The first three weeks after the Jan. 11 closure of the Alaskan Way Viaduct may be the toughest for drivers.

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Time is running out for Seattle commuters to find new roads, before the Washington State Department of Transportation closes its 66-year-old Alaskan Way Viaduct forever the night of Jan. 11. The first three weeks after the viaduct closure may be the toughest, until the week of Feb. 4, when contractors complete the surface ramps that lead into a new downtown tunnel.

Traffic jams will likely be worse than the nine-day “Viadoom” closure when a mile of viaduct in Sodo was demolished in 2011, or the 10-day precautionary closure in 2016 while tunnel drill Bertha passed under the viaduct at Yesler Way.

Unlike past shutdowns, this closure will last three weeks, and not only blocks the viaduct and Sodo areas, but also most Highway 99 lanes at Republican Street, just north of downtown. Two existing ramps in Sodo will close Jan. 4, a week before the viaduct does.

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This is the third in a series of Q&As based on reader questions.

Part 1: When does the viaduct close? How much is the tunnel toll?

Part 2: Are pedestrian and bike paths going to stay open? How will I get around?

Part 4: Will we get “one last drive” on the viaduct? Will there be Wi-Fi inside the tunnel? 


Jump to a question

Where will buses detour during the Jan. 11 shutdown?

Can I transfer from bus to train at Sodo Station?

Where will buses go when Highway 99 reopens?

Where will traffic go when Elliott and Western ramps are lost?

What are the hazards inside the tunnel?

Highway 99 Project

Can the tunnel survive earthquakes?

Could tsunamis flood the tunnel?

What will the tunnel be called?

What happens to the iconic SOUTHBOUND 99 sign?


Where will buses detour during the Jan. 11 shutdown?

Viaduct buses that serve nearly 30,000 passengers a day between downtown and West Seattle, White Center and Burien, including routes C and 120, will detour along Sodo streets. King County Metro’s online guide is at kingcounty.gov/getready.

Buses will travel on upper Spokane Street and take the Fourth Avenue South loop ramp (with a temporary bus lane) down to reach the Sodo Busway, next to the Sound Transit light-rail tracks. They will head north, then go left at Royal Brougham Way South to reach Fourth Avenue South. Buses will continue past heavy traffic, taking Prefontaine Place South to Third Avenue.

Leaving downtown, these buses will use the Edgar Martinez Drive overpass to reach First Avenue South. But in afternoon peaks, they’ll shift to downhill Columbia Street and roll along East Marginal Way South and the lower West Seattle swing bridge. Metro will be more nimble than usual, changing paths as blockages happen, said Bill Bryant, Metro service development director.

Can I transfer from bus to train at Sodo Station?

No. Metro says its 13 detoured bus routes won’t stop in Sodo. This decision removes the option for those riders to switch to light rail, heading into downtown. (Metro and Sound Transit buses that normally stop in Sodo, including light-rail connections, will continue to do so.)

Bryant said the existing bus stop at Sodo Station doesn’t have enough curb space to handle all 87 buses expected in the busiest morning hour. So they will continue north on the Sodo Busway. This won’t be so bad, he said, because that road is transit-only and leads to a temporary bus lane on Royal Brougham Way South. Morning trains may be packed anyway with south suburban commuters fleeing I-5 congestion.

Where will buses go when Highway 99 reopens?

After the tunnel opens, WSDOT needs two more weeks to finish the new Alaskan Way South offramp that northbound buses will use. In late February, the 13 viaduct bus routes return to the Highway 99 bus lane they’ve used since 2011. From the new interchange, they’ll proceed to First Avenue and mix with other traffic, before turning uphill onto a new bus lane at Cherry Street, to reach Third Avenue.

Aurora Avenue North routes such as E and 5 will weave over to the new left-side Denny Way exit, mixing with general traffic. Metro insists this layout won’t delay buses, but experience suggests otherwise at the upper West Seattle Bridge, where buses crawl with cars in the spiral ramp to Sodo. The Aurora-Denny exit will loosen to two lanes at Harrison Street, but ongoing construction – to make lower Aurora an urban street with intersections – will sometimes block lanes in 2019-20.

Eventually, the 13 bus routes from Burien and West Seattle on Highway 99 will shift in 2020 to permanent bus lanes on surface Alaskan Way from the stadiums until Columbia Street, which is being rebuilt to provide two-way bus access into downtown.

Where will traffic go when the Elliott and Western ramps are lost? 

