climate change as it plans, constructs, and maintains the state

highway network (Kinsella and McGuire 2005). The key climate changes

of concern to state highways are sea level rise, coastal storm surges, and

increased frequency and intensity of heavy rainfall events. The primary assets

at risk are bridges, culverts, causeways and coastal roads, pavement surfaces, surface drainage, and hillside slopes.

Transit New Zealand proceeded with a two-stage assessment to identify

those areas requiring action. Stage 1 involved assessing the need to act

now to manage future potential impacts of climate change. Three criteria

were used:

• Level of certainty that the climate change impact will occur at the

magnitude predicted in the specified time frame,

• Intended design life of the state highway asset, and

• Capacity of the agency’s current asset management practice to manage the impact.

The results of the Stage 1 assessment revealed that current asset management practice is generally adequate to deal with impacts of climate change

for most of the network, but that bridges and culverts with an intended

design life of more than 25 years may require case-by-case consideration

to ensure protection (Kinsella and McGuire 2005).

Stage 2 involved assessing the economic feasibility of acting now to manage future potential impacts of climate change and was focused on bridges

and culverts with design lives of greater than 25 years. Making several simplifying assumptions, the analysis examined three options: (a) doing nothing,

(b) retrofitting all existing bridges and culverts now to avoid future climate

change impacts, and (c) designing all new bridges and culverts to accommodate future climate changes to 2080. The analysis revealed that it would not

be economical to retrofit the existing stock of bridges and culverts, but it

(continued)

Meeting the Challenges 157
158 Potential Impacts of Climate Change on U.S. Transportation

Hazard Reduction Program, begun in 1977, which has provided much of

the underlying research for seismic standards (see Box 5-3).

New Infrastructure Investment, Transportation Planning, 

and Controls on Land Use

One of the most effective strategies for reducing the risks of climate change

is to avoid placing people and infrastructure in vulnerable locations, such

as coastal areas. Chapter 3 described the continuing development pressures

on coastal counties despite the increased risk of flooding and damage from

storm surge and wave action accompanying projected rising sea levels.

Many areas along the Atlantic, Gulf, and Pacific coasts will be affected. Once

in place, settlement patterns and supporting infrastructure are difficult to

change. In New York City, for example, a major concern of emergency

planners is handling the evacuation of some 2.3 million New Yorkers from

flood-prone areas in the event of a Category 3 or greater hurricane (New

York City Transit 2007). Continued development of such vulnerable areas

BOX 5-2 (continued)

Climate Change and Asset Management: New Zealand Transit’s

Approach to Addressing Impacts of Climate Change

would be preferable to repair the assets when a specific loss or need became

evident. The primary reasons for this conclusion were uncertainties about

where and when the impacts of climate change will manifest themselves and

the historical number of bridges and culverts lost prematurely because of

other events. Retrofitting all new bridges and culverts to take climate change

into account was also determined not to be economical. Nevertheless, the

agency decided that, where possible, provision should be made for subsequent retrofitting (either lifting or lengthening the bridge) in the event impacts

are experienced. For major bridges (and culverts) where retrofitting is not

practical, the structure should be designed for projected future impacts of climate change on the basis of the best available information (Kinsella and

McGuire 2005).

Transit New Zealand has amended its Bridge Manual to include consideration of relevant impacts of climate change as a design factor. In addition,

the agency will continue to monitor climate change data and developments

and review its policy when appropriate.
BOX 5-3

Development of Seismic Standards in the United States

In 1977 Congress passed the Earthquake Hazards Reduction Act, which

established the National Earthquake Hazard Reduction Program (NEHRP)—

a long-term earthquake risk reduction program. Member agencies include

the United States Geological Survey, the National Science Foundation, the

Federal Emergency Management Agency, and the National Institute of

Standards and Technology—agencies engaged primarily in research and

development. The mission of NEHRP is broad and includes understanding

the science of earthquakes and their effects, improving earthquake hazard

identification and risk assessment methods, and developing effective practices (e.g., model building codes) and policies to reduce earthquake losses

(NEHRP 2007).

One of the primary accomplishments of NEHRP has been the development of design standards for the seismic safety of buildings, both new

and existing, which serve as a basis for national model building codes.

Seismic standards and guidelines have also been developed for lifelines—

telecommunications, transportation, water, sewage, electric power, gas, and

liquid fuel lines. Adoption of the standards is voluntary, but some states,

such as California, have incorporated the model national codes into state

regulations, and the federal government has adopted the standards for its

own buildings and as a prerequisite for obtaining federal funds. FHWA, for

example, requires that federally assisted bridge and highway projects meet

minimum seismic standards.

The development of seismic specifications for bridges began in the 1970s

with the San Fernando earthquake and was spurred by the occurrence of subsequent major earthquakes. For example, the 1989 Loma Prieta earthquake

led the American Association of State Highway and Transportation Officials

to adopt a standard seismic specification for bridges in 1990. In response to

the limitations of a “one-size-fits-all” approach, a modified performancebased standard was proposed in 1997, but it was rejected as being too

complex and having too high a return frequency (2,500 years) relative to

other hazards (Buckle 2006). (A performance-based national consensus

standard has been developed for buildings.) Nevertheless, revisions are

under way, and the performance-based approach, which takes into account

different performance requirements and levels of risk, could be a model for

the development of standards to address the impacts of climate change. A

program such as NEHRP would be essential to fund the necessary supporting research and testing.

Meeting the Challenges 159
160 Potential Impacts of Climate Change on U.S. Transportation

will only place more communities and businesses at risk and increase the

difficulty of evacuation in the event of a major storm.

Why do transportation planners fail to consider development patterns

in making investment decisions? The short answer is that they do, but not

from the perspective of land use control. Public-sector transportation

planners typically forecast expected land use patterns over a 25- to 30-year

period as the basis for modeling future travel demand and infrastructure

investment needs (Meyer and Miller 2001). However, they rarely consider

whether such investments are desirable, or what development may result

from building or expanding transportation networks (Amekudzi and

Meyer 2005).9 Although the long-term capital improvement and budgeting

process is different in the private sector (see Chapter 4), it suffers from the

same limitations. One of the main reasons for the disconnect between

transportation investment decisions and land use and development decisions can be traced to governance arrangements. Decisions concerning

large-scale transportation infrastructure investments are the responsibility

of states, regional authorities, and the private sector. Local governments and

a few states (e.g., Florida, California) control land use decisions through

comprehensive plans, zoning ordinances, permitting, and building codes.

Locally controlled land use planning, the typical situation in the United

States, has too limited a perspective to account for the broadly shared risks

of climate change. Local governments are interested primarily in the jobs

and economic development that growth may bring to their communities,

although in many localities, the costs of uncontrolled growth in terms of

crowded roads and schools are being recognized. In some locations, greater

integration of transportation and land use planning is resulting from smart

growth policies, which recognize the impact of transportation investments

on regional development and economic growth and vice versa; such integration is not common, however.

Transportation planners cannot resolve these issues single-handedly.

The developers of any strategy that involves imposing land use controls to

address climate change would need to build consensus among key decision makers in both transportation and land use, probably at the regional

level—a challenging proposition. Nevertheless, if transportation planners

9 Meyer (2006) notes two locations—Lake Tahoe, Nevada, and Cape Cod, Massachusetts—where

transportation planners have identified environmentally sensitive areas that are off limits to new

infrastructure and development, but these are the exceptions rather than the rule.
Meeting the Challenges 161

were required to work more closely with land use planners and consider

potential impacts of climate change in the development of long-term investment plans, the issues would become more visible.

At present, the Safe, Accountable, Flexible, Efficient Transportation

Equity Act: A Legacy for Users (SAFETEA-LU) encourages greater collaboration and partnership among transportation planners and state and local

agencies responsible for land use management, among others, in plan

development.10 In the reauthorization of this legislation, such collaboration should be required, as should consideration of climate change impacts

and their effects on infrastructure plans and investments, particularly in

vulnerable locations.

At the local level, some metropolitan planning organizations (MPOs)

have already begun to adopt more flexible, scenario-based approaches in

developing their long-range transportation investment plans (see Box 5-4).

The impetus has come in part from the desire to provide local communities

with a framework within which to better understand the impacts of growth

and the difficult trade-offs among social, economic, and environmental

goals in planning future transportation investments. Use of geographic

information systems and modeling has enabled planners to illustrate and

quantify the impacts of a range of regional growth scenarios on land use and

area traffic, among other factors. At the end of the planning process, one scenario typically is selected as the preferred option. Development and

monitoring of performance measures enable local planners to examine the

effects of their choices and revisit the plans periodically to take into account

new developments and changes in local priorities.

Scenario planning could be adapted to take potential climate changes

into account in the development of future regional transportation plans.

For example, projections of current development patterns and supporting

transportation infrastructure, when overlaid on maps showing current elevations and expected sea level rise, could illustrate the increased risks of

allowing uncontrolled development in vulnerable coastal areas and the

desirability of managed growth policies and protection of critical infrastructure. Climate scientists, perhaps at local universities, could assist in the

10 More specifically, Section 6001 and the Final Rule on Statewide and Metropolitan Transportation

Planning (Federal Register 2007) require that long-range transportation plans be developed in

consultation with agencies responsible for land use management, natural resources, environmental

protection, conservation, and historic preservation, and that state conservation plans or maps and

inventories of natural or historic resources be consulted.
162 Potential Impacts of Climate Change on U.S. Transportation

BOX 5-4

Scenario Analysis in Transportation Planning

Scenario analysis as practiced by transportation planners is a process through

which public agencies, private entities, and citizens work together to envision the long-term future of their communities (FHWA 2005b). Scenario

planning starts with a business-as-usual baseline scenario, incorporating current plans or trends for a region. Then, a range of alternative future scenarios

is identified on the basis of community input, through the use of tools and

transportation models incorporating geographic information to identify impacts both quantitatively and visually. Typically, one scenario is chosen as the

preferred alternative and is adopted as the region’s vision for the future.

According to a recent survey, MPOs are the lead sponsors of scenario planning, followed by nonprofit organizations (e.g., environmental groups) and

local governments (Bartholomew 2005). Numerous localities—Salt Lake

City, Houston, Sacramento, Portland, Los Angeles, and Chicago, among

others—have adopted this approach.

The recently released 2035 Regional Transportation Plan for Greater

Houston is a good example of the use of scenarios to examine the impacts

of different land development choices on travel congestion, transit use, and

population growth in floodplains and hurricane evacuation zones (Houston–

Galveston Area Council 2007). Facing a projected 75 percent increase in

population and a 60 percent increase in employment over the next 30 years,

the council of governments for the greater Houston area—the Houston–

Galveston Area Council—spearheaded the Envision Houston Region initiative

in 2005 to engage elected officials, residents, and other stakeholders in

planning and creating a long-term growth strategy to 2035. Four scenarios

were considered, ranging from the status quo to a scenario assuming highdensity mixed-use development along transit corridors and town centers; the

latter is the selected Envision scenario, which planners believe offers a reasonable path forward and has considerable community support.

The regional plan also is notable for taking the first steps toward integrating climate change into the transportation planning process. The planners

noted the vulnerability of the region to tropical storms and flooding, likely

to be intensified by climate change and land subsidence, and the scenarios

considered compared population growth in sensitive floodplains and hurricane evacuation areas. The chosen Envision scenario showed a reduction in

population in both areas, alleviating demand on evacuation routes as compared with the baseline, status quo scenario.
Meeting the Challenges 163

planning process by identifying plausible impact scenarios. University of

Washington climate scientists, for example, developed projections of sea

level rise for Seattle that became a consideration in designing a major rehabilitation of the Alaskan Way Seawall.11

In those major metropolitan areas highly vulnerable to the impacts of

climate change, where projected sea level rise combined with storm surge

could threaten already densely developed areas—parts of New York City,

Miami, and San Francisco, for example—options such as levees and storm

barrier systems are likely to be considered to protect valuable real estate.

These options are costly, they can create environmental problems, and

they may provide a false sense of security.12 Moreover, as was the experience in New Orleans, levees can encourage development in “protected”

flood risk areas (ASFPM 2007). In small communities, exposure to impacts

of climate change may necessitate abandoning homes, businesses, and

infrastructure and relocating inland. For example, reduced sea ice along

Alaska’s Arctic coast is already eroding shoreline and exposing coastal areas

to the action of winter storm surges and waves, a pattern that will be exacerbated by further sea level rise. Some 200 Native American villages are at

risk and may soon be abandoned for inland locations (ACIA 2004).

CROSSCUTTING ISSUES

Flood Insurance

Private insurers may be able to accomplish what government cannot in

terms of land use control. Some major insurers, for example, are refusing

to write new or renew existing homeowners’ policies in areas already vulnerable to hurricanes and other severe storms, which are likely to intensify

in a warming climate (Adams 2006). Florida, Texas, Louisiana, Mississippi,

Hawaii, New York City, and Long Island are among the affected areas thus

11 Sea level projections from the climate impacts research group at the University of Washington

suggested that the city’s current design standards for the new seawall did not adequately account

for the potential projected rise in sea level. Given the magnitude of the long-term financial and

transportation impacts of the Alaskan Way Seawall project, the City Auditor’s Office recommended

that the city obtain a comprehensive, independent analysis that would consider all available

scientific sources in estimating the probabilities of expected increases in sea level and their

rate (Soo Hoo and Sumitani 2005).

12 Levees interfere with the natural attenuation of flows from floodwaters, cause backwaters, generally

increase the depth and velocity of floodwaters, and encourage channel degradation and eventual

bank erosion (ASFPM 2007).
164 Potential Impacts of Climate Change on U.S. Transportation

far. Some states, such as Florida, have stepped up to become insurers of last

resort for coastal homes and businesses, but the high costs of providing

coverage are unlikely to be sustainable or would result in prohibitive premium increases in many cases if the costs were passed on to homeowners.

Moreover, the provision of insurance in hazard-prone areas that is not

actuarially sound is bad public policy.

The federal government is already the insurer of last resort for homeowners and businesses that cannot secure affordable private flood

insurance in flood hazard areas. In 1968 Congress authorized the National

Flood Insurance Program (NFIP) to mitigate increasing taxpayer-funded

flood relief. The Federal Emergency Management Agency (FEMA) administers the program and maps the nation’s floodplains; these maps serve as

the basis for determining the eligibility of homeowners and businesses for

NFIP funding. To become eligible, a community must adopt and enforce

floodplain management ordinances and building code requirements to

reduce future flood damage.13 In exchange, NFIP makes federally backed,

affordable flood insurance available to homeowners, renters, and businesses in mapped Special Flood Hazard Areas (SFHAs) through licensed

agents and insurance companies. Flood insurance is required to secure

financing for buying, building, or improving a structure in SFHAs. New

buildings must be elevated to or above the predicted 100-year flood level,

and foundations must be designed to resist flood loads (Elliott 2005).

Buildings that are repaired or improved after floods must be brought into

compliance with these ordinances if the repair costs 50 percent or more of

the market value of the structure.

Over the years, NFIP has been criticized for encouraging more development in these flood-prone areas than would have occurred without the

program (Elliott 2005; Burby 2006). Others suggest that the program has

had little impact because many properties (e.g., beach houses) are purchased without a mortgage and thus need not comply with floodplain

ordinances. Communities have also been slow to enact and enforce floodplain management measures. Finally, flood insurance is not required of

properties located behind levees that have been certified for 100-year

storms, even though such properties are at enhanced risk for any flood

that exceeds the 100-year storm. Because climate change is projected to

13 Details of the program were accessed from the FEMA website at www.fema.gov/about/programs/

nfip.shtm on May 9, 2007.
Meeting the Challenges 165

trigger more intense storms and sea level rise will extend the areas of

flood damage in some SFHAs, FEMA and congressional oversight committees should reevaluate the risk reduction effectiveness of the program.

FEMA is engaged in a multiyear map modernization program to provide reliable digital flood hazard data and maps in support of NFIP.

However, the maps are based on historical data and thus do not take

account of climate change. The SFHA boundaries are keyed to the 100-year

storm, the base elevation data are inadequate (NRC 2007), and the pace of

updating is slow. In fact, some states have taken over the task of updating

to speed up the process. Further additions to flood zone maps may be

needed and are particularly important to transportation engineers because

these maps have become a quasi–design standard for determining appropriate drainage capacity, for example, for transportation infrastructure in

coastal areas.

Monitoring Technologies and New Materials

Better monitoring technologies and new materials could offer engineers

alternatives to costly infrastructure retrofit or replacement in advance of

climate change. For example, better systems for monitoring impacts of

climate change on infrastructure could provide engineers with an early

warning of problems, buying time for making the necessary modifications.

This approach would also provide a good solution for less critical infrastructure facilities for which the costs of retrofitting in anticipation of

climate change are not economical. In Alaska, where climate warming is

occurring more rapidly than in the lower 48 states, engineers are closely

monitoring bridge foundations for scour. Hotter, dryer summers have led

to increased glacial melting and longer periods of high stream flows, leading to both increased sediment transport on rivers and scour at bridge

crossings. A network of sonars has been installed on several scour-critical

bridges around the state. The monitoring data are sent regularly to the

Alaska Department of Transportation and Public Facilities (J. Conaway,

United States Geological Survey, personal communication, March 8, 2006),

an approach that could be adapted for use in other states.14

Sensors and other “smart” technologies yet to be developed could also

be used more widely to monitor changing climate conditions and issue

14 The FHWA scour program requires bridge owners to evaluate bridges for potential scour associated

with the 100-year storm and a 500-year superflood event (FHWA 2005a).
166 Potential Impacts of Climate Change on U.S. Transportation

warnings when thresholds are exceeded. Sensors are already available that

monitor changing pressures on a building or bridge and issue a warning

when the pressures become abnormal (Meyer 2006). Sensors could also be

embedded in pavements and bridge decks, for example, to monitor stress

and strain as temperatures change, enabling remedial action to be taken

before failure occurs. The collapse of the Minneapolis Interstate 35W bridge

in August 2007 brought renewed attention to the need for better technologies to monitor bridge conditions. Numerous technologies are available:

X-ray machines can spot hidden cracks in girders, computerized monitors

can track minute changes in stresses on steel beams, and sensors embedded

in concrete can track corrosion of steel reinforcing beams. The costs are not

small—one estimate to install monitoring equipment on a large bridge was

$250,000—but relative to retrofitting or replacing a failed structure, the

costs are marginal (Inside ITS 2007). Advances in material sciences (applications of nanotechnologies),15 computer processing, and communications

capabilities, as well as in sensor technologies, could provide a fertile field for

the development of devices for monitoring climate changes and communicating the results to the appropriate infrastructure owners.

New materials also hold promise for addressing some climate changes.

For example, temperature extremes, particularly increases in very hot days

and heat waves, are likely to affect both pavements and rails. Changnon 

et al. (1996) report that highways and railroads were damaged by heatinduced heaving and buckling of joints during the 1995 heat wave in

Chicago. Extreme heat can also cause misalignment of rail lines and derailments, although the use of continuous welded rail should prevent kinks

from occurring (Changnon 2006). Continued research and development

of materials that can withstand high temperatures would be productive, as

would effective mechanisms for sharing new knowledge.

Data, Models, and Decision Support Tools

Data systems for monitoring the impacts of climate change can be an

effective tool for determining appropriate adaptation strategies. One such

system is the Alaska Engineering Design Information System (AEDIS),

described in Chapter 3. AEDIS provides geographic-specific data on tem15 Nanotechnology is a field of applied science focused on control of matter on a scale smaller than 

1 micrometer, normally 1 to 100 nanometers, as well as the fabrication of devices on this same scale.
Meeting the Challenges 167

peratures, precipitation levels, permafrost, and snow depth collected

from weather stations located around the state. The data are intended to

help in deriving engineering design parameters (e.g., load-bearing capacity), scheduling maintenance and repairs, and selecting optimum

locations for transportation infrastructure (T. Douglas, Cold Regions

Research and Engineering Laboratory, personal communication, March

9, 2006). As trend data accumulate, AEDIS could provide a useful repository of information on the longer-term impacts of climate change on

infrastructure that could be linked with a database of response strategies

and costs—from changes in maintenance practices, to use of new materials, to design changes.

Improving information on weather for transportation infrastructure

applications is another important area for development, particularly in

view of the potential for more climate extremes. The national needs

assessment report of the Weather Information for Surface Transportation

initiative (OFCM 2002)—a joint effort of the National Oceanic and

Atmospheric Administration (NOAA) and FHWA—identifies as a particular need more accurate information at higher spatial (e.g., surface

temperatures) and temporal resolutions (OFCM 2002). The information

must also be provided with sufficient lead time (for forecasts) and currency (for observations) to guide operational decisions. Providing the

data will require improved weather detection and forecasting; better

understanding of thresholds for precipitation, temperature, winds, and

the like, which affect transportation operations and, if exceeded, could

cause significant interruptions in operations or infrastructure failure;

and improvements in data integration and real-time communication to

both transportation operators and system users (Lockwood 2006). Clarus,

a major initiative of FHWA’s Surface Transportation Weather Program,16

is already working to develop and demonstrate an integrated nationwide

surface weather observing, forecasting, and data management system. A

range of observational technologies, from remote to fixed sensors to vehicle probes, are being tested as sources of real-time data, as is a suite of

tools to make use of the data. Such efforts could have application for

other transportation modes.

16 The Surface Transportation Weather Program was authorized in SAFETEA-LU for $5 million

annually for 4 years. The primary focus is on alleviating the impacts of adverse weather on the

safety and reliability of the nation’s highways.
168 Potential Impacts of Climate Change on U.S. Transportation

The 2004 and 2005 hurricane seasons provided a vivid illustration of

the need for improvements in modeling of the effects of storm surge

and wave action, which will be aggravated by sea level rise. NOAA’s Sea,

Lake, and Overland Surge from Hurricanes model and, more recently,

the Advanced Circulation Model (ADCIRC) (described in Chapter 2)

have been used to estimate the threat from storm surge.17 These models

use historical input data that are infrequently updated. For example,

when ADCIRC was run with input data through the 2005 hurricane season, it was found that the magnitude of the 100-year storm-surge flood

would now reoccur at an interval of 75 years. After Hurricane Katrina, considerable research was also conducted on wave action on bridges (J. Krolak,

briefing, Wave Force Symposium, Turner–Fairbank Highway Research

Center, July 27, 2006); the results of this research should help in revising

coastal bridge design standards.

If extreme weather events require evacuation of affected areas, better

modeling to support evacuation efforts will be needed. Some MPOs are

using travel demand models to estimate the time required to evacuate

regional areas for different types of emergencies, but this is not common

practice. For example, according to modeling estimates provided after

Hurricane Rita by the Houston–Galveston Area Council, the council of governments for the Houston metropolitan area, it would take 80 to 120 hours

to evacuate 3 million residents from Galveston, Houston, and other coastal

areas, assuming use of contraflow and optimum flow conditions. The necessary lead time far exceeds the ability of meteorologists to predict the

landfall and trajectory of hurricanes (Houston–Galveston Area Council

2007), and this has led local governments to consider hardening public

facilities on higher ground and encouraging residents in nonvulnerable

coastal areas to shelter in place. Simulation models are also being used to

help identify optimal evacuation routes, compute estimated evacuation

times, and determine traffic management needs for an emergency planning

area (Goldblatt and Weinisch 2005). However, these models must be

upgraded to provide more real-time information to assist emergency man17 ADCIRC is being applied in southern Louisiana by the U.S. Army Corps of Engineers New Orleans

District to design levee heights and alignments, by FEMA to establish flooding probabilities for

insurance purposes, by the State of Louisiana at the Center for the Study of Public Health Impacts

of Hurricanes to operationally predict hurricane inundation, and by the Louisiana State Department

of Natural Resources to assess coastal restoration projects (information from the ADCIRC website,

accessed at www.adcirc.org on October 10, 2007).
Meeting the Challenges 169

agers and transportation providers in responding to an incident (e.g., by

changing routing instructions and notifying emergency response teams).

New Partnerships and Organizational Arrangements

Adapting successfully to climate change will require forging new partnerships and organizational arrangements that better align with the impacts

of climate change, which do not follow modal, jurisdictional, or corporate

boundaries. As discussed earlier, decision making in the transportation

sector is structured around these boundaries. Transportation planning is

conducted primarily at the regional level, often in a bottom-up process

that starts with local jurisdictions. Railroads, trucking, and waterborne

commerce are largely private enterprises with varying levels of federal

participation.

Partnerships could involve closer collaboration between transportation

agencies and emergency responders. Tabletop exercises, for example, in

which emergency managers and critical transportation agencies, among

others, role play their responses to hypothetical emergency situations (e.g.,

a terrorist attack, a major hurricane), provide an opportunity for such coordination and contact. Other relevant partnerships could involve local

collaboration between university climate scientists and regional transportation planners; greater interaction between transportation planners and

those who control land use (both described previously); and creation of a

more formal process for better communication among transportation professionals, climate scientists, and other relevant scientific disciplines, along

with a repository for transportation-relevant climate change information.

The creation of regional and multistate organizational arrangements to

address climate change is a formidable challenge but could yield enormous

payoffs in the ability to respond not only to climate change but also to

other natural and man-made disasters (e.g., earthquakes, terrorist incidents). The transportation sector has some models for cross-jurisdictional

arrangements, such as regional authorities for specific facilities (e.g., the

Alameda Corridor in California).18 Regional and multistate emergency

18 Created as a Joint Powers Authority by affected cities, the Ports of Los Angeles and Long Beach,

and the Los Angeles County Metropolitan Transportation Authority, the Alameda Corridor

Transportation Authority guided the development of a 20-mile-long rail cargo expressway. The

expressway separates freight rail from street traffic and passenger trains while linking the ports to

the transcontinental rail network near downtown Los Angeles.
170 Potential Impacts of Climate Change on U.S. Transportation

response operations that include transportation are beginning to emerge in

the wake of hurricanes and other disasters, such as the events of September

11, 2001. These might serve as the nucleus for multistate regional compacts

to address other issues, such as the impacts of climate change (Deen 2006).

State-mandated regional compacts for addressing regional air quality

issues offer another model.19 One could imagine the emergence of similar

arrangements to address such problems as the impact of sea level rise on

coastal real estate and infrastructure in the tristate New York area or other

coastal areas, the effects of drought on shipping along inland waterways, or

the impact of hurricanes in the Gulf Coast region.

