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Project overview

Major project elements

An aerial map shows where the project improvements are located. The new Portage Bay Bridge and the adjacent SR 520 Trail will span between the new Montlake lid and I-5. The Roanoke lid will be built over SR 520 between 10th Avenue East and Delmar Drive East. The 10th Avenue East and Delmar Drive East overpasses will also be upgraded during lid construction. New or upgraded bike and pedestrian connections will be built on and near the lid, and we will improve the Bill Dawson Trail where it travels under SR 520.
Major elements of the project include the new Roanoke lid, upgraded overpasses over SR 520, 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.

New Portage Bay Bridges

We will build two new bridges to replace the aging Portage Bay Bridge: one bridge for eastbound traffic and one for westbound traffic. Both bridges will have wider highway shoulders to allow disabled vehicles to pull over without blocking traffic. We will also make improvements for transit and carpool access by extending HOV improvements to I-5 and providing a connection to the dedicated, reversible transit/HOV connection between SR 520 and Seattle’s I-5 express lanes/Mercer Street interchange.

A rendering shows an example of an area where people can enjoy experiencing the lid and the new open green space. Benches and viewpoints will be available around the lid.
The new Roanoke lid will provide green spaces for community members to enjoy.

Roanoke Lid

The Roanoke Lid will be a three-acre landscaped lid over SR 520 between 10th Avenue East and Delmar Drive East. With connections to local city trails for cyclists and pedestrians (more below), this lid creates new open space and viewpoints for the community.

Skanska is working with WSDOT to limit travel disruptions while rebuilding the overpasses that connect North Capitol Hill and Montlake to Roanoke Park and Portage Bay. We will maintain a crossing over SR 520 when lid construction begins. The crossing will have clear markings for drivers, cyclists and pedestrians. More information on the lid construction is to come.

A rendering shows an example of the improvements that may be made where the Bill Dawson Trail crosses underneath SR 520. Some of the improvements include new landscaping and hardscaping (rocks, boulders, etc.), upgraded pavement, and artwork.
The Bill Dawson Trail will travel under the new Portage Bay Bridge.

Bicycle and pedestrian connections

We will extend the SR 520 Trail over Portage Bay, add a new bike and pedestrian crossing over I-5 and build trail connections to Seattle’s dispersed trail network.

Construction at a glance

Building the project in three stages

The contractor, Skanska, will build this project in stages:

Stage 1: 2024 – 2028

A graphic shows that a new work trestle will be built on the north and south sides of the existing Portage Bay Bridge. Crews will work from this trestle to build the new north bridge. In 2025, Skanska will also begin building a section of the Roanoke lid.
Crews will build a work trestle and the new north bridge during Stage 1. In 2025, crews will start building the Roanoke lid.
  • Build temporary work trestles around the current bridge.
  • Begin construction on the new “north” bridge.
  • In 2025, begin construction on the new lid between 10th Avenue East and Delmar Drive East (Roanoke Lid), including the temporary overpass.

Stage 2: 2027 – 2030

The new north bridge will be located north of the existing Portage Bay Bridge. Once it is completed, both directions of traffic will temporarily shift to the north bridge while crews remove the existing Portage Bay Bridge. As part of construction for the Roanoke lid, Skanska will build a temporary overpasses over SR 520. This will be a temporary detour route while the 10th Avenue East and Delmar Drive East overpasses are removed and rebuilt.
All traffic will shift to the new north bridge once it is completed. Local traffic over SR 520 will be shifted to a temporary overpass while the 10th Avenue East and Delmar Drive East overpasses are rebuilt.
  • Temporarily shift all traffic to the newly completed north bridge.
  • Begin removal of the south bridge.
  • Remove 10th Avenue East and Delmar Drive East overpasses over SR 520.
  • Travelers will begin using new temporary overpass over SR 520 as part of the Roanoke Lid construction.

Stage 3: 2029 – 2031

The graphic image shows where traffic will be shifted to for the final alignment. Crews will also finish construction for the lid in 2031.
Crews will build the south bridge and complete the Roanoke lid.
  • Construct the new south bridge.
  • Rebuild the 10th Avenue East and Delmar Drive East overpasses.
  • Complete the new Roanoke Lid.

Anticipated project completion: 2031

View our bridge removal and rebuilding plan

See how we will build the trestle, shift traffic, and remove and rebuild the bridges over the next few years.

Removing the existing bridge

To minimize vibration and dust during construction, we will take a “surgical” approach to removing the existing bridge, taking it apart piece by piece. We will transport each piece of the bridge off-site, where it will be further broken down for recycling at a location away from neighbors.

