Northwest Seaport Alliance (Seattle / Tacoma)

About the Northwest Seaport Alliance

The Northwest Seaport Alliance is a singular entity in the US container-port landscape: it is a port development authority formed on August 4, 2015 when the Port of Seattle and the Port of Tacoma — historically rivals thirty-two miles apart along Puget Sound — combined their marine cargo operations into a single managed pool. The two original ports retain their separate legal existences and continue to handle non-container business independently, but every container, autos, and break-bulk operation in the combined Puget Sound complex is now administered by the Alliance under a unified commercial tariff. The structural driver was competitive pressure from the British Columbia gateways: through the early 2010s, Vancouver and Prince Rupert tripled their share of trans-Pacific container traffic and overtook the combined Seattle-Tacoma volume for the first time, and the political and commercial response was to consolidate rather than continue competing internally.

Governance of the Alliance reflects that bilateral origin story. Both the Port of Seattle commission (elected by King County voters) and the Port of Tacoma commission (elected by Pierce County voters) serve as joint Managing Members, and the Alliance itself is a separate legal entity that holds the operational portfolio of both. The combined footprint covers about 1,754 acres of marine terminal property — roughly 760 acres on the Seattle side (the North Harbor) and 993 acres on the Tacoma side (the South Harbor) — with ten container terminals across the two harbours, twenty-three berths in total, and forty-seven container cranes spread across the complex. Combined throughput sits in the three-million-TEU range in recent years, which puts the Alliance as the sixth-busiest US container port and the second-largest Pacific gateway after the San Pedro Bay complex.

Primary cargo and trade profile

The five primary cargo categories registered for this gateway are autos, agricultural goods, consumer electronics, machinery, and furniture. Two of those — autos and agricultural goods — are the editorial signature that distinguishes the Alliance from the Pacific-twin gateways further south. The autos line reflects the long-running Asian-finished-vehicle rotation that has historically discharged on the Tacoma side, where Husky Terminal and the surrounding marine infrastructure are configured for roll-on-roll-off operations at scale. The agricultural-goods category is substantially an export line: the Pacific Northwest agricultural and forest-products backland — Washington, Oregon, Idaho, eastern Montana — channels grain, oilseeds, prepared fruit and vegetable products, and fish-and-seafood exports back to Asia through this gateway, which is the dominant US West Coast outbound agricultural routing once California's Central Valley exports out of Oakland are excluded.

On trading partners the picture is heavily trans-Pacific — China (including Hong Kong), Japan, South Korea, and Vietnam dominate the inbound side — but with one unusual local twist. The Alliance is also the dominant US container gateway to Alaska: regular sailings from Tacoma to Anchorage operated by TOTE Maritime and Matson handle the bulk of the supply chain that keeps the Alaskan retail and industrial economy running, and that domestic-routing line is a meaningful slice of Tacoma's overall TEU mix in a way that does not appear at any other West Coast container gateway. For category-level imported value the authoritative reference is the USITC DataWeb, and for Alliance-specific TEU and vessel-call data the cleanest source is the Northwest Seaport Alliance about page, which publishes monthly throughput updates.

Harbor Maintenance Fee and CBP code

Every commercial ocean shipment that discharges at any Alliance terminal is liable for the federal Harbor Maintenance Fee at 0.125% of declared cargo value, identical to the federal regime at every other US ocean port. The fee is authorised under 19 CFR §24.24, collected by CBP at entry, and channelled into the Harbor Maintenance Trust Fund used by the US Army Corps of Engineers to dredge federal navigation channels. At this latitude that dredging work is less intensive than at the lower-channel Gulf or river-port gateways because Puget Sound provides naturally deepwater approaches to both Seattle and Tacoma, but the federal channel-maintenance obligation exists regardless and the trust fund mechanic applies in the usual way. The site reads the current rate from CBP CSMS #65741993 at every build so the figure on display always tracks the Treasury publication.

The CBP Schedule D port code assigned to the combined Alliance is 3001. That single code covers both the Seattle and Tacoma marine terminals on the entry summary, despite the underlying split into two harbours and two legal port jurisdictions. A Form 7501 entry filer routes the entry to this code regardless of whether the vessel discharges at a Seattle or a Tacoma terminal. The authoritative list of port codes is the current CBP ACE Appendix E Schedule D publication, refreshed periodically by CBP and cross-checked by this site on every data build.

Terminal handling and dwell fees

The non-federal cost lines at the Alliance follow the same three-bucket model used across the industry — terminal handling charges, demurrage on overstays, and chassis detention — but the rate envelope is closer to the Southeast ports than to the Pacific complex. Indicative terminal handling sits around $250 to $425 per TEU at the Alliance terminals, depending on operator and contract, which is meaningfully below the NY-NJ envelope and slightly below the San Pedro Bay envelope. The Alliance publishes its master tariff at the Northwest Seaport Alliance commercial portal, which links downstream to each terminal operator's detailed per-service schedules.