The development of organizational arrangements “right-sized” to

address the problems for transportation infrastructure created by climate change may require state or federal action. The California Coastal

Commission is a good example of a state initiative designed to resolve a

regional problem. In the early 1970s, many Californians became alarmed

that private development was cutting off public access to the shore and by

voter initiative petitioned the state to exert its stewardship role to protect

coastal assets for future generations. In 1976 the state legislature enacted

the California Coastal Act and established a permanent California Coastal

Commission, which plans and regulates development and use of natural

resources along the coast in partnership with local governments and in

keeping with the requirements of the Coastal Act (California Coastal

Commission 2007). One could imagine a similar arrangement to mediate

land use and development issues in vulnerable coastal areas in light of

projected climate changes.

FINDINGS

Adaptation is unavoidable to address the impacts of climate change due to

GHG emissions released into the atmosphere decades ago or longer. The

prudent strategy is for transportation professionals to begin now to take a

19 In the eastern half of the United States, for example, where regional ozone is an important

concern, organizations such as the Ozone Transport Commission and the ad hoc Ozone Transport

Assessment Group were established, the former in 1991 under the auspices of the federal Clean

Air Act Amendments. In the west, where degrading visibility in scenic areas is a growing problem,

the Grand Canyon Visibility Transport Commission and its successor, the Western Regional Air

Partnership, were established as voluntary organizations representing western states, tribes, and

the federal government. The main purpose of these groups is to recommend and implement multistate mitigation strategies for air pollution that extend beyond any one state border (NRC 2004a).
more proactive approach in addressing both past and potential future

impacts of climate change. A wide array of adaptation options is available.

The most immediate response is likely to come through changes in

transportation operating and maintenance practices. These changes will

involve incorporating responses to more extreme weather events into

routine operations, improving collaboration with emergency managers,

recognizing weather and emergency management as integral functions of

transportation agency operations, and widely sharing best practices. To

make decisions about rehabilitating or retrofitting transportation infrastructure with long service lives, transportation planners and engineers will

need to consider how climate change will affect these facilities 50 years or

more into the future. Design changes may also be required to harden longlived infrastructure in locations particularly vulnerable to climate changes.

The development of new standards to address climate change will be a

time-consuming process, requiring research and testing and the consensus

of practicing engineers. In view of the myriad of potential climate change

impacts to be considered, the scientific community and relevant professional organizations should take the lead in initiating a program soon, with

federal support for the necessary research and testing. Relocation of some

transportation systems, such as coastal roads and rail lines, may ultimately

prove necessary. Costly levees or storm barrier systems may be considered

to protect valuable real estate in selected densely populated exposed areas.

One of the most effective strategies for reducing the risks of climate

change is to avoid placing people and infrastructure in vulnerable locations. This is not always possible in highly developed areas, but more

stringent land use controls and flood insurance requirements could help

curb further development. Federal planning regulations should require

that transportation planners take climate change into account in developing long-range plans, as well as collaborate with agencies responsible for

land use, so that the consequences of infrastructure investment decisions

for land use and vice versa can be more clearly identified. FEMA should

reevaluate the risk reduction effectiveness of NFIP. At a minimum, updating of flood zone maps to account for sea level rise (incorporating land

subsidence) should be a priority in coastal areas.

Better monitoring technologies and new materials could also provide

alternatives to costly upgrading of some infrastructure. More widespread

use of sensors for monitoring impacts of climate change and new heatresistant paving materials are examples. More refined data (e.g., better

Meeting the Challenges 171
elevation data for floodplain mapping, more accurate data on surface

temperatures) and improved modeling—from weather forecasting to

modeling of expected storm surge and real-time evacuation scenarios—

are needed as well.

Adapting to climate change will also require new partnerships and

organizational arrangements that better align with climate impacts than

do current modal, jurisdictional, and corporate boundaries around which

decision making in the transportation sector is structured. Some models

for regional and multistate cooperation exist in regional emergency

response initiatives and in regional authorities and compacts for air quality,

but state or federal incentives may be necessary to ensure the development

of organizations “right-sized” to address the problems for transportation

infrastructure raised by climate change.

At the federal level, an interagency working group could be created,

focused solely on adaptation issues for the transportation sector, to help

shape existing agency research programs. The U.S. Department of

Transportation would be the natural lead for this activity.

Embracing these adaptation strategies would require overcoming

many of the barriers outlined in Chapter 4. First and foremost, transportation leaders would need to agree that climate change is a problem

that warrants action. Thinking longer term, adopting more risk-based

approaches to investment decisions, and forging new partnerships and

organizational arrangements are among the greatest challenges. The next

and final chapter provides the committee’s recommendations for moving

forward.

REFERENCES

Abbreviations

ACIA Arctic Climate Impact Assessment

ASFPM Association of State Floodplain Managers

DHS U.S. Department of Homeland Security

FHWA Federal Highway Administration

IPCC Intergovernmental Panel on Climate Change

NEHRP National Earthquake Hazards Reduction Program

NRC National Research Council

OFCM Office of the Federal Coordinator for Meteorological

Services and Supporting Research

172 Potential Impacts of Climate Change on U.S. Transportation
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Amekudzi, A., and M. Meyer. 2005. NCHRP Report 541: Consideration of

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Meeting the Challenges 173
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174 Potential Impacts of Climate Change on U.S. Transportation
ANNEX 5-1A Potential Climate Changes, Impacts on Land Transportation, and Adaptation Options

Impacts on Land Transportation (Highways, Rail, Pipeline) Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials OtherTemperature:

increases in veryhot days andheat waves

Limitations on periods

of constructionactivity due to healthand safety concerns;restrictions typicallybegin at 29.5°C(85°F); heat exhaustion possible at40.5°C (105°F)

Vehicle overheating and

tire deterioration

Impacts on pavement and

concrete constructionpractices

Thermal expansion on

bridge expansion jointsand paved surfaces

Impacts on landscaping in

highway and streetrights-of-way

Concerns regarding pavement integrity, e.g.,

softening, traffic-relatedrutting, migration of liquid asphalt; sustained airtemperature over 32°C(90°F) is a significantthreshold

Rail-track deformities; air

temperature above 43°C

(110°F) can lead toequipment failure

Shifting construction

schedules to coolerparts of the day

Development of new,

heat-resistantpaving materials

Greater use of heattolerant street and

highway landscaping

Greater use of continuous welded rail lines

(continued)
Temperature:

decreases in verycold days

Temperature:

increases inArctic temperatures

Regional changes in

snow and ice removalcosts and environmental impacts fromsalt and chemicaluse (reduction overall, but increases insome regions)

Fewer cold-related

restrictions for maintenance workers

Decreased utility of 

unimproved roads thatrely on frozen ground forpassage

Thawing of permafrost,

causing subsidence ofroads, rail beds, bridgesupports (cave-in), andpipelines

Shorter season for ice

roads

Reduction in snow and

ice removal

Extension of construction and maintenance seasonShortening of season

for use of ice roads

Shortening of season

for use of ice roads

Lengthening of potential construction

season

Increased use of sonars

to monitor streambed flow and bridgescour

Use of insulation in the

road prism

Use of different types

of passive refrigeration schemes,including thermosiphons, rockgalleries, and “coldculverts”

Relocation of sections of roads and

rail lines to morestable ground

ANNEX 5-1A (continued) Potential Climate Changes, Impacts on Land Transportation, and Adaptation Options

Impacts on Land Transportation (Highways, Rail, Pipeline) Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
Temperature: later

onset of seasonalfreeze and earlieronset of seasonalthaw

Sea level rise,

added to stormsurge

Changes in seasonal

weight restrictions

Changes in seasonal

fuel requirements

Improved mobility and

safety associatedwith a reduction inwinter weather

Longer construction

season

More frequent interruptions in travel on

coastal and lowlying roadways andrail service due tostorm surges

More severe storm

surges, requiringevacuation

Reduced pavement

deterioration resulting from lessexposure to freezing,snow, and ice, butpossibility of morefreeze–thaw conditions in somelocations

Inundation of roads

and rail lines incoastal areas

More frequent or severe

flooding of underground tunnels andlow-lying infrastructure

Erosion of road base

and bridge supports

Bridge scourReduced clearance

under bridges

Loss of coastal wetlands and barrier

shoreline

Land subsidence

Relaxation of seasonal

weight restrictions

Shortening of season

for use of ice roads

Elevation of streets,

bridges, and raillines

Addition of drainage

canals near coastalroads

Elevation and protection of bridge,

tunnel, and transitentrances

Additional pumping

capacity for tunnels

Relocation of sections

of roads and raillines inland

Protection of highvalue coastal real

estate with levees,seawalls, and dikes

Strengthening and

heightening ofexisting levees,seawalls, and dikes

Restriction of most 

vulnerable coastalareas from furtherdevelopment

Increase in flood

insurance rates tohelp restrict development

(continued)
Precipitation:

increase inintense precipitation events

Increases in weatherrelated delaysIncreases in traffic disruptionsIncreased flooding of

evacuation routes

Disruption of construction activitiesChanges in rain, snowfall, and seasonal

flooding that affectsafety and maintenance operations

Increases in flooding of

roadways, rail lines, andsubterranean tunnels

Overloading of drainage

systems, causing backups and street flooding

Increases in road scouring,

road washout, damagesto railbed support structures, and landslidesand mudslides thatdamage roadways andtracks

Impacts on soil moisture

levels, affecting structural integrity of roads,bridges, and tunnels

Expansion of systems

for monitoring scourof bridge piers andabutments

Increase in monitoring

of land slopes anddrainage systems

Increases in monitoring

of pipelines for exposure, shifting, andscour in shallowwaters

Increases in real-time

monitoring of floodlevels

Integration of emergency

evacuation procedures into operations

Protection of critical

evacuation routes

Upgrading of road

drainage systems

Protection of bridge

piers and abutmentswith riprap

Increases in culvert

capacity

Increases in pumping

capacity for tunnels

Addition of slope retention structures and

retaining facilitiesfor landslides

Increases in the standard for drainage

capacity for new

Return of some

coastal areas tonature

Greater use of sensors for

monitoring waterflows

Restriction of development in

floodplains

ANNEX 5-1A (continued) Potential Climate Changes, Impacts on Land Transportation, and Adaptation Options

Impacts on Land Transportation (Highways, Rail, Pipeline) Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
Precipitation:

increases indrought conditions for someregions

Precipitation:

changes in seasonal precipitation and riverflow patterns

Storms: more frequent strong

hurricanes(Category 4–5)

Increased susceptibility

to wildfires, causingroad closures due tofire threat or reducedvisibility

Benefits for safety and

reduced interruptions if frozenprecipitation shiftsto rainfall, depending on terrain

More debris on roads

and rail lines, interrupting travel andshipping

More frequent and

potentially moreextensive emergencyevacuations

Adverse impacts of standing water on road basesIncreases in scouring of

pipeline roadbeds anddamages to pipelines

Increased susceptibility to

wildfires that threatentransportation infrastructure directly

Increased susceptibility to

mudslides in areasdeforested by wildfires

Increased risk of floods

from runoff, landslides,slope failures, and damage to roads if precipitation changes fromsnow to rain in winterand spring thaws

Greater probability of infrastructure failuresIncreased threat to stability

of bridge decks

Increased damage to signs,

lighting fixtures andsupports

Vegetation managementEmergency evacuation

procedures thatbecome more routine

Improvements in ability

to forecast landfalland trajectory ofhurricanes

transportation infrastructure and majorrehabilitation projects(e.g., assuming a500-year rather thana 100-year storm)

Changes in bridge

design to tie decksmore securely tosubstructure andstrengthen foundations

Strengthening and

heightening oflevees

Restriction of further

development invulnerable coastallocations

(continued)
Decreased expected lifetime of highways

exposed to storm surge

Improvements in monitoring of road

conditions andissuance of real-timemessages tomotorists

Improvements in modeling of emergency

evacuation

Increases in drainage

capacity for newtransportation infrastructure or majorrehabilitation projects (e.g., assumingmore frequent returnperiods)

Removal of traffic bottlenecks on critical

evacuation routesand building of moresystem redundancy

Adoption of modular

construction techniques where infrastructure is in danger of failure

Development of modular

traffic features androad sign systems foreasier replacement

Increase in flood

insurance rates tohelp restrictdevelopment

Return of some

coastal areas tonature

ANNEX 5-1A (continued) Potential Climate Changes, Impacts on Land Transportation, and Adaptation Options

Impacts on Land Transportation (Highways, Rail, Pipeline) Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
ANNEX 5-1B Potential Climate Changes, Impacts on Marine Transportation, and Adaptation Options

Impacts on Marine Transportation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials OtherTemperature:

increases in veryhot days andheat waves

Temperature:

decreases in verycold days

Temperature:

increases inArctic temperatures

Impacts on shipping

due to warmer waterin rivers and lakes

Less ice accumulation

on vessels, decks,riggings, and docks;less ice fog; fewerice jams in ports

Longer ocean transport

season and moreice-free ports innorthern regions

Possible availability of

a Northern Sea Routeor a NorthwestPassage

Improvement in operating conditions from

less ice accumulation, fog, and jams

Longer ice-free shipping season and

increased access tomore ice-free portsand resources inremote areas

Longer season for

barge transport

(continued)
Temperature: later

onset of seasonalfreeze and earlieronset of seasonalthaw

Sea level rise,

added to stormsurge

Extended shipping 

season for inlandwaterways (especiallythe St. LawrenceSeaway and theGreat Lakes) due toreduced ice coverage

More severe storm

surges, requiringevacuation

Changes in harbor and port

facilities to accommodate higher tides andstorm surges

Reduced clearance under

bridges

Impacts on navigability of

channels: some will bemore accessible (andfarther inland) becauseof deeper waters, whileothers will be restrictedbecause of changes insedimentation

Increases in summer

load restrictions

More frequent bridge

openings to handleshipping

Design of shallowerbottom vessels for

seaway travel

Raising of dock and

wharf levels andretrofitting of otherfacilities to provideadequate clearance

Protection of terminal

and warehouseentrances

Elevation of bridges

and other structures

More dredging, but

environmental andinstitutional issues

Shifts to other transportation modesMore dredging of

some channels

Raising or construction of new jetties

and seawalls toprotect harbors

ANNEX 5-1B (continued) Potential Climate Changes, Impacts on Marine Transportation, and Adaptation Options

Impacts on Marine Transportation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
Precipitation:

increase inintense precipitation events

Precipitation:

increases indrought conditions for someregions

Precipitation:

changes in seasonal precipitation and riverflow patterns

Increases in weatherrelated delaysImpacts on river transportation routes and

seasons

Periodic channel closings or restrictions if

flooding increases

Benefits for safety and

reduced interruptions if frozenprecipitation shiftsto rainfall

Impacts on harbor infrastructure from wave

damage and stormsurges

Changes in underwater

surface and silt anddebris buildup can affectchannel depth

Changes in silt deposition

leading to reduced depthof some inland waterways and impacts onlong-term viability ofsome inland navigationroutes

Restrictions on shipping due to channel

depth along inlandwaterways and onother river travel

Restrictions on shipping due to channel

depth along inlandwaterways and onother river travel

Strengthening of harbor

infrastructure to protect it from stormsurge and wavedamage

Protection of terminal

and warehouseentrances fromflooding

More dredging on

some shippingchannels

More dredging on

some shippingchannels and harbors

Release of water

from upstreamsources

Shifts to other transportation modesMore dredging on

some shippingchannels

(continued)
Storms: more frequent strong

hurricanes(Category 4–5)

Implications for emergency evacuation

planning, facilitymaintenance, andsafety management

Greater challenge to robustness of infrastructureDamage to harbor infrastructure from waves

and storm surges

Damage to cranes and

other dock and terminalfacilities

Emergency evacuation

procedures thatbecome more routine

Hardening of docks,

wharves, and terminals to withstandstorm surge andwave action

ANNEX 5-1B (continued) Potential Climate Changes, Impacts on Marine Transportation, and Adaptation Options

Impacts on Marine Transportation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
Temperature:

increases in veryhot days andheat waves

Temperature:

decreases in verycold days

Delays due to excessive

heat

Impact on lift-off load

limits at high-altitude or hot-weatherairports with insufficient runwaylengths, resulting inflight cancellationsor limits on payload(i.e., weight restrictions), or both

More energy consumption on the groundChanges in snow and

ice removal costsand environmentalimpacts from saltand chemical use

Reduction in need for

deicing

Heat-related weathering

and buckling of pavements and concretefacilities

Heat-related weathering of

vehicle stock

Increase in payload

restrictions on aircraft at high-altitudeor hot-weather airports

Increase in flight cancellationsReduction in snow and

ice removal

Reduction in airplane

deicing

Development of new

heat-resistant runway paving materials

Extension of runway

lengths at highaltitude or hotweather airports, iffeasible

ANNEX 5-1C Potential Climate Changes, Impacts on Air Transportation, and Adaptation Options

Impacts on Aviation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other

(continued)
Temperature:

increases inArctic temperatures

Temperature: later

onset of seasonalfreeze and earlieronset of seasonalthaw

Sea level rise,

added to stormsurge

Fewer limitations on

ground crew work atairports, typicallyrestricted at windchills below −29°C

(−20°F)

Potential for closure or

restrictions for several of the top 50airports that lie in

Thawing of permafrost,

undermining runwayfoundations

Inundation of airport runways located in coastal

areas

Development of new

runway paving materials

Major repair of some

runways

Elevation of some runways

Relocation of some

landing strips

Construction or raising of protective

dikes and levees

ANNEX 5-1C (continued) Potential Climate Changes, Impacts on Air Transportation, and Adaptation Options

Impacts on Aviation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
Precipitation:

increase inintense precipitation events

Precipitation:

increases indrought conditions for someregions

coastal zones,affecting service tothe highest-densitypopulations in theUnited States

Increases in delays due

to convectiveweather

Storm water runoff that

exceeds the capacityof collection systems, causingflooding, delays, andairport closings

Implications for emergency evacuation

planning, facilitymaintenance, andsafety management

Decreased visibility at

airports located indrought-susceptibleareas with potentialfor increased wildfires

Impacts on structural

integrity of airport facilities

Destruction or disabling of

navigation aid instruments

Runway and other infrastructure damage due to

flooding

Inadequate or damaged

pavement drainage systems

More disruption and

delays in air service

More airport closures

Increases in drainage

capacity andimprovement ofdrainage systemssupporting runwaysand other paved surfaces

Relocation of some

runways, if feasible

(continued)
Precipitation:

changes in seasonal precipitation and riverflow patterns

Storms: more frequent strong

hurricanes(Category 4–5)

Benefits for safety and

reduced interruptions if frozenprecipitation shiftsto rainfall

More frequent interruptions in air service

Inadequate or damaged

pavement drainage systems

Damage to landside facilities (e.g., terminals,

navigation aids, fencing around perimeters, signs)

Increases in drainage

capacity andimprovement ofdrainage systemssupporting runwaysand other paved surfaces

Hardening of terminals

and other facilities

ANNEX 5-1C (continued) Potential Climate Changes, Impacts on Air Transportation, and Adaptation Options

Impacts on Aviation Adaptation Options

Changes in 

Potential Climate Operations and Infrastructure Design 

Change Interruptions Infrastructure Changes in Operations and Materials Other
189

6

Summing Up

The charge to this committee was to review the current scientific

understanding of climate change from the perspective of those

changes of particular relevance for U.S. transportation, including the

limits of current knowledge; to identify potential impacts on U.S. transportation infrastructure and operations; to consider adaptation options;

and to offer recommendations on actions that can be taken to prepare for

climate change and on needed research. In this final chapter, the committee presents its consensus findings and recommendations in response to

this charge, along with its principal supporting arguments. The committee’s consensus position was informed by the five papers commissioned

for this study; the 1-day conference held midway through the study to

obtain the input of a broad range of transportation academicians and

practitioners, climate scientists, and other experts; reviews of previous

studies that examined the potential impacts of climate change on transportation, with a focus on adaptation strategies; numerous briefings on a

wide range of relevant topics presented at committee meetings; and the

committee’s own expertise and judgment. The chapter is organized on

the basis of a series of questions that guided the committee’s thinking.

WHICH CLIMATE CHANGES ARE MOST RELEVANT 

FOR U.S. TRANSPORTATION?

Finding: The past several decades of historical regional climate

patterns commonly used by transportation planners to guide their

operations and investments may no longer be a reliable guide for

future plans. In particular, future climate will include new classes

(in terms of magnitude and frequency) of weather and climate
190 Potential Impacts of Climate Change on U.S. Transportation

extremes, such as record rainfall and record heat waves, not experienced in modern times as human-induced changes are

superimposed on the climate’s natural variability.

Transportation planners and engineers typically extrapolate from historical weather and climate patterns in planning and designing infrastructure.

The past will not be a good predictor of future conditions, however, as

climate changes bring new weather patterns and climate extremes that

exceed current experience. Projections of future climate are often depicted

as gradual changes, such as the rise in global temperatures or in sea levels

projected over this century. However, climate changes are unlikely to be

experienced in such a smooth manner because human-induced changes

will be amplified in some years by naturally fluctuating conditions,

reflected in potentially sudden and dramatic changes at the regional or

local level, where transportation infrastructure is located. Warming temperatures may trigger weather extremes and surprises, such as more rapid

melting of the Arctic sea ice or more rapid rise in sea levels than is projected by current climate models.

On the basis of current knowledge, climate scientists have identified

five climate changes of particular importance to U.S. transportation and

estimated the probability of their occurrence during the 21st century:

• Increases in very hot days and heat waves (very likely),1

• Increases in Arctic temperatures (virtually certain),

• Rising sea levels (virtually certain),

• Increases in intense precipitation events (very likely), and

• Increases in hurricane intensity (likely).

HOW WILL CLIMATE CHANGE AFFECT U.S. TRANSPORTATION?

Finding: Climate change will affect transportation primarily

through increases in several types of weather and climate extremes,

such as very hot days; intense precipitation events; intense hurri1 The Intergovernmental Panel on Climate Change (IPCC) (2007) Working Group I established

the following terminology to describe uncertainty, that is, the probability of occurrence: virtually

certain, >99 percent; extremely likely, >95 percent; very likely, >90 percent; likely, >66 percent;

more likely than not, >50 percent; unlikely, <33 percent; very unlikely, <10 percent; extremely

unlikely, <5 percent.
canes; drought; and rising sea levels, coupled with storm surges

and land subsidence. The impacts will vary by mode of transportation and region of the country, but they will be widespread and

costly in both human and economic terms and will require significant changes in the planning, design, construction, operation, and

maintenance of transportation systems.

Transportation infrastructure was designed for typical weather patterns

and environmental conditions, reflecting local climate and incorporating

assumptions about a reasonable range of temperatures and precipitation

levels. It will be affected most by those climate changes that cause environmental conditions to extend outside the range for which the system

was designed.

Finding: Potentially, the greatest impact of climate change for

North America’s transportation systems will be flooding of coastal

roads, railways, transit systems, and runways because of global

rising sea levels, coupled with storm surges and exacerbated in

some locations by land subsidence.

Fully 53 percent of the U.S. population now lives in counties with coastal

regions, many among the most densely populated in the nation. If development pressures continue in vulnerable coastal areas, and there is every

reason to believe they will, the impacts of climate change will be magnified as increasing numbers of people and businesses are placed in harm’s

way, and the infrastructure is expanded or new infrastructure is built to

accommodate the growth. The Atlantic and Gulf Coasts are particularly

vulnerable because they have already experienced high levels of erosion,

land subsidence, and loss of wetlands. Their vulnerability to the storm

surges and wave action that accompany strong tropical storms was amply

demonstrated during the 2005 hurricane season. Sea level rise and coastal

flooding also pose risks for the East Coast, as well as the Pacific Northwest

and parts of the California coast.

The impacts of climate change will not be limited to coastal areas.

For example, watersheds supplying water to the St. Lawrence Seaway and

the Great Lakes, as well as the Upper Midwest river system, are likely to

experience drier conditions, resulting in lower water levels and reduced

capacity to ship agricultural and other bulk commodities, although a

longer shipping season could offset some of the adverse economic

Summing Up 191
effects. Thawing permafrost in Alaska is already creating settlement and

land subsidence problems for roads, rail lines, runways, and pipelines.

Higher temperature extremes (mainly heat waves) in some U.S. regions

could lead to more frequent buckling of pavements and misalignment of

rail lines. More severe weather events with intense precipitation could

increase the severity of extensive flooding events, such as the storms that

plagued the Midwest during the 1993 flooding of the Mississippi and

Missouri River system, the Chicago area in 1996, and the Houston

region during Tropical Storm Allison in 2001. Flooding of a waterway

system can knock out barge operations on the river itself, rail operations

on rights-of-way adjacent to the river, and even highway approaches to

bridges crossing flooded rivers.

Not all climate change impacts will be negative. For example, the

marine transportation sector could benefit from more open seas in the

Arctic, creating new and shorter shipping routes and reducing transport

time and costs. In cold regions, expected temperature rises, particularly

decreases in very cold days and later onset of seasonal freezes and earlier

onset of seasonal thaws, could mean reduced costs of snow and ice control for departments of transportation and safer travel conditions for

passenger vehicles and freight.

Recommendation 1: Federal, state, and local governments, in

collaboration with owners and operators of infrastructure,

such as ports and airports, and private railroad and pipeline

companies, should inventory critical transportation infrastructure in light of climate change projections to determine

whether, when, and where projected climate changes in their

regions might be consequential.

Inventorying transportation assets essential to maintaining network performance to determine their potential vulnerability to projected climate

changes is a sensible first step. Information about projected climate

changes is currently available from climate scientists for large subcontinental regions—a scale more relevant than global projections for regional

and local transportation infrastructure. Although such an inventory must

be updated periodically as new scientific knowledge about climate change

becomes available, inventorying is a relatively low-cost activity. Many of

the tools needed for the purpose [e.g., geographic information systems

(GIS)] are available. The inventorying process itself should help identify

192 Potential Impacts of Climate Change on U.S. Transportation
with greater precision the data needed on transportation-relevant climate

changes and encourage collaboration between transportation professionals and climate scientists.

HOW SHOULD TRANSPORTATION DECISION MAKERS RESPOND?

Finding: Public authorities and officials at various governmental

levels and executives of private companies are continually making

short- and long-term investment decisions that have implications

for how the transportation system will respond to climate change

in the near and long terms.

