- BG - Broad Gauge
- MG - Metre Gauge
- NG - Narrow Gauge
- SG - Standard Gauge
Broad Gauge (BG)
The first gauge used in India was one of 5' 6" (1676mm), settled upon in the belief that it offered greater stability in the face of Indian weather and the perceived threat of cyclonic winds, and offered economies in freight haulage.
Metre Gauge (MG)
In 1868, a decision was taken to permit the introduction of a smaller gauge in order to increase quickly the construction of railways in India.
Narrow Gauge (NG)
Later, two even narrower gauges (2' and 2' 6") were allowed to be used for feeder lines.
Although this 4 ft 8 1⁄2 in (1,435 mm) gauge was the most usual throughout the world it was not adopted in India. There were two exceptions:-
- Yamuna River, Okhla Canal Construction Tramway used from 1869 to 1874 to build the headworks from the Yamuna River at Okhla. It was Standard Gauge tramway used to carry stone.
- Calcutta Tramways Company adopted the Standard Gauge on its electric tramcars from 1900 onwards, on conversion from the MG horse drawn tram system.
Unique rail Gauges
- Nalhati-Azimganj Railway, the original name for the Indian Branch Railway; constructed in 1863 used a 4ft(1222cm) gauge, later converted to BG.
- Sone Canal Construction Railway/Tramway used a 4ft(1222cm) gauge during the construction 1868-74
- Arakkonam-Conjeevaram Tramway, absorbed into the Indian Tramway Co. was a 3'6"(1067mm) gauge line which opened in 1865, converted in 1878 to MG.
- Chirimiri Colliery Railway used a 3ft 0in(915mm) gauge locomotives operational from 1932.
Following the introduction of the metre gauge, the Government of India(GoI) occasionally allowed existing broad gauge lines to be converted to metre gauge and vice versa where expedient.
Despite four Commissions of Inquiry, the GoI did little te resolve the continuing problem of transhipment wherever there was a break-of-gauge.
Starting about 1980, Indian Railways resolved to convert its legacy of metre and narrow gauge lines to broad gauge standards. This project is ongoing.