A walking tour of the work zone for the State Route 99 tunnel project will be held at 6 p.m. Thursday, Sept. 6 in Seattle. The tour will take the public by the site being prepared for the arrival of the world’s largest-diameter tunnel-boring machine in 2013.

The mile-long, round-trip walking tour will show the massive work zone where crews are digging the launch pit for the 300-foot-long tunnel-boring machine.

“There’s a lot of amazing equipment and activity happening on site right now and we want people to see and understand what’s going on,” said Linea Laird, Alaskan Way Viaduct Replacement Program administrator. “This is the first of many opportunities we’ll offer for a better glimpse of construction.”

Although the five-story-tall tunneling machine won’t take the stage until next year, its supporting cast – including a fleet of massive cranes, drill rigs and excavators at work to the west of CenturyLink Field – are impressive in their own right. In addition to digging the 80-foot-deep pit where the machine will begin its northward journey, crews are building a new overpass and putting the finishing touches on a new section of SR 99 to replace the south end of the Alaskan Way Viaduct.

The tour will begin at Milepost 31, the Alaskan Way Viaduct Replacement Program’s information center in Pioneer Square. This center houses interactive exhibits, a model of the SR 99 tunnel-boring machine and the latest project information.

Milepost 31 is located at 211 First Ave. S., Seattle.

For those who can’t attend, a new self-guided tour is available. Displays have been installed along the bicycle/pedestrian path to describe construction activities, machinery at work and the area’s history.

Access to the path’s north entrance is available at South King Street and Alaskan Way South, a few blocks south of Colman Dock or the south entrance at South Atlantic Street and Alaskan Way South, west of Safeco Field.

Maps are available at Milepost 31. Construction cameras and Flickr photos also provide a regularly updated view of the work zone.

More information about the Alaskan Way Viaduct Replacement Program is at www.alaskanwayviaduct.org and Milepost 31, which is open 11 a.m. to 5 p.m. Tuesdays through Saturdays and is open late during Pioneer Square’s First Thursday Art Walk. Admission to Milepost 31 is free.