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General
Safety
Costs/Funding
Environment
What part of SR 99 will be replaced?
This program will replace the portion of SR 99 that runs along the Seattle waterfront from around South Holgate Street up to the Battery Street Tunnel. The seawall along the waterfront will also be replaced.
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How are you involving minority and/or low-income communities in this program?
We engage minority and low-income populations by building relationships with community stakeholders, translating materials, and staffing information booths at cultural festivals. We know this program will affect those who depend on the social service agencies concentrated in the downtown area. Members of our program team have met with several social service agencies adjacent to the viaduct to understand their concerns for their operations and clients.
We are always looking for new opportunities to meaningfully involve traditionally underrepresented communities. E-mail us if your community would like a briefing or translated materials.
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Why is the viaduct a safety issue?
The 1950s-era viaduct was already showing signs of age and deterioration before the 2001 Nisqually earthquake, but the earthquake heightened the need for its replacement. The major risk facing the viaduct is its seismic vulnerability. The viaduct stands on fill soil bounded by the seawall. Marine organisms have slowly eaten away parts of the seawall and weakened it. In an earthquake, the fill soil is subject to liquefaction, where a shaking motion causes the soils to turn into a quicksand-like condition. Another major earthquake could collapse the seawall and liquefy the soil, damaging the viaduct beyond repair.
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What happens if the viaduct, seawall, or both are closed before they are replaced?
We worked together with the City of Seattle to prepare an emergency response plan, in the event the viaduct is closed due to an earthquake or a traffic accident. This plan will help people move out of downtown safely and restore access to downtown as soon as possible.
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Is the viaduct still a safe structure on which to drive?
We conduct routine safety inspections and perform necessary maintenance to keep the viaduct and seawall safe for public use.
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Are there roadway restrictions on the viaduct?
In 2001, we imposed roadway restrictions that remain in effect today. Vehicles weighing more than 105,500 pounds are prohibited, and trucks and buses must travel in the right-hand lane only. Further restrictions could be imposed in the future.
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Is it safe to build in the liquefiable soil that is along the Seattle waterfront?
We take the liquefiable soil beneath the existing structure into account when planning a replacement for the viaduct. Soils can be strengthened by injecting, mixing, or replacing them with cement grout. The extent and type of soil strengthening required for this program will depend on the final design chosen for the central waterfront area.
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How do you estimate costs?
In 2002 WSDOT introduced the Cost Estimating Validation Process (CEVP) to help deliver major projects. A key difference between conventional estimating and CEVP is the expression of project cost and schedule as a range rather than as a single number. This range accounts for risk factors that might otherwise cause costs to balloon over time. Cost information is given for the year of expenditure and includes everything, even “unknown” issues that may arise. CEVP has been successful enough in determining accurate costs that other states now use it as a model. WSDOT mandates that all projects of more than $100 million use this process.
During CEVP workshops, the program’s engineers sit down with national experts in construction and risk assessment to identify uncertainties and determine cost ranges. The process takes into account risks and uncertainties such as inflation, material costs, and schedule delays. The process is then repeated each year until construction begins. During the life of the program, this process allows us to focus on opportunities to reduce those risks that are the highest drivers of cost.
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What has been done to ensure the program does not go over budget?
The cost estimate range for this program takes into account hard costs (i.e., concrete, steel), the cost of money and schedule factors that will affect the ultimate cost. A delay in starting construction is a major factor that could add to the cost. Moving ahead with the north and south end projects is one way to make sure taxpayer dollars are spent responsibly.
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How much does replacing the seawall cost?
The cost for replacing the central seawall is $400 million. The cost estimate for the viaduct replacement program includes the cost of replacing the seawall.
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How has the program considered environmental impacts?
We released a draft Environmental Impact Statement (EIS) in 2004, and a supplemental draft EIS in 2006. The draft EIS evaluated the impacts of five alternatives: rebuild, aerial, tunnel, bypass tunnel, and surface. The supplemental draft EIS updated this information for the tunnel and the elevated structure alternatives. These documents are available in the Library.
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How can you be sure that important tribal artifacts will not be discovered when soil under the viaduct is excavated, similar to what happened in Port Angeles?
For this program we know that Elliott Bay has a very different configuration of rocks and soil than the Port Angeles site. The historic shoreline here was more likely a narrow strip of land straddled by low bluffs and a deep water bay. Large settlements of people were more prone to head toward greater food resources along areas of the Duwamish River and to the east - far inland from the historic shoreline.
While significant discoveries are not expected, we are taking the steps necessary to fully investigate the program area and reach agreements with tribal governments on how to handle artifacts or human remains if discovered. We also use extensive surveys by archaeologists and other soil experts leading up to excavation. Before any major excavation is started, we drill beneath the surface in small increments to test out the soil content. All drilling work is monitored by archaeologists and geomorphologists.
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Do you consider any previous research on potential archaeological sites beneath the viaduct?
Yes. We are currently conducting an extensive review of all known data sources on the site. These sources include a geologic history from the University of Washington to identify ancient shorelines, other historic data on shorelines and patterns of fill and development, and extensive input from five tribes with historical usage of the Elliott Bay shoreline areas.
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How have you consulted with the tribes so far?
We have involved the five tribes with ties to the area early and often as design work has progressed. Face-to-face meetings with tribal representatives and multi-tribal meetings have helped us pinpoint areas of concern well before any construction activity begins. Identifying these concerns early means that we can adapt designs to avoid disturbances if needed, and consider different construction techniques to allow for discovery and recovery of resources. Prior to any construction, we will finalize agreements on tribal contacts and protocols in the event that archaeological remains are discovered inadvertently.
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