The tunnel under Seattle won't open until at least January or early February.

The Washington Department of Transportation was hoping for an October opening of the SR 99 tunnel but said Monday that it won't be ready until early 2019.

Ahead of the tunnel's opening, the state plans to close State Route 99 through Seattle for about three weeks beginning Jan. 11.

Also see | Getting around the SR 99 closure

Closing SR 99 is the only way crews can finish the project, which will include a realignment of the state highway. When the viaduct closes, an estimated 90,000 drivers who normally use it will be rerouted. During past viaduct closures, congestion has increased on all major roads in the area.

WATCH: Special presentation on new tunnel under Seattle

The state says drivers should expect "region-wide congestion" for up to six weeks as crews finish final connections to and from the new tunnel. There could be a "shakeout period" of weeks or months as people change their commute patterns.

Also see | A brief history of the Seattle viaduct

"We need drivers to change their habits for three weeks to prevent gridlock," said Brian Nielsen, administrator of the Alaskan Way Viaduct Replacement Program. "We recognize everyone's strategies will be different based on their needs but consider other ways to get to and from your destination if you can."

The tunnel will be free to use when it first opens. It will be tolled sometime later in 2019. The Washington State Transportation Commission is expected to set the toll rates next month. Those rates will range from $1 to $2.25.

Had it not been for the overheating and breakdown of Bertha, the tunnel boring machine, in late 2013, the tunnel could have been opened by the fall of 2016 or possibly earlier.

FULL VIDEO: Officials announce new details on opening of SR 99 tunnel

WATCH: Aerial view of Seattle tunnel construction

After Bertha was disassembled, the state estimated the tunnel would open in early 2019. It was thought the opening date could be pushed up to October. However, the state says several factors played into a decision made last week to open the tunnel in 2019. There are several contractors that must still finish their work prior to the three-week closure of SR 99. Additionally, officials say they wanted to avoid a highway closure during the holidays while giving drivers time to plan ahead.

Also see | Crews test ventilation system in Seattle’s SR 99 tunnel

State spokesperson Laura Newborn says WSDOT has been in regular contact with the city and other agencies, adding there is good progress by the contractor on completing integrating testing of the tunnels complex systems controlling everything from electronic signs to fire suppression to ventilation.

One of those tests resulted in air pressure from fans in the tunnel’s north operations building being diverted into an elevator shaft, blowing out wallboard and damaging an elevator door on August 31. Newborn said that problem was found to be mechanical in nature, and the contractor is proceeding with a fix with a minor design change.