A Sustainable Accessibility Approach in Transportation Planning: The Case of Istanbul

Abstract

Accessibility constitutes one of the core determinants of urban quality of life. Sustainable accessibility refers to the capacity of individuals to reach essential services in an environmentally, economically, and socially equitable manner. Particularly in large metropolitan areas, this concept is intrinsically linked to the efficiency of public transport systems and the spatial distribution of urban services. This study evaluates Istanbul's public transport-based accessibility by employing the cumulative opportunities method using travel-time and employment data. The analyses were conducted within a Geographic Information Systems (GIS) environment, enabling a spatially integrated assessment. In line with the literature, thresholds of 30, 60, and 90 minutes were adopted. For each threshold, the 2022 baseline and a hypothetical 2040 scenario, assuming the completion of all planned transport investments, were modelled and comparatively examined. Findings reveal a clear improvement in accessibility across all threshold values in the 2040 scenario as a result of anticipated transport and employment investments. Within a 60 minute travel time, the average employment accessibility increases from 24.41% to 32.55%. At the 90 minute threshold, the lowest accessibility levels rise substantially. However, the minimum value within the 30 minute threshold remains unchanged, indicating that in certain areas, rapid access to major employment centers is still unattainable. The study concludes that enhancing sustainable accessibility in Istanbul requires strengthening the public transport network, ensuring a more balanced spatial distribution of urban services, and improving transport infrastructure in peripheral neighborhoods. These policy directions not only aim to elevate overall accessibility levels but also to alleviate intra-urban spatial inequities. Accordingly, the study underscores the need for accessibility-based approaches to receive greater emphasis in urban planning practice and provides insights that can inform future transport policy development for Istanbul.