Namma Metro reduces length of underground stations by 40 meters in Phase 3A to save money

Length reduced from 210m to 170m, cost slashed by Rs 2,920 crore to Rs 25,485 crore

Bengaluru: Namma Metro's Phase 3A will feature underground stations 40 metres shorter than planned after authorities slashed the overall estimated cost by Rs 2,920 crore, according to two senior officials with direct knowledge of the matter.

Also called the Red Line, this 36.59-km corridor will connect Sarjapur in the southeast to Hebbal in the north via the CBD. Its tentative deadline is 2031.

In December 2024, the Karnataka cabinet approved Phase 3A’s Detailed Project Report (DPR), which had estimated the overall cost at Rs 28,405 crore, or Rs 776.3 crore per km, the most expensive in Namma Metro's history.

However, when the DPR was sent to the Ministry of Housing and Urban Affairs (MoHUA) for approval, it found the cost "significantly higher" than benchmark norms.

The DPR had based the cost of Phase 3A's 14.44-km underground section on the Pink Line, which is currently under construction. The ministry asked Bangalore Metro Rail Corporation Limited (BMRCL) to appoint an independent consultant to reassess and reduce the cost, DH reported in June.

The BMRCL appointed French multinational consultancy Systra to reassess the cost estimates. The company submitted its draft report recently, and the ministry is currently reviewing it.

A senior BMRCL official privy to the deliberations told DH that the cost variation was due to three specific components: per-kilometre tunnelling, length of underground stations, and Electrical and Mechanical (E&M) works.

While tunnelling cost and station length had the major variation, the difference in the cost of E&M works was minor — only a couple of crores of rupees.

The major dispute focused on tunnelling costs.

The BMRCL’s original estimate was Rs 300 crore per kilometre [using the Last Accepted Rate (LAR) for 2024]. However, MoHUA’s benchmark was substantially lower: Rs 125 crore in 2019 and Rs 159 crore in 2024.

According to the official, tunnelling through Bengaluru's soil strata is challenging because it changes every 25-30 metres. "There just cannot be a uniform benchmark cost for all cities because of the fundamental difference in soil strata," he pointed out.

The consultant looked at metro systems in Chennai and other cities, and suggested optimisation. Accordingly, the length of underground stations has been reduced from 210 metres to 170 metres. This was done by optimising operational rooms located on both ends of the platform, the official explained.

"Reducing the length of underground stations was challenging because they require controlled environments," the official explained. "Since the platform length is required to be only 135 metres for a six-coach train, there is not going to be any major change for commuters."

Some existing underground stations on the Namma Metro network are only 190 metres long. After the optimisation, the tunnelling cost has been reduced to Rs 210 crore per kilometre. This will lead to reduced costs of land and all other components, the official added.

The official clarified that there will be no change in alignment and other systems.

"The consultant is still discussing the draft report with the ministry, which is also looking at metro systems in other cities. The ministry will now decide whether to approve Phase 3A with the reduced cost or seek further optimisation," the official added.

He declined to specify whether the ministry would approve the DPR by the end of this year.

Although Phase 3A construction will begin only after the ministry's approval comes through, the BMRCL is set to begin preliminary work in the next few months.

In early October, it floated tenders worth Rs 6.86 crore to carry out geotechnical investigations in four packages. November 3 is the last date for submitting the bids. Contractors will have 150 days from the award date to complete the work.

The geotechnical investigation is the first stage of groundwork for building a metro line. It involves examining the physical properties of soil and rocks to determine the depth and design of foundations — for piers in the case of elevated sections and for tunnels in the case of underground stretches.

The study also helps identify the type of Tunnel Boring Machines (TBMs) needed for tunnelling and enables contractors to estimate construction costs, another senior BMRCL official said.

BMRCL officials say that the state government's approval in December 2024 allows them to carry out preliminary works such as geotechnical investigations and utility identification.

Phase 3A will run underground from Koramangala 2nd Block through the CBD. It will feature double-deck viaduct (metro-cum-road) in the overground sections: Sarjapur to Iblur (14 km) and Agara to Koramangala 3rd Block (2.45 km).

Phase 3A’s alignment is roughly the same as the proposed tunnel road, which will run from Silk Board Junction to Hebbal.

The first official said the two projects would not cross anywhere until Hebbal, where necessary changes have already been made.