cutting greenhouse gas emissions is only the … greenhouse gas emissions is only the beginning: a...
TRANSCRIPT
CuttingGreenhouse
GasEmissionsIsOnly
theBeginning:A
LiteratureReviewof
theCo-Benefitsof
ReducingVehicleMiles
Traveled
March2017 AWhitePaperfromtheNationalCenterforSustainableTransportation
KevinFang,UniversityofCalifornia,Davis
JameyVolker,UniversityofCalifornia,Davis
AbouttheNationalCenterforSustainableTransportation
TheNationalCenterforSustainableTransportationisaconsortiumofleadinguniversitiescommittedtoadvancinganenvironmentallysustainabletransportationsystemthroughcutting-edgeresearch,directpolicyengagement,andeducationofourfutureleaders.Consortiummembersinclude:UniversityofCalifornia,Davis;UniversityofCalifornia,Riverside;UniversityofSouthernCalifornia;CaliforniaStateUniversity,LongBeach;GeorgiaInstituteofTechnology;andUniversityofVermont.Moreinformationcanbefoundat:ncst.ucdavis.edu.
U.S.DepartmentofTransportation(USDOT)Disclaimer
Thecontentsofthisreportreflecttheviewsoftheauthors,whoareresponsibleforthefactsandtheaccuracyoftheinformationpresentedherein.ThisdocumentisdisseminatedunderthesponsorshipoftheUnitedStatesDepartmentofTransportation’sUniversityTransportationCentersprogram,intheinterestofinformationexchange.TheU.S.Governmentassumesnoliabilityforthecontentsorusethereof.
Acknowledgments
ThisstudywasfundedbyagrantfromtheNationalCenterforSustainableTransportation(NCST),supportedbyUSDOTthroughtheUniversityTransportationCentersprogram.TheauthorswouldliketothanktheNCSTandUSDOTfortheirsupportofuniversity-basedresearchintransportation,andespeciallyforthefundingprovidedinsupportofthisproject.
CuttingGreenhouseGasEmissionsIsOnlytheBeginning:ALiteratureReview
oftheCo-BenefitsofReducingVehicleMilesTraveled
ANationalCenterforSustainableTransportationWhitePaper
March2017
KevinFang,InstituteofTransportationStudies,UniversityofCalifornia,Davis
JameyVolker,InstituteofTransportationStudies,UniversityofCalifornia,Davis
i
TABLEOFCONTENTS
Introduction...........................................................................................................................1
AirPollutantEmissions...........................................................................................................2
GHGandCriteriaAirPollutantEmissionsfromVehicularOperation.................................................2
LifeCycleEmissions..........................................................................................................................5
EmissionsfromBuilding-RelatedEnergyUse....................................................................................5
WaterPollution......................................................................................................................6
HealthandSafety...................................................................................................................6
VehicleCollisionsandFatalities........................................................................................................6
PhysicalHealth.................................................................................................................................8
HealthImpactsofAirPollution.........................................................................................................9
MentalHealth..................................................................................................................................9
WildlifeImpacts....................................................................................................................10
CongestionandAccessibility..................................................................................................11
FiscalMatters........................................................................................................................12
HouseholdCosts–DirectImpacts...................................................................................................12
HouseholdCosts–IndirectImpacts................................................................................................13
PublicCosts–IndirectImpacts.......................................................................................................13
GovernmentRevenues–DirectImpacts.........................................................................................14
GovernmentRevenues–IndirectImpacts......................................................................................14
Conclusion.............................................................................................................................15
References............................................................................................................................16
1
Introduction
Traditionalevaluationofthetransportationsystemfocusesonautomobiletrafficflowandcongestionreduction.However,thisparadigmisshifting.Inanefforttocombatglobalwarmingandreducegreenhousegas(GHG)emissions,anumberofcities,regions,andstatesacrosstheUnitedStateshavebeguntodeemphasizevehicledelaymetricssuchasautomobileLevelofService(LOS).Intheirplace,policymakersareconsideringalternativetransportationimpactmetricsthatmorecloselyapproximatethetrueenvironmentalimpactsofdriving.OnemetricincreasinglycomingintouseisthetotalamountofdrivingorVehicleMilesTraveled(VMT).SincepassingtheseminalGlobalWarmingSolutionsAct(AB32)in2006,CaliforniahasenactedtwomajorlawsoverthepastdecadethatarespurringeffortstoreduceVMT:SenateBill375(2008)andSB743(2013).SB375addressesregionalGHGemissionsreductionsfrompassengertravel.ForeachregionintheStatewithametropolitanplanningorganization(MPO),thelawrequirestheCaliforniaAirResourcesBoard(ARB)tosetandregularlyupdatepercapitaGHGemissionsreductiontargetsfor2020and2035.Toachievethosetargets,SB375requireseachMPOtoadopta“sustainablecommunitiesstrategy”(SCS)aspartofitsregionaltransportationplan.VMTreductionsareakeystrategyinSCSs.SenateBill743(2013)directstheGovernor’sOfficeofPlanningandResearch(OPR)torevisetheguidelinesfordeterminingthesignificanceoftransportationimpactsduringanalysesconductedundertheCaliforniaEnvironmentalQualityAct(CEQA).SB743requiresareplacementmetricthatwill“promotethereductionofgreenhousegasemissions,thedevelopmentofmultimodaltransportationnetworks,andadiversityoflanduses.”Itmandatesthat“automobiledelay,asdescribedsolelyby[LOS]shallnotbeconsideredasignificantimpactontheenvironment”underCEQA,exceptin“locationsspecificallyidentifiedintheguidelines,ifany.”VMTisOPR’scurrentlyrecommendedreplacementmetric(OPR,2016).WhilestategoalsforreducingGHGemissionshavebeenonemotivationfortheshifttoVMTmeasures,reductionsinVMTproducemanyotherpotentialbenefits,referredtoas“co-benefits,”suchasreductionsinotherairpollutantemissions,waterpollution,wildlifemortality,andtrafficcongestion,aswellasimprovementsinsafetyandhealth,andsavingsinpublicandprivatecosts.SuchbenefitsmayprovideadditionaljustificationforreducingVMT.Inthispaper,wereviewtheliteraturetoexplorethepresenceandmagnitudeofpotentialco-benefitsofreducingVMT,providingCalifornia-specificexampleswhereavailable.Figure1showstheconceptualframeworkguidingourliteraturereview.ItemsshadedingreenindicatecharacteristicsthatcaninfluenceVMT.Itemsshadedinredindicateco-benefitspotentiallysensitivetoVMT.
