Impact/Purpose:

Robust forecasts of land use, emissions, and activity patterns are essential for air quality model predictions. The objectives of this proposal are to:

1. Apply an integrated transportation-land use model (ITLUM) to investigate the impacts of regional development scenarios and trade policies on the magnitude and spatial distribution of emissions of ozone precursors. ITLUM-based forecasts will be compared with four pre-determined metropolitan development scenarios: i) low-density, segregated-use development based on extensive highway provision; ii) concentrated, contiguous regional growth within 1-mile of transportation corridors; iii) concentrated growth in existing and new communities with distinct boundaries; iv) high-density development and balanced-use zoning.

2. Compare the air quality impacts of regional development scenarios on predicted ozone concentrations and human exposure patterns using a photochemical grid model.

3. Test the hypothesis that predicted human exposure patterns based on ITLUM emission forecasts will differ from those based on the U.S. EPA’s post-Clean Air Act Amendment emission scenario projections.

4. Test the hypothesis that changes in land use and dry deposition patterns have at least as significant an impact on future air quality as changes in on-road vehicle emission control technologies.

Description:

Urban development results in changes to land use and land cover and, consequently, to biogenic and anthropogenic emissions, meteorological processes, and processes such as dry deposition that influence future predictions of air quality. This study examines the impacts of alternative regional development patterns using Austin, Texas as a case study.

The Austin – Round Rock Metropolitan Statistical Area (MSA) is located in Central Texas and includes Travis, Williamson, Hays, Bastrop and Caldwell Counties. The Austin MSA is among the most rapidly growing urban areas in the United States with a current population of approximately 1.7 million concentrated in Travis County. Williamson (5th), Hays (26th), Bastrop (30th), and Caldwell (51st) Counties were among the 100 fastest growing counties by percent change in the country, while Travis (32nd) County was one of 100 fastest growing counties by numeric change in the country between 2000 and 2001.

Urban growth scenarios evaluated in this study were developed using two distinct approaches: visioning and mathematical modeling. Visioning is a highly community-oriented planning technique used to create regional land use and transportation goals. It is typically performed as a cooperative, inclusive process among business owners, community residents, interest groups, and local officials and results in broad goals and principles which can guide future policies and plans. In contrast, land use models are based on historical trends and attempt to forecast or predict what future land use patterns will look like based on those trends (along with changes in any policy, land use, travel cost or other variable that the analyst has incorporated into the model). They are typically driven by technical experts, relying on data for calibration and model specification, and result in a set of probable future trends and indicators which can guide the implementation of growth management strategies. Consequently, direct comparisons of results for the two methods are not really relevant. However, it is important to understand both approaches offer their own relative advantages from a planning perspective and the visioning and modeling processes appear quite complementary. Both regional visioning and land use modeling approaches can provide key inputs to models of travel demand, emissions, and air quality.

Four urban growth scenarios were developed through a community-driven regional visioning initiative known as Envision Central Texas (ECT). The ECT process engaged state and local government, business, environmental, and community development organizations, and elected leaders from the five counties. Based on information discussed in public workshops, the ECT process projected a set of four possible growth scenarios. All of the scenarios are based on a doubling of population in 20 to 40 years from 2001, but assume different types of growth. ECT Scenario A assumes low-density, segregated-use development based on extensive highway provision; ECT Scenario B assumes concentrated, contiguous regional growth within 1-mile of transportation corridors; ECT Scenario C concentrates growth in existing and new communities with distinct boundaries; ECT Scenario D assumes high-density development in existing towns and cities with balanced-use zoning.

For this study, projected biogenic and anthropogenic emission inventories, along with land cover estimates for estimation of dry deposition velocities were developed for the year 2030 for each of the four ECT visioning scenarios. Air quality modeling was performed using the Comprehensive Air Quality Model with extensions (CAMx), which is currently the photochemical model used by the State of Texas for attainment demonstrations. Austin was among the first areas to prepare an Early Action Compact (EAC) or voluntary State Implementation Plan (SIP) under the National Ambient Air Quality Standard (NAAQS) for ozone concentrations averaged over 8-hours. As part of the EAC, the September 13 – 20, 1999 multi-day high ozone episode with projected 2007 emissions was developed for use in CAMx. The four regional visioning scenarios were used with the identical meteorological data and CAMx configuration developed for the 2007 EAC case (referred to in this report as the Base Case). The focus of the work with the ECT scenarios was to examine the response of biogenic emissions, air pollutant deposition velocities, and overall regional air quality, as represented by ozone concentrations, to land use development. The ECT scenarios were compared based on their impact to daily maximum 1-hour ozone concentrations, hourly episodic ozone concentrations, and population exposure. The influences of changes in biogenic emissions and deposition velocities from each of the four ECT scenarios on daily maximum 1-hour ozone concentrations and hourly episodic ozone concentrations were considered both separately, and in tandem for the five-county Austin area. The influences of changes in anthropogenic emissions from area and non-road mobile sources and on-road mobile sources were also considered separately and in tandem.

