The Tamil Nadu government has granted in-principle approval for an ambitious infrastructure undertaking that will see the construction of what is set to become India’s longest double-decker viaduct along the Grand Southern Trunk (GST) Road in south Chennai. 
The proposed elevated corridor will extend over approximately 18.4 kilometres, linking the Kalaignar Centenary Bus Terminus (KCBT) at Kilambakkam with Chettipunniyam near Mahindra City. Designed to decongest one of the city’s busiest transport corridors, the structure will feature a six-lane highway on the lower deck and be engineered to support a future metro rail line on the upper deck. 
Officials from the National Highways Authority of India (NHAI) and the Tamil Nadu Highways Department, along with representatives of the Chennai Metro Rail Limited (CMRL), recently finalised the plan during a high-level meeting chaired by Chief Secretary N. Muruganandam. The in-principle go-ahead clears the way for preparation of a revised Detailed Project Report (DPR), which will incorporate metro alignment provisions and modern traffic management solutions. 
Once complete, the viaduct is expected to significantly improve connectivity between Chennai’s suburban areas and the city centre, easing traffic bottlenecks along the GST Road and enhancing commuter experience for both metro and road users. Current metro development plans include expansion from the airport to KCBT, with a further extension proposed towards Chengalpattu after approvals. 
Construction tenders will be invited after regulatory approvals of the DPR are secured. The project aims to set a benchmark in urban transport infrastructure by integrating high-capacity roadways with future-ready mass transit corridors in one elevated structure.