Guides
Port congestion, explained
How the numbers on this site work: the three distinct dwell metrics kept apart, what a TEU is, how demurrage and free time work, and how the import-friction read is built. Each guide is built on the same live data as the board, so the examples are real and current.
Reading the metrics
What is dwell time in shipping? Container, vessel, and port dwell explained
Dwell time in shipping is how long something sits in one place at a port, and the trade uses that one word for three different clocks: vessel dwell, box dwell, and the ship queue. Vessel dwell is how long a ship sits at a berth, box dwell is how long an import container sits on the terminal, and ships waiting is a count of vessels queued offshore before a berth opens. The ship queue updates weekly and the Port of Los Angeles box-dwell report every business day; the national vessel-dwell series is archived.
From ship to your warehouse: the import chain
An import container moves through a fixed sequence: it arrives on a ship, is discharged at the terminal, sits in the yard, leaves by truck or rail, and reaches a distribution center. Each public congestion metric sits at one point on that chain, and the costly delays cluster on land, in the yard and at the gate, not at sea.
Dwell time in trucking: what detention means for the driver's clock
Dwell time in trucking is the time a truck and its driver sit at a shipper's or receiver's dock waiting to be loaded or unloaded, and the industry usually calls it detention rather than dwell. It is not the port-side dwell this site otherwise reports (a ship at berth, a box on the terminal, or the ship queue), and it is not the container-equipment fee also called detention elsewhere on this site. There is no federal detention rate schedule; carriers set rates commercially, and the hours-of-service clock keeps running while a driver waits.
What causes port congestion at US container ports?
Port congestion happens when ships, containers or trucks arrive faster than a port's berths, yards, gates and rail can clear them. The usual causes are ships bunching up on late schedules or an import surge, boxes left sitting in the yard, chassis, truck and rail shortfalls, and labor or weather stoppages, and each one shows up first on a different measured clock.
Volumes and demand
What is a TEU?
A TEU is a twenty-foot equivalent unit, the standard way ports count container volume. One twenty-foot box is 1 TEU and one forty-foot box is 2 TEU, so a port's monthly TEU total mixes both sizes into one comparable number. The monthly statistics split that volume into loaded imports, loaded exports and empties.
Why LA/Long Beach dominates, and when freight shifts east
LA/Long Beach is the largest container gateway in the US because it is the closest major port complex to Asia's factories, where most US containerized imports originate. Freight shifts toward East and Gulf Coast ports when West Coast labor risk, canal economics or the rate gap between routes tips the math, and those shifts show up slowly in the volume data.
Shipping peak season: when and why US imports surge
Shipping peak season runs August to October as retailers land holiday stock before the fourth quarter. Loaded-import TEU and the ship queue show its timing. From 2019 to 2025 those three months carried more than a quarter of the year's imports in six years of seven, but the single heaviest month fell inside them only three times.
Reading the monthly TEU release
A port's monthly TEU release is its official count of the containers it handled, published a few weeks after the month closes. Read it three ways: against the prior month, against the same month a year ago, and against the pre-pandemic 2019 baseline. Loaded imports are the demand signal and empties are the repositioning tell.
What moves ocean freight rates
Ocean freight rates move on three forces: how much vessel capacity carriers offer, how much cargo demand is chasing it, and whatever disruption is reshaping the routes. This site does not track ocean spot rates and carries no rate feed. It reports container volumes and port congestion, which are context around rates, not the rates themselves.
DWT to TEU conversion: why there is no fixed ratio
There is no fixed way to convert DWT to TEU, because they measure different things: deadweight tonnage is the total weight a ship can carry, fuel, water, ballast and stores as well as cargo, while TEU capacity is a count of twenty-foot container slots. Ships with nearly the same deadweight are built with different slot counts, so any ratio describes one ship, not a rule.
Warehousing at the Port of Los Angeles: how imports drive warehouse demand
Warehousing at the Port of Los Angeles happens in two places: on port land, through the Foreign-Trade Zone the port manages, and in the large private warehouse markets of Los Angeles and the Inland Empire, where imported cargo is unloaded, stored and sent on. Import volume drives demand for that space, and three public numbers track it: the port's loaded imports, brokers' warehouse vacancy rates and federal counts of warehouse jobs.
Fees and the clock
Demurrage, detention and free time
Demurrage and detention are two different late fees on a container. Demurrage is charged when your import box sits in the terminal's yard past the free time; detention is charged when you keep the carrier's container too long after you take it away. The last free day is the deadline before demurrage starts to accrue.
The clocks an importer watches
An import container passes a fixed set of milestones, and each one starts or stops a clock the importer cares about: estimated arrival, berth, discharge, available for pickup, the last free day and outgate. Knowing which public congestion metric lights up which clock turns a tracking screen into a plan.
Container milestone tracking: the timestamps and who publishes them
Container milestone tracking means following one container through the timestamped events logged as it moves. At the destination terminal those are vessel discharge, available for pickup, the last free day, gate-out and, for rail-bound boxes, the on-dock rail load, and each comes from a different system: a port community or terminal-availability platform, the terminal operator, or the ocean carrier's own tracking tool. An unexplained gap between two of them is usually yard congestion, a hold, or a missed appointment.
What does import dwell date mean on a container tracking screen?
There is no standard definition of an import dwell date: it is not an event in the industry's container tracking standard, and no US regulator defines it. Where a tracking screen or terminal portal shows one, it most likely marks where that system starts counting the box's days on the terminal, usually discharge from the ship. It is a counting date, not a billing one: demurrage runs from the free-time dates, which a US invoice must state along with the container availability date.
Dwell fee vs demurrage: what is the difference?
Demurrage is the standard charge for a loaded container left on a marine terminal past its free time, set in a carrier's or terminal's tariff and covered by federal billing rules. A dwell fee is not a standard charge: the name has been used for separate fees on long-sitting import boxes, one approved by the Ports of Los Angeles and Long Beach in 2021 and never collected, and one Port Houston charges today on top of demurrage.