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Figure1.ConceptualFramework
AirPollutantEmissions
GHGandCriteriaAirPollutantEmissionsfromVehicularOperation
Motorvehiclesemitpollutantsintotheatmosphereasby-productsofcombustion(tailpipeemissions)andthroughothermechanismssuchasfuelevaporation,tireandbrakewear,andcreationofroaddustfromthewearingofpavement.Emissionsofmajorconcernincludegreenhousegasesandcriteriaairpollutants,eachofwhichisamajorpolicyconcerninCalifornia.ReducingtheState’sGHGemissionshasbeenstatepriorityforoveradecade,asreflectedbytheaforementionedAB32,SB375andSB743.Criteriaairpollutantsaresubstancesforwhichnationalandstatestandardshavebeensetonthebasisofhumanhealth.Californiahaslongstandingairqualityproblems,withlargeareasofthestateunabletoattainnationalambientairqualitystandards(NAAQS)forcriteriapollutants.Of52counties,39areinnon-attainmentforatleastonepollutant.Fourcountiesareinnon-attainmentforfivepollutants,andninecountiesareinnon-attainmentforfourpollutants.Transportationisamajorsourceofemissions.Table1showsemissionsofcriteriaairpollutantsandGHGsfromtheoperationofon-roadvehiclesinCalifornia(notincludinglife-cycleemissions).Forcriteriaairpollutants,operationofon-roadvehiclesarethesourceforamajorityofcarbonmonoxide(CO),anearmajorityofnitrogenoxides(NOx),andadouble-digitpercentshareofparticulatematter(PM)2.5.Forgreenhousegases,approximately33percentofcarbondioxideequivalent(CO2e)emissionscomesfromtheoperationofon-roadvehicles.
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Estimatesofvehiclesnationwideprojectthattheaveragepassengervehicleemitsapproximately5.5metrictonsofCO2eperyear(USEnvironmentalProtectionAgency,2005).Thisequatestoapproximately1.01poundsofCO2epermile.
Table1.Criteriaairpollutant/greenhousegasemissionsfromon-roadtransportation
operationsinCaliforniaandpotentialemissionsreduction1
Emissions(Tons/yr)
ROG CO NOx SOx PM PM10 PM2.5 CO2e
Total 634,596 2,690,886 768,555 38,354 928,560 532,849 152,574 486,670,304Fromon-roadtransportation* 147,278 1,437,220 373,585 1,964 15,764 28,309 15,721 159,559,517
Shareofemissionsfromroadtransportation* 23.2% 53.4% 48.6% 5.1% 1.7% 5.3% 10.3% 32.8%
Ifon-road
transportationemissions
decreasedby…
Emissions(tons/yr)woulddecreaseby…
ROG CO NOx Sox PM PM10 PM2.5 CO2e
1% 1,473 14,372 3,736 20 158 283 157 1,595,5955% 7,364 71,861 18,679 98 788 1,415 786 7,977,97610% 14,728 143,722 37,358 196 1,576 2,831 1,572 15,955,95215% 22,092 215,583 56,038 295 2,365 4,246 2,358 23,933,927
Ifon-road
transportationemissions
decreasedby…
Totalstatewideemissionswoulddropby…
ROG CO Nox Sox PM PM10 PM2.5 CO2e
1% 0.2% 0.5% 0.5% 0.1% 0.0% 0.1% 0.1% 0.3%5% 1.2% 2.7% 2.4% 0.3% 0.1% 0.3% 0.5% 1.6%10% 2.3% 5.3% 4.9% 0.5% 0.2% 0.5% 1.0% 3.3%15% 3.5% 8.0% 7.3% 0.8% 0.3% 0.8% 1.5% 4.9%
*Includestailpipeandotheroperationalemissions(e.g.evaporation,brakedust,tirewear)frommobiletransportationsources.Doesnotincludeothertransportation-relatedlifecycleemissions(e.g.vehiclemanufacturing,fuelrefining)Table1alsoshowspotentialmassreductionsofpollutantsifon-roadtransportationemissionsdecreasedbymodestpercentages.TherecouldbereductionsofuptomillionsoftonsofreducedCO2eemissionsanduptohundredsofthousandsoftonsofcriteriaairpollutantemissions.Statetargetsforsomeemissions(e.g.CO2)requireasteepreductionoverthecomingyearsanddecades.Inordertoreachthosetargets,improvementsinvehicleefficiency,fuels,andVMTwilleachneedtocontributesubstantially.Ifper-capitaVMTdoesnotdecline,VMTincreases(throughpopulationgrowth)wouldlikelyprecludeachievingGHGreductiongoalsbyoutweighingimprovementsinvehicleefficiencyandfuelcarboncontent(CaliforniaAirResourcesBoard,2016).Thus,whileimprovementsinvehicleefficiencyandfuelpollutantcontentwillmeaneachreducedmileofvehicletraveleliminateslesspollutioninanabsolute
1 CriteriaairpollutantemissionsfromCaliforniaAirResourcesBoard(2013)–CaliforniaAlmanacofEmissionsandAirQuality[2012data]CO2eemissionsfromCaliforniaAirResourcesBoard(2016)–CaliforniaGreenhouseGasInventory[2014data]
