Transshipment incidence, vessel-class composition, and carrier dominance: the footloose effect in container port throughput volatility

This study examines year-to-year container throughput volatility in 170 global ports between 2014 and 2024, with a focus on the footloose nature of transshipment cargo. This period is marked by major disruptions, including supply-chain congestion and geopolitical tensions. A volatility index is developed to assess how three operational drivers shape this instability: transshipment incidence, vessel-class composition, and dominant-carrier market share. Ports are grouped into low-, medium-, and high-intensity clusters for each indicator. The results reveal three main patterns. First, higher transshipment incidence is associated with greater volatility, although regional differences persist. Second, ports with balanced participation of large and feeder vessels, characteristic of hub-and-spoke systems, exhibit the highest volatility, with mainline services being more fluctuation-prone than feeder operations. Third, greater market-share concentration in a single carrier increases exposure to strategic decisions, intensifying volatility. Overall, the findings show how specific operational configurations amplify the footloose nature of transshipment traffic, providing new evidence on the drivers of port-level volatility.