Indian railways uses four gauges:
The 1,676 mm (5 ft 6 in) broad gauge which is wider than the 1,435 mm (4 ft 8 1â„2 in) standard gauge; the 1,000 mm (3 ft 3 3â„8 in) metre gauge; and two narrow gauges, 762 mm (2 ft 6 in) and 610 mm (2 ft).
Track sections are rated for speeds ranging from 75 to 160 km/h (47 to 99 mph).
The total length of track used by Indian Railways is about 115,000 km (71,000 mi) while the total route length of the network is 65,000 km (40,000 mi). About 23,541 km (14,628 mi) or 36% of the route-kilometre was electrified as on 31 March 2013.
Broad gauge is the predominant gauge used by Indian Railways. Indian broad gauge—1,676 mm (5 ft 6 in)—is the most widely used gauge in India with 105,000 km (65,000 mi) of track length (91% of entire track length of all the gauges) and 56,000 km (35,000 mi) of route-kilometre (86% of entire route-kilometre of all the gauges).
In some regions with less traffic, the metre gauge (1,000 mm/​3 ft 3 3â„8 in) is common, although the Unigauge project is in progress to convert all tracks to broad gauge. The metre gauge has about 8,000 km (5,000 mi) of track length (7% of entire track length of all the gauges) and 7,000 km (4,300 mi) of route-kilometre (10% of entire route-kilometre of all the gauges).
The Narrow gauges are present on a few routes, lying in hilly terrains and in some erstwhile private railways (on cost considerations), which are usually difficult to convert to broad gauge. Narrow gauges have 2,000 route-kilometre. The Kalka-Shimla Railway, the Kangra Valley Railway and the Darjeeling Himalayan Railway are three notable hill lines that use narrow gauge, but the Nilgiri Mountain Railway is a metre gauge track. These four rail lines will not be converted under the Unigauge project.
The share of broad gauge in the total route-kilometre has been steadily rising, increasing from 47% (25,258 route-km) in 1951 to 86% in 2012 whereas the share of metre gauge has declined from 45% (24,185 route-km) to 10% in the same period and the share of narrow gauges has decreased from 8% to 3%.
About 21,500 route-km of Indian railways is electrified.
Sleepers (ties) are made up of prestressed concrete, or steel or cast iron posts, though teak sleepers are still in use on a few older lines. The prestressed concrete sleeper is in wide use today. Metal sleepers were extensively used before the advent of concrete sleepers.
Indian Railways divides the country into four zones on the basis of the range of track temperature. The greatest temperature variations occur in Rajasthan.
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