Congestion and Accessibility: What Is the Relationship?

This research explores the complex relationship between traffic congestion and accessibility. Congestion describes both operating conditions on transportation networks, and individual access to opportunities. The effects of congestion variations remain relatively understudied. Accordingly, this research proposes 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 therefore with increased accessibility. Finally, congestion is in part a phenomenon of perception and behavior. Congestion and individual travel data for the Los Angeles region are used to explore the localized spatial relationship between congestion and accessibility. As the multifaceted framework suggests, congestion varies substantially by neighborhood. Some neighborhoods examined in this analysis appear to be more “congestion adapted” than others. While individual tripmaking is to a large degree a function of individual and household characteristics, we construct a model to account for such characteristics. We conclude that conventional network-based measures of congestion delays paint an incomplete and perhaps misleading picture of the effects of traffic congestion and call for a fresh look at both the down- and upsides of traffic congestion.