# Where's all the submerged bridges? **URL:** \ **Category:** Factual Questions\ **Created:** [January 20, 2007, 1:36pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704 "2007-01-20T13:36:07Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [January 20, 2007, 1:36pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/1 "2007-01-20T13:36:07Z")
In another thread, someone asked about travelling between continents without flying. Which reminded me of a small question in my mind of why it seems that everything is either a bridge over, or a tunnel under water. It seems like it shouldn’t be all that much more difficult a task to build a submerged bridge that is partially buoyant. This would make it free from both surface weather and ground quakes. It seems like it should be easier to build as well. If you set it to float 50 feet under water, you just have each link have a set of ropes or something which you can use to run them into each other as you lower them, and then automatic connectors. You would probably need to anchor it periodically against currents, but this doesn’t seem too honerous. But the only reference I see to such a bridge is that there still hasn’t been one built anywhere. You would think that there would be several small ones somewhere. Even Seattle has a floating bridge. What gives? ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [January 20, 2007, 1:50pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/2 "2007-01-20T13:50:08Z")
Because the cars’ motors would swamp? Because the little fishies would nibble our trousers? Because nobody would want to use one? Because it offers no advantage whatsoever over a bridge that **is not** submerged? :rolleyes: ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [January 20, 2007, 2:33pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/3 "2007-01-20T14:33:16Z")
I’ve been fascinated by this concept since I read a science fiction story about. I think it was by Harry Harrison, who writes the Stainless Steel Rat series. Such a tunnel has been proposed to connect Vancouver Island (home of the provinical capital Victoria) with the British Columbia mainland at Vancouver. But this page says that it would be more expensive than the alternatives: [http://www.th.gov.bc.ca/Publications/reports\_and\_studies/fixed\_link/fixed\_link.htm](http://www.th.gov.bc.ca/Publications/reports_and_studies/fixed_link/fixed_link.htm) There’s a company in Norway that hopes to build them. Their website stresses esthetic and environmental benefits without mentioning (as far as I see) any cost savings. I take that as an tacit admission that it would be more expensive than the alternatives. See [http://www.nsft.no/discover\_the\_floating\_tunnel.html](http://www.nsft.no/discover_the_floating_tunnel.html) ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [January 20, 2007, 2:55pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/4 "2007-01-20T14:55:38Z")
[QUOTE=Bosda Di’Chi of Tricor] Because the cars’ motors would swamp? Because the little fishies would nibble our trousers? Because nobody would want to use one? Because it offers no advantage whatsoever over a bridge that **is not** submerged? :rolleyes: [/QUOTE] Watertight of course… And as said, it has the advantage of having a stable environment surrounding it. Or theoretically at least. I’m not arguing for it, it just seems like something someone would have done at least once in the last few millenia. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 20, 2007, 2:58pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/5 "2007-01-20T14:58:09Z")
[QUOTE=bibliophage] I’ve been fascinated by this concept since I read a science fiction story about. I think it was by Harry Harrison, who writes the Stainless Steel Rat series. [/QUOTE] Yep, _A Transatlantic Tunnel, Hurrah!_ ---
**Author:** ![Tapioca\_Dextrin](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@Tapioca\_Dextrin](https://boards.straightdope.com/u/Tapioca_Dextrin)\ **Post date:** [January 20, 2007, 3:09pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/6 "2007-01-20T15:09:08Z")
[QUOTE=Sage Rat] And as said, it has the advantage of having a stable environment surrounding it. Or theoretically at least. [/QUOTE] Personally, I’d prefer a 100ft of solid rock if I was interested in a stable environment. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [January 20, 2007, 3:58pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/7 "2007-01-20T15:58:20Z")
[QUOTE=Tapioca Dextrin] Personally, I’d prefer a 100ft of solid rock if I was interested in a stable environment. [/QUOTE] If you’re connecting continents, I would be a bit worried about faultlines though. ---
**Author:** ![Sublight](https://avatars.discourse-cdn.com/v4/letter/s/439d5e/32.png) [@Sublight](https://boards.straightdope.com/u/Sublight)\ **Post date:** [January 20, 2007, 4:09pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/8 "2007-01-20T16:09:24Z")
I think water currents would put a lot more stress on the structure than winds or earthquakes would. Also, it could mean closing off a channel to shipping traffic depending on the depth available; one good whack from a containership and you’ve now got a broken tube rapidly filling with water. ---
**Author:** ![chela](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chela/32/21582_2.png) [@chela](https://boards.straightdope.com/u/chela)\ **Post date:** [January 20, 2007, 6:20pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/9 "2007-01-20T18:20:32Z")
There are structures that are Bridge/Tunnels (fixed yet). There is the Monitor MerrimacMemorial Bridge Tunnel in VA., and the Oresund Bridge tunnel connecting Denmark and Sweden. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [January 20, 2007, 7:27pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/10 "2007-01-20T19:27:24Z")
