The Darjeeling line was built to a gauge of 2 feet (600mm) to enable the line to traverse the tightly twisting route through the hills. In 1886, though, the well tanks and under cylinder wings were retained, a narrow saddle tank was inserted between the dome and the chimney, partly to get increased water capacity and partly to get better balance between the axle loads with the pull on the draw bar. Regarding the Official opening date of Darjeeling Himalayan Railway (DHR) are, from Siliguri to Kurseong is 23-08-1880, from Kurseong to Sonada 01-08-1881, Sonada to Jorebunglow 05-04-1881, Jorebunglow to Darjeeling 04-07-1881 and from Darjeeling to Darjeeling Bazar is 16-06-1886. Usually the construction stage, light engines are worked on the section much before the official date of opening.
The Ghoom Station is the highest point reached by the railway (7,407ft), and from here there is a descent for four miles down a spur to Darjeeling Station (6,812ft). Loops are the speciality of Darjeeling Himalayan Railway it helps in gaining height for the rail line skiting along the mountain with the radius of curve as minimum as possible. Loop No. 3 at Chunbhati km 23/14 between Rangtong and Chunbhati station is popularly known as Loop No.2 and technically it is the first loop now. This loop is double circle. Loop at Agony Point km.32 was between Tindharia and Gayabari stations existed and is popularly known as Loop no.3, though it is the second loop. The last loop near Batasia, popularly known as “Batasia Loop” is km.75/1. This loop is the most beautiful loop out of the existing loops. There are 132 unmanned level crossings in the route.
Most of the steam engines in these days have been replaced by diesel electric or electric traction. Some narrow gauge lines still feature the old “iron horses”.DHR is a work of genius and technological achievement of 1881. It has social and cultural importance. It is beautiful and has out-standing universal appeal. As one of the outcomes of the Industrial revolution and based on its unique features, it is considered to be of lasting significance to mankind. It must be saved for posterity. These are all the criteria necessary for World Heritage.
National Rail Museum (India), the focus of India’s Rail heritage, submitted a proposal to UNESCO on 29th June 1998 for inscribing the Darjeeling Himalayan Railway (DHR) as a World HERITAGE Site. Accordingly, UNESCO’S World Heritage Committee inscribed DHR as a World Heritage Site on 2nd December 1999. The DHR has popularly known by the name as ‘Toy Train’ which is in fact was never an official term it is just a popular expression found in literature.