This is one of the elderly mountain railways in the country that was established in the year 1899 by the British government in the India. At first the Nilgiri Mountain Railway was operated by the Madras Railway Company and it depends solely on steam locomotives.
The Nilgiri Mountain Railway has also been added to the UNESCO’s World Heritage Site and soon it came to be known as the "Mountain Railways of India." The gauge of the track is 3 ft 33⁄8 in and it totally separated from other meter gauge tracks in the country. In short it is the only railway in India that runs on 3 ft 33⁄8 in gauge track.
Abt rack and pinion systems are used in this railway that facilitates the train to climb the steep gradients. This system has been installed between Coonoor and Mettupalayam. The steam locomotive that is used in this railway is 'X' Class steam rack locomotives. The locomotives used in Nilgiri Himalayan Railway are made in Switzerland and are manufactured by Swiss Locomotive and Machine Works, which is based in Winterthur.
The gradient of the rack section is 1 in 24.5 and between Udagamandalam and Coonoor the trains are powered by YDM4 Diesel Locomotives by using adhesion traction. From 2007 onwards, there have been some changes in the operation of the NMR. From this year onwards, one train is operated over the rack section in a single day and the destination is Ooty from Mettupalayam.
There has been plan to connect the train to Nilgiri Express that travels to Chennai from Mettupalayam via Coimbatore. In the month of April and May, a summer special train is also from Mettupalayam to Ooty. Four daily trains are there between Coonoor and Udagamandalam in each way.
The locomotives serving the NMR are repaired in Connor shed and the repairing job of carriages is carried out at Mettupalayam.