An enhanced transit accessibility evaluation framework by integrating Public Transport Accessibility Levels (PTAL) and transit gap

Rapid urbanization has presented many challenges, notably spatial imbalances between the transit supply and demand within cities. The inequitable distribution of transit supply, which include the transit infrastructure and services, may lead to formation of areas where transit is under provisioned. This work aims to develop an enhanced framework for measuring spatial disparities in accessing transit systems by combining established concepts of Public Transport Accessibility Levels (PTAL) and transit gap. The proposed framework incorporates PTAL as a supply indicator and transit dependent population as the demand indicator while estimating the transit gap. PTAL takes into account the intricate relationship between transit infrastructure and transit services, an aspect that was overlooked by the previous studies on transit gap. Inclusion of PTAL enhances the transit gap evaluation method by offering a deeper understanding and a holistic perspective on the transit system. We demonstrate the proposed approach with an application in Singapore. Additionally, we propose a new classification system based on PTAL and transit gap to distinguish areas where high transit gap is a result of very high demand rather than poor supply. Results show that 44.82 % of the transit dependent population in Singapore lives in high transit gap area out of which 4.69 % population stays in transit desert zones, where supply is poor, and 40.13 % lives in transit stressed zone, where demand is very high. The study also developed a simple decision framework based on PTAL and transit gap scores to suggest effective policy measures for reducing the spatial disparity in transit system accessibility. The findings from the work can aid policymakers and transport planners in land-use and transport planning of cities.