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sense,steeplyreducingtargetsmeanthat,fortheforeseeablefuture,VMTreductionwillcontinuetoprovideasubstantialshareoftheneededemissionsreductiontohittargets.Vehicleswhichhavenotailpipeemissions(e.g.plug-inhybridandfullyelectricvehicles)stillleadtosomeairpollutantemissions,throughtheelectricitygenerationrequiredforcharging.Emissionscanbesubstantiallylessdependingonthecarboncontentoftheenergygrid(McLaren,etal.2016).Californiahasarelativelyhighproportionofenergygeneratedfromrenewables;however,asubstantial(thoughshrinking)shareofelectricityusedinCaliforniaisgeneratedfromsourcesthatemitGHGsorcriteriaairpollutants(CaliforniaEnergyCommission,2016).Thus,reducingeventheVMTdrivenbyzerotailpipeemissionsvehicleswouldreduceGHGandlocalairpollutantemissions.ApotentialconfoundingfactorwhendiscussingpotentialemissionsbenefitsofreducedVMTistravelspeed,asemissionsofseveralcriteriaairpollutantsandGHGsaresensitivetotravelspeed(TransportationResearchBoard,1995;BarthandBoriboonsomsin,2009).Inconventionalvehicles,poweredbyinternalcombustionengines(ICEs),greaterper-mileemissionstendtotakeplaceathigherspeeds(e.g.60mphorgreater)wheremoreenergyisrequiredtomoveavehicle,aswellasatlowerspeeds(e.g.lessthan30mphaveragetravelspeeds),wherethestop-and-goconditionsofcongestioncauseextraaccelerationcycles,energylosttobraking,longervehicleoperationtime.Theeffectofspeedisdifferentonhybridandbatteryelectricvehicles.Nikowitz,etal.(2016)showthatunlikeICEs,whichhavegreatestenergyuse(andinturnemissions)atlowandhighspeeds,hybridandbatteryelectricvehicleshavegreatestenergyuseunderhighspeedandaggressivedrivingscenarios(seeTable2).Emergingadvancedvehicletechnologiessuchasregenerativebrakingrecoverssomeoftheenergylostinstopandgoconditions.Electricmotorsinbatteryelectricandhybridvehiclesshutoffwhenthevehicleisstopped.Similar“start-stop”technologyisincreasinglycommoninICE-poweredvehicles.IncreaseddeploymentoftechnologypointstoadecreasedsensitivityofemissionsreductionstothespeedofVMTinthefuture.
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Table2.Relativeenergyconsumptionforinternalcombustion,hybrid,andbatteryelectric
vehiclesunderdifferentdrivecyclescenarios2
Scenario
Citydriving Highwaydriving Aggressivedriving
Testcycle UDDS HWFET US06
Testcycleparameters
19.59mphaveragespeed,frequentstopsandstarts
48.3mphaveragespeed,onestart/stop
48.4mphaveragespeed,somestops,rapidacceleration
Make Vehicletype Energyconsumptionrelativetolowestenergyconsumption
2012FordFocus
InternalCombustion
Engine32%greater Lowest 37%greater
2010ToyotaPrius Hybrid Lowest 4%greater 60%greater2012NissanLeaf Batteryelectric Lowest 19%greater 72%greater
LifeCycleEmissions
Beyondreducingtailpipeemissions,VMTreductionalsoreduceslifecycleemissions,suchasthosefromfuelrefining,vehiclemanufacture,roadwayconstruction,androadwaymaintenance(ChesterandHorvath,2009;ChesterandMadanat,2010,ChehovitzandGalehouse,2010;Hendriks,etal.,2004).TheseadditionalsourcesincreaseestimatesofGHGemissionsfromroadvehiclesbyapproximately63percentovertailpipeemissionsalone,andincreaseestimatesofcriteriaairpollutantemissionsfrom1.1to800timesgreater.TotheextentthatVMTreductions(1)reducefuelpurchases,(2)causeoraretheresultofdecisionsofwould-bedriverstoselltheirvehiclesorforegopurchasinganadditionalvehicle,or(3)reduceroadwayrepairburdens,theyreducelife-cycleemissions.
EmissionsfromBuilding-RelatedEnergyUse
CompactdevelopmentisakeyVMTreductionstrategy,asitleadstobothshortertripdistancesandgreateruseofalternativemodes(EwingandCervero,2010,TransportationResearchBoard2009).Stoneetal.(2007)estimatethatbuildingcompactdevelopmenttoreduceVMTwouldalsoreducecriteriaairpollutantandcarbondioxideemissionsataregionallevelbetweenfiveandsixpercentoveraconventionalgrowthscenario,evenwhenaccountingforchangesintravelspeeds.CompactdevelopmentcanalsopromoteairpollutantandGHGemissionsreductionsthroughdecreasedbuildingenergyuse.Morecompacthousingunitshaveasmallervolumeofairtoheatandcool.Additionally,attachedhousingunitshavelessexposedsurfaceareathroughwhichenergyislost.Overall,EwingandRong(2008),estimatehouseholdslivingincompactcountiesuseapproximately20percentenergythanhouseholdslivinginsprawlingcounties,evenwhiletakingintoaccountotherfactorssuchasincome,andtheurbanheatislandeffect.
