India's First Road-Rail Underwater Tunnel Under Brahmaputra: All You Need to Know

India's first underwater road-cum-rail tunnel is set to be built beneath the Brahmaputra river, connecting Gohpur and Numaligarh in Assam — a project that has drawn in the Ministry of Defence as a stakeholder due to its significant strategic value for the country.

The Union Cabinet approved the project in February, clearing the way for what will be an unprecedented piece of infrastructure in India's history.

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The 33.7-km tunnel was originally conceived as a road-only project, with the Detailed Project Report (DPR) prepared on that basis. However, a policy decision at the highest level of the central government — taken after consultations with the Ministry of Defence — changed its character entirely.

The MoD proposed converting it into a Twin Tube Underwater Road Rail Tunnel, citing the project's strategic importance for national security and border connectivity. With that, the MoD became a formal stakeholder in the project.

The total capital cost of the project is Rs 18,662.02 crore, shared between the Ministry of Road Transport and Highways (MoRTH) and the Ministry of Defence in an 80:20 ratio.

The Assam government will additionally contribute 50% of the State GST on the construction cost, amounting to Rs 539 crore.

The construction cost of the tunnel itself — excluding approach roads — is Rs 11,982.36 crore, with a construction period estimated at five years.

The tunnel will run 15.79 km beneath the Brahmaputra, with approach roads stretching a further 17.91 km. It will comprise twin tubes, each carrying a 2-lane highway. One of the tubes will additionally carry a rail facility, to be used only during emergencies and exigencies. In normal times, the full 4-lane road facility will be operational.

Cross passages will be provided between the two tubes every 500 metres for safety. The tunnel will sit between 52 and 57 metres — roughly 170 to 187 feet — beneath the riverbed.

On the railway side, the tunnel will connect the Rangia-Mukongselek Railway Section under the Rangia Division of Northeast Frontier Railway on the Gohpur side, and the Furkating-Mariani loop line section under the Tinsukia Division on the Numaligarh side.

The most striking aspect of the project is the transformation it will bring to travel times in the region. The current road distance between Gohpur and Numaligarh is 240 km, taking approximately six hours to cover.

The tunnel will reduce that to just 34 km, with a travel time of around 20 minutes — an increase in average speed of 100%.

The tunnel's benefits extend well beyond Gohpur and Numaligarh. It will offer an alternative route that bypasses Kaziranga National Park, protecting both the environment and the park's wildlife from increased road traffic pressure.

Connectivity between Nagaland's Dimapur and Arunachal Pradesh's Itanagar will also improve significantly — the existing distance of 260 km will be reduced to approximately 170 km, cutting travel time and opening faster access to Arunachal Pradesh.

The project is also expected to generate 80 lakh human-days of employment and provide a boost to tourism across the Northeast, while improving overall logistics efficiency in a region that has long been constrained by geography.