Are you ready for the longest highway closure Puget Sound has ever seen?

SEATTLE - Q13 News got a sneak peek inside an almost complete State Route 99 tunnel Thursday.

The new concrete stretches for 9,000 feet and it will replace the viaduct.

“It will be a period of traffic woes for folks it will be difficult to get around,” David Sowers of the Washington Department of Transportation said.

The iconic viaduct will shut down on Jan. 11th leading to the longest highway closure Puget Sound has ever seen.

“It's a real time experiment we haven't done this exact thing before,” Bill Bryant of King County Metro said.

You know the delays will be bad when you have traffic experts preparing commuters for the worst.  WSDOT says more than 90,000 cars go through the viaduct everyday.

“Try a different method of transportation into work, into downtown, if you can change your commute,” Heather Marx of SDOT said.

During the three week closure until the new tunnel is on-line, more buses will be on standby and an extra water taxi will take on more passengers to and from West Seattle but if you plan to drive you just have to grin and bear it.

“Our transportation operation center is open 24/7 we can make those signal changes on the fly,” Marx said.

If you are wondering why the closure is expected to be as long as three weeks, it's because they have to take down a lot of detours created during the project.

Years ago WSDOT built then buried the on and off ramps to the tunnel in order to create detours so they could keep traffic flowing during construction. So now those two ramps will have to be unburied and new ramps built to finish the whole project.

The north end of the tunnel will have a temporary wall come down to realign SR 99 into the tunnel.

The south end near the stadiums will have detours come down and new roads built.

No one really knows how much longer your commute will be starting Jan. 11, but Bryant says his guess would be betweem 20 to 30 minutes or longer.

Even if you do not typically use the viaduct expect traffic gridlock across Seattle due to the closure especially if there are unexpected events like a bad accident.