2 Drivecycles–USEnvironmentalProtectionAgency(2016)Energyconsumption–AdaptedfromNikowitz,etal.(2016)
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WaterPollution
Motorvehicletravelcancausedepositionofpollutantsontoroadways,whichcanthenbecarriedbystormwaterrunoffintowaterways.Fuel,oil,andotherliquidsusedinmotorvehiclescanleakfromvehiclesontotheground(Delucchi,2000).Brakedustandtirewearcanfurthercauseparticlestobedepositedontotheground(ThorpeandHarrison,2008).Brakepadsandtirecompoundsaremadeoutofcompoundsthatincludemetal.OnestudyestimatesthatapproximatelyhalfofallcopperinSanFranciscoBaycouldhaveoriginatedfrombrakepads(NixonandSaphores,2003).InCaliforniaasawhole,upto232,000poundsofcopper,13,280poundsoflead,and92,800poundsofzincinstormwaterareattributabletobrakepaddust(NixonandSaphores,2003).Motorvehiclesrequireroadwaysfortravel.Pavedroadwaysaregenerallyimpervioussurfaceswhichpreventinfiltrationofstormwaterintheground.Impervioussurfacescanincreasetherate,volume,speed,andtemperatureofstormwaterrunoff(USEnvironmentalProtectionAgency,2003),andcantransportpollutantsviathatrunoffintowaterways.Wearingdownofroadwayscanfurthercauseparticlestobedepositedontotheground(ThorpeandHarrison,2008).Mostmotorvehiclesalsoconsumeliquidfuel,thestorageandhandlingofwhichcanresultinfueltankleaksandspills(Delucchi,2000).Californiahashadatleast38,000confirmedcasesofleaksfromundergroundstoragetanks(NixonandSaphores,2003).ReducingVMTcutsconsumptionoffuelandcouldreducefuelspillagerisks.Thesereductionswouldbeadditionaltoreductionsgainedthroughgreatervehicleefficiencyandadoptionofalternativefuelvehicles.TheVictoriaTransportationPolicyInstitute(2015)estimatesthatmotorvehicle-relatedwaterpollutionfromroadwayrunoff,oilspills,androadsaltingcostapproximately42billiondollarsperyearor1.4centspermile.
HealthandSafety
VehicleCollisionsandFatalities
Apluralityof“unintentionalinjurydeaths”(deathsnotcausedbyoldage,disease,suicideandhomicide)aretransportationrelated(Savage,2013).AccordingtotheNationalHighwayTrafficSafetyAdministration’sFatalityAnalysisReportingSystem(FARS),32,675individualswerekilledinmotorvehiclecrashesin2014(NHTSA,2015).3,074ofthesefatalitiesoccurredinCalifornia,7.9fatalitiesperevery100,000peopleperyear.Thesefatalitiesarenotjustbornebymotorvehicleoccupants,butbyotherusersaswell.InCalifornia,morethanonequarterofthosekilledinmotorvehiclecollisionsarepedestrians,bicyclists,orusersofothernon-motorizedmodes.
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Wherethereismoredriving,therearemorevehicle-relatedfatalities.ComparingmotorvehiclefatalitiesbystatefromFARSandVMTdatafromtheBureauofTransportationStatistics(2015)showsastrongpositivecorrelation(r=0.82)betweenVMTpercapitaandfatalitiesfrommotorvehiclecrashespercapita(authorscalculation,seeFigure3).DataalsoindicatesthateachmiledrivenisalsomoredangerousinareaswithhighVMT.AgaincomparingdatafromFARSandtheBTS,thereisamoderatelystrongpositivecorrelation(r=0.50)betweenVMTpercapitaanddeathspermiletraveled(authorscalculation,seeFigure4).Ifthenumberofvehicle-relatedfatalitieswerepurelyamatterofexposure,everymiletraveledshouldhavethesameamountofriskregardlessofwherethatmilewasdriven.TherewouldthusbenocorrelationbetweenVMTpercapitaandfatalitiespermile.However,stateswithhigherVMTtendtohavemoremotorvehiclecrashdeathspermilethanlowerVMTstates.SinceincreasingVMTisassociatedwithmorevehicle-relatedfatalitiespercapitaandpermile,residentsofstateswheretheycanfulfilltheirtravelneedswithfewerorshortervehicletrips(andthuswithlowerVMT)enjoyreducedtransportationsafetyrisks.Usingpublictransitalternativesisassociatedwithlessriskthanmotorvehicletravel.Savage(2013)estimatesthatdriversorpassengersofcarsorlighttrucksexperienced7.28fatalitiesperbillionmilestraveledfrom2000-2009.Comparatively,ridersofAmtrak,commuterrail,urbanmasstransitrailsystems,buses,andcommercialaviationexperience0.43fatalitiesperbillionmilestraveledorfewer.
