What most people do not realise is that Standard Gauge railways make up 58% of the world railway route km.
And vastly more track mileage.
1525mm (5 foot) : 14%
1675mm (5ft 6in) : 10%
1067mm (3ft 6in) : 9%
1000mm (metre) : 7%
1600mm (5ft 3") : 1.2%
I think the main thing here is not so much the preponderance at present
of this or that gauge since this is what needs to be explained. Why was the logic of standardisation based on the example of Britain not followed?
Mills argues that in the gauge wars in Australia the "track gauge" became an oversimplification (or to be more precise a false proxy) for the real capital and operational costs of railways as a whole. There was no proper understand of railway economics nor the inclination to make reasonable inquiries.
He quotes from an 1872 minority report of the Queensland Royal Commission as follows:
"The chief causes of difference of cost in railways are really as follows:
1st Heavy works to obtain superior gradients to enable the same power to take greater loads.
2nd Heavy works to obtain curves of large radius for high speeds.
3rd Heavy rails, fastenings and sleepers.
4th Greater dimensions of formation, ballast, drainage etc.
5th Greater strenths of bridges for greater weight and speed.
6th Works for accommodating large traffic at stations.
These and similar works, and not gauge
, cause the vast differences of cost .... "
END QUOTE [emphasis added] (p.180 "The myth of Standard Gauge")
He also sums up two key experiences (not doubt these have been well covered elsewhere in this forum):
1. The British parliament in August 1846 voted for "standardise" the gauges as 1435mm in England, Scotland and Wales AND 1600mm in Ireland primarily because of the predominance of the built railways in the respective regions.
QUOTE: "The mandating of those gauges followed recommendations delivered by the Gauge Royal Commission. This commission probed the relative technical and economic advantages/disadvantages of the 4ft. 81/2in. and 7ft. 0in. gauges. However, its findings on these matters played no part in its recommendation.
Its recommendation to adopt 4ft. 81/2in. as the British standard was justified purely in terms of minimisation of changeover costs - it argued that a change from 7ft. 0in. to 4ft. 81/2in. would inconvenenience fewer people than the reverse change. This recommendation, and its subsequent adoption by Parliament, was thus motivated by political rather than considerations of railway system economies."
END QUOTE [emphasis added] (pp.48-49)
(I would dispute that this is purely a political decision since to minimise adding to the "sunk costs" of the extant railways is surely an economic consideration. The same imperative prevents conversions today.)
2. the economic integration of the North and South in the United States following the civil war compelled the conversion of 13,000 miles of track in the South from 5' to 4'9" over two days in 1886 (with gradual conversion by about 1900 to 4' 8.1/2"). (p.83) The likewise integration of the Australian "colonies" has been compelling the same conversion for the past 150 years but the initial decisions were made on shortsighted decisions by each about what was best for "their colony".
Despite the lead from Britain and warnings about the problems of break-of-gauge, railways around the world "experimented" with different gauges in overlapping systems. Note that the British act was six and a half years before Victorian Lieutenant Governor Latrobe decided on 5'3" against the "recommendation" to follow NSW's change back to 4' 8.1/2". Also worth noting that whereas the British held a Royal Commission BEFORE passing their Act of Parliament the Victorian colony held one AFTER Latrobe's decision had been made. (It is clear from Mills thesis that the "blame the engineers"/Shields vs. Wallace hypothesis is untenable.)
IMHO the world could have easily been dominated by 5' or 5'3" and Australia could have been dominated by 3'6" (a la South Africa). The key advantage in either is having the same gauge.