What is the West Approach Bridge North construction phase?
The West Approach Bridge North (WABN) phase is the next construction phase of the SR 520, I-5 to Medina: Bridge Replacement and HOV Project.
The three-lane, 1.2-mile-long structure will be built to modern earthquake standards and will connect westbound travelers from the new floating bridge to the Montlake vicinity in Seattle. The existing west approach bridge will carry three lanes of eastbound traffic.
As shown in the simulation below, the WABN phase is the first construction phase west of the new SR 520 floating bridge. After additional funding is secured, WSDOT can build the final I-5 to Medina project.
Visualization of the WABN phase compared to the existing corridor and full I-5 to Medina project. Click to open in a PDF (1.09 mb)
The WABN phase aligns with the analysis and sequencing described in our environmental impact statement. We are committed to delivering the entire SR 520 program from I-5 to Redmond as we receive additional funding. More information on I-5 to Medina project construction activities begins with chapter 3 and continues in chapter 6 of the I-5 to Medina project final EIS.
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Key features of the WABN construction phase
Key features of the WABN construction phase. Click to open as a PDF (867 kb).
Bridge and corridor safety
- Addresses next major vulnerable structure on the west side
- Incorporates corridor and local traffic mobility improvements
- Extends a six-lane corridor with transit/HOV lanes from Redmond to the Montlake vicinity
Community and environmental benefits
- Advances aquatic, wetland, and parks mitigation
- Constructs the permanent regional shared-use path between Redmond and Seattle
- Improves bicycle and pedestrian connectivity
- Maintains existing bus service and access
- Improves transit connectivity and reliability by extending the HOV/transit lane to Seattle
- Reduces concrete volumes by nearly 50 percent as a result of baseline design refinements
Future-compatibility
- Advances the next phase of the full corridor
- Accommodates potential future light rail
- Incorporates ongoing community input
- Interim design at Montlake does not preclude future decisions
Construction period
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Common questions
What will the West Approach Bridge look like when complete?
Visualization of the new west approach bridge. Click to open as a PDF (277 kb).
More draft designs and additional context available in our Feb. 2013 open house materials (pdf 2.01 mb).
From September to November 2012, the West Approach Bridge design team worked closely with the Seattle Design Commission to refine the baseline design established in the final EIS.
WSDOT will incorporate the following design techniques to minimize effects:
- Streamlined bridge design with fewer columns than prior designs. This design reduces overall materials and equipment needs.
- Use of pre-cast materials built off-site to minimize activity on Lake Washington.
- Reduce concrete volumes by nearly 50 percent as a result of baseline design refinements
Why is WSDOT moving forward with WABN before full funding is secured?
As is common with large projects like the I-5 to Medina Project, full funding is often not available at the time that construction begins. We are actively seeking additional funding with the help of our local, state, and federal partners, and are committed to delivering all project elements covered in our federal record of decision. However, given the reality of the funding environment and what we can deliver today, we have worked closely with the city of Seattle to ensure that WABN is forward-compatible and does not preclude us from delivering elements like the community-connecting lid at Montlake during future construction phases.
While we cannot predict with certainty when future funding will be obtained, sources like potential tolling on I-90 are promising future sources.
Why is WSDOT removing ramps in the Arboretum?
In the ultimate build-out of the I-5 to Medina project, all of the Arboretum on- and off-ramps to and from SR 520 will be removed. The decision to remove the Arboretum ramps was made after WSDOT heard from neighborhoods and representatives of the Arboretum, the city of Seattle, regulatory agencies, and corridor legislators. The intent of this design was to respect the concerns of the neighborhoods and the city, restore the area where the ramps were built, and redirect traffic away from the Arboretum.
For the WABN phase of construction, the westbound Arboretum off-ramp will be removed, along with the unused R.H. Thomson ramps. After the ramp is removed, westbound traffic from SR 520 will instead exit on the existing 24th Avenue overpass or at Montlake Boulevard like they do today. This shift is consistent with our construction plan evaluated in the final environmental impact statement. The eastbound Arboretum on-ramp to SR 520 will remain in place and open until a future construction phase.
Will local traffic operations be different from today?
Today, traffic exits directly at the Arboretum and either turns left to travel south on Lake Washington Boulevard through the Arboretum, or turns right on Lake Washington Boulevard towards Montlake Boulevard.
