Integrating Life-cycle Environmental and Economic Assessment withTransportation and Land Use PlanningMikhail V. Chester,*,† Matthew J. Nahlik,† Andrew M. Fraser,† Mindy A. Kimball,§

and Venu M. Garikapati†

†Civil, Environmental, & Sustainability Engineering, Arizona State University, 501 E Tyler Mall, Room 252, mail code 5306, Tempe,Arizona 85287-5306, United States§School of Sustainability, Arizona State University, 501 E Tyler Mall, Room 252, mail code 5502, Tempe, Arizona 85287-5502,United States

*S Supporting Information

ABSTRACT: The environmental outcomes of urban form changes should couple life-cycle and behavioral assessment methodsto better understand urban sustainability policy outcomes. Using Phoenix, Arizona light rail as a case study, an integratedtransportation and land use life-cycle assessment (ITLU-LCA) framework is developed to assess the changes to energyconsumption and air emissions from transit-oriented neighborhood designs. Residential travel, commercial travel, and buildingenergy use are included and the framework integrates household behavior change assessment to explore the environmental andeconomic outcomes of policies that affect infrastructure. The results show that upfront environmental and economic investmentsare needed (through more energy-intense building materials for high-density structures) to produce long run benefits in reducedbuilding energy use and automobile travel. The annualized life-cycle benefits of transit-oriented developments in Phoenix canrange from 1.7 to 230 Gg CO2e depending on the aggressiveness of residential density. Midpoint impact stressors for respiratoryeffects and photochemical smog formation are also assessed and can be reduced by 1.2−170 Mg PM10e and 41−5200 Mg O3eannually. These benefits will come at an additional construction cost of up to $410 million resulting in a cost of avoided CO2e at$16−29 and household cost savings.

■ INTRODUCTIONAn integrated transportation and land use (ITLU) life-cycleassessment (LCA) framework that includes behavioral changesfrom urban form changes is needed for assessing theenvironmental outcomes of urban infrastructure policy. Sucha framework would lead to a stronger understanding of theoutcomes of urban form redesign and the household and travelchanges that it creates, and how up-front environmental costs(e.g., in deployment of new transit lines and construction ofmixed-use high-density buildings) may lead to opportunities forlong-run environmental benefits. Using Phoenix, Arizona as acase study, this framework is developed and applied to land usedensification strategies currently being considered near thecity’s new light rail line. It requires the joining of building andtransportation infrastructure and technology changes usingexisting methods developed by LCA practitioners withassessment of behavioral changes. A prospective assessment isused to evaluate how physical changes to transportation andland use result in long-term household and transportation

energy use that ultimately affect air emissions. By developingthe ITLU-LCA at the neighborhood scale, it becomes possibleto recommend land use changes that are sensitive to the socio-demographic and economic needs of the local community whilereducing air emissions and household costs.Environmental LCA of transportation and land use systems

has so far focused on understanding how vehicle movementand building use require other infrastructure and supply chainprocesses.1−3 The state-of-the-art approaches have sought tounderstand the interdependencies of infrastructure and quantifyindirect impacts. It is uncommon for LCA practitioners todevelop behavioral analyses. A framework that links infra-structure design with behavioral outcomes and the resultingenergy use and environmental impacts can help planners, city

Received: July 8, 2013Revised: September 14, 2013Accepted: September 20, 2013Published: September 20, 2013

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managers, engineers, and policymakers identify the character-istics of urban design that produce less environmental impactsand more economic stability in cities.To advance this concept, an ITLU-LCA framework is

developed using potential new development around threeproposed LRT extension line stations in Phoenix. Theframework builds upon an initial model of the existing LRTline and its 28 stations that focused on residentialconstruction.4 In this study, we improve the framework bycreating methods that (i) assess new building construction aswell as building reuse, (ii) are sensitive to residential andmixed-use development and the transportation impacts for bothresidential and commercial travel, and (iii) allow for sociallyand economically sensitive land use configurations that result inthe deployment of particular building designs that maintainaffordability and local community needs. The assessmentincludes energy use and greenhouse gas (GHG) emissions aswell as the potential for human health respiratory impacts andsmog formation.

