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Traffic is about to get worse where Aurora Avenue meets Mercer Street, as at least a year of city road construction forces cars and buses into fewer lanes.

The squeeze begins Monday at 9:30 a.m.

On Aurora Avenue, which carries 75,000 vehicles a day, traffic will be squeezed into two lanes each way, and shifted into temporary alignments. That way, the old underpass can be demolished and rebuilt, where Mercer dives below Aurora.

That work is part of the $99 million “Mercer West” project to create a widened, six-lane route for Mercer beneath Aurora, with broad sidewalks.

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Seattle elected officials hope the changes will make walking, bicycling and transit trips easier, and help South Lake Union evolve into a pleasant destination that attracts more biotech and software jobs.

Navigation would become simpler, as the city completes a direct two-way route from Interbay to I-5, combining the new Mercer East boulevard with Mercer West, by 2015. But travel speeds in cars aren’t expected to change much.

Construction bottlenecks include:

• Bus lanes on Aurora Avenue North will terminate near Mercer — so buses will be merging into the two lanes of general traffic, each direction. State law requires drivers to yield to merging transit buses, and Route 358 by itself sends about 80 buses a day each direction. In addition, bus routes 5,


26 Express

and 28 Express

will be affected. Bus stops at Aurora and Mercer will close.

• The northbound exit from Aurora to Mercer will close. This will create an extreme crash risk, as drivers leaving the Battery Street Tunnel suddenly decelerate and merge right, to make an earlier right turn at Republican Street.

• Mercer Street, where it’s now four lanes westbound, will shrink to two westbound lanes from Fifth Avenue North to the Aurora crossing.

• The southbound offramp from Aurora to Broad Street closes.

• Sidewalks will be blocked on Aurora above Mercer Street.

By the time Mercer West is done, more road work will arrive, to connect the north portal of the Highway 99 tunnel with Mercer Street during 2015.

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

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