Congestion And Accessibility: What’S The Relationship?

This project conceptually and empirically explores the complex relationship between congestion and accessibility. While congestion alters individual access to opportunities, its effects vary significantly across people, places, and time - variations that remain relatively understudied. This report begins by proposing a conceptual framework with three components. First, congestion can constrain mobility and thus indirectly reduce accessibility. Second, congestion is associated with agglomerations of activity and with increased accessibility. Finally, congestion is in part a phenomenon of perception and behavior, cognitively altering an individual’s choice set of destinations and altering actual access to opportunities. Congestion and individual travel data for the Los Angeles region are used to explore the localized spatial relationship between congestion and accessibility. As our multifaceted framework suggests, congestion does not have a uniform effect on accessibility, but varies substantially by neighborhood. Our analysis finds that in some neighborhoods congestion appears to be associated with depressed levels of access, as conventional wisdom would suggest. Other neighborhoods, however, appear to be more “congestion adapted,” allowing high levels of activity participation despite high levels of congestion. To account for personal characteristics such as income that may influence the spatial analysis, we construct a model of the number of daily trips as a function of an array of personal and household characteristics. Residuals from the model suggest that place-­‐based neighborhood effects explain the relatively higher levels of travel by residents found in the “congestion adapted” neighborhoods.