The problematic of the choice between various alternatives is permanent and crucial in the projects of road infrastructures. The designer must use objective and global methods for proposing to the decision maker, who is generally a political entity, an optimal alternative. The complexity of the many fields affected by the road infrastructure and the diversity of the various participants of the study process are different elements to integrate in this choice. Only multicriteria decision making methods (MCDM), associated with a dialogue integrated into all the stages of the study process, can be used by the designer as well as possible to considerate this complexity. The use of such methods also makes it possible to bind the objective aspects of the choice, based in particular on technical evaluation of the performance indicators describing the alternatives for each criteria, with its subjective aspects, which are the relative consideration of importance of each criteria, also called weighting. These multicriteria decision making methods used simultaneously with dialogue integrated into all the steps of the procedure are clearly at the basis of a study process ensuring the design and the realization of a sustainability road infrastructure. They indeed make it possible to consider social, by the dialogue of the various actors, economic and environmental dimensions by the using of adequate criteria. Moreover, the consideration of the needs for the future generations, by the taking into account of the life cycle of the road infrastructure, is easy to realize. The author proposes an actualized methodology for the road design project process, which is based on the integration of these principles in the procedure. An evaluation of the various multicriteria decision making methods was carried out in a real case in Switzerland. It results the following main remarks for a good use of these methods for the designer and the decision maker: to use a partial aggregation method like Electre III, using in particular the notion of the fuzzy criteria, permits to better moderate the judgments and to use easily various indicators; a strong separation during the design process between the weighting, which is realized before the alternatives generation, and the evaluation of the criteria is necessary; the objective judgment is realized by the designer and the subjective weighting is done by the decision maker. For the covering abstract see ITRD E135448.
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