Diagnosing double vulnerability in aging cities: A spatial coupling framework applied to elderly pedestrian crash risk and hospital accessibility in Seoul

Abstract As cities worldwide undergo rapid population aging, older adults face compounding spatial disadvantages when high pedestrian crash risk and poor healthcare accessibility converge in the same neighborhoods. Yet existing literature has largely examined these two dimensions separately, leaving the spatial co-occurrence of traffic danger and medical underservice — and its implications for urban governance — underexplored. Using Seoul, South Korea, as a case study, this research constructs an integrated framework encompassing risk identification, accessibility assessment, and spatial coupling analysis. This framework is evaluated using 9,190 elderly pedestrian crashes recorded between 2020 and 2024, alongside facility attributes from 59 general hospitals. The Gaussian two-step floating catchment area (Ga2SFCA) method is employed to evaluate potential medical access under 15minute and 30minute walking thresholds. The results demonstrate that both elderly pedestrian crash risk and hospital accessibility exhibit significant spatial heterogeneity across Seoul. High-risk areas are predominantly concentrated in the urban core and along major transport corridors, whereas zones lacking adequate medical access are widely distributed in the urban periphery. As the walking threshold is extended from 15 to 30 minutes, the service catchment improves and the number of medium-accessibility areas increases substantially; however, the overall pattern of spatial inequality remains largely unchanged. Further spatial coupling analysis identifies 10 administrative neighborhoods (dongs) that remain consistently classified as high-risk–low-accessibility (HL) under both threshold settings, representing typical zones of double vulnerability faced by older pedestrians. In contrast, only one dong is classified as high-risk–high-accessibility (HH) under the 30-minute threshold, suggesting that relatively high healthcare accessibility does not necessarily correspond to reduced collision exposure. Beyond the Seoul context, this study proposes a transferable spatial coupling framework for diagnosing double vulnerability in aging cities, offering a replicable methodology for identifying priority intervention zones where traffic risk and healthcare underservice spatially converge.