Back to the original OP, the two preserved civil war locomotives the General and the Texas (from the 1862 Andrews raid, the prototype of the Disney movie The Great Locomotive Chase) were originally built in New Jersey, sent to the Western and Atlantic railroad in Georgia where they ran on the 5 foot rails for a number of years. They got narrowed to the 4’ 8.5" gauge later in life, the General made a tour for the centennial of the raid in 1962. I have pictures of me leaning on the cab side during that tour, I was in grade school then and a train nut.
I dunno about that, but I have read that since long wheelbase steam locomotives are no longer a factor, some roads have tightened up to 4’ 8" It reduces a phenomena called hunting where the truck veers back and forth a smidge.
In the 1956 film version of Round The World In Eighty Days, when the characters are traveling by train through the western U.S., we see several exterior shots of the track where there is an “inner” rail between the two rails at standard gauge–as if there were supposed to have been another kind of train that used maybe a three-foot gauge. Although all this was probably filmed indoors on a sound stage, to me it’s always looked as if it was authentically filmed outside using the real tracks of a working railroad. (Except of course the part where the engineer smokes his pipe while waiting for the buffaloes to pass by–that’s obviously fake.)
Was there ever such an inner rail on the early Transcontinental Railroad? Were there narrow-gauge trains, or was it used for something else.
I seem to recall reading that the US train sequences in …In Eighty Days were filmed on the, then still active for everyday traffic, 3ft. gauge section of the Denver & Rio Grande Western Railroad, in Colorado / New Mexico (a couple of bits of same still running today as “tourist / heritage rail”). A stretch of this part of the D&RGWR at its eastern end, was dual-gauge (4ft. 8-and-a-half, and 3ft.) – possibly the filming was done on this part of the line.
I also remember reading that the film-makers – for reasons which no doubt seemed good to them – used for the sequences, an elderly non-functional steam loco which was preserved at some point on the 3ft. gauge system; the train was actually hauled by the system’s only 3ft. gauge diesel loco (which was apparently disliked by the line’s conservative operating staff), disguised as a coach or boxcar and marshalled in the train, immediately behind the “dead” steam loco.