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-1 â¢ Special Report 245 M MM%Wkwo Implications for Air Quality and Energy Use TRANSPORTATION RESEARCH BOARD National Research Council
TRANSPORTATION RESEARCH BOARD 1995 EXECUTIVE COMMITTEE Chairman: Lillian C. Borrone, Director, Port Department, The Port Authority of New York and NcwJersey New York City Vice Chairman: James W. van Loben Sels, Director, California Department of Transportation, Sacramento Executive Director: Robert B. Skinner,Jr., Transportation Research Board Edward H. Arnold, Chairman and President, Arnold Industries, Lebanon, Pennsylvania Sharon D. Banks, General Manager, AC Transit, Oakland, California BrianJ. L. Berry, Lloyd Viel Berkner Regental Professor and Chair, Bruton Center for Development Sttidies, University of Texas at Dallas Dss'ight M. Bosver, Director, Idaho Transportation Department, Boise John B. Breen, The Nasser I. Al-Rashid Chair in Civil Engineering, Department of Civil Engineering, The University of Texas at Austin William F. Bundy, Director, Rhode Island Department of Transportation, Providence David Burwell, President, Rails-to-Trails Conservancy, 'Washington, D.C. A. Ray Chamberlain, Vice President, Freight Policy, American Trucking Associations, Alexandria, Virginia (Past Chairman, 1993) Ray W. Clough (Nishkian Professor of Structural Engineering, Emeritus, University of California, Berkeley), Structures Consultant, Sunriver, Oregon James C. PeLong, Director of Aviation, Denver International Airport, Colorado James N. Dcnn, Commissioner, Minnesota Department of Transportation, St. Paul, Minnesota DennisJ. Fitzgerald, Executive Director, Capital District Transportation Authority Albany, New York James A. Hagen, Chairman of the Board, Conrail Inc., Philadelphia, Pennsylvania Delon Hampton, Chairman and CEO, Delon Hampton & Associates, Chartered, Washington, D.C. Lester A. Hod, I-Ianiilton Professor, Department of Civil Engineering, University of Virginia, Charlottesville Don C. Kelly, Secretary, Kentucky Transportation Cabinet, Frankfort Robert Kochanow'ski, Executive Director, Southwestern Pennsylvania Regional Planning Commission, Pittsburgh James L. Lammie, President and CEO, Parsons Brinckerhoff, Inc., New York City Charles P. O'Leary,Jr., Commissioner, New Hampshire Department of Transportation, Concord Jude W. P. Patin (Brig. Gen., U.S. Army, retired), Secretary Louisiana Department of Transportation and Development, Baton Rouge Craig E. Philip, President, Ingram Barge Company, Nashville, Tennessee Darrel Rensink, Director, losva Department of Transportation, Ames Joseph M. Sussman,JR East Professor and Professor of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge (Past Chairman, 1994) Martin Wachs, Director, Institute of Transportaliots Stttdies, School of Public Policy and Social Research, University of California, Los Angeles David N. Worniley, Dean of Engineering, Pennsylvania State University, University Park Howard Yerusalim, Vice President, KCI Technologies, Inc., Hunt Valley, Maryland Mike Acott, President, National Asphalt Pavement Association, Lanham, Maryland (ex officio) Roy A. Allen, Vice President, Research and Test Department, Association of American Railroads, Washington, D.C. (ex officio) / Andrew H. Card,Jr., President and CEO, American Automobile Manufacturers Association, Washington, D.C. (ex officio) ThomasJ. Donohue, President and CEO, American Trucking Associations, Inc., Alexandria, Virginia (ex officio) Francis B. Francois, Executive Director, American Association of Stale Highway and Transportation Officials, Washington, D.C. (ex officio) Jack R. Gilstrap, Executive Vice President, American Public Transit Association, Washington, D.C. (ex officio) AlbertJ. Herberger (Vice Adm., U.S. Navy, retired), Administrator, Maritime Administration, U.S. Department of Transportation (ex officio) David R. Hinson, Administrator, Federal Aviation Administration, I.I.S. Department of Transportation (ex officio) T. R. Lakshmanan, Director, Bureau of Transportation Statistics, U.S. Department of Transportation (ex officio Gordon J. Linton, Administrator, Federal Transit Administration, U.S. Department of Transportation (ex officio) Ricardo Martinez, Administrator, National Highway Traffic Safety Administration, U.S. Department of Transportation (ex officio) Jolene M. Molitoris, Administrator, Federal Railroad Administration, U.S. Department of Transportation (ex officio) Dharmendra K. Sharma, Administrator, Research and Special Programs Administration, U.S. Department of Transportation (ex officio) Rodney B. Slater, Administrator, Federal Highway Administration, U.S. Department of Transportation (ex officio) Arthur E. Williams (Lt. Gen., U.S. Army), Chief of Engineers and Consmancler, U.S. Arm)' Corps of Engineers, Washington, D.C. (ex officio)
Special Report 245 EXPANDING METRUP011TAN HIGHWAYS Implications for Air Quality and Energy Use Committee for Study of Impacts of Highway Capacity Improvements on Air Quality and Energy Consumption TRANSPORTATION RESEARCH BOARD National Research Council National Academy Press Washington, D.C. 1995
Transportation Research Board Special Report 245 Subscriber Categories IA planning and administration lB energy and environment Transportation Research Board publications are available by ordering directly from TRB. They may also be obtained on a regular basis through organizational or individual affiliation with TRB; affiliates or library subscribers are eligible for substantial discounts. For further informa- tion, write to the Transportation Research Board, National Research Council, 2101 Constitu- tion Avenue, NW, Washington, D.C. 20418. Copyright 1995 by the National Academy of Sciences. All rights reserved. Printed in the United States of America. NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the Na- tional Academy of Sciences, the National Academy of Engineering, and the Institute of Medi- cine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to the proce- dures approved by a Report Review Committee consisting of members of the National Acad- emy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The study was sponsored by the Transportation Research Board, the American Association of State Highway and Transportation Officials, the Federal Highway Administration of the U.S. Department of Transportation, and the Environmental Protection Agency. Transportation Research Board funds came from unrestricted contributions of the Association of American Railroads, the UPS Foundation, Norfolk Southern Corporation, and Consolidated Rail Corporation. Library of Congress Cataloging-in-Publication Data Expanding metropolitan highways: implications for air quality and energy use/Committee for a Study of the Impacts of Highway Capacity Improvements on Air Quality and Energy Consumption. P. cm.â(Special report: 245) Includes bibliographical references. ISBN 0-309-06107-5 1. Highway capacityâUnited States. 2. Traffic flowâUnited States. 3. AirâPollutionâEconomic aspectsâUnited States. 4. Energy consumptionâUnited States. I. National Research Council (U.S.). Transportation Research Board. Committee for a Study of the Impacts of Highway Capacity Improvements on Air Quality and Energy Consumption. 11. Series: Special report (National Research Council (U.S.). Transportation Research Board) : 245. HE336.H48E95 1995 388.4'13142'0973âdc2O 95-4464 CIP Cover design: Karen L. White
Committee for Study of Impacts of Highway Capacity Improvements on Air Quality and Energy Consumption PAUL E. PETERSON, Chairman, Harvard University, Cambridge, Massachusetts PAUL E. BENSON, California Department of Transportation, Sacramento ROBERT G. DULLA, Sierra Research, Sacramento, California GENEVIEVE GIUuANO, University of Southern California, Los Angeles DAVID L. GREENE, Oak Ridge National Laboratory, Tennessee FRANK S. KOPPELMAN, Northwestern University, Evanston, Illinois KENNETH J. LEONARD, Wisconsin Department of Transportation, Madison EDWIN S. MILLS, Northwestern University, Evanston, Illinois STEPHEN H. PUTMAN, University of Pennsylvania, Philadelphia WILLIAM R. REILLY, Catalina Engineering, Inc., Tucson, Arizona MICHAEL A. REPLOGLE, Environmental Defense Fund, Washington, D.C. GORDON A. SHUNK, Texas Transportation Institute, Arlington KENNETH E. SULZER, San Diego Association of Governments, California GEORGE V. WICKSTROM, Metropolitan Washington Council of Governments (retired), Kensington, Maryland CATHERINE WITHERSPOON, South Coast Air Quality Management District, Diamond Bar, California JULIAN WOLPERT, Princeton University, Princeton, New Jersey Liaison Representatives DAVID H. CLAWSON, American Association of State Highway and Transportation Officials FREDERICK DUCCA, Federal Highway Administration, U.S. Depart- ment of Transportation
ROBIN MILES-MCLEAN, Environmental Protection Agency STEPHEN BLAKE, National Cooperative Highway Research Program, Transportation Research Board Transportation Research Board Staff NANCY P. HUMPHREY, Study Director
ProtaGo The Clean Air Act Amendments of 1990 (CAAA) raised the impor- tance of air quality as a goal for the transportation sector alongside the more traditional goals of mobility and safety. Transportation agen- cies face an enormous challenge to provide a transportation system that meets these multiple goals. In particular, highway projectsâthe backbone of traditional transportation programsâhave come under intense scrutiny. Once thought to reduce congestion and air pollution, projects that expand highway capacity are now being questioned for their stimulative effect on motor vehicle travel and their support of dispersed metropolitan development patterns, which foster additional automobile dependence and thereby increase emissions. Legislation similar to the CAAA has not been passed recently in the energy area. However, in the past decade low gasoline prices, grow- ing motor vehicle ownership, and increased motor vehicle travel have raised transportation's share of total petroleum consumption in the United States and increased U.S. energy dependence on foreign oil sources. Although energy efficiency measures are important, they are not viewed as having the same urgency as measures to improve air quality, nor are energy issues likely to be subjects of litigation when highway expansion projects are proposed.
