Metro Railway Kolkata has equipped all new trains with a regenerative braking system that turns the traction motors into generators during deceleration. Instead of wasting kinetic energy as heat, each rake feeds electricity back into the grid.

The city now runs 37 such rakes. In 2024-25 they returned about 10.8 million kilowatt-hours to the network, trimming the power bill by roughly Rs 82 million and avoiding an estimated 13 500 tonnes of CO₂. A study by the operator shows the technology can recapture 17–20 per cent of a train’s energy use, mirroring practices in London, Tokyo and New York.

Besides lowering carbon output, regenerative braking lengthens the service life of wheels, brake discs and pads, cutting maintenance costs.

In a further green move, the metro is installing a 4 MW advanced-chemical-cell battery storage system—the first on Indian Railways—which is due to become operational in July 2025.