Transportation decision makers have an opportunity now to prepare for

projected climate changes. Decisions made today, particularly those related

to the redesign and retrofitting of existing or the location and design of

new transportation infrastructure, will affect how well the system adapts to

climate change far into the future. Many transportation facilities, such as

bridges, large culverts, and rail and port facilities, are designed with long

service lives and help shape development patterns that, once in place, are

difficult to change. Thus, transportation planners and engineers should

consider how projected climate changes in their regions might affect these

facilities.

Recommendation 2: State and local governments and private

infrastructure providers should incorporate climate change

into their long-term capital improvement plans, facility

designs, maintenance practices, operations, and emergency

response plans.

Taking measures now to evaluate and protect the most vulnerable infrastructure should pay off by diminishing near-term maintenance

expenditures and reducing the risk of catastrophic failure, with its toll on

human life and disruption of economic activity. Such measures might

include strengthening or elevating some coastal roads, rail lines, and

bridges, particularly those that serve as evacuation routes, or upgrading

parallel routes where they are available.2 In the longer term, relocation of

Summing Up 193

2 States in particularly vulnerable regions such as the Gulf Coast could consider securing and

banking rights-of-way for alternative evacuation routes, should they prove necessary.
rights-of-way farther inland or installation of costly storm barrier systems

to protect selected areas (e.g., parts of New York City or Miami) might be

considered.

Finding: The significant costs of redesigning and retrofitting transportation infrastructure to adapt to potential impacts of climate

change suggest the need for more strategic, risk-based approaches

to investment decisions.

Designing transportation facilities to more robust standards to hedge

against potentially negative impacts of climate change will produce much

more costly designs that are likely to be unacceptable given limited budgets. More strategic and selective risk-based approaches are needed for

determining appropriate design standards and investment priorities.

Transportation professionals already take risk into account, particularly

in designing facilities. For example, structures are designed to withstand

certain wind speeds on the basis of probabilistic assessments of wind

speed occurrence using historical data on wind speed frequency. Drainage

requirements for many transportation facilities are sized to accommodate the 100-year storm, a probabilistic assessment of storm frequency.

Engineers also commonly incorporate safety factors into designs or

design standards to account for unforeseen events or abnormal forces on

structures. In general, however, transportation decision makers have a long

way to go to take full advantage of quantitative, risk-based approaches that

incorporate uncertainty and probabilistic assessments in making investment and design decisions.

Recommendation 3: Transportation planners and engineers

should use more probabilistic investment analyses and

design approaches that incorporate techniques for trading

off the costs of making the infrastructure more robust

against the economic costs of failure. At a more general level,

these techniques could also be used to communicate these

trade-offs to policy makers who make investment decisions

and authorize funding.

At present, the necessary data and certitude about projections of future climate, particularly at the local and regional levels, are not available to permit

a comprehensive probabilistic risk assessment and analysis. However, more

194 Potential Impacts of Climate Change on U.S. Transportation
simplified approaches can be used by transportation planners and engineers to incorporate many of these risk assessment concepts into their

planning and design. One model is the California Seismic Retrofit

Program. Following the Loma Prieta earthquake in 1989, the California

Department of Transportation developed a risk-based approach for analyzing the vulnerability of highway bridges statewide to earthquakes and

their criticality to the network to make it possible to determine investment

priorities for retrofitting and replacement. The program established a

higher performance standard for 750 structures to protect the investment

in these major facilities and ensure that these vital transportation lifelines

would remain in service after a major seismic event to provide access for

emergency responders. The state’s 11 major toll bridges were handled separately because their complexity demanded a time-consuming dynamic

analysis. For most other bridges, the standard was “no collapse” under a

maximum seismic event, consistent with the geographic location of the

bridge. The objective was to avoid loss of life; however, some damage to a

structure was acceptable as long as it remained intact and could be

reopened for service soon after the event.

Extending and incorporating such techniques to include climate

change will require more complete data on the likelihood of climaterelated hazards and their economic consequences. It will also necessitate

continuing education of current planners and engineers and training of

future professionals. Finally, educating policy makers to gain their support

will entail communicating the information so that the trade-offs and

investment priorities are clear. It may also require new eligibility criteria in

funding programs, and new funding sources may also be necessary to

make the investments identified by the application of these techniques.

WHAT DATA AND DECISION SUPPORT TOOLS ARE NEEDED?

Finding: Transportation professionals often lack sufficiently detailed

information about expected climate changes and their timing to take

appropriate action.

Transportation decision makers note that one of the most difficult aspects

of addressing climate change is obtaining the relevant information in the

form they need for planning and design. This difficulty is not limited to the

transportation sector. A recent National Research Council report (NRC

Summing Up 195
2007) found that while the scientific understanding of climate change has

made great progress, the use of that knowledge to support decision making

and formulate mitigation and adaptation strategies is much less well developed. Climate change is understood with greatest confidence as a global or

continental phenomenon, while transportation planners as well as other

decision makers need local and regional climate projections. They also

need a better understanding of how projected climate changes, such as

changes in temperature and precipitation, will affect the environment (e.g.,

soil moisture, runoff) in which the infrastructure is situated, which will

vary from region to region. Climate projections themselves are presented

by climate scientists as a portfolio of plausible scenarios and outcomes,

which are continually refined and revised as new knowledge accumulates.

Transportation planners need to have a better understanding of which scenarios are most plausible for their regions and most significant for their

operations and plans.

Recommendation 4: The National Oceanic and Atmospheric

Administration, the U.S. Department of Transportation

(USDOT), the U.S. Geological Survey, and other relevant

agencies should work together to institute a process for better communication among transportation professionals,

climate scientists, and other relevant scientific disciplines,

and establish a clearinghouse for transportation-relevant climate change information.

All professions should benefit from the collaboration. Transportation professionals would be encouraged to define with greater precision the climate

data needed to improve transportation decisions, such as temperature and

precipitation thresholds at finer-grained geographic scales or climate conditions that would create unacceptable performance outcomes. Climate

scientists would be challenged to elaborate on the possibilities and limitations of projecting impacts of climate change at the levels of geographic

specificity that are most useful for transportation planners. And hydrologists and others would be challenged to consider how the environment

would influence these effects and their impacts on transportation infrastructure. One promising approach might be for the federal government to

support a number of pilot projects in which federal agencies would work

closely with local transportation planners to include the full range of relevant climate information that could affect a specific project.

196 Potential Impacts of Climate Change on U.S. Transportation
Finding: Better decision support tools are also needed to assist

transportation decision makers.

Recommendation 5: Ongoing and planned research at federal and state agencies and universities that provide climate

data and decision support tools should include the needs of

transportation decision makers.

For example, the research program of the USDOT Center for Climate

Change and Environmental Forecasting could be charged with expanding

its existing research program in this area and provided the necessary funding. Needed tools include accurate digital elevation maps in coastal areas for

forecasting the effects of flooding and storm surge heights; GIS that can be

used to map the locations of critical infrastructure, overlaid with information on climate change effects (e.g., sea level rise, permafrost melt); greater

use of scenarios that include climate change in the development of longrange regional transportation plans to pinpoint likely vulnerabilities (e.g.,

areas susceptible to sea level rise, aggravated by storm surge) and ways to

address them; and better transportation network models for examining the

systemwide effects of the loss of critical transportation infrastructure links.

WHICH ADAPTATION STRATEGIES MAKE SENSE?

Transportation decision makers have a wide range of adaptation options

from which to choose in determining how best to adjust to climate

change. One way to organize these options is around the timescales used

by transportation professionals in their decision making. For example,

operational decisions are typically focused on the short term and thus will

be concerned mainly with near-term changes in weather and climate conditions. Decisions about rehabilitating or retrofitting infrastructure are

made with a longer time horizon in mind. Such decisions will determine

the performance of those assets with long service lives for many decades

and thus should take longer-term climate projections into consideration

so likely hazards can be assessed. Decisions about new infrastructure or

major capacity additions involve the longest time frame because they will

shape land use and development patterns for years to come and thus may

require consideration of climate change projections that extend into the

22nd century. Other adaptation options, such as monitoring and use of

technology or new organizational arrangements, cut across timescales and

Summing Up 197
offer adaptation options in their own right or ways to better incorporate

climate change in transportation decision making.

Operational Responses

Finding: Projected increases in extreme weather and climate

underscore the importance of emergency response plans in vulnerable locations and require that transportation providers work

more closely with weather forecasters and emergency planners

and assume a greater role in evacuation planning and emergency

response.

U.S. transportation providers already address the impacts of weather on

transportation system operations in a diverse range of climatic conditions.

For example, snow and ice control accounts for about 40 percent of annual

highway operating budgets in the northern U.S. states. Likewise, hurricane

planning has become a major focus of transportation operations in the

Gulf Coast states, where transportation providers are forging close relationships with emergency responders to handle severe weather events.

As climate changes induce new extremes (e.g., more intense storms,

more intense precipitation), operational responses are likely to become

more routine and proactive than today’s approach of treating severe

weather on an ad hoc, emergency basis. For example, if hurricanes

increase in intensity, as is likely to be the case, establishment of evacuation

routes and use of contraflow operations may become as commonplace as

the current use of snow emergency routes in the Northeast and Midwest.

More accurate and timely weather prediction and communication of

storm warnings in real time to those potentially in harm’s way will become

more important.

Recommendation 6: Transportation agencies and service

providers should build on the experience in those locations

where transportation is well integrated into emergency

response and evacuation plans.

Following the events of September 11, 2001, and the experience with

Hurricanes Katrina and Rita, coordination between state and local

emergency managers—the first responders in an emergency—and

transportation agencies and service providers improved, particularly in

198 Potential Impacts of Climate Change on U.S. Transportation
those locations with recurring natural disasters, such as hurricanes. In

some locations, transportation is represented at emergency operations

centers—command posts that can be activated rapidly in an emergency.

Transportation agencies and service providers are also working closely

with weather forecasters and emergency response planners to convey

their own lead-time requirements so they can provide the personnel and

equipment necessary for evacuation and protect their own assets.

Transportation agencies and service providers in locations where collaboration is not as advanced should build on this experience.

Monitoring and Use of Technology

Finding: Greater use of technology would enable infrastructure

providers to monitor climate changes and receive advance warning of potential failures due to water levels and currents, wave

action, winds, and temperatures exceeding what the infrastructure was designed to withstand.

Monitoring infrastructure conditions, particularly the impacts of weather

and climate extremes, offers an alternative to preventive retrofitting or

reconstruction of some facilities. It is also an activity that can begin immediately. In Alaska, which is experiencing more accelerated climate changes

than the lower 48 states, the Alyeska Pipeline Company already monitors

the right-of-way of the Trans-Alaska Pipeline System to spot land subsidence problems, particularly along the 800 miles of pipeline elevated on

vertical supports. Alaskan engineers also closely monitor bridge supports,

which are experiencing damage from earlier winter runoff and increased

stream flow. In the future, sensors and other “smart” technologies could be

embedded in the infrastructure to monitor changing climate conditions

and impacts and provide warning when pressure or stress thresholds are

being exceeded. Development of more heat-resistant materials could help

protect pavements and some rail facilities, in particular, from the adverse

impacts of projected temperature extremes.

Recommendation 7: Federal and academic research programs

should encourage the development and implementation of

monitoring technologies that could provide advance warning

of pending failures due to the effects of weather and climate

extremes on major transportation facilities.

Summing Up 199
Advances in sensor technologies, computer processing, and communications capabilities should provide a fertile field for the development of

smart devices that can be used for monitoring changing climate conditions and communicating the results to the appropriate transportation

infrastructure owners. Advances in material sciences should enable the

development of new materials that can withstand climate extremes.

Sharing of Best Practices

Finding: The geographic extent of the United States—from Alaska

to Florida and from Maine to Hawaii—and its diversity of weather

and climate conditions can provide a laboratory for identifying best

practices and sharing information as the climate changes.

As a result of climate change, many areas of the United States will experience new climate-induced weather patterns. These changes, however,

may not necessarily require the development of new operating and maintenance strategies. The United States has a diverse climate, ranging from

subtropical to arctic and from arid to wet, with several regions being subject to temperature extremes and such events as blizzards, hurricanes,

tornadoes, floods, wildfires, avalanches, and mudslides. As climate patterns change, transfer of best practices from one location to another will

be essential.

Recommendation 8: The American Association of State

Highway and Transportation Officials (AASHTO), the Federal

Highway Administration, the Association of American

Railroads, the American Public Transportation Association,

the American Association of Port Authorities, the Airport

Operators Council, associations for oil and gas pipelines, and

other relevant transportation professional and research

organizations should develop a mechanism to encourage sharing of best practices for addressing the potential impacts of

climate change.

This effort should build on technology transfer mechanisms that already

exist, such as AASHTO’s technology-sharing program. Technology should

be defined broadly to include probabilistic decision-making tools, as well

as monitoring technologies, new materials, and operating and maintenance strategies.

200 Potential Impacts of Climate Change on U.S. Transportation
Design Changes

Finding: Reevaluating, developing, and regularly updating

design standards for transportation infrastructure to address the

impacts of climate change will require a broad-based research and

testing program and a substantial implementation effort.

Operational responses are geared to addressing near-term impacts of

climate change, but rehabilitating or retrofitting transportation facilities—

many of which are designed to have long service lives—requires that

transportation planners and engineers consider how climate changes

will affect the performance of these facilities 50 or more years into the

future. Opportunities for adaptation are limited once a facility has been

renovated unless engineers build in the potential to make subsequent

changes. Addressing climate change will also require reevaluation, development, and regular updating of design standards that guide infrastructure

design.

Environmental factors are integral to the design of transportation

infrastructure. Conditions such as temperature, freeze–thaw cycles, and

duration and intensity of precipitation determine subsurface and foundation designs, the choice of materials, and drainage capacity. Engineers,

however, have given little thought to whether current design standards

are adequate to accommodate climate change. For example, will drainage

capacity be adequate for expected increases in intense precipitation

events? Many infrastructure components are currently designed for the

100-year storm, but projections indicate that today’s 100-year precipitation event is likely to occur every 50 or perhaps even every 20 years by the

end of this century. What new materials and operating practices might be

needed when very hot temperatures and heat waves become more frequent? Are infrastructure components sufficiently strong to withstand the

forces of larger and more frequent storm surges and more powerful wave

action, the effects of which were vividly demonstrated when Hurricane

Katrina simply lifted bridge decks off their supporting structures?

Developing standards is a time-consuming consensus process that

typically involves professional organizations in an extensive research and

testing program. Changes in design practices tend to be incremental, and

building to higher standards to strengthen transportation infrastructure

so it can accommodate the adverse impacts of climate change must be

weighed against the costs involved.

Summing Up 201
Recommendation 9: USDOT should take a leadership role,

along with those professional organizations in the forefront

of civil engineering practice across all modes, to initiate

immediately a federally funded, multiagency research program for ongoing reevaluation of existing and development

of new design standards as progress is made in understanding future climate conditions and the options available for

addressing them. A research plan and cost proposal should

be developed for submission to Congress for authorization

and funding of this program.

Developing standards to address climate change in a timely manner

requires leadership by the scientific community and professional associations and, given the scope of the potential impacts, a broadly based,

federally sponsored research program. The initial focus of such a program

should be on essential links in transportation networks, particularly those

vulnerable to climate changes in coastal areas or in low-lying areas in

riverside locations. A good model is the congressionally mandated

National Earthquake Hazard Reduction Program, begun in 1977, which

established a research effort and a coordination mechanism to reduce the

risks to life and property from earthquakes through the development of

standards that afford different levels of protection for different levels of

risk. If a similar program is to be launched to address climate change in a

timely manner, it should be initiated soon.

Recommendation 10: In the short term, state and federally

funded transportation infrastructure rehabilitation projects

in highly vulnerable locations should be rebuilt to higher

standards, and greater attention should be paid to the provision of redundant power and communications systems to

ensure rapid restoration of transportation services in the

event of failure.

Following Hurricane Katrina, for example, the Federal Highway

Administration recognized that current design standards for coastal highway bridges—which were based on a riverine environment and a 50-year

storm—were inadequate. The agency approved and shared in the cost of

rebuilding bridges damaged in the hurricane to a higher design standard,

and it recommended the development of bridge design standards more

202 Potential Impacts of Climate Change on U.S. Transportation
appropriate for a coastal environment, which take into account the combined effects of storm surge and wave action and assume a more severe

storm event (e.g., a 100-year or even a 500-year storm). AASHTO is leading the effort to develop a new consensus standard. Hurricane Katrina also

showed the importance of power and communications systems to the

restoration of transportation services (e.g., operation of traffic lights, rail

signal systems, pumping stations, air traffic control facilities, and nighttime running lights).

Finding: Federal agencies have not focused generally on adaptation in addressing climate change.

The development of appropriate design standards to accommodate climate change is only one of several possible adaptation strategies that may

require federal leadership, research, and funding.

Recommendation 11: USDOT should take the lead in developing an interagency working group focused on adaptation.

This initiative would not necessarily require new funding beyond that

recommended above. Better collaboration among federal agencies could

help focus attention on adaptation issues and shape existing research

programs.

Transportation Planning and Land Use Controls

Finding: Transportation planners are not currently required to

consider climate change impacts and their effects on infrastructure investments, particularly in vulnerable locations.

One of the most effective strategies for reducing the risks of climate

change is to avoid placing people and infrastructure in vulnerable locations. Transportation planners currently consider expected land use

patterns when forecasting future travel demand and infrastructure needs.

However, they rarely question whether such development is desirable,

much less what effects climate change might have on the provision and

development of infrastructure in vulnerable locations. In part, this situation stems from governance arrangements. States, regional authorities,

and the private sector are responsible for large-scale transportation

Summing Up 203
investment decisions, but local governments and a few states control land

use decisions through comprehensive plans, zoning ordinances, permitting, and building codes. In some locations, transportation and land use

planning are becoming more integrated as a result of smart growth policies, which recognize the impact of transportation investments on regional

development and economic growth and vice versa; however, such integration is uncommon.

Recommendation 12: Federal planning regulations should

require that climate change be included as a factor in the

development of public-sector, long-range transportation

plans; eliminate any perception that such plans should be

limited to 20 to 30 years; and require collaboration in plan

development with agencies responsible for land use, environmental protection, and natural resource management to

foster more integrated transportation–land use decision

making.

Current surface transportation legislation encourages such collaboration.

During reauthorization, requiring transportation planners to both consider

climate change and collaborate with land use planners in the preparation of

public-sector, long-range plans could go a long way toward making these

issues more visible. Some metropolitan planning organizations are already

using scenario-based approaches to illustrate the trade-offs among social,

economic, and environmental goals and understand the impacts of different long-range investment plans. Scenario planning could be adapted to

take potential climate changes into account, and the results could provide

the basis for discussion with local governments and developers responsible

for land use decisions, particularly in vulnerable areas.

Finding: Locally controlled land use planning, which is typical

throughout the country, has too limited a perspective to account

for the broadly shared risks of climate change.

Any strategy that involves land use controls to address climate change

would need to build consensus among key decision makers in transportation and land use, probably at the regional level—a challenging proposition.

Federal and state incentives may be needed to encourage new organizational arrangements, a topic discussed later in this chapter.

204 Potential Impacts of Climate Change on U.S. Transportation
Insurance

Finding: The National Flood Insurance Program and the flood

insurance rate maps (FIRMs) that determine program eligibility

do not take climate change into account.

The federal government is the insurer of last resort for homeowners and

businesses that cannot secure affordable private flood insurance in specially

designated flood hazard areas. The National Flood Insurance Program,

authorized by Congress in 1968 to mitigate increasing taxpayer-funded

flood relief, is administered by the Federal Emergency Management

Agency (FEMA). FEMA maps the nation’s floodplains, and eligible homeowners and businesses receive below-cost insurance. In return, the local

community must adopt and enforce floodplain management measures,

including building code ordinances for new construction and rebuilding

after a disaster, to reduce flood damage. In practice, critics contend that

the program has resulted in more development than would otherwise

have occurred in these areas. Moreover, the accuracy of the FIRMs used

to determine program eligibility is woefully inadequate, despite a mapping modernization program. Flood hazard area boundaries are keyed to

the 100-year storm, and base elevation data are inadequate. The maps are

based on historical data and thus do not factor in such climate changes as

sea level rise and storm surge.

Recommendation 13: FEMA should reevaluate the risk reduction effectiveness of the National Flood Insurance Program

and the FIRMs, particularly in view of projected increases in

intense precipitation and storms. At a minimum, updated

flood zone maps that account for sea level rise (incorporating

land subsidence) should be a priority in coastal areas.

Climate change may trigger more intense storms, and sea level rise will

extend the scope of flood damage in some special flood hazard areas.

FEMA and congressional oversight committees should reevaluate the risk

reduction effectiveness of the National Flood Insurance Program in light of

these projected changes. The FIRMs should account for climate change

and the likelihood that it will extend the boundaries of some special flood

hazard areas, which are keyed to the 100-year storm. These changes are

particularly important to transportation engineers because the FIRMs have

Summing Up 205
become a quasi–design standard, for example, for determining appropriate

drainage capacity for transportation infrastructure in coastal areas.

New Organizational Arrangements

Finding: Current institutional arrangements for transportation

planning and operations were not organized to address climate

change and may not be adequate for the purpose.

The impacts of climate change do not follow modal, corporate, or jurisdictional boundaries, yet decision making in the transportation sector is

structured around these boundaries. Transportation planning is conducted primarily at the regional level, often through a bottom-up process

that starts with local jurisdictions. Railroads, trucking, and waterborne

commerce are largely private enterprises with varying levels of federal

participation. Thus, existing institutional arrangements are not well

suited to addressing climate change. Some models of cross-jurisdictional

cooperation exist, such as regional authorities for specific facilities (e.g.,

the Alameda Corridor); regional and multistate emergency response

agreements; and state-mandated regional authorities, such as those

responsible for air quality improvement. One could imagine the emergence of similar arrangements to address, for example, the impact of sea

level rise on coastal real estate and infrastructure in the tristate New

York area or other coastal areas, or the effects of drought on shipping

along inland waterways, or the impact of hurricanes in the Gulf Coast

region. However, state or federal incentives may be required to ensure

the development of such organizational arrangements at the regional or

multistate level.

Recommendation 14: Incentives incorporated in federal and

state legislation should be considered as a means of addressing and mitigating the impacts of climate change through

regional and multistate efforts.

For example, states could use updated FIRMs or their own state maps to

identify geographic areas vulnerable to climate change and craft policies

for restricting transportation investments and limiting insurance in these

locations.

206 Potential Impacts of Climate Change on U.S. Transportation
WHAT ACTIONS AND RESEARCH ARE NEEDED 

TO PREPARE FOR CLIMATE CHANGE?

At the outset of this study, the committee was asked to provide recommendations on actions to be taken to prepare for climate change and on

needed research. The committee interpreted this charge broadly, particularly as it applies to research. Many of its recommendations relate to the

development and sharing of information, decision support tools, and

new technologies and materials, as well as research more narrowly defined.

The committee also attempted to identify who should implement each of

its recommendations.

Actions to prepare for climate change can be taken almost immediately.

The committee recommends that transportation agencies and service

providers inventory critical infrastructure in light of climate change projections (Recommendation 1); incorporate climate change into their

long-term capital improvement plans, facility designs, maintenance practices, operations, and emergency response plans (Recommendation 2);

incorporate more probabilistic investment analyses and design approaches

and communicate the results of these analyses to policy makers in ways that

highlight trade-offs and investment priorities (Recommendation 3); and

build on the experience of locations where transportation is well integrated

into emergency response and evacuation plans to prepare for projected

weather and climate extremes (Recommendation 6).

Other steps depend on federal and state action. Federal planning regulations should require inclusion of climate change in the development

of long-range plans and collaboration between transportation and land

use agencies (Recommendation 12); state and federally funded transportation infrastructure rehabilitation projects in highly vulnerable

locations should be rebuilt to higher standards until design standards can

be assessed more broadly in light of climate change (Recommendation

10); FEMA should reevaluate the risk reduction effectiveness of the

National Flood Insurance Program and update the FIRMs, both in light

of climate change (Recommendation 13); and federal and state legislation should incorporate incentives to encourage the development of

regional and multistate efforts to address the impacts of climate change

(Recommendation 14).

Research needs, broadly defined, include establishing a process for

better communication among transportation professionals, climate scientists, and other relevant scientific disciplines and a clearinghouse for

Summing Up 207
transportation-relevant information on climate change (Recommendation

4); developing climate data and decision support tools that incorporate the

needs of transportation decision makers (Recommendation 5); developing

and implementing monitoring technologies for major transportation

facilities to provide advance warning of pending failures due to severe

weather events and climate extremes (Recommendation 7); developing

a mechanism for sharing best practices to address potential impacts of

climate change (Recommendation 8); initiating a federally funded, multiagency research program for reevaluation of existing and development of

new design standards to address the impacts of climate change, including

a research plan and cost proposal for immediate submission to Congress

(Recommendation 9); and creating a federal-level interagency working

group focused on adaptation (Recommendation 11). Most of these initiatives would require federal action; others would require action by

professional organizations and university researchers. In all cases, leadership and continuing commitment would be essential.

REFERENCES

Abbreviations

IPCC Intergovernmental Panel on Climate Change

NRC National Research Council

IPCC. 2007. Summary for Policymakers. In Climate Change 2007: The Physical Science

Basis. Contribution of Working Group I to the Fourth Assessment Report of the

Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning,

Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.), Cambridge

University Press, Cambridge, United Kingdom, and New York.

NRC. 2007. Evaluating Progress of the U.S. Climate Change Science Program: Methods

and Preliminary Results. National Academies Press, Washington, D.C.

208 Potential Impacts of Climate Change on U.S. Transportation
209

APPENDIX A

Detailed Statement of Task

This study will focus on and emphasize the consequences of climate

change for U.S. transportation and adaptation strategies. It will

summarize possible consequences for transportation, such as from sealevel rise, higher mean temperatures with less extreme low temperatures

and more hot extremes, and, possibly, more frequent and severe rain

events. U.S. transportation options for adapting to impacts will be analyzed, including possible need to alter assumptions about infrastructure

design and operations; ability to incorporate uncertainty in long-range

decision making; and capability of institutions to plan and act on mitigation and adaptation strategies at the state and regional levels.

The study will also provide federal, state, and local transportation

officials in the United States with an overview of the scientific consensus

regarding climate change—including uncertainty about its nature and

extent.

