TRADELANES DTB Monthly · December 2025

December didn’t compress the window. It removed the moment when the window could be trusted.

Published April 22, 2026 · Framework TradeLanes DTB Monthly v1.1 · Status Operator-facing

1. Opening

Layer 1 · Headline · Opening Frame The instinct at this point in the quarter is to look for decay. Three consecutive months of mounting late-stage compression would make a clean story: September, October, and November each showed schedules tightening inside the 72-hour boundary. The expected read for December was more of the same, at greater magnitude. That isn’t what the data shows. December’s receiving windows didn’t compress at the network level. The median window at T-0d measured 137 hours - eight hours wider than at T-4w, not narrower. Only 27.9% of voyages compressed their window across the horizon. The share of events arriving inside 72 hours fell to 20.7%, the lowest of the quarter. By the late-stage measure the system eased. But eight times as many events moved. And they moved earlier in the horizon than they had in any prior month of the quarter. This edition rejects the decay framing the quarter was building toward. December was a churn month at the network level, and a convergence month in specific terminal pockets. The operator’s problem wasn’t that the window collapsed late. The problem was that the window never settled - and the commit decision had to be made against a shape the schedule had not yet finished drawing. An ops-review methodology note covering a suppressed carrier-terminal data pipeline artifact appears in Section 4.

Two things were true in December - the aggregate story (median window widened from 129h to 137h) beside the voyage story (one in six vessels never settled). The contradiction is the story.

2. The Mechanism

Layer 2 · Sustained Churn · USSAV Garden City as terminal anchor The quarter-level narrative - decay, compression, collapse - describes a window that works under stable conditions and breaks when the compression zone arrives. It assumes a stable plan that a late revision invalidates. December’s mechanism was structurally different. The plan itself didn’t stabilize. Sustained Churn is the primary mechanism. Nearly one in four December voyages - 24.8% - showed sustained, unsettled revision activity: sustained mid-horizon movement, no stable endpoint. These vessels didn’t drift late or jump at the end. They never stopped moving long enough for a plan to settle against them. Sustained Churn outranked Steady Drift, Post-ERD Compression, and Late-Stage Jump by a wide margin. And Sustained Churn was not evenly distributed. It concentrated heavily at USSAV Garden City - one terminal carried the overwhelming majority of the month's Sustained Churn voyages. Many carriers, one place. The mechanism is cross-carrier but terminal-specific. The alliances didn’t produce the pattern independently and happen to converge there. They converged there because Garden City is where the pattern operates. Two supporting characteristics shape how Sustained Churn expressed itself in December: High event volume concentrated mid-horizon. December produced roughly eight times September’s CRW event volume across fourteen times as many voyages, and 57.6% of those events arrived beyond T-7. The mass of schedule movement happened between T-14 and T-7 - squarely inside the planning horizon, well outside the compression zone. Volume alone is workload. Volume inside the planning horizon is failure. Weak dual-signal divergence. Only 5.5% of voyages showed ERD and CY Cut moving in opposite directions. 43.8% had only one field active at a time. The failure mode wasn’t synchronization breakdown between the two signals - it was sustained instability in one or both signals, independently, across the horizon.

The three-element read

Contradiction. The median window expanded from 129 hours to 137 hours across December. And yet nearly one in four voyages never had a stable moment to plan against - and nearly all of them were at one terminal. Both are true because the aggregate hides where the mechanism operates. Operator implication. You didn’t plan against a decay. You planned against a schedule that kept moving until there was no time left to replan. The compression zone isn’t where the decision broke. The decision broke earlier - when the plan never settled and the commit deadline arrived anyway. Failure mode. Clustered revisions arrive mid-horizon. The window reshapes. The exporter waits for stability. Stability doesn’t come. The commit deadline arrives. The exporter commits against the latest shape - which becomes stale within 48 hours, because the pattern that produced mid-horizon instability is still active.

*

Where December’s revisions arrived, relative to ERD. 57.6% beyond T-7 - mass sits in the planning horizon, not the compression zone. Only 20.7% landed inside 72 hours.*

3. Bridge to Evidence

Layer 2 → Layer 3 · From claim to patterns If Sustained Churn is the mechanism, three patterns must appear in the data: 1. Revision activity concentrated inside the planning horizon, not at its endpoints. 2. A non-trivial share of voyages showing sustained instability rather than directional drift. 3. That share concentrating at specific terminals, not distributed across the network. Here’s what December showed.

4. Quantified Proof

Layer 3 · Three findings that anchor the mechanism Nearly one in four December voyages exhibited Sustained Churn. 24.8% of the December cohort - 142 voyages - showed sustained, unsettled revision activity. Sustained Churn was the dominant non-stable voyage-level pattern, outranking Steady Drift, Post-ERD Compression, and Late-Stage Jump combined.

