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1st Avenue South Bridge


Monthly maintenance closures

  • Regular maintenance on the 1st Avenue South Bridge occurs the first Thursday of every month and may include openings of the drawspans.
  • The maintenance work begins at 3:30 a.m. and ends by 6 a.m. Drivers may experience slight delays.

About the bridge

The 1st Avenue South Bridge is one of the major routes between downtown Seattle and the cities south of Seattle, as well as the Sea-Tac Airport. Spanning the Duwamish River, the bridge carries thousands of vehicles each day with hundreds of boats passing under it monthly carrying millions of dollars worth of consumer goods.

1st Ave. South Bridge

- The northbound span is at the top of the photo. This is the original bridge.
- The newer southbound span is at the bottom of the photo.


Bridge openings

The 1st Avenue South Bridge opens frequently for marine traffic on the Duwamish River. Maritime law pre-dates most other law giving boats the right-of-way. However, there are a few restrictions on when the bridge will open for marine vessels.

Restriction information:

  • Bridge openings for marine vessels are not allowed Monday - Friday, from 6 - 9 a.m. and 3 - 6 p.m. with the following exceptions:
    • The draws shall open at any time for a vessel of 5000 gross tons and over, a vessel towing a vessel of 5000 gross tons and over and a vessel proceeding to pick up for towing a vessel of 5000 gross tons and over.
    • Bridge openings are allowed at any time on the weekends and on all Federal holidays except Columbus Day.

Maintenance of the bridge

We open the bridge for maintenance regularly to ensure the drawspan remains in good working order. The number of maintenance openings each month depends on whether WSDOT bridge crews find anything that needs to be repaired or replaced due to normal wear and tear.

Routine maintenance work includes:

  • On a weekly basis, workers scrape off the old grease and re-lubricate the giant zipper-like mechanism that opens the northbound span.
  • Testing to ensure the drawspans can be opened and the safety gates operated manually should the computerized bridge control panels fail.
  • Checking for and replace broken and missing rivets.
  • Checking hydraulic fluid levels on a regular basis.
  • Applying paint and applications that inhibit rust.
  • Cleaning, monitoring and replacing the oil and hydraulic fluid levels for the southbound span.

This regular work ensures both spans have a long working life ahead of them. The northbound bridge is already 56 years old and still in good working condition. The southbound span is just 14 years old, with many more years ahead of it with proper and consistent maintenance.

How a bridge opening works

The captain of a boat will call our bridge tender to open the bridge. Sometimes we receive advance notice, other times the boats will call as they chug toward the bridge.

Our bridge tender will first activate the warning and stop lights on the span farthest away from the boat to stop vehicle traffic on that bridge. After the vehicles are stopped, the bridge tender lowers the safety gates. We open the far span first as a safety measure. If we were to open the span closest to the boat first, there is always the possibility that a boat could sail right through, not realizing the second span isn't open yet and hit it. By opening the far span first, we ensure the span closest to the boat acts as a visual signal to the captain.

After traffic is stopped on the span, our bridge tender walks outside to a deck and visually checks to make sure there are no cars, pedestrians or cyclists still on the bridge. Then, the tender releases the locks on the bridge and begins to open it using a computer and joystick. Once one span is open, the bridge tender repeats the process with the second span. Because the bridges operate independently with separate control panels, the bridge tender cannot open and close both bridges simultaneously. On the few occasions when you see both bridges open and close together, it means there are two bridge tenders in the tower and each is operating one span.

After the boat has gone through, the bridge tender begins closing the span. The span that opened first is always the one that is closed first. That helps ensure that drivers on both ends of the bridge wait approximately the same amount of time.

Our bridge tenders are quite familiar with the tugboats and barges that move up and down the river. They have become quite good at judging how soon they will need to stop traffic and begin opening the span to ensure the least affect on drivers while still meeting the needs of the boat. Our tenders do not open the bridge any earlier than necessary to help keep traffic flowing as long as possible.

1st Ave. Bridge Upstream South Park
Looking up the Duwamish River. Many of the businesses that line the waterway send barges filled with consumer goods through the bridge every week.

A role in the economy

Because Duwamish Waterway is a critical cargo waterway, WSDOT must balance the needs of people and the economy. No one can control the tides and many of these boats are dependent on the tides to move in and out of the area to reach the shipping and distribution businesses that serve Puget Sound and the west coast.

The mission of the Washington State Department of Transportation is to keep people and business moving by operating and improving the state’s transportation systems vital to our taxpayers and communities. That includes the marine imports and exports that are so important to our economy.

Who knew?

A little known fact – the northbound span of the 1st Avenue South Bridge is technically a floating bridge. A series of chambers make up the bridge piers at either end of the span and there is a long horizontal, encased walkway-like structure under the water and mud of the Duwamish River that connects the bridge piers. Water is pumped in and out of the chambers to help keep the bridge steady and level. When lower areas need to be inspected, water is pumped into the higher chambers so the lower chambers and enclosed walkway are accessible. A person can actually walk from one end of the bridge to the other underwater!

History of the bridge

The bridge is formally named the Duwamish River Bridge, although it is more popularly and widely known as the 1st Avenue South Bridge. It opened to traffic in 1956.

For many years, a single span crossed the Duwamish River. As traffic grew more congested, reversible lanes were created on the bridge using traffic cones. Each weekday morning, crews created an additional northbound lane by reducing the southbound lanes. Then in the evening, the process would be reversed.

In the early 90’s work began on building a second bridge that would carry southbound traffic. The new southbound span opened in 1996. From 1996 through 1998, northbound traffic was also diverted onto the new span while the approaches to the old bridge were demolished and rebuilt. In 1998, the old bridge with new approaches was reopened to northbound traffic and the new, 1996 span was converted to use exclusively for southbound traffic.

What kind of bridge is it?

The spans are bascule bridges. Bascule bridges are moveable bridges with a counterweight that balances the span when it opens for boat traffic.

How can I get more information?

To request a bridge opening, go to:

For general bridge information:
Nicole Daniels
WSDOT Communications