The original drawbridge over the Duwamish River was built in 1931 and closed four years ago due to safety concerns.
Its replacement includes a number of upgrades, including better earthquake protection.
The $163 million bridge is opening about 9 months later than previously planned, as the contractor blamed hard clay under the Duwamish River for slowing down excavation of the drawbridge support structures.
The new bridge is expected to carry 20,000 vehicles and nearly 3,000 heavy-duty trucks each day. It will also carry an estimated 10 million tons of freight each year, including aerospace parts to local Boeing facilities.
It's good news for small businesses in the neighborhood who say the bridge is a lifeline to many of their customers, and business has slowed in the years since the bridge closed.
The bridge is scheduled to open to traffic Monday morning.