Finance & Business
More ships can still mean less usable capacity
An AEI-shared working paper, Shipping to America, finds utilization losses of 20–40 percentage points during disruptions, preceding visible port congestion. Its utilization measure is not container load fullness.
Five authors matched AIS position and speed records to vessel characteristics for January 2016–March 2025. They recorded 58,582 U.S.-bound trips across six main routes covering roughly 80–90% of containerized maritime imports. Effective ton-mile capacity subtracts waiting, canal delays, rerouting and slowdowns from the fleet’s potential.
By early 2022 deployed potential capacity exceeded pre-pandemic levels by over 60%, yet aggregate utilization fell from about 89% to below 70%. Ships waiting or taking detours do not translate directly into deliveries; shifting ports can shift congestion.
A calibrated model of shared fleets, congestion and sourcing estimates welfare losses equivalent to 0.69% of output for the 2021 West Coast crisis and 0.35% for Red Sea attacks. These are consumer-income-equivalent counterfactuals, not measured GDP declines.
Tariff decongestion effects depend on conditions, rather than proving tariffs always help. AIS cannot identify cargo origins and destinations precisely. We checked methods, relevant charts and policy sections, without reproducing the model or auditing every mathematical appendix.
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