Hammocks isolate their contents from jiggling. Trains jiggle and have room for hammocks, especially if you don't mind whacking the walls or other hammocks. Since collisions are apparently desirable (see bumper cars and US thoroughfares), we might enjoy closely packed hanging harnesses. I tried hanging from the ceiling pole on the subway the other day, and it was great fun swinging about, especially when leaving the station. Does anyone think that the synchronized oscillation of masses inside the train could pose an instability hazard?-- Ketchupybread, Jul 13 2011 <Pedant> The locomotive does the pulling. The word you want is train. Some modern passenger trains don't have locomotives at all.-- spidermother, Jul 13 2011 Baked. People have been traveling in hammocks on trains since the Crimean War (1st recorded instance), if not longer. Super-Baked. (ref: _Engines of War_, by Christian Wolmar, Public Affairs Books, pub.)
And no, the "synchronized oscillation of masses" would not cause problems. Think about cattle cars or, for that matter, troop trains during the Crimean War.
Better luck next time.-- Alterother, Jul 13 2011 random, halfbakery