The Role of Transit Service Area Definition in Accessibility-based Evaluation

Abstract

This empirical study examines the importance of service area definition, when utilizing accessibility-based evaluation in transit projects. We analyze two transit projects: (1) Metro Transit A-Line in Minnesota and (2) Harris County Transit Re-Imagined Bus Network in Texas. The results indicate that the choice of transit service areas have a significant impact on the value of ab- solute accessibility measures. The trend shows the narrower the service area, the higher the value of the absolute accessibility measure. The results, however, are inconsistent between projects when relative accessibility measures such as percentage change between scenarios is used as an accessibility-based evaluation measure. We conclude service area definition is of only moderate importance for scenario comparisons within the same analysis boundary. When comparing different regions or areas within different boundaries, the service area definition could have a significant impact on all results. This is case-dependent and varies greatly from project to project, which requires calculating both the absolute and relative accessibility measures in an accessibility-based evaluation. In addition, decomposing the accessibility changes in the separate portions of transit projects reveals that the light rail investments have negligible impacts on accessibility levels, while restructuring of the bus network has a slight positive impact on accessibility levels. The findings have important implications for the deployment of accessibility-based evaluation on transit projects.