The Adjusted Transit Accessibility Index: A proximity-independent measure of public transit accessibility

This study introduces the adjusted transit accessibility index (ATAI), a proximity-normalized public transit accessibility measure that isolates public transit system performance from the impacts of land use and geography. The ATAI utilizes a residual modeling framework to quantify the difference between observed public transit access and a regional benchmark predicted by a baseline mode, such as the automobile. We apply this approach to a case study of Buffalo, New York, quantifying accessibility to grocery stores and jobs using time- and opportunity-based accessibility measures, respectively. The results show that our methodology highlights over- and underserved areas that are not identified by classical public transit accessibility metrics, and that our methodology successfully disentangles public transit performance from the strong spatial dependence that classical accessibility metrics exhibit. Thus, the ATAI provides a more nuanced diagnostic tool for policymakers seeking to evaluate transit service quality after accounting for spatial and land-use effects.