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JANUARY | 2021

Emissions of Carbon Dioxide

in the Transportation Sector

DECEMBER | 2022

At a Glance

e largest source of emissions of carbon dioxide (CO2, the most common greenhouse gas) in the

United States is the transportation sector. Emissions from transportation surpassed emissions from

the electric power sector ve years ago and now constitute two-fths of domestic emissions from

burning fossil fuels.

In this report, the Congressional Budget Oce provides an overview of CO2 emissions in the trans-

portation sector, describing the sources of and trends in such emissions and projecting their future

path.

• In 2021, CO2 emissions in the transportation sector were 6percent less than they were in 2005.

e decline in emissions from transportation has contributed to a drop of about 20percent in

total CO2 emissions in the United States since 2005; most of that overall reduction has come from

the electric power sector.

• Reducing emissions from transportation has been difficult because of the value that people

place on transportation and the dominance of a single fuel source—petroleum. Demand for

transportation is much less sensitive to price changes than is demand for electric power, and

people have had few cost-eective alternatives to motor fuels.

• Most emissions in the transportation sector come from cars and trucks. Motor vehicles

accounted for 83percent of CO2 emissions from transportation in 2019. Personal vehicles and

commercial trucks (the predominant forms of passenger and freight transportation) averaged more

CO2 emissions per passenger-mile or ton-mile than most other modes of transportation.

• CO2 emissions have declined since 2005—despite an increase in travel by car and truck—

because vehicles have become more efficient. e use of motor vehicles has expanded with

economic growth, but the average fuel economy of new light-duty vehicles (cars and light-duty

trucks, including sport utility vehicles, crossover utility vehicles, minivans, and pickup trucks) rose

from 20miles per gallon in 2005 to 25miles per gallon in 2021.

• Tighter standards for fuel economy and emissions, along with greater use of electric vehicles, are

projected to reduce emissions moderately over the next decade. CBO projects CO2 emissions in

the transportation sector to decrease by 9percent from 2021 to 2032as the vehicle eet becomes

increasingly ecient to comply with more stringent fuel economy standards. Sales of electric

vehicles, which accounted for 4percent of the market in 2021, are expected to grow substantially.

e use of electric vehicles is expected to contribute to greater emissions reductions in future

decades than it does today because the electric power sector is projected to continue to become

progressively less carbon intensive.

