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What is " GAUGE " ?








　　　　In accordance with Oxford Dictionary, " GAUGE" is defined as distance between rails on a railway. For easy understanding, I clasify a railway gauge into four categories below.

(1) Standard Gauge

　　　　Standard Gauge is generally considered as 4'8.5" (1435mm), which,I heard, was calculated on the average of distance between wheels of the cart.In railway history,the various gauges from 4'1" to 5'6" had been tried to take as a standard. And today this 4'8.5" (1435mm) gauge is adopted by major railway firms around the world. Japan Railway also has chosen it for the Shinkansen (high-speed) Line.
　　　　In Japan, some of private company railways adopt 4'8.5" (1435mm) and some of tram cars run on rails of 4'6" (1372mm) gauge, while the gauge of Japan Railway except Shinkansen is 3'6"(1067mm). Such diversity of railway gauge is resulted from historical context.
　　　　As a British heritage railway of a standard gauge operated on a large scale, "Severn Valley Railway" is well known .

(2) Over Narrow Gauge

　　　　This "Over Narrow" is not all accepted as one of railway technical terms.However,I have to hesitate to call 3'6" (1067mm) a narrow gauge. By same reason,I wish to include 3' (914mm) gauge and metre gauge (1000mm) into this category.Please remind yourselves of big haulers in Japan Railway (3'6"gauge) or Denver & Rio Grande Western Railroad(3'gauge )*.
*　N O T E
Main line of Denver & Rio Grande Western Railroad is laid through the mountainous area of Colorado in U.S.A.,which means that its locomotive needs strong haulage. So the structure of its frame is very much specialized in order to have a high-powered i.e.large-sized locomotive run on the rails of the comparatively narrow gauge(3'). That is called "Outside Frame". A frame of almost all steam locomotives is installed inside of driving-wheels. However, the frame of DRGW's locomotive is installed outside of them !! As a result,its rods are attached to not driving wheels but counter-weights outside of the frame. Can you imagine such a strange structure?
The counter-weights are specialized parts for "Outside Frame". See the below animation marked in red.

(3) Narrow Gauge

　　　　Generally speaking of Narrow Gauge Railway, its distance is seemed to be less than 3'6" (1067mm).However I wish to give a definition to Narrow Gague as less than 2'6"(762mm), since 3' or 3'6" gauge is beyond my concept to a narrow gauge. As for me a narrow gauge railway is a synonym for a tiny light-railway.
　　　　There is not a little advantage in narrow gauge railway. It is constructed and operated at low cost.It is able to run on a narrow edge of steep mountain and through a sharp slalom or a small tunnel. Then a lot of them were built in mountainous terrain for astbestos and timber or for sightseeing into creek,valley,lake and forest around the national park. Especially in Wales,there were laid a lot of light railways from seaside to mine or valley. To our regret, not all of them are preserved as a heritage.

(4) 15" gauge

　　　　There seems to be somewhat a difference between the typical narrow gauge above and this one. Generally 15" (38mm) gauge railway was built as a MINIATURE of a standard gauge not only for the tourist but also for the public transportation at the local area where it would have been totally uneconomical to provide a standard gauge line. Among these 15" gauge railways,"Romney Hythe and Dymchurch Railway" and "Ravenglass and Eskdale Railway" are well known.




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