Mumbai Metro Line 4: first Thane section now due in December 2026

Lire en français : Métro de Mumbai : Alstom sort la première des 39 rames de la ligne 4

The first 10.5 km of Mumbai Metro Line 4, between Gaimukh and Cadbury Junction in Thane, is now due to open in December 2026, Maharashtra's transport minister says, later than the Diwali target set in August. Alstom's 39 driverless trains should carry passengers from August 2027.

Transport Minister Pratap Sarnaik gave the December date on 27 October, Swarajya reported. Two months earlier, the Mumbai Metropolitan Region Development Authority (MMRDA) had said it expected services to start around Diwali or by the end of 2026, subject to the remaining safety approvals, according to the Free Press Journal.

Line 4 and its extension 4A form an elevated corridor from Wadala in central Mumbai through Kasarvadavali to Gaimukh in Thane, which Alstom puts at 35.3 km with 32 stations. Larsen & Toubro holds the integrated systems contract, and Alstom will supply 39 Metropolis trainsets of six cars, its Urbalis Forward CBTC signalling at the driverless GoA4 level and five years of maintenance, the company announced on 26 August 2025. It put the contract at a few hundred million euros.

An earlier version of this article said trials would begin in September 2025 and that a first section would open in February 2026. Neither happened; the contract had only just been signed in August 2025.

Certification step by step

The first section has cleared several hurdles. The Research Designs and Standards Organisation certified it on 2 June 2026 after tests of speed, signalling, safety systems, rolling stock and track. Rolling stock for the opening phase was then cleared at the end of August, Swarajya reported, and the Commissioner of Metro Rail Safety inspected the pit line at Gaimukh. The final CMRS approval is the remaining step.

That pit line is a stopgap. The main Line 4 depot is not finished, so MMRDA built a facility with four tracks at Gaimukh for stabling, inspection and routine maintenance. Six trains are planned for the first phase. They will not be the new Alstom units: MMRDA intends to start with trains from its other metro lines, Alstom India's Champak Panda told PTI, as reported by PSU Watch.

Alstom's first train due in December

Alstom unveiled the first Line 4 trainset at its Sri City plant in Andhra Pradesh on 14 October. The company says it built it in 14 months. The train is designed for 90 km/h, with an operating speed of 80 km/h, and has wheelchair spaces and bicycle racks. Panda said it would ship at the end of November and reach Mumbai in the first or second week of December, after three to four more weeks of signalling integration and validation.

Running borrowed trains on a line built for driverless operation is the delicate part. Each train must carry onboard equipment that talks to the line's CBTC system, or the service has to start in a slower, lower-capacity mode until the full fleet arrives. Alstom supplying both the trains and the signalling for the final fleet removes one interface, but not for the opening months.

Once in Mumbai, the first Alstom train faces runs up to 90 km/h, braking and ride tests, then certification by RDSO and the CMRS. Our French edition covered the rollout of the first trainset, and Alstom is building the same Metropolis family for Hanoi's metro. The next milestone is the CMRS approval that would let the Gaimukh–Cadbury Junction section open.

Sources: Alstom press release (26/08/2025); Railway-News, from Alstom (16/10/2026); PSU Watch (14/10/2026); Free Press Journal (23/08/2026); Swarajya (30/08/2026); Swarajya (27/10/2026).

Photo: an Alstom Metropolis train on Mumbai Metro Line 3, from the same family as the Line 4 trains, November 2025. Rupturestriker, CC0 1.0, via Wikimedia Commons.

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