Drawing heavily upon analyses already prepared, the study will summarize current and projected contributions of transportation to climate

change and the potential effects, costs, and benefits of strategies to reduce

transportation’s impact. This would include strategies, for example, that

affect land use patterns, influence mode choice, and involve alternatively

fueled or more efficient motor vehicles.

The study will identify critical areas of needed research. The final report

will include findings and recommendations regarding needed research and

suggested actions to prepare for the possibility of climate change.
210

APPENDIX B

Contribution of U.S. Transportation Sector

to Greenhouse Gas Emissions 

and Assessment of Mitigation Strategies

The body of this report describes how climate change is expected to

impact the U.S. transportation sector and identifies ways in which

this impact might be ameliorated. The committee’s charge also directed

it to review what is known about the contribution of transportation to

greenhouse gas (GHG) emissions:

Drawing heavily upon analyses already prepared, the study will

summarize current and projected contributions of transportation to

climate change and the potential effects, costs, and benefits of strategies to reduce transportation’s impact. This would include strategies,

for example, that affect land use patterns, influence mode choice, and

involve alternatively fueled or more efficient motor vehicles.

This appendix addresses this aspect of the committee’s charge.

HOW THE TRANSPORTATION SECTOR INFLUENCES 

CLIMATE CHANGE

Transportation vehicles emit GHGs when fuel undergoes combustion in

their engines. The vast majority of these combustion-related emissions

consist of carbon dioxide (CO2).1 But road transport vehicles also emit

1 The U.S. Energy Information Agency’s annual publication Emissions of Greenhouse Gases in the

United States provides estimates of transport sector emissions of CO2, CH4, and N2O. In 2003,

CO2 accounted for 97 percent of the total, when each gas is converted into its global warming
small amounts of nitrous oxide (N2O) and methane (CH4). Aircraft operating at high altitudes emit not only nitrogen oxides (NOx) [which

increases the rate of ozone production by speeding the oxidation of carbon monoxide (CO) and CH4] but also water vapor [which generates

contrails that, depending on the time of day they are produced, either

reflect solar radiation back into space (daytime) or trap it (nighttime)]

(IPCC 1999; see also Stuber et al. 2006).

Transport activity is also associated with two additional categories of

emissions: (a) those produced in the extraction, production, and distribution of transport fuels and (b) those produced in the manufacture,

distribution, and disposal of transport vehicles.2 A rough idea of the relative significance of these additional categories of emissions can be obtained

from life-cycle studies that attempt to track all emissions related to a vehicle and its fuel. One of the best known of these studies estimates that the

life-cycle CO2 emissions generated by a 1996-vintage midsize U.S. passenger car using gasoline as its fuel total 263 g/km, of which the vehicle

manufacturing cycle (including disposal) accounts for 18 g/km (6.8 percent); the fuel cycle, 49 g/km (18.7 percent); and fuel combustion, 196 g/km

(74.5 percent) (Weiss et al. 2000, 5–8).3

In this appendix, the committee attempts to provide as comprehensive a picture as possible of transport-related GHG emissions. It was not

feasible to include emissions from each life-cycle stage or emissions of

each GHG gas; we do, however, take care to identify which emissions are

included in the data presented.

CURRENT AND PROJECTED TRANSPORT-RELATED GREENHOUSE

GAS EMISSIONS

According to the 2005 edition of the International Energy Agency (IEA)

publication CO2 Emissions from Fuel Combustion, worldwide CO2 emisContribution to Emissions and Assessment of Strategies 211

potential. Nearly all the remainder was accounted for by N2O (U.S. Energy Information

Administration 2004, 31, 49, 62). This publication provides no information on aerosols produced

by transport activity, but these are believed to be relatively insignificant.

2 The second of these categories is of concern only with respect to road vehicles. The number of

nonroad vehicles (locomotives, ships, and aircraft) is so small that the GHG emissions related to

their manufacture, distribution, and disposal are minimal.

3 The report assumes 95 percent recycling of metals and 50 percent recycling of plastics. In the report,

the emissions figures are stated in grams of carbon per kilometer. For consistency with the other

emissions data in this appendix, the figures have been converted here to grams of CO2 per kilometer.
sions from fuel combustion in 2003 totaled 25.0 billion tonnes (IEA 2005).

The transport sector accounted for 5.9 billion tonnes, or 23.6 percent of

this total (IEA 2005).4 Another IEA publication (IEA 2006) provides “reference case” projections of emissions for 2050. According to that report,

total CO2 emissions from fuel consumption in 2050 will be 57.6 billion

tonnes (IEA 2006). Transport sector emissions will be 11.7 billion tonnes,

or 20.3 percent of this total.

The two IEA publications just cited do not provide a high level of

modal detail. However, the World Business Council for Sustainable

Development’s Sustainable Mobility Project (SMP) has published detailed

modal estimates of emissions from fuel combustion for 2000 and projections at 5-year intervals to 2050 (World Business Council for Sustainable

Development 2004).5 The SMP also published estimates and projections

of CO2, N2O, and CH4 emissions from the production and distribution of

transport fuels. The SMP’s figures were generated by a model that was

benchmarked to the IEA transport sector totals. Table B-1 shows the estimates and projections generated by this model.

Light-duty passenger vehicles (LDVs), consisting of passenger cars,

pickup trucks, sport utility vehicles (SUVs), and minivans, account for

the largest share of transport-related emissions. This will continue to be

the case even in 2050 if present trends continue. However, emissions from

other modes, notably air transport and trucks used to haul freight, are

extremely significant and are projected to grow faster than emissions

from LDVs.

The SMP report also provides estimates and projections of transportrelated emissions by country/region. These are shown in Figure B-1. The

United States is included in the region “OECD [Organisation for Economic

Co-operation and Development] North America” along with Canada and

Mexico.

One notable feature of Figure B-1 is the differences in relative growth

rates of emissions within different countries/regions. Generally speaking,

212 Potential Impacts of Climate Change on U.S. Transportation

4 These are emissions from fuel combustion.

5 The documentation for this model, as well as the model itself, can be found at www.

sustainablemobility.org. The SMP characterizes its projections as what might occur “if present

trends continue.” For a description of what is meant by the phrase “if present trends continue,”

see Box 2.1 in the SMP report (p. 27). The report also can be found at the web address just cited.

The report draws on 2003 data, the most recent available at the time the report was published. This

appendix, which draws heavily on the SMP report, uses 2003 data because it would have been

impractical to update the data contained in the SMP report.
Contribution to Emissions and Assessment of Strategies 213

TABLE B-1 World Transport Well-to-Wheels (Vehicle + Upstream) 

CO2-Equivalent Emissions by Mode (megatonnes)

Year AAGR (%)

Mode 2000 2025 2050 2000–2025 2025–2050

Freight + passenger rail 207 341 503 2.0 1.6

Bus 396 436 480 0.4 0.4

Air 733 1,487 2,583 2.9 2.2

Freight truck 1,446 2,423 3,582 2.1 1.6

Light-duty passenger vehicle 2,798 4,152 5,901 1.6 1.4

Two- and three-wheeler 110 209 313 2.6 1.6

Water 638 826 1,015 1.0 0.8

Total 6,328 9,874 14,378 1.8 1.5

Note: AAGR = annual average growth rate.

Source: Data generated by the International Energy Agency/Sustainable Mobility Project (IEA/SMP) Spreadsheet Model.

0.0

2000.0

4000.0

6000.0

8000.0

10000.0

12000.0

14000.0

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Year

Megatonnes

Africa

Latin America

Middle East

India

Other Asia

China

Eastern Europe

FSU

OECD Pacific

OECD Europe

OECD North America

FIGURE B-1 Transport greenhouse gas emissions by region (all modes). (Source:

Data generated by IEA/SMP Spreadsheet Model.)
emissions from countries not presently members of the OECD are projected to grow much more rapidly than emissions from countries that are

members of the three OECD regions. The factors responsible for this

faster growth are discussed in more detail below.

IEA estimates that U.S. transport-sector emissions from fuel combustion in 2003 totaled 1.8 billion tonnes, of which road transport (LDVs,

motorized two- and three-wheelers, buses, medium- and heavy-duty

trucks) accounted for 85 percent. The U.S. Environmental Protection

Agency (EPA) provides estimates having a greater level of modal detail

(see Table B-2). Comparison of the figures from Table B-2 with those from

Table B-1 implies that in 2003, U.S. transport emissions of CO2 from fuel

combustion accounted for 30 to 31 percent of total world transport CO2

emissions from fuel combustion, depending on whether international aviation and marine bunkers are included.6 The emissions factors developed

by the SMP for the production and distribution of each type of transport

fuel suggest that including fuel cycle emissions would add another 17.5

percent to the U.S. total (and 15.0 percent to the world total).

EPA does not publish projections of future emissions at a similar level

of detail. And, as already noted, the SMP’s projections are for OECD

North America (i.e., the United States, Canada, and Mexico). According

to the SMP data in Figure B-1, OECD North American transport-related

emissions will have fallen from 37 percent of the world transport-related

total to 26 percent by 2050. This decline in share is accounted for not by

any absolute reduction in North American emissions but by the much

more rapid rate of growth projected for emissions in regions (other than

the other two OECD regions) outside North America.

STRATEGIES FOR REDUCING TRANSPORT-RELATED 

GREENHOUSE GAS EMISSIONS

The charge to the committee quoted above recognizes that a range of

possible approaches exist by which transport-related GHG emissions

214 Potential Impacts of Climate Change on U.S. Transportation

6 “International aviation and marine bunkers” denotes fuel loaded on transport vehicles in the

United States but consumed in international operations. Generally speaking, “international

bunkers” are not included in national totals, though they are included in the world totals cited

above. The IEA estimates that in 2003, the combustion of international aviation bunkers

accounted for 359 million tonnes of CO2 emissions. The combustion of international marine

bunkers is estimated to have accounted for 459 million tonnes of CO2 emissions.
TABLE B-2 U.S. CO2 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector, 2003 (Tg CO2 Eq.)

Fuel Type

Distillate Mode

Fuel Oil Aviation Residual Natural Sharea

Vehicle Type Gasoline (Diesel) Jet Fuel Gasoline Fuel Oil Gas LPG Electricity Mode Totala (%) 

Road vehicles 1,464.1 78.9

Automobiles 630.2 3.4 0.0 633.6 34.2Light-duty trucks 460.9 17.6 0.0 0.3 478.8 25.8Other trucks 39.6 301.1 0.5 341.2 18.4Buses 0.3 8.0 0.6 0.0 8.9 0.5Motorcycles 1.6 1.6 0.1

Rail 39.6 3.2 42.8 2.3Waterborne 82.1 4.4

Ships and boats 17.0 29.5 46.5 2.5Ships (bunkers) 6.0 18.6 24.6 1.3Boats (recreational) 11.0 11.0 0.6

Aircraft 230.8 12.4

Commercial aircraft 122.8 122.8 6.6Military aircraft 20.5 20.5 1.1General aviation 9.4 2.2 11.6 0.6Other aircraft 16.3 16.3 0.9Aircraft (bunkers) 59.6 59.6 3.2

Pipeline 34.8 34.8 1.9Fuel totala 1,166.6 369.7 228.6 2.2 48.1 35.4 0.8 3.2 1,854.6 100.0

Fuel sharea (%) 62.9 19.9 12.3 0.1 2.6 1.9 0.0 0.2Note: Totals may not sum because of independent rounding. LPG = liquefied petroleum gas.aIncludes aircraft and waterborne international bunkers.Source: USEPA 2005, Table 3-7.
might be reduced. The committee believes that the best way of organizing the present discussion of this range of approaches is through the use

of the “ASIF decomposition.” The CO2 emissions from fuel combustion

by transport vehicles can be characterized by the following equation:

G = A∗Si∗Ii∗Fi,j

where

G = CO2 emissions from fuel combustion by transport;

A = total transport activity;

Si = modal structure of transport activity;

Ii = energy consumption (fuel intensity) of each transport mode; and

Fi,j = GHG emissions characteristics of each transport fuel (i = transport mode, j = fuel type).

The product of the first two variables on the right-hand side of this

equation, A and Si, is the demand for transport services provided by

transport mode i. The product of the last two variables, Ii and Fi,j, is the

GHG generated by each unit of transportation service provided by mode

i using fuel type j.7

Historically, the primary driver of transport-related GHG emissions

has been the growth of total transport activity (A). The primary offsetting

factor has been a reduction in the energy required to produce each unit of

transport services (I). However, improvements in transport energy efficiency have been overwhelmed by the increase in transport activity.

Changes in the modal structure of transport activity (S) have tended to

boost GHG emissions in two ways. First, activity has tended to shift from

less energy-intensive transport modes (e.g., rail) to more energy-intensive

modes (e.g., truck). Second, in some modes (e.g., LDVs), the load factor

(the percentage of vehicle capacity actually utilized) has fallen sharply.8

Changes in the emissions characteristics of transport fuels (F) have had

little impact one way or another.

216 Potential Impacts of Climate Change on U.S. Transportation

7 This formulation was originally popularized by Lee Schipper. This particular version is taken from

IEA (see IEA 2000, 22).

8 In both trucking and air transport, improvements in average load factors have tended to offset some

of the impact of the inherently higher energy intensiveness of the mode. The energy intensiveness

of the modes (I) has increased somewhat as a result. (It takes more energy to move heavier

average loads.) But the increase in energy required is considerably less than proportional to the

increase in load.
Reducing the Volume of Transport Activity (A) or 

Altering the Modal Structure of Transport Activity (S)

The SMP report projects that worldwide personal transport activity, which

totaled 32.3 trillion passenger-kilometers (pkm) in 2000, will grow to 

74.0 trillion pkm by 20509 (see Figure B-2). Worldwide goods transport

activity (excluding waterborne),10 which in 2000 totaled 14.4 trillion

tonne-kilometers (tkm),11 is projected to grow to 45.9 tkm (see Figure B-3).

These projections imply average annual rates of growth of 1.7 percent for

personal transport activity and 2.3 percent for goods transport activity

(again excluding waterborne).

Figures B-2 and B-3 also indicate that rates of growth of both personal

and goods transport activity are likely to vary widely across countries/

Contribution to Emissions and Assessment of Strategies 217

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Year

Trillions of Passenger-Kilometers

Africa

Latin America

Middle East

India

Other Asia

China

Eastern Europe

FSU

OECD Pacific 

OECD Europe

OECD North America

FIGURE B-2 Passenger transport activity by region. (Source: World Business

Council for Sustainable Development 2004, Figure 2-2, p. 30.)

9 Passenger-kilometer is defined as the transportation of one passenger a distance of 1 kilometer.

10 The SMP report does not project waterborne freight activity. According to the United Nations

Conference on Trade and Development (UNCTAD 2005), in 2000, world seaborne trade totaled

23.7 trillion tonne-miles, or 43.9 tonne-kilometers (tkm). Of this total, 41 percent was oil and oil

products, 29 percent was the five main dry bulk commodities (including iron ore, coal, and grain),

and 30 percent was other dry cargoes (including containerized cargoes). We assume that the

“miles” reported by UNCTAD (2005) are nautical miles. If so, this means that in 2000, ocean

shipping accounted for 75 percent of all tkm of freight carried.

11 Tonne-kilometer is defined as the transportation of 1 metric ton (tonne) of freight a distance of 

1 kilometer.
regions, reflecting basic economic and demographic changes discussed

below. At present, the majority of both personal and goods transport

activity occurs within or between countries that are members of the

OECD.12 Over the next half-century, however, transport activity is projected to grow much more rapidly in those countries that are not presently

OECD members. These higher growth rates, if achieved, imply that nonOECD personal transport activity will exceed OECD personal transport

activity by about 2025. The crossover point for goods transport activity is

likely to be even sooner—perhaps as early as 2015.

Drivers of the Volume of Personal and Goods Transport Activity

Numerous factors influence the rate of growth of personal and goods

transport activity, but the following are especially important: (a) the level

and rate of growth of real per capita income, (b) the rate of population

218 Potential Impacts of Climate Change on U.S. Transportation

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Year

Trillions of Tonne-Kilometers

Africa

Latin America

Middle East

India

Other Asia

China

EasternEurope

FSU

OECD Pacific

OECD Europe

OECD North America

FIGURE B-3 Goods transport activity (excluding waterborne). (Note: Waterborne

activity not available by country/region. According to the United Nations

Conference on Trade and the Environment, in 2000, worldwide waterborne

transport activity totaled 43.9 trillion tkm.) (Source: World Business Council

for Sustainable Development 2004, Figure 2-5, p. 32.)

12 The OECD was formed in 1961 by the following countries: Austria, Belgium, Canada, Denmark,

France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal,

Spain Sweden, Switzerland, Turkey, the United Kingdom, and the United States. The following

countries have since joined: Japan (1964), Finland (1969), Australia (1971), New Zealand

(1973), Mexico (1994), the Czech Republic (1995), Hungary (1996), Poland (1996), the

Republic of Korea (1996), and Slovakia (2000).
growth, (c) the share of population residing in urban areas, and (d) the

spatial organization of urban areas (also called “urban form”). In addition, a potentially salient factor is the impact of telecommuting and the

Internet on travel demand.

Level and Rate of Growth of Real per Capita Income Transportation

activity both drives and is driven by the level and rate of growth of real per

capita income. This should not be surprising. Transportation services are

a major enabler of economic growth, and as people become wealthier, they

find more reasons to travel. Figure B-4 shows the relationship between real

gross domestic product (GDP) per capita and per capita personal travel in

2000 for the countries/regions included in the SMP report.13 In 2000, the

average resident of an OECD country traveled 5.7 times as many kilometers per year as did the average resident of a non-OECD country—a

slightly lower ratio than that between the average real per capita incomes

of the two country groupings.

Contribution to Emissions and Assessment of Strategies 219

13 Similar data for goods transport activity are not provided because the information on waterborne

origin–destination pairs needed to assign that important transport activity to countries/regions is

lacking.

OECD North America

OECD Europe

OECD Pacific

FSU

Eastern Europe

China

Other Asia

India

Middle East

Latin America

Africa

0.0

5.0

10.0

15.0

20.0

25.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Per Capita Real Income (thousands of US$, Purchasing Power Parity Basis)

Per Capita Personal Travel Activity (thousands of km)

FIGURE B-4 Per capita personal travel activity versus per capita real income.

(Source: Data generated by IEA/SMP Spreadsheet Model.)
Figure B-5 shows the relationship between the projected rate of change

in real GDP per capita and the projected rate of change in per capita personal travel over the period 2000–2050. Note the difference in the relative

positions in the two exhibits of the three OECD regions and those nonOECD countries/regions in which economic growth is projected to grow

the most rapidly.

Given the relationship between real per capita income growth and per

capita personal (and probably also goods) transport activity, it is obvious

that if the former were slower, so would be the latter. However, most people (especially those living in countries where real per capita GDP is

relatively low today but is projected to grow rapidly) would find highly

unpalatable a strategy of deliberately slowing growth in real GDP per

capita in order to slow the growth of travel activity. This does not mean

that the link between real per capita income growth and per capita travel

activity is immutable. But it does mean that if this link is to be weakened,

220 Potential Impacts of Climate Change on U.S. Transportation

Africa

Latin America

Middle East

India

Other Asia

China

Eastern Europe

FSU

OECD Pacific

OECD Europe

OECD North 

America

-0.5%

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 3.5% 4.0% 4.5%

Projected Change in Real Gross Domestic Product per Capita

(Purchasing Power Parity Basis)

Projected Change in per Capita Personal Transport Demand

FIGURE B-5 Projected change in real per capita personal transport demand versus

projected change in real gross domestic product per capita (purchasing power parity

basis), 2000–2050. (Source: Data generated from IEA/SMP Spreadsheet Model.)
the measures employed will have to be less draconian than limiting economic growth. This issue is revisited below.

Rate of Population Growth The projected trends in real per capita

income growth, if realized, will be a powerful force serving to increase

transport activity. However, another factor that has exerted a powerful

influence in increasing transport activity in the recent past—population

growth—will be waning in importance in the future.

Population growth rates are falling everywhere. This should not be surprising. Figure B-6 illustrates how extraordinary population growth during

the last half of the 20th century truly was. This explosion of world population was caused by reduced mortality in the less developed regions—a

reduction that was not accompanied (at least initially) by declining fertility rates in these regions. One major factor enabling this rapid growth in

population was the increased ability to transport food, especially by ship

and rail. The growth in population, together with improved transport,

stimulated the demand for finished goods. During the last quarter of the

Contribution to Emissions and Assessment of Strategies 221

Millions

100

80

60

40

20

0

1750 1800 1850 1900 1950 2000 2050

0

2

4

6

Population size

8

10

Billions

Annual increments

Population size

Population increment

FIGURE B-6 Long-term world population growth, 1750–2050 (projected).

(Source: UN 1999, Figure 1, p. 7. Reprinted with permission of the United

Nations Population Division.)
20th century, the rate of population growth began to fall, largely because of

declines in fertility.

As with real per capita income growth, the pattern of population

growth over the period 2000–2050 will differ by region.

As a result of sharp fertility declines, the average age of the population

in many countries will be rising. In 1950, the median age of the world’s

population was 23.5 years. It is estimated to have increased to 28.1 years

by 2005, and by 2050 is projected to reach 37.8 years.14

Share of Population Residing in Urban Areas Most personal travel is

within or between urban areas. Urban areas depend on transport systems

to supply them with food, energy, raw materials, and finished goods. It is

not surprising, therefore, to find a link between urbanization and transport activity.

In 1950, about half of the people in the more developed regions lived

in cities15 (see Table B-3). By 2000 this figure had increased to nearly 75

percent.16 However, the growth in urbanization is tapering off in the countries of the more developed regions. In the next 30 years, the percentage of

people living in urban areas in these countries will increase only to 82 percent. The total urban population in these regions will experience a

relatively small increase, with most of that increase occurring in North

America (the United States and Canada).17 In contrast, urban populations

in countries located in the less developed regions will grow rapidly.

Spatial Organization of Urban Areas (Urban Form) The spatial organization of urban areas exerts an independent influence on the total volume

of personal and goods transport activity, as well as on modal choice. When

222 Potential Impacts of Climate Change on U.S. Transportation

14 The median age of the U.S. population, which was 30.0 years in 1950, is estimated to have

reached 36.1 years by 2005 and is projected to grow to 41.1 years by 2050 (UN 2005, 

Table VIII-12).

15 The categorization of countries into those located in “more developed regions” and “less

developed regions” is used by the United Nations “for statistical convenience and [does] not

necessarily express a judgment about the stage reached by a particular country or area in the

developing process” (UN 2005, ii). Generally speaking, countries in the more developed regions

are members of the OECD, while those in the less developed regions are not. But there are some

important exceptions. Russia and the European portions of the former Soviet Union are included

in the more developed regions but are not OECD members. Mexico, South Korea, and Turkey are

OECD members but are designated by the United Nations as being in the less developed regions.

16 In 2000, 80 percent of the U.S. population lived in metropolitan areas as defined by the U.S.

Census.

17 The figure for the United States is projected to increase to 87 percent by 2030 (UN 2003,

Tables A-3 and A-5).
Contribution to Emissions and Assessment of Strategies 223

TABLE B-3 World Urbanization Trends, 1950–2030 (Projected)

More Developed Regions Less Developed Regions

Northern Regional Regional

Europe Americaa Japan Total China India Total

Urban Population (billions)

1950 0.28 0.11 0.03 0.43 0.07 0.06 0.31

1975 0.45 0.18 0.06 0.70 0.16 0.13 0.81

2000 0.53 0.25 0.08 0.88 0.60 0.28 1.97

2030 (projected) 0.55 0.35 0.09 1.01 0.88 0.59 3.93

Change 2000–2030 0.02 0.10 0.01 0.13 0.28 0.31 1.96

Average Annual Rate of Change (%)

1950–1975 1.9 2.0 3.2 2.0 3.4 3.1 3.9

1975–2000 0.7 1.3 1.1 0.9 5.4 3.1 3.6

2000–2030 0.1 1.2 0.2 0.5 1.3 2.5 2.3

(projected)

Percentage Urban

1950 51 64 35 53 13 17 18

1975 66 74 57 67 17 21 27

2000 73 79 65 74 36 28 41

2030 (projected) 80 87 73 82 61 41 57

Change 2000–2030 7 8 8 8 25 13 16

aNorthern America = Bermuda, Canada, Greenland, Saint-Pierre-et-Miquelon, and United States.

Source: UN 2003, Tables A.2, A.3, and A.6. (Reprinted with permission of the United Nations Population Division.)

people talk about eliminating “unnecessary” travel or “unlinking” economic growth from transport activity, they generally are referring to the

deliberate alteration of urban areas’ spatial organization to influence the

total volume of personal and goods transport activity, the choice of modes

by which the demand for that activity is fulfilled, and the capacity utilization rates (i.e., load factors) of the vehicles being used.

How the Spatial Organization of Urban Areas Affects and Is Affected by

Transport Activity and Modal Availability Throughout history, the size

and shape of cities have been constrained by the ability of their transport

systems to supply them with food and raw materials, to enable their residents to congregate in numbers sufficient to convert these raw materials
into finished goods efficiently and to conduct other business requiring

face-to-face interaction, and to transport their finished goods to distant

markets. The development of inexpensive waterborne transportation

eased the first and third of these constraints. But cities were still severely

limited in size by their ability to move people from their homes to work

and back on a daily basis.

Until roughly the middle of the 19th century, the area of a city like

London was constrained by the distance people could walk from home to

work.18 The development of railways linking the suburbs and the central

business district (CBD), together with the development of means of moving masses of people underground within the CBD, enabled Londoners

and residents of other major cities to live much greater distances from

their work. However, the availability of these modes of high-speed public transport did not necessarily change the need for people’s activities

other than commuting to be located within a relatively short distance of

where they lived.

Only when automobile availability became widespread did the location

constraints on these other activities ease. Indeed, noncommute activities

now account for the majority of personal trips and miles traveled in most

high-income countries. Table B-4 illustrates this point for the United States

with data from the 2001 National Personal Transportation Survey.

The spatial organization of urban activity also affects and is affected

by goods transport. Before the advent of the automobile and the truck,

nearly all large cities had a single, relatively compact CBD where a large

share of the city’s employment was concentrated. (In the terminology

used by urban planners, these cities were “monocentric.”) The location of

the CBD was usually determined by its proximity to waterborne (and

later to rail) transportation. The development of the motorized truck

freed CBDs from these constraints.

