The Alaskan Way Viaduct will be closed this weekend for semiannual inspection and repairs, and open Saturday morning for public walking tours.

State Route 99 between the Battery Street Tunnel and Spokane Street will be closed to traffic from 6 a.m. Saturday through 6 p.m. Sunday.

Walking tours of the upper deck are scheduled between 9:30 a.m. and noon on Saturday, starting at the Seneca off-ramp. Bridge engineers will talk about the history of the waterfront, how they inspect and maintain the viaduct, what construction has already begun, and what options are considered for replacing the structure.

Tours will last about 45 minutes. Reservations are required. Call 1-888-AWV-LINE, or e-mail viaduct@wsdot.wa.gov.

Since the 2001 Nisqually earthquake engineers inspect the structure every three months and close the viaduct to do a full inspection every six.

A crew from the Bridge Preservation Office with the Washington State Department of Transportation will check monitors on the viaduct to catch widening cracks. State and city transportation crews will repair guardrails, bridge rails, expansion joints, drainage systems and traffic cameras.

They will also do preventative maintenance on the fire and ventilations systems in the Battery Street Tunnel. The tunnel will be closed Saturday night to allow engineers to do additional surveying in preparation for construction in the tunnel next year.

Matthew G. Miller is a freelance writer and may be reached through wseditor@robinsonnews.com.