Underground urbanism: Master Plans and Sectorial Plans

The urbanization process leads many urban areas and megacities to be densely built and to overcome their physical and operational limits; in several cases, urban population density is growing faster than their infrastructures. Considering land use constraints, for mitigating some disagreeable living conditions and for creating new population opportunities, city planners have different opportunities involving the two opposite vertical directions: upward, erecting higher buildings or downward, developing a more intense use of the underground space. Both directions are characterized by positive and negative aspects and require suitable local condition to be built. In this paper, main issues related to the urban underground planning procedures are highlighted, taking also in consideration that after some very old visionary approaches, no relevant debates and concrete results have been further developed. Several underground-related technicalities are described and analyzed, mainly at sectorial level (f.i. mass transport systems, infrastructures for energy and water supply, storage facilities) however, experiences of a global urban planning – involving a holistic approach inside a City Master Plan – are still very few (Helsinki). A collection of some best practices is reviewed in this paper. Particular emphasis is devoted to the integrated planning approach and the related tools for the subsurface space assessment: the role of different planning tools for the rational use of the underground space in urban areas is analyzed and a variety of planning levels are discussed, from the more general one – the Master Plan – to the more sectorial ones. Moreover, the more recent visions for future cities – Smart, Resilient, Low-carbon and Post-Carbon Cities – are producing relevant and very useful technical and management solutions and the role of Integrated Mater Plans in this transition is further discussed.