Developing a Comprehensive US Transit Accessibility Database

This paper discusses the development of a national public transit accessibility evaluation framework, focusing on lessons learned, data source evaluation and selection, calculation methodology, and examples of accessibility evaluation results. In both practice and in research, accessibility evaluation remains experimental and methodologically fragmented. This heightens the “first mover†risk for agencies seeking to implement accessibility-based planning practices, as they must select a method which might produce results that can only be interpreted locally. Development of a common baseline accessibility metric could advance the use of accessibility- based planning. The accessibility evaluation framework described here builds on methods developed in earlier project, extended for use on a national scale and at the Census block level. Application on a national scale involves assembling and processing a comprehensive national database of public transit network topology and travel times. This database incorporates the significant computational advancement of calculating accessibility continuously for every minute within a departure time window of interest. Values for contiguous departure time spans can then be averaged or analyzed for variance over time. This significantly increases computational complexity, but provides a very robust representation of the interaction between transit service frequency and accessibility at multiple departure times.