ISO/TC 43/SC 1/WG 33 - Measuring method for comparing traffic noise on different road surfaces

This document specifies a method of comparing traffic noise on different road surfaces for various compositions of road traffic for the purpose of evaluating different road surface types. Sound levels representing either light or heavy vehicles at selected speeds are assigned to a certain road surface. The method is applicable to traffic travelling at constant speed, i.e. free-flowing conditions at posted speeds of 50 km/h and upwards. For conditions where traffic is not free flowing, such as at junctions and where the traffic is congested, the method is not applicable. A standard method for comparing the noise characteristics of road surfaces gives road and environment authorities a tool for establishing common practices or limits regarding the use of road surfaces meeting certain noise criteria. However, it is not within the scope of ISO 11819 (all parts) to suggest such criteria. The statistical pass-by (SPB) method is suitable for use for the following main purposes: — to classify road surfaces according to their influence on traffic noise (surface classification); — to assist in verifying conformity of production of road surfaces; — to evaluate acoustic performance of road surfaces throughout operation relative to new condition; — to evaluate the influence of different road surfaces on traffic noise at sites irrespective of condition and service time; — to evaluate acoustic performance of a road surface relative to a reference surface. Due to practical restrictions, the method cannot be applied at all possible locations. However, the backing board method can allow some locations to be tested that were not previously acceptable. Clause 5 gives a general description of the SPB method.

This document describes a test method for measuring in situ the sound absorption coefficient of road surfaces as a function of frequency in the range from 250 Hz to 4 kHz. Normal incidence is assumed. However, the test method can be applied at oblique incidence although with some limitations (see Annex F). The test method is intended for the following applications: — determination of the sound absorption properties of road surfaces in actual use; — comparison of sound absorption design specifications of road surfaces with actual performance data of the surface after completion of the construction work. The complex reflection factor can also be determined by this method.

This document specifies two tyres intended to serve as reference tyres when using the close-proximity (CPX) method specified in ISO 11819-2. The CPX method is a method for evaluating different road surfaces with respect to their influence on traffic noise, under conditions when tyre/road noise dominates. This method ideally requires the use of standardized tyres, which have noise characteristics that are broadly representative of the effect of road surfaces on the noise emission of passenger car and heavy vehicle tyres. However, such tyres are not specified in ISO 11819-2. This document serves to specify these standardized tyres.

ISO 11819-2:2017 specifies a method of evaluating different road surfaces with respect to their influence on traffic noise, under conditions when tyre/road noise dominates. The interpretation of the results applies to free-flowing traffic travelling on essentially level roads at constant speeds of 40 km/h and upwards, in which cases tyre/road noise is assumed to dominate (although in some countries it is possible that tyre/road noise does not dominate at 40 km/h when the proportion of heavy vehicles is high). For other driving conditions where traffic is not free-flowing, such as at junctions or under heavy acceleration, and where the traffic is congested, the influence of the road surface on noise emission is more complex. This is also the case for roads with high longitudinal gradients and a high proportion of heavy vehicles. A standard method for comparing noise characteristics of road surfaces gives road and environment authorities a tool for establishing common practices or limits as to the use of surfacings meeting certain noise criteria. However, it is not within the scope of this document to suggest such criteria. ISO 11819-1 defines another method: the statistical pass-by (SPB) method. The close-proximity (CPX) method specified in the present document has the same main objectives as the SPB method, but is intended to be used specifically in applications that are complementary to it, such as: - noise characterization of road surfaces at almost any arbitrary site, with the main purpose of checking compliance with a surface specification (an example for conformity of production is suggested in Reference [1]); - checking the acoustic effect of maintenance and condition, e.g. wear of and damage to surfaces, as well as clogging and the effect of cleaning of porous surfaces; - checking the longitudinal and lateral homogeneity of a road section; - the development of quieter road surfaces and research on tyre/road interaction. NOTE This document does not describe the conditions of application for formal purposes of the measurement with the CPX method. Such conditions may be defined in other standards or legal texts. However, suggestions for the applicability of ISO 11819-1 and this document are provided in Annex D. Measurements with the CPX method are faster and more practical than with the SPB method, but are more limited in the sense that it is relevant only in cases where tyre/road noise dominates and power unit noise can be neglected. Furthermore, it cannot take heavy vehicle tyre/road noise into account as fully as the SPB method can, since it uses a light truck tyre as a proxy for heavy vehicle tyres and does not take power unit noise into account. The CPX method specified in this document is intended to measure the properties of road surfaces, not the properties of tyres. If the method is used for research purposes, to provide an indication of differences between tyres, the loads and inflations would normally be adjusted to other values than specified in this document.

ISO/TS 11819-3:2017 specifies two tyres intended to serve as reference tyres when using the close-proximity (CPX) method specified in ISO 11819-2. The CPX method is a method for evaluating different road surfaces with respect to their influence on traffic noise, under conditions when tyre/road noise dominates. This method ideally requires the use of standardized tyres, which have noise characteristics that are broadly representative of the effect of road surfaces on the noise emission of passenger car and heavy vehicle tyres. However, such tyres are not specified in ISO 11819-2. This document serves to specify these standardized tyres.

ISO 11819-4:2013 specifies a modified version of the statistical pass-by (SPB) method that uses a microphone mounted on a backing board instead of a microphone in normal, free-field conditions. It is applicable to measurements taken in an urban, built-up, environment or in the presence of safety barriers, noise barriers, embankments or road cuttings.