Urban Form And Travel Patterns At The Regional Scale Considering Polycentric Urban Structure

Increasing concerns about climate change have attracted global interests in reducing auto travel. Regional average vehicle miles traveled (VMT) vary across the urbanized areas in the U.S., suggesting a potential influence of development patterns on greenhouse gas emission. To explore the contribution of development control to driving reduction at the regional scale, this dissertation estimated impacts of urban form on two travel outcomes at the metropolitan scale: daily vehicle miles traveled (DVMT) per capita and daily transit passenger miles (DPMT) per capita. To overcome major problems of previous studies, i.e., lack of generalizability and multicollinearity, a cross-sectional analysis of 203 U.S. urbanized areas was conducted, using directed acyclic graph and structural equation modeling. A literature review revealed gaps in the previous research: while individual-level behavioral studies have identified distance from the center as the most influential factor on VMT, regional-level studies have not reflected this relationship and failed to deliver effective implications for land use policies. A method to identify regional centers was evaluated to appropriately measure polycentric urban structure of contemporary metropolitan areas. The evaluation found that lower density cutoff, wider reference area, and equal treatment between central business district (CBD) and subcenters yielded better performance in McMillen's two-stage nonparametric method. Results also showed that for polycentric areas, the use of a polycentric model produced a better model fit than the monocentric model. Major findings of this dissertation include 1) higher regional concentration, greater local density and less road supply per capita lowered VMT, and 2) higher local density and more transit supply per capita increased PMT. These results imply that different approaches to development control are needed for different sustainable transportation goals - intensifying regional centers such as infill developments for VMT reduction, and compact neighborhood development approaches, such as transit oriented development for transit promotion. However, CBD has a limited capacity and indiscreet compact developments at the urban fringe can lead to decentralization from the regional perspective, and consequently result in increased VMT. This study suggests polycentricism as a potential solution for the contradictive development principle. By allowing dispersion and concentration at the same time, urban form control at the regional level will be more beneficial than conventional local-level control.