Urban accessibility in a 15-minute city: a measure in the city of Naples, Italy.

Cities accessible in 15 minutes represent a new possibility for reorganizing the urban system (times, spaces and activities) to try to respond to many current challenges, including ageing populations, energy saving and, more recently, Covid-19. A renewed concept of urban accessibility, together with the redefinition of public spaces and "soft" ways of moving (pedestrian and cycle) to reach neighbourhood services, represent a starting point not only from which to face new challenges but also to rediscover the sense of community, especially at the neighbourhood scale. The 15-minute city draws its origins from the concept of the "neighbourhood unit", developed in 1923 in a competition for the city of Chicago, to define compact residential neighbourhoods where the proximity between services and homes contributed to set out the identity character of that part of the city and to create "the sense of belonging" of a community to a place. The events of the last year strongly re-propose experimentation with this approach, also following the proposal by the mayor of Paris, Anne Hidalgo, aimed at giving a new face to Paris starting from the creation of extensive pedestrian green areas on the large boulevards that are now crossed by the cars and, therefore, to allow the inhabitants to reach, by walking, essential urban services within the 15-minute threshold. Other cities, such as New York and Milan, have also begun to work to make their neighbourhoods, especially peripheral ones, accessible in 15 minutes on foot or by bicycle, without neglecting the goal of transforming these neighbourhoods into attractive places for social gathering for local communities. In this perspective, the research work aims at identifying the urban characteristics that define a 15-minute city, starting from the cities that are launching this experimentation. Among the urban characteristics, the geomorphological, physical (concerning both the spaces and the paths, such as the geometry of the pedestrian and cycle networks), functional (distribution and location of services), socio-economic (of the population) and settlement ones are taken into consideration. According to the weights of the variables identified as significant, the work defines different areas accessible in 15 minutes based on users’ willingness to walk and the geomorphological, physical, settlement and functional characteristics identified in each urban area. The work is carried out in selected districts of the city of Naples which, due to their demographic, morphological and settlement characteristics, make them a significant area of experimentation.