In addition, a goal of this study was to test the hypothesis that changes in land use and dry deposition patterns have at least as significant an impact on future air quality as changes in on-road vehicle emission control technologies. The Energy Independence and Security Act of 2007, which focuses on improving vehicle fuel economy and reducing U.S. dependence on foreign oil, includes a mandatory Renewable Fuel Standard which requires significant increases in the use of biofuels through 2022. For at least the next few years, it is expected that the majority of this mandate will be met by corn ethanol. E85 is a blend of 85% denatured fuel ethanol and 15% gasoline that can be used in flex fuel vehicles (FFVs). An additional photochemical modeling run was performed in which on-road mobile source emissions for ECT A were modified to simulate use of E85 by 30% of the gasoline fleet.

Key findings from the analysis of the ECT studies are summarized below:

• Although VMT is predicted to continue increasing, emissions of NOx and VOCs from on-road mobile sources are predicted to decrease through approximately 2025 due to the phase-in of new emission standards. Similarly, NOx emissions from non-road mobile sources in the Austin area are also predicted to decrease due to the phase-in of new emission standards, while VOC emissions are predicted to increase by 5-9%.
• Future changes in daily maximum 1-hour ozone concentrations due to the combined changes in dry deposition, biogenic emissions, and anthropogenic emissions in the ECT scenarios ranged from -11 ppb to -2 ppb, with typical values of -6 ppb. Differences due to changes in biogenic emissions and dry deposition only between ECT A (continuation of current development patterns) and the Base Case ranged from -0.9 ppb to +0.1 ppb. Differences due to changes in anthropogenic emissions only between ECT A and the Base Case were far more significant, ranging from -9 ppb to -2 ppb.
• Maximum differences in hourly ozone concentrations due to changes in biogenic emissions and dry deposition only between the ECT scenarios and the Base Case ranged from -1.4 ppb to +0.7 ppb. Maximum differences in hourly ozone concentrations due to changes in anthropogenic emissions only between the ECT scenarios and the Base Case were far more significant, ranging from -14 ppb to +22 ppb.
• Differences in ozone concentrations between the ECT scenarios (-3 ppb to +5 ppb) were smaller than the differences between the ECT scenarios and the Base Case. Doubling of population and implementation of new federal mobile source standards produced greater changes in emissions and air quality than differences in spatial patterns due to different types of regional development. These results imply that the pattern of urban development is not as significant as reductions in emissions per capita, but the effects of urbanization patterns are non-negligible.
• Future changes in daily maximum 1-hour ozone concentrations due to the introduction of E85 relative to ECT A ranged from -0.4 to 0.0 ppb, with typical values of -0.2 ppb for the Austin area. Although these impacts appear small, they are comparable in magnitude to some commonly employed air pollution control measures that were adopted as part of Austin’s Early Action Compact. Differences in hourly ozone concentrations due to the introduction of E85 are relatively smaller than changes due to development patterns.
• For the ECT scenarios, concentrated high-density development in existing towns with balanced-use zoning produced lower exposure to high ozone concentrations than a more typical pattern of urban sprawl. Evaluating daily population exposure can provide additional information about the magnitude and spatial distributions of changes in ozone due to urban development.

Urban land use models (LUMs) seek to predict a region’s future spatial distribution of households and employment, and provide key inputs to models of travel demand, emissions, and air quality. Integrated transport-land use models (ITLUMs) allow analysts to anticipate system response to new policies, preference functions, economic conditions and other scenarios. With increasing computational power and theoretical advances, many operational LUMs have been developed. Although many limitations remain, innovative research in this area is still emerging due to the complexity of transport-land use systems. The year 2030 travel conditions and household and employment distributions for the Austin-Round Rock MSA Texas were predicted using two ITLUMs. The first utilizes a gravity-based land use model (G-LUM) and a standard travel demand model (TDM) and is a variation of Steven Putman’s Integrated Transportation-Land Use Package (ITLUP). The second, a new land use change and land use intensity (LUC-LUI) model, examines land use change at the parcel level and applies systems of equations for land use intensity (household and employment counts by type) at the level of travel analysis zones (TAZs).