Two supporting findings anchor how the churn expressed itself: 57.6% of December change events arrived beyond T-7. The mass of schedule movement happened between T-14 and T-7, with another 28.9% arriving beyond T-14. Only 20.7% of events landed in the compression zone (inside T-3). This is the single most important distribution in the month. It locates the mechanism outside the 72-hour boundary and inside the planning horizon. Robustness check: stripping the suppressed artifact (see methodology note below) shifts this distribution by no more than 0.2 percentage points in any bin. Event volume grew roughly eightfold over September. December produced 3,779 valid events (post-suppression) across 572 voyages; September produced 459 events across 117 voyages. The system wasn’t quieter. It was more active by every absolute measure - and the activity concentrated in the zone where plans are still forming.

*

Sept → Dec trajectory. Event volume grew 8x while late-stage share fell from 42% to 21%. Both lines are real. Share-based framing hides the volume story.*

5. The Illustrative Case

Layer 3 · The mechanism in one voyage CMA CGM CALLAO CAIWS at USSAV Garden City. 35 revisions across 33 days. All from a single source - the terminal itself. Every CY Cut revision arrived paired with an ERD revision in the same minute, with matching magnitudes on 17 of 17 pairs. This is the terminal pushing the whole window forward as a single unit. The window opened on October 29 at ERD Nov 15 | CY Cut Nov 21 - a 6-day gate window for shippers planning Savannah drayage. Over the next 33 days the window translated forward by 11 days. ERD and CY Cut moved in lockstep through six of seven snapshot horizons - paired in the same minute, same magnitude. The three largest pushes came early: a 5-day bump on October 27, a 7-day bump on October 31, and another 5-day bump on November 5. Seventeen days of forward motion in the first half of the horizon, concentrated in three terminal cascade events. At T-1w, one snapshot caught the terminal briefly out of lockstep: ERD advanced 2 days while CY Cut advanced only 1, compressing the gate-to-cut span to 4.96 days for a period that resolved by T-3d. Every other snapshot held the 5.96-day span intact. The window closed at ERD Nov 26 | CY Cut Dec 2 - not because the schedule stabilized, but because the calendar caught it. An exporter who committed drayage at T-4w committed to a November 15 gate opening. By the time the voyage actually departed, that opening had been Nov 26 for weeks. The cargo had to hit the yard 11 days later than the plan the exporter had built every downstream decision against. Driver schedules, rail appointments, trucking provider capacity - all built against dates that no longer existed after the terminal’s third push. The window didn’t break. It moved - and once, briefly, it breathed.

CALLAO trajectory - ERD and CY Cut moving forward together across the horizon in three large paired pushes (Oct 27, Oct 31, Nov 5) with one T-1w compression moment. The mechanism in one voyage.

6. Concentration and Repeat Offenders

Part A - Concentration

Where Sustained Churn operated at scale Section 2 named USSAV Garden City as the terminal that carries Sustained Churn in December. This section shows what that looks like at scale. USSAV Garden City - the mechanism in detail. Three of the post-suppression top-10 most-active voyages were at Garden City: BRIGHTON 022E (ONEY), CMA CGM CALLAO CAIWS (CMDU), and MOL PROFICIENCY 250E (ONEY). All three show paired ERD and CY Cut activity - genuine Balanced Churn, not carrier-specific anomaly. Across December, Garden City accumulated 2,041 valid events across 151 vessels, spread across six alliance carriers (CMDU, EGLV, MSCU, ONEY, YMLU, ZIMU). The convergence signature is structural - the same terminal is drawing simultaneous scheduling activity from every major alliance. A single convergence event at Garden City on December 9 illustrates the compound-risk pattern in one date. Ten vessels shared the same ERD day across six carriers, all major alliances represented. The pattern repeats: December 2 (7 vessels, 3 carriers) and December 20 (7 vessels, 4 carriers). Garden City is not reacting to convergence. It is operating in it. The compound-risk intersection - Sustained Churn vessels landing in High or Extreme Convergence windows - concentrates at Garden City. Exporter plans go stale through mid-horizon revisions at exactly the moment the terminal is absorbing gate pressure from aligned alliance schedules. Neither layer alone produces the failure. The intersection does. USTIW - a second, lower-magnitude cluster. Three vessels in the post-suppression top-10 were at Tacoma: HYUNDAI SUPREME 0154 (ONEY), HMM VANCOUVER 0302 (ONEY), and SKAGEN MAERSK 552W (MAEU). The revision signature is Balanced Churn - paired ERD and CY Cut activity, not carrier-specific anomaly. USTIW’s concentration is lower magnitude than Garden City’s and its voyages are fewer, but the pattern is analytically the same. USORF - deferred pending methodology review. Four vessels at Norfolk appear in the top-10 by residual ERD and docCut activity. The CY Cut signature that initially placed these vessels among the month’s most active has been identified as a pipeline artifact (see Section 4 methodology note) and suppressed. A concentration finding at Norfolk may be warranted once the underlying data can be validated independently. This edition does not make one.

