FAQs
FAQs
Have additional questions?
Email viaduct@wsdot.wa.gov or call 1-888-AWV-LINE (298-5463)
Viaduct questions
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+ Is most of the traffic using the viaduct today going to downtown or through downtown?
The viaduct carries approximately 110,000 vehicles per day just south of the mid-town ramps. Of this amount, approximately 17,000 vehicles enter or exit downtown at Columbia and Seneca streets, and 33,000 exit or enter at Elliott and Western avenues toward Belltown, Uptown, and neighborhoods along the 15th Avenue and Elliott Avenue corridor. The remaining 60,000 vehicles continue north through the Battery Street Tunnel, either exiting in the South Lake Union/Queen Anne area or continuing north across the Ship Canal.
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+ Is the viaduct still a safe structure on which to drive?
Routine safety inspections and maintenance keep the viaduct and seawall safe for public use. In 2008, crews strengthened four column footings where the viaduct had settled approximately five-and-a-half inches into the ground since the 2001 Nisqually earthquake. The column safety project limits settlement in this area of the viaduct and prevents further damage to the structure.
We also installed a system designed to close the viaduct automatically in the event of a moderate to severe earthquake in the greater Seattle area. The new automated closure system consists of traffic gates at all viaduct access points controlled by an earthquake detection system. When the earthquake monitoring system detects significant ground movement, it will simultaneously lower all nine traffic gates and safely close the viaduct in two minutes.
SR 99 tunnel questions
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+ Will the tunnel be another "Big Dig?"
Boston's "Big Dig" project was substantially larger and more complex than the SR 99 tunnel. It was eight miles long with multiple tunnels and bridges, including a signature cable-stayed bridge over the Charles River. The project was built while traffic was maintained through the construction zone and businesses stayed open with heavy equipment operating outside their doorsteps. This approach required extensive traffic management and mitigation.
The SR 99 tunnel will be less than half the length of what was constructed in Boston. By using a tunnel boring machine, we will minimize traffic disruptions and impacts to the waterfront and downtown.
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+ How is this bored tunnel different from the tunnel that was rejected in 2007?
The tunnel proposed to Seattle voters in 2007 was a cut-and-cover tunnel, which would have been constructed by excavating a 60-foot-deep trench along the central waterfront. It would have required closure of the viaduct for several years, causing disruption to traffic and businesses.
The bored tunnel will be located beneath downtown and Belltown and be up to 200 feet below the surface, minimizing impacts on businesses and traffic. Traffic will be able to stay on the viaduct through most of the bored tunnel's construction.
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+ Is building a tunnel more risky than a new viaduct?
Constructing a tunnel is not necessarily any more risky - in terms of cost and schedule - than constructing a new viaduct. A new elevated structure on the waterfront would take between six-and-a-half and seven years to construct. It would also require working in difficult geotechnical conditions, maintaining access to businesses and detouring traffic from the viaduct for three years during construction.
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+ Will there be cost overruns on the tunnel?
We signed a design-build contract with Seattle Tunnel Partners in January 2011. Design-build combines project design and construction in a single contract.
More than 90 percent of the design-build work will be performed for a fixed price. The remaining amount includes work such as grouting to control ground settlement, building repairs along the tunnel route, unplanned repairs to the boring machine and work stoppages due to differing site conditions. For these items, we established risk sharing with the design-builder.
We have set aside $205 million for known and unknown risks during tunnel construction. This amounts to 15 percent of the design-build contract, which is on the high end of industry standards.
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+ Will there be restrictions on freight using the tunnel?
Most freight will be able to use the SR 99 tunnel. Vehicles hauling hazardous or combustible materials will be prohibited from the tunnel, similar to current restrictions in the Battery Street Tunnel and on the viaduct during peak hours. These vehicles will take I-5 or the waterfront, as they do today.
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+ Will the tunnel work if transit is not funded?
New transit service is an essential part of the Alaskan Way Viaduct replacement, because it would provide a reliable and efficient way for Seattle residents to get to and from downtown. Without added transit service, drivers would have a more difficult time reaching the tunnel, because city streets would likely be more congested. This would become more important as the city and region continue to grow.
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+ Will the tunnel help the environment?
Moving SR 99 traffic underground will have several environmental benefits. New stormwater atreatment will improve water quality in Elliott Bay, and traffic noise will be contained within the tunnel. New open space and public access will also be created on the waterfront once the viaduct is removed.
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+ How was agreement reached on the viaduct's central waterfront replacement?
Agreement was reached after an intensive public outreach effort. A 29-memeber Stakeholder Advisory Committee, which provided feedback on replacement options, met 16 times, and a majority asked that a bored tunnel replacement be considered further. Ten public meetings and more than 85 community briefings were also held. Comments from the public covered a range of topics, focusing on preserving capacity for the future and opening up Seattle's waterfront.
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+ Will the tunnel be safe?
Structural engineers agree that tunnels can be one of the safest places to be during an earthquake. The SR 99 tunnel is being designed to withstand an earthquake that only happens every 2,500 years on average (in the range of 9.0 on the Richter scale) without collapsing.
The tunnel will have emergency passages to safe refuge areas, and state-of-the-art ventilation, fire detection and suppression, security and lighting systems. It will be monitored 24 hours a day by WSDOT, similar to the I-90 tunnel today.
