State announces two-week closure of viaduct for Bertha State Route 99 will be closed for the length of the Alaskan Way viaduct for about two weeks while Berth bores beneath

WSDOT announced the closure of the viaduct for about two weeks starting April 29. WSDOT announced the closure of the viaduct for about two weeks starting April 29. Photo: SCOTT SUNDE, SEATTLEPI.COM STAFF Photo: SCOTT SUNDE, SEATTLEPI.COM STAFF Image 1 of / 54 Caption Close State announces two-week closure of viaduct for Bertha 1 / 54 Back to Gallery

The Alaskan Way viaduct will close for about two weeks starting April 29, the state announced Friday afternoon.

State Department of Transportation officials have been planning for the closure while tunneling machine Bertha digs beneath the viaduct, though the the exact length of the closure isn't set in stone.

About 90,000 vehicles use the viaduct daily, so WSDOT is anticipating major congestion in the region during the closure, it said in a news release.

"When we closed the viaduct for nine days in 2011, we saw significant congestion on Seattle city streets and nearby highways," said David Sowers, deputy administrator of the Alaskan Way Viaduct Replacement Program, in the news release. "We'll do everything we can to ease congestion, but unfortunately there's no way to close a major highway without disrupting traffic."

To help ease the mess, WSDOT and other local agencies created 99closure.org, a page full of resources to help drivers plan around the closure.

The reasoning behind the closure is to allow for better monitoring of the viaduct during the tunneling, viaduct program administrator Todd Trepanier has said before.

Seattle Tunnel Partners, the contractor digging the tunnel, plans to keep digging 24 hours a day while under the viaduct, said Chris Dixon, the project's general manager, in a January conference call.

During the same call, Trepanier did not say whether there was a contingency plan should the tunneling machine break down again -- it already lost two years to a breakdown only about 1,000 feet into the nearly two-mile tunnel -- but instead assured reporters the operation would go smoothly.

"There is not a risk here of the tunnel damaging the viaduct and causing a long-term closure of the viaduct," Trepanier said during the call.

He did say the city and WSDOT have plans already in place should something force closure of the viaduct, just not specific to this project.

Work to build the tunnel to replace the viaduct is more than 27 months behind schedule now, and Seattle Tunnel Partners has asked its insurance company to pay for extra costs totaling more than $143 million. The insurer has sued to avoid paying those claims, and the state has also sued the contractor, essentially to reserve its right to future claims.