www.cbo.gov/publication/58566

Contents

Carbon Dioxide Emissions From Transportation and Other Sectors 2

Trends in Carbon Dioxide Emissions 3

Challenges in Reducing Emissions From Transportation 4

Sources of Transportation-Related Emissions 5

Passenger Transportation 6

Emissions From the Dierent Modes of Passenger Transportation 7

Dierences in Emissions Within Modes of Passenger Transportation 8

Freight Transportation 9

Emissions From the Dierent Modes of Freight Transportation 10

Trends in Transportation Sector Emissions 11

Growth in Motor Vehicle Travel 12

Changes in Fuel Economy 13

Projections of Carbon Dioxide Emissions From Transportation 14

Changes in Standards, Electric Vehicle Incentives, and Emissions 15

CAFE Standards 16

Greenhouse Gas Emissions Standards 17

Demand for Electric Vehicles 18

Emissions Attributable to Electric Vehicles 19

Eects of Economic Growth and Oil Prices on Future Emissions 20

AppendixA: Analytic Method 23

AppendixB: Data Sources for Figures 25

About This Document 29

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JANUARY2021EmissionsofCarbonDioxideintheTransportationSectorDECEMBER2022©Tupungato/Shutterstock.comAtaGlanceThelargestsourceofemissionsofcarbondioxide(CO2,themostcommongreenhousegas)intheUnitedStatesisthetransportationsector.Emissionsfromtransportationsurpassedemissionsfromtheelectricpowersectorfiveyearsagoandnowconstitutetwo-fifthsofdomesticemissionsfromburningfossilfuels.Inthisreport,theCongressionalBudgetOfficeprovidesanoverviewofCO2emissionsinthetrans-portationsector,describingthesourcesofandtrendsinsuchemissionsandprojectingtheirfuturepath.•In2021,CO2emissionsinthetransportationsectorwere6percentlessthantheywerein2005.Thedeclineinemissionsfromtransportationhascontributedtoadropofabout20percentintotalCO2emissionsintheUnitedStatessince2005;mostofthatoverallreductionhascomefromtheelectricpowersector.•Reducingemissionsfromtransportationhasbeendifficultbecauseofthevaluethatpeopleplaceontransportationandthedominanceofasinglefuelsource—petroleum.Demandfortransportationismuchlesssensitivetopricechangesthanisdemandforelectricpower,andpeoplehavehadfewcost-effectivealternativestomotorfuels.•Mostemissionsinthetransportationsectorcomefromcarsandtrucks.Motorvehiclesaccountedfor83percentofCO2emissionsfromtransportationin2019.Personalvehiclesandcommercialtrucks(thepredominantformsofpassengerandfreighttransportation)averagedmoreCO2emissionsperpassenger-mileorton-milethanmostothermodesoftransportation.•CO2emissionshavedeclinedsince2005—despiteanincreaseintravelbycarandtruck—becausevehicleshavebecomemoreefficient.Theuseofmotorvehicleshasexpandedwitheconomicgrowth,buttheaveragefueleconomyofnewlight-dutyvehicles(carsandlight-dutytrucks,includingsportutilityvehicles,crossoverutilityvehicles,minivans,andpickuptrucks)rosefrom20milespergallonin2005to25milespergallonin2021.•Tighterstandardsforfueleconomyandemissions,alongwithgreateruseofelectricvehicles,areprojectedtoreduceemissionsmoderatelyoverthenextdecade.CBOprojectsCO2emissionsinthetransportationsectortodecreaseby9percentfrom2021to2032asthevehiclefleetbecomesincreasinglyefficienttocomplywithmorestringentfueleconomystandards.Salesofelectricvehicles,whichaccountedfor4percentofthemarketin2021,areexpectedtogrowsubstantially.Theuseofelectricvehiclesisexpectedtocontributetogreateremissionsreductionsinfuturedecadesthanitdoestodaybecausetheelectricpowersectorisprojectedtocontinuetobecomeprogressivelylesscarbonintensive.www.cbo.gov/publication/58566ContentsCarbonDioxideEmissionsFromTransportationandOtherSectors2TrendsinCarbonDioxideEmissions3ChallengesinReducingEmissionsFromTransportation4SourcesofTransportation-RelatedEmissions5PassengerTransportation6EmissionsFromtheDifferentModesofPassengerTransportation7DifferencesinEmissionsWithinModesofPassengerTransportation8FreightTransportation9EmissionsFromtheDifferentModesofFreightTransportation10TrendsinTransportationSectorEmissions11GrowthinMotorVehicleTravel12ChangesinFuelEconomy13ProjectionsofCarbonDioxideEmissionsFromTransportation14ChangesinStandards,ElectricVehicleIncentives,andEmissions15CAFEStandards16GreenhouseGasEmissionsStandards17DemandforElectricVehicles18EmissionsAttributabletoElectricVehicles19EffectsofEconomicGrowthandOilPricesonFutureEmissions20AppendixA:AnalyticMethod23AppendixB:DataSourcesforFigures25AboutThisDocument29NotesToproducethisreport,theCongressionalBudgetOfficeadapteddatafrommanysources.ForadescriptionofCBO’sanalyticmethod,seeAppendixA.CitationsforthefiguresarelistedinAppendixB.Numbersinthetextandfiguresmaynotadduptototalsbecauseofrounding.Unlessthisreportindicatesotherwise,allyearsreferredtoarecalendaryears.EmissionsofCarbonDioxideintheTransportationSectorTheaccumulationofgreenhousegasesintheatmospherecontributestoclimatechange.Themostprevalentofthosegases,carbondioxide(CO2),isreleasedwhenfossilfuels(suchascoal,oil,andnaturalgas)andthederivativesofoilthatarefrequentlyusedtopowertransportation(namely,gasoline,dieselfuel,andjetfuel)areburned.Climatechangeimposescostsonpeopleandcountriesaroundtheworld,includingtheUnitedStates.TransportationisthelargestsourceofgreenhousegasemissionsintheUnitedStates,andCO2emissionsrepresentroughly97percentoftheglobalwarmingpotentialofallgreenhousegasemissionsfromtransportation.1Beforethecoronaviruspandemic,CO2emissionsfromtransportationhadrisen(inamountandasashareofemissions)forsev-eralyears.Inthisreport,theCongressionalBudgetOfficeprovidesanoverviewofCO2emissionsandidentifiesthesourcesofthoseemissionsinthetransportationsector.Thereportalsodiscussesfactorsthatdeterminetransportation-relatedemissionsandpresentstheagency’sprojectionsoftheirpathoverthenext10years.2EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022CarbonDioxideEmissionsFromTransportationandOtherSectorsIn2021,worldwideemissionsofgreenhousegasesfromallsourcesamountedto40.8billionmetrictons(BMT).2GreenhousegasemissionsintheUnitedStatesareestimatedtoaccountforalmostone-sixthofthatamount—6.4BMT.3OfthoseU.S.emissions,5.0BMT(or80percent)wereCO2;methane,nitrousoxide,andother(mainlyfluorinated)gasesfromagriculture,industry,energyproduction,andwastemanagementaccountedfortheremain-ingamount.4About92percent(or4.6BMT)ofU.S.CO2emissionsstemmedfromburningfossilfuelstoproduceenergy.Theremaining8percentofthoseemissionswereunrelatedtoenergyproduction;theyresultedfromindustrial,agricultural,andwastemanagementprocesses.Historically,about15percentoftotalCO2emissionsintheUnitedStateswereoffsetbythenetabsorptionofCO2bythenation’sforestsandsoil.In2021,CO2emissionsfromtransportationintheUnitedStatestotaled1.7BMT—themostfromanysectoroftheeconomy.WithCO2emissionsof1.5BMT,theelectricpowersectorwasthesecondlargestsourcethatyear.