Figure2.Motor-vehiclerelateddeathspercapitaincreasesasVMTpercapitaincreases
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Figure3.Motor-vehiclerelateddeathspermileincreasesasVMTpercapitaincreases
PhysicalHealth
Drivingorridinginmotorvehiclesisasedentarybehavior.SeveralstudiesfindassociationsbetweenVMTandweight.Forexample,obesityandBodyMassIndex(BMI)arepositivelyassociatedwithVMTperlicenseddriver(JacobsonandKing,2009;Behzad,King,andJacobson,2012).GeographicareaswithhighVMTpercapitaarealsoassociatedwithpoorerhealthoutcomesresultingfromreducedphysicalactivity.ResidentsofcountiesintheUnitedStateswithhighVMTpercapitaarelesslikelytowalkforleisure,morelikelytobeobese,havehigherBMIlevels,andhaveagreaterprevalenceofhypertension(Ewing,etal.2003).AmongCaliforniacounties,thosewiththehighestmeanobesityalsotendtohavethehighestmeanVMTpercapita(Lopez-Zetina,Lee,andFriis,2006).Potentiallycontributingtothispatternaremorenightswithinsufficientsleepandhighersmokingratesfoundwithincreaseddrivingtime(Ding,etal.2014).Whiletransitusersalsorideinmotorizedvehicles,transitusersaremorelikelytoengageinsignificantphysicalactivity,walkingtoandfromtransitstops.BesserandDannenberg(2012)foundthatbusandrailuserswalkanaverageof24minutesperdaytoandfromtransit.MorethanaquarteroftransitridersfulfilltheUSSurgeonGeneral’srecommendationof30minutesofphysicalactivityperdayjustfromwalkingto/fromstopsandstations.Ontheotherhand,
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increasedtimedrivingissignificantlyassociatedwithnotmeetingthephysicalactivityrecommendation(Ding,etal.2014).Usersofnon-motorizedmodesbydefinitionengageinphysicalactivitywhiletraveling.TheCaltransStrategicManagementPlan(CSMP)setsagoalofdoubling2010walkingandtransitlevels,andtriplingbicyclinglevelsby2020.AnepidemiologicalanalysisofthatCSMPdescribethatachievingthisgoalwouldreducechronicdiseaseand“wouldconstituteamajorpublichealthachievementonparwithCalifornia’ssuccessfuleffortsattobaccocontrol.”(Maizlish,2016,p.5).
HealthImpactsofAirPollution
Asdiscussedpreviously,roadtransportationandVMTcontributetoairpollutantemissions.Criteriaairpollutantscanleadtoavarietyofhealtheffects.Forexample,nitrogenoxidesandvolatileorganiccompoundsreactwithoxygenintheairtocreateozone,whichcanhaveseveralnegativehealtheffectsincludingchestpain,coughing,throatirritation,airwayinflammation,reducedlungfunction,andaggravationofotherrespiratoryconditions(USEnvironmentalProtectionAgency,2016a).Particulatematterposesparticularlyacutehealthimpactsassmallparticulates(lessthan10μmindiameter)canenterthelungsorbloodstreamandcauseorexacerbateheartandlungissues,andevenleadtoprematuredeath(USEnvironmentalProtectionAgency,2016b).Californiahasespeciallypoorairqualityattainmentforbothozoneandparticulatematter.Table3showspermileestimatesofthecostofmotorvehicle-relatedairpollutionbyMcCubbinandDelucchi(1999).Costsrangefromseveralcentspermileformostozone,carbonmonoxide,nitrogenoxides,andairtoxics,tomorethan12dollarspermileforparticulatematter.Thehigherestimateforparticulatematterreflectsthegreaterhealtheffects,includingmortality,thatcanbetriggeredbyparticulatematter.
Table3.Gasoline-poweredmotorvehicleairpollutioncostpermile3
PM O3 CO NO2Air
Toxics
Cost(2015$) 12.60 0.08 0.08 0.65 0.05
*Originaldatain1991dollars.Dataaboveisaverageoflow/highestimatefromoriginalstudy.Costsincludeemissionsfromtailpipe,upstreamfuelandvehicleproduction,androaddust.
MentalHealth
Inadditiontophysicalhealth,longdrivingcommutescanalsohaveanegativeimpactonmentalhealth.Hennessy(2008)identifiesseveralexamplesfromstudiesassociatinglongdrivingcommuteswithpoormentalhealthoutcomesandrelatedconsequences,includingstress,negativemood,poorconcentration,drivererrorandtrafficcollisions.Hennessyalso3BasedoffMcCubbinandDelucchi(1999)
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findsthatasstressdriversexperiencewhiledrivingincreases,workplacehostilityandobstructionismriseamongmen.OtherstudiescorroborateHennessy'sfindings.GeeandTakeuchi(2004),forexample,findthattrafficstresscorrelateswithdepressivesymptoms.Ding,etal.(2014)findthemoretotaltimeapersonspendsdrivingperday,themorelikelytheyaretoreportapoor/fairqualityoflife,high/veryhighphysiologicaldistress,beingstressedfortime,andthattheirhealthinterfereswithsocialactivities.Inadditiontonegativementalhealthoutcomesfordrivers,VMTcanalsocauseworsementalhealthforpeopleintheneighborhoodswherethatdrivingoccursororiginates.AreviewofliteraturebyPohankaandFitzgerald(2004)notesthatresidentsofdispersed,andthusgenerallyauto-dependent,suburbanareascanfaceincreasedbloodpressure,headaches,andsocialisolation,whichisdisadvantageousasthepresenceofsocialrelationshipsispositivelycorrelatedwithhealth.Additionally,theaforementioneddepressivesymptomsidentifiedbyGeeandTakeuchiaresignificantlyworseinneighborhoodswithahigh“vehicularburden”,whichincreaseswithmotorizedtransportinanarea.Builtenvironmentsthatreduceautomobiledependenceandpromotewalkingcanresultinlowerratesofdementia(Xiaetal.,2013).
