Abstract
Through this paper, after a description of a synthetic indicator of urban transport sustainability, an analysis of some major problems concerning the definition of such parameters will be carried out.
Particularly, three issues will be analysed: a) the assessing of the running fleet for the selected site; b) the sharing of the yearly fleet by age and emissions categories; c) the foreseen of future vehicle fleet by age and fuel categories. Suitable proposals for coping with these problems will be also described.