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

[pageleftintentionallyblank]

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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