CPX road surface measurements - commitment to research and standardisation pays off

Road noise is significantly influenced by the acoustic properties of road surfaces. In order to record these, G+P introduced the first CPX measurement system in Switzerland in 2008. Almost 15 years of know-how and continuous development of the measurement system, through research and standardisation work, have paid off. Our customers benefit from reliable and robust results with the highest repeatability. For the canton of Fribourg, which is fully committed to “whispering” road surfaces, accurate measurement results are essential for the implementation of its noise protection strategy.

CPX road surface measurements - commitment to research and standardisation pays off
CPX road surface measurements - commitment to research and standardisation pays off
CPX road surface measurements - commitment to research and standardisation pays off

On the track of rolling noises

Since the Federal Council adopted the "National Action Plan to Reduce Noise Pollution" on 28 June 2017, road owners in Switzerland have increasingly opted for low-noise road surfaces. The action plan provides for combating road noise at the source. Quiet road surfaces play a decisive role here. They reduce rolling noise through a very fine surface texture and accessible cavities in the pavement.

Grolimund + Partner AG discovered the potential of so-called “whispering” road surfaces early on. Since 2008, G+P has been assessing the acoustic quality of road surfaces throughout Switzerland with CPX trailer measurements, thus supporting the federal government as well as cities and cantons in the implementation of their noise abatement projects.

CPX measurement vehicle from G+P on a low-noise road surface in Jaun FR. The measuring trailer contains two measuring tyres with two microphones per tyre, which continuously record the rolling noise. In parallel, the air, road surface and tyre temperatures are measured.

The processed measurement data are used in numerous areas of noise protection. For example, cantons and cities use the measurement data in noise calculation models or to set priorities in road maintenance.

The canton of Fribourg relies on whispering road surfaces

As far as the installation of low noise road surfaces is concerned, the canton of Fribourg is among the leaders in Switzerland. 25 percent of the cantonal roads are already equipped with low-noise surfaces. In order to protect people affected by road noise, the canton of Fribourg is going one step further. In the contract with road construction companies, target values are set for acoustic effectiveness. The companies must guarantee a noise reduction of six dB after installation and a reduction of five dB five years after installation.

To verify compliance with these target values, G+P carries out CPX measurements periodically on behalf of the Canton of Fribourg. Since failure to comply with the contractually stipulated noise reduction can have major financial consequences (up to and including replacement of the pavement), the measurements must meet the highest accuracy requirements.

Measurement results with minimal inaccuracies are not only required for checking work contracts, but also for research purposes. To extend the service life of its low-noise pavements, the canton of Fribourg has been carrying out cleaning work on selected test sections for several years. The aim is to keep the surface pores, which are essential for noise reduction, free of dirt ingress.

But when and how often does a whispering road surface need to be cleaned? CPX measurement results provide the basis for a site-specific answer to this question.

Highest accuracy thanks to standardisation work

The requirements for the implementation and evaluation of measurements with the CPX method are defined in the ISO 11819-2 and ISO 11819-3 standards. However, for the so-called acceptance measurements in the canton of Fribourg, the accuracy requirements defined in the standards are too low.

In cooperation with the VSS (Association of Swiss Road Experts), G+P has defined the supplementary requirements for acceptance measurements in the national annex to SN ISO 11819-2. Stricter specifications for the measurement methodology guarantee high repeatability and minimal inaccuracies in the measurements.

The high reliability of the G+P CPX system was confirmed in September 2020 during comparative measurements in the Netherlands. In comparison with seven other CPX measurement systems from Belgium, Germany, Austria and the Netherlands, the G+P measurement results were closest to the reference.

The CPX trailer method allows efficient acoustic measurement of individual streets or entire road networks. The CPX measurement system from G+P is in use almost all over Switzerland. From municipal roads to national roads, everything is there.

The continuous knowledge gained from our daily work flows directly into the improvement of our CPX measurement system. With us, you benefit from particularly robust measurement results, which are suitable for the acoustic recording of individual streets or entire road networks, right up to the testing of contractual criteria.


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