|Operator(s)||East Central Railway, Northeast Frontier Railway|
|Line length||804 km (500 mi)|
|Track gauge||1,676 mm (5 ft 6 in) Broad gauge|
|Operating speed||110 km/h|
The 804 km (500 mi) long trunk line, been treated in more detail in smaller sections:
The earliest railway tracks in Assam were laid in the Dibrugarh area in 1882 for the transportation of tea and coal. The first passenger railway was also in that area.
Linking Guwahati was the challenge. In response to the demands of tea planters in Assam for a rail link to Chittagong port, the Assam Bengal Railway started construction of a railway track on the eastern side of Bengal in 1891. A 150 km (93 mi) track between Chittagong and Comilla was opened to traffic in 1895. The Comilla–Akhaura–Kulaura–Badarpur section was opened in 1896–1898 and finally extended to Lumding in 1903. The Assam Bengal Railway constructed a branch line to Guwahati, connecting the city to the eastern line in 1900.
During the period 1884–1889, Assam Behar State Railway linked Parbatipur, now in Bangladesh, with Katihar in Bihar. North Bengal State Railway had opened a metre gauge line from Parbatipur and the line subsequently got extended beyond the Teesta, and through Geetaldaha to Golokganj in Assam. During the 1900–1910 period, the Eastern Bengal Railway built the Golakganj–Amingaon branch line, thus connecting the western bank of the Brahmaputra to Bihar and the rest of India. Katihar got linked to Barauni around the turn of the century.
With the partition of India railways in Assam got delinked from those in the rest of India. Indian Railway took up the Assam Link project in 1948 to build a rail link between Fakiragram and Kishanganj. Fakiragram was connected to the Indian railway system in 1950 through the Indian portion of North Bengal with a metre gauge track. The New Jalpaiguri–New Bongaigaon section was partly new construction, partly old line converted to broad gauge in 1966. Broad gauge reached Guwahati in 1984.
The 3.19 kilometres (1.98 mi) long rail-cum-road bridge located at Munger 55 km downstream of the Rajendra Setu, links Jamalpur station on the Sahibganj Loop line of Eastern Railway to the Barauni–Katihar section of East Central Railway.
The 2,240 m (7,350 ft) long Farakka Barrage carries a rail-cum-road bridge across the Ganges. The rail bridge was thrown open to the public in 1971, thereby linking Kolkata with North Bengal and Assam.
The construction of the 1.49 km (0.93 mi) long Saraighat Bridge, the first rail-cum-road bridge across the Brahmaputra, was an event of great excitement. Jawaharlal Nehru, India’s first prime minister formally laid the foundation stone on 10 January 1960 and it was completed in 1962, connecting the two parts of the metre gauge railways in Assam.