Thus, the widespread ownership of motorized road vehicles allowed

workers to both live and work almost anywhere they wished within a

metropolitan region. The resulting decline in average residential and

employment densities has undermined the viability of public transport,

224 Potential Impacts of Climate Change on U.S. Transportation

18 Indeed, the first traffic count of people entering the 1 square mile City of London between 8 a.m.

and 8 p.m. (1854) found that horse-drawn omnibuses were the means by which the largest number

of people (44,000) were transported into town; 31,000 arrived by train; and 26,000 entered by

using private carriages or hackney cabs. But all these modes of transport were dwarfed by the

200,000 who walked.
especially rail-based public transport. Only cities that have managed to

maintain strong CBDs and that developed high-speed public transport

systems before the automobile came to dominate personal travel have

managed to keep the share of commuting travel by private car relatively

low.19 And this is only true for workers traveling to work in the CBD;

those with jobs outside the CBD generally commute to work by car.

Magnitude of the Impact of the Spatial Organization of Urban Areas on

Transport Activity and Modal Choice Studies have demonstrated a statistically significant relationship between the spatial organization of urban

areas and the volume of personal travel activity. But just how quantitatively

significant is this relationship? Two recent U.S. studies provide information

on this question. A Transportation Research Board policy study is also

under way that is examining the relationships among development patterns, vehicle miles traveled (VMT), and the energy conservation benefits

of denser development patterns.

Ewing et al. (2002) ranked 83 U.S. cities in terms of a “sprawl index”

composed of four components: residential density; the neighborhood mix

of homes, jobs, and services; the strength of activity centers and downtowns; and the accessibility of street networks. They compiled information

on the rate of vehicle ownership, the share of commuters taking transit to

work, the share of commuters walking to work, the average commute time,

Contribution to Emissions and Assessment of Strategies 225

TABLE B-4 Characteristics of U.S. “Daily” or “Short Distance” 

Personal Travel, 2001

Trips Kilometers

Annual travel (per capita) 1,481 24,459

Purpose of travel

Commuting/business 18% 26%

School, church 10% 6%

Shopping 19% 13%

Family, personal business, escort 25% 20%

Social/recreational, vacation, visiting friends, and other 28% 35%

Source: CRA International compilation from the 2001 National Household Travel Survey (BTS 2001).

19 The share of commuters working in Manhattan who drive to work is just over 10 percent. The

data for commuters working in central London are similar.
and the vehicle miles traveled per household per day for each of these cities.

Table B-5 shows the average of these transport indicators and the average

sprawl index20 for the 10 “most sprawling” and the 10 “least sprawling”

cities. The latter category excludes two clear outliers—New York City and

Jersey City21—which are shown separately in Table B-5.

The range in the researchers’ sprawl index between these two groups of

cities—73.43—is almost three standard deviations. Over this range, there

is an 11 percent difference in the number of cars per hundred households

(180 versus 162) and a 29 percent difference in the number of VMT per

household per day (70.18 versus 54.45). For both groups of cities, the share

of commuters taking public transit to work averages below 10 percent, and

the share of commuters walking to work averages less than 5 percent. The

average daily one-way commute time in both groups of cities is identical—

26 minutes.

226 Potential Impacts of Climate Change on U.S. Transportation

TABLE B-5 How Personal Transportation Demand Is Influenced by Urban Form

Vehicle Miles 

Sprawl Vehicles Transit to Walk to Commute Traveled per 

MSA/PMSA Name Index per 100 HH Work (%) Work (%) Time (min) HH (mi/day)

Average—10 most 58.86 180 2.1 1.92 26 70.18

sprawling

Average—10 least 132.29 162 7.0 3.56 26 54.45

sprawling (excluding 

outliers)

Difference—10 most 73.43 −18 4.9 1.64 0 −15.73

sprawling and 

10 least sprawling 

(excluding outliers)

Excluding outliers

Jersey City, N.J. PMSA 162.27 93 34.2 8.71 33 N/A

New York, N.Y. PMSA 177.78 74 48.5 9.61 39 40.19

Note: HH = household; MSA = metropolitan statistical area; PMSA = primary metropolitan statistical area.

Source: Derived from Ewing et al. 2002, Appendix 3.

20 The sprawl index is scaled so that 25 units is equal to one standard deviation. The index ranges

in value from 14.22 to 177.78, with a lower value indicating greater sprawl.

21 The New York City region (which includes Jersey City) accounts for approximately 40 percent of

all U.S. public transport trips.
The second study, conducted by Bento et al. (2005), covered 114 U.S.

urban areas. Instead of developing a sprawl index, these researchers used

the actual values of different variables that they believe reflect the spatial

organization of these urban areas. They used these characteristics, plus

other control variables, to predict the average VMT per household, the

average probability of driving to work by workers, and the average annual

commute miles for the “average U.S. household” if it resided in each

urban area. Table B-6 shows these predicted values for six U.S. urban

areas: Atlanta, Boston, Chicago, Houston, New York, and San Diego. The

difference in predicted average annual VMT per household between

Atlanta and Boston (the latter being the “most compact” urban area other

than New York City) is 25 percent (16,899 versus 12,704 VMT). The predicted average probability of driving to work by workers does not fall

below 70 percent for any city except New York City. The average number

of commute miles driven per year ranges between 4,500 and 5,600 miles.

The differences in transport activity and modal choice among U.S.

urban areas reported in the above two studies are not trivial, but they

need to be placed in perspective. Cities change slowly, and their changes

are heavily path dependent. Transforming a city with the spatial organization of Atlanta into one with the spatial organization of Boston would

be a tremendous task requiring many decades, if it could be accomplished at all. Making marginal changes over time might be practical, but

even this would not be easy. Moreover, marginal changes are likely to

yield only marginal results.

Impact of Telecommuting and the Internet on Travel Demand Some

have argued that the development of telecommuting and the Internet

could reduce travel demand significantly. This does not appear to be happening. Mokhtarian (2003) summarizes the evidence as follows:

Overall, substitution, complementarity, modification, and neutrality

within and across transportation modes are all happening simultaneously. The net outcome of these partially counteracting effects, if

current trends continue, is likely to be faster growth in telecommunications than in travel, resulting in an increasing share of interactions

falling to telecommunications, but with continued growth in travel in

absolute terms. The empirical evidence to date is quite limited in its

ability to assess the extent of true causality between telecommunications and travel, and more research is needed in that area. At this

point, what we can say with confidence is that the empirical evidence

Contribution to Emissions and Assessment of Strategies 227
TABLE B-6 How Transport Demand Is Influenced by Urban Form

Characteristic Minimuma Maximuma Atlanta Boston Chicago Houston New York San Diego

Lane density (area of roads per 100 square 1.6 10.6 3.9 4.3 4.7 5.2 5.3 4.2

miles of land)

Land area (km2) 135 7,683 2,944 2,308 4,104 3,049 7,683 1,788

Population 158,553 16,044,012 2,157,806 2,775,370 6,792,087 2,901,851 16,044,012 2,348,417Density (people/km2) 446 2,240 733 1,202 1,655 952 2,088 1,314

Rail transit supply (10,000 mi/km2) 0 5.7 0.7 1.8 1.9 0.0 5.7 0.2

Nonrail transit supply (10,000 mi/km2) 0.1 4.3 1.0 1.3 2.8 1.4 3.0 1.6

Jobs–housing balance (standardized) 0.12 0.58 0.44 0.28 0.35 0.44 0.41 0.58Population centrality (standardized) 0.11 0.22 0.11 0.17 0.15 0.13 0.20 0.20City shape 0.04 0.99 0.26 0.82 0.48 0.80 0.73 0.36Predicted average vehicle miles traveled 16,899 12,704 14,408 15,685 9,453 16,493

per household

Predicted average probability of driving to 0.87 0.73 0.74 0.90 0.40 0.84

work by workers

Predicted average commute miles driven 5,450 4,565 4,620 5,641 2,496 5,247aRefers to sample of 114 urban areas.Source: Bento et al. 2005, p. 477. (Copyright 2005 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology. Reprinted with the permission of the MIT

Press Journals.)
Contribution to Emissions and Assessment of Strategies

for net complementarity is substantial, although not definitive, and

the empirical evidence for net substitution appears to be virtually

nonexistent. (p. 43)

However, she issues the following caution:

The caveat, “if current trends continue,” is a nontrivial one. My

expectations for the future are largely predicated on the assumption

that the real price of travel will continue to decline or at least remain

relatively stable. Should the price of travel escalate markedly . . .

the substitutability of telecommunications will obviously become

more attractive. Shifts towards telecommunications substitution may

also occur for reasons such as an increasing societal commitment

to more environmentally benign or sustainable communications

modes, but experience suggests that such impacts will be modest

at best. (p. 54)

Personal and Goods Transport Demand: Summary

Growth in personal and goods transport demand is the most important

single factor driving the increase in transport-related GHG emissions. This

growth is being propelled by growth in real GDP per capita, by population

growth, by urbanization, and by the spatial organization of urban areas

(urban form). The latter factor is also causing shifts in modal use (public

transport to LDVs for personal transport and rail to truck for goods transport) that likewise serve to boost transport-related GHG emissions.

The correlation between economic growth and increased transport

demand has proved to be very robust, but it is not immutable. Reducing

it would be a slow process that would require substantial changes in

almost every aspect of people’s lives. This does not mean that efforts to

induce change should not be made; it does mean that such efforts would

not likely bear immediate fruit.

Reducing Vehicle Energy Consumption 

per Unit of Transport Activity (I)

Hundreds (if not thousands) of studies describe and analyze the potential of various technologies to reduce the fuel consumption of transport

vehicles. Most of these studies focus on personal vehicles—by far the

most numerous road vehicles. The majority of the studies also give the

229
greatest attention to improvements in power train technologies. No

attempt is made here to provide an encyclopedic account of the results

presented in this vast body of material. Rather, the discussion is confined

to broad categories of technologies. Addressed in turn are technologies

with the potential to reduce the fuel consumption of road vehicles, those

with the potential to reduce the fuel consumption of nonroad vehicles,

factors influencing the extent to which the potential of a technology to

reduce transport-related GHG emissions is realized, and the impact of

vehicle capacity utilization (load factor) on energy use.

Technologies with the Potential to Reduce the Fuel Consumption 

of Road Vehicles22

Road vehicles (automobiles, trucks of all sizes, buses, and powered twoand three-wheelers) account for 76 percent of all transport energy use

worldwide and for 82 percent of U.S. transport energy use. LDVs (cars,

light trucks, and powered two- and three-wheelers) account for the lion’s

share of this total—46 percent worldwide and 62 percent for the United

States. Most of the remainder—24 percent worldwide and 20 percent for

the United States—is accounted for by medium and heavy freight trucks.

Engine Technologies Road vehicles utilize one of two fundamental

engine technologies—spark ignition or compression ignition. Other technologies, such as gas turbines, have been tried, but have proved

unsatisfactory for powering road vehicles. There are, however, a very limited number of vehicles powered solely by electric batteries.

Spark-Ignition Internal Combustion Engines Most spark-ignition engines

in use today are fueled by petroleum gasoline, but they also can run on synthetic gasoline derived from gas-to-liquid processes, on ethanol (or blends

of gasoline and ethanol), on compressed natural gas, on liquefied petroleum gases, or on hydrogen.

In the intake system of spark-ignition engines, air is mixed with small

amounts of fuel. In the past, this process was carried out in the carburetor, where the fuel was drawn into the airflow mechanically. To meet

more stringent emissions requirements, the carburetor has been replaced

in nearly all engines by port-injection systems or direct-injection systems. The latter are particularly effective in reducing fuel consumption

230 Potential Impacts of Climate Change on U.S. Transportation

22 The material in this section is an edited version of IEA 2006, Chapter 5.
and CO2 emissions; this is especially true for several combustion technologies now in development, such as lean-burn technologies.23

Conventional engine architectures use valves activated mechanically

by one or more camshafts to control the gas flow into the combustion

chamber and the expulsion of the exhaust gases. Variable valve control is

an advanced system that allows better management of valve timing and

substantially reduces the need for the throttle plates in gasoline engines.

Some mechanical systems for valve timing have already been introduced.

Other systems, based on electromagnetic or electrohydraulic actuation

technologies, are currently being developed. Variable valve control can

also enable modular use of the engine, completely obviating the need for

some of the cylinders when little engine power is required. This solution

diminishes fuel consumption even further and has already been introduced in some large cars.

Controlled auto ignition (CAI) is another new combustion process

being actively explored to improve fuel economy and lower the exhaust

emissions of spark-ignition internal combustion engines. CAI engines

use a highly diluted mixture of fuel, air, and residual gases that can autoignite in a four-stroke engine without preheating of the intake air or an

increase in the compression ratio.

Technologies that reduce or eliminate pumping losses and throttled

operations, combined with turbochargers and technologies that help contain knock, can result in significant reductions in engine size, also allowing

substantial fuel economy improvements and reductions in CO2 emissions.

Many in the automotive industry believe engine downsizing—including

the use of turbochargers—can reduce engine displacement size by up to

30 percent. Downsizing the engine also has a positive effect on the whole

vehicle design, reducing vehicle inertia and therefore engine load.

Almost all recent-model vehicles equipped with a spark-ignition

engine are fully capable with low-level ethanol fuel blends, such as E5 or

E10 (5 percent and 10 percent ethanol blends, respectively). To use blends

of more than 10 percent ethanol, some engine modifications may be necessary because of ethanol’s low compatibility with certain materials and

elastomer components. Using compatible materials would eliminate

Contribution to Emissions and Assessment of Strategies 231

23 A lean-burn engine is designed to operate with a very high air-to-fuel ratio under light-load

conditions. When little power is required, lower amounts of fuel are injected into the combustion

chamber, only in the area around the spark. This reduces the need for throttling and limits NOx.
these problems, and the use of such materials is already common in some

countries, such as the United States and Brazil. The cost of making vehicles fully compatible with E10 is negligible, and the cost remains very low

for full compatibility with E85 (an 85 percent ethanol fuel blend.)

If engines were designed exclusively for pure ethanol or ethanol-rich

blends, their costs would be roughly the same as today, but their fuel

economy (expressed in liters of gasoline equivalent per 100 km) would be

better than that of engines designed for conventional gasoline with the

same performance.24 Similar effects would be seen in CO2 tailpipe emissions. These improvements are possible because the high octane number

of ethanol-rich blends, along with the cooling effect from ethanol’s high

latent heat of vaporization, would allow higher compression ratios in

engines designed for ethanol-rich blends, especially those using the most

advanced injection systems available, such as direct-injection systems.

Technologies such as direct injection and turbochargers that could lead

to downsizing of spark-ignition engines also favor the introduction of

ethanol as a transportation fuel.

Compression-Ignition Engines Compression-ignition engines (commonly

known as diesel engines) are similar to four-stroke spark-ignition engines,

with a few essential differences. One difference is that they do not need to

be controlled by a throttle. Instead, the power output is controlled by the

amount of fuel injected into the cylinder, without airflow limitation. This

characteristic reduces the pumping losses that occur in the aspiration phase

in spark-ignition engines. Diesel engines do not need spark plugs. The airfuel mixture used in these engines self-ignites when the fuel is injected into

the combustion chamber. As a result, diesel engines can run lean and reach

much higher compression ratios than conventional spark-ignition engines.

Diesel indirect-injection engines (the conventional injection technology used in compression-ignition engines until a few years ago) were

characterized by fuel delivery in a prechamber designed to ensure proper

mixing of the atomized fuel with the compression-heated air. Precise

control of fuel delivery was not easy to achieve in these systems. In recent

years, indirect-injection systems have been replaced by common-rail sys232 Potential Impacts of Climate Change on U.S. Transportation

24 According to the Transportation Energy Data Book, 25th edition (Davis and Diegel 2006, B-3),

the combustion of a gallon of ethanol produces only about two-thirds the heat of a gallon of

gasoline (75,670 Btu versus 115,600 Btu). This means a gallon of “gasoline equivalent” ethanol

consists of about 1.5 gallons of actual ethanol.
tems. These systems still use a pump to store fuel at very high pressure in

a reservoir (the common rail), which is connected to the combustion

chamber by fuel injectors. Rail systems permit the activation of the injectors rather than the pump, eliminating the buildup of pressure before

each individual injection. This makes it possible to control very precisely

the amount of fuel injected and the timing of each injection, thereby

maximizing performance and optimizing fuel use.

The fact that diesel engines can work with higher compression ratios

than gasoline engines and without a throttle favors the use of intake-air

compressors, usually in the form of turbochargers. Such compressors are

generally coupled with intercoolers and aftercoolers to increase the density of the air entering the combustion chamber. Turbocharged diesel

engines, working with common rail and direct injection, are now an established technology. They equip most of the light-duty diesel vehicles sold

in Europe and virtually all new heavy-duty trucks sold around the world.25

Two important barriers to the increased use of diesel engines have

been their relatively high emissions of particulate matter and NOx. A

modern exhaust system for diesel engines includes a two-way oxidation

catalyst and, in the most recent versions, a particulate filter.26 The two-way

oxidation catalyst is similar to the catalytic converter used in gasolinefueled cars. It converts unburned hydrocarbons and CO into CO2 and

water. These converters are not as effective as those used in gasoline-fueled

vehicles. On the other hand, CO and hydrocarbon emissions from compression-ignition engines are inherently low because of the leaner fuel

mixture. Oxidation catalysts reduce particulate mass by as much as 50 percent. The problem of ultrafine particulates, one of the most dangerous

emissions in terms of health effects, remains unresolved at this point.

The aftertreatment of NOx emissions in diesel engines presents a difficult technical challenge because of the oxygen-rich state of the exhaust

under lean conditions. The formation of NOx can be reduced by using

cooled intake-air compression (whereby an intercooler and aftercooler

lower the temperature of the air-to-fuel mix in the cylinder) and by exhaust

Contribution to Emissions and Assessment of Strategies 233

25 Variable valve control, already described for gasoline engines, also offers improvements in diesel

engines, although its ability to reduce fuel consumption is lower for compression-ignition engines

than for spark-ignition engines because the latter suffer from higher pumping losses.

26 A diesel particulate filter may take the form of a ceramic honeycomb monolith. It may also consist

of sintered metal, foamed metal structures, fiber mats, or other materials. It removes particulate from

the diesel exhaust by physical filtration, capturing the particulate matter on its walls.
gas recirculation. Research in the field of aftertreatment systems continues,

including efforts to integrate NOx reduction with particulate filters.

Hybrid Vehicles The term “hybrid” refers to any vehicle that can use different energy sources in combination. Currently, the term usually refers

to hybrid-electric vehicles,27 which are powered by a drivetrain that combines a conventional internal combustion engine (powered by gasoline,

diesel, or an alternative fuel) and an electric motor. Hybrid-electric vehicles can be built in a range of engine architectures with varying sizes for

the combustion engine and electric motor, each of which involves different trade-offs in terms of cost, efficiency, and performance.

In series hybrids, an electric motor drives the wheels and derives its

energy from a battery or an engine, generally an internal-combustion

engine, used as a power generator.28 The power generator supplies the average power required to operate the vehicle and accessories, while a battery

stores the excess energy and provides it when needed. Like electric vehicles,

series hybrids may use regenerative braking to recharge the battery. A further efficiency gain is achieved by the fact that the engine is largely

uncoupled from the load because of road conditions and can be kept working at a range of operating points where its efficiency is high. This type of

engine use offers advantages for the aftertreatment of exhaust gases.

In parallel hybrids, motion is delivered to the wheels by both an internal

combustion engine and an electric motor. The internal combustion engine

is no longer used exclusively as a power plant, but works jointly with the

electric motor to deliver movement to the vehicle. “Mild” parallel hybrids

have an electric motor that acts as a starter and can serve as an alternator

during braking (regenerative braking), while an internal combustion engine

powers the drivetrain. In mild hybrid configurations, the electric motor may

also provide extra torque and extra power when needed. The electric motor

used in mild hybrids is usually located between the engine and the transmission or, in “light” designs, in the same position as a standard alternator.

Full hybrids can operate in internal-combustion mode, in hybrid

mode, or even in all-electric mode, the latter being used mainly for cold

starts and for urban driving at ranges below 50 km. The electric energy is

stored in large batteries during the periods of internal combustion engine

234 Potential Impacts of Climate Change on U.S. Transportation

27 There are hybrid vehicles that use hydraulic fluid rather than batteries as a power “accumulator.”

28Diesel-electric railroad locomotives are series hybrids. Their diesel engine drives a generator that

provides power to electric traction motors.
driving and regenerative braking. In some cases, electricity is stored by

charging the battery from the grid (plug-in hybrids).

Hybrid drivetrains are a promising technology not only for LDVs but

also for heavy- and medium-duty vehicles that operate locally and for

urban buses. Hybrid solutions are not particularly suitable for heavyduty trucks and intercity buses because the driving cycle of those vehicles

is characterized by long driving periods at steady speeds.

The main barrier to greater market penetration of hybrid vehicles is

their cost, which is still higher than that of competing vehicles, notably

diesel. In their most advanced configurations, diesel vehicles offer fuel

economies not far behind those of hybrids. Reducing the cost, weight,

and size of batteries is the greatest technology challenge facing hybrid

development.

Diesel hybrids achieve smaller reductions in fuel consumption relative to hybrids that incorporate gasoline engines; nevertheless, full diesel

hybrids may be the most efficient vehicles in the long run. Diesel hybrid

engines will be best suited to urban buses and medium freight trucks,

although further improvements in battery technology are needed for this

type of application.

Table B-7 shows estimates of CO2 emissions from new midsized U.S.

passenger cars equipped with the above engine technologies identified

during the three time intervals 2003–2015, 2015–2030, and 2030–2050.

On the basis of a 2003–2015 gasoline internal combustion engine vehicle

equal to 100, Table B-8 shows an index of the emissions from each engine

type during each of the three periods.

Fuel Cell Vehicles A fuel cell is an electrochemical device that converts

hydrogen and oxygen into water and produces electricity in the process.

Fuel cell vehicles are propelled by electric motors, with electricity produced within the vehicle.

Proton-exchange-membrane (PEM) fuel cells are particularly suited

to powering passenger cars and buses because of their fast start-up time,

favorable power density, and high power-to-weight ratio. Fueled with

pure hydrogen from storage tanks or onboard reformers, PEM fuel cells

use a solid polymer as an electrolyte and porous carbon electrodes with a

platinum catalyst. They operate at relatively low temperatures of around

80°C. This has the advantage of allowing the fuel cell to start quickly, but

cooling of the cell is required to prevent overheating. The platinum catalyst is costly and extremely sensitive to CO poisoning. Research efforts are

Contribution to Emissions and Assessment of Strategies 235
TABLE B-7 Tailpipe CO2 Emissions for Midsized U.S. Passenger Cars 

Using Different Engine Technologies (g/km)

Time Period

Engine Technology 2003–2015 2015–2030 2030–2050

Spark ignition

Gasoline ICEa 130–234 122–219 114–204

Dedicated ethanol ICEb 120–215 112–200 103–185

Flexible fuel vehicle ICEc 133–239 125–224 116–209

Light hybrid, gasoline ICEd 119–214 111–199 103–185

Mild hybrid, gasoline ICEd 108–194 99–178 94–168

Full hybrid, gasoline ICEd 99–178 94–169 89–160

Compression ignition

Diesel ICEe 108–193 105–188 102–183

Light hybrid, diesel ICEf 96–173 94–168 91–163

Mild hybrid, diesel ICEf 87–155 83–149 80–143

Full hybrid, diesel ICEf 83–148 80–143 77–138

Note: These estimates refer to a midsized vehicle and assume that roughly half of the potential improvements due to

advanced vehicle technologies will improve vehicle fuel economy. (In the case of hybrids, this share rises to 100 percent,

but hybrid power trains could also be used to increase performance rather than fuel economy.) The estimates also assume

that considerable learning and optimization will occur between 2010 and 2050, in addition to large-scale production of the

vehicles. Footnotes below indicate assumptions concerning what technologies are introduced and when. ICE = internal

combustion engine.

a2003–2015: Conventional engine, stoichiometric combustion, increased use of variable valve control. 2015–2030:

Turbocharged engine with direct injection and variable valve control, engine downsizing. Progressive introduction of

advanced combustion technologies with NOx traps. 2030–2050: Downsized turbocharged engine with direct injection and

variable valve control using advanced combustion technologies (CAI) with NOx traps. b2003–2015: Conventional engine, stoichiometric combustion. 2015–2030: Turbocharged engine combustion with direct

injection and variable valve control. Progressive introduction of advanced combustion technologies needing NOx traps, progressive downsizing. 2030–2050: Turbocharged downsized engine with direct injection and variable valve control, using

advanced combustion technologies with NOx traps. c2003–2015: Conventional engine, stoichiometric combustion. 2015–2030: Ethanol-hybrid turbocharged engine with direct

injection and variable valve control, downsizing. Progressive introduction of advanced combustion technologies needing

NOx traps. 2030–2050: Downsized ethanol-hybrid turbocharged engine with direct injection and variable valve control

using advanced combustion technologies with NOx traps. d2003–2015: Wide introduction of starter-alternator systems, mild hybrid engines on some models, full hybrids mainly on

large LDVs. 2015–2030: Higher penetration of mild hybrids, even on small vehicles, wide diffusion of full hybrids on large

LDVs. Large hybrid shares for minibuses and medium freight trucks. ICE improved in light hybrids, slightly less for mild

and full hybrids. 2030–2050: A large share of ICE vehicles sold on the market equipped with hybrid systems. ICE improved

in light hybrids, slightly less so for mild and full hybrids.

e2003–2015: Second-generation common rail, progressive downsizing. 2015–2030: Turbocharged downsized engine, variable valve control, possibly heat recovery, particulate filter and NOx trap (or selective catalytic reduction systems, especially

on large engines). 2030–2050: Turbocharged downsized engine, variable valve control, and possibly heat recovery.

Particulate filter and NOx trap (or selective catalytic reduction systems, especially on large engines). f

2003–2015: Introduction of starter-alternator systems; hybrid motorizations on large LDVs; initial diffusion of hybrids in

buses, minibuses, and freight trucks. 2015–2030: Penetration of mild hybrids on small vehicles, wider diffusion of full hybrids

on large vehicles. Larger shares of hybrid buses, minibuses, freight trucks. ICE improved as for diesel engines in light hybrids,

slightly less so for mild and full hybrids. 2030–2050: Further cost reductions leading to large shares of new vehicles equipped

with hybrid systems. ICE improved as for diesel engines in light hybrids, slightly less so for mild and full hybrids.

