The Northwest Seaport Alliance (NWSA) has become the latest US port to upgrade its facilities to accommodate bigger containerships.

NWSA, a tie up between the ports of Seattle and Tacoma, has authorised work on its deep-water Terminal 5 more than $300m in infrastructure improvements to the facility.

“The modernization of Terminal 5 represents a transformative investment in our region to support our state’s economy,” said Stephanie Bowman, Port of Seattle commission president and co-chair of the NWSA.

“These actions will ensure robust and competitive marine cargo and maritime industrial activities in our harbor for the next 30 years, sustaining and creating family-wage jobs and economic opportunity for the region.”

Clare Petrich, Port of Tacoma commission president and co-chair of the NWSA, added: “Terminal 5 will be able to handle the largest marine cargo vessels now being deployed in the Asia-Pacific trade route quickly and efficiently, providing a critical link for Washington state exports to Asian markets, both for agricultural products…as well containerized cargo for customers.”

NWSA said modernizing Terminal 5 allows it to expand its cargo-handling capabilities and remain competitive in the shipping industry.

The partnership said vessels regularly visiting the ports have grown in capacity from 4,800-teu in 1997 to 14,000-teu today.

NWSA said the new ultra-large container ships, however, require larger, heavier cranes with a longer reach, which in turn requires strengthening the dock and upgrading utilities.

NWSA said the deal, including future Phase II commitment, represents about $500m in private and public investment in the region’s economy.

Phase one construction is expected to be complete in 2021 and will mark seven years since NWSA first unveiled plans to upgrade Terminal 5.

The investments in Terminal 5 will be coordinated with the proposed new tenant, Stevedoring Services of America Terminals (SSAT) and Terminal International Limited (TIL Group).

The proposal calls for a new 32-year lease with these two terminal operators, which, together, are in partnership with several of the world’s largest ocean carriers.

NWSA says combined its ports are the fourth-largest container gateway in North America as well as a major center for bulk, breakbulk, project/heavy-lift cargoes, cars and trucks.