Illustration of a multiplex transportation network. (a) Multiplex public transportation network of Shenzhen. Bus stops (light green dots), subway stations (red squares), transfer zones (orange polygons), ordinary zones (grey polygons), and four inter-links (dashed lines) between the two network layers are illustrated. (b) Path depicted in blue represents a unimodal subway trip. Path depicted in green represents a multimode trip using both bus and subway transportation. (c)–(e) SDNs of one destination zone during 7:00 a.m.–8:00 a.m., 1:00 p.m.–2:00 p.m., and 7:00 p.m.–8:00 p.m.