Using a fuzzy approach for evaluating sustainability of transportation system pollution-reducing policies: a case study

In recent years a wide debate between stakeholders and experts from different fields has developed about the concept of sustainability and sustainable development. In transportation systems analysis the idea of sustainable mobility has received increasing attention, finding a reference point in the concept of the “three pillars of sustainability”, which considers the idea of sustainability from a three-dimensional perspective (social, economic and environmental). This paper presents an innovative Fuzzy Multi-Level (FML) model, which formalizes and implements this conceptual approach, using the theory of fuzzy systems, useful as a tool for evaluating sustainability of transportation policies. The model works on three different levels, starting from a set of indicators used as input variables, and gives a fuzzy indicator of the sustainability offered by the alternative policies analysed; furthermore, intermediate fuzzy inference systems, based on rules formulated by experts, provide information about combined dimensions of sustainability (equity, viability and bearableness). A comparative analysis of the FML model and the Analytic Hierarchy Process (AHP) method, applied to the evaluation of different pollution-reducing policies, has been developed. The interpretation of results yields information about the use of the FML model as an alternative to traditional methods of sustainability evaluation and suggests further developments of research to improve its effectiveness.