A port that has been disrupted does not return to normal when the disruption ends. Backlogs persist for weeks or months afterwards, and the delay is a property of how the system recovers rather than of the original event.
Terminals have a hard capacity ceiling
A container terminal can only move a certain number of boxes a day, set by the number of cranes, the size of the yard and the labour available to work the shifts.
When arrivals exceed that ceiling, the excess does not disappear. It accumulates as ships waiting offshore and as containers stacked in the yard awaiting collection.
Clearing the accumulation requires running above normal throughput for a sustained period, but the ceiling that caused the backlog is the same ceiling that limits the recovery.
A full yard works more slowly than an empty one
Containers are stacked several high, and retrieving one from the bottom of a pile means moving everything above it first, which consumes crane time producing no throughput.
As yard occupancy rises, the average number of unproductive moves per retrieval rises with it, so the terminal's effective capacity falls exactly when it is most needed.
This is why congestion is self-reinforcing. The condition of being backed up makes a terminal slower, which deepens the backlog further.
The bottleneck moves inland
Boxes leaving the terminal need road chassis, drivers and space at inland warehouses, and each of those is a separate constraint that can bind independently.
Chassis are a common choke point, because a container sitting at a warehouse waiting to be unloaded is occupying equipment that cannot be used for anything else.
When warehouses are full, importers slow their collections, which pushes the accumulation back into the terminal yard and slows the terminal again.
Empties have to leave before the space returns
An unpacked container becomes an empty that must be returned, and empties compete for the same gates, yard space and vessel slots as loaded boxes.
Carriers control when empties are accepted, and during congestion those windows narrow, leaving empties parked wherever they happen to be.
Until empties are cleared, the yard space they occupy is unavailable, which is why a port can look busy while moving very little of commercial value.
Schedules take longest of all to recover
Vessels operate on rotations across multiple ports, so a ship delayed at one terminal arrives late everywhere else on its loop for the remainder of the cycle.
Carriers respond by skipping calls or by cancelling sailings entirely to reset the rotation, which removes capacity from the trade at the moment shippers most want it.
Reliability therefore takes far longer to restore than throughput, and the reappearance of predictable arrival times is the last stage of a recovery rather than the first.