Geographical performance and determinants of coordinated development reforms in China’s coastal port clusters: evidence from a natural experiment on port layout planning

China’s coordinated development reform in 2006 is the starting point of contemporary port reforms and the best platform for exploring the persistent barriers to China’s port coordination and the causes behind repeated reform restarts. This study assesses the geographical impact of 2006 reform in coastal port clusters and explains why the reform fell short of expectation. Using 1998–2019 panel data covering 59 coastal ports and 13 types of cargoes, reform impacts are evaluated through spatial distribution, specialization, and growth fluctuations. The results reveal that the reform modestly slowed throughput decentralization across port clusters, it failed to reverse the overall trend. Moreover, intra-cluster specialization also declined slightly since 2006. To further analyze the general and specific factors that influenced the performance, a quasi-DID approach was combined with policy text analysis. Compared with smaller ports, the main ports designated under the National Coastal Port Layout Plan (hereafter ‘the Plan’) experienced slower throughput growth,a sustained loss of market share, and no notable increase in dominant cargoes. These outcomes are attributable to institutional constraints and lagging concepts. The findings illuminate the constraints and dynamics shaping China’s coastal port geography since 2006 and offer actionable policy insights for future regional port integration.