Tunnel machine Bertha is to resume digging beneath the Alaskan Way Viaduct on Friday.

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This stretch of the vast Highway 99 tunnel tube, some 53 feet inside diameter, is ready to be outfitted soon with double roadway decks near Pioneer Square. Southbound traffic will someday use the top level, and northbound traffic the lower level.

So far, workers at Seattle Tunnel Partners have installed 400 feet of highway decks, out of 1,560 feet that’s been excavated to date, along with many of the future ramps for the Sodo portal.

Tunnel-boring machine Bertha is to dig beneath the old Alaskan Way Viaduct starting Friday – causing an estimated two-week shutdown of the Viaduct, as a precaution by the Washington State Department of Transportation.

Some 90,000 drivers and 30,000 transit riders per weekday will need to detour or reduce trips, not to mention thousands of north-end commuters who will be delayed by spillover congestion.