(Formoreinformationaboutemissionsinthatsector,seeCongressionalBudgetOffice,EmissionsofCarbonDioxideintheElectricPowerSector[December2022],www.cbo.gov/publication/58419.)Together,theremainingenergy-relatedsources—theindustrial,residential,andcommercialsectors—contributedanaddi-tional1.4BMT.SharesofEnergy-RelatedEmissionsofCarbonDioxide,byEconomicSector,2021Total4.6BillionMetricTonsTransportation38%ElectricPower33%Industrial17%Residential7%Commercial5%Emissionsofcarbondioxideinthetransportationsectoraccountedfor38percentofenergy-relatedemissionsintheUnitedStatesin2021—thelargestshareofsuchemissionsofanysectoroftheeconomy.3December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORTrendsinCarbonDioxideEmissionsIn2017,CO2emissionsfromtransportation,whichhadpeakedinthemid-2000s,surpassedemissionsfromelectricpower.Afterthe2007–2009recession,transportation-relatedemis-sionsdeclined,buttheyhadreboundedandwereheadingtowardtheirprerecessionpeakwhenthepandemichitinearly2020.Totalenergy-relatedemissionsofCO2intheUnitedStatespeakedin2005anddeclinedbyabout20percentby2021—anaveragereductionofroughly0.07BMTperyear.Three-quartersofthatreductioncamefromtheelectricpowersector.Emissionsfromthetrans-portationsectordeclinedby6percentoverthesameperiod—anaverageof0.01BMTperyear.Thatchangeaccountedforonlyone-tenthoftheoverallreductioninenergy-relatedemissions.Theindustrial,residential,andcommercialsectorswereresponsiblefortherestofthedecline.Whereasreductionsofemissionsintheindustrialsectormaybeoffsetbycorrespondingincreasesinemissionsinothercountries,reductionsinthetransportationsectorarenotlikelytobe.PoliciesthatloweremissionsofgreenhousegasesintheUnitedStatesbutleadtooffsettingincreasesinemissionselsewhere—say,bycausingactivityincarbon-intensiveindustriestoshifttoothercountries—wouldleaveglobalemissions(andthusclimatechange)largelyunaffected.Energy-RelatedEmissionsofCarbonDioxide,byEconomicSector,1975to2021BillionsofMetricTons00.51.01.52.02.53.019761981198619911996200120062011201620211,5002,0002,5003,000TransportationElectricPowerIndustrialResidentialCommercialTransportationElectricPowerTransportationbecametheleadingsourceofCO2emissionsintheUnitedStatesin2017afteremissionsintheelectricpowersectordeclinedsubstantially.4EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022ChallengesinReducingEmissionsFromTransportationReductionsinemissionsfromtransportationhavebeenhardertoachievethanthoseintheelectricpowersectorforthreemainreasons.First,thedemandfortransportationservicesisnotverysensitivetothepriceofsuchservices.Demandfortransportationisbuiltintotheplacesthatpeoplelive,work,andsocializeandtheplacesthatbusinessesproduceandselltheirgoods.Thoselocationscanchange,butsuchchangetypicallyhappensslowly.Second,thetransportationsectorisoverwhelminglydependentonasinglefossilfuel,petroleum.Althoughthepriceofpetroleumishigherthanthatofotherfossilfuelsperunitofenergy(inpartbecauseofthecostofrefiningitintousablefuels),fewcost-effectivealternativesarecurrentlyavailable.Infact,thepriceofembeddedCO2(whatfinaluserspayforenergypermetrictonofCO2released)inthetransportationsectorismorethantwicethepriceintheothersectors.Third,peopletendtoownvehiclesforalongtime,delayingtheeffectsofimprovementsinthefuelefficiencyofnewvehicles.Thedifficultyinreducingtransportationemissionscanbeillustratedbyconsideringtheeffectsondifferentsectorsofanemissionstax—forexample,onethatwouldstartat$25permetrictonandgrowataninflation-adjustedrateof5percentperyear.5ThetransportationsectorwouldexperienceasmallerreductioninCO2emissionsthanothersectorswouldasaresultofsuchatax—a3percentreductioncomparedwithareductionof34percentintheelectricpowersectorandof6percentintheindustrial,residential,andcommercialsectorscombined,CBOestimates.EstimatedEffectsofa$25-per-TonTaxonEnergy-RelatedEmissionsofCarbonDioxideThatGrowsatanInflation-AdjustedAnnualRateof5Percent,byEconomicSectorBillionsofMetricTons00.51.01.52.0202320322023203220232032TransportationElectricPowerIndustrial,Residential,andCommercialWithTaxWithoutTaxThisillustrativecaseinvolvingataxoneachmetrictonofCO2emitteddemonstratesonekeychallengetoreducingtransportationemissions:Demandfortransportationismuchlesssensitivetochangesinpricesthanisdemandforelectricpower,thesecondleadingsourceofemissions.5December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORSourcesofTransportation-RelatedEmissionsPersonalvehicles—cars,light-dutytrucks(includingsportutilityvehicles,crossoverutilityvehicles,minivans,andpickuptrucks),andmotorcycles—wereresponsiblefor58percentofemissionsinthetransportationsectorin2019.(Althoughdatafor2020wereavailable,CBOused2019asitsreferenceyearbecauseemissionsin2020wereaffectedbythecorona-viruspandemic.)Emissionsfromcommercialtrucksandallbusesaccountedfor25percent.Together,thefollowingmodesoftransportationaccountedfortheremaining17percent:air(includingcommercialpassengeraviation,generalaviation,aircargo,andmilitaryavia-tion),pipelines(forwhichfuelisburnedtopowercompressorsthatkeepoilandnaturalgasflowingatasteadyrate),rail(passengerrailroads,railtransit,andfreightrailroads),andwater(includingshipsandboats).Thisreportfocusesonmotorvehicles(personalvehiclesaswellascommercialtrucksandbuses)becausetheyaccountforthebulkofemissions.Butemissionsreductionscouldbeachievedintheothermodesoftransportation.Forinstance,improvementsinaircraftdesignhaveledtoemissionsreductionsinaviation,andalternativefuelscouldsomedayreduceemissionsfromotherformsoftransportation.Thefigurebelowreflectsalltransportationregardlessofwhetherpeopleorgoodsarebeingtransported;intherestofthissection,passengerandfreighttransportationarediscussedseparately.SharesofTransportation-RelatedCarbonDioxideEmissions,byModeofTransportation,2019Air10%Rail2%Pipeline3%Water2%CommercialTruckandBus25%PersonalVehicle58%Total1.8BillionMetricTonsMotorvehicles—personalvehiclesandcommercialtrucksandbuses—accountedfor83percentofemissionsinthetransportationsectorin2019.6EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022PassengerTransportationIn2019,mostpassengertravel—81percentofallpassenger-miles—tookplaceinper-sonalvehicles.(Apassenger-milerepresentsonepersontravelingonemile.TheBureauofTransportationStatisticscautionsthatthemileagemayreflectsomedouble-countingandmayexcludesmallamountsofself-propelledtravelfromwalkingandbiking.)Forlong-distancetravel,airtravelwastheprimaryalternativetomotorvehicles;forlocaltravel,busandrailtransitwerethemainalternatives.Railtransitsystemsfallintotwocategories:heavyrailandlightrail.Usuallyinurbancentersandoftenunderground,heavy-railtransit(commonlycalledasubwayormetro)servesalargevolumeofpassengers.Light-railtransit(suchasstreetcarsandtrolleys)servesfewerpassen-gersthanheavyrailandistypicallyatstreetlevel.PassengerrailroadsincludeAmtrakandcommuterrailroads,whichoperateonrailroadtracksandtypicallyprovideservicebetweenthecenterofametropolitanareaanditsoutlyingareas.SharesofPassenger-MilesTraveled,byModeofTransportation,2019Rail1%Bus6%Air12%PersonalVehicle81%Total6.1TrillionPassenger-MilesMostpassengertraveloccursinpersonalvehicles.Air,bus,andrail(includingheavy-andlight-railtransitandpassengerrailroads)accountformuchsmallersharesofpassengertravel.7December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTOREmissionsFromtheDifferentModesofPassengerTransportationIn2019,CO2emissionsfrompersonalvehiclesaveraged0.47poundsperpassenger-mile.6Averageemissionsfromothermodesofpassengertransportation—heavy-andlight-railtran-sit,passengerrailroads,commercialairtravel,andbus—werealllowerperpassenger-mile.Emissionsfrombustransportationaveraged0.39poundsofCO2perpassenger-milein2019;thataverageencompassesseveralkindsofbusoperationswithvaryingemissions.Transitbuses,forexample,averaged0.95poundsperpassenger-mile,largelybecausetheyoftenoperatedatonlyafractionoftheircapacity.