What is broad gauge ,narrow gauge …

1. Broad gauge:  –The width in case of Broad gauge between two parallel tracks is 1. 676 m . The trains running on a broad gauge has larger carriages. These serve most densely populated districts that are usually fertile. Example: Connectivity between major cities such as Delhi – Mumbai.
2. Metre gauge – A metre gauge railway track has 1000 mm distance between the two parallel tracks which is the standard size for most of the trains worldwide. All the metre gauge lines except the heritage Nilgiri Mountain Railway are being converted to broad gauge as part of Project Unigauge, These are laid in less densely populated districts. Example: districts far from major cities (smaller districts in Rajasthan and Madhya Pradesh).
3. Narrow gauge  – India has two different narrow gauge systems, 2 ft 6 in) (762 mm) and 2 ft(610 mm) Narrow gauge railways are served for sparsely populated districts.
All the narrow gauge lines except heritage lines Kalka–Shimla Railway, Darjeeling Himalayan Railway and Matheran Hill Railway are being converted to broad gauge as part of Project UnigaugeExamples: Hill stations of north east region and ranges of Southern India.