@Article{ 
  butprasol07,
  author = { Buttazzo, Giuseppe and Pratelli, Aldo and Solimini, Sergio and Stepanov, Eugene },
  title = { Optimal urban networks via mass transportation },
  journal = { Springer Lecture Notes in Mathematics },
  year = { 2009 },
  volume = { 1961 },
  pages = { 160 pp. },
  URL = { http://cvgmt.sns.it/paper/778/ },
  note = { cvgmt preprint}
}