■ NEIGHBORHOOD CHANGES AND INFILLPOTENTIAL

Changes in energy consumption and air emissions of GHGsand conventional air pollutants are assessed over a 60 yearlifetime from the investment in transit-oriented developments(TOD) in place of low-density outward growth. This timeframe is consistent with typical building lifetimes in existingLCA literature.5−7 Midpoint life-cycle impact assessmentmethods are used to assess human health respiratory andphotochemical smog stressors that result from air emissions.8

Site Selection. The light rail stations are selected to assessdifferent TOD design goals along several new rail lines that areplanned for 2023.9 TOD is high-density mixed residential andcommercial land use around high capacity transit. Each of thethree sites selected has unique infrastructure characteristics,residential profiles, and commercial (retail and office) activityneeds and the TODs are designed differently to meet these.The three sites are shown in Figure 1 and are currently

predominantly either low-density residential (West and North)or commercial (East). New neighborhoods are designed foreach TOD with sensitivity to the socio-economic profiles ofcurrent residents. Furthermore, interviews with local officialswere conducted to understand what the long-term housing,economic activity, and job goals were in each region.10−14 TheWest station has many vacant lots and is a predominantly low-income community. At the North station, the site is currentlydominated by middle-income single-family homes with fewvacant lots. There is demand along the North extension forcommercial establishments.15 The East station is in downtownMesa’s Main Street neighborhood, an area that has beentargeted for revitalization. The site has many vacant lotsincluding an 11 acre parcel. Mesa city officials are advocatingmixed-use developments that will attract regional light railtransit (LRT) riders.10,16

Neighborhood Design. Each site is modeled with fourdifferent growth scenarios that range from single-family homeinfill to more aggressive mixed-use high-density infill througheither adaptive reuse or new construction. Land use character-istics are detailed in the Supporting Information (SI) Table S4.Adaptive reuse is the process of reusing existing buildings(sometimes abandoned) where the structure and majorarchitectural features are kept while the interiors arereconstructed. In each scenario the primary criteria for landselection is that development must be within walking distanceof the LRT station, 0.5 miles, consistent with distances cited inprevious TOD literature.17,18 The current socio-economicconditions, potential for commercial activity, and need foroffice versus retail at each site were considered in the design ofthe TODs. These considerations resulted in the inclusion ofaffordable housing that replaces the building stock removed,and commercial deployment strategies that meet the needs ofthe residents (e.g., markets and low-rent commercial space inlower-income neighborhoods and higher-end retail in the high-income East neighborhood). Public green space is alsoincluded. For each neighborhood, the number of current

Figure 1. Phoenix light rail infrastructure. The existing light rail line is shown as a thick black line and the yellow circles are the existing stations. Theexpansion lines and stations are shown as blue lines and blue circles. The three expansion stations evaluated are the small red circles with a 1/2 milebuffer to illustrate the typical catchment area for transit riders. A 3/4 mile buffer around the current and expansion is shown in color to identify thetransit-accessible household region that was studied for TOD household travel characteristics. For each TOD, the planned train station is shown as atrain icon in a white square with the catchment area. Blue parcels are vacant and dedicated surface parking lots. Yellow area is low value residentialparcels. The solid red area is low value commercial parcels. The striped red area is commercial parcels that would likely be part of focused transitimprovement zones given their proximity to stations.

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parks were assessed and where none existed space wasallocated. The land use assessment is shown in Figure 1.The four scenarios capture increasing commitments to

density. Scenario 1 uses low-density development on vacantand surface parking lots through the construction of single-family homes. This scenario is designed to assess transportationbenefits (both in shifting of automobile trips to transit andreduced trip distances) and evaluates policy outcomes that shiftthe next new home from suburban growth to infill. Scenario 2models both high-density homes (apartments) and multistorycommercial spaces integrated into mixed-use buildings, againon vacant and surface parking lots. In Scenario 3, in addition tonew construction on vacant and surface lots, adaptive reuse ofexisting buildings is assessed. Commercial and industrialbuildings that are in the lowest quartile of market value areidentified and reconstructed into high-density mixed-use.Lastly, in Scenario 4, all residential, commercial, and industrialbuildings in the lowest quartile of market value are demolishedand new high-density mixed-use buildings are constructed. Foreach site, residential and commercial buildings are placed byfirst meeting the below-market-rate housing needs of theneighborhood, then meeting the commercial office space needsof the city, and last placing mixed-use commercial retail andadditional residential.For each of the four scenarios, the infill proposals are referred

to as TOD and the neighborhoods are compared to acorresponding suburban growth business-as-usual (BAU)counterpart. The BAU counterparts assume that the samenumber of dwelling units and commercial space that aremodeled in the TOD scenario is instead constructed as low-density single-family homes and single-story commercial spacesnot within walking distance to LRT systems, consistent withtypical suburban Phoenix construction.Environmental Impact Assessment. The energy use and

emissions (NOx, SOx, PM10, PM2.5, CO, VOCs, CO2, CH4, andN2O) from all buildings and transportation life-cycle processesin both the TOD and BAU configurations are first assessed.Emissions are converted into equivalent midpoint impactpotentials using the U.S. Environmental Protection Agency’sTool for the Reduction and Assessment of Chemical Impacts(TRACI).19 Greenhouse gas (GHG) emissions (CO2e), humanhealth respiratory impact potential (PM10e), and photo-chemical smog formation potential (O3e) are assessed, thelatter two using TRACI. GHG emissions include CO2, CH4,and N2O and are normalized to CO2e using IPCC 100 yearradiative forcing factors of 24 and 298 for CH4 and N2O.

