Chennai's underground expansion: a 26-kilometer artery beneath the city

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: The Yellow Line represents a massive engineering shift for Chennai, moving beyond surface-level transit into deep subterranean infrastructure. Stretching over 16 miles, this corridor is designed to weave through the urban fabric, balancing elevated tracks with significant underground segments to redefine how millions navigate the metropolitan landscape.

The Yellow Line (also known as Line 4) is a cornerstone of Chennai Metro's Phase II expansion. Spanning 26.1 km between Lighthouse and Poonamallee Bypass, the project features a complex mix of infrastructure: 18 stations will be at grade or elevated, while nine are planned underground. This structural diversity reflects an effort to balance accessibility with the geographical constraints of an expanding city. Interestingly, the corridor's identity shifted recently, with its color code officially changing from Orange to Yellow in 2025.

The project is part of a broader second phase announced by the Government of Tamil Nadu in July 2016, which originally envisioned three lines totaling 104 km. The specific trajectory for Line 4 was refined in 2017 to include an extension from Lighthouse toward Poonamallee, featuring an intersection with the Madhavaram–Sholinganallur line at Alwarthirunagar. While earlier designs suggested 30 stations, a revised plan announced by CMRL in May 2023 solidified the current count at 27 stations.

Financing this massive undertaking involves significant international and domestic investment. A total of ₹632.46 billion (US$6.6 billion) is projected for stage two, including a starting ₹47.1 billion (US$490 million) credit from Japan International Cooperation Agency. Construction officially commenced in November 2020, with Alstom awarded the contract for metro coaches in late 2022. The line is currently slated to begin operations on specific stretches by October 2026, coinciding with a planned visit from Prime Minister Narendra Modi.

Looking ahead, the corridor's reach is already being debated. In June 2025, the state government approved a proposal to extend the fourth line an additional 52.9 km toward Parandur in two phases. This ambitious expansion would eventually connect Poonamallee Bypass to Sunguvarchatram and then further to Parandur, while another eastward extension from Lighthouse to High Court remains in the planning stages.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• How Chennai is building a massive, multi-modal transit network to transform urban mobility
• India's first elevated railway line took over three decades to reach its final destination
• Mumbai's Green Line Metro: A Massive Infrastructure Project Spanning 60 Kilometers of Elevated Rail
• The ₹30,000 crore underground artery reshaping Mumbai's transit landscape
• The engineering of Pune's elevated lifeline: the Pink Line
• How a party for Russian immigrants became a kingmaker in Israeli politics
• How a 1990s Ahmedabad romance became a defining television hit for modern Indian audiences
• Yogyakarta’s name borrows Rama’s city of Ayodhya
• The architect of Maharashtra and the leader who held India's four most vital portfolios
• Yokohama grew from a sandbar fishing village overnight
• Yaoundé began as a German rubber and ivory post
• The 1999 merger that fractured a city’s football identity

More in Cities · More in Countries & Cities · Latest · A–Z · All topics