The bridge is seeing heavy evening traffic today and anticipates approximately a 50 percent increase in traffic levels this holiday weekend, spokeswoman Mary Currie said today.
"Traffic is at a crawl now," Currie said. "It is moving but it's moving pretty slowly."
The Golden Gate Bridge was crossed by 39,799 southbound vehicles on Saturday, Feb. 19, 2011, and 49,889 on Saturday, Feb. 13, 2010, according to data from the Golden Gate Bridge District.
The Bay Bridge's westbound upper deck closed Friday night for work including the construction of a detour near the toll plaza, lane striping and the placement of a guide rail, according to Caltrans officials.
The detour will shift westbound traffic to the south of its existing path. It will make room for construction crews to demolish sections of the existing roadway to make way for a new inclined section for the new east span of the bridge.
The bridge's upper deck will be closed until 5 a.m. Tuesday, although weather could delay the deck's reopening.
Eastbound traffic, carried on the lower deck, and vehicle travel between Treasure Island and San Francisco are unaffected by the closure.