The 75-year-old Bay Bridge is still in daily use by 280,000 commuters even though a section of its upper deck fell to the lower during the 1989 earthquake. But the east span will soon be replaced by the world’s longest single-tower, self-anchored suspension bridge. Crews raised 16 pieces, some weighing 1,000 tons, to build the 525-foot tower. Now teams are draping a single, mile-long steel cable made of more than 17,000 wires across the 2,047-foot span. Replaceable steel beams between the tower’s four legs can absorb the energy of an earthquake, and drivers will have open views of the San Francisco Bay from five lanes. Total cost: $6.3 billion.