What if we build vehicles that could actually just travel on the surface of the water?
Don’t be a fool man! Any vehicle put on the surface of the water will sink. Wait…perhaps you’re on to something there. We could build vehicles out of witches!
Caligula maybe bridged the bay of Naples with ships (2-3 miles, depending), maybe rode Incitatus across it, which/who he maybe made a Senator, because it’s good to be the Emperor.
What next!? Vehicles flying through the air like the birds!?
We could test it out by building bridges between the Hawaiian islands. I knew one Brit who thought they already had bridges, because his teenage stepdaughter spent a summer in the US including Hawaii, and she told him – or so he said – that she and her group drove to another island. I lived in Hawaii for 2-1/2 years, never learned of a bridge to another island and told him so. He openly acted like a was stupid for not knowing about any Hawaiian bridges, because his stepdaughter had obviously ridden across them. 
!!! And he definitely meant a bridge to another main island such as Maui or Molokai. He never did believe me. I still have no idea what that was all about. Could have been a flat-out misunderstanding, such as she told him they visited someplace like Ford Island, which is in the middle of Pearl Harbor and connected to Oahu by the Admiral Clarey Bridge. But he insisted that was not the case.
Well OK then but would it be stupid?
Honestly I think with sufficient funds and manpower we could make floating sections and link them together and create this bridge.
The real question is can we maintain it for any length of time - I’m guessing a good deal of it will have broken free and drifted off or sank within a year.
Why not just build a floating road? Pykrete is the way to go.
I think we agree it should be floating, but you need to make it in sections so it doesn’t snap under strain. The remaining questions are how do you reliably tie the sections together so they have enough play but still remain attached, and how do you secure it in place so it doesn’t drift away.
Hey, are you looking for investors?
I’ll be damned if I’m going to ride a witch across the ocean.
We could just wait until the Great Pacific Garbage Patch gets big enough, and then pave it.
No way. Want to build a floating bridge? Sure, just design it to resist the tides, waves, and earthquakes. Plus I’m sure it would be no problem to ask the worlds fleet of merchant vessels to just stay on one side or the other.
Want to build a proper bridge, as Alec Guinness said in the Bridge On The River Kwai? Why not start with just one pier. Put it in the middle of the ocean, with its average depth of 15,000 feet. Yep, just build something roughly 10 times the height of the WTC in the middle of the ocean. Good luck with that. Then even with a very ambitious 4000’ average span, you’re going to repeat that for more than once per mile across the ocean. While you’re building it, anyone else in the world who wants to use steel or concrete is going to have to just wait till you’re done. Then when you’re all done, you’ve built the greatest terrorist magnet in history. Plus you have to build a huge platform every so often so vehicles can refuel and get repairs. Plus you have to straddle the ring of fire on both ends
You know, it’s because of guys like you we never sent an astronaut to the moon or Alpha Centauri.
I don’t need a bridge or a boat. I just have Jesus carry me.
How about an underwater tube? Down below the surface low enough that shipping could pass over it?
A bridge just isn’t practical and eventually you will all decide to build an ultimate cruise ship.
Hokkaido to Attu is only like 1400 miles, that would be the longest open-ocean stretch. It would be a sinusoidal-ish structure where half the bridge is sub-surface tunnels, linked to sections above the water, hence yielding the minimum of interference with sea traffic. Once at Attu, it becomes a series of ridiculously long island hops to Alaska.
Easy! Build a giant ferry where when you drive onto it from one shore you start driving toward the other end, by the time you get to the other end of the ferry it has arrived on the other shore and you drive off without ever having to stop.
Perfectly practical and eliminates the need to have the bridge span the entire length.
But what happens if you break down or the kids take too long on their bathroom break? The ferry could end up heading back in the other direction by the time you reach the end.