The two-mile, double-decker, deep-bore tunnel is replacing the Alaskan Way Viaduct, an unsightly, earthquake-damaged elevated highway that runs along the city’s picturesque waterfront.

Leaders and planners had long derided the hulking concrete eyesore that separates popular waterfront attractions such as the Seattle Aquarium and Washington State Ferries from landmarks, including Pike Place Market and the Seattle Art Museum.

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Now the celebrated replacement, 18 years after the Nisqually earthquake nearly brought the viaduct down, is expected not only to reorient the city’s expanding skyline but finally merge its downtown with its tourist-heavy waterfront.

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Eight acres of new public parks, with a landscaped promenade and space for cycling and recreation, will emerge along 26 blocks from what are now the highway’s shadows.

“When we started studying options for the viaduct replacement … we looked at the Embarcadero in San Francisco and understood what a great benefit opening up the waterfront to the public and having better access was going to be,” said Paula J. Hammond, senior vice president at WSP USA, a multinational engineering and design firm.

Hammond spent 35 years with the Washington State Department of Transportation (WSDOT) and was transportation secretary during the early years of planning for the viaduct replacement. “I think in the end, it will be just like in Boston, where visitors and residents walk along the Greenway and no one remembers all the haggling that went on,” Hammond said. “They love that corridor, and they love the parks and the open space, and think it was smartest thing Boston ever did.”

The new Highway 99 tunnel stretches from the industrial tangle south of downtown, near one of the West Coast’s biggest seaports and two major stadiums, north to where the late Microsoft co-founder and philanthropist Paul Allen over the past decade transformed a sleepy neighborhood into a vibrant commercial and residential corridor, now anchored by Amazon. The tunnel will carry traffic along two lanes in each direction on two levels, with a posted speed limit of 45 mph.

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The $3.3 billion viaduct replacement is among a number of big-ticket transportation projects that will shift the way people and freight move around the region. Among them is an extension of the region’s light-rail system running north of Seattle and another east across the Interstate 90 floating bridge to connect high-tech suburbs across Lake Washington.

The project is similar to how Maryland’s light-rail Purple Line and phase two of the Metro Silver Line extension into Loudoun County, Va., will fill gaps in the Washington,D.C. region’s transportation network.

Washington state permanently closed the viaduct Jan. 11, sending 90,000 vehicles a day scrambling for alternative routes. Demolition will begin shortly after the tunnel opens.

'Building a 21st-century city'

Built during the freeway construction frenzy of the 1950s as one of two north-south corridors through Seattle, the viaduct is part of State Route 99, a patchwork of surface streets, freeway segments and the 3,000-foot Battery Street tunnel.

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Homeless residents in tents and sleeping bags find shelter between the six-story concrete columns and parking lots.

Mehran Sepehr, a business consultant who used to take the viaduct to his downtown offices multiple days a week, said he will miss the view it afforded from the top — the downtown skyline to the east and the expanse of Puget Sound to the west and the Olympic Mountains beyond.

“I think for Seattle to be a truly great city, the viaduct had to come down,” said Sepehr, who moved to Seattle in 2001, the year the Nisqually earthquake hit. “This city’s relationship with the water is one of its defining characteristics, and removing that artificial barrier between downtown and the waterfront will open up a whole new avenue for this city.”

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Among those like him who used to drive nervously across the viaduct’s weathered frame, residents living within earshot of its unrelenting din and confused visitors negotiating its Gotham City-like underside, there are few tears being shed over the viaduct’s demise.

Yet deciding how to replace the downtown highway embroiled this city in more than a decade of political drama. There were myriad citizen forums, three advisory ballot measures and an embarrassing two-year stall by a storied tunnel-drilling machine called Bertha. Throughout the process, every mayor and mayoral candidate in Seattle staked out a position on replacing the viaduct and about 90 replacement proposals were put forth before then-Gov. Christine Gregoire (D) put an end to it in 2009, announcing that the tunnel would be her pick. By then, the state had spent more than $325 million.

“This is not just about replacing a road,” Gregoire said at a January 2009 news conference. “This is about building a 21st-century city.”

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Her motivation was safety, Gregoire said recently. “I knew it was just a matter of time before Mother Nature took down both the viaduct and the 520 bridge,” she said, referring to one of two floating bridges across Lake Washington.

Initially, Gregoire and state transportation planners were against a deep-bore tunnel option as irresponsible and too expensive. But as the political debate raged, pressure from interest groups mounted and technology brought the cost of a tunnel within a budget officials thought was manageable.

Gregoire recalls sitting down for dinner with former British Columbia premier Gordon Campbell, who, looking out toward Elliott Bay, spotted the viaduct and inquired, “What is that monstrosity?”

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In replacing it, she said, “We’ll create an iconic waterfront, and everyone will look back and wonder what was wrong with us. Why didn’t we do this a long time ago?”

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Not everyone.

Former Seattle mayor Michael McGinn (D), who won office in 2009 campaigning against the tunnel, continues to believe the state made the wrong choice.

McGinn was among a group of environmentalists who favored what he said was the more climate-conscious option of expanding transit and improving surrounding streets and nearby Interstate 5 to handle spillover traffic.

McGinn points to San Francisco’s Embarcadero Freeway and the New York’s West Side Highway as successful examples of deteriorating highways that were demolished and not replaced — and not missed.

“This is the new face of climate change denialism … and it runs deep in both political parties,” McGinn said.

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Increasingly, states and the federal government will be forced to make these kinds of transportation decisions, the former mayor said. “Do we continue doubling down and expanding the highway infrastructure, or do we, when the time comes, transition to transit, biking and walking as well as walkable communities?

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“So I’m not sure what we are celebrating here,” McGinn said.

The viaduct replacement has frequently invited comparisons to Boston’s infamous Big Dig, the rerouting of that city’s elevated downtown highway into an underground tunnel that was plagued by design flaws, enormous cost overruns and delays.

The comparisons dogged Washington transportation officials, who early on had visited Boston and other cities to learn what went well and what did not.

The state chose a design-build contract for the viaduct project, meaning the contractor, Seattle Tunnel Partners, was given creative freedom but would share in the risk of the project, which is three years behind schedule, including the two years Bertha was idle. The state’s $3.3 billion budget, almost two-thirds of it from state gas-tax revenue, includes the demolition of the viaduct; rebuilding streets at the tunnel’s portal and a portion of the major rebuild; and expansion of Alaskan Way, the street along the waterfront and beneath the viaduct. (Meanwhile, contractors have sued for up to $600 million to cover delays and repairs associated with Bertha’s breakdown.)

Beginning midyear, the tunnel will have variable-rate tolls — meaning they will fluctuate depending on the time of day — ranging from $1 to $2.25.

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Designed with fire suppression and air monitoring and ventilation to measure and reduce the levels of vehicle emissions, the Highway 99 tunnel was built to withstand a 9.0-magnitude earthquake (which occur every 2,500 years, on average). A 24-hour tunnel control center will have direct lines to emergency responders.

From the window of his antique store, which he has run for the past 40 years, Ken Eubank can see beyond the columns of the viaduct to a waterfront park, the Seattle Great Wheel and out toward Elliott Bay and Puget Sound.

His Seattle Antiques Market, wedged between a storage business and Seattle’s only dedicated blues club, which closed on New Year’s Day, is among the warehouses and small businesses operating in the shadow of the viaduct.

And while, like most, he is not sorry to see the viaduct go, its removal leaves him and other nearby business owners with something of a quandary. Eubank said he will probably mothball his store during the months of demolition this spring, and he has not decided whether he will reopen.

“My business plan is really good,” Eubank jokes. “My exit plan is terrible.”