WildlifeImpacts
Manyofthesameroadwayimpactsthataffectthehealthofpeoplecanalsoaffectwildlife.FormanandAlexander(1998)outlineseveralpotentialecologicalimpactsofroads.Forinstance,vehiclescandirectlyharmwildlifein“roadkill”events,withanestimatedonemillionvertebrateskilledperdayonUSroads.ShillingandWaetjen(2016)discussthatinCalifornia,5,950wildlife-relatedincidentswerereportedtotheCaliforniaHighwayPatrolfromaone-yearperiodbetween2015and2016.Additionally,about7,000reportsofanimalcarcassesaremadeannuallytothevolunteerCaliforniaRoadkillObservationSystem.Overall,ShillingandWaetjenestimatethatreportedandunreportedanimal-vehiclecollisionscostCaliforniaapproximately$225millionperyear.Duetovaryingavoidanceofroadways,impactsdifferbyspeciestypes.Amphibiansandreptilesareespeciallyatriskonnarrow,low-trafficroads,largermammalsareatriskonnarrow,high-speedroads,andbirdsandsmallmammalsatriskonwide,high-speedroads,FormanandAlexander(1998).Roadwayavoidanceisitselfanimpact,withlowerpopulationsofspeciesadjacenttoroadwaysFormanandAlexander(1998).Speciescanbeaffectedanddeterredbycharacteristicssuchasroadnoise,airpollution,alteredorpollutedwaterrunoff,andnighttimelighting.Roadwayavoidancetendstobehigheradjacenttohigherspeedandhighertrafficroads.Duetotheimpactsofroadkillandroadavoidance,roadwaysalsoactasbarriersforspeciesmovement.Roadwayscuttingthroughhabitatcanisolatepopulationsofspeciesintosmallergroups.Isolatedpopulationshaveahigherriskforextinctionandcanhavenegativeimpactsongeneticdiversity(Coffin,2007;HoldereggerandDiGiulio,2010).
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MorecompactdevelopmentpatternsthatareassociatedwithlowerVMTwouldconsumelesslandandconceivablysubjectlessterritorytoroadavoidanceandpotentialhabitatfragmentation.AcomparisonofvariousdevelopmentscenariosacrosstheSacramentoandSanFranciscoBayAreaspredictedthatthemostcompactgrowthscenariowouldsavenearly50percentofagriculturallysensitivelandacreageandsteep-slopedareas,andcloseto100percentofwetlandareas(Landis,1995).
CongestionandAccessibility
Broadly,congestionoccurswhenthefree-flowcapacityofaroadwayiseitherexceededbydemand(e.g.freewaysenteringcentralbusinessdistrictsduringpeak-hourcommutes)orimpeded(e.g.whenthereareautoaccidents,roadworkorotherroadclosures).Ineithercase,congestionincreasesasmorevehicletravelisloadedontotheroadway(FalcocchioandLevinson,2015;Downs,2004).Conversely,reducingtotalVMTinaregioncanreducecongestionontheregionalroadnetwork,albeitsubjecttotemporalandspatialcaveats.Fromatemporalstandpoint,unlessthereisanexplicitcostimposedonusingcongestedroadways(e.g.acongestioncharge)ordrivingpassengervehiclesingeneral,congestionreductionsonthoseroadwayswillcommonlyincreasethedemandforusingthemandultimatelycausecongestiontoreboundtonear-preexistinglevelsinthelong-term.Thisiscalledthe“PrincipleofTripleConvergence”–sometripmakersintheregionchangetheirtravellocations(routes),timesand/ormodestotakeadvantageofthereducedcongestionontheroadwaysinquestion(Downs,2004).This“tripleconvergence”isthereasonwhyroadwayexpansionsoftendonotreducecongestioninthelong-term(HandyandBoarnet,2014),andwhy,accordingtoDowns(2004,p.22]),“buildinglightrailsystemsorsubwaysrarelyreducespeak-hourtrafficcongestion.”However,recentresearchindicatesthattransitmaycauseamoresizeableandenduringreductioninpeak-hourcongestionthanpreviouslythought.Anderson(2014)usedachoicemodel,calibratedusingdatafromtheLosAngelesmetroarea,thatunlikemostpreviousstudiesaccountedfortheheterogeneityincongestionlevelsonroadwaysintheregion,whichincreasedthepredictedcongestion-reducingeffectsoftransitbysixtimes.AsAnderson(2014,p.2764)explains,since“driversonheavilycongestedroadshaveamuchhighermarginalimpactoncongestionthandriversontheaverageroad,”andsincetransitridersareoftenthosewhowouldhavetodriveon“themostcongestedroadsatthemostcongestedtimes,”transithasa“largeimpactonreducingtrafficcongestion.”Spatially,VMTreductionsalleviatecongestioninthespecificlocationswherenetvehicletraveliscurtailed.Andevenwhereurban(orsuburban)densificationincreasesnetlocalizedvehicletravelandcongestiondespitereducingpercapita(orevennetregional)VMT,itgenerallyincreaseslocalaccessibilitytojobsandotherdesireddestinations,decreasingthetimeandcostofreachingthosedestinations.InastudyofcongestionandaccessibilityintheLosAngeles
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region,Mondscheinetal.(2015,p.v)foundthat“high-densityareasintheregionprovidebetteraccesstojobsthanthoseareaswheretrafficconditionsarerelativelylesscongested.”Similarly,forLosAngelesfirms,theyfoundthat“physicalproximitytootherfirms,ratherthanareacongestionlevels,istheprimarycomponentoffirms’abilitytoaccessothersimilarfirms”(Mondscheinetal.,2015,p.viii).Insum,increasingregionalVMT,allelseequal,willincreaseregionalcongestion.Andconversely,reducingregionalVMTcanreduceregionalcongestion,thoughcongestionlevelsmayreboundsomewhatinthelong-term.EvenwhereVMT-reducingdensificationincreaseslocalcongestion,ittendstoimprovelocalaccessibility.
