Drewry's World Container Index rose 4% to $4,526 per 40ft container on Aug 20, its third weekly gain in a row, with the Transpacific doing the work. Shanghai to Los Angeles climbed 9% to $6,802 and Shanghai to New York climbed 9% to $9,507. The prior week the index had moved only 1%.

Rate benchmarks are built from transactions that have already cleared. They confirm a market condition after it has been priced. Booking data sits upstream of that. When shippers start competing for the same space, it shows up in booked TEU against capacity before it shows up in the rate a forwarder pays. That gap is the reason Vizion built SDPI, and the last two weeks on the Transpacific are a clean example of it.

What SDPI measures

SDPI scores booking pressure on every major container loop. For each lane it compares TEU-weighted booking pressure against a 12-month baseline and expresses the result as a z-score: how far the current reading sits from normal. A 7-day reading captures the most recent week, a 28-day reading captures the month, and the difference between them (Δz) tells you which direction pressure is moving. A lane reads as tightening when its z-score is at or above +0.30. It reads as easing when Δz falls to −0.15 or lower.

The Aug 21 pull, covering bookings through Aug 19, is the one to hold up against the WCI.

Transpacific West Coast was already there

TPac to US West Coast is the largest lane in the pull at 478,568 booked TEU over 28 days. Its 28-day pressure z-score sits at +0.78 and its 7-day score at +0.70, both well past the tightening threshold. A 28-day average that high means pressure had been elevated across the whole window from Jul 23 to Aug 19, which covers the stretch when the WCI was still printing single-digit weekly moves.

Asia to Mexico West Coast and Asia to Canada West Coast are tightening with it, at +0.83 and +0.44 on the 7-day read. Every West Coast gateway on the North American side is running above baseline.

The tightening spread to most of the tonnage in two weeks

Between the Aug 7 pull and the Aug 21 pull, the share of booked TEU sitting in tightening lanes went from 37.5% to 57.4%. Easing tonnage fell from 62.5% to 30.9%. Twenty-two of the 40 mapped lanes changed stage, nine of them into tightening, carrying 1.02M TEU, and eight out, carrying 0.41M.

Total booked TEU across all 40 lanes fell 5.0% over the same period. That combination is the tell. Pressure rose while volume slipped, which points to capacity coming out faster than demand. Drewry's own read of the same week agrees: carriers are managing supply through blank sailings, with seven announced for the coming week on the Transpacific, and August capacity on Asia to USEC down 9% month over month.

The East Coast and Gulf tell a different story than the rates do

Here is where the booking view and the rate view split. Shanghai to New York rose 9% in the same WCI print as Los Angeles. But TPac to US East Coast is easing in the SDPI pull: 7-day pressure at +0.34, down 0.35 from its 28-day level, on volume down 18%. TPac to US Gulf is easing harder, with Δz at −0.72 on volume down 6%.

East Coast rates are rising on a shrinking demand base. The capacity withdrawal Drewry describes explains the rate. The booking data says shippers are already backing away from those routings. A forwarder reading only the index sees one Transpacific. A forwarder reading the booking data sees a West Coast lane that is tight on demand and an East Coast lane that is tight on supply, and those two conditions call for different decisions on Q4 space.

What the signal says now

Pressure on TPac West Coast is high and has started to roll over. The 7-day score (+0.70) sits below the 28-day score (+0.78), a Δz of −0.09, and 28-day volume is 9% below baseline. That is a lane past its recent peak, still well inside tightening, on a demand base that is thinning.

Rates can keep moving for a while after that point. Drewry expects the index to hold next week on constrained capacity, and Panama Canal surcharges on Asia to USEC and Gulf routings land in September. But the booking signal led the rate index on the way up, and it will lead it on the way down. The next two pulls will show whether West Coast pressure stabilizes or keeps sliding toward the threshold.

See it on your own lanes

SDPI runs on every major container loop, refreshed on a two-week cycle, with lane-level pressure, direction, and booked TEU behind each reading. If you are pricing Q4 Transpacific space off the WCI alone, you are working from a signal that arrives after the decision window has closed. Request a demo to see the current pull on the lanes you ship.