A slew of changes will begin Friday night and the effects will likely stretch all the way onto I-5.
It'll be a lot of brake lights, tested patience and changes that will last until 2015.
A little bit of pain now will help in the long run.
Seattle Dept. of Transportation's Eric Tweit wants it clear: your commute is going to be unpleasant.
"We want people to be aware that it's going to take more time to get through here. We expect backups on Mercer Street to the west," he said.
Here's a look at what to expect starting this weekend:
State Route 99 from Valley St. to the south end of the Battery Street Tunnel will be closed. That starts at 11 p.m. Friday and lasts until 5 Monday morning.
Traffic traveling through Seattle via SR 99 will be directed to I-5 north of Seattle at 85th St. or south of Seattle at E Marginal Way.
Mercer isn't spared, though.
It will be closed between 5th Avenue and Dexter.
Traffic heading east towards I-5 will be detoured to Denny Way at 5th Ave. N and will reconnect to Mercer St. at Dexter Ave. N to continue east.
This is all part of a larger plan.
Mercer will get lanes going in each direction.
But the key is the exit from the new downtown tunnel.
It will open up around Broad in three years.
Highway 99 gets attention too.
Two lanes on the north side will close permanently for Monday morning.
Here's how things will look come Monday:
Highway 99 will have traffic shifted with two lanes open in each direction. That is expected to last for two years.
The northbound off-ramp from 99 to Mercer will be closed.
Mercer will go down to two lanes eastbound between 4th and 9th avenues.
One bright spot comes along Broad to I-5. It will go back to traffic in both directions with eastbound back open.
But in a year, it'll be closed permanently and torn down. It simply takes time.
"Because we're in a pretty tight space. We don't have a lot of room like you have on a highway project," Tweit said.
A congested corridor about to get a whole lot worse.
Stay tuned. There's even more to come through the summer.
Adding to the pain this weekend: a Sounders game, a street race and more tourist traffic.