The Delhi Metro Rail Corporation (DMRC) has successfully completed an underground tunnel between Chhatarpur Mandir and IGNOU Station as part of the Golden Line corridor under its ambitious Phase 4 expansion. This 1,475-m -long tunnel, constructed using a 97-m-long Tunnel Boring Machine (TBM), marks a significant breakthrough in connecting Tughlakabad and Aerocity. Engineering Feat and Challenges The tunnel, designed for parallel circular tunnels for up and down movement, was built at an average depth of 26 m, reaching a maximum depth of 36 metres at some points. Featuring 1,048 tunnel rings with an inner diameter of 5.8 metres, this segment stands as one of Delhi Metro’s deepest underground passages. Constructed using the Earth Pressure Balancing Method (EPBM), the tunnel components were manufactured at a mechanised casting yard in Mundka and steam-cured to accelerate strength development. The tunnelling operation, which began on December 4, 2023, overcame challenging geological conditions, including steep gradients, mica, and hard rock formations. Notably, damage to the screw auger necessitated its replacement during construction, adding complexity to the project. Phase 4 Expansion and Future Prospects As part of Phase 4, DMRC is developing 40.109 km of underground lines, with the Aerocity-Tughlakabad corridor spanning 19.343 km. This expansion will enhance connectivity, reduce congestion, and improve public transport infrastructure in Delhi NCR. Industry and Market Outlook The Delhi Metro’s Phase 4 expansion underscores the increasing investment in urban transit projects, reflecting India’s commitment to sustainable and efficient mass transport. As more Indian cities embrace metro networks, the demand for advanced tunnelling technologies, urban rail infrastructure, and smart mobility solutions will continue to rise. With metro projects playing a crucial role in urban development, initiatives like the Golden Line are expected to boost real estate values, commercial activity, and overall urban efficiency in the coming years.