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+ Are there roadway restrictions on the viaduct?
In 2001, we imposed roadway restrictions that remain in effect today. Vehicles with a gross weight of more than 105,500 lbs. are prohibited. Trucks and buses must travel in the right-hand lane only. Further restrictions could be imposed in the future.
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+ How will the tunnel and city street and transit improvements help the economy?
The viaduct section of SR 99 is a main north-south route through Seattle, carrying more than 100,000 vehicles per day. Many commuters and industries, particularly the Port of Seattle, depend on this vital corridor as an alternative to I-5, since the stretch of I-5 through downtown Seattle is the most congested section of freeway in the state. Replacing the viaduct with a tunnel will ensure this capacity is available as the region grows. City street improvements and transit investments will also help accomodate future growth.
A major advantage of this bored tunnel is that it minimizes construction disruptions for businesses and the traveling public. It allows us to build the rest of the new SR 99 corridor while the remaining viaduct stays open to traffic. The SR 99 closures required during construction of a cut-and-cover tunnel or new viaduct would have required longer trips on detour routes through downtown Seattle for three to four years.
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+ Will the tunnel work for freight?
The SR 99 tunnel will maintain freight routes through Seattle and preserve I-5 for regional and state freight trips. It will also provide a route through the city for vehicles that would otherwise use city streets.
Some freight trips destined for Ballard and the Interbay industrial area will likely use the new Alaskan Way street along the waterfront, with its crossing over the railroad tracks to Elliott and Western avenues. Traffic signals along the waterfront will be operated to ensure through trips move efficiently.
Freight trips leaving Port of Seattle terminals will also have improved access to I-5 and I-90 as a result of SR 519 and Spokane Street improvements and a new overpass at South Atlantic Street, which is included in our south-end viaduct replacement project.
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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 further weakened the structure, 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.
View a simulation (YouTube) of what could happen to the viaduct if a strong earthquake were to shake the Puget Sound region (or watch non-YouTube version - requires Windows Media Player).
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+ What part of SR 99 will be replaced?
We are replacing the double-deck bridge section of SR 99 that runs along Seattle’s waterfront. This structure is called the Alaskan Way Viaduct, because it parallels the Alaskan Way surface street.
The viaduct’s south end, almost half of the structure, was demolished in October 2011, after we shifted SR 99 traffic onto a newly built section of SR 99 near the stadiums. The remaining viaduct along the downtown waterfront will be removed in 2016, after the SR 99 tunnel opens to traffic.
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+ What happens if the viaduct, seawall or both are closed before they are replaced?
We worked 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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+ How will drivers from West Seattle and south King County get to downtown Seattle?
Drivers heading north on SR 99 will have access to downtown Seattle via an off-ramp to a new Alaskan Way street. The new Alaskan Way will provide several east-west connections to downtown. This access will replace the function of today’s single midtown viaduct off-ramp. Depending on the destination, some trips will get shorter while others may take a few minutes longer.
West Seattle residents can also reach downtown using the new Spokane Street Viaduct off-ramp to Fourth Avenue South.
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+ How will northwest Seattle residents get to SR 99?
Residents from northwest Seattle will have two options to get to or through downtown Seattle. They could travel along Elliott Avenue, as they do today, and drive down a new bridge over the railroad tracks near Pike Place Market to a new Alaskan Way street along the waterfront. Alaskan Way will connect directly to SR 99 near South Royal Brougham Way.
If northwest Seattle residents want to use the SR 99 tunnel, they could take the new two-way Mercer Street to Sixth Avenue North and enter the tunnel at Republican Street. They could also use any of the existing connections to Aurora Avenue north of Mercer Street.
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+ Have similar tunnels been built elsewhere or is a new technology being used?
There are a number of successful tunnel projects with sizes similar to the SR 99 tunnel, which is being designed with an exterior diameter of 57.5 feet and length of 1.7 miles. Examples include:
- China' Shanghai Yangtze River Tunnel: Includes two bores, each about 5 miles long with a 50.6-foot diameter.
- Germany's Fourth Elbe River Tunnel: Includes a single bore with a length of about 2 miles and a 46.6 foot diameter.
- Spain's Madrid M30: Includes bores with a length of about 5 miles and a 49.5-foot diameter.
Tunnel boring machines have been developing at a rapid rate with a major increase in diameter, better ground control, and improved reliability. These machines can now safely and efficiently excavate almost and type of soil, rock or groundwater conditions.
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+ Where will the tunnel be located?
The tunnel route begins on Alaskan Way South south of South King Street, then moves toward First Avenue near Yesler Way, turns north near Stewart Street and ends at Sixth Avenue North and Thomas Street.
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+ How will tunnel construction affect waterfront traffic and ferry access?
In spring 2012, crews clearing space for tunnel construction rerouted six blocks of waterfront traffic (pdf 353 kb) from Alaskan Way to a newly improved road beneath the viaduct. The traffic switch - which will last through at least early 2014 - changes the way drivers, bicyclists and pedestrians travel along the waterfront south of Spring street. It also affects ferry access and parking.
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+ How will we pay for viaduct replacement?
The state’s viaduct replacement projects are estimated to cost $3.1 billion. Funding comes from state, federal and local sources, as well as the Port of Seattle and tolls.