vi Preface The current concern over the effects of highway building on both the environment and energy use is part of a broader debate over the appropriate direction of metropolitan development and the role of transportation in that process. Many view incremental, evolutionary change as the only realistic and politically feasible course in moving to a less polluting, more energy-efficient transportation system. Others seek major revisions in land use policies and significant increases in the price of motor vehicle travel to promote these goals; they view the CAAA as a strategic instrument for change. The varied approaches re- flect different visions of the future; different judgments about the ap- propriate balance among economic growth, environmental protection, and energy conservation; and different views about the effectiveness of technology versus behavior change for achieving these goals. This study is cognizant of these larger issues, but it is focused on the more practical questions that policy makers and planners face in complying with the CAAA. Its purpose is to review the current state of knowledge, evaluate the scientific evidence, and narrow the areas of disagreement about the impacts of highway capacity additions on traffic flow characteristics, travel demand, land use, vehicle emissions, air quality, and energy use. Its intended audiences are key policy mak- ers in Congress, the Environmental Protection Agency (EPA), the Fed- eral Highway Administration (FHWA), and the Department of Energy; implementers and overseers of the CAAA, including congressional staff, state and local air quality and transportation agencies, and the courts; and the research community. The study, which was initiated by the Transportation Research Board (TRB) Executive Committee, received broad funding support from FHWA; the American Associa- tion of State Highway and Transportation Officials (through the Na- tional Cooperative Highway Research Program); EPA; and TRB's In- stitute for Strategic Transportation Studies, supported by unrestricted grants from the UPS Foundation, the Association of American Railroads, Consolidated Rail Corporation, and Norfolk-Southern Corporation. TRB formed a study panel of 16 experts under the leadership of Paul E. Peterson, Henry Shattuck Professor of Government at Harvard Uni- versity. The committee includes specialists in travel behavior and travel demand modeling, traffic engineering, vehicle emissions and air quality modeling, motor vehicle fuel economy, transportation and
Preface vii land use, land use modeling, and transportation and air quality plan- ning. Panel members are drawn from universities, state government, metropolitan planning organizations, environmental organizations, and consulting firms. With one exception, the committee endorses all of the report find- ings and recommendations. One committee member, Michael A. Replogle, agreed with many elements of the report but dissented from some of the key findings. His statement is presented in its entirety as Appendix E. In accord with National Research Council policies, this appendix provides the opportunity for the expression of views not shared by the majority of the committee. That a minority view has been offered is not surprising because the study raises complex and difficult questions that have confounded scholars for decades. The committee wishes to acknowledge the work of many individ- uals and organizations who contributed to this report. Nancy P. Humphrey managed the study and drafted major portions of the final report under the guidance of the committee and the supervision of Robert F. Skinner, Jr., former Director of Studies and Information Ser- vices and current Executive Director of TRB, and Stephen R. Godwin, current Director of Studies and Information Services. Mr. Godwin drafted Chapter 5 and Appendix D. Suzanne Schneider, Assistant Executive Director of TRB, managed the report review process. In accordance with the National Research Council report review proce- dures, the report was reviewed by an independent group of reviewers. The committee also wishes to thank many individuals outside TRB whose advice it sought in the course of its deliberations. William Schroeer of EPAs Office of Policy, Planning, and Evaluation and John German of the Certification Division of EPAs Office of Mobile Sources provided useful input to the committee on EPAs regulatory policies and on the Federal Test Procedure Review Project, respectively. Greig Harvey of Deakin, Harvey, Skabardonis, Inc., provided the committee with an overview of the recent court case against the Metropolitan Transportation Commission of the San Francisco Bay Area and its im- plications for conformity analysis requirements and modeling proce- dures. Finally, Randy Guensler of the Georgia Institute of Technology prepared special analyses, based on his dissertation results, for the dis- cussion of the uncertainty of emission rate estimates from current models contained in Chapter 3.
viii Preface The committee also commissioned several papers to inform its deliberations. The papers are appended to the report to make the information available to a broad audience. The interpretations and conclusions reached in the papers are those of the authors; the key findings endorsed by the committee appear in the main body of the report. Harry S. Cohen of Cambridge Systematics, Inc., prepared a lit- erature review of the effects of highway capacity additions on travel demand. The major findings of that report are included in Chapter 4 with supporting detail in Appendix B. Two papers were commissioned on heavy-duty diesel vehicles, because their response to highway capacity additions differs from that of light-duty vehicles. K. G. Duleep of Energy and Environmental Analysis, Inc., reviewed the emission and energy characteristics of heavy-duty diesel vehicles and provided an assessment of how they might be affected by highway capacity ad- ditions. His paper is included in its entirety as Appendix A, and its findings are discussed in Chapter 3. Lance R. Grenzeback of Cam- bridge Systematics, Inc., examined the likely effect of changes in high- way capacity on truck travel. His paper is included as Appendix C, and its findings are discussed in Chapter 4. These two papers make a significant contribution to an area about which little has been written. The final report was edited and prepared for publication under the supervision of Nancy A. Ackerman, Director of Reports and Editorial Services, TRB. Special appreciation is expressed to Luanne Crayton, Norman Solomon, and Lisa Wormser, who edited the report, and to Marguerite Schneider and Frances Holland, who assisted in meetings, logistics, and communications with the committee and provided word processing support for numerous drafts.
