during the pandemic-induced crisis: first, when ports were affected by lockdown and staff availability, then a longer period from the end of 2021, when the pressure from demand challenged handling throughput first. In comparison, a port such as Durban in South Africa experienced bursts of stress prior to the pandemic, which may be related to known systemic in-country infrastructure management issues.

Transshipment hubs such as Algeciras, Singapore, and Tanjung Pelepas appear to exhibit similar erratic fluctuations in their stress patterns compared to gateway ports serving as final vessel destinations or departures. Therefore, port-level stress data can serve as valuable complementary information and provide insights alongside other established indicators and data on port and/or logistics performance (like the World Bank’s Container Port Performance Index (CPPI) and the Logistics Performance Index (LPI)).

A port is heavily dependent on its hinterland connections to facilitate cargo flows. Port congestion has notable impacts on the availability of assets like drayage trucks and rail ramps as connections to inland destinations. A shortage of chassis to haul containers by road can severely limit capacity, as experienced on the United States West Coast during the COVID-19 pandemic for example. These chassis are also utilized for container storage at some rail yards and distribution facilities.

There exists a divergence between the increasingly demanding punctuality and flexibility of modern supply chains, such as e-commerce fulfillment, and the rigidity inherent to maritime shipping networks optimized for economies of scale through post-Panamax vessels. Shippers and cargo owners often respond by increasing inventory holdings and placing additional orders as a buffer, creating a demand-amplifying “bullwhip effect” that propagates backward through supply chains. This surge in demand, driven by actual consumption compounded by precautionary stockpiling, can overload shipping resources, especially the available container equipment pool. Container availability and shortages became the primary propagation and backpropagation mechanism disrupting maritime logistics networks. In this context, containers were spending 20 percent more dwell time immobilized within the logistics system on vessels, chassis, and container yards.

The stress stemming from the declining velocity of container movements initiates a negative feedback loop that occurs with a short time lag (Figure 6). As containers spend more dwell time at terminals or inland locations due to lack of capacity, it progressively impairs velocity and fluidity across all components of the transport chain. Maintaining the same level of service necessitates deploying additional assets, which only further exacerbates prevailing congestion. For instance, if a container yard is congested, it restricts the terminal’s capacity to handle vessel operations since inbound containers cannot be expeditiously unloaded due to a shortage of yard space. As could be seen during the COVID-19 pandemic, localized disruptions near major ports can create significant cargo backups in the hinterland.

Figure 6. Disruptions in Global Maritime Supply Chains and the GSCSI 11