CNetS faculty Filippo Radicchi and Santo Fortunato, along with collaborators Siddharth Patwardhan, Şirag Erkol and Marc Barthelemy, have developed theoretical and computational frameworks to study the shape of multilayer transport networks within cities. They have found that, when optimized to reduce transit time to a central node, such networks undergo sharp phase transitions from symmetric to asymmetric shapes depending on their size, the relative efficiency of the transportation layers, and the cost of switching between the layers. The findings have been validated on the real transportation networks of the cities of Atlanta, Boston, and Toronto. The paper has just been published in Nature Communications.