(Emissionsperpassenger-miledeclineasthenumberofoccupantsincreases.)EmissionsofCO2fromintercitybuses(includingcharterbusesandtourbuses,whicharesometimesreferredtoasmotorcoaches)weremuchlower,averaging0.15poundsperpassenger-mile,slightlylessthantheaverageforrailtransit.Trafficcongestionandtravelspeeds,whichareinfluencedbytravelgrowth,canaffecttheefficiencywithwhichmotorvehiclesburnfuelandproduceemissions.Anextra0.04BMTofgreenhousegases—about2percentofalltransportation-relatedemissions—wereemittedin2019asaresultofcongestion.7AverageCarbonDioxideEmissionsperPassenger-Mile,byModeofTransportation,2019PoundsofCarbonDioxideperPassenger-Mile0.470.390.340.300.17RailTransitPassengerRailroadAirBusPersonalVehicleCarbondioxideemissionsperpassenger-milefromtravelbypersonalvehiclesarehigheronaper-milebasisthanemissionsfromotherformsofpassengertravel.Heavy-andlight-railtransitproducerelativelyfewemissionsperpassenger-mile.8EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022DifferencesinEmissionsWithinModesofPassengerTransportationAverageemissionsobscuresubstantialdifferenceswithineachmodeoftransportation.Severalfactors—includingvehiclesize,averageoccupancy,thetypeoffuelused,andfuelefficiency—affectemissionsperpassenger-mile.Conventionalcarstypicallyhavegreaterfueleconomythanlightdutytrucks.Newervehiclesareusuallymorefuelefficientthanolderones.Andsmallervehiclesgetbettermileage,onaverage,thanlargerones.Themostpop-ularsizecarin2020emitted0.60poundsofCO2pervehiclemile,whereasonecategoryoflargepickuptrucksbuiltinthatyearhadaverageemissionsthatwerenearlytwicethatamount—1.18poundsofCO2pervehiclemile.8Atransitsystem’semissionsdependontheaveragecarboncontentoftheelectricityusedtopowerit(thatis,theamountofCO2releasedintheprocessofgeneratingthatelectricity)aswellasthesystem’sloadfactor(thepercentageofthesystem’sseatsthatarefilled,onaverage).Emissionsfromheavy-railtransitsystemsin2019variedgreatly,rangingfrom0.09poundsofCO2perpassenger-mileto0.99pounds.Somepublictransportationsystemsmayofferfrequentserviceandalargenetworkofroutestoprovidegreatermobilityfortheirusers;thoseofferingscanreduceasystem’sloadfactorandthusincreaseitsemissionspermiletraveled.EmissionsofCarbonDioxideFromHeavy-RailTransitSystems,byCarbonContentofElectricityandLoadFactor,2019PoundsofCarbonDioxideperPassenger-Mile●●●●●●●●●●●●●00.20.40.60.81.002505007501,000●●●●●●●●●●●●●0255075100CarbonContentofElectricityLoadFactorPercentPoundsperMegawattHour(Symbolsizerepresentsvolumeofpassenger-miles.)NewYorkCitySubwaySanFranciscoBARTWashingtonMetroChicago“L”NewYorkCitySubwaySanFranciscoBARTWashingtonMetroChicago“L”Emissionsperpassenger-milecanvarysubstantiallywithinaparticularmode.Forinstance,subwaysthatuseelectricitywithlesscarboncontentandsystemsthataremoreheavilyutilizedtendtohaveloweremissionsperpassenger-mile.9December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORFreightTransportationEmissionsfromfreighttransportationdependontheweightofthecargo.In2019,truckscarried43percentofallton-miles;railroads,29percent;andpipelinesandwatertranspor-tation,mostoftherest.(Aton-milerepresentsonetonoffreighttransportedonemile.)Measuredintermsofweight,aircargoaccountedforlessthan1percentoffreighttranspor-tation.(Whenthevalueofcargoisusedinsteadofitsweighttomeasurefreighttranspor-tation,truckingstillaccountedforthelargestshareofsuchtransportation.Butwhereastheweightofgoodsshippedbyrailroadexceededthatofgoodsshippedbyair,thevalueofgoodsshippedbyairwasgreater.)SharesofTon-MilesofFreight,byModeofTransportation,2019AirLessthan1%Water10%Pipeline18%Rail29%Truck43%Total5.5TrillionTon-MilesTruckingistheprimaryformoffreighttransportation,althoughitdoesnotdominatefreighttransportationasmuchasmotorvehiclesdopassengertravel.10EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022EmissionsFromtheDifferentModesofFreightTransportationCO2emissionsperton-milefromthedifferentmodesoffreighttransportationvarygreatly—farmorethanthosefromthedifferentmodesofpassengertransportation.Perton-mile,truckingproducedmoreCO2emissions,onaverage,thanmostothermodesoffreighttransportationbutfarlessthanaircargo.AverageCarbonDioxideEmissionsperTon-MileofFreight,byModeofTransportation,2019PoundsofCarbonDioxideperTon-Mile2.570.400.140.130.05RailPipelineWaterTruckAirPerton-mile,emissionsfromtrucking,thepredominantmodeoffreighttransportation,wereeighttimesthosefromrail.Andemissionsperton-milefromaircargoweresixtimesthosefromtrucks.11December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORTrendsinTransportationSectorEmissionsChangesinthevolumeofmotorvehicletransportationandchangesinvehicles’fuelefficiencyarethetwofactorsthathavemostinfluencedemissions.Inthelate1970sandearly1980s,improvementsinthefueleconomyoflight-dutyvehicles(thatis,passengercarsandlight-dutytrucks)partiallyoffsetthesubstantialincreaseinvehiclemilestraveledbyroad.9Inthemid-1980s,fueleconomyplateauedandthendecreasedslightlyasconsumersshiftedfromtraditionalautomobilestolessefficienttrucksandsportutilityvehicles;asaresult,emissionsgenerallyroseashighwayuseincreased.Atwo-decadestretchoftravelgrowthfromthemid-1980stothemid-2000sstoppedwiththe2007–2009recession.Becauseofthatbreakinthetrendandfurtherimprovementsinfueleconomy,transportationemissionsin2019wereslightlylowerthantheirprerecessionhigh.Emissionsfellsharplyin2020asaresultofthepandemicbutreboundedin2021.EmissionsofCarbonDioxideintheTransportationSector,MotorVehicleMilesTraveled,andEmissionsperMileTraveledbyLight-DutyVehiclesMeasuredasaPercentageofTheirValuein1975Percent●●●145243510501001502002501976198119861991199620012006201120162021CO2EmissionsFromTransportationEmissionsperMileTraveledbyLight-DutyVehiclesMotorVehicleMilesTraveledTransportationsectoremissionshavenotrisennearlyasmuchasvehiclemilestraveledbecausegainsinfueleconomyhavereducedemissionspermileoftravel.12EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022GrowthinMotorVehicleTravelThedemandforpassengerandfreighttransportationbymotorvehiclehashistoricallynotbeenverysensitivetothecostofsuchtransportationandhastypicallydeclinedonlyduringeconomicrecessions.From1990tothemid-2000s,vehiclemilestraveledbypassengerandfreightmotorvehiclesgrewsteadily.The2007–2009recessiondisruptedthatlong-termgrowth:Freighttransportationbytruck,inparticular,fell—droppingby14percentfrom2008to2011—beforeslowlyclimbingbacktowardits2008level.In2020,thegrowthofmotorvehicletravelwastemporarilyreversedbythepandemic.Aseconomicactivityslowedandpeopletraveledlessduringthefirstyearofthepandemic,thenumberofvehiclemilestraveledbypassengermotorvehiclesdroppedby12percent.MilesTraveledbyPassengerandFreightMotorVehicles,1990to2020TrillionsofVehicleMilesTraveled00.51.01.52.02.53.03.51990199520002005201020152020PassengerFreightMeasuredintermsofmotorvehiclemilestraveled,passengerandfreighttransportbymotorvehiclegrewatsimilarratesinthe1990sandearly2000s.Freighttransportbymotorvehiclefellasaresultofthe2007–2009recession,andpassengertraveldroppedin2020duringthecoronaviruspandemic.13December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORChangesinFuelEconomyCorporateaveragefueleconomy(CAFE)standardssetbytheNationalHighwayTrafficSafetyAdministration(NHTSA)governfuelconsumptionforlight-dutyvehicles.ThestandardsrequireeachautomanufacturertomeetannualtargetsforthefueleconomyofitsentireU.S.fleet,weightedtoreflectthesalesofdifferentmodels.Thosefleet-widetargetsaccountfordifferentstandardsforvehiclesofdifferentsizes.ThefueleconomyratingsthatareusedtodeterminecompliancewithCAFEstandardsarecalculatedusingaseriesoflabo-ratorytestsoffuelconsumptionunderspecificconditions.Estimated“real-world”dataaboutfueleconomyandemissionsaremeasuredusingteststhatincorporateawiderrangeofconditionsthanthoseusedtodeterminecompliancewithCAFEstandards.Thatwiderrangeofconditions—includinghotandcoldweather,higherspeeds,andfasteraccelerations—betterreflectstheconditionstheaveragedriverislikelytoencounter.Thefueleconomyvaluesfoundonthewindowstickersofnewcars,whichareroughly20to30percentlowerthanthevaluesusedtodeterminecompliancewithCAFEstandards,arebasedonthesametestsasthoseusedforthereal-worlddata,thoughthecalculationsofthetwomeasuresdifferslightly:Highwaydrivingisweightedmoreheavilyinthemixofdrivingbetweencityandhighwayconditionsusedtocalculatethereal-worldmeasurethanitisinthecalculationofthestickervalue.Averagereal-worldfueleconomyfornewlight-dutyvehiclesincreasedfromanaverageof20milespergallonin2005toanaverageof25milespergallonin2021.