Replacing viaduct with tunnel: a closer look
When the state Department of Transportation announced last week that it has chosen the tunnel as the preferred way to replace the ailing Alaskan Way Viaduct, it wasn't much of...
Seattle Times staff reporter
When the state Department of Transportation announced last week that it has chosen the tunnel as the preferred way to replace the ailing Alaskan Way Viaduct, it wasn't much of a surprise.
For months the state had hinted that it was favoring a tunnel, and virtually all the city's political, business and arts power brokers want to tear down the existing viaduct and open up the Seattle waterfront.
But a tunnel, which would stretch about 1.1 miles along Seattle's central waterfront, is hardly a sure thing. It would cost about $1 billion more than the runner-up option, rebuilding the existing viaduct, and there is no money to do either project. While city officials talk boldly about raising the tunnel money, and are reluctant even to acknowledge the rebuild alternative, no promises have been made.
Here are some questions that have been raised about the viaduct project:
Q: Why does the viaduct need to be replaced?
A: The viaduct, and the adjoining seawall, are at risk of failure from earthquakes. That was made clear during the February 2001 Nisqually earthquake, which cracked viaduct supports and moved the structure several inches. The viaduct, built in 1953, carries 110,000 cars a day and is downtown Seattle's only north-south alternative to already overloaded Interstate 5.
Q: How badly was the viaduct damaged during the earthquake?
Because the viaduct was built before current seismic standards were in place, it lacks reinforcing steel in some areas. That dramatically reduces the viaduct's ability to absorb the shaking from an earthquake. Equally vulnerable is the Alaskan Way seawall, and the soil beneath the viaduct. If the seawall were to fail in an earthquake, the viaduct could fail along with it.
Q: Does last week's announcement of the tunnel as a preferred alternative mean the tunnel will be built?
A: Not necessarily. While state, federal and city officials have chosen the tunnel as the preferred alternative for the writing of an environmental impact statement, funding questions need to be resolved, so the option of rebuilding the viaduct also will be studied, as a contingency plan.
This is what the city doesn't like, because it wants the viaduct removed from the waterfront, but state officials say it would be foolish not to have a backup plan if the funding falls through.
Q: How much would the options cost and how long will it take to replace the viaduct?
A: The tunnel would cost between $3.4 billion and $4.1 billion and would take from seven to nine years to build. Rebuilding the viaduct would cost $2.7 billion to $3.1 billion, and construction would take six to eight years. The costs include replacing the seawall and are based on an assumption of available funding and construction beginning in 2009. Any delays would increase the costs.
Q: How much of the tunnel's cost estimate is for the seawall replacement?
A: Replacing the seawall alone is expected to cost between $600 million and $800 million. With the preferred alternative, the westernmost side of the tunnel will act as the new seawall. That is about one-third of the length of the seawall. The remaining two-thirds would still need to be built. All the cost estimates for the tunnel and the rebuild option include the seawall.
Q: Where would the money come from?
A: No single government agency can fund a project of this magnitude. A large amount of the cost would be paid by the state because the viaduct is a state highway, but the source of the money has not been determined. There could be another gas-tax increase.
The city is hoping to receive $1 billion from the federal government as part of a mega-projects bill now in Congress. Some money could come from the three-county Regional Transportation Investment District, which could put a package of projects and taxes to voters as early as next fall. The Port of Seattle has also said it would contribute but hasn't named an amount.
The only money dedicated to viaduct replacement is $177 million as part of the nickel-a-gallon gas-tax increase approved by the Legislature.
Q: Which option would carry the most traffic?
A: Both would carry the same amount of traffic, although some vehicles, such as those carrying hazardous materials, would be banned from the tunnel. The new viaduct's capacity would be roughly the same as the viaduct's capacity is today.
Q: What are the pros and cons of each option?
A: The tunnel has the support of all the government agencies; its west wall would serve as a new seawall along the central waterfront; it creates enormous potential for a viaduct-free Seattle waterfront; it could be easier to find money for; and it reduces noise pollution on the waterfront.
On the down side, it would cost the most, and the popular views from the viaduct would be eliminated.
The rebuild option retains the views of the waterfront from the road and is less expensive than the tunnel. The cons are that it retains the physical and visual barrier to the waterfront, is just as noisy as the viaduct and is narrow. And the seawall would have to be replaced as a separate project.
Q: Are tunnels safe?
A: Structural engineers say that underground tunnels are one of the safest places to be during an earthquake because tunnels move with the earth. The 2001 earthquake damaged no Seattle tunnels, which includes the Interstate 90 tunnels, the Battery Street tunnel, Metro's downtown bus tunnel and the 100-year-old Burlington Northern Santa Fe Railway tunnel under downtown.
The new tunnel would be required to meet federal safety standards, which include fire suppression, emergency escape routes and shoulders.
Q: What will happen to traffic during construction?
A: The state has always said it would keep part of the viaduct open during construction, but now will look into closing it instead. A study, prompted by a request from several Seattle waterfront-business owners, found closing the viaduct during construction could save $300 million to $500 million and could shorten construction by as much as 2-½ years.
But traffic would be a mess. A closed viaduct would add 25,000 cars to I-5 downtown each day by 2010, an 8 percent increase, and 33,000 cars to downtown streets, a 36 percent increase. No matter what is done, traffic problems would be severe.
The state says I-5 is already overburdened and couldn't handle the viaduct spillover, and much of it will go to city streets. This will be addressed in the environmental impact statement.
Q: Isn't there opposition to the tunnel?
A: Yes. People's Waterfront Coalition, a group of planners and environmentalists, wants to tear down the viaduct and not replace it. The state studied this and found traffic along Alaskan Way would more than quadruple and the number of cars on downtown streets would grow as much as 50 percent.
Several organizations, led by Magnolia residents, have formed to support the rebuild option and have said they'd fight any tax measures to build a tunnel. And a Magnolia woman, Elizabeth Campbell, has filed an initiative that would block tunnel construction. Magnolia residents like the rebuild option because they say it would provide better access to their neighborhood.
Q: Is this initiative legal?
A: That's unclear.
The Department of Transportation could challenge the initiative under the state Growth Management Act, which protects "essential public facilities" including highways and transit lines that are meant to serve growing populations. The provision is meant to deter local governments or "not in my backyard" groups from blocking regional projects.
The Seattle Monorail Project made a similar argument recently against "Monorail Recall" Initiative 83, before city voters rejected I-83 last month. The courts haven't taken it up.
Susan Gilmore: 206-464-2054 or email@example.com
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