Measurements In Close Proximity Research Articles

Acoustic road surface maintenance on low noise asphalts in Switzerland with grinding

This study investigates the effectiveness of grinding techniques on special low-noise pavements as well as conventional asphalt surfaces in order to restore or enhance their noise-reducing properties. This study analyzes 17 different test tracks where grinding techniques were applied, featuring various surface types and stages of aging. The research employs Close-Proximity-Measurements (CPX) and additional methods to evaluate surface characteristics. Initial results reveal significant acoustic improvements from grinding, especially on surfaces with 4- and 8-mm maximum aggregate size. However, the durability of these measures varies, with 4~mm surfaces returning to baseline after 2-4 years, while 8 mm surfaces benefit for approximately 4 years. The study demonstrates that grinding methods can enhance acoustics through surface texture improvement and partially reactivating previously clogged pore spaces. The effectiveness depends on the initial acoustic state and grinding depth, emphasizing the importance of setting clear objectives for optimal results. In summary, this study underscores the effectiveness of grinding in enhancing the acoustic quality of low-noise road surfaces. Moreover, its integration into road surface maintenance strategies is a new tool for extending the functional and acoustic lifespan of low-noise road surfaces.

On application of sound power radiation of rolling tyre measured using CPX-based methodology

The present paper provides a comprehensive account of sound power radiation measurement from a rolling tyre, utilising a methodology that employs an advanced PolyU Mark III Close-Proximity (CPX) trailer enclosure which is aimed to provide CPX measurement per relevant ISO stsandard with suppressed background noise within the interior. The interior walls and ceiling of the enclosure are equipped with diffuser panels, creating a reverberant environment suitable for sound power measurement using the comparison method. The optimal design of the enclosure, which minimizes acoustic resonance and ensures a uniform distribution of acoustic energy, is determined through extensive numerical simulations. During tyre/road sound power measurements, the spatially averaged sound pressure level (SPL) distributions within the enclosure are obtained with a reference sound source (RSS) of known sound power. The relationships between the RSS SWLs and the corresponding SPLs are established at all vehicle speeds. These relationships can then be utilised to deduce the total SWL, as well as its 1/3-octave spectrum, from the captured averaged SPL radiated by a tyre rolling at any vehicle speed. The effectiveness of the CPX-based sound power measurement are illustrated. Additionally, the potential of utilising the measured SWLs for predicting pass-by noise radiation to roadside is discussed.

Experimental investigation of road surface parameters affecting tire/road noise

It is known that tire/road noise is strongly affected by the properties of the road surface such as its profile and sound absorption coefficient. Several parameters, represented by mean profile depth (MPD), have been proposed or standardized as surface profile parameters, but none of them clearly explains the relationship with tire/road noise generation. This study attempted to identify a new surface parameter that correlates more closely with tire/road noise. Surface profile measurements and close proximity (CPX) measurements were conducted on several road surfaces with different properties on test tracks. Tire P1, the reference tire for the CPX method, and two types of passenger car tires were used for the CPX measurements. According to our experience, the variation of the peak height of the road surface with distance is closely related to the excitation input to the tires and thus noise generation. Therefore, we devised a road profile parameter to quantitatively evaluate the variation of peak height. A relatively strong correlation was observed between this parameter and the CPX level. The validity of this parameter will be verified by further measurements on general roads in the future.

New road surface noise corrections for New Zealand

New Zealand’s transport agency has developed a close-proximity (CPX) noise trailer and primarily operates it as a road surface research tool. Early CPX survey data revealed very high longitudinal variability in the performance of porous asphalts on the highway network (±5 dB). Further study and optimization of porous asphalt mixes has resulted in high-performance low-noise surfaces that are reliably 5 dB quieter than standard NZ porous asphalt. The new surfaces and improved surface data inspired a recalibration of NZ’s implementation of the CRTN road-traffic noise model, for which a novel method based on CPX survey data and individual vehicle pass-by measurements was employed. The relationship between CPX and wayside levels was more complex than anticipated; CPX measurements did not capture all the surface attributes/interactions contributing to the wayside level (such as porosity, directivity). The methodology proved successful and a new table of surface corrections has been published, embodying the recalibration of CRTN for NZ in 2023. CRTN predictions using the new corrections have performed well when evaluated against independent road-traffic noise monitoring data from NZ highways.