contoots Executive Summary ................................. Introduction ..................................11 Regulatory Context 13 Study Focus 21 Definition of Terms 22 Overview of Impacts 24 Assessment of Impacts 29 Organization of Report 31 2 Contribution of Motor Vehicle Transportation to Air Pollution and Energy Consumption ...........38 Transportation and Air Quality 38 Transportation and Energy Consumption 61 Modeling Air Quality and Energy Impacts 65 Summary 75 3 Traffic Flow Characteristics ......................87 Overview of Expected Impacts 87 Review of Effects on Emissions 90 Summary Assessment of Effects on Emissions and Air Quality 122
Review of Effects on Energy Use 124 Summary Assessment and Recommendations for Improving the Knowledge Base 127 4 Travel Demand ................................138 Determinants of Metropolitan Travel Demand and Recent Travel Trends in the United States 138 Overview of Expected Impacts and Definition of Terms 143 Theoretical Understanding of Travel Choices and Impacts 149 Review of Evidence from Studies 152 Review of Impacts from Travel Demand Models 159 Summary Assessment of the State of Knowledge 162 Review of Impacts on Truck Travel 164 Recommendations for Improving the Knowledge Base 167 5 Land Use and Urban Form .......................174 Background 176 Theory Linking Transportation and Land Use 183 Empirical Evidence 185 Results from Models 190 Implications of Changes in Population Density for Travel and Emissions 194 Summary 201 Recommendations for Improving the Knowledge Base 203 6 Findings and Conclusions .......................210 Overview 211 Crosscutting Issues 213 Findings for Individual Impact Areas 215 Summary Assessment of Net Effects 224 Recommendations for Research, Modeling Improvements, and Data Collection 227 Concluding Observations 230
Appendix A Emission and Energy Characteristics of Heavy-Duty Diesel-Powered Trucks and Buses 237 K. G. Duleep Appendix B Review of Empirical Studies of Induced Traffic 295 Harry S. Cohen Appendix C Impact of Changes in Highway Capacity on Truck Travel 310 Lance R. Grenzeback Appendix D Review of Studies of Transportation Investments and Land Use 345 Appendix E Minority Statement of Michael A. Replogle 354 Study Committee Biographical Information .............. 381
EXOGutivo summary The Clean Air Act Amendments of 1990 (CAAA) and complementary provisions of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) introduced new constraints on the transportation sec- tor to help ensure that transportation activities do not delay expedi- tious attainment of national health standards for air quality. As a re- sult highway projects that expand capacity have come under particular scrutiny in many metropolitan areas for their potential to increase motor vehicle traffic and emissionsâa primary source of air pollu- tion. The issue is already at the center of legal challenges or threats of litigation in several metropolitan areas, potentially stalling local high- way construction programs. For years transportation agencies have responded to traffic growth by expanding highway capacity to maintain reasonable levels of service. Capacity expansions ranging from small-scale signal-timing improvements to construction of major highways were expected to re- lieve congestion without substantial negative effects on air quality. In fact, capacity enhancements that raised travel speeds and smoothed traffic flows were believed to reduce vehicle emissions and improve
2 EXPANDING METROPOLITAN HIGHWAYS energy efficiency. Further, it was widely accepted that new highway capacity was essential to the continued economic growth and com- petitiveness of major metropolitan areas. These views are now being challenged. Some analysts and envi- ronmental groups argue that adding highway capacity will result in more traffic, higher emission levels, and greater energy consumption in the long run by stimulating motor vehicle travel and encouraging dispersed, automobile-oriented development. In addition they see continued highway expansion as antithetical to a more environmen- tally oriented and resource-conscious future that stresses the revital- ization of older urban and inner suburban neighborhoods and sup- ports transit and nonmotorized forms of transport. These issues are part of a larger debate over the appropriate direc- tion of metropolitan growth and the role of transportation in that process. This debate involves value judgments about the relative im- portance of mobility, economic growth, environmental protection, and energy conservation. It considers a broad range of policies, from investments in transportation supply to demand management and pricing strategies. This study is focused on a more specific topic:, the effects of in- vestment in highway capacity on air quality and energy use in metro- politan areas. Its primary audience is metropolitan planning organi- zations (MPOs), state officials, legislators, and courts with oversight responsibilities. These agencies and officials are being asked to meet the regulatory requirements of the CAAA by making judgments about the environmental effects of highway capacity expansion on the basis of their interpretation of the best available evidence. Energy issues do not convey the same urgency or require the same regulatory analysis, yet transportation's increasing consumption of the nation's petroleum resources is of concern. To the extent that energy efficiency and en- ergy use are affected by changes in traffic flow characteristics and travel volume from highway capacity expansion, these effects are con- sidered in this study. The purpose of this study is to review the current state of knowl- edge, evaluate the scientific evidence, and narrow the areas of dis- agreement about the impacts of highway capacity additions on traffic flow characteristics, travel demand, land use, vehicle emissions, air quality, and energy use. The state of modeling practice is also exam-
Executive Summary 3 med to assess the reliability of forecasting tools available to planning agencies; research, modeling improvements, and data collection are recommended to help narrow the gap between regulatory require- ments and analytic capabilities. International experience relevant to the study charge was consid- ered, and alternatives to highway capacity expansion, such as "traffic calming," were examined to the extent they shed light on the effect of changes in traffic flow characteristics on vehicle emissions and en- ergy use. In most cases, however, the experience of other countries, particularly European countries, is not directly applicable to the United States because of considerable differences in land availability and cost, population density, mode choice, pricing structures, and in- stitutional governance of regional growth. Wholesale adoption of Eu- ropean transport strategies might produce some reductions in vehicle energy use and emissions and concomitant improvement in metro- politan air quality, but, in the committee's judgment, it would also im- pose substantial social and economic costs and raise questions about institutional and political feasibility. REGULATORY CONTEXT Under the CAAA the U.S. Department of Transportation (DOT) and MPOs are directly accountable for demonstrating the compatibility of transportation investments with timely attainment of national air quality standards. According to the current interpretation in Envi- ronmental Protection Agency (EPA) regulations, the act provides a grace period for states to revise their air quality attainment plans, which set emissions limits by source. In the meantime, transportation agencies in metropolitan areas that have not attained national stan- dards must meet strict interim conformity requirements to prevent air quality degradation. Specifically, nonattainment areas are required to prove that (a) projects in regional transportation improvement pro- grams and plans will not lead to motor vehicle emissions higher than in a 1990 baseline year and (b) by building these projects, emissions will be lower in future years than if the projects are not built (the "buildâno-build" test).
4 EXPANDING METROPOLITAN HIGHWAYS Once EPA approves new state air quality attainment plans the con- formity test changes: the emissions that result from carrying out re- gional transportation improvement programs and plans in nonattain- ment areas must not exceed target emissions caps for transportation sources established in the EPA-approved state air quality plans. The conformity test still requires a regional emissions analysis, but the cri- terion for comparison is less demanding: predicted regional emissions from transportation sources must be within state-determined emis- sions budget caps. The most analytically demanding comparisonâ estimating changes in emission levels in future years from marginal expansions of regional transportation networks relative to maintaining the status quoâwould no longer be required. The committee did not limit its examination of the effects of high- way capacity additions to a specific time frame. However, particular attention was paid to the 20-year time frame established by the CAAA for attainment of air quality standards, because this represents the planning and forecasting horizon within which local planning agen- cies are required to make judgments about the air quality effects of highway projects. ANALYTIC REQUIREMENTS Providing a precise assessment of the net effects of expansions of high- way capacity on air quality and energy use is not straightforward. Addressing the questions raised in this study requires modeling a com- plex sequence of interrelated eventsâfrom initial impacts on traffic flows to longer-term consequences on travel demand, automobile ownership, and residential and business location in a metropolitan area. It also requires modeling the emissions generated by the pre- dicted travel impacts and forecasting their effects on air quality at or near the points of emission and throughout the region. There is sig- nificant uncertainty in predicting precise quantitative outcomes at each stage in the analysis. In addition, different levels of analysis are required to distinguish project-level from regional effects. Determination of initial effects is complicated by the network char- acter of the transportation system. The ability of drivers to change their route, time, and mode of travel means that adding highway ca-
