THE LOADED BOX · VSSI MONTHLY

March 2026 · Vessel Schedule Stability Index

The median window held dead flat across the horizon. A flat aggregate is not a settled plan - it is movement that netted out.

Where in the planning horizon the window actually moved - and what that means for commitments still open.

Published May 05, 2026 · Framework TradeLanes VSSI Monthly v1.1 · Companion publication Safe-to-Gate Monthly March 2026

1. The Reading

The median cargo receiving window held at 136 hours at every snapshot from T-4w through to the final - dead flat across the planning horizon. On aggregate the window did not move.

Volume tells the operational story. March was the heaviest month of the quarter: 6,368 CRW revision events across 674 distinct vessel-voyages - roughly 9.4 revisions per voyage, and broad-based across carriers and ports, not isolated to one alliance. Just over half - 52.1% - of those events landed beyond T-7, outside the 72-hour zone where exporters, terminals, and carriers usually fight over the window.

A flat median is the trap. It does not mean schedules sat still; it means per-voyage movement netted out in aggregate while individual voyages kept moving mid-horizon. The window's instability did not leave in March - it averaged away on the chart, under the heaviest revision load of the quarter.

2. The Mechanism

Sustained Churn pattern · Terminal anchor

The mechanism in March 2026 is paired ERD and CY Cut activity. 47.6% of voyages with movement showed both fields revising together (co-moving) - the largest class in the dual-signal breakdown, and among the operational cohort that carries an Earliest Return Date the paired share reaches 50.7%. Standalone ERD activity was the next-largest class at 19.4%; only 4.2% showed the two fields moving in opposite directions. The dominant mode stayed paired and sustained, not divergent.

USSAV Savannah carried the month's heaviest revision load and its top balanced-activity voyages - the terminal anchor consistent across the quarter.

The median at T-4w sat at 136 hours and finished at 136 hours. The shape on the chart is flat. Where the movement sat - mid-horizon, per voyage - is what shows the mechanism the aggregate hides.

The three-element read

Contradiction. The median window did not move - and 674 voyages produced 6,368 revision events, the quarter's heaviest load. The aggregate hides where the mechanism operates: not in the median, but in the concentration.

Operator implication. Plans committed at T-4w faced revision activity arriving between T-14 and T-3, inside the same horizon where rail commits lock and dispatch chains warm. The information arrived before the plan closed, but not before the commit chain opened.

Failure mode. Plan committed at T-4w. Mid-horizon revisions arrive in paired moves at the terminal. The window reshapes as a unit. By T-3, the window the operator committed against no longer exists. FELIXSTOWE 527E at USSAV Garden City (departure March 31, 2026) recorded 23 ERD and 23 CY Cut revisions - the receiving window redrawn as a single unit, over and over, through the planning horizon.

3. Key Metrics

Two metrics reinforce the same finding. Revision events are concentrated mid-horizon. Late-stage share - events landing inside 72h of ERD - sits below the mid-horizon mass.

The breakdown matters more than the aggregate. Beyond T-14: 28.4%. T-14 to T-7: 23.7%. T-7 to T-3: 16.7%. T-3 to T-1: 8.8%. Final 24h: 4.2%. Post-ERD: 11.7%. The mass sits between T-14 and T-7 - the zone where rail commits and drayage dispatch are being finalized.

4. VSSI-P - Port-Level Snapshot

Where the mechanism operated

Per-port observed patterns:

• Savannah (USSAV) - High. 158 distinct vessel-voyages, 2,892 CRW revisions - the month's heaviest load and terminal anchor. Late-stage (inside 72h) on 19.6% of events; longer-horizon stability movement (>7d) on 63.4%. The mechanism lives here: paired mid-horizon revision, cross-carrier, at one terminal.
• Norfolk (USORF) - Elevated. 134 vessel-voyages, 1,317 CRW revisions. Late-stage on 31.3% of events; longer-horizon movement (>7d) on 51.6%. See the note below.
• Houston (USHOU) - Elevated. 110 vessel-voyages, 546 CRW revisions. Late-stage on 18.3% of events; longer-horizon movement (>7d) on 63.0%.
• Newark (USEWR) - Elevated. 64 vessel-voyages, 268 CRW revisions, with an unusually late-stage-concentrated profile - 65.7% of events inside 72h and only 11.6% showing longer-horizon movement. The concentration is late-stage rather than mid-horizon.
• Oakland (USOAK) - Elevated. 60 vessel-voyages, 257 CRW revisions. Late-stage on 27.6% of events; longer-horizon movement (>7d) on 22.6%.
• Los Angeles (USLAX) - Elevated. 57 vessel-voyages, 519 CRW revisions - the largest U.S. gateway by throughput, but the churn concentrates elsewhere. Late-stage on 29.3% of events; longer-horizon movement (>7d) on 28.1%. The contrast with Savannah locates March's instability at Garden City, not at the largest gateway.

