The longest rail tunnel in the world is Japan’s Seikan tunnel which is 53.9 km long, located beneath Tsugaru Strait and connects Hokkaido Island with Aomori Prefecture. Its surveying commenced by 24 April 1946 and its construction by 28 September 1971. This tunnel was opened on 13 March 1988. Such a tunnel is now in India!
Boring of India’s first underwater rail tunnel running under the Hooghly river connecting Howrah and Kolkata got completed on 23 May 2017 before its scheduled deadline of July. Its final commissioning is scheduled by December 2019. Its initial deadline was 2012 which was first postponed to 2015. The companies responsible for the construction are Afcons Transtonnelstroy and Kolkata Metro Railway Corporation Ltd. The machine Rachna was used to dig it.
The total length of the entire project is 16.6 km, out of which 10.8 km runs under ground. Of this, 502 meters is under water. The stretch of 16.6 km will have 12 stations, 6 of which are underground and 6 are on elevated tracks. The total project costs 750 million USD ( about 500 crore INR) The operation was delayed several times due to land allocation, slum relocation, route alignment problems and so on..