Kosi Mahasetu

The Kosi Mahasetu (Kosi Bridge) is a 1.62 km rail-cum-road bridge spanning the Kosi river between Nirmali and Saraigarh in Bihar's Mithila region. The project's significance is historical as much as engineering: the bridge restores a rail link that was severed by the 1934 Bihar–Nepal earthquake, which destroyed the original Kosi rail bridge and forced 86 years of detours through Mansi-Saharsa-Forbesganj.

IRCON International executed the bridge between 2003 and 2020 at ₹510 crore. The 17-year construction window was extended by chronic Kosi river course-shifts (the river is famously 'Bihar's sorrow' for its frequent channel migration) and funding gaps. Foundation works were rebuilt twice as the river shifted course mid-construction.

Inaugurated by Prime Minister Modi on 18 September 2020, the bridge connects Mithila — historically one of Bihar's most economically isolated regions — to the Bihar plains rail grid. Travel between Nirmali and Saraigarh dropped from 6 hours (via the Mansi detour) to 6 minutes by direct rail.

The bridge handles broad-gauge passenger + freight rail on the lower deck and a 2-lane road on the upper deck. Design accounts for the Kosi's seasonal flood discharge of 8 lakh cusecs and Zone V seismic exposure.