Celebrating 520's final chapter: Construction is a go on the Portage Bay Bridge and Roanoke Lid Project!

By Allie Breyer

This past August, we broke ground on the Portage Bay Bridge and Roanoke Lid Project. This is the final major project in the SR 520 corridor. Construction on the SR 520 Program started in 2011 with the SR 520 pontoon construction project. The Portage Bay Project will complete SR 520’s reconstruction from I-405 in Bellevue to I-5 in Seattle.

Check out the highlights from the groundbreaking ceremony in the video below:

Another construction project?

We get it. You may not be celebrating more construction in this area. If we can offer a silver lining, this project brings us one step closer to completing all major construction projects on the SR 520 corridor. When the project is complete in 2031, we will have transformed the 12.8-mile-long corridor with safer bridges, dedicated lanes for busses and carpools and five landscaped lids. It will also include a bicycle and pedestrian trail from Bellevue Way to Capitol Hill in Seattle. That’s almost 6 miles.

Why do we need a new Portage Bay bridge?

We built the Portage Bay Bridge in the early 1960s using hollow concrete columns. This design was great at the time because it saved weight and materials. We now know that it’s not-so-great for withstanding earthquakes. In the event of a large quake, those columns could collapse, putting the bridge and everyone who uses it at risk.

That’s why we need to build a new one. This project will replace the old bridge with two bridges that can bear the shaking and stress of an earthquake without breaking. These new bridges will use solid foundations and modern engineering techniques so they’re safer and stronger.

Drawing of Portage Bay bridge, 1960. Courtesy of the Seattle Municipal Archives, #63342, Series 2613-07.

This project also:

• Improves connections for busses, carpools and vanpools.
• Extends the regional SR 520 Trail across Portage Bay.
• Creates a new bicycle and pedestrian crossing over I-5.
• Builds a highway lid over SR 520 with three acres of landscaped open space.

All these improvements help to connect communities and support travelers of all kinds.

Major elements of the project include the new Roanoke lid, the new Portage Bay Bridge, an extension of the SR 520 Trail, and new or upgraded bike and pedestrian connections from the lid and the Bill Dawson Trail.

What you can expect this fall:

Since breaking ground this past summer, we’ve been getting everything ready for major construction work. This work will begin in November.

Here’s what you can expect this fall:

• Piledriving in Portage Bay: As soon as November 6, we'll begin driving large steel or concrete poles deep into the ground to create a foundation for the temporary work trestle. These poles are known as “piles”. This process involves heavy machinery that either vibrates or hammers the piles into place. This is one of the noisier parts of construction. If you live nearby, you can expect to hear loud noises and feel vibrations when crews are driving piles. This will be the first of six piledriving seasons allowed on the project. Each season lasts from September – April, though piledriving may not occur each season.
• Lane closures, parking restrictions and detours: Around East Roanoke Street, Delmar Drive East and Boyer Avenue East, you may notice temporary lane closures and detours. Parking in some areas will also be restricted. It might slow you down, so give yourself extra time when traveling through these spots.
• Increased truck traffic on East Lake Washington Boulevard : You may see more trucks on the road and increased traffic. Crews will be moving materials and equipment to the site.
• Tree and vegetation removal around Boyer Avenue East: We will need to remove some trees and vegetation to make room for construction. But don’t worry – we’ve got a whole plan to replace them. For every tree we take down, we’ll plant another – and sometimes two! – when the project is complete.
• Increased barge traffic in Portage Bay: You may see boats tugging barges into Portage Bay from either Elliot Bay or Lake Washington.

Map graphic showing locations of construction work happening this fall. 

How will the bridge be built?

We’re building the project in three stages so we can maintain traffic over the bay. Over the next year, crews will build two temporary work trestles to the north and south of the current bridge. A trestle is a temporary platform that lets crews bring the material and equipment they need to build the new permanent bridges. We’ll also begin construction on the new “north” westbound bridge.

Crews will build work trestles and the new north bridge during Stage 1. In 2025, crews will start building the Roanoke lid.

Learn more about the three stages of construction and how we will build the trestles, shift traffic and remove and rebuild the bridges over the next few years.

How you can stay informed

We are committed to keeping you updated throughout construction. For the most up-to-date information about SR 520 construction activities and planned road closures, we encourage you to sign up for weekly email updates and regularly visit our Construction Corner webpage and project webpage.

We’ll also host monthly construction update meetings virtually. We’ll send information via our email list.

If you have questions or concerns, feel free to reach out to us directly by phone or email:

• SR 520 Program information line: 206-200-9484 (M-F, 8 a.m. to 5 p.m.)
• Portage Bay project 24-hour construction hotline: 206-319-4520
• Email: sr520bridge@wsdot.wa.gov