Executive Summary 5 pacity and thus reducing travel time at one location in the system will affect other locations as users take advantage of the new capacity. Mod- ifications in traffic flows and volumes on this broader system of facil- ities, and their effects on emissions and energy use, must be taken into account. User responses also change over time. The response to large re- ductions in travel time is likely to be greater in the long run than ini- tially, as highway capacity additions influence decisions about loca- tion and automobile ownership. The key uncertainty is at what point, or whether at any point, the emissions increases from the new devel- opment and traffic growth stimulated by the capacity addition will off- set the initial emission reductions gained from smoothing traffic flows. Assessment of net project effects on emissions and energy use depends on the length of time over which the effects are analyzed and the value placed on long-term versus more immediate effects. The longer the prediction period the more likely other, often unpredictable factors such as changes in demographic or economic conditions are to inter- vene and diminish forecasting accuracy. Forecasts of the net effects of adding highway capacity also involve comparisons with alternatives. Not investing in highway capacity or undertaking other investments or demand management strategies has consequences for air quality and energy use. A comparison of out- comes requires estimating how sensitive users are to changes in travel time and cost and to what extent travel by transit or other modes can be substituted for automobile travel. It also requires understanding how growth would be distributed both within and outside the met- ropolitan area if highway capacity expansions were restricted. Para- doxically, because of past and ongoing efforts to reduce vehicular emissions, it will become more difficult to discern differences in emis- sions resulting from different transportation and demand management strategies. These alternative strategies all represent small changes to a declining base of emissions from highway sources. FINDINGS After examining the considerable literature on the relationships among transportation investment, travel demand, and land use as well
6 EXPANDING METROPOLITAN HIGHWAYS as the current state of the art in modeling emissions, travel demand, and land use, the committee finds that the analytical methods in use are inadequate for addressing regulatory requirements. The accuracy implied by the interim conformity regulations issued by EPA, in par- ticular, exceeds current modeling capabilities. The net differences in emission levels between the build and no-build scenarios are typically smaller than the error terms of the models. Modeled estimates are imprecise and limited in their account of changes in traffic flow char- acteristics, trip making, and land use attributable to transportation investments. The current regulatory requirements demand a level of analytic precision beyond the current state of the art in modeling. The state of emissions modeling illustrates the problem well. In the- ory the initial effect of a highway capacity addition on traffic flow char- acteristics and the resulting changes in vehicle emissions should be measurable for the current fleet. Despite considerable research and ve- hicle testing, however, no definitive and comprehensive conclusions can be reached. Virtually all motor vehicle testing has been based on a limited set of driving test cycles that inadequately represent current urban driving conditions. In addition, current emission models rely on average trip speed as the sole descriptor of traffic flows. Variabil- ity in speed, road grade, and other factors that strongly influence emis- sions is not explicitly incorporated into the models. Changes in vehicle emission rates thus cannot be predicted reliably for a wide range of changes in average trip speeds, many of which are in the range of average speed changes expected from highway capacity additions. Current emissions models were developed to estimate motor vehi- cle emissions at the regional level. They cannot be appropriately ap- plied to estimate the emissions effect of changes in traffic flow pat- terns at specific highway locations. Even for regional estimates, current models significantly underpredict emissions of some pollu- tants. Models can be developed that are more sensitive to vehicle op- erations and traffic conditions; some research and testing have already begun. However, development and incorporation of new models into the regulatory process will take substantial time and investment and require close coordination between the transportation and the regu- latory communities. The initial effects on energy use from highway capacity additions can be predicted more reliably than effects on emissions because fuel
Executive Summary 7 economy is not as sensitive as emissions to traffic flow conditions, par- ticularly speed variation. However, energy and emissions estimates must both be linked with reliable data on the likely impacts of highway capacity additions on traffic, travel demand, and location decisions. Here, too, the available travel demand and land use models provide imprecise and limited estimates of likely outcomes. Improve- ments in modeling capability will also require substantial investment. More research and improved models can help narrow the gap be- tween regulatory requirements and analytic capabilities. The confor- mity tests required by current regulations will themselves change as the buildâno-build test is phased out once state air quality plans are approved by EPA. However, the complex and indirect relationship be- tween highway capacity additions, air quality, and energy use, which is heavily dependent 6n local conditions, makes it impossible to gen- eralize about the effects of added highway capacity on air quality and energy use, even with improved models. On the basis of current knowledge, it cannot be said that highway capacity projects are always effective measures for reducing emissions and energy use. Neither can it be said that they necessarily increase emissions and energy use in all cases and under all conditions. Effects are highly dependent on specific circumstances, such as the type of capacity addition, location of the project in the region, extent and duration of preexisting congestion, prevailing atmospheric and topo- graphic conditions, and development potential of the area. Nevertheless, some general findings do apply. Within developed areas, traffic flow improvements such as better traffic signal timing and left-turn lanes that alleviate bottlenecks may reduce some emis- sions and improve energy efficiency by reducing speed variation and smoothing traffic flows without risking large offsetting increases from new development and related traffic growth. However, the cumula- tive effect of multiple small improvements in traffic flows may attract increased traffic, at least in the vicinity of the improvements. In less- developed portions of growing metropolitan areasâwhere devel- opable land is available and most growth is occurringâmajor high- way capacity additions such as a freeway bypass or a major interchange reconstruction are likely to attract further development to these loca- tions and increase motor vehicle travel, emissions, and energy use in these areas. Whether these outcomes lead to a net increase in regional
8 EXPANDING METROPOLITAN HIGHWAYS emissions and energy use depends on whether the highway expan- sion redistributes growth that would have occurred elsewhere in the region or whether it stimulates productivity gains that result in net new growth. CONCLUDING OBSERVATIONS Despite the considerable uncertainties in predicting the effects of expanding highway capacity on air quality given the current state of knowledge and modeling practice, policy makers and planners must comply with current environmental regulatory requirements and make decisions on the basis of the best available information. Thus, the committee thought it should provide its best judgment on the likely payoffs of pursuing current policies. In its opinion, the current regulatory focus on curbing growth in motor vehicle travel by limiting highway capacity is at best an indirect approach for achieving emissions reductions from the transportation sector that is likely to have relatively small effects, positive or nega- tive, on metropolitan air quality by current attainment deadlines. His- torically, measures to control traffic demand have had limited effects (Apogee Research, Inc. 1994). According to estimates from local stud- ies using current emission models, these traditional transportation control measures (TCMs), which include traffic flow improvements among others, are likely to yield changes of 1 or 2 percentage points individually in regional emissions of key pollutants by attainment deadlines (DOT and EPA 1993, 9). The effects of traffic flow im- provements could be positive or negative, depending on offsetting in- creases in traffic. These are small changes on a declining base, given EPA projections of continuing emission reductions for carbon monox- ide and volatile organic compounds (DOT and EPA 1993, 9). In the committee's opinion, major highway capacity additions are likely to have larger effects on travel and to increase emissions in the affected transportation corridors in the long run unless some miti- gating strategy is implemented in conjunction with the capacity ad- dition. However, because of the large investment implicit in current metropolitan spatial patterns, it may be years before changes in land use and related traffic patterns induced by the added capacity make a significant difference in regional emission levels and air quality.