20 Thehuman health respiratory emissions (PM10, PM2.5, SOx, andNOx) are normalized to particulate matter (10 μm andsmaller)-equivalent (PM10e) and potential smog-formingemissions (CH4, CO, VOC, and NOx) are normalized toozone-equivalent (O3e). These impact potentials were chosenfor their significance to the Phoenix metropolitan area.21

TRACI midpoint equivalency factors are provided in the SITable S1.Changes in the Use of Residential and Commercial

Buildings. Through GIS, an analysis of Maricopa County’sbuilding assessor database was used to identify available land fordevelopment, and later joined with LCA modeling tools forassessing building designs.Building Designs. Residential, commercial, and mixed-use

building prototypes are created to capture the variety ofbuilding designs that could be used within the TODs. Sevenbuilding models are developed and span from low-density to

high-density designs: a single family detached home, singlestory commercial building, three story apartment building, fourstory mixed-use building, six story mixed-use building, six storycommercial building, and a 12 story mixed-use building. Thefour and six story mixed-use building each feature one floor ofcommercial space at street level and the 12 story mixed-usefeatures two floors of commercial space. Below-market-rateresidential buildings are also considered through a lower-costdesign that can ultimately pass along ownership/rental savingsto low-income residents.Development in Scenarios 2, 3, and 4 were designed with

consideration for residential dwelling units, commercial retail,commercial office, grocery and restaurant space. PreviousLCA’s of neighborhoods have used a one size fits all approachthat does not allow for an understanding of environmentaleffects in neighborhood design trade-offs.3,22 The ratio ofcommercial properties to residential properties is based on anassessment of TODs in Los Angeles, a city that has also soughtto transition lower-density auto-oriented neighborhoods tohigh-density around new rail systems.23,24

Building Construction. Energy use and air emissions areproduced during the construction of buildings as a result of rawmaterial extraction, processing, transport, and constructionactivities. The impacts from building construction weremodeled using Athena Impact Estimator.25 Material inputsfor each of the seven buildings were estimated throughengineering material and cost estimation approaches.26 Thedesigns are validated through personal communications withlocal developers who are actively constructing TODs.27

Additionally, the impacts associated with providing parkingare included in the construction of each building.28,29 Formultifamily and mixed-use buildings, a parking structure with1.5 parking spaces per residential dwelling unit and per-square-foot zoning requirements for commercial space are included.30

Building Use Phase. Residential and commercial buildingenergy use was determined from analysis of several surveys andforecasts are developed for energy use changes into the future.Previous LCA studies of buildings have found that approx-imately 90% of a building’s environmental impacts can beattributed to the use phase.31 For residential buildings, ananalysis of the American Housing Survey (AHS) was developedto show how energy use has changed with building age in thePhoenix metro area. AHS reports the average monthlyconsumption of electricity and natural gas.32,33 To forecastbuilding energy use changes, an exponential function was fit forthe relationship between building age and energy use followingKimball et al. (2013). Energy consumption per floor area hasbeen decreasing with newer buildings (for both single andmultifamily buildings) and energy use in 2040 was estimated(halfway through the 60 year analysis time frame). AHS alsoshows that the use of natural gas in newer buildings isdiminishing and it is assumed that TOD buildings will not usenatural gas. The forecasted annual electricity demand for asingle-family home is 12 300 kWh and for a multifamilydwelling unit 11 400 kWh. CBECS (2003)14 is used to estimatethe annual electricity demand for each commercial businesstype. The most recent local building energy codes haveincreased insulation requirements for exterior walls, roofs,windows, and efficiency requirements for heating, ventilating,and air-conditioning.34 However, there is evidence to suggestthat increased plug loads have counteracted efficiency gains.35,36

It is assumed that new commercial establishments meet 2009International Energy Conservation Codes (IECC). Electricity

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demand for the five major commercial establishments areGrocery, 51 kWH/ft2/yr; Sitdown Resturants and Fast Food,47.5 kWh/ft2/yr; Retail, 17.85 kwh/ft2/yr; and Office, 11.9kWh/ft2/yr. Future changes in energy consumption resultingfrom efficiencies in building systems or electronics andappliances are uncertain and future research in this area willbe valuable. For the future power generation mix it is assumedthat Arizona meets their 2025 renewable energy goal of 15%but does not pursue more renewables afterward. An uncertaintyassessment of the changing electricity mix is presented in theSI. GREET electricity pathways are used to assess the upstreamimpacts from extraction, processing, transport of fuel inputs,and combustion processes.37

