Urban sustainable mobility challenge and governance amid depopulation in China

Urban shrinkage confronts policymakers with a sustainability dilemma directly at odds with SDG 11: persistent congestion coexists with surplus bus capacity as populations fall. Arbitrary service reductions entrench a car-dependency trap, fuelling a self-reinforcing “shrinkage-congestion” spiral. Using 1 km2 cell data for 298 Chinese cities, we show that nearly half of traffic congestion (55.22% moderate to severe) and 150,921 bus stops are anchored in depopulating tracts. Passive mitigation is strikingly inefficient: each 1000-person/km2 decline yields a mere 1.5 % lagged reduction in congestion probability, underscoring the urgency of proactive, green-bus-oriented governance. Spatial-econometric models reveal non-linear interactions between population density, congestion probability, and bus supply. Maintaining 10-15 bus stops or 15-20 bus routes per km2 ensures low congestion under most population densities. However, beyond 10,000 people/km2 in high-congestion areas, the marginal benefit of adding buses diminishes sharply, making integrated mobility solutions essential. These findings provide a transferable, evidence-based paradigm for sustainable mobility in shrinking cities and a replicable SDG 11.2 implementation framework under depopulation.