Executive Summary 9 Curtailment of all highway capacity expansion that has any poten- tial for increasing emissions risks pitting environmental against eco- nomic concerns. In the past, when environmental goals have con- flicted with economic objectives, the response has been to delay or reassess environmental regulations. It is easy to envision these pres- sures building again. In addition, requiring policy decisions to hinge on uncertain model outputs leaves the entire process vulnerable to error and manipulation. In the committee's view, a more constructive approach is to look for ways to reconcile air quality with economic goals. The committee believes that technology improvements can yield more significant ben- efits for air quality relative to the current focus on curbing travel growth. Catalytic converters, electronic fuel injection, and unleaded gasoline have resulted in substantial reductions in vehicle emissions in the past 20 years (Nizich et al. 1994). EPA predicts further emis- sion reductions for major pollutants on the order of one-quarter to one-third from 1990 baseline levels by attainment deadlines simply from continued vehicle fleet turnover and implementation of CAAA- required vehicular and fuel standards and enhanced vehicle inspec- tion and maintenance programs (Nizich et al. 1994, 5-4, 5-6). Market solutions also have promise, although the feasibility of some approaches is untested. For example, potential increases in traffic from new highway capacity such as added expressway lanes might be reduced by imposing tolls varied by time of day (i.e., congestion pricing) and collected electronically to control travel growth on the expanded facility. A recent National Research Council report on con- gestion pricing (NRC 1994) has examined in depth the technical and political feasibility of this approach. Applied in a limited setting, it would not require major changes in current highway finance patterns. It would allow highway capacity to be provided where it is needed but could mitigate negative effects on emissions from travel growth. In the long run, stronger measures, such as pricing motor vehicle travel to better reflect the full social costs of highway travel and the introduction of areawide, time-of-day tolls, may be necessary to pro- vide direct incentives for reducing or shifting travel demand in ways that use highway capacity more efficiently and with less cost to the environment. Local land use and zoning measures that increase build- ing density and support mixed-use development could be introduced
10 EXPANDING METROPOLITAN HIGHWAYS more widely. Land use measures may reduce areawide automobile travel and emissions, but the changes are likely to occur gradually and will have more significant effects if they are implemented in conjunc- tion with pricing measures. Finally, radical advances in vehicle tech- nology could produce cleaner transportation, substantially reducing the level of vehicle emissions. These more radical solutions are neither new nor easy. Major tech- nological improvements require substantial investment and time to produce results. Changes in pricing or land use policies require sig- nificant institutional changesâsuch as more powerful regional insti- tutions to coordinate areawide pricing schemes and land use strate- giesâand more public acceptance than has been demonstrated in the past. In the judgment of the committee, however, as long-run alter- natives to current policy, they offer better prospects for reconciling economic and environmental goals. REFERENCES ABBREVIATIONS DOT U.S. Department of Transportation EPA Environmental Protection Agency NRC National Research Council Apogee Research, Inc. 1994. Costs and Effectiveness of Transportation Control Measures (TCMs): A Review and Analysis of the Literature. National Association of Regional Councils, Bethesda, Md. DOT and EPA. 1993. Clean Air Through Transportation: Challenges in Meet- ing National Air Quality Standards. Aug. Nizich, S.V, T.C. McMullen, and D.C. Misenheimer. 1994. National Air Pol- lutant Emission Trends, 1900-1 993. EPA-454/R-94-027. Office of Air Quality Planning and Standards, Research Triangle Park, NC., Oct., 314 pp. NRC. 1994. Special Report 242: Curbing Gridlock: Peak-Period Fees to Relieve Traffic Congestion, Volumes I and 2. Transportation Research Board and Commission on Behavioral and Social Sciences and Education, National Academy Press, Washington, D.C.
Introdution The Clean Air Act Amendments of 1990 (CAAA) (Public Law 101- 549, 42 U.S.C. 7401, et seq.) and complementary provisions of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) (Public Law 102-240, 49 U.S.C. 101 note) tightened controls on the transportation sector to help ensure that transportation activities con- tribute to timely attainment of national health standards for air qual- ity. As a result traditional transportation projects, such as additions to highway capacity, have come under close scrutiny as potential con- tributors to air pollution. For years transportation officials have relied on adding highway capacityâbuilding new expressways and adding lanes to existing free- waysâto accommodate travel demand in growing metropolitan areas. Such increases in capacity were thought not only to bring congestion relief but also to improve air quality and fuel efficiency by contribut- ing to freer-flowing traffic conditions. This conventional wisdom has been challenged by environmental planners and other analysts who take a long-term perspective on the 11
12 EXPANDING METROPOLITAN HIGHWAYS effects of additional highway capacity. They concede that adding high- way capacity may initially reduce some vehicle emissions and improve fuel efficiency by smoothing traffic flows and reducing stop-and-go traf- fic, although the benefits may not be as significant as were once believed. However, these positive effects may be eroded over time by growth in travel stimulated by the new capacity. Improved levels of highway ser- vice may encourage shifts from less polluting modes of transportation and induce new or longer trips once discouraged by congested condi- tions. As traffic volume grows, traffic operations may deteriorate, pro- ducing levels of congestion comparable with previous conditions but at higher traffic volumes. In the long run, these analysts maintain, new highway capacity will improve access and may encourage development in low-density areas not amenable to transit. Low-density development requires more frequent and longer trips, increasing emission levels and energy use and further degrading air quality. The issue of highway capacity and air quality is already at the cen- ter of legal challenges brought by environmental groups to many ad- ditions to highway capacity in metropolitan areas. This issue is likely to receive more attention as metropolitan areas grapple with the stricter requirements of the CAAA. The act allows citizen suits to be brought for the first time against the U.S. Department of Transporta- tion (DOT) and the Environmental Protection Agency (EPA) for non- compliance with legislative requirements and timetables, which opens the door to increased litigation. Assessment of the precise consequences for air pollution and en- ergy use of any particular addition to highway capacity is uncertain, given the current state of knowledge and modeling practice. Travel demand forecasting modelsâthe basis for determining the effect of increased highway capacity on travel demandâwere originally devel- oped to help determine the appropriate size of new capital facilities. They are not well suited to providing the detailed data, such as speed data and travel data by time of day, needed for modeling and analysis of vehicle emissions and air quality impacts. Nor can most current travel demand models adequately measure the effect of improvenients in highway service on the amount of travel or on land use patterns, which in turn could affect future demand for travel and its distribu- tion in a region. Emissions models, which measure the polluting effects of motor vehicle travel, inadequately represent the emission performance of
Introduction 13 in-service vehicles. Current data on the relationship between vehicle speeds and emission levelsâcritical to analyzing highway capacity projects that will change the distribution of traffic speed levels and variability of speedsâare based on averages that mask wide variances across individual vehicle performance, roadway conditions, and dri- ving behavior. Moreover, the models do not adequately capture major suspected sources of emissions from vehicle accelerations and high speeds, although some research is under way to understand these phenomena. Planning agencies often apply current speed-emission relationships as if they were precisely known. Despite the limitations of the existing knowledge base, engineers and scientists are being pressed to provide reliable estimates of the likely effects of adding highway capacity on emissions and energy use to assist legislators, state officials, metropolitan planning organiza- tions (MPOs), and judges in reaching decisions on these issues. Thus a review of the current state of knowledge has been undertaken to evaluate the scientific evidence concerning these effects and to nar- row areas of disagreement. The specific questions at issue are de- scribed and, where possible, research or analyses that could be con- ducted to speed their resolution are recommended. More specifically, the study committee Critically reviews existing research of the links among highway capacity, traffic flow characteristics, travel demand, land use, ve- hicle emissions, air quality, and energy use in metropolitan areas; Identifies the conditions most likely to affect emissions and en- ergy use; Reviews the reliability of models and analyses that regional and state planning agencies use to forecast travel demand and land use, emission levels, and energy consumption; and Recommends research strategies, modeling improvements, and data collection efforts to improve analytic capabilities. REGULATORY CONTEXT The enactment of the CAAA has refocused attention on the effects of transportation activity on air quality, but legislation to set standards for alleviating air pollution and improving the fuel efficiency of motor vehicles dates back to the 1970s.
14 EXPANDING METROPOLITAN HIGHWAYS Clean Air Legislation and Regulatory Requirements The harmful effects of air pollution on public health were formally recognized by the requirements of the Clean Air Act Amendments of 1970 (Public Law 91-604, 84 Stat. 1676), which mandated establish- ment of national ambient air quality standards (NAAQS) for six pol- lutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (03), particulates (PM-b), and sulfur dioxide (SO2) (Curran et al. 1994, 19). There is no standard for carbon dioxide, the princi- pal greenhouse gas, because carbon dioxide is not toxic and therefore has no direct negative health impact. Historical Trends Since 1970 substantial gains have been made in reducing pollution from transportation sources, primarily through technological improvements such as catalytic converters and electronic fuel injection, which are now standard equipment on cars,' and through the use of lead-free gasoline. Between 1970 and 1993, for example, highway vehicle emissions of CO and volatile organic compounds (VOCs)2 (which are a precursor of ozone) declined by 32 percent and 53 percent, respectively; highway vehicle emissions of lead were effectively eliminated (Nizich et al. 1994a, 3-11, 3-13, 3-16; Figure 1-1). However, highway vehicle emis- sions of nitrogen oxides (N0)âthe other ozone precursorâremained nearly constant (Nizich et al. 1994a, 3-12) .3 Although the emissions models on which these estimates are based typically have underesti- mated absolute emission levels, the trend has been downward. Despite more than two decades of progress in improving air qual- ity, EPA estimated that in 1993 about 59 million people lived in coun- ties that violated one or more of the NAAQS (Curran et al. 1994, 14).4 Thus, the CAAA contain stringent requirements for further reductions in emissions from transportation sources, backed up by strict moni- toring and sanctions for nonperformance, to bring nonattainment areas (i.e., those areas not attaining NAAQS) into compliance.
