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Case Study:
Sacramento, California
Context
Related Work
The Sacramento analysis is the first application of MEPLAN in the U.S., but it is not the only application of a transportation-land use model. A number of metropolitan areas have used the Disagreggated Residential Allocation Model/Employment Allocation Model (DRAM/EMPAL) to forecast land use as a function of transportation accessibility (Putman, 1996). DRAM/EMPAL, however, is limited in its ability to test the impacts of land use-related policies. The TRANUS modeling system (De la Barra, 1989) is closely related to MEPLAN, and is currently being applied in Baltimore, MD to test the impacts of "Smart Growth" policies (see Box 1). UrbanSim is a model developed in the U.S. by Paul Waddell of the University of Washington under the National Cooperative Highway Research Program (NCHRP). UrbanSim has been applied in Honolulu, Portland, and Salt Lake City. The model contains a number of promising advances that should improve the quality of urban modeling further and will continue to expand the range of policies that can be modeled.
In a related analysis for the Sacramento region, Johnston and de la Barra (2000) show how land use projections from an economically based urban model can be disaggregated to small areas using GIS (see Box 2). The results in turn can be used to estimate the footprint of urban development, and to derive estimates of runoff, sedimentation, habitat impacts, and development-related costs.
Box 1. Applying TRANUS to Model "Smart Growth" in Baltimore
The Baltimore Metropolitan Council is in the process of calibrating TRANUS, an integrated transportation-land use model, for the region. The model will be used to evaluate the impacts of transportation investments on land development, as well as the transportation, economic, and environmental impacts of "smart growth" policies. The model will also be used to evaluate impacts on different income groups, using consumer surplus measures.
Contact the Baltimore Metropolitan Council for more information, or see Liu (1998) for a description of the model structure. |
Box 2. Linking Urban Models and GIS
Johnston and de la Barra (2000) demonstrate the benefits of linking a regional land use-transportation model with a GIS to identify physical and environmental impacts of development. Their application is based on the TRANUS model which they developed for the Sacramento area. TRANUS is in many respects similar to the MEPLAN model, which was also applied in Sacramento as described in this case study.
The Sacramento TRANUS application includes 58 internal districts. Forecasts for each district were developed by land use category, including agricultural/mining/forestry, industrial, office high density, office low density, residential high density, and residential low density.
Once district-level land use forecasts were produced, these forecasts were disaggregated to small areas using the California Urban Futures Model (CUFM), developed by John Landis at the University of California - Berkeley (Landis, 1995). CUFM allocates development to polygons, which are ranked according to profitability for the developer. Profitability can be determined by a variety of variables such as local government fees and land prices; in this analysis it is calculated based on accessibility. Developable land units are created by overlaying GIS coverages such as city boundaries, wetlands, slope, land use type, and roads. A total of 272,000 polygons were created in this application.
A potentially quicker alternative to polygon-based disaggregation would be the use of a cell-based (raster) mapping technique, as described in the Envision Utah and SPARTACUS case studies. Using either technique, the amount of projected development by type can then be overlaid with other GIS layers, such as sensitive habitats or agricultural land. Functions can also be applied to estimate impermeable surface area, infrastructure costs, or other impacts according to the type and density of development. |
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