Big weekend for a big bridge

SAN FRANCISCO--This weekend, the James "Sunny Jim" Rolph Bridge (known to most simply as the Bay Bridge) is undergoing yet another phase of renovation on its way to a much-needed seismic upgrade. On this weekend's to-do list is moving a 288-foot, 3,300-ton chunk of the bridge to make room for its eventual replacement.

The bridge connects San Francisco to Oakland and the rest of the East Bay, making a stopover on Yerba Buena Island, which sits in the middle of the bay. It has seen much change since it opened in the 1930s, much of it involving the eastern span, which connects Yerba Buena Island with Oakland. After a section of the bridge collapsed in the 1989 Loma Prieta earthquake, it was determined that the entire bridge needed seismic upgrades. The San Francisco side simply needed seismic retrofits, but the eastern will be completely replaced. (Shown here is the east span of the bridge, with the current bridge in the foreground and new construction in the background.)

This weekend, the California Department of Transportion, or CalTrans, will pass a huge milestone in that years-long process. Before the new bridge span can be built, a temporary S-curve bypass needs to be put in to allow traffic to flow through while the replacement piece is constructed and moved into place.

To pull off this feat, CalTrans has closed the bridge to all traffic from 8 p.m. Thursday through 5 a.m. Tuesday. Though most people won't have the opportunity to see this impressive work in progress, we were able to ride along on a press tour Friday to see the upgrade in action. Click through for a look at just some of the engineering power it takes to pull off such a massive project.