A methodological Investigation of the 15-Minute City (15-MC) studies

Abstract

In contemporary urban planning visions, where sustainable mobility, localization and proximity are paramount, the concept of the 15-minute city (15-MC), which focuses on strategically placing essential amenities within 15-minute walking or biking distances, is gaining significant importance. As efforts are being undertaken to translate the 15-MC concept into practical action, it is critical to address two key limitations of existing research: 1. A heavy reliance on open-source datasets, such as OpenStreetMap (OSM), which are often criticized for their limited point of interest (POI) data quality, and 2. The tendency to compute access uniformly across different sociodemographic groups, without taking into account how different internal and external attributes may affect their walking speed, thus shaping their 15-MC experiences. The study addresses these gaps by two approaches: #1. calculating 15-MC accessibility scores in six differently-sized regions in Virginia, United States, and empirically comparing OSM's point datasets with its less contentious alternative, Google Maps data, and #2. developing a novel geospatial methodology for evaluating 15-MC accessibility scores, focusing on how factors like topographic elevation, age, and (self-identified) gender in the Roanoke-Salem region of Virginia, USA, generate varied accessibility for different groups. Our results show that, average 15-MC accessibility scores obtained from the OSM's point-based POI data were significantly lower than those obtained from Google POI data in small-medium sized cities. The overall inequality (measured by Gini indices) deviates from the standard range of Google-based values when the OSM's point-based POI data is used. The study also emphasizes the limitations of prior studies' simplistic approach to estimating 15-MC accessibility, which usually overestimates pedestrian accessibility by disregarding topographic and demographic variables. In contrast, we believe the proposed new method provides a more realistic depiction of 15-MC accessibility as it captures the nuanced variation of walk speed that creates different levels of accessibility for different groups. The findings are intended to assist researchers and policymakers in better understanding the emerging 15-MC concept, which may eventually improve their city's accessibility for a range of demographic groups. As many local planners and lawmakers increasingly focus on implementing the 15-MC in different parts of the world, the comparative findings can help them reassess which factors contribute to creating more accurate, inclusive, and equitable urban environments that enhance residents' livability.