Chennai is set to host a rare three-level rail corridor, where suburban trains, MRTS services and Metro Rail will operate one above the other, marking a major milestone in the city’s evolving transport landscape.

The Hindu has reported that in the coming years, suburban trains will continue at ground level, the Velachery–St Thomas Mount MRTS line will run above them, and Chennai Metro Rail’s Phase II trains will glide across a second elevated tier.

The MRTS extension from Chennai Beach to St Thomas Mount is nearing completion, with three new stations—Puzhuthivakkam, Adambakkam and St Thomas Mount bringing the corridor closer to seamless multimodal integration.

Meanwhile, Corridor 5 of Chennai Metro Phase II, stretching 47 km from Madhavaram to Sholinganallur, cuts across key neighbourhoods including Anna Nagar, Koyambedu, Alandur and Adambakkam.

A particularly complex section lies between St Thomas Mount and Adambakkam, where the MRTS and Metro networks share a 500-metre elevated alignment, allowing trains from both systems to cross at different levels.

According to T Archunan, Director (Projects), Chennai Metro Rail Limited, the construction of this segment has just been completed.

“Initially, it was decided that Railways will build the viaduct for MRTS and CMRL networks. Then, plans changed. After constructing their viaduct, Railways handed over the work to the CMRL, who built their viaduct on the second level. The work that went behind building this alignment was nothing short of a challenge,” he was quoted as saying by TH.

“Be it building the viaduct over the suburban track or on top of the upcoming MRTS line, we constructed this 500-metre line amid extreme space constraints. It turned out to be a time-consuming process and was carried out by L&T. We had to specially customise and manufacture a light-weight launching girder for building this stretch,” he added.

Construction demanded meticulous planning, including temporary suspension of suburban train services during midnight hours last year, following special approval from the Commissioner of Railway Safety.

“Since cranes couldn’t be deployed for construction over railway tracks, a lightweight launching girder was brought in to erect and place the I-girders (a horizontal support beam). While the launching girders used in the phase II project for placing U-girders weigh nearly 400 tonnes, the one used in the small section was 100 tonnes due to the nature of the work. This was the first time they were used for I-girders,” Archunan added.

Departing from its usual precast method, CMRL adopted on-site construction techniques for this stretch.

“We had to carry out what is known as a ‘cast in-situ portal’ (a structure or frame used in construction), wherein the portals were joined together, piece by piece, at the site. We developed a unique suspended support system in which structural supports were derived from the existing piers of the MRTS network,” he said.