Port congestion is what happens when ships can’t load or unload cargo fast enough, creating a bottleneck that ripples through the entire supply chain. At its simplest, it means more cargo is arriving at a port than the port can handle, so ships, trucks, and containers all start backing up. During the worst of the pandemic-era shipping crisis, dozens of container ships sat anchored off major ports for days or weeks waiting for an open berth. But congestion isn’t just a pandemic story. It’s a structural challenge in global trade that directly affects how much you pay for goods.
How a Backlog Forms
A port terminal works like a highly choreographed relay race. A ship arrives, docks at a berth, and massive cranes lift containers off the deck. Those containers get stacked in a yard, then loaded onto trucks or rail cars headed inland. When any step in that sequence slows down, the entire system backs up.
The first visible sign is usually vessel bunching, where multiple ships arrive at roughly the same time and overwhelm the port’s available berths. Ships that can’t dock immediately drop anchor offshore and wait. While they wait, the containers already in the yard aren’t moving out fast enough, which means there’s nowhere to put the next ship’s cargo even once a berth opens. This creates a compounding effect: each delay makes the next one worse. A port that normally turns a container ship around in about 35 hours might see that stretch to 50 or 60 hours during heavy congestion, and the delays cascade outward to every other port on that ship’s route.
What Causes Congestion
There’s rarely a single cause. Congestion typically results from several problems hitting at once.
Demand surges are the most common trigger. During the pandemic, consumer spending shifted dramatically toward physical goods ordered online, and the resulting wave of international container shipments overwhelmed ports, particularly in the United States. Research from Louisiana State University found that this surge in import volume was likely the primary driver of U.S. port delays, with disruptions then propagating throughout the entire supply system.
Labor shortages play a major role. Ports need thousands of workers operating cranes, driving trucks, processing paperwork, and maintaining equipment. COVID-era workforce reductions hit hard, and analysis of the timeline of outbreaks and government restrictions suggests that limited workforce availability during successive waves of the virus directly worsened port performance. Labor disputes have a similar effect, leading to measurable declines in container volumes and ship calls at affected ports.
Equipment and infrastructure gaps compound the problem. A shortage of truck drivers means containers sit in the yard longer than they should. A shortage of empty shipping containers (which became severe in North America during the pandemic) means exporters can’t load outbound cargo, further clogging terminals. And many ports simply weren’t built to handle today’s mega-ships, which carry 20,000 or more containers and require deeper channels, longer berths, and bigger cranes than older terminals can provide.
The Cost of Waiting
Port congestion hits wallets in several ways, starting with freight rates. Research published in Maritime Transport Research found a clear, statistically significant link: when congestion rises, so do shipping costs. The effect is strongest in Asia, where a 1% increase in congestion produces more than a 1% jump in container freight rates. The same study estimated that simply returning to pre-pandemic congestion levels in Asia would cut containership freight costs by at least 25%.
Beyond freight rates, shippers face demurrage and detention fees. Demurrage is the charge a port levies when a container sits in the terminal yard past its free storage window, often just a few days. Detention is the fee for keeping a shipping container out too long before returning it. During peak congestion, these charges can add hundreds of dollars per container per day, costs that importers eventually pass along to consumers. For perishable goods or time-sensitive products, the delays themselves can be even more expensive than the fees, spoiling inventory or causing stockouts on store shelves.
How Shipping Lines Respond
When congestion makes it impossible to stay on schedule, carriers adapt in ways that can make things worse for certain customers. The most common tactic is the blank sailing (also called a void sailing), where a ship skips one or more ports on its scheduled route. If a vessel spends too long stuck at a congested port, the carrier may cut the next port of call entirely to get back on schedule and reach its main hub on time. That means cargo destined for the skipped port gets delayed further or rerouted, and the businesses waiting for those shipments have little recourse.
Carriers also slow-steam (reduce speed) to time their arrivals better, or divert ships to less congested nearby ports. These workarounds keep the broader network functional but shift delays and costs onto individual shippers and the inland transportation networks that suddenly have to move cargo from an unexpected port.
How Congestion Is Measured
Port authorities and shipping analysts track several metrics to quantify congestion. The most intuitive is vessel dwell time: how long a ship stays in port from arrival to departure. At major U.S. ports, container ship dwell times have been trending upward. For comparison, tanker vessels at top U.S. ports averaged about 41 hours in port during 2022, and that figure has remained mostly static since mid-2022. Container ships historically spent less time in port than tankers, but that gap has been narrowing as container terminal congestion has grown.
Other key indicators include arrival process time (how long a ship waits between arriving at the port area and actually reaching the berth), berth productivity (how many container moves happen per hour while a ship is docked), and container dwell time (how long a box sits in the yard before being picked up). When arrival process times climb and berth productivity drops simultaneously, that’s a clear signal of worsening congestion.
Where Congestion Is Building Now
As of early-to-mid 2025, congestion pressures have shifted geographically. According to S&P Global’s quarterly port analysis, Northern Europe has seen notable declines in berth productivity driven by larger average ship sizes and rising arrival wait times. Northeast Asia is experiencing similar trends, with longer waits before docking and lower efficiency once ships reach the berth. The Mediterranean has seen increases in both arrival process times and container dwell times, pointing to growing bottlenecks.
Southeast Asia tells a different story. Major gateway ports like Singapore, Tanjung Pelepas, Manila, and Port Klang have actually improved their efficiency, keeping operations stable despite the broader global pressures. This variation highlights that congestion isn’t a single global condition. It’s highly regional, shaped by local infrastructure, labor markets, trade patterns, and how much investment a port has made in capacity.
Technology That Eases the Bottleneck
Ports are increasingly turning to automation and artificial intelligence to handle more cargo without expanding their physical footprint. Semi-automated terminals use automated stacking cranes to organize containers in the yard and autonomous guided vehicles to shuttle boxes between the berth and the storage area, while human operators still manage the ship-to-shore cranes. Fully automated terminals take this further, running container handling, crane operations, and internal transport with minimal human intervention.
AI is adding another layer. The port of Valencia, Spain, for example, uses machine learning models to forecast truck traffic and optimize operations in real time, helping prevent the kind of landside bottlenecks that often contribute as much to congestion as the waterside ones. Other ports are integrating AI into scheduling systems to space out vessel arrivals and reduce bunching, the cascading problem that starts most congestion episodes in the first place. These tools don’t eliminate congestion, but they raise the ceiling on how much cargo a terminal can move before delays start compounding.