For calculating strategic noise exposure maps, environmental impact assessments (EIA), and modeling noise mitigation measures in Flanders, the Dutch Standard Calculation Method II (SRM II) or, since 2021, the European calculation method CNOSSOS-EU for noise exposure maps is used. Both methods incorporate the acoustic properties of road surfaces through specific correction terms. These terms are crucial for advice on potential road surfacing measures, as they determine the influence of the road surface on sound emission and significantly impact calculation results and recommendations.
The most recent and correct acoustic road surface correction terms are essential. As road surface types vary by country, specific Flemish road surface correction terms have been developed based on CPX (noise emission) measurements on the most common Flemish road surfaces. The figures show an evolution: the terms were originally determined in 2016, updated for NGCS in 2022, and in 2026, a new update followed after an extensive CPX measurement campaign in 2025.
In 2016, the acoustic reference spectrum was based on in-house CPX measurements on SMA-C of various ages. Since 2025, the technical specification CEN/TS 18194:2025 includes a reference spectrum based on CPX measurements from several European countries, including Belgium, on SMA11 and DAC11 surfaces. The global CPX level at 80 km/h is 99.0 dB(A), with an associated spectrum and speed-dependent term h.
Subsequently, for each road surface type, the global correction term, the correction term per octave band, and the speed index bm (for SRM II) or coefficient m (for CNOSSOS-EU) were determined. Table 2 provides an overview of these global and spectral acoustic road surface correction terms at 80 km/h relative to the reference road surface, along with the speed index bm. These values are useful for acoustic modeling with SRM II and for providing advice.
Based on the correction terms at 80 km/h and the speed term bm, the acoustic road surface correction terms at 70 km/h are calculated. These values, presented in Table 3, can be used in calculations with CNOSSOS-EU. Due to insufficient measurement data for heavy vehicles, these values can also be temporarily applied as correction terms for heavy traffic at a reference speed of 70 km/h in both SRM II and CNOSSOS-EU.
The current correction terms, background information, and reports can be found in the report “Acoustic Road Surface Correction Terms 2026”. Historical correction terms are available in the document or on the page regarding the acoustic road surface correction terms from 2016.
