Many commuters in Indian metros wonder: why does the mobile signal vanish once the train goes underground? The answer lies in basic physics plus regulatory, technical, and commercial challenges. Concrete, steel and soil all severely block or weaken radio-frequency signals used by mobile networks. Unless there are dedicated systems inside tunnels and stations - like signal boosters, distributed antenna systems (DAS) or in-building solutions (IBS) - phones will struggle to get a connection. 

India has been trying to fix this. Cities like Chennai, Pune and Lucknow-Kanpur are deploying IBS or signal boosters in underground stretches. For example, BSNL has tied up with ACES India to provide uninterrupted 4G in the underground sections of Kanpur, Lucknow and Agra.

But the problem persists in many metro systems. Often, commercial terms between metro authorities, telecom operators and neutral providers stall implementation. In Mumbai’s Line 3, operators have complained that the rates from the neutral host provider are “unviable,” leading to signal shutdowns.

In short: yes, progress is being made - in parts of India - but the problem is far from fully solved.