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An Innovative Methodological Framework to Analyze the Impact of Built Environment Characteristics on Activity­Travel Choices Chandra R. Bhat, University of Texas at Austin Jessica Y. Guo, University of Wisconsin­Madison T here has been increasing interest in the land estimation techniques, units of analysis, empirical con- use­transportation connection in the past decade, texts, travel behavior dimensions, and BE characteristics motivated by the possibility that design policies and their scales used across the studies, it is difficult to associated with the built environment (BE) (land use, urban compare results. Academia agrees that it is premature to form, and street network attributes) can be used to manage draw any conclusions about the impacts of BE on activ- and shape individual traveler behavior and aggregate travel ity­travel behavior. Further, two issues need to be demand. It is important to determine whether the empiri- addressed: (a) The relationship between BE and travel cally observed association between BE and travel behav- behavior can be complex, and (b) the true causal impact ior­related variables is a reflection of underlying causality of BE on travel behavior can be assessed only if the asso- or whether it is attributable to the relationship between BE ciation due to demographics-based residential sorting is and the characteristics of people who choose to live in par- controlled for. These issues are discussed in the next two ticular BEs. sections (see also Boarnet and Crane 2001; Crane 2000; Literature debating the causal versus the associative Krizek 2003; and Handy 1996). nature of the relationship between the BE and travel behavior, including whether any causal effect is enough to cause a shift in travel patterns, is inconclusive. This COMPLEX NATURE OF THE BUILT relationship is the focus of design policies manifested in ENVIRONMENT­TRAVEL BEHAVIOR new urbanism and smart growth concepts. A review by RELATIONSHIP Ewing and Cervero (2001) describes studies that have found elasticity effects of BE attributes on travel demand Three elements characterizing the complex relationship variables. Other recent studies have also found signifi- between BE and travel are discussed below. cant effects of BE on one or more dimensions of activ- ity/travel behavior (see Rajamani et al. 2003; Krizek 2003; Shay and Khattak 2005; Bhat et al. 2005; Bhat Multidimensional Nature and Singh 2000; and Rodriguez et al. 2005). However, several studies reviewed by Crane (2000) and some other BE and travel are multidimensional in nature. That is, works (see, for example, Boarnet and Sarmiento 1998; there are many aspects to BE, including accessibility to Boarnet and Crane 2001; Bhat and Lockwood 2004; transit stops, presence and connectivity of walk and bike Bhat et al. 2005; and Bhat and Zhao 2002) have found paths, land use mix, street network density (such as aver- that BE measures have little to no impact on such dimen- age length of links and number of intersections per unit sions of travel behavior as activity­trip frequency and area), block sizes, and proportion of street frontage with nonmotorized mode use. However, because of different buildings. Similarly, there are many dimensions of travel, 137