SEATTLE -- Traffic moved slowly through the construction zone in the northbound lanes of Interstate 5 from Tacoma to Seattle on Saturday as crews began paving the Spokane Street on ramp and replacing five expansion joints at the exit to Interstate 90.

The flow of traffic through the construction zone hit an average of 17 mph before noon, according to the state Department of Transportation. The volume of traffic was expected to gradually increase throughout the day, but traffic was still moving consistently albeit slowly late Saturday afternoon. Transportation officials said the feared congestion during the 19-day project may not be as bad as previously thought.

Officials said Saturday's traffic was approximately 60 percent lighter than the load expected on a normal Saturday. They said the change in traffic flow indicates many of the drivers have taken early measures to avoid the construction area and find alternate routes.

Three northbound lanes of I-5 were closed on Friday night in preparation for the repaving work, as well as the Columbian Way ramp to northbound I-5, the West Seattle freeway and Spokane Street on ramps to northbound I-5 and the northbound I-5 ramp to I-90 and Dearborn.

The I-5 express lanes are operating southbound all weekend.

The northbound lanes be closed for 19 days until Aug. 29 while crews work on the roadway south of downtown Seattle. Crews will repave 1.13 miles of the freeway as well as other key area. Besides repaving, they will replace or repair deteriorating expansion joints that connect concrete freeway deck slabs. Officials said on Saturday said crews are on schedule.

The speed limit through that segment of freeway will be 45 mph during the entire project. There will be no high-occupancy-vehicle lane in the construction zone. The HOV lane will be shifted to Airport Way, but only trucks, buses, van pools and emergency vehicles will be allowed to use the lane.

Rain or shine, crews to push forward on Sunday

With rain a possibility for Sunday, transportation officials said crews have a giant blow dryer on standby in case they need to manually dry the roadway to keep to the paving schedule.

"It's got a fan on it like a jet engine that runs it and it burns lots of fuel - over two-hundred gallons an hour," said Paul Johnson with the department. "So, you're getting a lot of power there and a lot of wind blowing down the pavement - we can dry the area out in 20-to-30 minutes."'

Monday's commute may not be as steady

The full effect of the construction project on traffic may not be known until Monday morning, when weekday commuters will face the major hurdle on the roadway for the first time. The disruption affects some 126,000 drivers who may be significantly delayed if not enough drivers manage to find an alternate route or an alternate form of transportation.

Transportation officials said in the worst-case scenario, traffic backup could stretch as far as 30 miles in the northbound lanes of I-5 if most drivers who use the roadway daily do not change their routine.

In the best-case scenario, if the majority of drivers will use alternate transportation or avoid the roadway altogether, traffic might be sluggish through the construction zone, but continue moving, officials said.

Also on Monday begins the second stage of the project, during which more ramps will be open and drivers will be able to travel eastbound onto I-90. There will be no access from northbound lanes to the Forth Avenue South off-ramp during this stage, which extends through Friday, Aug. 17.

Alternate routes to seek, alternate route to avoid

There are several alternate routes drivers can take in order to avoid the stretch of I-5 from Tacoma to Seattle. They include:

Airport Way S.

Fourth Avenue S.

First Avenue S.

Alaskan Way S.

SR 99 I-405

East Marginal Way

Drivers should note Rainier Avenue in Renton is not a suitable alternate route, as another construction project will keep the remain closed until August 15.

On Saturday, a contractor began tearing down an old bridge over the roadway. The bridge construction is necessary to transport fuselages for the Boeing 737-900 from Wichita to the Renton Assembly plant. The 900 is too large for the present bridges.

For More Information:

Check our online traffic section for continuing coverage of the I-5 construction project, get your questions answered by KOMO traffic reporter Jenni Hogan, and check travel times, live cameras and more:

http://www.komotv.com/traffic