While researching the Japanese ancestry of EMD locomotive engines, I came across information about a most interesting concept which I had first heard about in a college physics class ages ago. Thanks to the modern internet, I have rediscovered this information and also learned that an operational tunnel was actually built, which continues in operation to this day. A most interesting story, if you don't mind bending the category of "real trains" to include a form of transit that travels along a guided corridor, in this case a very long tunnel.
http://www.idlewords.com/2007/...n_burrito_tunnel.htm
Somebody must have consumed some serious chemical mixtures in order have written that article. I had great fun in reading it though. Thanks for posting it.