kcsivils Wrote:
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> But why were some lines built to gauges of 3'6"
> versus meter gauge or 3 ft?
>
> Why 30 inches instead of two feet or three feet?
>
> Where there actual engineering reasons for these
> decisions?
>
> Could it be political or military?
>
> Or did it come down to the whim of the engineer
> who designed the railroad?
In some cases track gauge was chosen politically. This was often the case in Britain in the early days, where many of the railway acts authorizing construction required a 56.5 inch track gauge, as well as in Russia (later) with its 5 foot gauge. Sometimes the gauge was chosen on a whim by the engineer in charge of building a given railroad. This may have incorporated valid engineering concerns, or for cost considerations, or in some cases for reasons lost to history. Track gauges much narrower than Stephenson's gauge were impractical in the early days due to the construction methods of the time. Cars with inside bearings and high centers of gravity tended to get "tippy" once they approached about twice the track gauge. Yes, the Ffestiniog with its ~2 foot gauge appeared during the 1830's, but it was a horse-powered industrial route and didn't have steam power or haul people until significantly later. By the early to mid 1860's development had made narrower track gauges increasingly viable and interest soon took off.
The specific gauge used by narrow gauge railways, again, varied. The U.S. favored 3 feet mostly because that was what the first significant U.S. narrow gauge railroad (Palmer's D&RG) settled on after concluding 2 foot was too limited. Metric-using countries tended to use 1 metre gauge for obvious reasons. India ended up adopting metre gauge, in spite of using imperial measurements at the time, simply because the local engineers decided that a gauge very nearly equal to 1 metre was the narrowest practical for 4-wide passenger seating. Britain for the most part favored 42 inch gauge as its narrow gauge of choice. Given usual construction methods of the time, that was about the narrowest that allowed a 2 foot wide firebox in locomotives (this problem, of course, was soon eliminated through development of construction methods). 42 inch gauge also permitted a potential loading gauge roughly equivalent to what some of the 56.5 inch gauge lines were using anyway, allowing for the same potential loads to be hauled simply at a reduced maximum speed. While narrow gauge railways didn't tend to catch on to a great degree in their home countries due to the pressures of standardization and compatibility, they had a tendency to become the favored local standards in their nations' respective colonies. 42 inch gauge and metre gauge today retain major networks in various countries. 3 foot barely exists on the international scene (mainly in Colombia) because the U.S. relatively limited international presence during that period.
Thirty inch gauge appeared somewhat later as an attempt to maximize on narrow gauge's construction economy whilst maintaining the ability to haul heavy loads--2 foot gauge having been proven to be a bit too limited. The Antofagasta railway linking Bolivia's interior to the coast was the largest and probably most significant of the early 30 inch gauge systems. It hauled substantial tonnage long distances through wretched terrain and eventually converted to metre gauge only due to the pressure of standardization. Nonetheless, 30 inch gauge never really caught on outside industrial or niche application; it appeared only after other track gauges were established nearly everywhere and never quite found a place.
