India, Nov. 5 -- Bolstered by the completion of the 33.5-km-long underground metro rail corridor between Aarey Colony and Cuffe Parade, also called the Aqua Line metro, efforts are on to link various parts of the Mumbai Metropolitan Region (MMR) through underground tunnels. These include the 10.25-km Thane-Borivali twin tunnel passing beneath the Sanjay Gandhi National Park (SGNP), a 21-km tunnel linking the BKC bullet train station to Shilphata in Navi Mumbai, a 6.5-km tunnel between Orange Gate and Marine Drive in south Mumbai, and a 16-km tunnel connecting the end of the Coastal Road at Worli with terminal two of the Chhatrapati Shivaji Maharaj International Airport (CSMIA) via the BKC bullet train station.

At the heart of these tunne...