Source: IEA 2006, Chapter 5, material taken from Table 5.2, p. 297; Tables 5.3–5.4, pp. 300–301; Table 5.5, p. 309; and

Tables 5.6–5-7, pp. 318–319. Reprinted with permission of OECD/IEA.
Contribution to Emissions and Assessment of Strategies 237

TABLE B-8 Index of CO2 Emissions from a Midsized New U.S.

Passenger Car Powered by Engine Type Shown During Period

Indicated (g/km; 2003–2015 Gasoline-Powered ICE = 100)

Time Period

Engine Technology 2003–2015 2015–2030 2030–2050

Spark ignition

Gasoline ICE 100 94 88

Dedicated ethanol ICE 92 86 79

Flexible fuel vehicle ICE 102 96 89

Light hybrid, gasoline ICE 92 85 79

Mild hybrid, gasoline ICE 83 76 72

Full hybrid, gasoline ICE 76 72 68

Compression ignition

Diesel ICE 83 81 78

Light hybrid, diesel ICE 74 72 70

Mild hybrid, diesel ICE 67 64 62

Full hybrid, diesel ICE 64 62 59

Note: ICE = internal combustion engine.

Source: Derived from Table B-7.

focusing on high-temperature membranes that would allow the use of

lower-cost and more robust catalyst systems.

The current cost of PEM fuel cells exceeds $2,000 per kilowatt (kW),

but costs could be cut to as low as $100 per kW through mass production

and experience with the technology. This reduction in cost might not be

sufficient, however. It is believed that the cost of fuel cells must fall to

below $50 per kW to make them competitive. Achieving this cost reduction would require fundamental advances in materials technology and

the achievement of higher power densities for fuel cells.

Onboard fuel storage is a major challenge. Existing onboard storage

options do not yet meet the technical and economic requirements for

making them competitive. Safety is also believed to be an issue. Gaseous

storage at 350 to 700 bar29 and liquid storage at −253°C are commercially

29 A bar is a unit of pressure. It is equivalent to 14.5 pounds per square inch (psi). Atmospheric

pressure is 14.7 psi. So 350 to 700 bar would be approximately equal to 350 to 700 times

atmospheric pressure, or 5,000 to 10,000 psi.
available but are very costly. Solid storage (for example, using hydrides)

offers potentially decisive advantages but is still under development, with

a number of materials being investigated.

At present, in the absence of further breakthroughs, gaseous storage

at 700 bar appears to be the technology of choice for passenger cars.

However, the cost of the tank is $600 to $800 per kilogram (kg) of hydrogen (H2), and 5 kg of storage capacity is needed to provide adequate

range for the vehicle.

Depending on the pace of technological development, the stack cost

of a PEM fuel cell could decline to $35 to 70 per kW by 2030. If this were

to happen, the cost of a fuel cell vehicle at that time would exceed that of

a conventional internal combustion engine vehicle by $2,200 to $7,600.

Determining CO2 emissions from hydrogen-powered fuel cell vehicles

is not straightforward. The fuel cells themselves do not produce any CO2

emissions. However, as discussed below, the processes used to produce the

hydrogen fuel can emit large quantities of CO2, making the “well-towheels” emissions from such vehicles comparable with (and sometimes

even higher than) those from conventional gasoline or diesel internal

combustion engines.

Nonengine Technologies While reductions in engine energy use attract

by far the most attention, other important technologies have the potential to reduce the amount of energy required to propel a vehicle.

Transmission Technologies Engines have ideal ranges of speed at which

they can operate. Operating outside these ranges increases fuel consumption and engine wear. A vehicle’s transmission allows its engine to

operate more closely to its ideal speed while permitting its driving wheels

to operate at the speed the driver chooses.

Transmissions use gears to reduce the speed of the engine to the speed

of the wheels. The larger the number of gears, the more likely it is that the

engine will be able to operate at its ideal speed across a wide range of

vehicle speeds and power requirements. But more gears mean more complexity and more internal friction.

Until the 1970s, most LDVs in the United States had three forward

gears—low, medium, and high. When fuel prices increased substantially

in the late 1970s and early 1980s, vehicles generally added a fourth gear,

sometimes called “overdrive.” More recently, transmissions have added

electronic controls and additional speeds. Today, transmissions with six

238 Potential Impacts of Climate Change on U.S. Transportation
forward speeds are being introduced, and seven-speed transmissions are

not unheard of.

Some vehicles are now equipped with a continuously variable transmission (CVT). CVTs use a system of belts and adjustable-diameter

pulleys to permit an infinite number of forward gear ratios. The engine

operates at a near-constant speed while the transmission adjusts continually to produce the speed required for the wheels. CVTs have not yet

achieved the power-handling capability to be used on the full range of

LDV sizes and weights. Also, they have suffered from reliability problems.

However, their use has been forecast to increase in the years ahead.

Technologies to Reduce Vehicle Weight The lighter a vehicle, the less fuel

it consumes. Vehicle mass can be reduced either by decreasing the size of

the vehicle or by changing the materials from which it is made. Lighter

cars can be propelled by lighter engines. A light power train, in turn,

requires less structural support and allows further reductions in the

weight of the vehicle frame, suspension, and brakes.

Steel is currently the main automotive material. Over the past decade,

steel made up an average of 55 percent of the weight of a fully fueled car

without cargo or passengers. Most of the remaining weight is accounted

for by iron (10 percent), aluminum (6 to 10 percent), and plastics. Cost

and the eventual need for large investments to modify the vehicle production process are the main barriers to the increased use of lightweight

materials. High-strength steel can cost as much as 50 percent more than

traditional steels, but less of the material is needed to achieve the same

performance.30 Lighter materials such as aluminum and magnesium cost

more than conventional mild steel, but their greater use could lead to

improved manufacturing processes, thereby reducing manufacturing

costs. Composite materials have extremely attractive properties but cost

a great deal more than metals.

Another source of weight reduction is the replacement of mechanical

or hydraulic systems by electrical or electronic systems. Steering can be

accomplished by electric motors actuated by joysticks rather than by

mechanical linkages between the steering wheel and the wheels of the car.

Contribution to Emissions and Assessment of Strategies 239

30 The type of steel used in vehicles has been changing. In 1977, 60 percent of the weight of the

average U.S. domestic car consisted of steel, 90 percent of which was conventional steel—including

cold-rolled and precoated steel. By 2003, the total steel share had fallen to 54 percent, with only

75 percent of that total consisting of conventional steel. During both years, the remainder is

accounted for by high-strength steel, stainless steel, and other steels.
This is known as “steering by wire.”“Braking by wire” also has been developed, as has “shifting by wire” and “throttle by wire.”

Lightweight technologies are being introduced progressively and will

continue to be developed.

Tire Technologies The energy requirements of the power train can be

reduced through the use of energy-efficient tires. For an LDV, fuel consumption can be reduced by 3 to 4 percent through the use of currently

available low-rolling-resistance tires. An additional reduction of 1 to 2 percent in fuel consumption can be achieved by accurately monitoring tire

pressure. Currently available technologies can automatically sense low

pressure and inform the driver.

Technologies to Improve Vehicle Aerodynamics Aerodynamic drag, which

is proportional to the square of a vehicle’s speed, is the main factor determining a vehicle’s need for power at high speeds. At this time, aerodynamic

issues affect most seriously long-haulage heavy-duty trucks and intercity

buses, and significant improvements are possible for such vehicles. At highway speeds, aerodynamic losses are estimated to account for 21 percent of

the energy use of a heavy-duty truck–trailer combination unit.

Technologies to Reduce the Energy Requirements of Onboard Equipment

The energy consumption of air conditioners and other onboard appliances

can account for up to half of a vehicle’s fuel consumption under certain conditions. A number of efforts are under way to reduce the energy used by

these devices. A particular focus has been on reducing the energy required

to operate a vehicle’s air conditioning system. Installation rates for air conditioners, already approaching 100 percent in both North America and the

OECD Pacific region, are growing rapidly in Europe. Fewer than 15 percent of LDVs sold in France in 1995 were equipped with air conditioning.

By 2000, that rate had risen to 60 percent, and it is expected to reach nearly

100 percent by 2010.

A significant barrier to greater market penetration of energy-efficient

onboard components is the fact that the energy consumed by these appliances is not always captured in current vehicle tests.31 This reduces the

incentive for manufacturers to use such devices. The public is largely

unaware of the fuel use of onboard appliances and the cost entailed: 1 kW240 Potential Impacts of Climate Change on U.S. Transportation

31We understand that this is not the case for the United States.
hour (kWh) of electricity generated on board costs just slightly less than 

1 liter of gasoline, exceeding by far the cost of electricity generated in central power plants.

Technologies with the Potential to Reduce Fuel Consumption by Nonroad

Vehicles While LDVs are, in the aggregate, the largest consumers of transport fuel and emitters of GHGs, vehicles such as medium and heavy

trucks, commercial aircraft, locomotives, and large waterborne vessels

actually use much more energy per vehicle each year. In 2003, the average

U.S. passenger car traveled about 12,000 miles and used about 550 gallons

of fuel. The average combination truck (i.e., a tractor unit with one or

more trailers) traveled about 62,000 miles and used about 12,000 gallons

of fuel. The average commercial aircraft traveled about 900,000 miles and

used about 2.3 million gallons of fuel.32 This appendix has already described

technologies applicable to medium and heavy freight trucks and to buses.

The discussion now turns to vehicles that do not travel on roads—aircraft,

waterborne vessels, and railroad locomotives.

Aircraft Commercial aircraft account for 12 percent of transport energy

use worldwide and 8 percent of that in the United States. Since the 1960s,

turbine engines fueled by a light petroleum product known as jet fuel have

powered virtually all new commercial aircraft. While the combustion

process of these turbine engines is quite efficient, the energy required to

lift an aircraft and its payload off the ground and propel it long distances

at high speeds is formidable. In fact, a large share of the payload transported by any aircraft is its own fuel. Not surprisingly, fuel usage and fuel

costs are therefore an extremely important component of the total operating cost of an air transport system, comparable in magnitude with crew

costs and ownership and investment costs.

In a review of historical and projected future trends in aircraft energy

use, Lee et al. (2001) analyze the relative contribution of different technological improvements and operational factors to reducing the energy

intensity of commercial aircraft during the period 1971–1998. As measured by megajoules per revenue passenger kilometer, this energy intensity

has declined by more than 60 percent—an average decline of about 3.3 percent a year.

Contribution to Emissions and Assessment of Strategies 241

32 These data were calculated from data provided in the Transportation Energy Data Book (Davis

and Diegel 2006) and National Transportation Statistics 2004 (BTS 2005).
Three technological factors—reduced specific fuel consumption, an

increase in aerodynamic efficiency, and improved structural efficiency—

have been responsible for much of this decline. Engine efficiency improved

by about 40 percent between 1959 and 1995, with most of the improvement being achieved before 1970 with the introduction of high-bypass

engines. Other factors include higher peak temperatures within the engine,

increased pressure ratios, and improved engine component efficiencies.

Aerodynamic efficiency has increased by approximately 15 percent historically, driven by better wing design and improved propulsion–airframe

integration. Improvements in structural efficiency have contributed less,

despite some improvements in the materials used to construct aircraft. As

has also been true for motor vehicles, reductions in aircraft weight produced by these improved materials have largely been traded off for other

technological improvements and passenger comfort.

Lee et al. (2001) project that over the next several decades, the energy

intensity of commercial aircraft will continue to decline, but at a slower

rate—1.2 to 2.2 percent per year, compared with the 3.3 percent average

annual decline experienced over the past several decades.

Waterborne Vessels Waterborne transport, including ocean shipping,

coastal shipping, and inland waterway transport, accounts for 10 percent of

transport energy use worldwide and for 4 percent of U.S. transport energy

use. (The U.S. figure includes recreational uses; the world figure does not.)

Almost all commercial vessels are powered by diesel engines. The

engines used in large oceangoing ships are the largest ever built. These

giant diesels can have up to 14 cylinders, each with a bore of 980 mm and

a stroke of 2,660 mm, giving the engine a displacement of nearly 1,000

liters. Most of these very large engines are classified as “slow speed.” That

is, they operate at about 100 revolutions per minute and are coupled

directly to the ship’s propeller, eliminating the need for reduction gears.

The diesel engines powering towboats or self-propelled barges on

inland waterways are much smaller—about the size of a large dieselelectric locomotive, though there may be more than one such engine.

Large towboats on U.S. inland waterways are rated at over 10,500 horsepower. Fuels used by waterborne transport vehicles are “heavy” grades of

diesel fuel and an even “heavier” petroleum product known as “residual

fuel oil.” Typically, these fuels are higher (often much higher) in sulfur

relative to other transport fuels.

242 Potential Impacts of Climate Change on U.S. Transportation
A report to the International Maritime Organization published in

March 2000 details the energy use and emissions characteristics of oceangoing vessels as of 1996 (IMO 2000). Table B-9 shows the emissions

estimated to result from the 138 million tonnes of distillate and residual

fuel consumed during that year by these ships. The same report identifies

and evaluates the impact of a range of technical and operational measures that could be applied to new and existing ships to reduce energy use

and CO2 emissions. Table B-10 summarizes the report’s findings concerning technical measures that might be applied.

Railroad Engines33 Railroad engines account for 3 percent of transport

energy use worldwide and for 2 percent of transport energy use in the

United States. Most railroad engines use electricity generated externally

or diesel fuel carried on board as their primary energy source. For the

world as a whole, 27 percent of energy used by railroads is externally generated electricity, 59 percent is diesel, and 12 percent is coal (virtually all

in China). Countries vary widely in the extent to which their railroads

rely on electric power. Railroads in Canada and the United States are

almost totally diesel powered. In Japan, 78 percent of the rail energy used

is electrical, and in Europe, 61 percent.34

Contribution to Emissions and Assessment of Strategies 243

33 The International Union of Railways conducted a project, Energy Efficiency Technology for

Railways, in which a range of technologies relating to railway energy efficiency including, but not

limited to, engine technologies were evaluated. The project can be accessed at www.railway-energy.

org/tfee/index.php.

34 The statistics in this paragraph were calculated from 2003 data provided by IEA.

TABLE B-9 Marine Emissions, 1996

Gas Component Range of Estimated Emissions (Mt)

Carbon monoxide 0.7–1.1

Nonmethane volatile organic compounds —

Methane —

Nitrous oxide —

Carbon dioxide 436–438

Sulfur dioxide, total 5.2–7.8

Generated by combustion of residual fuel oil 5.0–7.0

Generated by combustion of distillate 0.2–0.8

Nitrogen oxides 10.1–11.4

Source: IMO 2000, p. 11. (Reprinted with permission of IMO.)
244 Potential Impacts of Climate Change on U.S. Transportation

TABLE B-10 Marine CO2 Reductions by Technical Measure

Fuel/CO2 Savings 

Measure Potential (%) Subtotala (%) Totala (%)

New ships 5–30

Optimized hull shape 5–20 5–30

Choice of propeller 5–10

Efficiency optimized 10–12b 14–17b

2–5c 6–10c

Fuel (HFO to MDO) 4–5

Plant concepts 4–6 8–11

Fuel (HFO to MDO) 4–5

Machinery monitoring 0.5–1 0.5–1

Existing ships 4–20

Optimal hull maintenance 3–5 4–8

Propeller maintenance 1–3

Fuel injection 1–2 5–7

Fuel (HFO to MDO) 4–5

Efficiency rating 3–5 7–10

Fuel (HFO to MDO) 4–5

Efficiency rating + TC upgrade 5–7 9–12

Fuel (HFO to MDO) 4–5

Note: HFO = heavy fuel oil; MDO = marine diesel oil; TC = turbocharging.

a Potential for reduction from individual measures is documented by different sources; potential for

combinations of measures is based on estimates only. bState-of-the-art technique in new medium-speed engines running on HFO.

cSlow-speed engines when trade-off with NOx is acceptable.

Source: IMO 2000, p. 14. (Reprinted with permission of IMO.)

Recent years have seen major improvements in the efficiency of electric locomotives, brought about by the use of AC power. In the case of

diesel-powered locomotives, propulsion system developments have

focused primarily on improving the power, reliability, and efficiency of

the diesel engines used to generate onboard electric energy, as well as the

efficiency of the electric traction engines that deliver this energy to the

driving wheels. In addition, diesel locomotives have become subject to

emissions standards and, in some places, to noise standards.

Interest is growing in the use of fuel cells to provide auxiliary power for

diesel locomotives. This would permit the main diesel engine to be shut
down when the locomotive is not in use but still has power needs. Idle time

constitutes a surprisingly large share of the total time a diesel engine is in

operation. A recent study of locomotive duty cycles on Canadian railroads

found that engines were idling between 54 and 83 percent of the time.

Using either fuel cells as auxiliary power units or the “hybrid” approach

described above would permit engines to reduce the amount of idle time

substantially. Although fuel use and emissions are much greater when a

locomotive is operating at full power than when it is idling, the potential

improvements in both are nontrivial.

Factors Influencing the Extent to Which the Potential of a Technology

to Reduce Transport-Related Greenhouse Gas Emissions Is Realized

One of the most controversial issues in the debate over the use of new

technologies to reduce GHG emissions is how effective these technologies

will be when incorporated into actual transport vehicles in normal service. Invariably, ex post analyses of actual emissions reductions fall short

(sometimes considerably short) of their original claimed potential. The

discussion below reviews some of the more important factors that tend

to create this result.

Extent to Which a Technology’s Potential to Reduce Energy Consumption

Is Incorporated into the Vehicles in Which It Is Employed Most vehicle

technologies with the potential to reduce fuel consumption offer vehicle

designers a range of possibilities for how they may be used. Depending on

the decisions made by the designer, the share of this potential that is actually used to reduce fuel consumption can vary from zero to 100 percent.

The history of LDV fuel economy in the United States since the mid1980s provides a textbook example. The bottom line in Figure B-7 shows

the corporate average fuel economy (CAFE) of the new light vehicle fleet

as tested by EPA. New LDV CAFE rose sharply between 1979 and 1982,

increased slowly from 1983 through 1987, declined slowly from 1987

through 1994, and has remained nearly constant since.

This does not mean that vehicle technologies related to fuel consumption have failed to improve since the mid-1980s. EPA uses a measure

known as ton-miles per gallon as an (imperfect) reflection of changes in

the energy efficiency potential of the technologies actually incorporated

into vehicles. The top line of Figure B-7 tracks this indicator. It has grown

relatively steadily at a rate of about 1 to 2 percent per year throughout the

Contribution to Emissions and Assessment of Strategies 245
period, reflecting the new technologies that have been introduced and disseminated throughout the new vehicle fleet.

What explains the sharp contrast between the two lines in Figure B-7?

The brief answer is that for much of the period, most of the fuel economy

improvement potential has been used by vehicle designers to improve

vehicle performance, not fuel economy. Figures B-8a and B-8b show,

respectively, the evolution of passenger car and light truck acceleration

performance (measured as 0–60 mph time) between 1975 and 2006.

Figures B-9a and B-9b show similar data for the evolution of vehicle inertia weight.35 The sharp decline in inertia weight, rather than any radical

change in vehicle technology, largely explains the dramatic improvement

in new vehicle fleet fuel economy that occurred between the late 1970s and

the early 1980s. By the mid-1980s, as new energy-saving technologies

began to be introduced in a major way into LDVs, average vehicle weight

246 Potential Impacts of Climate Change on U.S. Transportation

0

5

10

15

20

25

30

35

40

45

50

1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005

Model Year

MPG or Ton-MPG

Combined Fleet LDV CAFE (as tested) Combined Fleet Ton-MPG

FIGURE B-7 U.S. light-duty vehicle corporate average fuel economy and technology capability. (Note: MPG = miles per gallon.) (Source: Heavenrich 2005,

Table 1, p. 10.)

35 Inertia weight is defined as the curb weight of the vehicle (including fuel) plus 300 pounds.
Contribution to Emissions and Assessment of Strategies 247

1975

1980

1985

1990

2005 1995

2000

15

20

25

30

9 10 11 12 13 14 15

0–60 Time (sec)

Combined City/Highway MPG (as tested)

1975

1980

1995 1990 1985 2000

2005

10

15

20

25

9 10 11 12 13 14 15

0–60 Time (sec)

Combined City/Highway MPG (as tested)

(a)

(b)

FIGURE B-8 (a) Car and (b) truck 55/45 laboratory MPG versus 0–60 time by

model year. (Source: Heavenrich 2006, Figures 6 and 7, p. 16.)
began to increase, and acceleration performance, which had remained relatively constant (or even deteriorated somewhat) between 1975 and 1980,

began to improve.

The increase in average weight resulted from two interrelated factors.

First, the average inertia weight within each vehicle size class grew. Second,

larger size classes made up a greater share of the total vehicle market. In

248 Potential Impacts of Climate Change on U.S. Transportation

1975

1980

1985

1990

1995

2000

2005

15

17

19

21

23

25

27

29

3000

Inertia Weight (pounds)

Combined City/Highway MPG (as tested)

2005

2000

1985 1990 1995

1980

1975

12

13

14

15

16

17

18

19

20

21

22

3500

Inertia Weight (pounds)

Combined City/Highway MPG (as tested)

(a)

(b)

3200 3400 3600 3800 4000 4200

3700 3900 4100 4300 4500 4700 4900

FIGURE B-9 (a) Car and (b) truck 55/45 laboratory MPG versus inertia weight by

model year. (Source: Heavenrich 2006, Figures 8 and 9, p. 17.)
particular, a greater share of the new LDV fleet began to be accounted for

by light trucks, especially vans and SUVs (see Figure B-10). By 2006, the

weight of the average LDV had exceeded its 1975 level. The acceleration

performance of both fleets of vehicles had improved dramatically.

The 2005 edition of the EPA report just referenced (Heavenrich 2005)

estimates the impact of vehicle weight and vehicle performance on the

“laboratory” (or “as tested”) fuel consumption of new U.S. passenger

cars, light trucks, and all LDVs. Table B-11, adapted from this report,

shows these results. The top line of the table shows the actual “laboratory” (or “as tested”) “combined” fuel economy (mpg) for new model

year 2005 cars, trucks, and the total LDV fleet. The next two rows show

estimates of what the 2004 fuel economy would have been had the inertia weight and 0–60 acceleration time been what they were in 1981 and

1987. The final two rows show similar results for size (interior volume)

and 0–60 acceleration time. In all cases, the model year 2004 fleet would

have exhibited improved fuel economy performance, with the increase in

some cases being as high as 30 percent.

Automobile manufacturers assert that these developments merely

reflected changes in consumer tastes as fuel prices fell sharply in the mid1980s and remained low in inflation-adjusted terms thereafter (until

recently). Environmentalists assert that the path of fuel economy improveContribution to Emissions and Assessment of Strategies 249

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1975

Model Year

Sales Fraction (%)

SUV

Car

Wagon

Van

Pickup

1980 1985 1990 1995 2000 2005

FIGURE B-10 Sales fraction by vehicle type (3-year moving average). (Source:

Heavenrich 2006, Figure 10, p. 18.)
ments over time reflects the failure of the U.S. government to increase its

vehicle energy efficiency standards once they reached their peak in the

mid-1980s. Whatever the reason, technological improvements have not

automatically translated into improved fuel economy over much of the

period shown.

Length of Time Required Between the First Commercial Use of a

Technology and When Its Impact on Fuel Consumption Is Felt

Throughout the Entire Vehicle Fleet New technologies are not introduced across a manufacturer’s entire fleet at one time. EPA has collected

data showing the length of time required to achieve various rates of fleet

penetration for successful new LDV technologies in the United States

(Heavenrich 2006, 62). Fifty percent penetration rates of 10 years are not

unusual, and 75 percent penetration rates can easily take 20 years to achieve.

Transport vehicles tend to last a long time. Half the cars built during

the 1990 model year were still on the road when the 2007 model year vehicles were first introduced. Heavy trucks last even longer. On the basis of

“minimal preliminary data,” the expected median lifetime for a model year

1990 heavy truck is 29 years (Davis and Diegel 2006, Tables 3-8 and 3-10).

250 Potential Impacts of Climate Change on U.S. Transportation

TABLE B-11 Effect of Performance, Size, and Weight Distribution 

on Laboratory 55/45 Fuel Economy

Laboratory 55/45 Fuel Percent Change from 

Economy (MPG) 2005 Actual Averages

Scenario Cars Trucks Both Cars Trucks Both

2005 actual average 28.8 21.3 24.5

Model year 2005 averages 

recalculated using 1981:

Weight distribution 31.9 30.2 31.0 10.8 41.8 26.6

Size distribution 28.4 21.2 24.3 −1.4 −0.5 −0.9

0–60 distribution 29.8 20.9 24.6 3.5 −1.9 0.3

Weight and 0–60 36.4 28.5 32.0 26.4 33.8 30.5

Size and 0–60 37.1 25.0 29.9 28.8 17.4 22.0

Ref. 1981 actual average 25.1 20.1 24.6 −12.8 −5.6 0.4

Source: Adapted from Heavenrich 2005, Table 24, p. 72.
Commercial aircraft are also very long-lived. DC-3 aircraft built 50 years

or more ago are still in commercial service in parts of the world. Boeing estimates that 8,800 of the world’s fleet of 17,000 commercial aircraft that were

operating in 2005 will still be operating in 2025 (Boeing Company 2006, 6).

Table B-12 shows estimates made by MIT’s Laboratory for Energy and

the Environment as to how long it might take for various new LDV technologies to have a significant impact on energy use and GHG emissions.

