15-, 10- or 5-minute city? A focus on accessibility to services in Turin, Italy

The concept of the 15-minute city is receiving increasing attention, both in planning practices and in the academic literature, especially now that the pandemic has made evident the need for a minimum set of proximity-based services accessible by active travel. Most issues of this concept can be traced back to more or less past planning ideas such as the garden city, the neighbourhood unit, the superblock etc.; however, further studies are needed, as many theoretical and methodological questions for its implementation remain unresolved. The paper presents a methodology to operationalise the concept of the 15-minute city, in order to show which parts of the city and what percentage of its population can access a location of a given service on foot within three time thresholds (5, 10 and 15 minutes). The methodology is tested on the Italian city of Turin. The results show that, at least in dense European cities such as the case study, the 15-minute threshold cannot always be assumed as the necessarily most appropriate target, since many services can already be reached by foot within this time, or even less, by the majority of the population. Moreover, the levels of accessibility to services are significantly determined by the number and spatial distribution of the locations of these services. Finally, a recovery of the operational research on accessibility measures and indicators that was developed in the field of regional sciences in the second half of the last century and in the last twenty years is recommended to complexify the operationalisation of the 15-minute city concept.