Realizable Accessibility: Assessing the Reliability of Public Transit Accessibility using High-resolution Real-time Data

Keywords: Public transit, accessibility, space-time prism, real-time data
Session Type: Virtual Paper Abstract
Day: Monday
Session Start / End Time: 2/28/2022 09:40 AM (Eastern Time (US & Canada)) - 2/28/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 61

Abstract

The widespread availability of public transit schedule and real-time vehicle location allows high-resolution measurement and analysis of public transit-based accessibility to jobs, health care and other crucial community resources. However, measuring accessibility based on transit schedules is an overestimate since the scheduled service is often not realized in practice. Retrospective measures based on real-time vehicle location data can also overestimate accessibility since they assume that transit users have perfect knowledge of delays and other departures from scheduled. In this paper, we introduce realizable real-time accessibility based on the space-time prism (STP) as a more conservative and practical accessibility measure. We moreover define accessibility unreliability to measure overestimation of the traditional measures. Based on fine-grained real-time big data General Transit Feed Specification (GTFS), the paper conducts a case study in the Central Ohio Transit Authority (COTA) bus system in Columbus, Ohio. Our results show that STPs based on realizable accessibility are consistently more conservative than schedule-based or retrospective-based STPs. We also find that the unreliability of both traditional measures will spread from urban center to suburban areas as the STP time budget increases. Temporal analyses also show that unreliability is higher in February and September, morning and afternoon rush hours, and middle of a week, which is highly consistent with prior findings of bus delay and risk of missing transfers and indicates their inherent connections. STPs based on realizable accessibility are a more practical, conservative, and robust measure for public transit planning.