What causes port congestion at US container ports?

Port congestion starts when work arrives faster than a container terminal can clear it. A terminal has a fixed number of berths, cranes, yard slots, gate lanes and rail tracks, and when one of them falls behind, the backlog spills into the step before it: ships wait offshore, boxes stack up in the yard, trucks queue at the gate. The causes below are the ones that recur at US container ports. Each is paired with the clock on this site that shows it first, because the clocks measure different things and move at different times.

Ships bunching up, and import surges

Carriers publish schedules that space arrivals out, but a ship held up by weather, a canal restriction or a slow port earlier in its rotation arrives late and lands on top of the next one. A terminal that could have worked the two one after the other has to make one wait. A surge in import demand does the same thing at scale: more ships, more boxes per call, and berths that stay occupied longer. The yearly version is shipping peak season, when holiday imports pile into late summer and fall, though a normal peak does not always produce a queue.

The clock that shows it first: the ship queue. The count of container ships waiting for a berth, from the Marine Exchange of Southern California and MARAD, updates weekly (LA/Long Beach ship queue, all US ports), and a separate weekly series counts the ships at anchor off each coast (ships at anchor). Volume is the slowest clock: monthly container counts land weeks after the month ends (busiest US container ports), so the queue reports a surge before the volume figures do.

The 2021-2022 congestion is the clearest case in the record. In the weekly count this site carries, the LA/Long Beach queue went from 26 ships on July 27, 2021 to a peak of 106 on January 14, 2022, and touched 106 again a week later. The Marine Exchange of Southern California's own count of the backlog topped out at 109 ships on January 9, 2022. The chart's dip in late November 2021, and its jump back on December 7, came right after a change in how ships waited: from November 16, 2021, ships took a place in line when they left their last port and waited about 150 miles offshore instead of anchoring near the coast. Read those few weeks with that change in mind.

The latest LA/Long Beach reading is 2 ships (reading of Oct 20, 2026).

How long ships then sat at the berth once they got one, vessel dwell, rose too: the BTS national average peaked at 37 hours in May 2022, but BTS stopped that series in mid-2023, so the US vessel dwell page is history, not a live reading.

Boxes that sit in the yard

A terminal yard works only if boxes leave about as fast as ships land them. When importers do not pull their containers, because their warehouses are full, a customs or carrier hold is unresolved, or no appointment, truck or chassis is free, the stacks grow and the yard gets harder to work: more boxes to dig through for each pickup and less room for the next ship's discharge. Empties add to it. At an import-heavy port, empty containers build up until carriers ship them back out, and they take yard space and chassis like any loaded box. The empty-container share shows that imbalance month by month, as a trade-lane measure rather than a congestion clock.

The clock that shows it first: box dwell. The Port of Los Angeles reports every business day how many import boxes are on its terminals and how long they have sat, in 0-4, 5-8 and 9+ day buckets (Los Angeles import-container dwell). A rising 9+ day share is the early sign of a yard filling with boxes that are not leaving.

On the port's report of Oct 21, 2026, 18.8% of the import boxes on its terminals had been there 9 days or more.

Chassis and trucks

A box that leaves by road needs a chassis under it and a drayage truck with an appointment to haul it. When chassis are stranded at inland warehouses or out of position, or there are too few drivers or appointment slots, boxes that are cleared to go stay put. The Port of Los Angeles described this chain in January 2021, early in the surge: the import-heavy imbalance had "reduced the number of chassis in circulation, caused inbound containers to stack up on terminals, and slowed the movement of trucks in and out of terminals." The port posts chassis availability on its own dashboard, but this site does not collect it, so on the clocks here a chassis or truck shortfall shows up first in the yard, as rising box dwell.

The truck planning-time index measures something nearby but different: how much extra time a trip takes on the roads around the port, from federal highway travel-time data, monthly. It is a road congestion read, not a wait at the terminal gate.

Rail handoffs

Boxes bound for inland rail ramps wait on the terminal for an on-dock train, or for a truck to an off-dock rail yard. When railcars, crews or inland rail yards fall behind, those boxes are the ones that pile up, and the backup can reach the sea: the Marine Exchange's Captain Kip Louttit told FreightWaves in January 2021 that the all-time record for ships at anchor off California came in 2004, during a rail staffing shortage.

The clock that shows it first: the on-dock rail count. Los Angeles and Long Beach both publish, every business day, how many import boxes are waiting for an on-dock train and how many have waited 9 days or more (port rail container dwell). The railroads' own terminal dwell, the average hours a railcar sits in a rail yard across BNSF's and Union Pacific's networks, rides on the same page as weekly context.

The latest reports showed 20,220 import boxes waiting for on-dock rail at Los Angeles, 33.3% of them for 9+ days (report of Oct 21, 2026), and 16,901 at Long Beach, 10.2% for 9+ days (report of Oct 21, 2026).

Labor and weather

Strikes, slowdowns and lockouts stop work at the berth, and storms, fog and high winds close terminals or stop the cranes, while ships keep arriving. The first clocks to move are the ship queue and the at-anchor count; box dwell follows if the gates close with boxes still on the terminal.

The October 2024 strike by the International Longshoremen's Association shows how fast it happens. Dockworkers set up picket lines at 36 East and Gulf Coast ports from 12:01 a.m. on October 1, 2024, the union and the employers reached a tentative agreement on October 3, and work resumed on October 4. In this site's weekly series of container ships at anchor off the East Coast (ships at anchor), the count was 8 on September 17 and 15 on September 24, reached 24 on October 1, the first day of the strike, and was back to 13 on October 8. The Gulf Coast count held at 2 through those weeks.

Slowdowns build more slowly. In the 2014-2015 West Coast dispute, after the dockworkers' contract expired on July 1, 2014, the Marine Exchange counted 28 container ships at anchor off Los Angeles and Long Beach on March 14, 2015, a level the 2021 surge went far past.

Reading the clocks together

No single number says a port is congested, because each cause shows up on a different clock first. The import-friction board reads three of them for each port complex, the ship queue, the truck index and loaded-import volume, against their own trailing-12-month normal, and the Los Angeles box-dwell and the Los Angeles and Long Beach rail counts sit beside it. Container dwell, vessel dwell and the ship queue are three different clocks; what is dwell time in shipping keeps them apart, and from ship to your warehouse shows where each one sits on the import chain.

The Dwell reports these clocks from the public record. It does not forecast congestion and it is not routing advice.