FiscalMatters
ReducingVMTalsohasmajorfiscalimpacts.Ithasbothdirectandindirectimpactsonbothhouseholdandpubliccosts.VMTcanalsohavemajorimpactsongovernmentalrevenues.
HouseholdCosts–DirectImpacts
Americanhouseholdspaymorefortransportationthananyothercategoryofhouseholdexpendituresexcepthousing(Haasetal.,2013).AccordingtoBureauofLaborStatisticsdata,householdsspentnearly20percentoftheirincomeontransportationonaverageinboth2000(18%)and2010(16%)(Moeckel,2017;Haasetal.,2013).Amajorreasonforthatisautoownershipanduseareexpensive–“themostexpensivecomponentoftransportationcostisautoownership”–andmanyU.S.householdsliveinsuburbanandexurbanareaswithpooraccessibilityandtransitconnectivity(Haasetal.,2013,20).ReducinghouseholdVMT(andcarownership)canthusreducetotalhouseholdcostsbothdirectlyandindirectly.Thedirectcostreductionsofdrivinglessarewellknown,andincludereducedfueluseandparkingcosts,lowermaintenancecostsaveragedovertime,and,forthosehouseholdsthatreducetheirVMTenoughtoselloneoftheirvehicles,license,registration,insurance,andadditionalmaintenancecostsavings(LevinsonandGillen,1998;CuiandLevinson,2016).Thecostofalternativestodrivingvarygreatlybylocation,alternative,valueoftime,andotherfactorsActivetransportationoptionslikewalkingandbicyclingcanbemuchcheaperforshortertripsthandrivingbecausetheyhavelowercapitalandoperatingcosts(e.g.thecostofwalkingshoesorabicycleversusthecostofavehicleandgasoline).Andtransit(e.g.busesandcommuterrail)canbecheaperthandrivingforlongertrips.Keeleretal.(1975),forexample,estimatedthecomparativecostsofahypotheticalcommuteintheSanFranciscoBayAreabydriving(1.5passengersperauto),ridingBayAreaRapidTransit(BART),andridingabus.Theyconcludedthatbothbusandrailtransitcanbecheaperfortheuseronanaveragebasisthandrivingatsufficientlyhighpassengerdensities.However,thepotentialforagivenhouseholdtoreduceitstransportationcostsbyreducingVMTlargelydependsonavailabilityofsufficientregionaltransitconnectivity,accessibilitytojobsandotheramenities(Haasetal.,2013;Haasetal.,2008;RenneandEwing,2013).
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HouseholdCosts–IndirectImpacts
AsisfrequentlydiscussedinboththeacademicliteratureandCaliforniapolicycircles,onewaytoreduceVMT–andachievetheassociatedhouseholdcostsavings–istoincreaseresidentialandemploymentdensitieswithinexistingurbanareas,andespeciallyneartransitstations(EwingandCervero,2010).Forresidences,abenefitofthistypeof“smartgrowth”isthatitcansubstantiallyreducehouseholdcosts,particularlytransportationcosts.Haasetal.(2008),forexample,developedamodelforestimatingaveragehouseholdtransportationcostsbyCensusblockbasedonannualhouseholdVMT,householdcarownershipandannualhouseholdtransituse.TheytestedtheirmodelintheMinneapolis-St.PaulmetropolitanregionandfoundthatreductionsinaverageannualhouseholdtransportationcostscorrelatedwithdecreasingVMT,decreasingautoownership,increasingtransittripsanddenser,moretransit-andjob-accessibleareas.Fromthatoriginalmodel,theCenterforNeighborhoodTechnology(CNT)developedtheHousing+TransportationIndex.CNThassinceexpandedandrefinedthemodel,butitsresultscontinuetoshowthatresidentialdensityisthesinglelargestpredictorofautoownershipanduse,andthushouseholdtransportationcosts(Haasetal.,2013).Householdsindenserandmoreaccessibleurbanareasoftenalsodemandlessenergyandwaterbecausetheyhavesmallerunitsandlots(Litman,2016;Buschetal.,2015).Whenallthecostsavingsoflivingindenserurbanareasarecombined,theavailableevidenceshowsthatthey“morethanoffset”theincreasedhousingcostsinthoseareas(Litman,2016,p.19;EwingandHamidi,2014).Inotherwords,whenallcostsareconsidered,ratherthanjusthousingcosts,livinginsmartgrowthcommunitiesisgenerallylessexpensivethanlivingelsewhere.WithspecificrespecttoCalifornia,onerecentstudyestimatedthatif85percentofnewhousingandjobsaddedinthestateuntil2030werelocatedwithinexistingurbanboundaries,itwouldreducepercapitaVMTbyabout12percentbelow2014levels(Buschetal.,2015).ThatcombinationofreducedVMTandmorecompactdevelopmentwould,inturn,resultinanestimated$250billioninhouseholdcostsavingscumulativeto2030(withanaverageannualsavingsperhouseholdin2030of$2,000)(Buschetal.,2015).Householdcostsanalyzedinthestudyincludeautofuel,ownershipandmaintenancecosts,aswellasresidentialenergyandwatercosts.
PublicCosts–IndirectImpacts
Inaddition,denserdevelopmentusuallyreducesthepercapitacostsofprovidingmanytypesofpublicinfrastructureandservices.Denserdevelopmentcan,amongotherthings,reduceroadandutilitylinelengths,andinturnreducetraveldistancesneededtoprovidepublicserviceslikepolice,garbagecollection,emergencyresponseandtransportingschoolchildren(Litman,2016;Buschetal.,2015;BurchellandMukherji,2003).Indeed,inhisreviewoftheliterature,Litman(2016)foundthat“[n]ocredible,peer-reviewedstudiesdemonstratethatcomprehensiveSmartGrowthpoliciesfailtosignificantlyreducepublicinfrastructureandservicecosts.”