Introduction 15 Highway vehicle emissions (millions of short tons) 100 80 We 4C 2( C., 70 80 93 70 80 93 70 80 93 Year FIGURE 1-1 Highway vehicle emissions of selected pollutants: 1970, 1980, and 1993 (Nizich et al. 1994a, E-11âE-13). Requirements of the 1990 CAAA The act requires additional technological advances, such as tougher tail pipe standards, enhanced vehicle 'inspection and maintenance programs, and cleaner fuels programs, which should result in further reductions in emissions as newer, cleaner vehicles replace older ones and as technology-oriented programs are implemented. These mea- sures, however, may not offset growth in emissions from motor vehi-
16 EXPANDING METROPOLITAN HIGHWAYS cle travel. For example, if vehicle miles traveled (VMT) grows at a rel- atively conservative rate of 2 percent per year' and no additional tech- nology advances are made other than those included in the CAAA, EPA estimates that tail pipe emission gains could be offset by 2002 for CO and VOC and by 2004 for NO,, (Figure 12).6 Thus, the CAAA mandate measures to limit automobile trips in the most severely polluted areas and require strict monitoring of VMT growth in less severe nonattainment areas. Deadlines for reaching attainment vary with the severity of air qua!- ity problems.7 Areas classified as marginal (40 for ozone) have 3 years from the baseline year, 1990, to attain NAAQS; areas classified as mod- erate (29 areas for ozone, 37 for carbon monoxide) have 6 years. The 12 areas classified as serious for ozone (and 1 for carbon monoxide) have 9 years, whereas the areas classified as severe (9 for ozone) have 15 to 17 years. Los Angeles, the only area classified as extreme (for ozone), has 20 years. Eighty-three areas have been designated as nonattainment for PM-b. Los Angeles is also the only area that does not meet the NO2 standard. Levels of effort also vary with the severity of air quality problems. Areas with ozone classifications of moderate or worse must submit revisions to State Implementation Plans (SIPs) (plans that codify a state's CAAA compliance actions) showing that within 6 years the poi- lutants that create ozone will be reduced by at least 15 percent from 1990 baseline emissions net of any growth in emissions during that period. These areas must achieve an additional 3 percent per year reduction in emissions until attainment is achieved. In addition to the latter requirements, areas classified as severe or extreme must adopt transportation control measures (TCMs) aimed at decreasing auto- mobile travel.8 Areas with carbon monoxide designations only, of moderate or worse, must comply with somewhat different requirements. They must forecast VMT annually beginning in 1992, and if actual VMT exceeds forecast, they must be ready to adopt contingency TCMs that must be included in SIPs. TCMs are required for carbon monoxide areas designated as serious. Finally, the CAAA provide strict sanctions for noncompliance. For example, approval of federally assisted highway projects can be with- held for failure to submit a SIP, EPA disapproval of a SIP, failure to
Introduction 17 make a required submission, or failure to implement any SIP require- ment.9 Once such sanctions have been imposedâand they must be imposed if EPA determines that the deficiency has not been corrected 18 months after being identifiedâDOT can only approve highway safety projects or projects that would not increase single-vehicle au- tomobile travel.'0 Conformity Requirements The requirements and timetables for meeting CAAA goals and sanc- tions for noncompliance are stringent, but not unlike mandates of earlier clean air legislation (e.g., in 1970 and 1977). To help ensure attainment of legislative mandates, regulations implementing the 1990 CAAA strengthen existing conformity requirements. Conformity is a determination made by MPOs and DOT that transportation plans, programs, and projects in nonattainment areas are in accord with the compliance standards contained in SIPs (FHWA 1992b, 12). The new conformity rules under the CAAA hold MPOs and DOT directly accountable for demonstrating that transportation activities will not cause or contribute to any new violation of air quality standards, in- crease the frequency or severity of existing violations, or delay timely attainment of standards (Federal Register 1993b, 62,188). EPA regulations provide a grace period for states to revise their SIPs; revised plans were due November 1994. However, stringent interim conformity guidelines are in effect until EPA has approved these plans to ensure that nonattainment areas do not fall behind in meeting target deadlines for achieving air quality standards. The salient feature of the interim conformity process is project-level review Specifically, MPOs in nonattainment and maintenance areas must show that (a) all feder- ally funded and "regionally significant projects," including nonfederal projects," in regional transportation improvement programs (TIPs) and plans will not lead to emissions higher than in a 1990 baseline year; and (b) by building these projects, emissions will be lower than if the pro- jects are not built. Once SIPs are approved by EPA,'2 the conformity test becomes less demanding: MPOs must demonstrate through a regional analysis that the emissions produced by implementation of transporta- tion plans and TIPs will not exceed target levels (known as emission
% Change in Motor Vehicle CO Emissions a ,ts 100 80 60 20 VMT Growth Â°2% Â±3% *4% 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year % Change in Motor Vehicle VOC Emissions 120 20 VMT Growth 2% Â±3% *4% 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year FIGURE 1-2 Relationship between travel growth and motor vehicle emissions (data from EPA Motor Vehicle Emission Laboratory, 1994).
Introduction 19 % Change in Motor Vehicle NOx Emissions 200 150 ibIs] 50 VMT Growth - Â°2% +3% *4% 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year Figure 1-2 (continued) budgets)13 for motor vehicle emission sources from nonattainment and maintenance areas contained in the SIPs. The conformity regulations thus provide the teeth to help guaran- tee compliance with air quality mandates. MPOs must reconcile emis- sion estimates from transportation plans and TIPs with those con- tained in the motor vehicle emission budgets in SIPs, conduct periodic testing to determine whether actual emissions are in line with esti- mates, and take remedial action if they are not. Court challenges have already been issued by environmental groups against several state transportation departments to ensure that conformity requirements and attainment deadlines are met.'4 IS TEA ISTEA complements the CAAA by reinforcing air quality conformity requirements. The act allows local areas flexibility to shift highway funds to transit and other cleaner modes, enhances the planning re-
20 EXPANDING METROPOLITAN HIGHWAYS sponsibilities of MPOs that are responsible for conformity analyses, and creates a new Congestion Mitigation and Air Quality Improve- ment Program to direct funds to projects and programs in nonattain- ment areas that will contribute directly to attainment of the NAAQS (FHWA 1992c, 16-17). Metropolitan transportation planning regu- lations, in particular, were revised in part to ensure greater consistency and coordination between development of transportation and air qual- ity plans (Federal Register 1993c).'5 Energy Regulation Legislation similar to the CAAA has not been passed recently in the energy area. In response to the oil embargo imposed by the Organi- zation of Petroleum Exporting Countries (OPEC) in 1973 and because the automotive sector is a major consumer of petroleum, Congress passed the Energy Policy and Conservation Act of 1975, which set fuel economy standards requiring that automotive manufacturers increase the corporate average fuel economy (CAFE) of automobiles and light trucks sold in the United States to 11.7 kpl (27.5 mpg) in the 1985 model year and thereafter (NRC 1992, 12). Between 1970 and 1992, in-use fuel economy for passenger cars rose from an average of 5.7 kpl (13.5 mpg) to 9.2 kpl (21.6 mpg), a 60 percent improvement (Davis 1994, 3-24). The introduction of CAFE standards, technology improvements such as electronic fuel in- jection and more efficient engines and transmissions, and the reduced weight of passenger vehicles were largely responsible. Although the standards have been achieved,'6 during the past decade the low price of gasoline, growing motor vehicle ownership, and increased motor vehicle travel have resulted in a steady increase of transportation's share of total petroleum consumption in the United States to 65 percent in 1992 (Davis 1994, 2-7). Also, other sectors have substituted alternative energy sources. Since 1989, U.S. energy dependence on foreign oil sources has reached levels only exceeded in 1979; oil imports accounted for 46 percent of U.S. petroleum con- sumption in 1992 (Davis 1994, 2-5). Thus, energy officials are seek- ing ways to improve fuel efficiency and reduce vehicle travel to cut back energy consumption.
