Unpacking the complex relationship between land use, vehicle travel, and transportation greenhouse gas (GHG) emissions




Choi, Kwangyul

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This dissertation research aims to disentangle the relationship between land use, vehicle travel, and transportation greenhouse gas (GHG) emissions. A great number of studies have paid attention to the impact of land use on transportation GHG emissions using vehicle miles traveled (VMT) as a substitute. Most studies equated VMT reduction with reduction of transportation GHG emissions. Few have examined in depth the varying components that affect transportation GHG emissions in vehicle travel operational dimensions. Moreover, few have applied the use of larger geographic-level land use. These studies, however, have limitations in examining a comprehensive relationship between land use and transportation GHG emissions. This dissertation research therefore focuses on the links between land-use measures at various geographic levels and household vehicle travel characteristics impacts on transportation GHG emissions. In doing so, this dissertation research consists of the three closely related research questions. Using the 2009 National Household Travel Survey (NHTS), this research first examines whether neighborhood-level land use attributes proportionally affect household daily VMT and transportation GHG emissions (CO2e). A series of multiple regression models developed in Chapter Four address the impact of land use on household vehicle travel characteristics and transportation GHG emissions. Results suggest that land use strategies at the neighborhood level such as densification, a mixture of land use, and improvement of road connectivity can play a significant role in reducing vehicle travel. However, these land use changes may cause traffic delays in the area. Chapter Five focuses on the impact of multiple geographic-level land use (i.e., neighborhood, county, and MSA) on both household VMT and transportation GHG emissions by applying hierarchical linear modeling. Results suggest that the effectiveness of similar strategies can vary by geographic scales at which those strategies are implemented. Chapter Six examines the intervening effects of vehicle travel characteristics on transportation GHG emissions by employing structural equation modeling. Results suggest that land use at various geographic levels influence not only household VMT but also vehicle travel speed and vehicle trip frequency, which together in turn affect household transportation GHG emissions. Finally, this research presents a case study of the Austin, TX region using the 2006 Austin Travel Survey (ATS) in Chapter Seven. Applying a path model similar to the one developed in the preceding chapter, this study scrutinizes the role of land use in reducing transportation GHG emissions in both regional and local contexts. Results suggest that densification and a mixture of land use are still effective land use strategies to reduce region-wide emissions. However, design improvement can be a double-edged sword because of its unintended effect of reduced vehicle travel speed. Overall, the findings contend that both travel demand management and mobility management at various geographic levels should be fully discussed in the early stages of planning. In addition, the role of metropolitan planning organizations (MPOs) in controlling regional development should be extended. The expansion of authorities and responsibilities of MPOs may enable the region at all levels to be developed more sustainably.


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