The land use and transportation effects of several distinctive policies were investigated. These include a business-as-usual (BAU) scenario, a road pricing scenario (congestion pricing plus a per-mile-traveled carbon tax, CPCT), and an urban growth boundary (UGB) scenario (prohibiting new development in presently peripheral, largely undeveloped zones). Implications of all three policies were analyzed using the G-LUM, and the BAU and CPCT scenarios were investigated using the LUC-LUI model system. Biogenic and anthropogenic emission inventories, along with land cover estimates for estimation of dry deposition velocities, were developed for each of five ITLUM scenarios. The ITLUM scenarios were compared based on their impact to daily maximum 1-hour ozone concentrations, hourly episodic ozone concentrations, and population exposure.

Key findings from the analysis of the ITLUM scenarios are summarized below:

• While fundamentally different, both the community-oriented visioning and land use modeling processes carry benefits and appear complementary.
• Three distinctive transportation and land use scenarios were investigated using the gravity-based LUM and a standard TDM. In addition to the business-as-usual (BAU) scenario, these include a road pricing policy which entails a flat-rate carbon-based tax on all Austin roadways and congestion pricing (CPCT) along Austin freeways, and an urban growth boundary (UGB) policy. The BAU and CPCT scenarios were predicted to have similar patterns of household and job distribution in year 2030. When implementing UGB policy, new development was constrained to predefined zones/neighborhoods, which either met a density threshold or were adjacent to a zone meeting the threshold. In terms of travel behavior impacts, the CPCT and UGB policies appear to be powerful tools for VMT reduction, though mode shift effects were marginal.
• The BAU and CPCT scenarios also were investigated using a wholly new LUM (coupled with a TDM). The new LUM models land use change at the level of individual parcels (using logit models) and then household and job counts at the level of traffic analysis zones, recognizing spatial autocorrelation (in a system of seemingly unrelated regression equations). The model results suggest that the CPCT policy results in less region-wide land consumption, with lands closer to regional freeways being somewhat more likely to develop. These two policies were estimated to generate similar household and employment distribution patterns, with households remaining concentrated centrally and along regional freeways, and employment densities rising over time near the region’s core. The CPCT policy appears effective in reducing regional VMT, increasing average speeds, and reducing traffic congestion, particularly during peak hours. These findings are consistent with the G-LUM-based model predictions.
• Consistent with the analysis of the ECT scenarios, VMT is predicted to continue increasing with the ITLUM scenarios, while emissions of NOx and VOCs from on-road mobile sources are predicted to decrease through approximately 2025 due to the phase-in of new emission standards. Similarly, NOx emissions from non-road mobile sources in the Austin area are also predicted to decrease due to the phase-in of new emission standards, while VOC emissions increase slightly.
• Future changes in daily maximum 1-hour ozone concentrations due to the combined changes in dry deposition, biogenic emissions, and anthropogenic emissions in the ITLUM scenarios ranged from -10 ppb to -2 ppb, with typical values of -5 ppb. Maximum decreases in hourly ozone concentrations of up to -16 ppb were predicted in the LUC-LUI scenarios. The G-LUM UGB scenario resulted in maximum decreases of up to -14 ppb as compared to -9.5 ppb in the G-LUM BAU scenario.
• For the ITLUM scenarios, lower exposure was typically predicted for the road pricing scenarios and with relatively higher values predicted for the urban growth boundary scenario.

These results imply that controlling the environmental impacts of urbanization involves multi-faceted strategies. Integrated modeling efforts, such as the ones described in this study, have the potential to facilitate policy decisions that support balanced growth for U.S. communities.

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The hypotheses will be investigated using a case study in the Austin, Texas Metropolitan Statistical Area. Biogenic and anthropogenic emissions will be quantified and mapped for each scenario and used as input to the Comprehensive Air Quality Model with Extensions to evaluate air quality and human exposure patterns and to test the hypotheses.

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