Changes in Automobile Travel. Changes in residentialand commercial neighborhood design with access to light railmay produce changes in travel behavior. Residents, shoppers,and workers, who would in the BAU scenarios not have publictransit alternatives and would likely have to travel further toaccess destinations, now have the opportunity to shifthousehold trips to transit and experience less household travel.To assess the transportation energy and environmental changesthat occur from the deployment of the TODs, travel analysis ofthe National Household Travel Survey (NHTS) is used.38

NHTS is used widely for travel behavior analysis as it providesinformation about daily travel at a disaggregate level. Like manymajor urban regions, Maricopa County paid for oversamplingin the 2009 survey. In addition to travel characteristics, socio-demographics and household characteristics are collected in thesurvey. Each household is geocoded in the survey responsesheet. With this information, two cohorts are identified: (i)suburban households and (ii) light-rail accessible urban corehouseholds. There is no true TOD resident in Phoenix yet, asdense developments near the light rail line that began operationin 2009 are still emerging. For the purpose of this study, thetravel behavior of residents living in a 0.75 mile buffer aroundthe current LRT stations were considered as transit-orientedresidents. It is anticipated that because these households are inthe urban core with access to high-capacity transit a greaterfraction of their trips will occur by transit and their automobiletravel will be less. It was assumed that future TOD residentswould have the same characteristics of the people around thecurrent LRT stations. To assess the travel behavior of residentsin low-density auto-oriented BAU scenarios, a suburbanboundary was used that follows the ring freeways of themetropolitan area. These ring freeways are roughly 10−15miles from the urban core and the newest low-density growth isanticipated outside of this region. Household travel character-istics inside these freeways but outside of the 0.75 mile light railbuffer were not assessed.Light rail and bus changes are not quantified because the

changes that result to these networks as a result of the threeTOD stations is estimated to be small. Even with redevelop-ment near the three stations, light rail is currently operatingwith significant excess capacity. Additionally, regardless of TODimplementation, bus route realignments will likely occur. As aresult, it is not obvious that TODs will result in changes in railand bus service that will lead to changing air quality effects.Furthermore, Kimball et al (2013)4 show that if new bus servicewere to expand, the air quality effects are small compared toautomobile and building energy use effects.Household Travel. There are significant differences in

travel characteristics between households in the core andsuburban areas. The average household size and the number of

trips per household do not differ significantly, but the averagetrip length per day for a suburban household is 38% more thanthat of the core resident. The average suburban householdtravels about 20 miles more per day than the core resident.Furthermore, core households have three times more transittrips. This can be due to a variety of reasons including access tohigher capacity transit lines, proximity to employment centers,and proximity to retail. Furthermore, a higher density of jobsexist in the core area.39 These benefits may not be due purely toproximity to services but may include parking policy thatreduces incentivizes for automobile ownership near transitlines.40 The differences in travel characteristics between thecore and suburban households are shown in the SI Tables S5 toS7. Of the total trips made by the NHTS Phoenix-area surveyrespondents, 24% were shopping, 10% work and 66%noncommercial.38 These three trip types were consideredseparately so the travel characteristics could be modeledappropriately for each of the three TODs.Given the uncertainty in travel behavior changes that result

from the placement of a household in the core instead ofsuburbs, a mode shift bounding analysis was developed. Thereis a dearth of data for Phoenix on how household travel changeswith access to light rail. The NHTS data set does not havesufficient temporal coverage since light rail began operation.Using a synthesis of household travel behavior changes byCervero and Arrington (2008),41 an uncertainty analysis isdeveloped for mode shifts. Based on surveys from TODs in theU.S., Cervero and Arrington (2008),41 found that the maximummode shift experienced was 44%. Based on results from anonboard light rail survey in Phoenix, a baseline shift of 30% isdetermined, and is similar to a density-based mode shiftassessment developed by Kimball et al. (2013) for the existingrail line.4,42 The effects of induced demand are considered buthave negligible effects on results. TOD residents may makemore trips given their proximity to commercial establishments,however, the impacts of these additional trips are smallcompared to the reduced trip distances by nonresidents to thesame commercial establishments.

