Studies into cost benefit of trams

Dear Fausto:
Here I send you some links with information regarding your question.
In the case of Barcelona you can find out about our Tram system in
In this website, Public Transportation: What is the cost benefit of trams over buses? ( you can find a short discussion of the topic and a lot of related links.
Here an example of Edinburgh: Transport Economics: The Return of Trams – Benefits and Costs (
Cervero, Robert & Guerra, Erick. Urban Densities and Transit: A Multi-dimensional Perspective  (
I hope help you with the information.