Free time at the Seattle and Tacoma terminals typically runs four calendar days from vessel discharge before demurrage starts. The escalating-band tier structure kicks in after that, designed as elsewhere to push the slot back to the next vessel rotation. One local wrinkle worth flagging is weather: Pacific Northwest winters can compress operating windows for outdoor gantry-crane work on certain days, and importers who plan inland delivery from this gateway in the December-through-February window should budget some cushion for that risk. Chassis detention from the regional Pacific Northwest equipment pool invoices separately and adds to the dwell total. The most durable defence against the dwell stack at this gateway, as at every other US container port, is pre-filing the entry and pre-paying duties so release happens the same day customs status flips to paid.

Sourcing decisions: NWSA versus the San Pedro Bay complex

The dominant sourcing question at this gateway is whether to route Asian-origin containers here or to the San Pedro Bay complex (Los Angeles and Long Beach). The Alliance wins on sailing time from Northeast Asia by roughly one day on most rotations, which translates into a measurably earlier cargo-availability date and matters most for retailers and manufacturers running tight replenishment cycles. The Alliance also wins on rail intermodal connectivity to the upper Midwest — Chicago, Minneapolis, and points east — because the BNSF and Union Pacific intermodal yards on the Pacific Northwest side are configured for that long-haul flow. The San Pedro Bay complex wins on rotation density and on Southern California distribution-centre reach, and on the broader carrier-service portfolio that the Pacific twins have built up over a century of trans-Pacific operation. For Boeing supply chain components moving into the Everett and Renton aircraft assembly footprint, the Alliance is almost always the right answer because the inland leg is short.

The country times product table further down this page lists the largest US importers of categories that typically move through this port, derived from the national trade picture rather than from a port-of-entry signal per pair. Treat the table as a discovery surface for which countries dominate the categories that flow through the Alliance, rather than as a guarantee that any specific country's shipment actually clears at Seattle or Tacoma. There is one further sourcing consideration unique to this gateway: the British Columbia ports of Vancouver and Prince Rupert remain a live commercial alternative for trans-Pacific routings into the upper Midwest and Eastern Canada, and the landed-cost comparison there involves customs, cross-border drayage, and Canadian-CBSA fees that the calculator on this site does not currently model.

Operators and infrastructure

The Alliance itself is the master landlord and tariff publisher. Day-to-day container operations are run by commercial terminal operators with distinct portfolios on each side of the complex. On the Seattle North Harbor side, SSA Marine operates Terminal 18, which is the largest single container terminal in Seattle and the marquee container facility on that side; additional Seattle terminals (T-5 reactivated for service, T-30, T-46) round out the North Harbor portfolio. On the Tacoma South Harbor side, Total Terminals International operates a major container facility at Husky Terminal, and Washington United Terminals and the Pierce County Terminal handle the remainder of the Tacoma container flow alongside the dedicated Alaska-service berths used by TOTE Maritime and Matson. The split-harbour layout is the underlying reason the Alliance publishes a unified commercial tariff but maintains operator-level free-time and gate-appointment schedules that vary by terminal — an importer routing a single shipment through the complex needs to read the right operator's schedule for the actual discharge berth.

Beyond the marine container terminals, the broader Puget Sound port complex carries significant break-bulk, project cargo, and cruise-passenger traffic that does not appear in the container TEU figures but does affect the operational rhythm at the harbours. The Port of Seattle also operates Seattle-Tacoma International Airport (Sea-Tac), one of the busiest air-cargo gateways on the US West Coast — air freight from Sea-Tac and ocean freight from the Alliance both feed the same regional distribution backland, and a meaningful share of high-value pharmaceutical, biotech, and electronics components transition between the two modes inside the same metropolitan area. None of that affects the federal duty calculation on a container shipment, but the modal interplay is part of why the Pacific Northwest attracts pharmaceutical and biotech supply-chain clustering that the Pacific complex further south does not draw at the same scale.

Looking forward

The Alliance's forward-looking exposure profile looks broadly trans-Pacific. The Section 122 emergency tariff cliff applies universally — any lapse drops the federal duty side by ten percentage points across every ocean shipment through this gateway. The Section 232 list bites modestly here because steel-aluminium is not in the primary cargo register, though any escalation that reaches autos or auto-parts could land on the Korean and Japanese finished-vehicle flow into Tacoma. The Section 301 China overlay matters for the Chinese share of consumer-electronics and machinery imports through the Alliance, but the Chinese share at this gateway is somewhat smaller than at the Pacific complex because Japanese, Korean, and Vietnamese flows have traditionally been more balanced in the rotation. The single most important structural forward question remains the BC port competition: any major capacity expansion at Vancouver or Prince Rupert can shift marginal trans-Pacific routing decisions north of the border, and the Alliance's commercial response to that pressure is what the post-2015 consolidation was designed to enable. A secondary forward thread worth flagging is the Alaska routing exposure: any disruption to TOTE Maritime or Matson sailings — or to Jones Act vessel availability more broadly — would land disproportionately on the Tacoma South Harbor's throughput because that domestic flow is a meaningful share of the local container mix even though it does not show up in the trans-Pacific carrier-rotation story.

Tariff rates from Tax Foundation, USITC, and Penn Wharton Budget Model. For commercial-stakes decisions, confirm against a licensed customs broker.