Commercial Trip Reduction. To estimate commercial tripchanges, trip generation rates for each retail purpose were usedwith TOD adjustment methods.43 As mixed-use developmentsare constructed near light rail, automobile travel throughout thecity may change. If the commercial establishment is placed inthe TOD to meet the new household demand instead of in thesuburbs then travel may occur by transit, biking, or walking, andthose that still access by car may have shorter trip distancesgiven the TOD’s centralized location. The Institute ofTransportation Engineer’s (ITE) trip generation manual isthe state-of-the-art method for estimating automobile travelfrom commercial and office establishments.44 However, themanual is based on data largely from suburban sites that mayinflate the actual travel that results from a centrally locatedTOD.43 Therefore, an adjustment methodology developed byNelson-Nygaard (2005) was applied to adjust to TOD-specifictrip generation.43 Assessments of below market rate housing,number of jobs created per household in the TOD, intersectiondensity, sidewalk density, and bike path density were developedto estimate the adjustments. These factors compensate foroverprediction of vehicular trips in dense neighborhoods by theITE trip generation manual and shorter commercial trip lengthsin densely developed areas. The reduction in commercial travelis therefore a result of shorter commercial trip lengths of TODresidents (3.76 miles) than the fringe residents (6.87 miles) and

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also the reductions warranted by the adjustment methodologywhich predicts about 20% fewer vehicle trips in the TODs.Transportation Energy and Environmental Assessment.

Energy use and air emissions from vehicle operation, fuelproduction, and vehicle manufacturing (to capture the effect ofreduced automobile travel on displacing the production of newvehicles) were estimated using the GREET1 (fuel cycle) andGREET2 (vehicle cycle) models.37,45 To assess transportationeffects over 60 years, vehicle manufacturing and fuel efficiencychanges were modeled with goals for future fuel economystandards. Currently, Phoenix light duty vehicles average 23.4mi/gal38 and future fuel economy standards of 35 mi/gal by2020 and 55 mi/gal by 2050 were used to build changingemissions profiles into the future.46 A 60 year average fueleconomy of 43.5 mi/gal was calculated by developing a timeseries for fuel economies from 2012 to 2071 assuming that the35 and 55 mi/gal standards will be met on time. Using theNHTS, a 7 year fleet turnover was calculated for the Phoenixmetropolitan statistical area. The material composition ofvehicles is assumed to change over time to reach the 55 mi/galgoal.45 Fuel production methods are expected to change withthe increase use of unconventional crude oil sources (e.g., oilsands). Currently, 8% oil sands are used and this is forecast toincrease to 15.7% by 2020. Vehicle manufacturing effects aremodeled with GREET2 and fuel production with GREET1. Anuncertainty assessment that includes fuel economy is presentedin the SI.

■ LIFE-CYCLE ENVIRONMENTAL IMPACTS OFURBAN INFILL

The ITLU-LCA results show that urban infill where transitinfrastructure has already been deployed has the potential toreduce life-cycle energy consumption, GHG emissions, andrespiratory and smog stressors, and the majority of benefits arefound in different life-cycle phases depending on the TODdesign. The benefits increase with more aggressive land usescenarios, particularly when commercial activity is promoted, asshown in Figure 2. Regardless of the TOD design (mixed-useemphasizing middle-income and commercial office, mixed-useemphasizing low-income with retail, or residential), larger up-front energy and environmental effects will occur duringbuilding construction than if low-density suburban growth were

to occur. However, mode-shifting to light rail coupled withshorter trips by both TOD residents and commercial activityleads to substantial transportation and building use phasebenefits as well as significant benefits in the supply chain.Figure 2 shows the total life-cycle energy consumption, GHG

emissions, respiratory impact potential, and smog formationpotential for all three sites over 60 years. These three LRTstations capture just a fraction of potential larger effects thatmay occur along more than 18 miles of planned rail lineextensions in the Phoenix metropolitan area.9 By designing theTODs to the specific needs of the neighborhood, environ-mental changes occur for different reasons. Understandingwhere in the life-cycle these changes occur will enable plannersand engineers to augment the neighborhood design with anunderstanding of the maximum possible environmentalbenefits. The uncertainty bars are based on optimistic andpessimistic cases for the electricity mix, fleet fuel economy,building energy use, household trip shifting to light rail, andcommercial travel distance reduction. The overlapping portionsof the uncertainty bars represent futures where TODdeployment produces environmental impacts equivalent orgreater than BAU scenarios. For this to occur, TOD userswould need to consume more energy in their homes, have lessefficient vehicles, and not change their behavior relative tocounterparts living away from the urban core. While possible,this outcome seems unlikely given that the TODs and theircommercial establishments would be more centrally located inPhoenix. This is discussed in more detail in the SI.