(Bycomparison,theaveragefueleconomyofthelargesttrucksinservicewas6milespergallonin2019.)10Emissionsofcarbondioxidepervehiclemilefornewlight-dutyvehiclesdroppedaccord-ingly—fromanaverageof0.99poundspervehiclemilein2005toanaverageof0.77poundspervehiclemilein2021.Real-WorldFuelEconomyofandCarbonDioxideEmissionsFromNewLight-DutyVehicles,1975to2021●25.30102030●0.7700.51.01.52.01976198119861991199620012006201120162021FuelEconomyEmissionsMilesperGallonPoundsofCarbonDioxideperMileThefueleconomyofnewlight-dutyvehiclesintheUnitedStateshasimprovedbyaboutonequarteroverthepast15years.Asfueleconomyimproved,CO2emissionratesfell.14EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022ProjectionsofCarbonDioxideEmissionsFromTransportationDrawingonestimatesfromtheEnergyInformationAdministration(EIA)andadjustingthemforsubsequentchangesinrelevantlawsandregulations,CBOprojectsthattransporta-tionemissionsofcarbondioxidewilldeclineoverthenextdecadeaselectricandothermorefuel-efficientvehicles(includingthoseproducedinaccordancewiththe2022increasestotheCAFEstandardsformodelyears2024,2025,and2026)constitutealargershareofthevehiclestock.Thereductionsinemissionratesareprojectedtooutweighincreasesinvehiclemilestraveled,reducingtotalCO2emissionsfromtransportation,onnet.InCBO’sprojec-tions,transportation-relatedemissionsofCO2fallby9percentfrom2021to2032—from1.74BMTto1.59BMT,whichis15percentlessthanthe1.86BMTofsuchemissionsproducedin2005.(ForadiscussionofthemethodthatCBOusedtomakeitsprojections,seeAppendixA.)CarbonDioxideEmissionsFromTransportation,1975to2032BillionsofMetricTons1.861.741.59Projected00.51.01.52.0197719821987199219972002200720122017202220272032CO2emissionsfrommotorvehiclesareprojectedtodeclineasrecentandscheduledincreasesinfueleconomystandardsfornewvehicles,combinedwithgreateruseofelectricvehicles,lowertheaveragerateofemissionsofvehiclesovertime.15December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORChangesinStandards,ElectricVehicleIncentives,andEmissionsIncreasesinCAFEandgreenhousegasemissionsstandardsandchangesinincentivesforpurchasingelectricvehiclestaketimetoimprovetheaveragefueleconomyofvehiclesontheroadbecausethestockofvehiclesisreplacedslowly.TheaverageageofpassengervehiclesdrivenintheUnitedStatesis12years,soevenseveralyearsafteranewstandardisadoptedorelectricvehiclesalesareboosted,mostvehiclesontheroadwillstillbeoldermodelsthatproducemoreemissions.InCBO’sprojections,regulatoryandlegislativechangesadoptedin2021and2022resultintransportation-relatedCO2emissionsin2032thatare0.16BMT(orabout10percent)lowerthantheagencyestimatestheywouldhavebeenwithoutthosechanges.FederalagenciesareconsideringadditionalchangestoCAFEandgreenhousegasemissionsstandards,butthoseplanshavenotbeenincorporatedintoCBO’semissionsprojectionsbecausetheproposalsremainpreliminary.InAugust2022,NHTSAannounceditsintenttoanalyzethepotentialenvironmentalimpactsofnewCAFEstandardsforpassengercarsandlight-dutytrucksstartingwithmodelyear2027andofnewfuelefficiencystandardsforheavy-dutypickuptrucksandvansstartingwithmodelyear2029.Similarly,EPAhasbegunworktoestablishnewemissionsstandardsforheavy-dutyvehiclesformodelyears2027through2030orlater.ProjectedCarbonDioxideEmissionsFromTransportationBeforeandAftertheChangesinFuelEconomyStandards,EmissionsStandards,andIncentivesforElectricVehiclesThatWereAdoptedin2021and2022BillionsofMetricTons●●1.591.7500.51.01.52.0202220242026202820302032BeforeChangesAfterChangesHigherfueleconomyandemissionsstandards,combinedwithincreasesinincentivesforpurchasingelectricvehicles,areprojectedtoreducetransportation-relatedCO2emissionsin2032byabout10percent.16EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022CAFEStandardsCAFEstandardswerefirstappliedtomodelyear1978vehiclesandincreasedthroughtheearly1980s.Thestandardsremainedunchangedformanyyearsthereafter.Inaccordancewithenergylegislationenactedin2007,theNationalHighwayTrafficSafetyAdministrationsethigherstandards,whichwereimplementedintwophases,oneformodelyears2012to2016andthesecondformodelyears2017to2025.Issuedin2020,theSafer,Affordable,Fuel-Efficient(SAFE)VehiclesRulereplacedthosestandardswithlowerstandards:WhereastheearlierPhase2standardsrequiredanincreaseinfueleconomyofabout5percenteachyear,therevisedstandardsmandateda1.5percentincreaseeachyearstartingin2021andwereprojectedtoresultinanindustry-wideaveragefleetfueleconomyofabout40milespergallonin2026.In2022,NHTSAraisedstandardsonceagain,bringingthemclosertotheoriginalPhase2standardsbyrequiringincreasesof8percentannuallyformodelyears2024and2025andanincreaseof10percentformodelyear2026;NHTSAprojectedthatthosenewstandardswouldresultinanindustry-widefleetaverage(amongcarsandlighttrucks)ofapproximately49milespergallonin2026.Afleet’saveragefueleconomydependsnotonlyonthefueleconomyofeachmodelofcarandtruckbutalsoonthemixofvehiclessold.Light-dutytrucks,whichincludepopularcompactsportutilityvehicles,representedonlyhalfofsalesofnewlight-dutyvehiclesasrecentlyas2013butoutsoldcars3to1by2021.(Althoughonlystandardsforlight-dutyvehiclesareshownbelow,NHTSAhassetadditionalPhase2standardsthatcurrentlyapplytocommercialtrucks,largepickuptrucks,vans,andallbusesandworktrucksofmodelyears2021to2027.)CAFEStandardsforandEstimatedFuelEconomyofNewLight-DutyVehicles,1978to2026MilesperGallonPassengerCarsLightTrucksSAFE2022RulePhase2EstimatedFuelEconomyStandardThe2022increaseinCAFEstandardsrepresentsasubstantialincreaseinfueleconomyoverthepreviousSAFERuleandreturnsthestandardsclosertotheearlierPhase2standards.17December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORGreenhouseGasEmissionsStandardsNewmotorvehiclesarealsosubjecttogreenhousegasemissionsstandardsestablishedbytheEnvironmentalProtectionAgency(EPA)undertheCleanAirAct.Formanyyears,EPAaligneditsstandardswithNHTSA’sCAFEprogram,butthetwosetsofstandardsdivergedwiththelatestregulatorychangesannouncedbytheagenciesforthe2023–2026period.EPAstatesthatthemodelyear2026emissionsstandardof161gramspermileisequiva-lenttoa55milepergallonfueleconomystandardiftheemissionsstandardwasmetsolelybyreducingtailpipeemissions.11Butmanufacturerscanreducetheiremissionstomeetthestandardinanumberofways,includingbyproducingalternative-fuelvehicles,improvingtheintegrityandefficiencyofair-conditioningsystems,andimplementingothertechnologiesthatimprovetheoperatingefficiencyoftheirvehicles.