Mumbai explores 11 tunnels amid surface constraints

The city began to change in the late 1990s when a large number of flyovers came to dominate the surrounding area. Today's flyovers are at maximum length due to the city's restriction on horizontal expansion and the fast rising vehicle density. Because the city is filled with bridges and elevated metro corridors, planners believe that subterranean construction is a feasible alternative for both road corridors and metro projects, despite the associated costs. Currently, the Mumbai Metropolitan Region (MMR) is home to at least 11 tunnel-based projects in various stages of development, ranging from east-west corridors to rail systems like the metro and bullet train. One of the city's first subterranean mass transit projects, the Metro 3 underground corridor (Colaba-Bandra-Seepz), is almost complete. Final touches are being applied to the nation's first underwater twin tunnels, which are a part of the Mumbai Coastal Road project. Work on the bullet train tunnel and Metro Line 7A (Andheri to domestic airport) is ongoing. Authorities have also invited tenders for four of the nine underpasses on the Western Express Highway (WEH) and Eastern Express Highway (EEH) for grade separation projects. Finally, contractors have been selected for three east-west tunnel-based road corridors.