| Summary: | This paper compares the relative performance of different measures of accessibility in relevant models. Specifically, the authors formulated three measures of accessibility: gravity-based accessibility, an aggregate measure of potential; trip-based accessibility, a disaggregate, utility-based measure of the value of travel alternatives; and activity-based accessibility, a theoretically richer disaggregate, utility-based measure of the value of alternative activities (including travel). These accessibility measures were used as explanatory variables in household vehicle ownership models and real estate market price models, comparing the explanatory power of each accessibility measure in each model as expressed by the confidence in the coefficient estimates and captured by the models' goodness-of-fit statistics. It was found that trip-based accessibility best represents preferences for accessibility in both vehicle ownership decisions and property valuations. This supports the theoretical value of disaggregate, utility-based accessibility measures over aggregate, potential-based measures. The fact that trip-based measures perform better than activity-based accessibility measures underscores several empirical and technical limitations. Finally, the authors noted that accurately representing accessibility preferences requires congruence between the granularity of the accessibility measure and that of the explained behavior. This emphasizes the importance of understanding what accessibility measures actually capture and ensuring that they align with the analysis purpose. Accessibility has attracted increasing interest as transportation and planning professionals have shifted their attention to the interactions between the transportation system and the larger urban system. Its importance and usefulness as an urban performance measure have been demonstrated widely. Glaeser noted that "all of the benefits of cities come ultimately from reduced transport costs for goods, people and ideas" (1). Although Glaeser did not use the term accessibility, his quote mirrors the accessibility concept in emphasizing the interaction between the transportation system (reduced transport costs) and the activity and land-use systems (goods, people, and ideas), as opposed to one or the other in isolation. The benefits Glaeser refers to can take many different forms. Investments in transportation infrastructure are often seen as a means of generating economic development. However, for project evaluation these benefits have traditionally been measured in travel time savings. Accessibility offers a more nuanced perspective aligned with the transportation as a derived demand paradigm. Specifically, accessibility captures how the transportation and land-use systems interact to generate opportunities for individuals (e.g., access to employment and other urban amenities). Essentially, accessibility is the raison d'être of an urban system. In practice, however, it remains relatively abstruse. Even professionals within the fields of transportation and urban planning are not always clear-or at least not in agreement-about what it encompasses or how it should be measured. Numerous increasingly sophisticated and complex measures of accessibility have been proposed, but how well can we operationalize them? Do they improve our abilities to predict relevant behaviors in the system? This paper examines how accessibility performs in predicting household vehicle ownership choices and estimating residential property valuations. Specifically, the appropriateness, advantages, and limitations of three different accessibility measures are explored-gravity-based, trip-based, and activity-based-in representing household and market preferences in models of these long-term choices. This study is part of our recent work in developing meaningful accessibility measures that capture the interaction between the day-to-day performance of the transportation system and people's long-term choices.
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