The first lap was a 185 km journey along the Eastern Bengal State Railway from Calcutta Station (later renamed Sealdah) to Damookdeah Ghat on the southern bank of the Padma River, then across the river in a ferry and the second lap of the journey, which was a 336 km metre gauge line of the North Bengal Railway that linked Saraghat on the northern bank of the Padma to Siliguri.

[2] In 1926 the metre-gauge section north of the bridge was converted to broad gauge, and so the entire Calcutta - Siliguri route became broad-gauge.

North Bengal State Railway opened a metre gauge line to Kaunia in 1879.

Two narrow gauge lines were laid by Eastern Bengal Railway from Kaunia to Dharla River.

The Assam Behar State Railway started building westward in 1884 and by 1889, Parbatipur was connected with Katihar in Bihar.