State Route 99 is closed from the West Seattle Bridge to the Battery Street Tunnel for approximately three weeks until the new tunnel under downtown Seattle opens in early February.

Here’s what you need to know if you’re commuting in your car, by public transit or just wondering if it’s worth it to leave the house.

RELATED: Why the Seattle viaduct will close for 3 weeks before Seattle tunnel opening

In your car

Southbound drivers who normally take SR 99 will have their last chance to exit just past the Battery Street tunnel onto Western Avenue. You can also get onto northbound SR 99 at Western Avenue just before the Battery Street Tunnel.

Northbound drivers who take SR 99 or State Route 509 can either exit onto Spokane Street and take SODO surface streets or hop on Interstate 5.

Alaskan Way will be open during the closure, allowing access to Colman Dock and waterfront businesses.

Try to drive during non-peak hours to relieve congestion. Peak hours are 6-10 a.m. and 3-7 p.m., although transportation officials expect traffic will pick-up earlier and last later during the closure.

Even if you don’t drive SR 99 you could feel the impact. That's because drivers who do take SR 99 could be using I-5 or surface streets instead, and drivers who typically take I-5 may move to I-405 in an effort to escape gridlock.

WATCH: Animation of getting around the SR 99 closure

On public transit

Bus

Twelve bus routes will be impacted by the closure: 21x, 37, 55, 56, 57, 113, 120, 121, 122, 123, 125, and the C Line. Those routes will still have the same destinations and will travel through similar areas, but travel time is expected to increase, and the route will vary slightly from what it has been.

During the viaduct closure, those buses will run on a temporary path through SODO on Fourth Avenue South. Find a map of those alternate routes here.

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If you’re planning to use a park-and-ride at a transit station or stop be aware they usually fill up early. However, some park-and-rides, including Tukwila, Mercer Island, Bellevue, and Kenmore, let you reserve your spot until 8:30 a.m. There is a monthly fee for that service, with the first month free.

Water taxi

The King County Water Taxi from West Seattle to the waterfront will add an additional vessel during the closure.

The boats will leave every 20 minutes and offer 12 sailings during the morning and evening commutes with additional midday service. There will not be any crossings on weekends.

King County is also offering on-demand shuttle service to and from Alaska Junction and the water taxi at the Seacrest Park water taxi dock through their new program Ride2. Residents within a defined service area can use the Ride2 app (iOS | Android) or call 855-233-1880 to book a ride to and from the Junction or waterfront. The service is available Monday through Friday, 5-9:30 a.m. and 2:30-7 p.m.

See the water taxi and shuttle schedule here.

Link light rail and Sounder

If you’re coming from the north, the Sounder train runs from Everett to Seattle with stops in Mukilteo and Edmonds. Coming from the south, the Sounder goes from Lakewood to Seattle with stops in Tacoma, Puyallup, Sumner, Auburn, Kent, and Tukwila.

Link light rail could be a good option if you’re headed into downtown Seattle from closer in. It runs from the University of Washington to Angle Lake, passing through downtown, Rainier Valley, Tukwila, and SeaTac.

WATCH: Timeline of viaduct closure and tunnel opening

Ways to battle gridlock

Join KING 5’s Seattle Tunnel Traffic Facebook group to stay up-to-date on the closure, tunnel construction, and get your traffic questions answered by KING 5 journalists.

Follow KING 5 traffic reporter Cam Johnson on Twitter and Facebook.

Download the KING 5 app (iOS | Android) for alerts on major collisions, backups, and tunnel news.

RELATED: How KING 5 is helping you navigate the viaduct closure

Bottom line: give yourself extra time to get somewhere or maybe just decide to stay home.