Removing the Alaskan Way Viaduct
After the new State Route 99 tunnel opens to drivers, the Alaskan Way Viaduct along Seattle's waterfront will be removed to make way for a new surface street built by the City of Seattle. This project will help transform Seattle’s waterfront while removing a vulnerable structure from our road network.
Why remove the viaduct
The Alaskan Way Viaduct was built in the 1950s and was damaged in the 2001 Nisqually Earthquake. While it has been strengthened and is safe for daily use, it remains seismically vulnerable. The viaduct’s role in moving people into and through downtown Seattle will be replaced by the new SR 99 tunnel and a new Alaskan Way surface street built once the viaduct is gone.
Scope of work
Viaduct removal work is scheduled to begin in February 2019 and take about six months. The major elements of this project are:
- Shifting Alaskan Way to the west of the viaduct (completed in October 2018).
- Removing the Alaskan Way Viaduct from South Dearborn Street to the Battery Street Tunnel.
- Removing the Columbia and Seneca street ramps.
- Building a new, temporary pedestrian bridge across Alaskan Way to Colman Dock.
- Restoring the area where the viaduct once stood and then turning the space over to the City of Seattle's Waterfront Seattle Program.
Removing a large concrete structure from a busy waterfront will be unavoidably disruptive. Our primary goal is to remove the viaduct safely and with as little disruption as possible to nearby people, property and businesses. The contractor, Kiewit, will follow a variety of standards and best practices as they design and conduct the work.
Reducing disruption by working in sections
Kiewit, the contractor for this project, will remove the viaduct as shown on the sequencing map below. Each rectangular box represents a viaduct frame that will be completely removed before crews advance to the next frame. Crews will do prep work ahead of active demolition and will finish with site restoration. Crews will be working at multiple locations at once to speed up the overall work.
Keeping people moving during demolition
- Lane closures will occur only in immediate proximity to active construction.
- One lane of Alaskan Way will be open in each direction adjacent to active construction. Elsewhere, two lanes will be open in each direction.
- Marion and Spring streets will not be closed at the same time.
- Madison and Columbia streets will not be closed at the same time.
- No more than three adjacent cross-streets will be closed at a time, with up to six cross-streets closed throughout the entire alignment.
- Temporary building and parking access restrictions according to previously negotiated Temporary Construction Easements.
- An ADA-accessible detour route will be provided during the Marion Street Pedestrian Bridge closure.
- A 24/7 two-way ADA shuttle will be available between Western Avenue and Alaskan Way during the closure of the Lenora Street Pedestrian Bridge.
Removing the viaduct frame by frame
The viaduct will be removed one frame at a time. Crews will use specialized equipment to remove the viaduct’s top and lower decks following the sequence below:
- First, crews will fence off the immediate area and complete prep work and staging.
- Next, crews use impact hammers to remove the roadway deck.
- Next, large hydraulic munchers will remove the girders and columns that support the deck. In some places, crews will sawcut pieces of the viaduct and lift them away with cranes.
- Crews will then begin removing the lower deck following the same process as described above.
- Finally, crews will remove the viaduct's foundations, in some places to five feet below grade, and restore the site.
Removing the Columbia and Seneca ramps
Removing the Columbia Street and Seneca Street ramps will be a slightly different process. Crews will use small excavators to remove the bridge deck, then forklifts and cranes to remove beams one-by-one. Material from the ramp structures will be lowered to the ground and then hauled away.
Reducing impacts to neighbors and protecting buildings
Removing a highway in an urban area is unavoidably disruptive. WSDOT and Kiewit's goals are to complete the work safely and quickly while reducing disruption where possible.
We’ll maintain a 24-hour noise hotline during construction at 1-888-AWV-LINE (298-5463).
Protecting buildings, infrastructure and utilities
- Kiewit will enclose active construction areas with fencing.
- When working in close proximity to buildings, Kiewit will use temporary barriers and heavy nets to keep debris contained.
- Debris containment materials will not be attached to buildings.
- Trees will be protected with ecology blocks and protective wrapping.
- Temporary building and parking access restrictions will be in effect according to previously negotiated Temporary Construction Easements.
Dust, light and vibration
- Water misting will be used to control dust during all viaduct removal activities. Runoff water from this activity will be collected and tested before being discharged to the sanitary sewer.
- If lighting is needed during work hours, it will face the project site and be shielded to minimize its impact on nearby residents and businesses. Lights will be used only during active operations.
- Vibration monitors will be placed along the alignment during vibration-producing activities.
The typical noisiest work hours for viaduct demolition will be:
- 7 a.m. to 8 p.m. weekdays
- 9 a.m. to 8 p.m. Saturdays
- 9 a.m. to 5 p.m. Sundays and holidays
- Seven stationary noise monitors will be placed at different locations along the alignment. During night work, crews will also use a portable monitor.
- Electronic systems will collect data from noise monitors and will automatically alert superintendents when crews approach or exceed noise limits.
- A noise inspector will be on-site during night work to ensure noise mitigation commitments are maintained, and to investigate hotline concerns about noise.
- If hazardous materials are encountered, crews will secure the work site and contain the materials within.
- Any soil believed to be hazardous will be tested, analyzed and disposed of at an off‑site hazmat facility.
- Materials suspected of containing lead or asbestos will be tested as required.
Maintaining access to the ferry terminal
Colman Dock will be accessible for drivers, pedestrians and bicyclists whenever the terminal is open.
During viaduct removal, Kiewit will construct a temporary pedestrian bridge along Columbia Street. This bridge will connect to Colman Dock via Columbia Street, connecting to the existing Marion Street Pedestrian Bridge via Western Avenue. A portion of the existing Marion Street Bridge will be removed during viaduct removal.
Building the new temporary bridge is expected to take up to four months. There may be a gap of up to 14 days between the closing of the current bridge and the opening of the new bridge. In that event, an ADA-accessible pedestrian route will be provided to and from Colman Dock.
The new bridge will be in place until a permanent bridge opens in conjunction with the end of Colman Dock construction in early 2023.
How to stay informed as work progresses
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