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CNOSSOS-EU explained: what it is, what it replaced, and who has to use it

Industry Standards · SoundPLAN Asia · · 9 min read

CNOSSOS-EU stands for Common Noise Assessment Methods in Europe. It is the calculation framework that European strategic noise maps must now be produced with, and it turns up increasingly often in specifications outside Europe because it is documented, harmonised and reproducible. It is also widely half-understood, so it is worth setting out exactly what it is, what legal instrument created it, and where its boundaries lie.

The legal chain, in order

Three instruments matter, and they stack:

  1. Directive 2002/49/EC, the Environmental Noise Directive - usually shortened to the END. This is the parent legislation. It requires Member States to produce strategic noise maps and, following them, noise action plans.
  2. Commission Directive (EU) 2015/996. Article 1 is a single sentence: Annex II to Directive 2002/49/EC is replaced by the text set out in the Annex to this Directive. That replacement text is CNOSSOS-EU. Article 2 required Member States to bring the necessary provisions into force by 31 December 2018 at the latest.
  3. Commission Delegated Directive (EU) 2021/1226. This amended Annex II again to reflect technical progress - clarified propagation formulas, updated tables, and improvements to the road, railway, aircraft and industrial source descriptions, including curve squeal on rail and the determination of aircraft noise event levels. Transposition deadline: 31 December 2021.

So "CNOSSOS-EU" today means Annex II as amended in 2021, not the 2015 text and not the earlier JRC research reports that carry the same name. If a specification simply says "CNOSSOS-EU", it is worth asking which version, because the source models changed.

What triggers a strategic noise map

The END does not require everybody to map everything. The thresholds are specific:

  • Agglomerations with more than 100,000 inhabitants
  • Major roads carrying more than 3 million vehicles per year
  • Major railways carrying more than 30,000 trains per year
  • Major airports with more than 50,000 movements per year, counting take-offs and landings

Maps and action plans are produced and published on a five-year cycle.

The point most people miss about the END

The Environmental Noise Directive sets no binding European limit values. It harmonises how noise is assessed, how it is reported and how exposure is counted. It leaves the question of what level is acceptable, and what must be done about it, to the Member States through their action plans.

This matters when a specification outside Europe cites CNOSSOS-EU. Citing the method tells you how to calculate. It tells you nothing about the criterion you have to meet. Those are two separate decisions and a project needs both of them written down.

What CNOSSOS-EU actually contains

This is where it differs most sharply from the standard most engineers in this region use daily. ISO 9613-2 is a propagation method: you bring your own sound power levels, it tells you what arrives at the receiver. CNOSSOS-EU is both. It specifies:

  • Source models for road traffic, railway traffic, industrial plant and aircraft - how to turn traffic flows, train types, plant inventories and flight movements into emission terms in the first place
  • A propagation method covering geometrical divergence, atmospheric absorption, ground effect, diffraction and reflection
  • The treatment of meteorology, through favourable and homogeneous propagation conditions combined by occurrence probability, rather than a single worst-case assumption
  • The receiver rules - assessment points on facades, and how exposure is attributed to dwellings and people

That last item is the reason CNOSSOS-EU produces a population exposure dataset rather than just contours, and it is why a CNOSSOS model needs a building and population layer that an ISO 9613-2 industrial model does not.

CNOSSOS-EU or ISO 9613-2?

Pick by the question, not by preference:

  • Site-specific industrial assessment - a plant permit, an expansion, an EIA noise chapter for a single facility. ISO 9613-2 is normally what the authority expects, and its assumptions and validity limits are worth knowing.
  • City or corridor-scale exposure mapping, particularly where results must be comparable with other authorities. CNOSSOS-EU, because the harmonised source models are the whole point.
  • Both, which is increasingly common - an industrial assessment whose results feed a wider strategic map. Running the two methods on one model is straightforward; reconciling two models built by different consultants on different methods is not.

Practical notes for projects outside Europe

Specifiers across Asia and the Gulf reference CNOSSOS-EU for good reasons - it is public, versioned and does not depend on a national method a foreign reviewer cannot obtain. Three things to settle before the work starts:

  1. Which version. 2015/996 as amended by 2021/1226 is the current one. Say so explicitly in the methodology section.
  2. Which criterion. CNOSSOS gives you Lden and Lnight; the project or the regulator must supply the acceptable values.
  3. Whether the input data exists. CNOSSOS source models expect traffic composition, speeds and road surface categories. If the local traffic data is a single daily total with no vehicle split, that gap governs the accuracy of the whole map, and it is better identified at scoping than at review.

SoundPLAN supports 50+ international calculation standards including ISO 9613-2, CNOSSOS-EU and ISO 9612. If you need to confirm how a particular version or national method is handled before you commit to it, ask us - we would rather answer that before a purchase than after.

Strategic noise mapping · The full standards list · Turning a noise map into decisions

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