Congestion and Accessibility: What's the Relationship?

This research examines how measures of transportation accessibility and congestion vary and relate in metropolitan areas. While congestion has been a perennial concern for transportation policymakers, planners, and researchers, traditional measures of congestion say little about the range and extent of opportunities that individuals are either gaining access to or missing out on because of the regional transportation system's functionality. Using GIS-based methods, empirical measures of accessibility will be developed that account both for mobility constraints at a given location and the potential destinations accessible within those constraints. These measures of accessibility will be compared to common measures of congestion at the local and regional scales. The project hypothesizes that within a region, the effects of congestion on accessibility are likely to vary considerably across a single region. Because of these differences, empirical measures of accessibility may provide researchers, engineers, planners, and policymakers with different insights into the transportation system's performance by emphasizing potential benefits for travelers rather than the mechanistic functioning of the infrastructure as do measures of congestion. This research, in other words, seeks to shift the unit of analysis in congestion measurement from the transportation network to travelers by focusing on accessibility instead of system performance.