How Motorists Actually Operate Their Vehicles The way vehicles are

operated has a significant influence on fuel consumption. Governments

test the fuel consumption performance of LDVs on dynamometers that

are programmed to follow a set sequence of actions (accelerating, stopping, operating at high speed, operating at low speed, etc.) for specific

intervals of time. Their ratings of vehicles’ fuel consumption are based on

these tests. However, vehicle operators typically do not operate their vehicles as implied by these test procedures. They accelerate more rapidly, drive

faster, and so on. This produces a significant gap between “as tested” and

“in-use” fuel consumption. For reporting purposes (but not for regulatory

compliance purposes), EPA currently adjusts “as tested” mpg downward by

15 percent to make it more comparable with the fuel economy vehicle

users are likely to experience in practice. However, the agency believes

that this adjustment factor, which is about two decades old, is outdated

and proposes increasing it to approximately 22 percent. According to

EPA, adoption of this new adjustment factor would result in the 2006

Contribution to Emissions and Assessment of Strategies 251

TABLE B-12 Timescales for New Light-Duty Vehicle Power Train Technologies

Implementation Phase (years)

Penetration Across 

Market New Vehicle Major Fleet Total Time 

Vehicle Technology Competitive Productiona Penetrationb for Impact

Turbocharged gasoline engine 5 10 10 20

Low-emissions diesel 5 15 10–15 30

Gasoline hybrid 5 20 10–15 35

Hydrogen fuel cell hybrid 15 25 20 55

aAccounts for more than one-third of new vehicle production.

bAccounts for more than one-third of all mileage driven.

Source: Heywood 2006, p. 62. Copyright 2006 by Scientific American, Inc. Reprinted with permission. All rights reserved.
U.S. new vehicle fleet’s adjusted fuel economy being reduced from its “as

tested” level of 24.6 mpg (9.6 L/100 km) to 19.1 mpg (12.3 L/100 km).

Using the current 15 percent adjustment factor, the adjusted fuel economy for the 2006 U.S. new vehicle fleet is 21.0 mpg (11.2 L/100 km)

(Heavenrich 2006, A.10–A.14).

Impact of Vehicle Capacity Utilization (i.e., Load Factor) on Energy Use

In the analysis thus far, reductions in energy use per vehicle kilometer

have been treated as producing corresponding reductions in energy use

per passenger kilometer or tonne-kilometer. The latter two measures, not

the former, represent the fulfillment of transport demand. Increasing a

vehicle’s average load of passengers or freight, while increasing energy use

somewhat, normally leads to a reduction in the energy required to produce a given volume of transport services. Fitting vehicle size to demand

is an important consideration in minimizing transport energy use.

Different transport modes have experienced varying degrees of success

in improving the capacity utilization of their vehicles. In the case of U.S.

commercial aviation, the increase in average load factor from about 55 percent in 1975 to the 80+ percent levels being experienced today is

responsible for a major share of the industry’s energy efficiency improvement per passenger kilometer. The average load factor of freight trucks has

also increased. However, U.S. LDV load factors have shown the opposite

trend. Between 1977 and 2001, the average number of occupants per vehicle declined from 1.9 to 1.6 passengers, or by 14 percent (Hu and Reuscher

2004, Table 16, p. 31). This helps explain why the number of Btu’s required

to propel the average U.S. passenger car 1 mile fell from 9,250 in 1970 to

5,572 in 2003 (i.e., by 40 percent), while the number of Btu’s required to

move one passenger 1 mile fell only from 4,868 to 3,549 (i.e., by 27 percent)

over the same period (Davis and Diegel 2006, Table 2-11, p. 2–13).

The percentage of a vehicle’s available capacity that can be used is the

result of a complex trade-off between cost and convenience. No form of

commercial transport can operate at 100 percent of capacity all the time.

But as operating costs increase, people are willing to sacrifice convenience

to reduce cost, and load factors rise. Public transport systems are especially sensitive to this trade-off. As noted above, low residential densities

and the decline of CBDs as the location of most jobs have reduced the

number of people wishing to travel from one given point to another,

especially during peak hours. Maintaining a level of service frequency

and service coverage necessary to make public transport services attrac252 Potential Impacts of Climate Change on U.S. Transportation
tive has collided with the need to use larger vehicles to reduce per seat

labor, energy, and capital costs.

Vehicle Fuel Consumption: Summary

New technologies have the potential to reduce substantially the energy

used by transport vehicles. The time required to develop, commercialize,

and disseminate new vehicle technologies probably is shorter than the

time required to alter the fundamental drivers of personal and goods

transport demand, but it is still measured in decades. In addition, there is

the problem of ensuring that the potential of new technologies to reduce

energy consumption in transport is actually realized. As the example of

U.S. LDVs after the mid-1980s shows, there is no guarantee that this will

occur. Fuel consumption is but one of many attributes of vehicle performance. Unless conditions are right (or can be made right), it is possible

that some (or even all) of this potential will end up improving these other

performance attributes rather than reducing vehicle fuel consumption.

Altering the Greenhouse Gas Emissions Characteristics 

of Transport Fuel (F )

Gaseous and liquid transport fuels can be produced from a wide range of

primary energy sources (see Figure B-11). Depending on the feedstock

used and the production method employed, CO2 emissions (sometimes

referred to as “well-to-tank” or WTT emissions) can vary widely, sometimes even being negative. As noted above, changes in the GHG emissions

characteristics of transport fuels have not contributed much one way or

the other to changes in transport-related GHG emissions over the past

several decades. This is due to the present overwhelming dominance of

petroleum-based fuels in transport and to the fact that all petroleumbased transport fuels emit approximately the same amount of CO2 per

unit of energy they provide (see Table B-13). In the future, however, WTT

emissions are likely to have much greater significance in determining

total transport-related GHG emissions.

Figure B-12, from the SMP’s final report, shows estimates of the

“well-to-tank,” “tank-to-wheels” (TTW, sometimes also called “tailpipe

emissions”), and “well-to-wheels” (WTW) emissions (the sum of WTT

and TTW emissions) generated by a wide range of vehicle–fuel combinations. The figure illustrates that for transport fuels such as hydrogen and

for power train technologies such as fuel cells, the WTT portion totally

dominates total transport-related CO2 emissions.

Contribution to Emissions and Assessment of Strategies 253
254 Potential Impacts of Climate Change on U.S. Transportation

FIGURE B-11 Possible transport fuel pathways (CNG = compressed natural gas;

DME = dimethyl ether; FC = fuel cell; FT = Fischer–Tropsch; ICE = internal

combustion engine; LPG = liquefied petroleum gas). (Source: World Business

Council for Sustainable Development 2004, Figure 3.1, p. 67.)

TABLE B-13 CO2 Emissions per Liter 

(Gasoline Equivalent)

CO2 Emissions Index 

Fuel (kg/liter) (Gasoline = 100)

Gasoline 2.416 100

Diesel (distillate) 2.582 107

Jet fuel 2.491 103

Ethanol 2.484 103

Biodiesel 2.672 111

Residual fuel (bunker fuel) 2.697 112

Source: Data generated from IEA/SMP Spreadsheet Model.
Contribution to Emissions and Assessment of Strategies 255

-150.0 -50.0 0.0 50.0 100.0 150.0 200.0 250.0 300.0 -100.0

LH2 EU-NG-Mix FC

CGH2 EU-EI-Mix onsite FC

CGH2 EU-NG-Mix onsite FC

CGH2 Residual Wood FCc

Methanol remote-NG FC

Gasoline FC

Diesel DI HEV

Gasoline DI HEV

LH2 EU-NG-Mix ICE

CNG EU-NG-Mix ICE

FT-Diesel Residual Wood DI ICE

FT-Diesel remote-NG DI ICE

RME Biodiesel DI ICEb

Advanced DI Diesel ICEa

Diesel DI ICE

Ethanol Poplar Plantation ICEb

Ethanol Sugar Beet ICEb

Advanced Gasoline ICEa

Gasoline DI ICE

Gasoline 2010 ICE

Greenhouse Gas Emissions (g/km)

Well-to-Tank Tank-to-Wheels Well-to-Wheels

a

 Estimated by the Institute for Internal Combustion Engines. 

b

 Estimated by British Petroleum, from General Motors data. c

 Net output from energy use in conversion process. 

FIGURE B-12 Well-to-wheels (well-to-tank + tank-to-wheels) GHG emissions for

various fuel and propulsion system combinations (CGH2 = gaseous hydrogen; CNG

= compressed natural gas; CO2 = carbon dioxide; DI = direct injection; EU =

European Union; FC = fuel cell; FT = Fischer–Tropsch; HEV = hybrid electric

vehicle; ICE = internal combustion engine; LH2 = liquid hydrogen; NG = natural

gas; RME = rapeseed methyl ester). (Source: World Business Council for

Sustainable Development 2004, adapted from Figure 3.3, p. 77.)

The wide range in WTT emissions for the various fuels illustrated in

Figure B-12 results largely from three factors:

• The growing of biomass used to manufacture biofuels (and possibly hydrogen) removes CO2 from the atmosphere. Gathering and

processing the biomass into fuel takes energy and results in the

emission of CO2. This offsets some of the CO2 removed from the
atmosphere by the growing of the biomass. But under plausible

assumptions, net WTT CO2 emissions for biomass-derived fuels

can still be negative.

• The production process for some biofuels (e.g., ethanol from

corn) generates coproducts that can displace other products that

require energy to produce and whose production emits CO2. How

these “coproduct credits” are allocated has a major impact on a

biofuel’s costs, the energy required to produce it, and its WTT

CO2 emissions (Farrell et al. 2006).

• The production of transport fuels from nonpetroleum fossil carbon sources (e.g., coal or natural gas) generates substantial CO2

emissions. However, if these emissions can be sequestered, the

WTT emissions from the production of these fuels can be

reduced to nearly zero.

Analysts differ on how each these factors should be treated in “scoring”

the WTT emissions characteristics of different transport fuels produced

by different processes from different primary energy sources. Therefore,

anyone reviewing the literature on this topic can expect to encounter a

range of estimates. The important thing now universally acknowledged is

that WTT emissions must be incorporated into any estimates of future

transport-related CO2 emissions.

Fueling Infrastructure

A vast supply infrastructure has developed to deliver petroleum-based

transport fuels to the vehicles that utilize them. As noted earlier, motor

vehicles can use some alternative fuel blends (e.g., E5 and E10) without

major modifications either to their engines or to their fuel systems. The

same is true of the current fuel supply infrastructure. Today’s petroleum

product pipelines routinely carry gasoline, diesel fuel, jet fuel, and

propane. They also can carry “mild” blends of gasoline and biofuels (such

as E5 and E10). But they cannot carry blends consisting of a majority of

biofuels (such as E85) or 100 percent ethanol. The only gaseous transport

fuel carried by pipeline is natural gas. Other gaseous transport fuels (in

particular, hydrogen) would require dedicated pipelines.

Another very important part of the transport fuel infrastructure is

the fueling stations that actually deliver fuel to vehicles. Most of these are

256 Potential Impacts of Climate Change on U.S. Transportation
not directly connected to a pipeline. Instead, they are supplied by tank

trucks that haul fuel from a distributing point (that is connected to a

pipeline) to individual fueling stations.

One of the most formidable challenges facing any new transport fuel

would be the establishment of an infrastructure capable of distributing

it widely. The enormous fixed costs involved in establishing such an

infrastructure mean it would not be established without assurance that

the demand for the products it would transport would be forthcoming.

Yet the vehicles that would be the source of this demand would not be

built and purchased without assurance that fuel to power them would be

available.

Efforts are being made in some states to establish “hydrogen highways.” These are routes along which enough hydrogen refueling stations

have been established to permit drivers of hydrogen-fueled vehicles to

travel on them. These stations are supplied by tanker trucks. While this

could help build initial demand for hydrogen as a transport fuel, it is not

a long-term solution to the fuel infrastructure problem.

HOW MUCH AND OVER WHAT TIME PERIOD MIGHT 

TRANSPORT-RELATED GHG EMISSIONS BE REDUCED?

This appendix has described a wide range of technological and nontechnological means of reducing transport-related GHG emissions.

In this final section, the committee attempts to indicate how much

transport-related GHG emissions might be reduced given the trends

thus far described.

As stated at the outset, the fundamental challenge is to reduce the

emissions produced per unit of transportation services provided more

rapidly than the demand for transportation services grows. While it may

be possible to reduce the rate of transportation demand growth somewhat without harming economic growth unacceptably, the committee is

aware of no forecast that projects that transportation demand will fail to

grow relatively rapidly in the decades ahead, especially in many of the

world’s less developed countries. The bulk of the responsibility for reducing emissions will therefore fall on improved vehicle technologies and

low-carbon or carbon-free fuels.

There is considerable uncertainty about what it might cost to commercialize and widely disseminate many of the more advanced vehicle

Contribution to Emissions and Assessment of Strategies 257
technology and fuel solutions. Given what is known about projected

demand growth, however, it is possible to simulate what might be feasible trajectories of advances in vehicle technology and fuel substitution.

To obtain a better sense of the potential impact of various technologies and fuels in reducing transport-related GHG emissions, the SMP

conducted a number of simulations using its spreadsheet model. The

benchmark was the SMP reference case projection showing total transport-related CO2 emissions doubling between 2000 and 2050, with most

of the growth in emissions occurring in the countries of the developing

world. While other analyses have examined this issue for individual

developed countries or regions, to the committee’s knowledge, the SMP

was the first to examine it for the world as a whole.

In these simulations, the focus was on total road transport. The exercise did not examine the technical or economic feasibility of any of the

actions being simulated. It was intended merely to help the SMP understand the impact on GHG emissions from road vehicles if the actions

described were taken. This enabled the SMP to compare its results with

those of other studies that likewise did not consider technical or economic

feasibility in deriving their results.

Single-Technology Simulation

The SMP began by examining the impact of single technologies on CO2

emissions from road transport worldwide. Figure B-13 shows results for

five such technologies—dieselization, hybridization, fuel cells, “carbonneutral” hydrogen, and biofuels. It was assumed that each power train

technology would achieve as close to 100 percent global sales penetration

as possible given the characteristics of the technology and that each fuel

would become as close to 100 percent of the global road transport fuel

pool as its characteristics would permit.

The SMP emphasized that these single-technology examples were

purely hypothetical. It is highly unlikely in practice that any single technology would achieve 100 percent penetration. Also, the examples cannot

be added together. Differences in the timing of the implementation of

these technologies and fuels in the developed and developing worlds were

largely ignored.

For both diesels and advanced hybrids, it was assumed that 100 percent sales penetration would be reached by 2030 and that these technologies

258 Potential Impacts of Climate Change on U.S. Transportation
would be used in LDVs and medium-duty trucks.36 In the case of fuel cell

vehicles, it was assumed that 100 percent sales penetration would be

reached by 2050.37 It was also assumed that the hydrogen used in these

vehicles would be produced by reforming natural gas and that carbon

sequestration would not be involved. The estimate of the impact of carbon-neutral hydrogen was generated by changing the WTT emissions

characteristics of the hydrogen used in the fuel cell case just described. To

focus on the impact of biofuels, it was assumed that these fuels would be

used in a world road vehicle fleet similar in energy use characteristics to

the SMP reference fleet. Diesel internal combustion engine technology

(using conventional diesel fuel) was assumed to have an 18 percent fuel

consumption benefit compared with the prevailing gasoline internal

Contribution to Emissions and Assessment of Strategies 259

0

2

4

6

8

10

12

2000 2010 2020 2030 2040 2050

Gigatonnes CO2-Equivalent GHGs

Reference Case

Diesels

Hybrids

Fuel Cells (hydrogen from

natural gas)

Fuel Cells (zero-carbon

hydrogen)

Advanced Biofuels (all road

vehicles)

FIGURE B-13 Hypothetical potential of individual technologies to lower road

transport well-to-wheels GHG emissions relative to the SMP reference case.

(Source: World Business Council for Sustainable Development 2004, 

Figure 4.7, p. 113.)

36 A very high proportion of heavy trucks and buses are already diesel powered. The SMP assumed

that hybrid technology would not see significant use in heavy-duty over-the-road trucks and buses

because of their operating characteristics. Public transport buses are already being viewed as

prime candidates for hybridization. These were not included in the SMP’s calculation, but their

omission makes relatively little difference in the results.

37 The SMP made the same assumptions concerning the types of vehicles to which fuel cells might

be applied as it did for hybrids.
combustion engine technology during the entire period. The fuel consumption benefit relative to gasoline internal combustion engine

technology was assumed to be 36 percent for diesel hybrids, 30 percent

for gasoline hybrids, and 45 percent for fuel cell vehicles.

From this single-technology assessment, it is evident that even if

implemented worldwide, diesels and hybrid internal combustion engines

fueled with conventional gasoline and diesel fuel or fuel cells fueled with

natural gas–derived hydrogen could no more than slow the growth in

road transport CO2 emissions during the period 2000–2050. Only the use

of carbon-neutral hydrogen in fuel cells and advanced biofuels in internal combustion engine–powered vehicles could largely or totally offset

the increase in CO2 emissions produced by the growth in road travel during the period 2000–2050.

This does not mean that vehicle energy use characteristics are irrelevant. They might not have a major impact on the trajectory of road

vehicle GHG emissions over the very long term, but they would have a

major impact on the amount of low-carbon or carbon-neutral fuel that

would have to be produced to power the world’s road vehicle fleet. This

means they could have a very important impact on the cost of significantly reducing GHG emissions from road vehicles.38

On the basis of these results, the SMP concluded that it is only

through a combination of fuel and power train solutions that significant

CO2 reduction can be attained. No single-technology pathway merits

selection as the sole long-run solution.

Combined-Technology Simulation

Since the substantial reduction of CO2 emissions from road vehicles is

likely to depend on the widespread adoption of several advanced vehicle

and fuel technologies, as well as other factors, the SMP decided to examine the combined impact of several actions, including the following:

• Fuels that are carbon neutral (defined by the SMP as ones that

reduce WTW CO2 emissions by at least 80 percent);

• Power trains that are highly energy efficient;

260 Potential Impacts of Climate Change on U.S. Transportation

38 The fuel economy benefit relative to gasoline internal combustion engine technology was

assumed to be 36 percent for diesel hybrids, 30 percent for gasoline hybrids, and 45 percent for

fuel cell vehicles.
• A change in the historical mix-shifting trend to larger vehicle categories; and

• Improved traffic flow and other changes in transport activity

resulting from better integration of transport systems, enabled, at

least in part, by information technology.

The SMP set an illustrative target of reducing annual worldwide CO2 emissions from road transport by half by 2050. This is equivalent to a decline in

yearly CO2 emissions of about 5 gigatonnes from levels that the SMP reference case projects would otherwise be reached and, by coincidence, returns

annual road vehicle CO2 emissions in 2050 to about their current levels.

For illustrative purposes, the CO2 reduction target was divided into

six increments. The timing and size of each increment are not fixed and

ultimately would be decided on the basis of sustainability and investment

choices at the national, regional, and global levels. The purpose of the

analysis was to illustrate what might be achieved if ambitious changes

were made beyond those in the SMP reference case, with no judgment as

to cost or the probability of each step being taken.

Increment 1. Dieselization: It was assumed that dieselization of LDVs

and medium-duty trucks would rise to around 45 percent globally by

2030 (that is, to about current European levels). Diesel engines were

assumed to consume about 18 percent less fuel (and emit 18 percent less

CO2) than current gasoline internal combustion engines.

Increment 2. Hybridization: It was assumed that the hybridization

(gasoline and diesel) of LDVs and medium-duty trucks would increase

to half of all internal combustion engine vehicles sold by 2030. Gasoline

hybrids were assumed to consume an average of 30 percent less fuel than

current gasoline internal combustion engines, and diesel hybrids were

assumed to consume an average of 24 percent less fuel than current diesels.39

Increment 3. Conventional and advanced biofuels: It was assumed that

the quantity of biofuels in the total worldwide gasoline and diesel pool

would rise steadily, reaching one-third by 2050. Conventional biofuels

(those yielding a 20 percent CO2 unit efficiency benefit) were capped at 

Contribution to Emissions and Assessment of Strategies 261

39 It is generally acknowledged that, because of the diesel’s initial superior energy efficiency, any

additional benefit from hybridizing a diesel is likely to be smaller than that from hybridizing a

gasoline engine.
5 percent of the total pool. The balance was assumed to be advanced biofuels (those yielding at least an 80 percent CO2 unit efficiency benefit).40

Increment 4. Fuel cells using hydrogen derived from fossil fuels (no

carbon sequestration): It was assumed that mass market sales of LDVs

and medium-duty trucks would start in 2020 and rise to half of all vehicle sales by 2050. It also was assumed that fuel cell–equipped vehicles

consume an average of 45 percent less energy than current gasoline internal combustion engines.

Increment 5. Carbon-neutral hydrogen used in fuel cells: It was

assumed that hydrogen sourcing for fuel cells would switch to centralized

production of carbon-neutral hydrogen over the period 2030–2050 once

hydrogen LDV fleets had reached significant penetration at the country

level. By 2050, 80 percent of hydrogen would be produced by carbonneutral processes.

The first five increments reflect the inherent properties of different

vehicle technologies and fuels. Actual reductions in CO2 emissions will be

determined not only by these properties but also by the mix of vehicles

purchased by consumers and businesses and by how these vehicles are

used on a daily basis. To reflect these two factors, two more increments

were included.

Increment 6. Additional improvement in fleet-level vehicle energy

efficiency: The SMP reference case projects an average improvement in the

energy efficiency of the on-road LDV fleet of about 0.4 percent per year,

with new vehicle sales showing an average 0.5 percent per year improvement in fuel economy. The improvement potential embodied in actual

vehicles is around 1.0 percent per year, but about half of this potential

improvement is offset because of vehicle purchasers’ preferences for larger

and heavy vehicles. In developing this increment, the SMP assumed that

preferences relating to the mix of vehicles chosen by purchasers and the

performance of these vehicles would change somewhat, leading to an

additional 10 percent average annual in-use improvement relative to the

reference case (i.e., average annual fleet-level improvement would rise

from about 0.4 percent to about 0.6 percent).

262 Potential Impacts of Climate Change on U.S. Transportation

40 This implies that these advanced biofuels are either gasoline from lignocellulosic sugar 

fermentation or diesel from biomass gasification/Fischer–Tropsch synthesis.
Increment 7. A 10 percent reduction in emissions due to better traffic flow and other efficiencies in road vehicle use: It was assumed that the

gap between on-road energy-use performance and the technological

improvements embodied in vehicles would narrow. How might this happen? For one thing, there are a number of opportunities relating to the

increased use of information technology in transport systems that might

enable the better management of travel demand. Improved routing information might permit trips to be shortened, while improved information

about road conditions might reduce the amount of time motorists spend

in their vehicles while idling in traffic. For another thing, more accurate

and current information about when public transport vehicles will arrive

and how long they will take to get to their destinations might encourage

additional use of public transport. Individually, none of these improvements would be major, and almost certainly there would be offsets. But

in combination, the SMP assumes that such factors could produce an

additional 10 percent reduction in road vehicle CO2 emissions.

Figure B-14 shows the results of the SMP combined-technologies

analysis just described. It confirms the impression conveyed by the three

single-technology analyses discussed above that the widespread adoption

of a combination of vehicle and fuel technologies (plus other factors)

would be required to return 2050 CO2 emissions from road vehicles to

their 2000 level.

SUMMARY

Any global warming that will be experienced during the next several

decades will largely be the result of GHG emissions that have already

occurred. As the main body of this report points out, regardless of what

else it might do, America’s transport sector will have to adjust to the consequences of this warming. But the transport sector in general, and

America’s transport sector in particular, is a significant source of GHG

emissions. If future warming is to be limited, GHG concentrations in the

atmosphere must be stabilized. This will require reducing GHG emissions not merely to below what they might otherwise be if present trends

were to continue but to well below current levels. The transport sector

will have to contribute to this reduction.

This appendix has identified several approaches by which transportrelated GHG emissions might be reduced. A common characteristic of

Contribution to Emissions and Assessment of Strategies 263
these approaches is that they take considerable time to be fully effective.

This means that if transport-related GHG emissions are to be reduced to

below their current levels by 2050, steps must be taken now to begin to

implement certain of these approaches.

REFERENCES

Abbreviations

BTS Bureau of Transportation Statistics

IEA International Energy Agency

IMO International Maritime Organization

IPCC Intergovernmental Panel on Climate Change

UN United Nations

264 Potential Impacts of Climate Change on U.S. Transportation

0

2

4

6

8

10

12

2000 2010 2020 2030 2040 2050

Gigatonnes CO2-Equivalent GHGs

Diesels (LDVs)

Hybrids (LDVs and MDTs)

Biofuels (80% low GHG sources by 2050)

Fuel Cells (fossil hydrogen)

Fuel Cells (80% low-GHG hydrogen by 2050)

Mix Shifting Yielding 10% Vehicle Efficiency Improvement

10% Vehicle Travel Reduction (all road vehicles)

Remaining GHGs

FIGURE B-14 Combined-technology case. (Source: Adapted from World

Business Council for Sustainable Development 2004, Figure 4.11, p. 117.)
UNCTAD United Nations Conference on Trade and Development

USEPA United States Environmental Protection Agency

WBSCD World Business Council on Sustainable Development

Bento, A. M., M. L. Cropper, A. M. Mobarak, and K. Vinha. 2005. The Effects of Urban

Spatial Structure on Travel Demand in the United States. Review of Economics and

Statistics, Vol. 87, No. 3, Aug., pp. 466–478.

Boeing Company. 2006. Current Market Outlook: 2006. www.boeing.com/commercial/

pdf/CMO_06.pdf. Accessed Jan. 30, 2008.

BTS. 2001. National Household Travel Survey. U.S. Department of Transportation.

BTS. 2005. National Transportation Statistics 2004. BTS02-08. U.S. Department of

Transportation.

Davis, S. C., and S. W. Diegel. 2006. Transportation Energy Data Book, 25th ed. ORNL6974. Oak Ridge National Laboratory, Oak Ridge, Tenn., May.

Ewing, R., R. Pendall, and D. Chen. 2002. Measuring Sprawl and Its Impact. Smart Growth

America. www.smartgrowthamerica.org/sprawlindex/MeasuringSprawl.pdf. Accessed

Jan. 30, 2008.

Farrell, A. E., R. J. Plevin, B. T. Turner, A. D. Jones, M. O’Hare, and D. M. Kammen.

2006. Ethanol Can Contribute to Energy and Environmental Goals. Science,

Vol. 311, No. 5760, Jan. 27, pp. 506–508.

Heavenrich, R. M. 2005. Light-Duty Automotive Technology and Fuel Economy Trends:

1975 Through 2005. EPA420-R-05-001. U.S. Environmental Protection Agency, July.

Heavenrich, R. M. 2006. Light-Duty Automotive Technology and Fuel Economy Trends:

1975 Through 2006. EPA420-R-06-001. U.S. Environmental Protection Agency,

July.

