Using spatially explicit high-granularity 3D geospatial data for quantifying public transport walking accessibility inequality and vulnerability in the x-minute city

Abstract

Public transport (PT) plays a crucial role as a fundamental urban amenity, facilitating access to destinations beyond walking distance. The concept of the x-minute city underscores the importance of having essential urban amenities like PT within a short active travel time, i.e., good PT walking accessibility. However, significant gaps persist in understanding two key aspects within the framework of the x-minute city: (1) PT walking accessibility that integrates high-granularity three-dimensional (3D) walkability constraints (including indoor footpaths) and accounts for inter-modal ridership weight differences, referred to as enhanced 3D PT walking accessibility (E3D-PTWA); and (2) vulnerability distribution arising from low E3D-PTWA and low income—a socioeconomic condition often accompanied by heightened PT dependency—thereby compounding vulnerability. This study addresses these gaps by focusing on Hong Kong as a case study of a transit-dependent and topographically complex city. Using the two-step floating catchment area (2SFCA) method and median-based measure, we compute E3D-PTWA at Hong Kong's fine-grained census unit, i.e., Large Subunit Groups (LSUGs), and its associated inequality and vulnerability across different districts. The results from this research reveal that districts in the New Territories and Kowloon exhibit a higher proportion of vulnerable LSUGs with both limited E3D-PTWA and low income, while districts on Hong Kong Island tend to have a lower percentage of such vulnerable groups. These findings emphasize the need to address the unequal distribution of PT services among the population and improve E3D-PTWA to promote sustainable and livable urban environments.