Step 1: Setting up the work zone

A rendering a work trestle that crews will work from to remove the existing Portage Bay Bridge. There are cranes on the work trestle that will be used to move equipment to and from the existing bridge.
The temporary work trestle will carry workers and machinery during bridge removal and construction.

Crews will build a temporary trestle (work bridge) in Portage Bay in order to construct the new permanent bridge. Crews will also install dust containment devices in the work zone and begin drilling into the bridge.

Step 2: Cutting into the bridge surface

An overhead rendering shows a section of the existing Portage Bay Bridge after crews have removed some pieces of the bridge surface. Underneath the surface are some support structures.
Crews will remove pieces of the bridge surface using a wet saw.

After crews have drilled holes in the bridge, they will use a wet saw to cut the surface of the bridge for removal. A wet saw helps minimize dust and reduces the use of concrete pulverizers and other loud equipment.

Step 3: Remove the bridge surface

An overhead rendering shows another section of the existing Portage Bay Bridge after some of the support structures have been removed. At this stage, there are only support columns remaining from the Portage Bay Bridge.
The bridge surface will be removed, which will only leave the bridge structures in Portage Bay.

Crews will remove the surface of the bridge from the structure supports. After bridge pieces are removed, crews will haul the pieces off-site to be broken down and recycled.

Step 4: Removing old bridge support structures

Another angle of the bridge removal process that shows the support columns in Portage Bay after the surface has been removed. Crews will remove the support columns using a wire saw.
After the bridge surface is removed, crews will remove the support structures using a wire saw.

Now that the bridge surface is removed, crews will remove the bridge supports (diaphragms and columns). We will cut the supports into pieces using a wire saw. The pieces will be hauled off-site to be broken down further and recycled.

Building the Roanoke Lid

We will rebuild the 10th Avenue East and Delmar Drive East overpasses when we build the new lid. Before we remove the overpasses, we will temporarily realign 10th Avenue East and Delmar Drive East and install a temporary overpass to maintain connections for travelers in the area.

Skanska will build a temporary overpass between Delmar Drive East and 10th Avenue East over SR 520 during lid construction and when they rebuild the existing overpasses. The exact location has not been determined yet.
A conceptual rendering that shows the removal of the existing overpasses and an approximate location
for the temporary crossing over SR 520.

The location of the temporary overpass and the phasing for this work are still being planned. This work is expected to start in 2025 and continue through 2031.

Traffic changes during construction

During construction, traffic will shift several times on SR 520 for bridge work and on local streets for lid construction. These structures need to be built in phases with careful planning so people can still get where they need to go. Skanska will limit full closures of SR 520 and will ensure neighbors can still cross over SR 520 while the 10th Avenue East and Delmar Drive East overpasses are being rebuilt.

Maintaining clear navigational openings for boaters

The project team will communicate with the boating community throughout construction, providing clearly marked work zones, exclusion zones and navigation openings for safe travels.

A rendering shows that buoys will be used to mark a clear pathway for boats (known as a navigational opening) under the work trestle. Barges in Portage Bay will also keep the pathway clear for boaters.
Skanska will maintain at least one navigational opening under the work trestle. The channel will be marked
with signage and green and red buoys.
A rendering shows a large work trestle that will be built and run parrallel to the existing Portage Bay Bridge.
Crews will build temporary work trestles next to the existing Portage Bay Bridge to work
from, which helps reduce impacts on boaters in Portage Bay.

Long-term detours for people walking, rolling and biking

Building new bike and pedestrian connections near SR 520 and around the Roanoke Lid will require temporary detours for travelers during construction. Beginning in 2025, crews will need to close the existing section of the Bill Dawson Trail between Montlake Boulevard and the Montlake Playfield for approximately four years. The trail will be closed while crews install girders for the new Portage Bay Bridge that will be located above the existing trail.

Detours will be available for people walking, rolling and biking. Skanska is currently working with Seattle Parks and Recreation and the Seattle Department of Transportation to develop clear detours. Example detours for people biking are shown below.

Sidewalks and existing bike connections will also temporarily be closed during lid construction. We will provide clear detours for all travelers when 10th Avenue East and Delmar Drive East are rebuilt.

Map showing detour routs for people walking, rolling and biking

Improving connections for people walking, rolling and biking

Over the past decade, WSDOT has added several major bicycle and pedestrian improvements to this project such as:

  • Half-mile extension of the SR 520 Trail from Montlake to Capitol Hill.
  • Dedicated bike and pedestrian crossing over I-5 from Harvard Avenue East and East Roanoke Street to Boylston Avenue East.
  • Wider sidewalks and bicycle lanes on 10th Avenue East near the project area.
  • Wider sidewalks and bicycle lanes on Delmar Drive East.