SEATTLE — The Alaskan Way Viaduct officially closed for good Friday night.

A portion of State Route 99 in Seattle will be closed for about three weeks until the new tunnel under downtown Seattle opens in early February. Until then, prepare to battle gridlock as travel times are expected to rise across the region.

RELATED: Survive the Seattle viaduct closure: What to know for your commute

Here’s what’s going to happen next as Seattle prepares to open the tunnel and demolish the viaduct.

Friday, February 1 at 10 p.m. – Battery Street Tunnel closes

The Battery Street Tunnel closes forever after the Friday, February 1 commute. Despite community proposals to save the tunnel, which included transforming it into a park, farm, or transit option, the city will fill in the tunnel with rubble from the demolished viaduct and seal it.

WSDOT says the tunnel’s age and condition mean it would require costly upgrades to make it safe for other uses.

Saturday, February 2 and Sunday, February 3 – Tunnel celebration

Didn’t get the opportunity to have a last hurrah on the viaduct? You still have a chance. The tunnel celebration includes an 8K fun run, bike ride, tunnel walk, and an art festival on the viaduct.

Visitors must register for a free ticket to walk through the two-mile-long tunnel beginning at the north portal in South Lake Union. You can then either walk back or take a shuttle from the south portal in SODO back to South Lake Union. Visitors also must get a ticket to go to the art festival on the viaduct via the Battery Street Tunnel.

Register for tickets on Eventbrite: Tunnel only | Viaduct only | Tunnel and viaduct | Viaduct and tunnel

No tickets are necessary to go to the festivals at the north and south portals, which will feature food trucks, music, and STEM activities.

The fun run, which takes place Saturday at 7:30 a.m., begins at the north portal, takes runners south on the viaduct, and then loops north through the tunnel. Register on tunneltoviaductrun.com.

The bike ride, which takes place Sunday at 8 a.m., has two routes: an 8.5-mile ride through the tunnel and back and a 12.5-mile ride that tacks on a ride on the viaduct on the return trip. Register on cascade.org.

Monday, February 4 – Tunnel tentatively opens

At this point WSDOT is aiming to open the tunnel right after the tunnel celebration. However, the agency hasn’t released any details about specific times the tunnel will be open to travelers.

Severe weather could push the tunnel opening date back, although contractors have built some contingency for rain and a day of snow into their construction timeline.

When the tunnel opens, travelers will need to adjust their routes from what they were used to taking on the viaduct. For example, the mid-structure exits to Western Avenue and Seneca Street and entrance from Columbia Street are going away. If drivers want to get on or off SR 99 to the heart of downtown, they will need to enter or exit the tunnel in SODO or South Lake Union and navigate on surface streets, such as Alaskan Way.

RELATED: Step-by-step guide to driving southbound on SR 99 after the tunnel opens

RELATED: Step-by-step guide to driving northbound on SR 99 after the tunnel opens

February 2019 – Viaduct demolition begins

About a week after the tunnel opens, contractors are expected to begin demolishing the viaduct.

Workers will systematically remove concrete pieces to demolish the structure; officials said it won't come down all at once like the Kingdome did in 2000.

Crews will remove portions of the viaduct in three-span segments, which is about the length of a city block. As crews remove the top deck of the viaduct, the rubble will fall to the lower deck and will then be trucked away. Workers can then remove the columns to the lower level and repeat the process for the lower deck.

Summer 2019 – Tunnel tolling begins

Drivers will have a few months to get used to the layout of the tunnel before tolls kick in.

When the Washington State Transportation Commission finalized tolling rates back in October, it said tolling could begin as early as summer. The commission is set to establish a start date for tolling at its February meeting.

Rate will range from $1 to $2.25.

Final SR 99 tunnel toll rates:

  • 12 a.m. – 6 a.m. $1
  • 6 a.m. – 7 a.m. $1.25
  • 7 a.m. – 9 a.m. $1.50
  • 9 a.m. – 3 p.m. $1.25
  • 3 p.m. – 6 p.m. $2.25
  • 6 p.m. – 11 p.m. $1.25
  • 11 p.m. – 12 a.m. $1
  • Weekends $1
  • Three percent increase every three years beginning July 2022

Summer 2019 – Viaduct demolition completed

Crews hope to finish demolishing the viaduct by summer.

Join KING 5's Seattle Tunnel Traffic Facebook group to stay up-to-date on the latest Seattle tunnel and viaduct news and get tips to battle traffic during the three-week viaduct closure in January.