(SuchtechnologiescanalsobeusedtomeetCAFEstandards.)Thedifferentpathwaystocompliancemakeitdifficulttodeterminewhetherthefueleconomystandardsoremissionsstandardshavethegreatereffectonemis-sions;CBOexpectsthatthechangesinCAFEstandardsandemissionsstandardswillhavesimilareffectsonCO2emissions.Thetimingofchangesinemissionsinrelationtochangesinthestandardsisaffectedbyasystemofemissionscredits.Manufacturerscanearncreditsbyachievingloweraverageannualemissionsthanrequiredunderthestandardandaccumulatethemforuseinfutureyears.Theycanalsosellthosecreditstootherautomakersthatwouldotherwisefallshortofthestandard.Suchtradinglowerstheoverallcostsfortheindustryofmeetingthestandards.Creditscanevenbeappliedretroactively:Firmshavethreeyearsinwhichtobankoracquirethenecessaryamountstoachievecompliance.(TheCAFEstandardsprogramhasasimilarcreditsystem.)Afteraccumulatingastockpileofcreditsintheearlyyearsoftheprogram,manufacturersusedanaverageof0.02BMTofcreditsperyearfrom2016to2020.Asaresult,vehiclesofthosemodelyearswillemitanaverageof0.02BMTofCO2moreovertheirlifetimethanthestandardswouldsuggest.Abankof0.10BMTofcreditsisexpectedtocarryoverfrom2021to2022.GreenhouseGasEmissionsStandardsandEstimatedEmissionsforNewLight-DutyVehicles,2012to2026GramsperMile05010015020025030020122014201620182020202220242026GreenhouseGasStandardEstimatedEmissionsFrom2012to2015,automanufacturersachievedbetteremissionsresultsthantheEPAstandard.Sincethen,theestimatedindustry-wideemissionratehasexceededthestandard.InDecember2021,EPAadoptedmorestringentstandardsformodelyears2023to2026.18EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022DemandforElectricVehiclesElectricvehiclesales(includingsalesofplug-inhybridsandall-electricvehicles)havegrownsubstantiallyoverthepastfewyearsasthecostofbatterieshasdeclined,theirstoragecapacityhasincreased,andcharginginfrastructurehasexpanded.In2021,610,000light-dutyelectricvehiclesweresold,andthree-quartersofthemreliedentirelyonelectricitytooperate.Thenumberofchargingstations,smallformanyyears,roughlydoubledfrom2019to2021.About6,600stationsofferedthefastestchargingrates(providingroughly300milesofchargeinonehourand15minutes)in2021.12(Bycomparison,approximately130,000stationssellgasoline.13)Electricvehiclesareexpectedtomakeupagrowingshareoflight-dutyvehiclesalesincomingyears.Projectionsofelectricvehiclesalesin2030varywidelybecausefederalsubsi-diesforchargingstationsandelectricvehicleschangedin2021and2022.Amongthechangeswereupto$7.5billioninfederalfundingfornewcharginginfrastructureandarevisedincometaxcreditofupto$7,500pervehicleforbuyersofqualifyingplug-inelectricvehicles.Manystatesalsoprovidefinancialincentivesforpurchasingelectricvehicles.AndinCalifornia,by2035,allnewcarssoldarerequiredtobefreeofCO2emissions.ElectricVehicles’ShareofNewLight-DutyVehicleSales,2011to2021Percent1.13.0All-ElectricPlug-inHybridsSalesofelectricvehiclesjumpedin2021toaccountfor4percentofallnewlight-dutyvehiclesales.ElectricVehicles’ShareofNewLight-DutyVehicleSalesinRecentYearsandSelectedProjectionsfor2030PercentLarsenandOthers(2022)ProjectedProjectionRangeCentralEstimate0.10.94.1MahajanandOthers(2022)YuzawaandOthers(2022)010203040507060201120162021203019325730345039Projectionsofthemarketshareofelectricvehiclesalesin2030varywidely.ThesevenprojectionsthatCBOexaminedrangefrom19percentto57percentofallnewlight-dutyvehiclesales.19December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTOREmissionsAttributabletoElectricVehiclesEvenassalesofelectricvehiclesareexpectedtorisesubstantially,theeffectofthatincreaseonoverallCO2emissionsdependsoninteractionswithCAFEstandardsandgreenhousegasemissionsstandards.Automanufacturersmightdelaytheadoptionoffuel-savingandemission-reducingfeaturesorlowerthepricesoftheirnon-electricofferingsinresponsetogreatersalesofelectricvehiclesandstillmeetstricterfueleconomyandemissionsstandards.Thosechangescouldoffsetreductionsinemissionsfromsalesofelectricvehicles.Whencomparingemissionsfromoperatingdifferenttypesofvehicles,theemissionsfromproducinganddistributingthepowertooperatethevehiclesarerelevant.Acargetting59.4milespergallon(thestandardfornewcarsin2026)willemitabout0.33poundsofCO2permilefromburningmotorfuel.Producinganddistributingthefuelalsocreatesgreenhousegases.Onaverage,thoseemissionsaddroughly30percenttotheemissionsreleasedfromthetailpipeofalight-dutyvehicle.14Noemissionsareproducedbythemotorofavehiclepoweredbyelectricity.However,gener-atingelectricityresultsinemissions,sothereductioninemissionsrepresentedbyanelectricvehiclealsodependsonwhereitsbatteryischarged.SomeregionsofthecountryhavemuchlowerCO2emissionratesfromelectricityproductionthanothers.Forexample,in2020,generatingonemegawatt-hourofelectricityintheCaliforniasubregionoftheWesternElectricityCoordinatingCouncilresultedinanaverageof514poundsofCO2,whereasgeneratingthesameamountofelectricityintheRockiessubregionyielded1,145poundsofCO2,onaverage.15Suchdifferencescanleadtosubstantialvariationinelectricvehicleemis-sions.Forinstance,apopularmodelofall-electricsedanpoweredinCaliforniain2020wasestimatedtoresultinemissionsof0.15poundsofCO2permile,butchargedinColorado,thatsamevehiclewasestimatedtoresultin0.33poundsofCO2permile.16Asthegenerationofelectricitybecomeslesscarbonintensiveinthefuture,emissionsattrib-utabletodrivingelectricvehicleswilldeclineaccordingly.CBOprojectsthatby2030,CO2emissionsintheelectricpowersectorwillfalltohalftheir2021level.17CarbonDioxideEmissionRateperMegawattHourofElectricityProduction,byState,2020PoundsofCarbonDioxideperMegawattHour1,000to1,499Lessthan500500to9991,500to2,000Emissionsattributabletoelectricvehicleusedependontheemissionsfromgeneratingtheelectricityusedtopowerthem.Somepartsofthecountry—particularlythosethatusemorerenewablesandnaturalgasthancoal—cangenerateelectricitywithmuchlowerCO2emissionratesthanothers.20EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022EffectsofEconomicGrowthandOilPricesonFutureEmissionsEconomicgrowthandthepriceofmotorvehiclefuelsaffecttotalvehiclemilestraveledand,inturn,totalCO2emissionsinthetransportationsector.Growththatwasfasterorslowerthananticipatedcouldcauseemissionstobehigherorlowerthanprojected.In2032,ifrealGDPwas8percenthigherthanitisintheEnergyInformationAgency’sbaselinescenario,transportationemissionswouldbe6percenthigherthanprojected,CBOestimates.If,instead,realGDPwas6percentlowerthanitisinEIA’sbaselinescenariooverthatperiod,emissionsfromtransportationwouldbe5percentlower.Uncertaintyaboutoilpricesisestimatedtohavelessofanimpactontransportationemis-sions.Ifhigher-than-anticipatedglobaldemandforliquidfuelsandlower-than-expectedsupplyresultedinoilpricesin2032thatwereroughlyhalfwhattheyareinEIA’sbaselinescenario,transportationemissionswouldbe2percenthigherthanprojected,CBOestimates.Alternatively,ifoilpricesin2032weredoubletheprojectedamounts,emissionsfromtransportationwouldbe1percentlower.CBO’sProjectionsofCarbonDioxideEmissionsFromTransportationUnderThreeScenariosforEconomicGrowth,2021to2032BillionsofMetricTons●●●1.591.691.5100.51.01.52.0202220242026202820302032EIA’sBaselineScenarioLowerGrowthHigherGrowthEconomicgrowthoverthenextdecadethatwashigherorlowerthanprojectedcouldincreaseordecreasetransportationemissionsbyseveralpercent.21December2022EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTOR1.EnvironmentalProtectionAgency,“GreenhouseGasEmissionsFromaTypicalPassengerVehicle,”EPA-420-F-18-008,(March2018),https://tinyurl.com/bwmm8a6s.2.InternationalEnergyAgency,GlobalEnergyReview:CO2Emissionsin2021(March2022),https://tinyurl.com/mpzxthcp.3.Toestimateenergy-relatedemissionsofCO2andothergreenhousegasesfor2021,CBOusedinformationfromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.Toestimatenon-energy-relatedemissions,CBOuseddatafromEnergyInformationAdministration,AnnualEnergyOutlook2018(February2018),www.eia.