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Rubin is Professor,Margaret Chase SmithPolicy Center, Universityof Maine, Orono, andChair of the TRBCommittee onTransportation Energy.Noland is Professor, E. J.Bloustein School ofPlanning and PublicPolicy, Rutgers, TheState University of NewJersey, New Brunswick,and Cochair, TRBSpecial Task Force onClimate Change andEnergy.

The rapid increases in the speed, efficiency,and accessibility of the transportation sys-tem over the past century have enabledunprecedented levels of social interaction

and economic productivity throughout the world.Transportation for personal mobility and for themovement of freight is integral to the high standardof living in developed nations and to fosteringgrowth in developing nations.

Transportation activity, however, is a major userof the world’s carbon-rich fossil fuels and a majorsource of carbon dioxide (CO2) and other green-house gas (GHG) emissions associated with climatechange. In the past 40 years, the developed world hasmitigated many of the adverse environmental andpublic health impacts from transportation emis-sions—particularly in reducing the tailpipe pollu-tants from the burning of gasoline and diesel fuels.

Challenging EndeavorYet the recent oil release in the Gulf of Mexico starklyand dramatically emphasizes that the environmentalimpacts of oil use remain a vexing problem. Address-ing the transportation sources of climate change, in particular, is a challenging and complicatedendeavor—climate change is possibly the greatestenvironmental and social challenge worldwide.Nonetheless, previous success in mitigating envi-ronmental problems instills a confidence that thetransportation sector can reduce its significant con-tributions to climate change.

GHG emissions accumulate in the atmosphere;reducing emissions therefore offers the best strategyfor preventing the buildup of GHGs to levels thatpose a major risk to human and natural systems. Sig-nificantly reducing GHG emissions from transporta-tion will require actions that go beyond increasingvehicle fuel efficiency and that encompass initiativesin all of the major passenger and freight modes.

Transportation GHG emissions consist largely ofCO2 from petroleum combustion (93 percent ofemissions) but also include non-CO2 emissions ofmethane and nitrous oxide from fuel combustion, aswell as hydrofluorocarbons from vehicle air condi-tioning units—see Table 1, next page (1). Globally,the transportation sector is responsible for 23 percentof energy-related GHG emissions, with approxi-mately three-quarters from road vehicles (2). In theUnited States, the transportation sector produces 34percent, reflecting the higher per capita consumptionof carbon-based fuels compared with the rest of theworld (see Figure 1, next page). Transportation alsoexerts an indirect effect on climate change by induc-ing land use changes in agriculture, settlement pat-terns, housing, and business locations.

INTRODUCTION

Transportation and Climate Change Developing Technologies, Policies, and StrategiesJ O N A T H A N D . R U B I N A N D R O B E R T B . N O L A N D

Traffic near Siam Square in Bangkok, Thailand.Expanding personal transportation networks play amajor role in the growth of developing nations.

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Body of EvidenceThis issue of TR News brings together leading expertsto provide an overview of transportation’s role inGHG buildup and in energy use. Several articleshighlight recent reports published by the Trans-portation Research Board and by other units of theNational Research Council (NRC). NRC is releasingreports in two series, America’s Energy Future andAmerica’s Climate Choices, that present the per-spective of all the major energy-consuming sectors.1

As explained in the NRC reports summarized inthis issue (page 6), a strong and credible body of evi-dence documents that the earth is warming and thatthis warming is caused largely by human activities,especially through the release of GHGs from theburning of petroleum and other fossil fuels. Manymodels of emissions trends and climate risks indicatethat GHG emissions may need to be reduced world-wide by 50 to 80 percent—perhaps by even more—by the middle of this century. To achieve these deepreductions will require actions that cut across allenergy-using sectors to effect a marked departurefrom the current trajectory of increasing emissions,as one of the new NRC reports makes clear.

Mix of Transportation StrategiesThe article by Fulton (page 15) notes that no singletransportation technology or policy action offers apromising means of achieving such deep reductions;instead, a mix of different technologies, policies, andstrategies is necessary. The mix likely will involvesustained increases in the fuel economy of all kindsof vehicles, switching to fuels with lower GHG emis-sions per mile, and reducing the demand for energy-and emissions-intensive transport services, with arange of actions from shifting modes to changingurban form.

The spectrum of actions includes the deploymentof intelligent transportation systems that improveoperational efficiency (see article by Barth and Bori-boonsomsin, page 26) and public policies that pro-mote less energy-intensive patterns of land use (seearticle by Gómez-Ibáñez and Humphrey, page 24). AsFrankel and Menzies point out (page 10), these out-comes require many well-informed and comple-mentary policy choices.