Map of traffic operations and routes in the Montlake area when WABN is open. Click to open in a larger PDF (1.12 mb).
When WABN is complete, the relocated ramp at 24th Avenue will provide drivers with the same opportunities to reach these destinations. Our analysis shows that approximately 50 percent of drivers exiting at 24th Avenue will turn right onto Lake Washington Boulevard to travel to Montlake Boulevard, while the other fifty percent of drivers will continue to turn left onto Lake Washington Boulevard. This movement is described in the “How will I travel to my destination?” graphic (pdf 1.12 mb).
Moving the Lake Washington Boulevard access further west to 24th Avenue is expected to reduce the amount of traffic traveling through the Arboretum, compared to today (using 2012 post-tolling data).
How will WSDOT protect local communities from additional traffic?
Overview of key design components of the WABN phase. Click to open in a PDF (911 kb)
WSDOT is planning several improvements in the Montlake vicinity to protect the neighborhood from cut through traffic:
- Adding capacity to the Montlake interchange
An additional westbound lane of storage will be added on Lake Washington Boulevard between 24th Avenue and Montlake Boulevard. The south curbline along Lake Washington Boulevard will remain as it is today.
24th Avenue will be restriped to accommodate two southbound lanes of traffic, as northbound traffic will not access 24th Avenue due to closure of the Museum of History & Industry.
- Clearly marking local access only routes
There will be a clearly marked “Local Access Only” sign placed on the neighborhood access road south of the ramp at 24th Avenue intended to discourage traffic from traveling into the neighborhood.
- Coordinate with the City of Seattle
WSDOT is partnering with SDOT to explore other means to prevent southbound traffic flow from 24th Avenue, as well as looking at other neighborhood traffic management strategies.
Additional community benefits will be advanced in future phases of the project. For example, the Montlake Interchange includes a lid (pdf 456 kb) which will provide opportunity to shift Lake Washington Boulevard further north and create a wider buffer for the neighborhood.
Has WSDOT conducted traffic analysis of the WABN phase?
In short, WSDOT’s traffic analysis results indicate that the WABN phase will not significantly increase overall traffic volumes in the Montlake area. Local travel times will be approximately the same after this phase is operational as they are under current conditions.
Traffic volume changes in Montlake area when WABN is open. Click to open in a PDF.
The key difference in Montlake area traffic flow is that the westbound Arboretum off-ramp will be removed, and its function replaced by a new off-ramp at 24th Avenue East. Local transit service will also be similar to today, and we have worked closely with local transit agencies to ensure that flyer stops remain throughout construction.
Additional details:
- View an information graphic (pdf 172 kb) that compares Montlake-area traffic volumes in 2012, when WABN is complete in 2016, and in the full-build design year of 2030.
- View an informational graphic (pdf 405 kb) that compares Montlake-area travel times with pre-tolling 2011 data, post-tolling 2016 data, and projected times for 2016 when WABN is complete.
How will WABN improve transit, vehicle, bicycle, pedestrian and open-space connections?
In fact, WABN has several benefits that will improve transit, vehicle, bike, pedestrian and open-space connections in the local area,
including:
- The regional bicycle/pedestrian path will be extended from the new floating bridge to Montlake Boulevard.
- The Montlake Triangle Project will implement a grade-separated bicycle / pedestrian facility connecting the regional shared use path to the Burke-Gilman Trail.
- A new public park will be developed at the Bryant Site (near the University of Washington campus).
- The stormwater facility to be developed at the former Museum of History & Industry location will be open to the public and designed to interface with adjacent park areas
Overview of transit and bicycle/pedestrian mobility. Click to open in a larger PDF
What mitigation is advanced with WABN construction?
WSDOT will initiate or fund required mitigation projects (pdf 2.87 mb) associated with the structure’s construction, including a new Arboretum trail, wetland and park mitigation, a stormwater treatment facility at the old MOHAI site, and removal of the westbound Arboretum off-ramp and the unused R.H. Thomson ramps.
As the I-5 to Medina project moves forward, WSDOT is committed to addressing the project’s other operational effects through mitigation measures outlined in the EIS.
Was WABN reviewed in the environmental impact statement?
