Contenu du sommaire

A new perspective, namely network city planning, has appeared and is in the process of being defined. Within its framework, the experiments of those city planning theoreticians who considered networks as fundamental elements in their city plans, such as Cerdà, Soria and Wright, may be analyzed. A study of the contribution of the work of I. Cerdà should make it possible to enlarge the analysis. The recent discovery of a fundamental part of his theoretical works has confirmed the central role which he gave to network infrastructures in the definition of "urbanization," or city planning. Cerdà worked out several projects which were the testing ground for the analysis and comparison of his theories. Among these, the experiment of Barcelona and the different redefinitions for the Project of the Eixample of Barcelona of 1859 provide an excellent point of view for analyzing the evolution of his thought on network city planning. In this context, reading Cerdà's work becomes quite modern and pertinent, especially for the present redefinition of urban forms which take as their starting point the concept of "road-inter-road", which may make it possible to rethink the function of city blocks. The relationship between urban form and the speed of transportation which therein develops thus becomes a central element of the discussion. In conclusion, the study of the structuration of the road system defined by Cerdà brings out the necessity of rehabilitating the notion of the "urban street" and to better articulate the road system in new urban poles.

Infrastructure and population age in a similar way. Both have age structures where wars, depression and growth periods leave their marks. After periods of growth, periods of infrastructure deterioration always follow in due time. While populations regenerate through births, infrastructure renewal is a major investment decision. If renewal is delayed, social costs rise and standards go down. The deterioration model proposed here describes the ageing process as a function of the type of material, technology and stress. The cohort survival approach is then applied to the existing stock of infrastructure. Elements which fail and no longer meet the requirements constitute an annual demand for renewal. For given budget constraints and supply standards, the demand for infrastructure renewal may be realized with different renewal strategies. This is shown for the stock of water mains in the City of Stuttgart, and a prognosis is given up to the year 2050.