Currently 26,000 vehicles a day – going to and from Belltown, Interbay or Ballard – use viaduct ramps that will be eliminated.  Of those, roughly half are expected to meander along the waterfront, while half are expected to use the tunnel, then swing east or west using Mercer Street or other arterials, state officials have long predicted.

Despite that shakeup, WSDOT also says traffic will disperse enough among connecting roads and crossings, that traffic will flow.

“Because people will have multiple options, we would expect the increase on any one of these routes to be below 300 vehicles per hour at peak times,” toll spokesman Ethan Bergerson said. Tolls ranging from $1 to $2.25, causing some drivers to avoid the tunnel, begin mid-2019.

WSDOT’s environmental statement in 2011 predicted afternoon trip times of 23 to 27 minutes between the Ballard and West Seattle bridges, regardless of whether drivers choose the tunnel or the surface Alaskan Way. Trips already take that long with the viaduct available – so the state numbers likely underestimate future driving times.

To keep Interbay drivers and others moving, WSDOT restored surface Alaskan Way to four lanes in mid-October. But ongoing waterfront construction will often close two lanes until early 2021, when a short bridge is finished from surface Alaskan Way to Belltown. An added benefit: The bridge will let drivers avoid being stuck behind freight trains that block waterfront Broad Street.

What are the hazards inside the tunnel?

Rear-end crashes. In a September drill, first responders simulated a wreck involving eight cars, three buses and 24 injured people. Curves within the tunnel will limit drivers’ ability to see clogged traffic ahead, so the speed limit is 45 mph. Overhead signs will warn of slowdowns and crashes.

Vehicle fires may release toxic fumes. A prolonged blaze may cause embedded moisture in the concrete to explode like popcorn kernels. The tunnel includes sprinklers, a fireproof mineral surface on roadway ceilings and ventilation fans to suck out smoke. Petroleum tankers are banned. Emergency exits, marked in green, lead to a protected hallway where people can walk toward the nearest tunnel end.

Can the tunnel survive earthquakes?

The tunnel is engineered to withstand a once-in-2,500 year earthquake, when tectonic plates slip in the Cascadia Subduction Zone. The tunnel’s 2-foot-thick reinforced concrete rings would resist shear better than a box. A strong quake may bend the tunnel a half-inch, Tim Moore, WSDOT megaprojects manager, has said. By comparison, the old viaduct gradually cracked and sank six inches since the Nisqually Earthquake of 2001. It might have collapsed had the quake lasted a half-minute longer, as depicted in a 2009 project video.

Could tsunamis flood the tunnel?

Unlikely. Though a Pacific tsunami would destroy coastal towns like Westport, Tokeland and Long Beach, waves would dissipate by the time they reach Puget Sound.

That leaves the Seattle Fault under West Seattle, Elliott Bay and Beacon Hill.  Scientists estimate it ruptured in the year 930, generating a 16-foot tsunami. A worst-case, magnitude 7.3 quake could send water 10 to 16 feet above sea level, barely high enough to reach the Sodo tunnel entrance, said T.J. McDonald, hazards information coordinator for the city’s Office of Emergency Management. “If the inundation depth is higher than the portal, it probably wouldn’t be by much,” McDonald said.  Even then, road decks and emergency exits sit several feet above the tunnel bottom, where water could surge without drowning people.

Local researchers are anticipating a more-likely 6.7 quake, enough to kill 1,600 people if unreinforced brick buildings tumble. Such magnitude would cause dangerous currents on shorelines, but not cause a tsunami.

What will the tunnel be called?

For now it’s the State Route 99 tunnel. A few people suggest “Christine Gregoire Tunnel” because she chose a bored tube as governor in January 2009. Her decision will create a quieter waterfront, and she ended eight years of public process and related engineering that cost taxpayers $325 million, legislative budgets show. On the other hand, Gregoire in 2010 insisted “there’s no reason to expect cost overruns.” (Tunnel builders have sued WSDOT and insurers for $624 million beyond the $1.44 billion contract, to cover two years’ delay when tunnel machine Bertha stalled Dec. 6, 2013.)

The ex-governor said she hasn’t thought about names. “I’m not dead,” emphasized Gregoire, 71, who leads the public-policy group Challenge SeattleNaming authority rests with the state Transportation Commission, which may choose a living person using “extra caution.”

What happens to the iconic SOUTHBOUND 99 sign?

The state expects to demolish the sign above the Columbia Street ramp, which starred in car commercials. Therefore it may be available to citizens or museums.

Do you have a question about the Highway 99 tunnel project? Tell us below.