Mercer Mess to Get Messier at South Lake Union

Drivers, beware.

A trip near Seattle Center will take five or 10 minutes longer for the next two years as work starts at the west end of the Mercer Street project.

The big change will be a new, two-way Mercer underpass beneath Aurora Avenue North. The six-lane boulevard will have sidewalks and a bike lane separate from traffic.

When the $95 million job is done in late 2015, drivers for the first time will be able to go west directly to the Center from Interstate 5 without making multiple turns on side streets.

And travel will be far safer for cyclists and pedestrians between the busy Uptown and South Lake Union neighborhoods.

However, until all that happens, think barricades and orange cones.

For the typical 75,000 or so vehicles using Aurora Avenue, think delays.

Same goes for the 35,000 motorists who now use Mercer.

Work begins with a full weekend closure of both Aurora and Mercer from 11 p.m. Friday, May 17, until 5 a.m. Monday, May 20.

Southbound through-traffic will be detoured to I-5 at North 85th Street. Local drivers may continue on Aurora down to the Dexter Avenue North exit.

Also that weekend:

• Traffic from South Seattle approaching downtown will be detoured off Highway 99 at East Marginal Way South near South Spokane Street.

• Even the sidewalks in the work zone will be closed.

Then, beyond the weekend closure:

• The existing four eastbound lanes of Mercer from Fourth Avenue North to Ninth Avenue North will be reduced to two, so backups there will worsen.

• A stretch of eastbound Broad Street will be reopened from the Center to South Lake Union, which may help a bit.

• The exit from northbound Aurora/Highway 99 to eastbound Mercer Street will close. That means today’s gridlock at the junction of Mercer and Dexter will be pushed to other locations.

Bus riders will not go unscathed, either. Changes including the loss of some stops will impact five routes. Some 80 buses a day pass through just on Route 358.

When all the dust begins to settle, an offramp from the future Highway 99 tunnel under Seattle will meet up with the new Mercer Street, just west of Aurora Avenue, in 2016.

When the project is complete, drivers heading to I-5 will not save much time. But those leaving I-5 and heading toward the Center will have an easier go of it, said Eric Tweit, project manager for the Seattle Department of Transportation.

“People are going to notice it’s much easier to get off (I-5). You may not be going 35 miles an hour, but it’s … an arterial street. So, it will work much better than turning right on Fairview, left on Valley, and then turning onto Broad Street and then figuring out where you go from there once you get across Aurora.”

In related work, Valley Street will be finished as a two-lane road with sidewalks and bike lanes this year, convenient to the Museum of History & Industry.

And as part of the tunnel project, the state will reconnect the east-west street grid — John, Thomas and Harrison streets, which were severed when the Aurora Avenue bridge was built back in the mid-1950s.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom

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