Introduction 21 STUDY FOCUS The conformity requirements of the CAAA and, to a lesser extent, concern for energy use will place transportation projectsâparticu- larly highway projects in the nation's most polluted areasâunder great scrutiny regarding their potential for stimulating automobile travel, raising emission levels, and further increasing dependence on fossil fuels. Local planning agencies, who are responsible for programming highway projects in urban areas and certifying their positive or neutral effects on air quality, are expected to have the analytic and modeling capabilities to forecast project impacts. Such requirements provide the impetus and the focus for this study. The committee did not limit its examination of the effects of highway capacity additions to a specific time frame. However, particular attention was paid to the 20-year time frame established by the CAAA for attainment of air quality standards, because this represents the planning and forecasting horizon within which local planning agencies must make decisions about the air quality effects of highway projects. The size of the investment in capacity enhancements also warrants close examination of potential impacts. Although construction of new highways has tapered off in recent years, the combination of new con- struction with capacity additions to existing highways continues to represent a large fraction of the public investment in transportation infrastructure by state and local governments. For example, accord- ing to the most recent estimates, capacity improvements to roads and bridges totaled $15.4 billion,'7 accounting for nearly two-fifths (38 percent) of total public capital outlays for highways, bridges, and transit combined (U.S. Congress. House. Committee on Public Works and Transportation. 1993, 4, 76). Alternative ways of meeting urban transportation needs are not examined in this study, nor are the costs and benefits of alternative approaches to improving air quality and reducing energy use in a met- ropolitan region analyzed. Instead the study is focused on examining the scientific basis for estimating the impacts of highway capacity enhancement projects, both favorable and unfavorable, on emissions, air quality, and energy consumption.
22 EXPANDING METROPOLITAN HIGHWAYS DEFINITION OF TERMS Highway capacity projects are defined broadly in this study (see ac- companying text box). Additions to highway capacity are often asso- ciated with major construction projects, such as building a new high- way where none existed before, bypassing an existing route, or adding one or more lanes to an existing highway. Nonetheless, smaller-scale projects, such as traffic signal timing improvements or removal of on- street parking, should also improve traffic flows and thus are included here. Less traditional measures that add capacity but attempt to re- strict or manage travel as part of the facility improvement, such as high-occupancy-vehicle (HOV) and express bus lanes or variable tolls by time of day (congestion pricing), are also covered in the definition of highway capacity projects. Finally, many of the new technologies that fall under the category of intelligent transportation systems should also be characterized as capacity enhancement measures be- cause their primary objective is to improve the efficiency of traffic flows on existing facilities. Highway engineers define capacity of a facility as the maximum hourly rate at which persons or vehicles can reasonably traverse a seg- ment of roadway during a given time under prevailing roadway, traf- fic, and control conditions (TRB 1992, 13).18 The concept of capac- ity thus involves throughput of people and goods as well as the more traditional notion of vehicle throughput. Both measures are consid- ered in this study, although lack of data on the former (e.g., vehicle occupancies) hampers analysis of emission and energy impacts on a person- or goods- throughput basis. Both freight movement on com- mercial vehicles and passenger transport are of interest because both types of traffic will be affected by capacity enhancements, although their emissions, energy use, and travel pattern changes will differ. Sep- arate papers to review the likely effects of highway capacity additions on heavy-duty diesel vehicles, particularly heavy-duty trucks, were commissioned for this study. A concept closely related to capacity is level of service. Although capacity refers to a facility's maximum carrying capacity, highways are rarely designed or planned to operate in this range. Instead, traffic engineers are concerned with estimating the maximum traffic that can be accommodated while maintaining certain operating conditions (TRB 1992, 1-3). These conditions, or levels of service, are defined as
Introduction 23 ILLUSTRATIVE MEASURES TO ADD HIGHWAY CAPACITY AND IMPROVE TRAFFIC FLOW New Highways âNew freeways or expressways âNew toll roads âNew arterial streets âNew local streets âBypass of an existing route Reconstruction and Major Widening of Existing Highways âNew lanes on existing freeways âNew lanes on existing arterials âHigh-occupancy-vehicle (HOV) or express bus lanes added to freeways or arterials âNew lanes on existing freeways or arterials with variable tolls by time of day (congestion pricing) âMinor lane additions or widening on arterials âAddition of auxiliary lanes on freeways or expressways âImprovement of freeway ramp geometry âIntersection reconstruction âGrade separation of major crossings Other Measures To Improve Traffic Flow âAdvanced vehicle control systems (AVCS)a âAdvanced traveler information systems (ATIS)' âFreeway access control measures, such as ramp metering and incident detection âSynchronization of traffic signals âRemoval of on-street parking âAddition of exclusive turn lanes One of the Intelligent Transportation System (ITS) technologies that would involve "smart cars," automatic headway and lateral controls, and automatic steering controls to allow vehicle platooning of electronically coupled trains of vehicles on freeways equipped with electronic control instrumentation (TRB 1991, 23). b This ITS technology would provide the traveler with information on location, traffic conditions, route guidance, and parking location (TRB 1991, 22).
24 EXPANDING METROPOLITAN HIGHWAYS ranges in traffic density and are related to qualitative measures, in- cluding speed and travel time, freedom to maneuver, traffic interrup- tions, motorist comfort and convenience, and safety (TRB 1992, 1-3). Six levels of service are defined for each type of facility for which analysis procedures are available (see text box). They have letter des- ignations from A to F, with Level-of-Service A representing the best operating conditions and Level-of-Service F the worst (TRB 1992, 1-3-1-4). Many capacity enhancements are directed toward improving traffic flow and level of service on a particular facility, and safety is also a consideration in some capacity projects (e.g., left-turn lanes). The study is focused on additions to highway capacity in metro- politan areas, because the nation's air quality problems are primarily concentrated in its large urban centers. However, the effects of proj- ects may extend beyond current borders. Over time, capacity addi- tions at the urban fringe, which expand development opportunities, may change and expand the geographic boundaries of areas that do not meet air quality standards. Moreover, the decision to add or restrict highway capacity in metropolitan areas could have impacts beyond regional boundaries, affecting the competitive position of one metro- politan area relative to another or of large metropolitan areas gener- ally relative to smaller areas, although systematic evidence of these ef- fects may be difficult to document. For example, businesses could move from congested urban areas that are unable to provide new high- way capacity to communities that can; if large metropolitan areas generally cannot provide the additional capacity, growth could be encouraged in medium-size and small cities. OVERVIEW OF IMPACTS Estimating the effects of highway capacity additions in metropolitan areas on air quality and energy use involves analyzing a lengthy chain of factors (Figure 1-3). In general, the need or demand for travel arises from the distribution of residences and businesses in a region and their activity requirements. Residential and business location in a region are, in turn, determined by historical development patterns, avail- ability of land, and zoning and land use policies. The amount and frequency of travel are affected by regional economic conditions, area
Introduction 25 LEVELS OF SERVICE Level-of-Service Aâfree flow. Drivers have freedom to select de- sired speeds, and ability to maneuver within the traffic stream is extremely high. Level-of-Service Bâin the range of stable flow, but the presence of other drivers in the traffic stream begins to be noticeable. Level-of-Service Câin the range of stable flow, but the operation of individual drivers becomes significantly affected by interactions with others in the traffic stream; the general level of comfort and convenience declines noticeably at this level. Level-of-Service Dâhigh-density, but stable, flow. Speed and free- dom to maneuver are severely restricted. Level-of-Service Eâoperating conditions at or near the capacity level. All speeds are reduced to a low, but relatively uniform, value. Freedom to maneuver within the traffic stream is extremely lim- ited. Operations are unstable, because small increases in flow or minor perturbations within the traffic stream will cause break- downs. Level-of-Service Fâforced or breakdown flow. The amount of traf- fic approaching a point exceeds the amount that can traverse the point and queues form behind such locations. Operations are char- acterized by stop-and-go waves and are extremely unstable. demographic and income characteristics, and the cost and availability of local transportation services. Regional travel is distributed as vehicle and passenger flows on the supply of transportation facilitiesâthe transportation networkâ which may include more than one mode (e.g., transit and highways) and more than one form of transport (e.g., automobiles, trucks, bicy- cles, and walking). Motor vehicles operating on specific links of the network emit pollutants and use energy in varying amounts depend- ing on the type of vehicle, its speed and operating condition (i.e., whether it is warmed up), and the length of the trip. In addition, other factors, such as local topography, meteorological conditions, and other
Historical Develop- ment Patterns Land Use and Zoning Policies Availability of Distribution of Land Residences and - Businesses in the Region Demographic and In- come Characteristics Regional Economic Conditions Cost & Availability of Transportation Travel Demand Highway Capacity Addition Traffic Flows Highway- I Energy Use related Emissions Other Emission Sources Regional Air Quality Meteorological Conditions FIGURE 1-3 Overview of initial and longer-term impacts of highway capacity additions and their effects on emissions, air quality, and energy use.
