The seventies are characterized by a significant internal migratory flow with a trend that is confirmed at the beginning of the eighties and causes the appearance of new areas of intervention and new cities protagonists of development, with consequent transformations of the territory and space urban. On a macroscopic level, this phenomenon translates into a relative stabilization of the north-eastern metropolitan area, of the so – called Frost-Belt (in which the places for decisions, economic leadership and the cultural industry continue to be concentrated) and in the significant growth of so – called Sun-Belt, that is, of the territories of the southern and south-western states.
The metropolitan structure is confirmed, differentiating itself according to various scales of importance and functionality: New York, San Francisco, Chicago and Houston are multi-functional service centers at national and international level; Philadelphia, Boston, Dallas, New Orleans are multifunctional centers at the regional level, while Washington, New Haven, Detroit and San José are configured as specialized service centers. In addition to these metropolitan areas, others characterized as centers of consumption are added: ultimately, a system of 25 metropolitan areas is configured in which the headquarters of the major corporations are concentrated, with locations also very far from the city center. At the same time, the increasingly marked infrastructure of the extra-urban area with a lower settlement density is proceeding, even away from metropolitan concentrations: the territorial service centers are strengthened (with the transformation of commercial shopping centers into multifunctional regional centers and more organized discount stores), while residential settlements are more concentrated, appearing in the form of condominiums rather than following the historical model of individual residences. The picture is completed by a strong decentralization of industrial production sites and the creation of office parks, that is, large areas equipped with greenery and parking lots for office buildings, which leave the city center.
The set of these transformations in the organization of physical space, which is historically based on a car-oriented society, has been favored in the last fifteen years by the widespread possibility of real-time information guaranteed by the development of communication technologies; it also took place thanks to the importance assumed by traditional raw materials such as oil or new materials such as siliceous sands in the internal economy, and on the international level by a strong expansion of the financial market. Greater attention is also paid to the environmental picture of the entire national territory, which is increasingly attacked by acid rain and marine oil pollution affecting hundreds of miles of coastline; as well as greater attention is paid to the quality of the urban environment,
Urban and territorial transformations and the use of the car continue to be closely linked, oscillating between two apparently opposite polarities, but which are connected with the generalized importance assumed by the theme of the city: on the one hand, in fact, in large metropolitan concentrations or in cities that they have a historical fabric, the new service areas are no longer strongly equipped with areas for private parking, to favor pedestrian use and to reduce breakdowns in the urban fabric; on the other hand, in the more limited provincial dimensions, the influx of cars is instead favored in the central areas, on the border of multifunctional pedestrian malls, to allow the development of a competitive social vitality to that of extra-urban service centers.
For example, in the early 1980s, in cities like Houston (Texas), the construction of an elevated pedestrian network generally connected to a shopping center and high-income services caused a progressive degradation of the areas on the ground, abandoned to cars, poor and minorities; that is, a functional problem was solved to the detriment of architectural quality and social integration. More recently in New York, in Lower Manhattan, as part of the renovation of a historic district (South Street Seaport), the creation of 300,000 square feet of service area took place without building parking spaces for private cars: it is an area of very busy city, although it can be accessed almost exclusively by public transport.