First Avenue South Bridge common questions

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. Answers to common questions are below.

 
Looking northbound on the 1st Avenue South Bridge
Looking northbound on the 1st Avenue South Bridge.

Traffic cameras

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. or 3 - 6 p.m. with the following exceptions: 

  • The bridge will open at any time for a vessel of 5,000 gross tons or more, or for a tugboat going upstream to get a vessel of 5,000 gross tons or more.
  • The bridge is opened upon request outside of peak hours, on weekends and all federal holidays except Columbus Day.

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. 

 
Inside the bridge tower. In the foreground you can see the control panel that operates the southbound bridge. The large book is a log of every opening, the type of boat, the direction and how long the opening lasted.
Inside the bridge tower. In the foreground you can see the control panel that operates the southbound bridge. The large book is a log of every opening, the type of boat, the direction and how long the opening lasted.

Maintenance of the bridge

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.

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 our bridge crews find anything that needs to be repaired or replaced due to normal wear and tear.

Photo of one of the gears that operate the drawspan of the older bridge.
One of the gears that operates the drawspan on the older bridge. When the span is opened, these gears begin turning and pull the bridge open.

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. 

A role in the economy 

Because Duwamish Waterway is a critical cargo waterway, we must balance the needs of people and the economy. No one can control the tides, and many of these boats are dependent on when the tides to move in and out of the area, which determines when the cargo reaches the shipping and distribution centers that serve Puget Sound and the west coast. Our mission 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! 

Photo of the backup system to open and close the bridges
If the computer system that operates the drawspans fails, we have a backup system to open and close the bridges. We test this system at least once a month. Besides opening and closing the bridges, it also operates the safety gates and warning lights.

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? 

Request a bridge opening

For general bridge information:
Nicole Daniels - WSDOT Communications
206-440-4479  - nicole.daniels@wsdot.wa.gov

 

Common questions

When does the bridge open for marine traffic? 

On weekdays from 6 - 9 a.m. and 3 - 6 p.m. the bridge will not open for marine traffic with two exceptions:

  • The bridge will open at any time for a vessel of 5,000 gross tons or more, or for a tugboat going upstream to get a vessel of 5,000 gross tons or more.
  • The bridge is opened upon request outside of peak hours, on weekends and all federal holidays except Columbus Day.

Historically, marine traffic has the right-of-way on many waterways around the Puget Sound. Maritime law pre-dates most other laws. 

Can WSDOT request a change to marine openings?

Changing the hours is a long and complicated process that literally requires an Act of Congress. Because the 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. 

Making operational changes to moveable bridges requires Congressional approval. First WSDOT must demonstrate a need to change the hours. To do that, we need comprehensive traffic studies of car counts and patterns. The area around the 1st Avenue S. Bridge has few traffic sensors to monitor traffic. New sensors and stoplights installed in the summer of 2010 will provide us with better data. WSDOT must make a request to the local Coast Guard for a change in operating hours. If the local Coast Guard office approves, the request is then sent to the Coast Guard headquarters in Washington, D.C. for review. The proposal will be then open to public comments. After the public comment period, the Coast Guard can then submit it to Congress for it to be written into law and voted on. This process can take two-three years.
 
What about short term changes to restricting marine traffic?

“Short term” is defined as anything that lasts 59 consecutive days or less. A short term change can be approved by the local Coast Guard office. Anything beyond 59 days must be approved by Congress.

How long does an opening last?

It depends on what type of marine vessel is going through. Some can take as little as five minutes, while others may last 30 minutes or more. The average opening lasts just under 11 minutes. However, it can take 20-30 minutes for the resulting congestion to dissipate. 

How come it seems like I wait longer than the traffic on the other end the bridge when there's an opening?

Our bridge tenders follow very strict protocol for opening and closing the spans. The first span that opens is always the first span that closes. That helps ensure that drivers on either end of the bridge wait approximately the same amount of time.

It seems like one drawspan opens first and then the other. Why can't you open them at the same time?

The bridges were built forty years apart and operate using completely different systems. The old bridge uses a gear-like mechanism, while the newer bridge operates using hydraulics. There are two separate control panels for each bridge.

Because of the complexities involved, the bridge operator can only open one at a time to ensure the safety of drivers and boats. Once one bridge is opened, the tender can then concentrate on opening the second one. Occasionally, you will see both bridges open and close at the same time. When that happens, it means there is a second operator in the bridge tower and the two are each operating a bridge. 

Why aren't there the same number of upstream openings listed as downstream on your bridge openings web page? Both spans are always opened for a boat.

We count upstream and downstream openings separately because we are noting the direction of the boat. Any number of factors can dictate whether an opening is required including the size of the boat and the tide.

For example, a tugboat going upstream to retrieve a barge may not need the bridge opened because it fits through it just fine. But several hours later, when it is pulling the barge downstream it may need the drawspan opened because the tide may be high or the barge may be too large to fit under the bridge.