Relationship between tyre cavity noise and road surface characteristics on low-noise pavements

• A normalised method for Tyre Cavity Noise measurements is not available. • Based on an existing CPX method, a normalisation procedure was designed. • This method was used on 24 road surfaces, together with CPX and texture measurements. • Results show that TCN is correlated to road texture levels within the 100 mm band. • TCN measurements could represent an adequate tool for road surface monitoring. In this work, a protocol to study Tyre Cavity Noise (TCN) was developed. Using this new method, TCN was measured on 24 different road pavements, together tyre noise emission measured with the Close-Proximity (CPX) method and road texture measurements. The results were used to model the relationship between TCN and road surface parameters. The analysis shows that the Standard Reference Test Tyre’s (SRTT) TCN is correlated to megatexture at low frequencies and that the correlation between TCN and outside noise emission is significant for frequencies lower than 1 kHz. The use of sensors placed inside the tyre for monitoring the acoustic performance of road pavements presents several advantages compared to the CPX method, such as a more compact design, lower cost and lower hazards both for the instrumentation and for other vehicles.

Advanced design of Close-Proximity (CPX) trailer enclosure acoustics on tyre/road noise measurement

The PolyU Mark II Twin-wheeled CPX trailer was developed for the measurement of tyre/road noise in Hong Kong urban environment according to a standard methodology (ISO/CD 11819-2) - the Close-Proximity (CPX) method. Numerical simulations of the acoustics of PolyU Mark II CPX enclosure were conducted and a good agreement between numerical and experimental results was obtained. In order to extend the capacity of the Mark II CPX trailer and enhance the acoustic performance within the enclosure for future tyre/road noise studies, the validated numerical simulations were carried on to design the next generation of the PolyU CPX system. Through analyzing the acoustic performance within the enclosures of different dimensions and the distributions of sound pressure level (SPL) inside the anechoic chamber, the geometry of the PolyU Mark III CPX enclosure was finally determined. With newly designed enhanced interior wall absorption, the new PolyU Mark III CPX enclosure design was delivered into numerical simulations for acoustic analysis. Fewer room modes and high uniformity of SPL distributions were observed within the new enclosure design. The PolyU Mark III CPX enclosure was fabricated based on the corresponding dimensions and the specific absorption layers. Great consistency was achieved between the numerical and measured results of the Mark III CPX enclosure. In addition, the PolyU Mark III CPX enclosure shows an improved acoustic property with a lower background noise level during road tests than Mark II CPX enclosure. The outcome of this study firmly establishes the feasibility of designing advanced CPX enclosure with numerical simulations with results that can be realized in realistic CPX measurement.

Correlation between tyre/road noise levels measured by the Coast-By and the Close-ProXimity methods

The paper deals with the relationships between tyre/road noise levels measured by the Coast-By (CB) and the Close-ProXimity (CPX) methods. For that purpose, tyre/road noise was measured for a passenger car fitted with four identical patterned tyres rolling on a set of 15 impervious road surfaces. The CPX and CB measurement methods have been used simultaneously on each road surface at vehicle speeds ranging between 50km/h and 110km/h. A very good correlation between overall CPX and CB noise levels recomposed between 400Hz and 4000Hz was observed which is consistent with previous results of the literature. With the whole set of road surfaces and frequencies, a fairly good correlation between the CPX and CB spectral noise levels was also observed. Taking each road surface individually, an excellent spectral correlation was observed, leading to a very accurate estimation of the overall CB noise levels from the CPX noise levels. Considering each one-third octave band frequency, the correlations between CPX and CB spectral noise levels were also good and enable to estimate the overall CB noise levels with the same accuracy as when using the correlation between the overall CPX and CB noise levels. As a perspective, the results could help to compare different tyre/road noise prediction models which have been calibrated or validated with different testing method (pass-by or close-proximity).

Inhomogeneity of low-noise wearing courses evaluated by tire/road noise measurements using the close-proximity method

Abstract Performing numerous analyses of tire/road noise measurements on low-noise pavements during the last several years, the authors observed significant inhomogeneity of the wearing course in numerous cases, while similar problems were almost non-existent when dense pavements were measured. Three main causes of low-noise pavement inhomogeneity can be defined. The first one is imperfections in the technology used for asphalt mix production and/or errors made during the laying process of the wearing course. The second one is clogging that takes place during the pavement’s service life. The third reason is related to uneven and/or excessive wear of the pavement (raveling and stripping of the aggregate may appear in this case). Findings of analyses of noise data acquired from low-noise pavements (based on 10 m long segments), using the close-proximity (CPX) method, are presented and discussed herein. Significant differences in measured averaged noise levels, up to 1.7 dB, between test sections of open-graded wearing courses that were the same in principle, located on the same road but in different lanes were found when performing CPX measurements. At the same time the test sections of a dense pavement differed by max. 0.5 dB only. The calculated A-weighted sound pressure level variability index Scpx, considered to be an indication of pavement homogeneity, reached the value of 1.69 dB over a 500 m long test section of the porous pavement while the Scpx values for dense pavements were much below 0.5 dB.