gov/outlooks/archive/aeo18/,thatagency’smostrecentlong-termprojectionsfromwhichCBOcouldmakeprojectionsofnon-energy-relatedemissions.4.Thecontributiontowarmingperphysicalunitofgasdiffersforthevariousgreenhousegases.Forsimplicity,greenhousegasesareoftenmeasuredintermsofmetrictonsofcarbondioxideequivalent,orMTCO2e—quantitiesofemissionsthat,overaperiodofyears(usuallyacentury),contributetothegreenhouseeffectbyasmuchasametrictonofCO2.SeeEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.5.Formoredetailsabouttheestimatedeffectsofthisillustrativeemissionstax,seeCongressionalBudgetOffice,“ImposeaTaxonEmissionsofGreenhouseGases,”inOptionsforReducingtheDeficit,2023to2032—VolumeI:LargerReductions(December2022),www.cbo.gov/budget-options/58638.6.Onepoundofcarboninafuel,whenburned,combineswithoxygentocreate3.7poundsofCO2.Agallonofgasolinecontainsabout5.3poundsofcarbon,soburningthatfuelreleases19.6poundsofCO2.7.DavidSchrankandothers,2021UrbanMobilityReport(TexasA&MTransportationInstitute,2021),https://mobility.tamu.edu/umr/report/.8.CBOcalculatedthosevaluesusingdatafromEnvironmentalProtectionAgency,The2021EPAAutomotiveTrendsReport:GreenhouseGasEmissions,FuelEconomy,andTechnologySince1975,EPA-420-R-21-023(November2021)www.epa.gov/automotive-trends.9.Light-dutyvehiclesincludeallpersonalvehiclesexceptmotorcycles.Light-dutyvehiclesaresubjecttofueleconomystandards,butmotorcyclesarenot.10.StacyC.DavisandRobertG.Boundy,TransportationEnergyandDataBook:Edition40(preparedbyOakRidgeNationalLaboratoryfortheDepartmentofEnergy,February2022,updatedJune2022),http://tedb.ornl.gov.11.EnvironmentalProtectionAgency,Revised2023andLaterModelYearLight-DutyVehicleGreenhouseGasEmissionsStandards:RegulatoryUpdate,EPA-420-F-21-077(December2021),https://tinyurl.com/27caws5n(PDF).12.DepartmentofEnergy,“ElectricVehicleChargingStationLocations”(accessedonSeptember6,2022),https://tinyurl.com/bd8f7rv.13.NACS,“U.S.ConvenienceStoreCount”(accessedonSeptember6,2022),https://tinyurl.com/mrxvsjyz.14.JohnM.DeCicco,FactorAnalysisofGreenhouseGasEmissionsFromAutomobiles,SocialScienceResearchNetworkworkingpaper(December2012),https://doi.org/10.2139/ssrn.2205144.Makinggasolineavailabletousersrequiresseveralsteps:Oilmustberemovedfromtheearth,movedtoarefinery,andrefinedintogasoline,andthatgasolinemustthenbedistributedtogasstations.15.TheCaliforniasubregion’semissionsaremoderatelylow,andtheRockiessubregion’semissionsaremoderatelyhigh;emissionscanbelowerorhigherthanthosevalues.TheCaliforniasubregionoftheWesternElectricityCoordinatingCouncildoesnotincludeallofthestateofCalifornia,sothestateaveragediffersfromthesubregionaverage.EnvironmentalProtectionAgency,“Emissions&GenerationResourceIntegratedDatabase(eGRID)SummaryData”(accessedonSeptember2,2022),www.epa.gov/egrid/summary-data.16.DepartmentofEnergyandEnvironmentalProtectionAgency,“BeyondTailpipeEmissionsCalculator”(accessedonSeptember2,2022),www.fueleconomy.gov/feg/Find.do?action=bt2.Thoseestimatesincludelossesfromthetransmissionanddistributionofelectricity.Lossesthatoccurwhenchargingelectricvehiclebatteriestypicallyaddanaverageof12percentto15percenttothoseamounts.SeeJohnVoelcker,“EVsExplained:ChargingLosses,”CarandDriver(April10,2021),https://tinyurl.com/bdhj83md.17.CongressionalBudgetOffice,EmissionsofCarbonDioxideintheElectricPowerSector(December2022),www.cbo.gov/publication/58419.AppendixA:AnalyticMethodThisappendixprovidesinformationaboutthemethodthattheCongressionalBudgetOfficeusedtoanalyzetrendsinenergy-relatedemissionsofcarbondioxide(CO2).TheEnvironmentalProtectionAgency(EPA)providesinformationabouttheamountandsourcesofemissionsofgreenhousegasesintheUnitedStates.1Initsannualinventory,EPAcatalogsemissionsofcarbondioxide,methane,nitrousoxide,andothergreenhousegases.BecauseEPA’s2022inventoryreportsemissionsthrough2020,informationabout2021isnotdirectlyavailable.AlthoughtheEnergyInformationAdministration(EIA)reportsenergy-relatedemissionsofCO2onasectoralbasisthrough2021,theagencydoesnotpubliclyreportnon-energy-relatedemissionsofCO2oremissionsofothergreenhousegases.Furthermore,EIA’sestimatesofannualenergy-relatedemissionsofCO2in2020differfromthoseofEPAbyabout5percent;muchofthedifferenceisattributabletotheestimatesofemissionsintheindustrialsector.Todescribetrendsinenergy-relatedemissionsofCO2through2021,CBObeganwithEPA’sestimatesofemissionsthrough2020foreachenergy-usingsectoroftheeconomy—transportation,electricpower,industrial,residential,andcommercial.UsingEIA’sestimatesofemissions,CBOthencalculatedthepercentageincreaseordecreaseintheestimateofemissionsineachofthose1.EnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.sectorsfrom2020to2021.2Toprojectemissionsfor2021,CBOappliedthepercentagechangesinEIA’sestimatestoEPA’sestimatesfor2020.Forprojectionsofenergy-relatedemissionsofCO2inthetransportationsectorfrom2022to2032,CBOappliedtheannualpercentagechangeintransportationemis-sionsbetween2020andeachofthoseyearsinEIA’smostrecentlong-termprojectionstoEPA’s2020estimate.3CBOthenadjustedtheresultingemissionstomakethemconsistentwithCBO’sprojectionsofgasolineuse,whichwererevisedtoreflecttheApril2022changetothecor-porateaveragefueleconomy(CAFE)standardsfor2024to2026andtoaccountforthereconciliationlegislationenactedin2022(PublicLaw117-169),neitherofwhichwerereflectedinEIA’slong-termprojections.Toestimatetheeffectsofthelaw’sprovisions,CBOreliedonasetofstudiesthatestimatedtheeffectsofthereconciliationactontransportationemissionsin2030.42.EnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php.3.EnergyInformationAdministration,AnnualEnergyOutlook2022(March2022),www.eia.gov/outlooks/aeo.4.JohnLarsenandothers,ATurningPointforU.S.ClimateProgress:AssessingtheClimateandCleanEnergyProvisionsintheInflationReductionAct(RhodiumGroup,August2022),https://tinyurl.com/2yddcr26;andMeganMahajanandothers,UpdatedInflationReductionActModelingUsingtheEnergyPolicySimulator(EnergyInnovation,August2022),https://tinyurl.com/yhcrc4n5.AppendixB:DataSourcesforFiguresSharesofEnergy-RelatedEmissionsofCarbonDioxide,byEconomicSector,2021CongressionalBudgetOffice,usingdatafromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.Energy-RelatedEmissionsofCarbonDioxide,byEconomicSector,1975to2021CongressionalBudgetOffice,usingdatafromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.EstimatedEffectsofa$25-per-TonTaxonEnergy-RelatedEmissionsofCarbonDioxideThatGrowsatanInflation-AdjustedAnnualRateof5Percent,byEconomicSectorRonGecan,HowCarbonDioxideEmissionsWouldRespondtoaTaxorAllowancePrice:AnUpdate,WorkingPaper2021-16(CongressionalBudgetOffice,December2021),www.cbo.gov/publication/57580.SharesofTransportation-RelatedCarbonDioxideEmissions,byModeofTransportation,2019CongressionalBudgetOffice,usingdatafromEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.SharesofPassenger-MilesTraveled,byModeofTransportation,2019CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-40,www.bts.gov/topics/national-transportation-statistics.AverageCarbonDioxideEmissionsperPassenger-Mile,byModeofTransportation,2019CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-40,www.bts.gov/topics/national-transportation-statistics;StacyC.DavisandRobertG.Boundy,TransportationEnergyandDataBook:Edition40(preparedbyOakRidgeNationalLaboratoryfortheDepartmentofEnergy,February2022,updatedJune2022),http://tedb.ornl.gov;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.26EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