  The mathematical study of the small-world concept has fostered quite some
interest, showing that small-world features can be identified for some abstract
classes of networks. However, passing to real complex systems, as for instance
transportation networks, shows a number of new problems that make current
analysis impossible. In this paper we show how a more refined kind of analysis,
relying on transportation efficiency, can in fact be used to overcome such
problems, and to give precious insights on the general characteristics of real
transportation networks, eventually providing a picture where the small-world
comes back as underlying construction principle.
