The new State Route 99 tunnel is scheduled to open in early 2019, but not before the longest highway closure in Puget Sound history.

Before the new tunnel opens to drivers, the Washington State Department of Transportation (WSDOT) will close State Route 99 through downtown Seattle for about three weeks to realign the highway. Crews will then move SR 99 from the earthquake-vulnerable Alaskan Way Viaduct into the tunnel.

Related | 3-week Viaduct closure coming ahead of Seattle tunnel opening

The closure is scheduled to begin Friday, January 11, 2019, and expected to cause major traffic congestion throughout the area.

When the tunnel opens, WSDOT says the viaduct and Battery Street tunnel will both permanently close as crews prepare to tear down the viaduct. The tunnel will be free to use when it first opens. It will be tolled sometime later in 2019.

WATCH: How Christmas plays into the opening of the tunnel

For some, the early 2019 opening date is a “delay” from a Thanksgiving opening, but for the Washington State Department of Transportation, it’s back to what they’ve been saying since August of 2017.

The fact is, the opening of the Seattle tunnel is late, years late. Based on the original contract with Seattle Tunnel Partners, the original opening date should have been December of 2015. When the state initially called for bids from companies to build the tunnel, the target date was the fall of 2016.

That’s two calls right there.

Brian Nielsen, the Alaskan Way Viaduct Replacement Program Administrator, said on Monday Thanksgiving wasn’t going to work, adding it was too risk threatening to disrupt traffic into the holiday season. January was a safer bet, besides the contractor isn’t quite finished yet with a turnover date now scheduled for early October.

How we got here

The tunnel is 10 years in the making, as then-Governor Christine Gregoire announced plans to tear down the Alaskan Way Viaduct in January 2008. A year later, the state, county, and city announced an agreement to replace the Viaduct with a tunnel.

By spring 2009, Gregoire approved a $2.8 billion funding plan. Four years after the funding was approved, the world’s largest tunneling machine was shipped from a factory in Japan to Seattle. Crews assembled Bertha in three months, and she started digging on July 30, 2013.

Project managers expected the nearly two-mile tunnel to be done in just over a year.

But by December, Bertha was in trouble. The giant machine was overheating, and she dug in fits and starts as managers attempted to figure out what was wrong.

Also see | Bertha breakthrough: Rumble from the deep

In January 2014, Bertha stopped and didn’t start digging for another two years. The problems were tied to seals and bearings.

Bertha resumed the dig in January 2016, but the problems continued. A sinkhole formed near the digging site, causing the project to be put on hold. Digging resumed after it was determined safe.

By April 2016, Bertha was back on track with just one more course correction in March 2017. Seattle Tunnel Partners discovered Bertha had veered about six inches off course. After adjustment, Bertha chugged along for the final 960 feet.

On April 3, 2017, Bertha broke through at Sixth Avenue North and Thomas Street in Seattle’s South Lake Union neighborhood.

The State Route 99 tunnel under Seattle is scheduled to open in early 2019.

Timeline: The effort to dig the SR 99 tunnel