Using Realtime GTFS to generate easy-to-use transit accessibility measures under travel time uncertainty

• Prior studies on transit accessibility under travel time uncertainty used complex measures with non-standard data formats. • This complexity has hindered reproducibility and replicability in research and planning. • We propose a framework using standardized Realtime GTFS to generate simple accessibility measures under uncertainty. Previous studies on measuring transit accessibility under travel time uncertainty often introduced complex measures based on non-standard data formats, hindering reproducibility and replicability in research and planning. To address this, we present a practical framework that leverages a standardized format for real-time transit data: Realtime General Transit Feed Specification (GTFS), to generate easy-to-use transit accessibility measures under travel time uncertainty. This framework first produces two datasets by correcting Scheduled GTFS data using Realtime GTFS information: Realtime P50 GTFS and Realtime P85 GTFS, which are used to compute two accessibility measures : median-corrected accessibility (using Realtime P50 GTFS) and dispersion-corrected accessibility (using Realtime P85 GTFS). These accessibility measures are applied in Columbus, Ohio, USA for an empirical study examining how overlooking travel time uncertainty issues can distort the analysis results of healthcare accessibility, inequality, and new transit project evaluation. Results indicate that scheduled accessibility (using Scheduled GTFS data) which overlooks travel time uncertainty overestimates healthcare accessibility by approximately 10.97 %. Moreover, this oversight fails to capture the benefits of the new transit service in improving accessibility and reducing inequality. Furthermore, although findings consistently suggest that lower-income neighbourhoods experience greater gains in healthcare accessibility compared to wealthier counterparts, our analysis unveils statistically significant differences when using the scheduled and dispersion-corrected accessibility measures. These findings underscore the importance of incorporating travel time uncertainty into public transit planning and evaluation. Our framework allows transit authorities and researchers to accurately measure accessibility and evaluate projects under travel time uncertainty using a standardized data format.