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WithspecificrespecttoCalifornia,therecentBuschetal.(2015)studyestimatedthatif85percentofnewhousingandjobsaddedinthestatethrough2030werelocatedwithinexistingurbanboundaries,itwouldresultin$8.2billioninavoidedpublichealthcostsand$18.5billionininfrastructurecostsavingscumulativeto2030(Buschetal.,2015).Publichealthcostsconsideredincludethoserelatedtopassengervehicleairpollutantemissions,suchasrespiratory-relatedERvisits,mortality,etc.Infrastructurecostsestimatedinclude“one-timecapitalcostsforbuildinglocalroads,waterandsewerinfrastructure;andongoingannualoperationsandmaintenancecosts”(Buschetal.,2015).Allcostsavingsestimatesarein2015dollars.
GovernmentRevenues–DirectImpacts
VMTreductioncanreducepublicrevenuesfromvolumetricgastaxesorVMTfees,ifthosefeesareheldconstantpergallonormile.AsVMTdeclines,sodoesthevolumeofgasconsumedormilestolled,and,correspondingly,theamountofrevenuereceived.However,decreasesingastaxorpotentialfutureVMTtaxrevenuecouldbemadeupbyincreasingthetaxrates.AndasbetweenvolumetricgastaxesandVMT-basedtaxes,revenuestabilitywouldlikelybemoreeasilyachievedwithaVMT-basedfee,giventherapidlyadvancingshifttoelectricandmorefuel-efficientvehiclesthatarereducingliquidfuelconsumption(NationalHighwayTrafficSafetyAdministration,2014;CaliforniaEnergyCommission,2016).ThatisonereasonstatesincludingCaliforniahavebeenstudyingVMTfees(CaliforniaDepartmentofTransportation,2016).AVMTfeewouldalsobeoneofthe“mosteffectiveway[s]tochangebehavior”toreduceVMT(Chapple,2015).However,fees,liketaxes,arecommonlypoliticallyunpopular,eventhosewithimmensesocialbenefit(Bedsworthetal.,2011).
GovernmentRevenues–IndirectImpacts
Aswithhouseholdandgovernmentalcosts,VMT-reducing“smartgrowth”landusepatternsalsoimpactgovernmentalrevenues.Litman(2016)surveyedtheliteratureandfoundthat“SmartGrowthtendstoincreaseeconomicdevelopment,includingproductivity,businessactivity,propertyvaluesandtaxrevenue.”Forexample,theChicagoMetropolitanAgencyforPlanning(CMAP)(2014)concluded,basedonacomparisonofChicago-arearesidentialprojectcasestudies,that“denserprojectsdrivehigherrevenues.”Percapitagrossdomesticproduct(GDP)alsotendstodeclinewithrisingVMTandincreasewithpercapitatransitridership,whichinturncanincreasetaxrevenues(KooshianandWinkelman,2011).MoststudieslookprimarilyateitherthecostimpactsortherevenueimpactsofsmartgrowthandreducingVMT,notboth.ButintworecentstudiesofMadison,WisconsinandWestDesMoines,Iowa,respectively,SmartGrowthAmerica(SGA)didamorecomprehensivefiscalimpactanalysis(SGA,2015a,2015b).Inthestudies,SGAcalculatedbothcostsandrevenues–thenetfiscalimpact–tothecitiesandtheirassociatedschooldistrictsacrossarangeofhigh-andlow-developmentdensityscenarios.TheWestDesMoinesstudyassessedthefiscalimpactoftheestimatedresidentialandcommercialgrowthinthecityover20yearsusingfourdifferentdensityscenarios(holdingthe
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productmixconstant),andestimatedthatthenetfiscalbenefitforthecityandthelocalschooldistrictwouldbe50percentgreaterforthemostcompactdevelopmentscenarioascomparedtothebasedensityscenario(currentWestDesMoinesdensity)(SGA,2015a).TheMadisonstudywasnarrowerinscope.Itanalyzedthefiscalimpactofdevelopinga1,400-acresiteacrossarangeofdevelopmentdensitiesandproductmixes.Comparingthebaselinedensityandproductmixscenariotothemorecompactdevelopmentscenariowiththesameproductmix,thestudyestimatedthatthelatter–compactdevelopment–wouldhaveaslightlygreater(about5percent)netfiscalbenefit.However,theauthorsalsoconcludedthattheirmodellikelyunderestimatedthenetfiscalbenefitofthemorecompactscenario(SGA,2015b).
Conclusion
ReducingVMTcanprovidemanyadditionalbenefitsbeyondreducingGHGemissions.Studiesshowabroadarrayofco-benefitsincludingenvironmental,human,andfiscalhealth.VMTreductionscanprovidetheseco-benefitsdirectly(e.g.loweringairpollutantemissionsandoperatingcostsofvehicleswithreduceduse)andindirectly(e.g.realizingthebenefitsofalternativestodriving).Asnoted,therearesomevariationsinthedepthofthesebenefits(e.g.spatialdifferencesinimpacts,andimpactsdependentonotherfactorsinadditiontoVMT),buttheevidenceisclearthat,overall,VMTreductionscanhelpforwardmultiplegoalsinadditiontoGHGreduction.Additionalresearchmeasuringcostsandbenefitsoftransportationonaperdistancetraveledbasis,whichwasnotyetavailableforallimpactsreviewedinthispaper,wouldbehelpfulinfurtherascertainingthedepthandbreadthofpotentialco-benefitsofVMTreductions.
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