Hi Feudo

Read this paper, it's Goooood

http://www.sciencedirect.com/science/article/pii/S0967070X11000254

http://dx.doi.org/10.1016/j.tranpol.2011.01.012

Regards

Dear Fausto:

Here I send you some links with information regarding your question.

In the case of Barcelona you can find the advantages of our Tram system in http://www.tram.cat/en/the-tram/advantages

In this website, Public Transportation: What is the cost benefit of trams over buses? (https://www.quora.com/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 Edimburg: Transport Economics: The Return of Trams - Benefits and Costs (https://www.tutor2u.net/economics/blog/transport-economics-the-return-of-trams-benefits-and-costs)

Cost-Benefit Analysis “Tram system Wiesbaden” (http://consult.ptvgroup.com/fileadmin/files_consult/Downloads/3_Referenzen/EN/PTV_TC_EN_Reference_Wiesbaden_Cost_benefit_analysis_Projectsheet.pdf)

Light rail transit and residential density in mid-size cities (http://www.governanceinstitute.edu.au/magma/media/upload/ckeditor/files/CURF%20Working%20Paper%205%20Light%20rail%20transit%20&%20residential%20density.pdf)

Cervero, Robert & Guerra, Erick. Urban Densities and Transit: A Multi-dimensional Perspective  (http://www.its.berkeley.edu/sites/default/files/publications/UCB/2011/VWP/UCB-ITS-VWP-2011-6.pdf)

I hope help you with the information.

Regards

Rolando

Check out this website: https://bathtrams.uk

It all depends on the existing street network. There is no by-default solution that could be universally applied.