Utility-based approaches to understanding the effects of urban compactness on travel behavior: a case of Seoul, Korea
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Automobile use is associated with significant problems such as air pollution and obesity. Decisions to use the automobile or its alternatives, including walk, bicycle, and public transit, are believed to be associated with urban form. However, in contrast to the hypothesis that compact urban form significantly reduces automobile travel, previous studies reported only a modest effect on travel behavior. These studies, largely built on microeconomic utility theory, are not sufficient for assessing the effect of compactness, for several reasons: (1) The studies postulate that travel invokes only disutility, but travel may also provide intrinsic utility or benefits insomuch as people travel for its own sake; (2) the studies have traditionally focused on how urban compactness reduces the distance between trip origin and destination and accordingly reduces trip time, but urban compactness also increases congestion and reduces trip speed, and thus increases trip time; and (3) the studies have mostly examined automobile commuting, but people travel for various purposes, using different travel modes, and the impact of urban compactness on the utility of non-automobile non-commuting travel has not been duly examined. On this ground, to better explain the effects that urban compactness has on travel behavior, this dissertation refines the concept of travel utility using two additions to the microeconomic utility theory: activity-based utility theory of derived travel demand and approaches to positive utility of travel. Accordingly, it designs a conceptual model that specifies travel utility as an intermediary between urban compactness and travel behavior and examines the behavior associated with and utility derived from travel mode choices for alternative purposes of travel. Twenty individual models are derived from the conceptual model and tested within the context of Seoul, Korea, using a confirmatory approach of structural equation modeling and data from geographic information systems and a structured sample survey, which is initially designed and validated by semi-structured interviews and subsequent statistical tests. By comparing the individual models, this research concludes that the urban compactness effect on travel behavior, represented by trip frequencies and supplemented by mode shares, is better explained when travel utility is considered and if travel purposes are separately examined. Major empirical findings are that urban compactness affects travel behavior mainly by increasing the benefits of travel in comparison to its modest effect on the cost reduction and people’s behavioral response to urban compactness is to shift modes of commuting travel, decrease travel for shopping, and increase travel for leisure. These purpose-specific findings have implications for transportation planners and public health planners by assisting them in linking plans and policies concerning urban compactness to travel purposes.