Long Beach (39 vessels), New York (30 vessels), and trace volume at smaller gateways fell below the eligibility threshold for primary ranking; observations are available for completeness. March's eligible ports all sat in the Elevated band or above - the quarter's heaviest month registered stress broadly, not narrowly.

Note on Norfolk. The Norfolk band reflects port-level voyage distribution. A subset of MAEU voyages at USORF shows a CY Cut revision pattern under data pipeline review (documented in Safe-to-Gate Monthly Dec 2025, Section 4 methodology note). If confirmed as a pipeline artifact, the corrected band will be reissued in a subsequent edition. The month's operational concentration sits at USSAV Garden City, not Norfolk.

5. Representative Vessel-Level Movements

Supporting sample · curated by the month's pattern · not a ranking

The following vessels illustrate how receiving windows moved in practice. Each card shows the voyage's identification, departure, revision activity, and the dominant pattern in the dual-signal space. The mix reflects the month's distribution - Sustained Churn voyages at Garden City predominate.

FELIXSTOWE · USSAV · ZIMU / 527E Departure: March 31, 2026 CRW revisions: 46 (23 ERD + 23 CY Cut) Pattern: Sustained Churn - paired ERD+CY revisions, the window redrawn as a single unit See this vessel in Safe-to-Gate Weekly →

ZIM CHINA · USSAV · ZIMU / 50E Departure: March 6, 2026 CRW revisions: 42 (21 ERD + 21 CY Cut) Pattern: Sustained Churn - paired ERD+CY revisions See this vessel in Safe-to-Gate Weekly →

SEASPAN EMISSARY · USSAV · HLCU / 609E Departure: March 13, 2026 CRW revisions: 39 (21 ERD + 18 CY Cut) Pattern: Sustained Churn - paired ERD+CY revisions See this vessel in Safe-to-Gate Weekly →

6. What This Means for Planning

The decision horizon changes under this pattern.

When late-stage volatility dominates, exporters can buffer. Commit at T-4w, recheck at T-3, absorb the last-72-hour shift through reserved equipment and pre-booked appointments. The system is designed for that decision sequence.

When mid-horizon volatility dominates - and March 2026 sits at 52.1% of events arriving beyond T-7 - the buffer moves inside the commit window. The plan is moving while it is being committed. Rail commits, labor scheduling, and drayage reservations are placed against a window the schedule has not finished drawing.

A flat median is the trap this month. It reads as calm. But the per-voyage movement that netted out in aggregate is exactly the movement an individual exporter feels on an individual booking. For a voyage already showing mid-horizon activity, the plan committed at T-4w will not be the plan that executes - whatever the network median says.

Cost is created when action is taken against a window that hasn't stopped moving. If the same voyage is showing mid-horizon activity, every dollar priced against that T-4w window is priced against a plan that will be rewritten.

7. Bottom Line

March 2026's median window held dead flat across the planning horizon while the mass of revision activity sat mid-horizon, before the commit chain closed. The flat aggregate is the headline trap: it averages away the per-voyage movement operators actually experience - under the heaviest revision load of the quarter.

The mechanism is mid-horizon revision activity, concentrated at USSAV Garden City. Volume ran to 6,368 events and stayed broad-based - the mode stayed paired and the anchor stayed at Garden City.

March opened the quarter the way it would close: the window moves as a unit, mid-horizon, at Garden City, and the exporter who commits early commits against a shape already being overtaken.

TRADELANES · VSSI MONTHLY · MARCH 2026

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Appendix A - Measurement Layer

Band vocabulary. Stable - window held through execution. Moderate - window moved within planning tolerance. Elevated - window structure under stress. High - window not reliable for commitment. Used consistently across Safe-to-Gate Weekly, Safe-to-Gate Monthly, and VSSI Monthly.

Outcome classification. Compressed, Mixed, Late expansion, Moderate drift, and Stable describe how each window moved between its first and final snapshot. The exact classification thresholds live in the internal methodology appendix and are not published.

Sustained Churn. Voyage-level volatility pattern describing windows that keep moving through the planning horizon without settling - paired ERD and CY Cut revision activity with weak directional consistency. The classification thresholds live in the internal methodology appendix and are not published.

Late-stage qualifier. Inside 72h, inside 24h, or outside 72h, measured as the time between the latest revision event and ERD_final.

Methodology note. Analysis covers March 2026 U.S. departures with observable schedule revisions: 6,368 events across 674 distinct vessel-voyages. Voyages are counted as distinct vessel-voyages (normalized vessel name plus terminal, split into distinct sailings), not booking or schedule-version rows. VSSI-P bands computed from voyage-level distribution using the current methodology; classification thresholds live in the internal methodology appendix and are not published.

Carrier-terminal suppression carry-forward. A pipeline artifact in CY Cut revisions for Maersk vessels at Norfolk's primary container terminal - first identified in Safe-to-Gate Monthly Dec 2025 - remains active. MAEU/USORF voyages appearing in residual top-activity lists with CY Cut activity that does not reflect underlying terminal behavior are excluded from concentration and repeat-offender findings in this edition. A fuller treatment will appear once engineering review resolves the underlying data.