- BG - Broad Gauge
- SG - Standard Gauge
- MG - Metre Gauge
- NG - Narrow 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.
Unique rail Gauges
- Nalhati-Azimganj Railway, the original name for the Indian Branch Railway; used a unique 4ft(1222cmmm) gauge.
- Arakkonam-Conjeeveram Tramway, absorbed into the Indian Tramway Co. was a 3'6"(1067mm) gauge line which opened in 1865.
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.