Cyclic subway networks are less risky in metropolises Ying Xiao, Hai-Tao Zhang, Bowen Xu, Tao Zhu, Guanrong Chen and Duxin Chen EPL, 121 4 (2018) 48004 Published online: 17 April 2018 DOI: 10.1209/0295-5075/121/48004