That would never work in the Bay Area because of the rough waters in the Bay and at the Golden Gate, but I wonder which one is more cost effective: 1) Low to the water, then under or 2) like the Golden Gate and Bay bridges?
MotionMan
I would think the high bridge. Tunneling and underwater work is difficult and expensive. Also, a high bridge, with a bit of oversimplification, just adds height over the low bridge design. For an example:
Merrimac-Monitor
Sunshine Skyway
Sunshine Skyway has about 30% more bridge length, significantly more bridge height, and lacks the tunnel segment, costing about $250 million. The Merrimac-Monitor cost $400 million, with a nearly mile long piece of tunnel (so both structures have about the same total length).