Energy Consumption and Greenhouse Gas Emissions.Automobile (22−51% of total) and building (22−44%) usephases constitute the majority of energy consumption andGHG emissions, however, life-cycle processes add 26−30%.Furthermore, the impacts from commercial activities are 1.9−3.3 times larger than those from residential. The impacts fromcommercial activities decrease relatively more than residentialactivities for all scenarios, showing how the benefits of TODsextend beyond those who live in the neighborhoods byreducing both the number of trips by automobile and the tripdistance. In Scenario 1, life-cycle energy consumption isreduced by 31% and total GHG emissions are reduced by27% over BAU. When mixed-use residential and commercialinfill occurs in Scenarios 2−4, the energy savings and GHG

Figure 2. Energy and environmental effects for three LRT stations over 60 year life-cycle. The red segments are the residential building phases andthe orange segments are the commercial buildings. The purple segments are the transportation phases associated with home-based nonshopping(HBNS, commuting and leisure travel not associated with shopping) and the blue segments are the transportation phases associated with home-based shopping (HBS). Black lines are the uncertainty in both the buildings (future building energy use and energy mixes) and transportation(mode-shift) technologies as well as the percentage of household trips shifted to light rail in the case of TOD.

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emissions reductions can be as high as 42% and 40%respectively, from both travel savings and decreases inhousehold energy consumption.The construction of buildings, manufacturing of automobiles,

and production of energy in the life-cycle are significant andwill not occur within the TOD neighborhoods or where traveloccurs. These upstream phases are 26−30% of the total life-cycle effects in each scenario. These remote emissions occur forseveral reasons in building construction (the raw materialsextraction, materials manufacturing, and transport are assumedto happen outside the region such as aggregate mining in Utahor lumber mills in northern Arizona), vehicle manufacturing(automobile parts manufacturing and vehicle assembly plants),building energy feedstock provision (raw material extraction forthe fuel used in power generation and transport to the plants),and gasoline production (petroleum extraction, fuel refiningand transport of both crude oil and refined gasoline). Theresults show that for every 10 Mg of TOD life-cycle GHGemissions in Scenario 4, 7.1 Mg result from electricitygeneration and vehicle operation emissions near or in themetro area. Building construction emits an additional 0.5 Mg inthe metro area while 0.7 Mg occur in Arizona due to electricityfeedstock production and 1.7 Mg occur outside of Arizona’sborders (from vehicle manufacturing and gasoline production).While local use-phase effects are often the focus of mitigationefforts, actions that reduce upstream emissions can havesignificant benefits outside the region.The Arizona Climate Change Advisory Group (CCAG)

projects that Arizona’s GHG annual emissions will be 147 Tgby 2020.47 Infilling the 74 acres in Scenario 4 has the potentialto reduce this state-wide footprint by 0.2 Tg/yr by targetingonly three of the ultimately 42 total stations that are planned inthe system by 2023. While the benefits of TOD in Scenario 1(shifting the next 424 single family homes constructed nearlight rail) are small compared to other scenarios, the strategy isexpected to lead to energy (1.4PJ) and GHG (99 Gg) benefitsat little to no additional cost. Scenario 1 highlights how policiesthat focus on the development of vacant and underutilized landin the urban core (and near transit services) before newdevelopment occurs in outlying areas has significant trans-portation benefits. While housing construction and energy useimpacts stay the same (since it is assumed that the same houseis shifted from the suburbs to the core), locating householdsalong transit and near services produces an opportunity to shiftautomobile travel to transit and results in shorter automobiletrip distances. With aggressive land-use calculations, moremixed-use development yields greater potential savings overlow-density BAU growth. In scenario 2, the substitution ofmixed-use high-density for single family home infill in TOD1produces energy and GHG benefits 38 times greater. Adding tothis adaptive reuse in low-value parcels (TOD3) results in 41times more savings and the most aggressive infill practices(TOD4) results in 140 times more savings over scenarioTOD1. These life-cycle benefits are contingent on several keytechnological and behavioral factors and it is important tounderstand how the results change with uncertainty.Human Health Respiratory Potential. Respiratory

impact stressors from primary and secondary particle formationcan be reduced by as much as 23% in the most aggressive TODinfill scenario, and in all scenarios the total life-cycle respiratoryemissions are dominated by the buildings phases. The miningof coal (in electricity feedstock production) for building energyuse is the largest portion of total respiratory emissions from

buildings processes. There are also significant contributionsfrom vehicle manufacturing, the result of bauxite mining foraluminum parts and the production of carbon-fiber plastics thatare necessary for lightweighting. While much focus thus far hasbeen related to the use phases (electricity generation orgasoline combustion), respiratory stressors are significantlyimpacted by upstream processes such as mining of rawmaterials, producing building materials, manufacturing vehicles,or generating and producing energy. The buildings phases are70−83% of the total respiratory potential impacts, but accountfor at most 23% of the savings.TOD infill should be accompanied by parallel efforts to

establish renewable energy goals and LRT adoption to ensurereduced exposure to respiratory impacts. In Scenarios 2−4, ifTODs are constructed but Arizona fails to meet renewableenergy targets and few residents shift to LRT, then respiratoryimpacts will not be reduced from the BAU scenarios. The TODbenefits are realized when a confluence of planning policies andtechnology improvements come together. It is important thatpolicy and decision makers recognize that the full benefits ofTODs are achieved when changes to transportation, land use,and energy systems are managed concurrently. Particulateemissions in the region are currently estimated to be 92 GgPM10e/yr,