Because CO2 emissions from transportation areroughly proportionate to the amount of petroleumconsumed, the price of gasoline, diesel, and alterna-tive fuels can affect emissions through fuel demandand supply. Despite recent spikes in the price ofpetroleum, however, U.S. transportation fuel costshave been relatively low. The low price, along withrising incomes, has favored heavier and larger per-sonal vehicles that tend to use more fuel and producegreater quantities of GHG emissions.

Regulatory ApproachesTo counter this, the U.S. government has taken sev-eral actions. For example, federal tax incentives andother policy initiatives are spurring the introductionof vehicles with battery-powered electric drives. Asexplained by Turrentine (page 32), this poses manychallenges, including integration with the electricityinfrastructure. In addition, the U.S. EnvironmentalProtection Agency and the National Highway TrafficSafety Administration have promulgated new per-formance regulations to increase the fuel economy ofcars and light trucks and to reduce vehicle emissionsof GHGs, including substances besides CO2 (see arti-cle by Noland, page 12).

At the state level, California is pioneering anapproach to control GHG emissions by regulatingfuels, seeking to spur the development and use oflow-carbon fuels such as advanced biofuels. In hisarticle (page 29), Sperling explains California’s low-carbon fuel standard, which accounts for the totalemissions from fuels, from production to consump-1 http://sites.nationalacademies.org/energy/;http://www.americasclimatechoices.org/index.shtml.

Transportation34%

Residential21%

Commercial18%

Industrial27%

TABLE 1 Total U.S. Greenhouse Gas Emissionsby the Transportation Sector, 2007

Million metric tonsin CO2-equivalent

warming potential

Carbon dioxide 1,902.5

Methane 5.1

Nitrous oxide 56.2

Hydrofluorocarbons 72.7

Total 2,036.5

(Source: Transportation Energy Data Book, Edition 28, Table11.4. www-cta.ornl.gov/data/tedb28/Edition28_Full_Doc.pdf.)

FIGURE 1 U.S. carbon dioxide emissions from fossil fuel consumption by the energy-use sector, 2007.(Source: Transportation Energy Data Book, Edition 28, Table 11.5. www-cta.ornl.gov/data/tedb28/Edition28_Full_Doc.pdf.)

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tion, to achieve net GHG reductions—a critical chal-lenge for all mitigation policies.

Modal InitiativesFreight activity and its modal distribution also mayneed to change substantially, depending on progressin boosting energy efficiency and diversifying theenergy supply, especially in the trucking sector (seearticle by Mintz, page 34). The international mar-itime sector, instrumental in providing cheap trans-portation for global trade, emits as much CO2 assome of the world’s most prosperous countries—andtherefore is becoming a target of policy interven-tions, as discussed by Corbett, Winebrake, and Wang(page 40).

The aviation sector is becoming a major contrib-utor to transportation emissions globally, and inter-national efforts to control emissions are under way.Aviation depends on liquid fuels with a high energycontent, prompting research to develop biofuels forthis vital and safety-conscious sector (see article byAnger and Putnam, page 45).

Opportunities for InnovationThe research challenge is beginning, with many issuesneeding more informed and careful analysis, as Meyerand Godwin point out (page 21). Meeting the chal-lenge of climate change will provide opportunitiesfor innovation—extensive and intensive innovationin technologies, practices, and policies. Although this

issue of TR News can cover only a sample of the needsfor research and innovation, the articles reflect theimportance of a large, varied, and vibrant transporta-tion research community going forward.

AcknowledgmentsMembers of several TRB committees were instru-mental in developing, assembling, and reviewing thearticles in this issue of TR News, including the TRBSpecial Task Force on Climate Change and Energy,the Transportation Energy Committee, the Alterna-tive Transportation Fuels and Technology Commit-tee, the Climate Change Joint Subcommittee, andthe Transportation and Sustainability Committee.Appreciation is expressed to TRB Senior ProgramOfficer Thomas R. Menzies, Jr., for his work with thecommittee chairs and authors and with TRB seniorstaff and the magazine’s editorial board in shaping thefinal content of this issue.

References 1. Emissions of Greenhouse Gases Report. DOE/EIA-0573, U.S.

Energy Information Administration, December 2009.2. Kahn Ribeiro, S., S. Kobayashi, M. Beuthe, J. Gasca, D.

Greene, D. S. Lee, Y. Muromachi, P. J. Newton, S. Plotkin,D. Sperling, R. Wit, and P. J. Zhou. Transport and Its Infra-structure. In Climate Change 2007: Mitigation—Contribu-tion of Working Group III to the Fourth Assessment Report ofthe Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P. R. Bosch, R. Dave, and L. A. Meyer (eds.)],Cambridge University Press, Cambridge, United Kingdom,and New York, 2007.

The changes in land usein the areas surroundingroadways and othertransportation networksindirectly contribute toclimate change.

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