Every night, in slum clusters strung along Delhi's railway lines, families fall asleep to the same sound: a freight train thundering past at nearly 100 decibels, almost double what India's Central Pollution Control Board (CPCB) considers safe for a residential area.

For years, this was treated as an unavoidable cost of living close to the tracks.

Now, a growing body of research led by scientists at Delhi Technological University (DTU) is measuring exactly how loud, how frequent, and how disruptive that exposure really is, and what could be done to make life safer for the millions of Indians who live beside railway corridors.

What the numbers reveal

The first clear signal came in 2024, when a DTU team led by Rajeev Kumar Mishra, an associate professor of environmental science and engineering, measured noise at 10 sites near Delhi's railway stations. Every location exceeded CPCB limits, and disturbed sleep emerged as the most common complaint among residents surveyed.

A follow-up study in 2025, conducted with the CSIR-Central Road Research Institute, went further, monitoring 1,057 train pass-bys across 14 informal settlements. Noise levels breached residential standards at every single site, in some cases by as much as 85%. 

Freight trains proved the loudest offenders, averaging around 100 decibels, while diesel locomotives were consistently louder than electric ones.

For context, the World Health Organization's environmental noise guidelines recommend railway exposure stay below 54 dB during the day and 44 dB at night, slightly stricter than CPCB's residential limits of 55 dB and 45 dB. 

Even by India's own standards, the DTU data suggests entire neighbourhoods are living with repeated exposure well outside recommended levels, night after night.

What prolonged noise exposure does to the body

Numbers on a decibel meter only tell part of the story. The WHO’s 2018 Environmental Noise Guidelines for Europe links long-term noise exposure to disturbed sleep, cardiovascular and metabolic disease, cognitive impairment in children, and adverse effects on mental health. 

Nocturnal noise, even when it doesn’t fully wake someone, can fragment sleep and trigger stress hormones, the research says. That, in turn, is linked to elevated blood pressure,........

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