USSAV Garden City - vessels opening each ERD day in December. December 9 stacked 10 vessels across 6 alliances on a single ERD day. Dec 2 and Dec 20 repeated the pattern. Convergence is how Garden City operates, not how it reacts.

Part B - Repeat Offenders

Prior-month qualifiers only · Temporal boundary rule Five December vessels appeared in prior-month top-10 concentration lists, qualifying as Repeat Offenders under the temporal boundary rule (qualification from prior months only): EVER MAGIC - USLAX, prior-month qualifier October KINGSTON - USSAV and USORF, prior-month qualifier October (twice) MSC ZONDA III - USSAV, prior-month qualifier November ZIM VIRGINIA - USORF, prior-month qualifier October The repeat pattern is geographically consistent with this edition’s concentration findings: four of five are at USSAV or USORF. The Garden City concentration is not new in December; what is new is its alignment with the month’s dominant voyage-level pattern.

7. Decision and Cost

Part A - The Decision Shift

Layer 4 · Operator behavior change The commit horizon is wrong. Exporters are committing drayage, rail, and appointment decisions at T-4w to T-2w against a schedule that takes its final shape between T-14 and T-7. December’s 57.6% beyond-T-7 mid-horizon mass isn’t a tail effect. It is where the schedule actually resolves. Planning against an earlier snapshot means committing against information the schedule hasn’t yet produced. The decision shift: move the commit window inward. Where operational constraints allow, defer the commit decision to the zone where the schedule has the highest information content - roughly T-7 to T-3 - even at the cost of tighter planning horizons. Accept the smaller window. Commit against a plan that’s real. Where the commit window can’t move - and for many rail-dependent exports it structurally cannot - the alternative is to commit at T-4w but rebuild contingency at T-7. Treat T-7 as a mandatory replanning checkpoint, not an observational one. The data says this is the moment the schedule has settled enough to plan against. It is also the last moment before the commit chain is irrecoverable. The deeper shift is a planning-unit change. The monthly network isn’t the right frame. The week isn’t the right frame. The terminal-day is the planning unit. When a vessel is opening into a Garden City week where six alliances are all publishing simultaneous ERDs, the plan is already stale at commit - because the terminal has already started pushing windows forward to absorb the convergence. Detect the intersection at commit, not at the gate.

The planning horizon from publication to ERD. Commit zone (T-4w to T-2w) sits misaligned with the information zone (T-14 to T-7) where the schedule actually resolves. Move the commit inward, or rebuild contingency at T-7.

Part B - Operational Cost Chain

Five steps from plan to cost - traced against CALLAO The cost chain traces the five canonical steps against CALLAO’s December trajectory at USSAV Garden City: 1. Plan. At T-4w, the exporter commits drayage against ERD Nov 15 / CY Cut Nov 21. Rail slot booked against Nov 15 arrival. Driver scheduled. Trucking appointment reserved. 2. Churn. Between T-41 and T-32 (October 27, October 31, November 5), the terminal pushes ERD and CY Cut forward together in three paired cascade events. Net forward motion: +17 days. Paired in the same minute, same magnitude. No reversal. 3. Pressure. Through mid-horizon, smaller paired corrections arrive alongside the large pushes. At T-1w, one snapshot catches the terminal briefly out of lockstep - a 24-hour compression that resolves by T-3d. Every check against the terminal returns a different ERD. 4. Commit. The commit deadline arrives. The driver is dispatched against the latest published window. By the time the truck is en route, the window has moved to Nov 26 - eleven days forward of the original plan. 5. Cost. Driver held roughly 48 hours waiting for the updated window. Container dwelled 11 days past the original plan. Appointment inventory has to be rebooked against the new date - a date the terminal is now absorbing the next week’s multi-alliance ERD day against. The cost cascade doesn’t fail at step 5. It fails at step 4 - when the commit has to be made against a schedule that hasn’t finished moving. Steps 1 through 3 produce the failure. Step 5 receipts it.

The operational cost cascade. Steps 1 through 4 produce the failure; step 5 receipts it. 11 days of forward translation from the original plan. Don’t move step 5. Move step 4.

8. System Statement + Forward Hook

Layer 4 → Close December 2025 was a churn month at the network level and a convergence month in specific terminal pockets. The operator’s problem wasn’t too many vessels at once. It was no stable point to act. The quarter-level reframe is larger than one month. Execution decay - the framing that carried September and October - describes a failure mode where a stable plan is invalidated by a late revision. That framing fit those months. It doesn’t fit December. If churn holds, the problem changes. It is no longer when the window closes. It is whether a plan can be made at all. And if the Garden City concentration holds, the question narrows further. The mechanism may not be a network-level pattern at all. It may be a single-terminal pattern that dominates the network-level picture because the rest of the network is quieter. Next edition will test whether January shifts the concentration - and whether the story is about Sustained Churn, or about a particular terminal running a particular pattern that no other terminal runs.

TRADELANES · DTB MONTHLY · DECEMBER 2025 tradelanes.co