022EmissionsofCarbonDioxideFromHeavy-RailTransitSystems,byCarbonContentofElectricityandLoadFactor,2019CongressionalBudgetOffice,usingdatafromFederalTransitAdministration,“NationalTransitDatabase(NTD)Data,”(accessedonSeptember6,2022),www.transit.dot.gov/ntd/ntd-data,andmethodsfromFederalTransitAdministration,PublicTransportation’sRoleinRespondingtoClimateChange(January2010),https://rosap.ntl.bts.gov/view/dot/17277.SharesofTon-MilesofFreight,byModeofTransportation,2019CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-50,www.bts.gov/topics/national-transportation-statistics.AverageCarbonDioxideEmissionsperTon-MileofFreight,byModeofTransportation,2019CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-50,www.bts.gov/topics/national-transportation-statistics;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.EmissionsofCarbonDioxideintheTransportationSector,MotorVehicleMilesTraveled,andEmissionsperMileTraveledbyLight-DutyVehiclesMeasuredasaPercentageofTheirValuein1975CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-35,www.bts.gov/topics/national-transportation-statistics;EnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9,andThe2021EPAAutomotiveTrendsReport:GreenhouseGasEmissions,FuelEconomy,andTechnologySince1975,EPA-420-R-21-023(November2021),www.epa.gov/automotive-trends.MilesTraveledbyPassengerandFreightMotorVehicles,1990to2020CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-35,www.bts.gov/topics/national-transportation-statistics.Real-WorldFuelEconomyofandCarbonDioxideEmissionsFromNewLight-DutyVehicles,1975to2021CongressionalBudgetOffice,usingdatafromEnvironmentalProtectionAgency,The2021EPAAutomotiveTrendsReport:GreenhouseGasEmissions,FuelEconomy,andTechnologySince1975,EPA-420-R-21-023(November2021),www.epa.gov/automotive-trends.CarbonDioxideEmissionsFromTransportation,1975to2032CongressionalBudgetOffice,usingdatafromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php,andAnnualEnergyOutlook2022(March2022),www.eia.gov/outlooks/aeo/;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.27APPENDIXB:DATASOURCESFORFIGURESEMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORProjectedCarbonDioxideEmissionsFromTransportationBeforeandAftertheChangesinFuelEconomyStandards,EmissionsStandards,andIncentivesforElectricVehiclesThatWereAdoptedin2021and2022CongressionalBudgetOffice,usingdatafromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php,andAnnualEnergyOutlook2022(March2022),www.eia.gov/outlooks/aeo/;EnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9;CorporateAverageFuelEconomyStandardsforModelYears2024–2026PassengerCarsandLightTrucks,87Fed.Reg.25710(May2,2022);JohnLarsenandothers,ATurningPointforUSClimateProgress:AssessingtheClimateandCleanEnergyProvisionsintheInflationReductionAct(RhodiumGroup,August2022),https://tinyurl.com/2yddcr26;andMeganMahajanandothers,UpdatedInflationReductionActModelingUsingTheEnergyPolicySimulator(EnergyInnovation,August2022),https://tinyurl.com/yhcrc4n5.CAFEStandardsforandEstimatedFuelEconomyofNewLight-DutyVehicles,1978to2026CongressionalBudgetOffice,usingdatafromNationalHighwayTrafficSafetyAdministration,“MY2011–2020ComplianceOverviewandCreditFlexibilityReport”(accessedonJuly18,2022),https://one.nhtsa.gov/cafe_pic/home/ldreports,“FleetFuelEconomyPerformanceReport”(October15,2019),https://tinyurl.com/yckjt9b9,and“SummaryofFuelEconomyPerformance(PublicVersion)”(December15,2014),https://tinyurl.com/c4dent4b(PDF);CorporateAverageFuelEconomyStandardsforModelYears2024–2026PassengerCarsandLightTrucks,87Fed.Reg.25710(May2,2022);TheSaferAffordableFuel-Efficient(SAFE)VehiclesRuleforModelYears2021–2026PassengerCarsandLightTrucks,85Fed.Reg.24174(April30,2020);and2017andLaterModelYearLight-DutyVehicleGreenhouseGasEmissionsandCorporateAverageFuelEconomyStandards,77Fed.Reg.62624(October15,2012).GreenhouseGasEmissionsStandardsandEstimatedEmissionsforNewLight-DutyVehicles,2012to2026CongressionalBudgetOffice,usingdatafromEnvironmentalProtectionAgency,Revised2023andLaterModelYearLight-DutyVehicleGreenhouseGasEmissionsStandards:RegulatoryUpdate,EPA-420-F-21-077(December2021),https://tinyurl.com/27caws5n(PDF),andThe2021EPAAutomotiveTrendsReport:GreenhouseGasEmissions,FuelEconomy,andTechnologySince1975,EPA-420-R-21-023(November2021),www.epa.gov/automotive-trends.ElectricVehicles’ShareofNewLight-DutyVehicleSales,2011to2021CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics2021(November2021),Table1-17,www.bts.gov/topics/national-transportation-statistics;andDepartmentofEnergy,“Light-DutyPlug-inElectricVehicleSalesintheUnitedStatesNearlyDoubledFrom2020to2021,”TransportationFactoftheWeek1227(February28,2022),https://tinyurl.com/2c3atdbp.28EMISSIONSOFCARBONDIOXIDEINTHETRANSPORTATIONSECTORDecember2022ElectricVehicles’ShareofNewLight-DutyVehicleSalesinRecentYearsandSelectedProjectionsfor2030CongressionalBudgetOffice,usingdatafromBureauofTransportationStatistics,NationalTransportationStatistics,Table1-17,www.bts.gov/topics/national-transportation-statistics;DepartmentofEnergy,“Light-DutyPlug-inElectricVehicleSalesintheUnitedStatesNearlyDoubledFrom2020to2021,”TransportationFactoftheWeek1227(February28,2022),https://tinyurl.com/2c3atdbp;JohnLarsenandothers,ATurningPointforUSClimateProgress:AssessingtheClimateandCleanEnergyProvisionsintheInflationReductionAct(RhodiumGroup,August2022),https://tinyurl.com/2yddcr26;MeganMahajanandothers,UpdatedInflationReductionActModelingUsingTheEnergyPolicySimulator(EnergyInnovation,August2022),https://tinyurl.com/yhcrc4n5;andKotaYuzawaandothers,ElectricVehicles:What’sNextVII:ConfrontingGreenflation(GoldmanSachs,March2022),https://tinyurl.com/f8atnecb.CarbonDioxideEmissionRateperMegawattHourofElectricityProduction,byState,2020CongressionalBudgetOffice,usingdatafromEnvironmentalProtectionAgency,“Emissions&GenerationResourceIntegratedDatabase(eGRID)”(accessedonJune21,2022),www.epa.gov/egrid.CBO’sProjectionsofCarbonDioxideEmissionsFromTransportationUnderThreeScenariosforEconomicGrowth,2021to2032CongressionalBudgetOffice,usingdatafromEnergyInformationAdministration,MonthlyEnergyReview(September2022),www.eia.gov/totalenergy/data/monthly/previous.php,andAnnualEnergyOutlook2022(March2022),www.eia.gov/outlooks/aeo/;andEnvironmentalProtectionAgency,InventoryofU.S.GreenhouseGasEmissionsandSinks:1990–2020,EPA430-R-22-003(April2022),https://tinyurl.com/2p8mhpe9.AboutThisDocumentThisreportwaspreparedattherequestoftheChairmanoftheHouseCommitteeontheBudget.InkeepingwiththeCongressionalBudgetOffice’smandatetoprovideobjective,impartialanalysis,thereportmakesnorecommendations.ChadShirleypreparedthereportwithcontributionsfromRonGecanandguidancefromJosephKile.DavidAdler,DavidAustin,NicholasChase,BenHopkins,AaronKrupkin,TessPrendergast,RobertReese,JosephRosenberg,NatalieTawil,andSusanWillieofferedcomments.MichaelDwyeroftheEnergyInformationAdministrationandRichardLattanziooftheCongressionalResearchServicecommentedonanearlierdraft.Theassistanceofexternalreviewersimpliesnoresponsibilityforthefinalproduct;thatresponsibilityrestssolelywithCBO.JeffreyKlingandRobertSunshinereviewedthereport.BoPeeryeditedit,andR.L.Rebachcre-atedthegraphicsandpreparedthetextforpublication.Thereportisavailableatwww.cbo.gov/publication/58566.CBOseeksfeedbacktomakeitsworkasusefulaspossible.Pleasesendcommentstocommunications@cbo.gov.PhillipL.SwagelDirectorDecember2022

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