New public transit accessibility metrics: system and system-facilitated accessibility measures

This study proposes a public transit accessibility measure that integrates intrazonal system accessibility, the ease of reaching transit stops, for system-facilitated accessibility, the ability to access opportunities using the transit network. The proposed accessibility measure addresses key limitations of traditional metrics, which often rely solely on gross travel times and overlook intrazonal variations in walking and waiting times. By calculating Public Transport Accessibility Levels (PTAL) at a fine spatial resolution of 400 m square grids and integrating them with zone-to-zone travel times, a modified impedance function is developed to create a more comprehensive system-facilitated accessibility index. Results from multiple linear regression show that the proposed measure outperforms traditional methods in explaining public transit mode share. A non-linear relationship is identified, indicating diminishing returns on transit mode share as accessibility improves beyond a threshold. Using the proposed accessibility measure, the study further evaluates Singapore’s alignment with the “20-Minute Town and 45-Minute City (20T-45C)” framework. Access to fourteen essential services categorised into four groups: (i) education, (ii) healthcare, (iii) commerce, and (iv) entertainment and community facilities, analysed within the town with a 20-minute travel time threshold. The analysis of job opportunities is conducted at the city level with a of 45 min threshold. The results reveal spatial disparities, with subzones in the Central, East, and Northeast Regions are well served, while many subzones in the North and West Regions remain underserved. A decision-making framework based on the cross-classification of PTAL and service accessibility is proposed to guide urban planners toward sustainable transit planning.