raddie

I admire your imagination, but you have given me an idea. The floating, but anchored, structure under the ocean could presumably be basically a hollow tube. If the two ends were above sea level, i.e. on the land, then traffic could travel through the tube. What you would have is a tunnel without needing to drill through the earth and rock etc. under the ocean. This would be cheaper to make than just using the tube as a base on which to build a bridge. I imagine that providing the anchor points to keep the tube in place would be cheaper than drilling the tunnel, but I don't really know if this would be the case. Of course the tube itself would need to be very strong and perhaps flexible to some degree. It would also need to be deep enough for ships to pass over it.

Certainly an idea worth considering, however, in my opinion such options are usually ruled out on safety grounds. If there was ever an impact which drove a hole in such an underwater tube structure, due to ship collision say, the flooding would surely be rapid and disastrous.