If all goes as planned, by this Friday the new tower of the east span of the Bay Bridge will loom over the old one.
"At about five o'clock this morning, our construction crews started lifting one of the four legs that we're going to be doing this time over 400 feet in the air," said Caltrans spokesman Bart Ney.
A giant crane will tip and lift four separate legs -- weighing a million pounds each -- to be fastened atop the existing sections of the new tower. Each leg is floated on a barge to the construction site. The process of installing them is done very slowly.
"That steel piece that's going up behind me is over a hundred feet long and it weighs almost 500 tons and it's going to take us 30 hours to get it from the water, all the way into place, and bolted before we can bring the next one out," said Ney.
All the pieces -- the legs, beams and cross-braces -- are designed to move independently during an earthquake to avoid catastrophic damage to the larger bridge.
"We basically create a structure that not only won't fall down in a major earthquake, but that is usable again to emergency services right after the earthquake and then with some retrofit work it can be put back into 100 percent public service," said Ney.
When stage four is completed later this week, the new tower will reach 480 feet into the air -- 91 feet taller than the current bridge structure. In April, a 45-foot top will be placed on the new tower bringing it to its final height of 525 feet.
Currently, engineers hope to complete the new east span by September 2013, perhaps just in time for the America's Cup.
Stormy weather is expected in the Bay Area later this week. Rain alone won't disrupt the process, but high winds could force some delays.