Rail gauge in India is complicated by historical usage of multiple track gauges. Indian Railways

Indian Railways

Indian Railways , abbreviated as IR , is a departmental undertaking of Government of India, which owns and operates most of India's rail transport. It is overseen by the Ministry of Railways of the Government of India....

 uses four: Broad Gauge

Broad gauge

Broad-gauge railways use a track gauge greater than the standard gauge of .- List :For list see: List of broad gauges, by gauge and country- History :...

 (BG), which is also called Indian gauge

Indian gauge

Indian gauge is a track gauge commonly used in India, Pakistan, Bangladesh, Sri Lanka, Argentina and Chile. It is also the gauge that is used on BART , in northern California.- Scotland :...

, Metre Gauge

Metre gauge

Metre gauge refers to narrow gauge railways and tramways with a track gauge of . In some African, American and Asian countries it is the main gauge. In Europe it has been used for local railways in France, Germany, and Belgium, most of which were closed down in mid 20th century. Only in Switzerland...

 (MG), Narrow Gauge (NG), and Narrow Gauge.

Project Unigauge

Project Unigauge

Project Unigauge is an ongoing exercise by Indian Railways to standardise most of the rail gauges in India at 1676 mm broad gauge....

 seeks to standardise the rail gauges in India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 by converting most of the MG and NG tracks to BG track. Some NG tracks on which heritage trains run in hilly regions (Simla

Simla

-Politics/History:Simla , the summer capital of British India, often refers generically to the government of the British Raj.-Places:* Shimla , city in the Indian state of Himachal Pradesh...

, Darjeeling, Ooty, Kangra

Kangra district

Kangra is the most populous district of the state of Himachal Pradesh, India. Dharamsala is the administrative headquarters of the district.-Geography:Kangra district of Himachal Pradesh is situated in Western Himalayas between 31°2 to...

, and Matheran

Matheran

- Getting to Matheran :Matheran is located about 100 km from Mumbai, 120 km from Pune. and 320 km from Surat. It lies on the busy Mumbai-Pune rail link and the nearest train station is at Neral, approximately 11 km from Matheran. From Neral, one can either rent a taxi to the...

) will not be converted.

Delhi Metro Rail Corporation has constructed Standard Gauge

Standard gauge

The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

 (SG) in Delhi

Delhi

Delhi , officially National Capital Territory of Delhi , is the largest metropolis by area and the second-largest by population in India, next to Mumbai. It is the eighth largest metropolis in the world by population with 16,753,265 inhabitants in the Territory at the 2011 Census...

 and started running metro trains in Delhi city in 2010. However, Delhi Metro is a separate urban mass rapid transit

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 system not owned by Indian Railways.

Overview

BG is the most widely used rail gauge in India with approximately 102000 km (63,380 mi) of track length and 54600 km (33,927 mi) of route length in 2011. In some regions MG is common for historical reasons and consists of 7500 km (4,660 mi) of route length. Narrow gauges are present on a few routes lying in hilly terrains and in some private railways because of cost considerations. Narrow gauges covered a total of 2400 km (1,491 mi) route length in 2011.

Nilgiri Mountain Railway

Nilgiri Mountain Railway

The Nilgiri Mountain Railway is a railway in Tamil Nadu, India, built by the British in 1908, and was initially operated by the Madras Railway Company. The railway still relies on its fleet of steam locomotives. NMR comes under the jurisdiction of the newly formed Salem Division...

, Darjeeling Himalayan Railway

Darjeeling Himalayan Railway

The Darjeeling Himalayan Railway, nicknamed the "Toy Train", is a narrow gauge railway from New Jalpaiguri to Darjeeling in West Bengal, run by the Indian Railways....

, Kalka-Shimla Railway

Kalka-Shimla Railway

The Kalka–Shimla Railway is a narrow gauge railway in North-West India travelling along a mostly mountainous route from Kalka to Shimla. It is known for breathtaking views of the hills and surrounding villages.- History :...

, Kangra Valley Railway

Kangra Valley Railway

The Kangra Valley Railway lies in the sub-Himalayan region and covers a distance of . from Pathankot to Jogindernagar. The Kangra valley railway comes under the Firozpur division of Northern Railway...

, and Matheran

Matheran

- Getting to Matheran :Matheran is located about 100 km from Mumbai, 120 km from Pune. and 320 km from Surat. It lies on the busy Mumbai-Pune rail link and the nearest train station is at Neral, approximately 11 km from Matheran. From Neral, one can either rent a taxi to the...

 Hill Railway are notable hill lines that use NG.

Broad Gauge

The Governor-General of India

Governor-General of India

The Governor-General of India was the head of the British administration in India, and later, after Indian independence, the representative of the monarch and de facto head of state. The office was created in 1773, with the title of Governor-General of the Presidency of Fort William...

 in the 1850s chose BG for India rather than the SG. The two main reasons given were greater stability during periods of high wind and unpredictable weather and greater space between the wheels for bigger inside cylinders (although this ceased to be a problem when outside cylinders were introduced).

The inability to source standard equipment was not seen to be a problem or was overlooked. The extra cost of longer sleepers was not considered to be a problem, though later the cost saving of shorter sleepers with MG was considered to be an advantage.

Standard Gauge

Small lengths of SG have existed in India for individual projects and short line lengths. The only surviving example was the Kolkata (Calcutta) tram system

Calcutta Tramways Company

The Calcutta Tramways Company Limited is a West Bengal, India government-run company which runs trams in Kolkata and buses in and around Kolkata...

 until 2010 when Delhi Metro Rail Corporation started metro train on 18.5 km-long SG track on Mundka-Inderlok-Kirti Nagar sections and on Central Secretariat-Badarpur sections.

Metre Gauge

In the 1880s, when the BG tracks had been laid over some routes, another Governor-General considered the introduction of infill MG lines to reduce the cost.

Narrow Gauge

Narrow gauges are present on a few routes lying in hilly terrains and in some private railways because of cost considerations. Narrow gauges covered a total of 2400 km (1,491 mi) route length in 2011.
NG railway tracks were constructed for cost considerations, and because simpler engineering permitting sharp turns in hilly regions. The argument was that if money could be saved building MG, then presumably more money could be saved by building NG. The design process during construction was taken to its extreme, with the gauge being carefully chosen to optimise costs for the traffic offering. The result being that each line might be a different gauge, even if it would have been more useful to have a through service.