WABN represents one phase of I-5 to Medina project construction; it is not a change to the overall project.
The final EIS for the I-5 to Medina project accounted for phased construction that prioritizes the replacement of vulnerable structures first.
WABN work aligns with the sequencing outlined in the EIS, and anticipated environmental impacts are also covered by this analysis.
View more information about west approach bridge construction beginning on page 3-36 of the final EIS (pdf 6.79 mb).
Additional information about construction sorted by key topic is available in Chapter 6 of the final EIS (pdf 7.51 mb).
How will WSDOT address noise impacts during this construction phase?
We do not anticipate noise to increase when WABN is complete compared to today’s conditions. Features of the WABN that will minimize noise include four-foot barriers along the bridge mainline and on- and off-ramps, quieter concrete pavement on the mainline, and encapsulated bridge joints.
During construction, WSDOT will work with surrounding communities as we develop and implement a Community Construction Management Plan, which will include identifying noise buffers and screening where appropriate.
As we move forward with construction, we’re committed to construction management practices that avoid, minimize, and mitigate the effects of our construction activities on neighbors, communities and the traveling public.
How have WSDOT and the City of Seattle worked together to understand community interests in the WABN phase?
Over the past 15 years, WSDOT has worked very hard to engage Seattle residents and neighborhoods in the process to refine the design of the west side, and has been actively listening. WSDOT recently concluded the Seattle Community Design Process, a robust effort that engaged hundreds of residents, solicited more than 1,600 comments, and helped us better understand public interests related to this part of the corridor. Additional information about WSDOT's past public involvement efforts is included in the final EIS Agency Coordination and Public Involvement Discipline Report (pdf 1.32 mb).
West Approach Bridge North design refinements made in recent months reflect what we heard through the process, and helped the Seattle City Council and Mayor understand the desires of the community. To that end, the Council recently passed out of committee Resolution 31427 that recommended actions in response to the Seattle Community Design Process Final Report:
Section 4. The City requests that the State construct the West Approach Bridge following the design recommendations in the [December 2012 Final Seattle Community Design] Report and those of the Seattle Design Commission. This includes a simple, clean structural design with a regional bicycle and pedestrian path. Consistent with the Report, the bridge should be constructed on the assumption that access to East Montlake Park from 24th Avenue East will be limited to bicycles and pedestrians.
Recognizing community concerns heard about this phase of construction, the resolution continues:
The City also requests that the State develop an interim design for the connection between the West Approach Bridge and the Montlake Area, including all transportation connections and connections among open spaces in the Area. The interim design would have several purposes.
- One is to ensure that these connections work as well as possible in the interim period between the construction of the bridge and the funding, design and construction of the other transportation improvements and related amenities in the Area.
- Another is to ensure that the choices necessarily made in the construction of the bridge do not unduly constrain the options for the other transportation improvements and amenities in the area, including but not limited to the Montlake Lid.
-A third is to ensure that the impacts of the bridge and the Project as a whole on the neighborhood and the community are adequately mitigated in the interim period.
Furthermore, the City of Seattle and WSDOT signed a memorandum of understanding (MOU) in fall 2011 that established a framework for working together to advance SR 520 Project delivery in the city. We provided a status update to the Seattle City Council on Feb. 4, 2013, about our progress implementing the MOU, along with an overview of the West Approach Bridge North phase. You can find briefing materials here.
How will the WABN phase be constructed?
As you can see in the below diagram, the WABN phase will be built in multiple stages. Click each image to open in a larger PDF.
Stage 1 - Approximately 4-6 months duration
- Make local street improvements
- Construct temporary ramp to Montlake Boulevard East and 24th Avenue East
- Extend 24th Avenue East
- Construct work bridge
- Conduct limited lane closures
Stage 2 - Approximately 20-24 months duration
- Construct stormwater facility at old MOHAI site
- Switch traffic to temporary ramp to Montlake and 24th Avenue East
- Remove RH Thompson Expressway ramps and westbound Lake Washington off-ramp
- Continue work bridge construction
- Construct West Approach Bridge North
- Conduct limited weekend and night closures
Stage 3 - Approximately 2-3 months duration
- Remove work bridge
- Conduct paving and grading work at the west end
- Reconfigure traffic to 6-lane
- Conduct limited weekend and night closures
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