<P> Historically, many narrow - gauge railways were built as part of specific industrial enterprises and were primarily industrial railways rather than general carriers . Some common uses for these industrial narrow - gauge railways were mining, logging, construction, tunnelling, quarrying, and the conveying of agricultural products . Extensive narrow - gauge networks were constructed in many parts of the world for these purposes . For example, mountain logging operations in the 19th century often used narrow - gauge railways to transport logs from mill sites to market . Significant sugarcane railways still operate in Cuba, Fiji, Java, the Philippines, and Queensland . Narrow - gauge railway equipment remains in common use for the construction of tunnels . </P> <P> Extensive narrow - gauge railway systems served the front - line trenches of both sides in World War I. They were a short - lived military application, and after the end of the war, the surplus equipment from these created a small boom in narrow - gauge railway building in Europe . </P> <P> Narrow - gauge railways usually cost less to build because they are usually lighter in construction, using smaller cars and locomotives (smaller loading gauge), as well as smaller bridges, smaller tunnels (smaller structure gauge) and tighter curves . Narrow gauge is thus often used in mountainous terrain, where the savings in civil engineering work can be substantial . It is also used in sparsely populated areas where the potential demand is too low for broader gauge railways to be economically viable . This is the case in some of Australia and most of Southern Africa, where extremely poor soils have led to population densities too low for standard gauge to be viable . </P> <P> For temporary railways that will be removed after short - term use, such as for construction, the logging industry, the mining industry, or large - scale construction projects, especially in confined spaces, such as the Channel Tunnel, a narrow - gauge railway is substantially cheaper and easier to install and remove . The use of such railways has almost vanished due to the capabilities of modern trucks . </P>

Which of the gauges is used by railway in the hilly areas