Shengyi Gao

UPlan: A Versatile Urban Growth Model for Transportation Planning

Urban models useful in transportation planning are reviewed, focusing especially on ones that are based on geographic information system (GIS) software. Then UPlan, a simple model written by the authors in the ArcView GIS, is described. Several different applications of UPlan are outlined, involving transportation planning and analysis of the growthinducing effects of new facilities, to demonstrate its use. Such models are coming into use for National Environmental Policy Act of 1969 assessments and for joint land use and transportation planning.

UPlan: Geographic Information System as Framework for Integrated Land Use Planning Model

A geographic information system (GIS) framework is appealing to model supply-side decisions because spatial relationships commonly used by developers to evaluate building sites, such as the proximity to transportation facilities, existing land uses, political boundaries, and environmentally sensitive areas, are defined precisely in the GIS layers. The GIS captures spatial synergisms that are lost in tabulations by traffic zone or larger forecasting districts. Further, the results are defined for individual parcels (grids). This method interfaces directly with the concerns of residents and other interest groups. Uncertainty and error in postmodel allocations from zones to parcels in existing land use models can significantly blur and degrade the relevance of forecasts made with existing models. The development patterns predicted by UPlan, a planning model, tend to be realistic and provide a basis for land use planning and evaluation. A GIS land use survey, supplemented with simulation model networks and census data, was used to calibrate the model. The calibrated UPlan model did a reasonably accurate job of allocating the various categories of land uses to predefined composite growth areas. The generalized UPlan model is applicable in a wide variety of rural, suburban, and urban settings. The model, as presented, was configured as a travel simulation integrated land use planning tool, but the method also can be used as the supply-side component within a comprehensive land use modeling framework.

Public Versus Private Mobility for Low-Income Households: Transit Improvements Versus Increased Car Ownership in the Sacramento, California, Region

Empirical studies have shown that welfare recipients who own cars have a high probability of moving from welfare to work. A travel demand model adopted by the Sacramento, California, Area Council of Governments was used to examine the possible impacts of car ownership promotion versus transit improvements on job accessibility, work trips, and traveler benefits at the system level. In the car scenario, the zero-car households that were assigned a car had higher job accessibility and larger positive changes in traveler benefits than those in the base case scenario. The other households had lower traveler benefits, compared with the base case, because of slight increases in congestion. In the transit scenario, all households had gains in traveler benefits, and the households without a car gained more than those with a car. The households without a car gained more in traveler benefits in the transit scenario than in the car scenario. The total gain in traveler benefits was higher in the transit scenario. In both scenarios, the changes in total travel time, congestion, and vehicle miles traveled were small, but mode shares changed substantially.

Integrated Impacts of Regional Development, Land Use Strategies and Transportation Planning on Future Air Pollution Emissions

Urban and regional air pollution is an increasingly critical problem in areas where rapid growth is occurring and future development is expected. Within the typical planning horizon, many modeling tools (e.g., land use, travel demand, and emissions models) are used to evaluate the impact of regional development, population trends, and infrastructure improvements on air quality. However, these models were not designed, nor are they generally used as a cohesive system with feedbacks between them. Consequently, there is a gap in our understanding of how different models interact and combine to influence emissions inventories associated with future policy scenarios. In this study, funded by the Environmental Protection Agency, an emissions modeling framework was developed using the UPlan, TP+/Viper, and UCDrive emission models for the San Joaquin Valley (SJV) in central California. Specifically, future land use and subsequent travel patterns and emissions inventories were examined based on four policy scenarios for the year 2030: baseline (following general plans, with no roadway expansion), controlled growth (compact urban boundary, higher residential densities, no roadway expansion), uncontrolled growth (low residential densities, roadway expansion), and as-planned (following general plans, with roadway expansion). The integrated modeling framework links emissions to levels of travel pattern variations under different land use policy and development strategies. For example, compared to a scenario with highly controlled urban growth strategies, less restraint on urban growth results in more than a 20% increase in vehicle miles traveled and about 18% higher emissions of primary pollutants at the regional scale in year 2030. By means of comparing and connecting land use, travel patterns and emissions, the sensitivity of SJV mobile emission inventories to different possible growth scenarios can be assessed.