Heywood, J. B. 2006. Fueling Our Transportation Future. Scientific American, Vol. 295,

No. 3, Sept., pp. 60–63.

Hu, P. S., and T. R. Reuscher. 2004. Summary of Travel Trends: 2001 National Household

Travel Survey. Federal Highway Administration, U.S. Department of

Transportation, Dec.

IEA. 2000. The Road from Kyoto: Current CO2 and Transport Policies in the IEA. Paris.

IEA. 2005. CO2 Emissions from Fuel Combustion: 1971–2003. Paris.

IEA. 2006. Energy Technology Perspectives: Scenarios and Strategies to 2050. Paris.

IMO. 2000. Study of Greenhouse Gas Emissions from Ships: Final Report to the

International Maritime Organization. MEPC 45/8, Issue No. 2-31. Norwegian

Marine Technology Research Institute, March.

IPCC. 1999. Aviation and the Global Atmosphere (J. E. Penner, D. H. Lister, D. J. Griggs,

D. J. Dokken, and M. McFarland, eds.), Cambridge University Press, Cambridge,

United Kingdom.

Lee, J. J., S. P. Lukachko, I. A. Waitz, and A. Schafer. 2001. Historical and Future Trends

in Aircraft Performance, Cost, and Emissions. Annual Review of Energy and

Environment, Vol. 26, Nov., pp. 167–200.

Mokhtarian, P. L. 2003. Telecommunications and Travel: The Case for

Complementarity. Journal of Industrial Ecology, Vol. 6, No. 2, pp. 43–57.

Contribution to Emissions and Assessment of Strategies 265
Stuber, N., P. Forster, G. Rädel, and K. Shine. 2006. The Importance of the Diurnal and

Annual Cycle of Air Traffic for Contrail Radiative Forcing. Nature, Vol. 441, No.

7095, June 15, pp. 864–867.

UN. 1999. The World at Six Billion. Population Division, Department of Economic

and Social Affairs, Oct. 12. www.un.org/esa/population/publications.sixbillion/

sixbillion.htm. Accessed Jan. 30, 2008.

UN. 2003. World Urbanization Prospects: The 2003 Revision. Population Division,

Department of Economic and Social Affairs. www.un.org/esa/population/

publications/wup2003/2003wup.htm. Accessed Jan. 30, 2008.

UN. 2005. World Population Prospects: The 2004 Projection. Population Division,

Department of Economic and Social Affairs, Feb.

UNCTAD. 2005. Review of Maritime Transport 2005. www.unctad.org/Templates/

WebFlyer.asp?intItemID=3588&lang=1. Accessed Jan. 30, 2008.

U.S. Energy Information Administration. 2004. Emissions of Greenhouse Gases in the

United States. DOE/EIA-0573. U.S. Department of Energy. www.eia.doe.gov/oiaf/

1605/archive/gg05rpt/index.html. Accessed Jan. 30, 2008.

USEPA. 2005. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2003. EPA430-R-05-003. Washington, D.C., April 15.

Weiss, M. A., J. B. Heywood, E. M. Drake, A. Schafer, and F. F. AuYeung. 2000. On the

Road in 2020: A Life-Cycle Analysis of New Automobile Technologies. Energy

Laboratory Report MIT EL 00-003. Cambridge, Mass., Oct.

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the Challenges to Sustainability. Sustainable Mobility Project, Geneva, Switzerland.

www.wbcsd.org/web/mobilitypubs.htm. Accessed Jan. 30, 2008.

266 Potential Impacts of Climate Change on U.S. Transportation
267

APPENDIX C

Commissioned Papers and Authors

Case Study of the Transportation Sector’s Response to and Recovery from

Hurricanes Katrina and Rita. Lance R. Grenzeback and Andrew T.

Lukmann, Cambridge Systematics, Inc., Jan. 10, 2007.

Climate Variability and Change with Implications for Transportation.

Thomas C. Peterson, Marjorie McGuirk, Tamara G. Houston,

Andrew H. Horvitz, National Oceanic and Atmospheric

Administration, and Michael F. Wehner, Lawrence Berkeley National

Laboratory, Dec. 6, 2006.

Design Standards for U.S. Transportation Infrastructure: The Implications

of Climate Change. Michael D. Meyer, Georgia Institute of

Technology, Dec. 18, 2006.

Operational Responses to Climate Change Impacts. Stephen C.

Lockwood, PB Consult, Dec. 29, 2006.

Transportation Planning, Climate Change, and Decisionmaking Under

Uncertainty. James A. Dewar and Martin Wachs, Dec. 13, 2006.

Note: The commissioned papers are available at www.trb.org/news/blurb_detail.asp?id=8808.
268

APPENDIX D

Conference Agenda and Participants

Conference on Climate Change Impacts on U.S. Transportation

Transportation Research Board

Division on Earth and Life Studies

National Research Council of the National Academies

Lecture Room

National Academy of Sciences Building

2100 C Street, NW, Washington, D.C.

October 12, 2006

AGENDA

8:30–8:45 a.m. Welcome, Overview of the Agenda, and

Introduction to Paper Presentations

Henry G. Schwartz, Jr., Committee Chair

8:45–9:45 a.m. Current State of Knowledge on Climate

Change and Implications for Transportation

Thomas R. Karl, moderator, committee member

David J. Karoly, University of Oklahoma,

presenter and discussant

Thomas C. Peterson, Marjorie McGuirk,

Tamara Houston, Andrew H. Horvitz,

National Oceanic and Atmospheric

Administration; and Michael F. Wehner,

Lawrence Berkeley National Laboratory,

paper authors

General Discussion
9:45 a.m.–12:30 p.m. Adaptive Responses to Climate Change

9:45–11:00 a.m. Reexamination of the Role of Transportation

Design Standards in Light of Potential

Impacts from Climate Change

Klaus H. Jacob, moderator, committee member

Jonathan L. Gifford, George Mason University,

presenter and discussant

Michael D. Meyer, Georgia Institute of

Technology, paper author

General Discussion

11:00–11:15 a.m. Break

11:15 a.m.–12:30 p.m. Operational Strategies to Address 

Climate Change

Alan C. Clark, moderator, committee member

Michael M. Ryan, H. W. Lochner, Inc.,

presenter and discussant

Stephen C. Lockwood, Parsons Brinckerhoff,

paper author

General Discussion

12:30–1:30 p.m. Lunch break

1:30–2:45 p.m. Case Study of the Transportation Sector’s

Response to and Recovery from Hurricanes

Katrina and Rita

George C. Eads, moderator, committee member

Michael S. Bronzini, George Mason University,

presenter and discussant

Lance R. Grenzeback and Andrew Lukmann,

Cambridge Systematics, Inc., paper authors

General Discussion

2:45–3:00 p.m. Break

Conference Agenda and Participants 269
270 Potential Impacts of Climate Change on U.S. Transportation

3:00–4:15 p.m. Survey on Approaches to Decision Making

Under Uncertainty

Robert J. Lempert, moderator, committee 

member

Paul S. Fischbeck, Carnegie Mellon University,

presenter and discussant

James A. Dewar and Martin Wachs, paper 

authors

General Discussion

4:15–5:00 p.m. Rapporteurs’ Report and General Discussion

Henry G. Schwartz, Jr., moderator, Committee 

Chair

Michael C. MacCracken, Climate Institute

Thomas B. Deen, Transportation Research 

Board (retired)

5:00 p.m. Adjourn

CONFERENCE PARTICIPANTS

Roemer Alfelor

Federal Highway Administration

William Anderson

Boston University

Vicki Arroyo

Pew Center on Global Climate

Change

Mitchell Baer

U.S. Department of Energy

Anjuli Bamzai

U.S. Department of Energy

Virginia Burkett

U.S. Geological Survey

David Connell

Union Pacific Railroad

Billy Connor

University of Alaska, Fairbanks

Mark Crowell

Federal Emergency Management

Administration

Robert Dalrymple

Johns Hopkins University
Conference Agenda and Participants 271

John Davies

U.S. Environmental Protection

Agency

Robert Dean

University of Florida

Brigid DeCoursey

Office of the Secretary

U.S. Department of Transportation

Kevin Eckerle

U.S. Senate Committee on

Commerce, Science, and

Transportation

Subcommittee on Climate Change

and Impacts

Gary Feuerberg

Research and Innovative

Technology Administration

Gary Gallegos

San Diego Association of

Governments

Mohan Gupta

Federal Aviation Administration

David Henderson

North Carolina Department of

Transportation

Robert Kafalenos

Federal Highway Administration

David Knight

Great Lakes Commission

Lourdes Maurice

Federal Aviation Administration

Carol Murray

New Hampshire Department of

Transportation

Gummada Murthy

Virginia Department of

Transportation

Richard Nelson

Nevada Department of

Transportation

George Newton

U.S. Arctic Research Commission

J. Rolf Olsen

Institute for Water Resources

U.S. Army Corps of Engineers

Harold Paul

Louisiana Transportation Research

Center

William Petak

University of Southern California

Craig Philip

Ingram Barge Company

Britt Poole

ICF International, Inc.

Joanne Potter

Cambridge Systematics, Inc.
272 Potential Impacts of Climate Change on U.S. Transportation

Ananth Prasad

Florida Department of

Transportation

Stuart Price

RSVP Communications

David Robinson

Rutgers University

Craig Rockey

Association of American Railroads

Adam Rose

Pennsylvania State University

Eric Salathe

University of Washington

Michael Savonis

Federal Highway Administration

Leland Smithson

American Association of State

Highway and Transportation

Officials

Richard Somerville

Scripps Institution of

Oceanography

Marty Spitzer

U.S. House of Representatives

Committee on Science

Subcommittee on the

Environment, Technology, and

Standards

Mark Stehly

Burlington Northern Santa Fe

Railway

Laura Steinberg

Tulane University

Anne Sudar

Institute for Water Resources

U.S. Army Corps of Engineers

Megumi Sumitani

Seattle Office of City Auditor

Victoria Sutton

Research and Innovative

Technology Administration

Anthony Taormina

Port of Hueneme

Kevin Wright

ICF International, Inc.

John Zamurs

New York State Department of

Transportation

Rae Zimmerman

New York University

Jeffrey Zupan

Regional Plan Association
273

Study Committee 

Biographical Information

Henry G. Schwartz, Jr., Chair, is a nationally recognized civil and environmental engineering leader who spent most of his career with Sverdrup

Civil, Inc. (now Jacobs Civil, Inc.), which he joined as a registered professional engineer in 1966. In 1993, Schwartz was named President and

then Chairman, directing the transportation, public works, and environmental activities of Sverdrup/Jacobs Civil, Inc., before retiring in 2003.

Dr. Schwartz’s projects included multibillion-dollar water and wastewater

treatment systems for the cities of San Diego, San Francisco, and Detroit,

as well as large civil infrastructure projects, such as highways, bridges,

dams, and railroads. Following his retirement, Dr. Schwartz was appointed Senior Professor and Director of the Engineering Management

Program at Washington University in St. Louis, a position he held until

fall 2006. He has served on the advisory boards for Carnegie Mellon

University, Washington University, and the University of Texas, Austin,

and is President of the Academy of Science of St. Louis. He is Founding

Chairman of the Water Environment Research Foundation and has

served as President of the Water Environment Federation. Dr. Schwartz is

Past President of the American Society of Civil Engineers and was a member of the Civil Engineering Research Foundation Board of Directors. He

was elected to the National Academy of Engineering in 1997 (Section 4:

Civil Engineering) and has served on National Research Council (NRC)

study committees, including the Committee for a Future Strategic Highway Research Program (SHRP), and on the NRC Board on Infrastructure

and the Constructed Environment and the Executive Committee of the

Transportation Research Board (TRB). Dr. Schwartz received a PhD from

the California Institute of Technology and master of science and bachelor of science degrees from Washington University; he also attended

Princeton University and Columbia University’s business program.
274 Potential Impacts of Climate Change on U.S. Transportation

Alan C. Clark is Director of the Houston–Galveston Area Council’s (HGAC’s) metropolitan planning organization (MPO), which is responsible

for development of the region’s multimodal transportation plans and air

quality programs. The MPO’s Transportation Policy Council approves the

programming of all federal highway and transit funds in Harris County

and the seven adjacent counties. Mr. Clark’s responsibilities also include

coordinating the Houston–Galveston area’s response to mandates

contained in the Clean Air Act Amendments of 1990. He has been a

transportation planner with H-GAC since 1983 and has managed its transportation and air quality programs since 1986. Mr. Clark has served as

an Adjunct Professor with Texas Southern University. Before coming to

H-GAC, he worked as a transportation planner with the Metropolitan

Transit Authority of Harris County and as a traffic engineering consultant.

He currently serves on the advisory councils of the Texas Transportation

Institute and the Center for Transportation Training and Research at Texas

Southern University. In 2006 he was appointed to the Federal Advisory

Committee for the U.S. Climate Change Science Program study on the

Impacts of Climate Variability and Change on Transportation Systems and

Infrastructure—Gulf Coast Case Study. Mr. Clark holds master’s degrees

in civil engineering and in city and regional planning from Ohio State

University. He completed his undergraduate degree in business administration at the University of Tennessee.

G. Edward Dickey is a consultant in water resources policy and planning;

Senior Advisor providing policy, political, and technical advice and representation services on the planning and implementation of large-scale water

projects at Dawson and Associates, a Washington-based representation

firm; and Affiliate Professor of Economics at Loyola College in Maryland.

He is former Chief of the Planning Division of the Headquarters Office

of the U.S. Army Corps of Engineers and former Acting Assistant

Secretary of the Army (Civil Works). Dr. Dickey has served on numerous

NRC committees, including the Committee to Review the New York City

Watershed Management Strategy, the Committee for the Study of Freight

Transportation Capacity for the Next Century, and most recently the

Panel on Adaptive Management for Resource Stewardship. He received

PhD and master of art degrees in economics from Northwestern University and a bachelor of arts degree in political economy from the Johns

Hopkins University.
George C. Eads is Senior Consultant at CRA International, Inc. [formerly

Charles River Associates (CRA)] in its Washington, D.C., office. Before

joining CRA in 1995, he held several positions at General Motors (GM)

Corporation, including Vice President and Chief Economist; Vice

President, Worldwide Economic and Market Analysis Staff; and Vice

President, Product Planning and Economics Staff. Before joining GM,

Dr. Eads was Dean of the School of Public Affairs at the University of

Maryland, College Park, where he also was a professor. Before that, he

served as a member of President Carter’s Council of Economic Advisors.

He has been involved in numerous projects concerning transport and

energy. In 1994 and 1995 he was a member of President Clinton’s policy

dialogue on reducing greenhouse gas emissions from personal motor

vehicles, popularly known as “Car Talk.” He coauthored the World Energy

Council’s 1998 Report Global Transport and Energy Development: The

Scope for Change. From 2000 to 2004, Dr. Eads devoted most of his time

to the World Business Council for Sustainable Development’s Sustainable

Mobility Project, a project funded and carried out by 12 leading international automotive and energy companies. During the first stage of this

project, he led the CRA contingent on the CRA–Massachusetts Institute

of Technology team that together produced the project’s first report,

Mobility 2001: World Mobility at the End of the Twentieth Century and Its

Sustainability. As lead consultant during the project’s second and final

phase, Dr. Eads drafted the project’s final report, Mobility 2030: Meeting

the Challenges to Sustainability, which was released in summer 2004 in

Brussels, Detroit, and Tokyo. Dr. Eads is a member of the Presidents’ Circle

at the National Academies and has served on the Institute of Medicine’s

Committee on the Consequences of Uninsurance. He is an at-large

Director of the National Bureau of Economic Research. He received a

PhD in economics from Yale University.

Robert E. Gallamore is currently a private consultant, having recently

retired as Director of the Transportation Center and Professor of

Managerial Economics and Decision Sciences in the Kellogg School of

Management, Northwestern University. Before joining the university in

August 2001, he was an executive on loan from Union Pacific Railroad to

the Transportation Technology Center in Pueblo, Colorado, where he was

Assistant Vice President of Communications Technologies and General

Manager of the North American Joint Positive Train Control Program.

Study Committee Biographical Information 275
He has also served in several positions with the federal government,

including Deputy Federal Railroad Administrator and Associate

Administrator for Planning of the Urban Mass Transportation

Administration. Dr. Gallamore served as Chairman of the TRB

Committee for a Study of the Feasibility of a Hazardous Materials

Transportation Cooperative Research Program and the Committee on

Freight Transportation Information Systems Security. He also served as

a member of the TRB Committee for a Review of the National

Transportation Science and Technology Strategy, the Steering Committee

for a Conference on Railroad Research Needs, and the Transportation

Panel of the Committee on Science and Technology for Countering

Terrorism. Dr. Gallamore currently chairs the NRC Committee for

Review of the Federal Railroad Administration Research and Development

Program. He received a PhD in political economy and government from

Harvard University.

Genevieve Giuliano is Senior Associate Dean of Research and Technology,

Director of the METRANS Transportation Center, and Professor in the

School of Policy, Planning, and Development at the University of Southern

California. Dr. Giuliano’s research interests include the relationship

between land use and transportation, transportation policy evaluation,

travel behavior, and the role of information technology in transportation.

She has published more than 130 papers and reports and has presented her

research at numerous conferences in the United States and abroad. She is

currently a member of two international research consortia and serves on

the editorial boards of several professional journals. She is a former member and chair of the TRB Executive Committee and a National Associate of

the National Academies. Dr. Giuliano has served on several NRC and TRB

policy study committees, including the Committee for the Study of

Impacts of Highway Capacity Improvements on Air Quality and Energy

Consumption; the Committee on Metropolitan Area Governance; the

Committee on International Comparison of National Policies and

Expectations Affecting Public Transit; the Committee for the Evaluation of

the Congestion Mitigation and Air Quality Improvement Program; and the

Committee on Transportation, Land Use, Physical Activity, and Health. She

is currently chairing the TRB policy study Committee on Funding Options

for Freight Transportation Projects of National Significance. Dr. Giuliano

is also founding Chair of the California Transportation Research and

276 Potential Impacts of Climate Change on U.S. Transportation
Technology Advisory Panel. She received a PhD in social sciences from the

University of California at Irvine.

William J. Gutowski, Jr., is Professor of Meteorology in the Department

of Geological and Atmospheric Sciences at Iowa State University. His

research is focused on the role of atmospheric dynamics in climate, with

emphasis on the dynamics of the hydrologic cycle and regional climate.

Dr. Gutowski’s research program entails a variety of modeling and data

analysis approaches to capture the necessary spatial and temporal scales of

these dynamics and involves working through the Regional Climate

Modeling Laboratory at Iowa State University. His work also includes

regional modeling of Arctic, African, and East Asian climates and involves

collaboration with scientists in these regions. Dr. Gutowski received a PhD

in meteorology from the Massachusetts Institute of Technology and a

bachelor of science degree in astronomy and physics from Yale University.

Randell H. Iwasaki was appointed Chief Deputy Director of the

California Department of Transportation (Caltrans) in November 2004.

In that capacity, he manages the day-to-day operations of the department,

including an operating budget of nearly $13 billion and more than 21,000

employees. A licensed civil engineer, Mr. Iwasaki has been with Caltrans

for more than 20 years and has served as the department’s Interim

Director; Deputy Director for Maintenance and Operations; Director of

Caltrans District 4, covering nine counties in the San Francisco Bay Area;

and Director of Caltrans District 9, covering the eastern portion of the

state. Mr. Iwasaki is a board member of the Intelligent Transportation

Society of America, the Foundation for Pavement Preservation, and the

Asian Pacific State Employee Association Foundation. He is chair of the

SHRP 2 Technical Coordinating Committee for Renewal Research and

serves on a TRB National Cooperative Highway Research Program panel

on work zone safety. He was also recently appointed to the ITS Advisory

Committee to Secretary Peters of the U.S. Department of Transportation.

Mr. Iwasaki earned a bachelor’s degree in engineering from California

Polytechnic State University, San Luis Obispo, and a master’s degree in

environmental engineering from California State University, Fresno.

Klaus H. Jacob is Special Research Scientist at the Lamont–Doherty Earth

Observatory of Columbia University, where he retired from a full-time

Study Committee Biographical Information 277
position in 2001. He is also an Adjunct Professor at the School of

International and Public Affairs at Columbia University, where he teaches

disaster risk management. During the first two decades of his 36-year

career with Columbia University, Dr. Jacob focused his research on basic

earth physics and plate-tectonic processes. In 1986 he cofounded the

National Science Foundation–supported National Center for Earthquake

Engineering Research, where he worked on engineering and risk management applications for seismic hazards assessment and design criteria for

large infrastructure projects. He has also worked intensively with federal,

state, and local emergency management communities on risk mitigation

strategies. Dr. Jacob’s recent research efforts include studying how global

climate change and related sea level rise affect the risks from coastal storm

surges, flooding, and inundation, primarily of infrastructure systems. This

research was applied in the recent Metropolitan East Coast Regional

Assessment, which examined the impacts of climate change scenarios on

the New York metropolitan area’s transportation infrastructure, among

other impact areas. Dr. Jacob has authored or coauthored more than 140

scientific and technical publications and book chapters. He is a member of

the American Geophysical Union, the Seismological Society of America,

the Earthquake Engineering Research Institute, the American Geological

Institute, and the New York Academy of Sciences. Dr. Jacob holds a doctorate in geophysics from Goethe University (Frankfurt, Germany), a

master of science degree in geophysics from Guttenberg University

(Mainz), and a bachelor of science degree in mathematics and physics

from the Technical University in Darmstadt.

Thomas R. Karl is Director of the National Climatic Data Center, a facility of the Commerce Department’s National Oceanic and Atmospheric

Administration, a position he has held since 1998. Before that, he was

Senior Scientist at the climate center, where he analyzed global climate

change, extreme weather events, and trends in global and U.S. climate over

the past 100 years. Dr. Karl is a Fellow of the American Meteorological

Society and the American Geophysical Union and past Chair of the

Division on Earth and Life Sciences’ Climate Research Committee. He has

edited numerous journals, has authored more than 100 peer-reviewed

journal articles, was lead author on several Intergovernmental Panel

Assessments of climate change, and served as Cochair of the U.S. National

Climate Assessment. In 2006 he was appointed to the Federal Advisory

278 Potential Impacts of Climate Change on U.S. Transportation
Committee for the U.S. Climate Change Science Program study on the

Impacts of Climate Variability and Change on Transportation Systems

and Infrastructure—Gulf Coast Case Study. Dr. Karl received an honorary

doctorate from North Carolina State University, a master’s degree in meteorology from the University of Wisconsin, and a bachelor’s degree from

Northern Illinois University.

Robert J. Lempert is Senior Scientist at the Rand Corporation and an

expert in science and technology policy, with a special focus on climate

change, energy, and the environment. An internationally known scholar

in the field of decision making under conditions of deep uncertainty,

Dr. Lempert is a Fellow of the American Physical Society, a member of the

National Academies’ Climate Research Committee, and a member of the

Council on Foreign Relations. Dr. Lempert is leading a National Science

Foundation–funded study on the use of scientific and other information

for climate change decision making under conditions of uncertainty. He

has led studies on climate change policy, long-term policy analysis, and

science and technology investment strategies for such clients as the White

House Office of Science and Technology Policy, the U.S. Department of

Energy, the National Science Foundation, and a variety of multinational

firms. A Professor of Policy Analysis in the Rand Graduate School,

Dr. Lempert teaches a course on complex adaptive systems and policy

analysis. He authored the book Shaping the Next One Hundred Years: New

Methods for Quantitative, Longer-Term Policy Analysis. Dr. Lempert holds

a PhD in applied physics from Harvard University and a BAS degree in

physics and political science from Stanford University.

Luisa M. Paiewonsky is Commissioner of the Massachusetts Highway

(MassHighway) Department, where she oversees a combined annual capital and operating budget of $890 million, manages 1,850 employees, and

has responsibility for more than 9,500 lane miles of roadway and 2,800

bridges. Before her appointment as Commissioner in 2005, Ms.

Paiewonsky served as Assistant Secretary of the Executive Office of

Transportation and before that as Deputy Commissioner of MassHighway,

responsible for the day-to-day operations of the commonwealth’s road and

bridge program. Ms. Paiewonsky rose through the MassHighway ranks

with a series of promotions that included a 4-year term as Director of the

Bureau of Transportation Planning and Development and Project

Study Committee Biographical Information 279
Manager for the $35 million Southeast Expressway High-Occupancy

Vehicle (HOV) project. She spearheaded MassHighway’s participation in

the development of the Anderson Regional Transportation Center, built

on a former Superfund site. Ms. Paiewonsky is President of the Boston

Chapter of the Women’s Transportation Seminar and a member of the

Northeast Association of State Highway and Transportation Officials. She

serves as a Massachusetts representative to TRB and is secretary of TRB’s

HOV Systems Committee. Ms. Paiewonsky graduated from Mount

Holyoke College with a bachelor’s degree in political science and Spanish.

She holds a master’s degree in city planning from Boston University.

Christopher R. Zeppie is Director of the Office of Environmental Policy,

Programs, and Compliance at the Port Authority of New York and New

Jersey. Since coming to the Port Authority in 1979, Mr. Zeppie has held

positions of increasing responsibility as Environmental Compliance

Specialist; Manager, Permits and Governmental Approvals; Attorney,

Environmental Law Division; Assistant Director, Office of Environmental

Management; and Chief Environmental Policy Officer. He is a member of

the Dean’s Council at the State University of New York at Stony Brook’s

School of Marine and Atmosphere Studies, the Advisory Committee of

the Environmental Division of the New York Academy of Sciences, the

Review Panel for the Stony Brook Storm Surge Research Group

Investigation of the Hydrologic Feasibility of Storm Surge Barriers to

Protect the Metropolitan New York–New Jersey Region, and a Stakeholder

Partner of the Infrastructure Group for the Metropolitan East Coast

Regional Assessment. Mr. Zeppie was appointed by Mayor Bloomberg to

serve on the Jamaica Bay Watershed Advisory Committee and will be representing the Port of New York and New Jersey as a delegate to the C40

Conference working group on Port Facilities in Rotterdam. He holds a

bachelor of science degree in biology and ecology from Manhattan

College, a master’s degree in marine environmental science from State

University of New York at Stony Brook, and a JD degree from St. John’s

University School of Law.

280 Potential Impacts of Climate Change on U.S. Transportation