Theory 16/Transport & Logistics /Maritime operations/3 min
Port Queues Are a Berth Problem
Congestion looks like too many ships. It may be too few decisions.
Port congestion is set by berth allocation and handling rate rather than by the number of vessels arriving, so queues can form at low traffic and clear at high traffic depending on scheduling, and adding berths without changing allocation can make queues worse.
01The evidence
- Analysis of port waiting lines has examined whether queues arise from insufficient berthing spaces or from handling arrangements, which frames congestion as an allocation problem rather than a volume problem.Maritime Technology and Research
02The tension
Congestion is treated as a capacity problem: more ships than berths, so build more berths. Ports that expand often see congestion return, and ports with spare capacity sometimes queue, which suggests the binding constraint is elsewhere.
03The theory
A berth is a machine with a handling rate, and a vessel occupies it for a time that depends on the allocation. If allocations are made to minimise individual waiting rather than system throughput, the schedule fragments and utilisation falls even when berths are available.
That makes congestion a scheduling phenomenon. Queues form when the allocation creates idle gaps that are too short to use, and they clear when the allocation is restructured, without any change in capacity.
The prediction is that queue length should correlate with allocation efficiency better than with arrival rate or berth count, and that a scheduling change should reduce waiting without new infrastructure.
The practical consequence is that congestion policy should start with allocation algorithms, which are cheap, before concrete, which is not.
04What this is not
Those models make waiting a function of arrivals relative to berths. This makes it a function of allocation, which explains queues with spare capacity and their return after expansion.
05Predictions
- P1Waiting time should correlate with allocation efficiency better than with berth count.
- P2Scheduling changes should reduce queues without new capacity.
- P3Expansion without allocation change should not reduce waiting durably.
06What would refute it
Queues tracking the arrival-to-berth ratio regardless of scheduling would restore the capacity model.
07What it would change
It would make port investment start with scheduling, and change how congestion is measured.
08Evidence base
- Port waiting lines: berthing space or handling arrangement?https://www.tandfonline.com/doi/pdf/10.1080/25725084.2023.2280416