Statistical estimation of low frequency tyre/road noise from numerical contact forces

This paper deals with the relation between tyre/road numerical contact data and close-proximity (CPX) rolling noise measurements. The noise was measured on several road surfaces together with the road texture in three dimensions on two-metre-long sections. A multi-asperity contact model was used to calculate successively the contact forces distribution and the contact pressure distribution between a tyre (slick or patterned) and the road during rolling. The correlation between third-octave contact force levels and noise levels was studied on a set of road surfaces with various textures. A high positive correlation was found at low frequency, which allows the estimation of noise levels by means of statistical relations for each third-octave band between 315Hz and 1000Hz for the slick tyre and between 315Hz and 800Hz for the patterned tyre. The results of the model are discussed in relation to the standard deviation of CPX measurements.

Noise Classification for Tendering Quiet Asphalt Wearing Courses

Road administrations request noise reducing pavements and the industry has introduced new products claimed to have noise reducing properties. As a cooperative effort, the Danish Road Directorate, the paving industry and consultants have established a system for specifying such asphalt wearing course systems. Road administrations can now tender pavements with a certain class of traffic noise reduction, based on the Close Proximity (CPX) noise measurement method, ISO/CD 11819-2.The system represents a first Danish attempt to contract road works comprising noise reducing asphalt wearing course systems based on their functionality. Further development is foreseen concerning the CPX measurement accuracy and the acceptance criteria to be used in contracting.

A noise classification system for low‐noise road surfacings ‐ experiences and status

As a result of an increasing pressure from the population as well as from road administrations a noise classification system for road surfacings was put into operation in the autumn 2006. The so‐called SRS‐system (a Danish abbreviation for noise reducing wearing courses) is provisional and non‐committal for a couple of years until sufficient experience has been collected. It is a comprehensive system including: Guidelines on the use of low‐noise asphalt surfacings for noise abatement. Method for declaration and documentation of noise reduction based on the CPX (close proximity)‐method. Paradigm for use in preparation of tendering documents and contracts. The measurement method is based upon the ISO draft standard describing the CPX‐method, but includes further specification. Reference values for dense asphalt concrete are defined, and 2 dB wide noise reduction classes A, B, and C are defined at 50 and 80 km/h. The method also specifies an inter‐calibration procedure (including definition of reference road sections) to be applied for different CPX measurement devices. Each year a specific calibration constant is issued for each device. The paper will also discuss the recent developments in the selection of future reference tyres for CPX measurements. Finally, a status of the classified surfacings will be presented.

Death light for insects : Business Week, Oct. 5, 1935

Performing numerous analyses of tire/road noise measurements on low-noise pavements during the last several years, the authors observed significant inhomogeneity of the wearing course in numerous cases, while similar problems were almost non-existent when dense pavements were measured.Three main causes of low-noise pavement inhomogeneity can be defined. The first one is imperfections in the technology used for asphalt mix production and/or errors made during the laying process of the wearing course. The second one is clogging that takes place during the pavement’s service life. The third reason is related to uneven and/or excessive wear of the pavement (raveling and stripping of the aggregate may appear in this case). Findings of analyses of noise data acquired from low-noise pavements (based on 10 m long segments), using the close-proximity (CPX) method, are presented and discussed herein.Significant differences in measured averaged noise levels, up to 1.7 dB, between test sections of open-graded wearing courses that were the same in principle, located on the same road but in different lanes were found when performing CPX measurements. At the same time the test sections of a dense pavement differed by max. 0.5 dB only. The calculated A-weighted sound pressure level variability index Scpx, considered to be an indication of pavement homogeneity, reached the value of 1.69 dB over a 500 m long test section of the porous pavement while the Scpx values for dense pavements were much below 0.5 dB.

Cotton-fabric reinforced roads : W. K. Beckham and W. H. Millls. ( Engineering News Record, Vol. 115 No. 14.)

Performing numerous analyses of tire/road noise measurements on low-noise pavements during the last several years, the authors observed significant inhomogeneity of the wearing course in numerous cases, while similar problems were almost non-existent when dense pavements were measured.Three main causes of low-noise pavement inhomogeneity can be defined. The first one is imperfections in the technology used for asphalt mix production and/or errors made during the laying process of the wearing course. The second one is clogging that takes place during the pavement’s service life. The third reason is related to uneven and/or excessive wear of the pavement (raveling and stripping of the aggregate may appear in this case). Findings of analyses of noise data acquired from low-noise pavements (based on 10 m long segments), using the close-proximity (CPX) method, are presented and discussed herein.Significant differences in measured averaged noise levels, up to 1.7 dB, between test sections of open-graded wearing courses that were the same in principle, located on the same road but in different lanes were found when performing CPX measurements. At the same time the test sections of a dense pavement differed by max. 0.5 dB only. The calculated A-weighted sound pressure level variability index Scpx, considered to be an indication of pavement homogeneity, reached the value of 1.69 dB over a 500 m long test section of the porous pavement while the Scpx values for dense pavements were much below 0.5 dB.