which of the gauges is used by railway in the hilly areas
Narrow-gauge railway 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.