48 and the avoided emissions from TOD infill at just3 stations has the potential to reduce these emissions by 0.2%.These three stations (74 total acres) are 0.0007% of the 10.6million acres in the metro area.

Smog Formation Potential. The Phoenix metropolitanarea is routinely out-of-attainment for ozone and each of theTOD designs offers opportunities for reducing smog-formingprecursors. Filling vacant and surface lots with low-densitysingle-family homes in Scenario 1 produces a 23% potentialsavings over BAU and higher-density designs (Scenarios 2−4)produce up to 34% savings. The buildings phases constitute50−67% of the total emissions, and are dominated by airemissions from electricity generation (26−39%of the totalemissions). In the transportation phases, the smog precursorsfrom gasoline production (which occur remotely) andcombustion are nearly equal, and together make up 23−39%of the total emissions. The dominating share of remote impactsoccur in gasoline production and are largely due to VOCsemitted by industrial boilers used in recovering petroleum andby transporting crude oil to refineries. The potential for localsmog formation is estimated at 3.8 Tg O3e/yr,

49 and Scenario 4can reduce emissions by 0.1%.

■ BENEFITS OF NEIGHBORHOOD-SPECIFIC INFILLDESIGNS

The results are specific to the designs of the neighborhoods.The placement of below-market-rate residential buildings toreplace existing low-value homes, and the placement ofcommercial office space based on the needs expressed by thecities produces energy use and environmental benefits whilemaintaining social and economic goals. Air emissions withinPhoenix will also decrease, however, epidemiological research isneeded to assess public health trade-offs between neighborhooddesigns.The results show that high-density residential buildings

produce 1.5−3 times the energy impacts per dwelling unit inconstruction but result in 10% reductions in energy use overlow-density single-family homes in the 60 years, a net benefit.Ensuring that long-run user benefits are realized through up-front financing and development requirements will be critical.

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Financing, development incentivizes, construction require-ments and building energy audits could be established toensure that developers take on energy-efficiency savings andthat these benefits will be passed along to inhabitants over thelong-term.The benefits of adaptive reuse are largely contingent on the

changes in a household’s building energy use, however,transportation benefits alone are significant. Scenarios 3 and4 contrast investments along light rail that either reuse andupgrade existing low value building stock (TOD3) or demolishthat building stock and construct new buildings (TOD4).Adaptive reuse reduces residential building constructionimpacts by 4−9% for energy use, 22−50% for GHG emissions,14−28% for respiratory stressors, and 18−44% for smog. Forcommercial structures, impacts are reduced by 4−19% forenergy use, 22−42% for GHG emissions, 14−27% forrespiratory stressors, and 18−43% for smog. There isuncertainty as to whether adaptive reuse of structures resultsin the same building envelope characteristics as newconstruction, and are used by inhabitants with behavior profilesthat ultimately result in energy savings. Additional research isneeded to better understand this dynamic.The reductions in transportation impacts in each scenario are

dominated by changes in commercial travel that results fromactivity changes from both inside and outside of the TOD. Theresults show how the locating of a commercial establishmentcloser to the urban core and with transit access (i) creates anopportunity for residents along the entire transit network toaccess the establishment without automobiles, (ii) reduces theaverage trip distance to that commercial service, and (iii)creates greater reductions in automobile use outside of theTOD than from residents within the TOD. In all of thescenarios, commercial travel is roughly 80−87% of total travel.In the TOD scenarios, only 7−14% of commercial travel is theresult of TOD residents. The TODs reduce residential travel by47% and commercial travel by 51%. For Scenarios 2−4, thereductions in energy use and environmental impacts fromnonresidents are 2.2−4.4 times larger than from those living inthe TODs. The commercial benefits are largely the result ofshorter automobile trip distances to commercial establishments(accounting for 79% of the total reductions). This shows thecity-wide benefits that infill can achieve. Focusing oncommercial office space, there are significant environmentalbenefits per job. It is estimated that the 6.6 million ft2 in the

East TOD will reduce GHG emissions by 131 Gg CO2e/yrcompared to the same commercial space in a typical low-density configuration. To maximize the environmental benefitsof neighborhood-specific TOD design requires financialinvestments and these investments can be prioritized to theinfrastructure changes that produce the greatest impactreductions.