Introduction 27 sources of emissions, interact with vehicle emissions to affect regional air quality. The primary objective of this study is to examine how an increase in the supply of highway facilities affects each of these factors (Figure 1-3). Initial impacts involve a change in traffic flows on the affected links (e.g., changes in the distribution of vehicle speeds, changes in speed variation, and shifts in traffic volumes) and the resulting change in emissions and energy use from the vehicles on those links. Over time the effects could involve a change in the amount of travel and in land use patterns, with corresponding effects on emissions and en- ergy use, as households and businesses react to the network addition. The incremental effects of all these changes on emissions, air quality, and energy use must be estimated to determine the full effects of the capacity increase. There is both a spatial and a temporal dimension to these analyses. A change in supply may involve adding capacity and improving traf- fic flow at only one location on the highway system. However, the net- work character of the system is likely to affect travel patterns at other locations. Traffic may be diverted from alternate routes, or travelers may shift their time of travel to preferred travel times to take advan- tage of the new capacity or change their mode of travel if they are en- couraged to reduce automobile trips by using transit or bicycle or by walking. If the addition to capacity is sufficiently large, it can induce new or longer trips, influence automobile purchasing decisions, and cause residents or businesses to change their location to take advan- tage of the improved access. Similarly, emissions from these changes are not confined to the location of the project, but depending on local atmospheric conditions (e.g., heat and wind patterns) may have broader effects on the air quality of the region and beyond. Individ- ual highway projects may not have measurable effects on regional air quality, but the cumulative impacts of many projects could. Thus, whereas a highway capacity enhancement project may be localized, its effects are unlikely to be. Project impacts will change over time. If a highway capacity addi- tion stimulates travel demand or encourages dispersed development patterns, these outcomes will erode initial gains from some capacity projects. However, some of these impacts, such as decisions about changes in the location of residences and businesses and the traffic
28 EXPANDING METROPOLITAN HIGHWAYS generated by these changes, are likely to take place over a period of years or even decades. Assessing the net effects of highway capacity projects on emissions and energy use depends on the length of time over which impacts are analyzed and how the flow of future effects is valued (i.e., discounted back to the present). Examination of project effects at a single point in time is misleading. The size and direction of the effects and the certainty of the pre- dictions depend on several factors. The context in which the capacity enhancement is made is critical: whether existing highways are heav- ily congested and travel demand is constrained; whether the area is heavily developed and thus the potential for growth is limited; or, con- versely, whether the area is relatively undeveloped but conditions for growth are present and thus the rate of growth in development and related traffic is likely to be accelerated. Each of these conditions will result in different project outcomes for travel behavior, land use, and urban form. The scale of effects also depends on the unit of analysis. Highway capacity additions may have significant effects on travel patterns and development activity in a particular corridor or subregional area. However, the effects may be small at the regional level, at least in the 20-year planning horizon required for metropolitan transportation planning and conformity purposes.'9 Highway capacity additions rep- resent small increments to large existing metropolitan transportation networks and to land use patterns that have evolved over many years. The type of project also matters. For example, minor capacity im- provements on arterialsâsuch as signalization improvements and ex- clusive turn lanesâmay smooth traffic flows, initially reducing emis- sions and energy use, without major offsetting increases in motor vehicle traffic.2Â° However, the size of the benefits will be commensu- rate with traffic levels on these local routes and may have little mea- surable impact on regional air quality. A series of relatively minor traf- fic flow improvements can have a cumulatively larger impact on motor vehicle traffic growth. Major capacity enhancement projects, such as a new freeway or a major new bypass, are likely to have more signif- icant initial effects on emissions and energy use (although effects can be negative as well as positive). They may have adverse effects in the longer term because of increased motor vehicle travel stimulated by the project.
Introduction 29 The effects of not adding highway capacity also must be considered in any assessment of net effects on highway emissions and energy use. Is there sufficient capacity in the existing highway network for trav- elers to change routes and times of travel without significantly adding to highway congestion levels and thereby increasing emissions and energy use? Can other investments in transit facilities or bikeways pro- vide alternative modes of transport with sufficient incentive for trav- elers to switch from automobile travel to keep highway congestion from growing? If highway congestion increases, will residents and businesses respond by moving to less congested suburban or exurban areas or to smaller, less congested metropolitan areas? Or will con- gestion simply become worse, making the capacity addition more valuable in the future relative to the no-build option? Finally, the level of certainty of the predictions will vary. Forecasts of emissions resulting from the initial adjustments in traffic flows and travel patterns because of a highway capacity project should be rela- tively straightforward, although technical issues involved in model- ing vehicle emissions and systems issues (i.e., route shifts and changes in time of travel) must be addressed. Forecasting longer-term effects such as shifts in travel demand and land use changes from capacity additions is more complex and requires predicting behavioral re- sponses that are not fully understood. The longer the time horizon for estimating impacts, the more other, often unpredictable, factors such as changes in demographic or economic conditions are likely to in- tervene, reducing the ability to forecast accurately. ASSESSMENT OF IMPACTS The difficulty of reaching consensus on the direction and size of ef- fects was demonstrated in a recent court case filed in 1989 by the Sierra Club Legal Defense Fund and Citizens for a Better Environment against the Metropolitan Transportation Commission (MTC), the MPO for the San Francisco Bay Area (U.S. District Court 1990a).2' Environmental groups sued MTC for noncompliance with the obli- gations contained in the Bay Area's 1982 SIP to meet federal air quality standards by 1987. A major issue of the court case concerned the extent to which large highway capacity expansions would adversely affect regional air qual-
30 EXPANDING METROPOLITAN HIGHWAYS ity and MTC's capacity to model and analyze these impacts. Court testimony by experts provides a good summary of the key arguments put forward by local planners and modelers, environmental groups, theoreticians, and practitioners concerning the effect on air quality of increased highway capacity. Environmental groups argued that adding highway capacity in a congested system would increase vehicle use by making automobile travel easier and more convenient, thereby offsetting at least some of the initial reduction in emissions from smoothing traffic flows.22 Specifically, drivers respond to improved levels of highway service by concentrating work trips more in traditional peak periods; shifting from transit and higher vehicle occupancies to automobile and lower, or single, vehicle occupancies; taking more individual trips rather than combining trips (trip chaining); and taking longer trips or trips that might otherwise have been forgone, ultimately producing levels of congestion comparable with previous conditions but at higher traffic volumes. In the long run, the argument continued, adding highway capacity in a congested system would encourage further decentralization of households and jobs and longer commuting by making travel to out- lying areas easier and faster. Because most major highway capacity investments are being made in suburban areas, these projects would change the distribution of development within the region; low-density, automobile-dependent development at the suburban fringe would be encouraged over redevelopment of core areas that could better sup- port public transit and nonmotorized travel modes. Moreover, if high- way transportation investment stimulates economic growth, as proj- ect proponents frequently claim, then capacity enhancements should increase overall levels of regional growth, drawing new jobs and households to the area and making it even more difficult for the region to meet environmental standards. Those who supported the MTC argued that capacity additions under most conditions would result in emission reductions and greater fuel efficiencies f