Night Noise and Sleep: What the WHO Says

The World Health Organization recommends keeping night-time road traffic noise below 45 dB Lnight outside the bedroom — and rail noise below 44 dB— because above those levels, population studies show measurable effects on sleep. England's official night noise maps don't even start reporting until 50 dB. That gap is worth understanding before you read any noise map, including ours: a postcode with no mapped night noise is not necessarily meeting the WHO guideline.

What is Lnight, exactly?

Lnight is the average sound level across the 8-hour night (23:00–07:00), averaged again over a whole year, modelled at the outside of a building façade. Every word of that definition matters. It is an outdoor figure — your bedroom with windows closed will be much quieter (ordinary double glazing cuts roughly 25–30 dB). It is an average— a night punctuated by one freight train an hour can share an Lnight with a steady hum, and the freight train wakes you where the hum doesn't. And in England's case it is modelled, not measured: the figures come from DEFRA's Strategic Noise Mapping Round 4 (2022), a computer model of major roads and railways — here's how that model works.

What does the WHO actually recommend?

Two documents matter, and they get conflated:

• WHO Night Noise Guidelines for Europe (2009) set a long-term target of 40 dB Lnight outside — roughly a quiet library — with 55 dBas an interim target for countries that can't achieve 40 dB yet. Below 30 dB, no substantial effects on sleep are observed; between 40 and 55 dB, effects on sleep appear and vulnerable groups (children, shift workers, the chronically ill, older people) are less able to protect themselves.
• WHO Environmental Noise Guidelines for the European Region (2018) — the current evidence review — make source-specific recommendations: road traffic below 45 dB Lnight, railway below 44 dB, aircraft below 40 dB. These are graded as "strong recommendations", meaning the panel judged the evidence for adverse sleep effects above these levels to be of sufficient quality to act on.

What does night noise actually do to sleep?

The clearest, best-evidenced effect is sleep fragmentation. Noise events — a lorry, a train pass — trigger arousals: brief shifts to lighter sleep stages, heart-rate spikes and body movements, most of which you never remember. Polysomnography studies show these reactions persist even in people who say they've "got used to" the noise; habituation is real but partial. The morning-after signature is reduced deep and REM sleep, more reported tiredness, and — in surveys — higher annoyance and use of sleeping medication in exposed populations.

Beyond sleep itself, long-term studies associate chronic exposure to high night-time transport noise with raised risks of hypertension and ischaemic heart disease. The proposed mechanism is plausible — repeated stress-hormone activation during sleep — but a caution is due here: these are associations from observational studies. They cannot fully rule out confounding (busy roads correlate with air pollution and deprivation), and the individual-level risk increase at moderate levels is small. The honest reading of the evidence: chronic night noise above the guideline values is a genuine public-health burden across a population, and a meaningful quality-of-life issue for the people at the top of the exposure range — not a reason for panic at 48 dB.

How England's night noise maps relate to the guidelines

England's strategic maps report Lnight in 5 dB bands starting at 50.0–54.9 dB. Everything below 50 dB — including the whole 40–50 dB range where the WHO says effects on sleep begin — is simply not reported. So when a postcode search on this site shows no mapped night noise, the correct reading is: the model puts this location below 50 dB from major roads and railways — quieter than the reported bands, but not certified WHO-compliant, and local sources the model ignores (minor roads, neighbours, venues) can still disturb sleep. Any mapped night band at all — 50 dB and up — is already above the 2018 guideline values.

Practical advice for sleeping through it

• Move the bedroom. The quiet side of the same house can be 10 dB+ lower — the single most effective step, and free.
• Windows: closed and upgraded beats open and hopeful. Secondary glazing over the existing window is the strongest retrofit for traffic noise, paired with acoustic trickle vents or a fresh-air unit so you can keep windows shut without stuffiness — full options and costs here.
• Mask intermittent noise. Arousals are triggered by the change in level, not the level itself. Steady broadband sound (a fan, a white-noise machine) raises the floor so events poke through less. Cheap and surprisingly effective for rail noise.
• Earplugs work if they fit. Well-fitted foam or moulded plugs attenuate 20 dB+. Takes a week or two to sleep comfortably in them.
• Track it before you spend. A phone sound-meter app on the bedside table overnight is not laboratory-grade, but it will show you the pattern — steady hum vs. 3am events — and that determines which fix to buy.

What to do next

• Check your postcode's night noise band — Lnight is shown separately for road and rail on every result.
• Moving or buying? Read checking noise levels before buying a house — and visit after 22:00 before you commit.
• Want the dB scale calibrated to real life first? Decibel levels explained.