Assam Mail
The Assam Mail was one of the better known metre-gauge trains in the Indian Railways system that was there from the pre-independence days. The train was discontinued in 1986 with the completion of the broad-gauge conversion of the metre-gauge line to Dibrugarh. 3 Up/ 4 Dn

Popularly known as 3 Up/ 4 Dn (Kalka Mail was 1 Up/ 2 Dn), it originally ran in the pre-independence days from , now in Bangladesh, to Guwahati. It travelled along the Santahar–Kaunia line up to Kaunia, then to  along Parbatipur–Lalmonirhat–Burimari line, crossing the Teesta. Thereafter, it took the now-defunct – route crossing the Dharla over the bridge, part of which has since been washed away, on to ,  and Amingaon covering  in 14 hrs 00 mins at speed of . Passengers to and from Kolkata and the rest of India traveled between Kolkata and Santahar by broad-gauge Darjeeling Mail or some other connection and then switched over to metre-gauge Assam Mail. Post Independence

After independence and partition of India in 1947, the train travel to Assam stopped temporarily (possibly till 1957). When Assam Link Project connected  to  Assam Mail started running along the Katihar–Siliguri line. It needed a loco reversal at  and traveled along what is now the New Jalpaiguri–Alipurduar–Samuktala Road line. Assam Mail was converted into a two part train. It ran from  to  (after Rajendra Setu and Saraighat Bridge came up), with the broad gauge part running up to Barauni from where the metre gauge part continued up to Dibrugarh. Passengers had to get down at Barauni and change trains. The metre gauge part of the Assam Mail from Barauni to Dibrugarh covered . It was one of the longer metre gauge runs in the country, running across the flood plains of the Kosi, the Dooars, Western Assam and finally Upper Assam. In 1986, when the Barauni–Guwahati line was converted into broad gauge the Assam Mail was renamed as the North East Express. The new Superfast train North East Express was introduced via Kanpur, Patna, Barauni, , Fakiragram Junction, covering  between  & Guwahati in 33 hrs 15 mins at speed of . 