■ VALUING URBAN FORMThe deployment of TODs will require up-front financialinvestments that will lead to life-cycle economic changes inaddition to environmental changes. Using the ITLU-LCAframework, a benefit-cost analysis is developed to assess theeconomic and environmental efficiencies that result from eachstrategy. Building construction, building use, vehicle ownership,and vehicle use costs are determined in 2012 dollars.Engineering estimation approaches are used to determine theconstruction costs for each building model. These costs arebased on data from RS Means (2011)26 and Phoenix-specificadjustment factors are used. Residential building use phasecosts include water, sewer, and energy and are estimated fromPhoenix-specific households in AHS (2011).33 For commercialbuildings, natural gas, and electricity costs are based on CBECS(2003).36 CBECS does not include water costs and othersurveys are used.50 Changes from commercial activity are notincluded given the uncertainty in estimating how shopping andoffice services will change. AAA (2012)51 is used for vehicle-related costs assuming a midsize sedan. Gasoline, electricity,and natural gas cost projections from EIA (2013)52 are used tofind each fuel’s average price over the 60 year analysis period.EIA (2013)52 forecasts the future costs (due to changingmethods of extraction, production, generation, and distribu-tion) of producing these energy sources. For each of the life-cycle phases, costs were calculated over 60 years for each TODand BAU and can be allocated to private developers and users.Figure 3 shows that the benefit-cost ratios in all scenarios are

economic advantages for TOD infill, and up to 14 Tg CO2e canbe avoided if TOD financial commitments are made. Higher-density residential buildings and mixed-use buildings cost morethan single-family homes (per dwelling unit) and single-storycommercial structures (per unit area), but these investmentsproduce opportunities for less automobile driving and buildingenergy expenditures in the long run. The savings in Scenario 1are on average $10,100 per household per year. In Scenarios 2−

Figure 3. Investments in User Savings and GHG Reductions. The left chart shows the total costs of BAU and TOD in each scenario and theeconomic benefits of TOD. The benefits of TOD increase with land area developed, largely the result of increasing commercial activity. The rightchart shows the cost of conserved GHG emissions. The chart shows how much it will cost (in $/Mg CO2e) to reduce GHG emissions by a desiredamount. Note that the cost of GHG reductions drops from Scenario 2 to 3, signifying that 3 is preferable to 2 provided that financial resources areavailable.

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4, the per-household savings are $8,900-$9,300. For Scenarios2−4, the larger up-front investment costs diminish the per-household savings, however, savings are passed along to moreresidents in the city. These additional up-front buildingconstruction costs must be spent to set the appropriate TODconditions that result in transportation life-cycle savings. Thebenefit-investment ratios range from 101:1 in Scenario 2 to149:1 in Scenario 3. The cost investments lead to botheconomic and environmental benefits. Commonly cited socialcosts for CO2 emissions range from $10/Mg to $100/Mg (witha median of $30/Mg).53 Arizona’s Climate Change AdvisoryGroup (CCAG) estimates that reducing CO2 emissions willresult in economic benefits from job creation and economicdevelopment at $12/Mg.47 The drop in $/Mg CO2e costs inScenario 3 is the result of the significant cost savings that arerealized in adaptive reuse over new construction. The resultsshow that for every additional dollar invested in developmentaround the light rail line, it is possible to generate between$84−149 in household energy and transportation savingsrealized by those living in the neighborhoods.

■ LCA AND URBAN FORM CHANGESThe findings, while focused on the energy and environmentalbenefits of TODs, provide insight into urban infill designs andpolicies. The ITLU-LCA framework is valuable for compart-mentalizing changes in impacts so that policymakers can craftfocused goals for each component of the highly interdependenttransportation and land use systems. From building con-struction to electricity generation to vehicle travel, eachcomponent of the system has the potential to reduce orincrease environmental impacts. Understanding the interfacingof these components is critical for developing policies thatrecognize and support the long-run benefits of upfrontinvestments and the cobenefits across the systems. Ultimately,however, commitment to more efficient infrastructure alone isinsufficient. Policymakers should recognize that infrastructurecan affect the environmental outcome of behaviors, however,incentivizes are needed (e.g., employer transit programs,revisiting of minimum parking standards, public financing ofhigh-density structures, electricity pricing, etc.) to support thesebehaviors in the long-run.

■ ASSOCIATED CONTENT*S Supporting InformationAdditional information as noted in the text. This material isavailable free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*(M.V.C.) Phone:1-480-965-9779; fax: 1-480-965-0557; e-mail: mchester@asu.edu.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe authors received no financial support for this research.

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