How AcoustaPLOT calculates your noise risk
AcoustaPLOT turns the same national datasets that inform UK planning policy into a clear, plain-English answer — using recognised standards, and honest about the limits of modelled data.
Methodology version: methodology-2026-09-05. If this page changes, this identifier changes with it — quote it if you need to show which version was in force when you bought your report.
The data we use
From your geocoded address we query real ground elevation data (Mapbox's global elevation dataset, sampled along the source-to-property line — falling back to a flat-site assumption for the initial screening estimate, and where elevation data is unavailable for the boundary tool), Defra Strategic Noise Maps (END Round 3, 2022), Department for Transport AADF traffic counts, OS OpenRoads and MasterMap, Network Rail geometry and NATS/CAA flight-path corridors.
Noise Risk Screening
Where your property falls within Defra END coverage we read the modelled road and railway noise bands (our primary source). Elsewhere we calculate the level with the UK Calculation of Road Traffic Noise (CRTN 1988) method applied to DfT data, converted to Lden and Lnight. Defra values take precedence; multiple sources are combined by logarithmic energy addition.
Acoustic Barrier Design (ISO 9613-2)
We extract a terrain cross-section from real elevation data (Mapbox's global elevation dataset, falling back to a flat-site assumption where terrain data is unavailable) along the source-to-property line and compute octave-band attenuation (divergence, atmospheric absorption, ground effect and barrier diffraction) to ISO 9613-2 §7.4. A single-ray calculation that treats the fence as infinitely long — iterating barrier heights 1.0–6.0 m to find the insertion loss at each — is what most published barrier tables use, but it materially overstates the benefit of a real, finite-length domestic garden fence. For the barrier height and return length we actually recommend, we instead integrate along the road as a line source and account for diffraction around the ends of the fence as well as over its top, which is a more realistic model of a garden boundary. The single-ray table is retained on this site only as a reference figure for long, continuous highway-scale schemes, and is never the recommended height for a domestic barrier. We deliberately use ISO 9613-2's own diffraction term (not the older Maekawa nomograph some consultants still use) rather than converting between the two, and where the two diverge our figure does not recommend a lower barrier than the Maekawa convention would — we would rather over-specify a fence than under-specify one.
Declared limitation. The barrier insertion-loss figure has been verified for formula correctness and geometry only. Every case in our validation archive to date is a prediction, not a measurement — we have not yet matched a real barrier's measured before-and-after noise levels to what the model predicted for it. Treat the stated dB reduction as indicative, not guaranteed, until a measured case is found and added to that record.
Risk bands
| Rating | Lden | Lnight | Meaning |
|---|---|---|---|
| LOW | < 45 | < 35 | At or below typical background. No significant impact indicated. |
| LOW-MODERATE | 45–50 | 35–40 | Perceptible but below significant health-effect thresholds. |
| MODERATE | 50–55 | 40–45 | Potential for moderate annoyance; glazing/ventilation relevant. |
| MODERATE-HIGH | 55–60 | 45–50 | Approaching SOAEL; adverse effects on sleep and concentration. |
| HIGH | 60–65 | 50–55 | Within SOAEL; regular disturbance and documented health effects. |
| HIGH-SEVERE | 65–70 | 55–60 | Above SOAEL; significant health effects including cardiovascular risk. |
| SEVERE | ≥ 70 | ≥ 60 | Approaching UAEL; professional survey and mitigation strongly advised. |
Reference thresholds: WHO road-noise guideline 53 dB Lden · SOAEL proxy 63 dB (England, owner-verified) · UAEL proxy 69 dB.
Accuracy & honesty
Estimates carry an explicit uncertainty range: Defra-derived Noise Risk Screening ±3–5 dB, calculated Noise Risk Screening ±5–8 dB, Acoustic Barrier Design ±5–8 dB. Our risk bands are 5 dB wide, so a result near a band boundary may in reality sit in the adjacent band, and a calculated (non-Defra) result can sit further out again — which is why every report states the band and the range together. Like a flood-risk map, AcoustaPLOT is a screening model, not an on-site measurement — where an exact measured figure is needed, a Measured Acoustic Survey survey is the appropriate route.
Standards & references
- ISO 9613-2:1996 — outdoor sound propagation
- Calculation of Road Traffic Noise (CRTN), DoT/Welsh Office, 1988
- WHO Environmental Noise Guidelines for the European Region (2018)
- BS 8233:2014; Noise Policy Statement for England (NPSE, 2010)
- Defra Strategic Noise Mapping (Environmental Noise Directive, Round 3, 2022)