The Howrah-Chennai trunk route runs along India's eastern seaboard and links the mineral and industrial belt of eastern India with the ports and manufacturing clusters of the south. It carries heavy passenger traffic alongside bulk freight - coal, iron ore, cement and foodgrains - and several of its sections have been running at or beyond capacity. Three of the four approved projects (Kharagpur-Bhadrak, Bhadrak-Haridaspur and Gummidipundi-Gudur) sit on this corridor, and their completion finishes its quadrupling. The fourth, Cuttack-Paradeep, feeds Paradip port in Odisha, tying port-bound cargo into the same upgraded spine.

Capacity, not speed, is the binding constraint on Indian freight. A saturated corridor forces freight trains to be held in loops while passenger services pass, which lengthens transit times and pushes shippers towards road haulage - the reason the railways' freight modal share has fallen over decades. Adding third and fourth lines to an existing high-density route is the cheapest way to reverse that, and the 76 million tonnes of additional annual capacity claimed for these four projects is the direct measure of the gain. For the exam, the link worth holding on to is the one between a Cabinet approval of this kind and the National Rail Plan's 45% freight modal share target: the approvals are the instalments in which that target is paid for.