With high-speed trains, much of the friction comes from air resistance. So how about running the trains in tunnels with the air sucked out? To maintain the vacuum, airlocks would close behind the train and open in front of the train as moves.

There would have to be emergency air-pressurization procedures for passenger cars, or perhaps it could be cargo only.

Would be geared for long range trains - would be too hard to maintain the vacuum with subways because of all the stops.
-- ootleman, Jan 13 2003

Maglev trains in Evacuated Tunnels http://faculty.wash...s/itrans/suppes.htm
Lots of math, references to actual patents [krelnik, Oct 17 2004]

Swissmetro http://www.swissmetro.com/
Under development in Switzerland! [krelnik, Oct 17 2004]

Transatlantic train travel http://www.readersd...magazine/travel.htm
More of a fun read than other references to the same thing [Trouvere, Oct 17 2004]

Evacuated Tube Transport Technologies (et3) http://www.et3.com
very low cost $2m/mile; the ETT portal site; active projects [et3dotcom, Oct 17 2004]

hyperloop http://www.teslamotors.com/blog/hyperloop
[xaviergisz, Aug 13 2013]

Rather than multiple airlocks, perhaps it'd be more efficient to leave the entire tube evacuated and have a special port for passenger to come and go.

It'd also have to be a beefy tunnel to take the 14.7 psi pressure imbalance (over 2000 lb/sqft.) I'll let you do the cost analysis. ;)
-- lumpy, Jan 13 2003


If the air was evacuated from the tunnel, but only in front of the train, and if a seal could be maintained between the train and the walls of the tunnel, then not only would there be no air resistance, it would also provide motive power from of the pressure difference. (+)
-- 2 fries shy of a happy meal, Jan 13 2003


A surprising amount of research has been done on running maglev trains through evacuated tunnels, mainly because maglev really starts to get efficient at speeds that are only practical in evacuated tunnels. See link.

He concludes that if you ran the system at 0.2 atmospheres (no worse than a commercial jet experiences), it would cost US $10 Millon per mile to build the infrastructure and you could go 300 MPH.
-- krelnik, Jan 13 2003


Sounds expensive, perhaps the trains could create the vacuum themselves. A bit like a track in the bush that is kept clear through regular use.

The tube would contain valves that allow pressurized air infront of the train out as it moves down the tube. The more vaccum the higher the train speeds the more air is evacuated etc etc.
-- madness, Jan 14 2003


We've done this one several times. It is also the stuff of Wibnis since at least the last couple of centuries.
-- DrCurry, Jan 14 2003


Crikey, I remember this from a children's technology book in the 70's. Made a comparison regarding Concorde and the limitations of speed.

The same book described satellite phones and GPS. It's obviously less practical to make a long vacuum tunnel than launch a vast array of electronics into geostationary orbit.
-- FloridaManatee, Jan 14 2003


If a train's window got broken all of the passengers eyes would pop out from the negative pressure.
-- jvanzand, Jun 17 2003


Quite why a train running entirely in a depressurised tunnel would need windows is well beyond me.
-- dfol, Jun 27 2003


There is no reason to use train size vehicles in the tunnels. The preferred vehicle size is well proven – it is the automobile. A 1200lb vehicle is much less costly to build, operate and maintain. The structural cost for the tube guideway structure is less than 5% of the cost of a tube capable of accommodating 200 ton trains, and is faster to build using off the shelf parts. Windows and transparent tubes are simulated with external cameras and LCD display “virtual window” with a choice of visual stimulus. The risk is much less than automobile, train or aircraft since there are no moving parts, the vehicles are automated (like an elevator), and the inside of the tube is immune to bad weather, and free from errant animals, children, or cars. Visit http://www.et3.com to learn more about ETT.
-- et3dotcom, Jul 07 2003


But if we evacuated the entire tunnel, would it float? (dodges fishbones)
-- Worldgineer, Jul 07 2003


The question of if floating the tubes (when moored at the surface or at any depth) is the strength of materials and the load to support. The stress is determined by the depth, so tubes designed for great depth would not be capable of floating. if you do a search on “submerged floating tunnels”, you will find detailed information as their was a conference a couple years ago on the subject, and several companies are involved.
-- et3dotcom, Jul 07 2003


I guess I deserved that.

[et3], just wanted to mention my admiration of halfbaked-to-baked entrepreneurs such as yourself.
-- Worldgineer, Jul 07 2003


the vacuum would also serve to reduce sound, A maglev unit might be entirely unnoticable while passing.
-- davidcreede, Jul 21 2003


Why don't you place a huge pump in train (ah... like a jet), that sucks air in at the front, and blasts it out the back? Wouldn't this be just as good?

You wouldn't need a jet powerful enough to push the train of course, just to move that amount of air from the front to rear (via a tube all way underneith it)?

I reckon you'd be surprised at what small power requirements that might need.
-- raintonr, Oct 24 2003


TLC did a fromtiers of construction show about this exact topic. In the show the made an evacuated tunnel that went from NY to London. The figured the train could go some ridiculous speed like 3500 km/h and get to London in just over an hour.

In the show they were pretty indepth about all the problems it would encounter, if you are really interested you should go to TLC.com and find the exaxt show.
-- SystemAdmin, Oct 24 2003


I wish I could give more than one bun! I came here to post this very same idea. By my math, the money spent in the wars in Iraq and Afghanistan could have funded such a project from New York to Los Angeles. With magnetic levitation, this idea would make Chuck Yeager jealous. Hell, with enough speed, you could go into sea-level orbit!
-- kevinthenerd, Jun 22 2008


Didn't Robert Heinlein talk about this in his story 'The Roads Must Roll'?
-- Moonguy, Jun 23 2008


My father's Naval Acadamy class - circa 1954 - used this as a practical exercise to determine if a train moving through a tunnel under vacuum could make it from NY to London without any propulsion.
-- phoenix, Jun 24 2008


//'The Roads Must Roll'// that was about 'conveyor belt' roads, thus the 'rolling roads'.
-- FlyingToaster, Jun 24 2008


Musk's been at it, numerous unmentioned problems, but still: <link>
-- bs0u0155, Aug 13 2013


yeah I read that yesterday; I was gonna link it to my own "Hydrogen Tunnel" post but [xavier] beat me to it.

Gotta admit that's an interesting (and I think new) take on it: depressurize to 1/1000 bar, use an electric-powered ducted fan to move and air-bearings for lift.
-- FlyingToaster, Aug 13 2013



random, halfbakery