[QUOTE=Bosda Di’Chi of Tricor] Because it offers no advantage whatsoever over a bridge that **is not** submerged? :rolleyes: [/QUOTE] Here’s one advantage Build a bridge above water, you gotta put in arches high and wide enough for the boats to go under. Put your tunnel in a submerged tube, boats can go over it with no problem. One disadvantage that I can see is that such a thing would be an easy target for terrorist attack. A few explosives at key points could sink the whole thing, and how can you police the entire length of the tube? ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [January 20, 2007, 7:56pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/11 "2007-01-20T19:56:36Z")
I’m with **Sublight**. The forces from currents, whether tidal or weather-related, will be absolutely enourmous. [QUOTE=Peter Morris] One disadvantage that I can see is that such a thing would be an easy target for terrorist attack. A few explosives at key points could sink the whole thing, and how can you police the entire length of the tube? [/QUOTE] Any suspension bridge could be vulnerable from such a coordinated attack. And regular immersed tube tunnel (sunk to the bed and then drained) are also vulnerable. Most civil engineering projects could be objected to on the ‘what about terrorism?’ stance. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [January 20, 2007, 7:57pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/12 "2007-01-20T19:57:38Z")
[QUOTE=chela] There are structures that are Bridge/Tunnels (fixed yet). There is the Monitor MerrimacMemorial Bridge Tunnel in VA., and the Oresund Bridge tunnel connecting Denmark and Sweden. [/QUOTE] But they’re just a regular bridge followed by a regular tunnel. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [January 20, 2007, 8:05pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/13 "2007-01-20T20:05:33Z")
Of course, the other problem is keeping millions of pounds of water pressure from crushing the thing, and preventing earthquakes from tearing the thing open. Big structures like bridges actually move a lot. They sway in the wind or current, they expand and contract when the temperature changes, they move when the ground moves. Look at even small bridges and you can see expansion joints made to absorb dimensional changes from heating an cooling. Now imagine a bridge miles long, that has to expand and contract as water temperature changes, with immense amounts of water pressure all around it. Good luck with that. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [January 20, 2007, 8:47pm UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/14 "2007-01-20T20:47:55Z")
[thread=363441]Here’s[/thread] a previous discussion on the technical merits and difficulties of a transAtlantic tunnel. In general, building structures in the ocean is much more complicated that you might think. As anyone familiar with the engineering and maintenance of marine structures knows, Poseidon likes to beat the living shit out of anything in his domain. Stranger ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [January 21, 2007, 12:49am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/15 "2007-01-21T00:49:03Z")
There was a show on the Discovery Channel about this. The summary is that the only reasonable way to use this tunnel would be a very high velocity train. Those are normally not compatible with a flexible, swaying track. The problem is not insurmountable but it is most definitely not trivial. There is people working on it. We will see. ---
**Author:** ![Captain\_Carrot](https://avatars.discourse-cdn.com/v4/letter/c/f0a364/32.png) [@Captain\_Carrot](https://boards.straightdope.com/u/Captain_Carrot)\ **Post date:** [January 21, 2007, 1:07am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/16 "2007-01-21T01:07:39Z")
> [@Peter Morris](#): > > Put your tunnel in a submerged tube, boats can go over it with no problem. That’s only true if the tube is quite deep and/or the boats have shallow keels. Many seagoing vessels are very large and require a lot of space to navigate. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [January 21, 2007, 1:17am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/17 "2007-01-21T01:17:57Z")
A variant of the proposed device is already in service. One example of which I am aware is a tunnel beneath the Detroit River connecting Detroit and Windsor. It is not identical to the proposal. Instead of tunneling beneath the river, they formed the tunnel out of pre-welded steel tubes, floated them out to the correct spot on barges, then lowered them beneath the water. In order to avoid impeding river traffic, they dug a trench across the river bottom so that they would not have the roadway sticking up into the channel, then threw mud on top of the tunnel to protect it from water currents. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [January 21, 2007, 1:45am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/18 "2007-01-21T01:45:00Z")
[QUOTE=tomndebb] A variant of the proposed device is already in service. One example of which I am aware is a tunnel beneath the Detroit River connecting Detroit and Windsor. It is not identical to the proposal. [/QUOTE] That’s the kind I mentioned earlier. There’s loads in use, including on the New York subway and BART. It’s completely different to the OP’s suggestion of deep-water anchored tubes. ---
**Author:** ![Sublight](https://avatars.discourse-cdn.com/v4/letter/s/439d5e/32.png) [@Sublight](https://boards.straightdope.com/u/Sublight)\ **Post date:** [January 21, 2007, 2:48am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/19 "2007-01-21T02:48:11Z")
**Sam Stone** brings up another good point: temperature change. Up in the air, it’s easy to put spacers to handle expansion and contraction. Underground, there’s not so much temperature variation in the surrounding earth. Suspended in water, you need some way to handle changes while still maintaining a watertight space. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [January 21, 2007, 5:22am UTC](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704/20 "2007-01-21T05:22:14Z")
[QUOTE=Captain Carrot] That’s only true if the tube is quite deep and/or the boats have shallow keels. Many seagoing vessels are very large and require a lot of space to navigate. [/QUOTE] How deep? 50 feet in the OP, is that deep enough? How 'bout 100 feet? 200? [Next page](https://boards.straightdope.com/t/wheres-all-the-submerged-bridges/388704.md?page=2)