Low-noise Road Surfaces Research Articles

Study on territory-wide application of low noise road surface in Hong Kong

Hong Kong is one of the metropolitan cities in the world, with highly concentrated road network system and densely populated developments. At times, it is inevitable to build residential buildings near noisy roads, and traffic noise is one of the environmental problems affecting the locals. The Government strives to pre-empt traffic noise issue through planning new road projects or new residential developments. Concerning traffic noise from existing roads, the Government has implemented noise mitigation measures, for instance, to resurface existing roads with Low Noise Road Surface (LNRS) materials, retrofitting of noise barrier or enclosure, to alleviate traffic noise impact. Moreover, the Government is continuously developing and trialing different LNRS materials such as Polymer Modified Stone Mastic Asphalt (PMSMA6) on roads in Hong Kong, which aims for wider application of LNRS. To explore the feasibility and effectiveness of the wider application of LNRS on local roads, the Government has recently conducted a territory-wide study on the application of LNRS on local roads in Hong Kong. This paper attempts to share the common local road characteristics of applying LNRS material and the latest technical findings, such as the effect on population exposure, of the territory-wide study in Hong Kong.

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.

Life cycle approach for evaluating the environmental and economic viability of low-noise asphalt pavements

This paper aims to make recommendations about the convenience of using low-noise pavements to mitigate traffic noise under different traffic and population scenarios. To do so, a life cycle approach has been applied by performing a Life-cycle Assessment (LCA) and Life-cycle Cost Analysis (LCCA). To account for the noise mitigation achieved by the road surfaces, which is the main benefit compared to conventional road surfaces, the damage effect of traffic noise has been incorporated in both analyses. Thus, open source noise emission and propagation modelling and Geographical Information System (GIS) tools have been used to determine the noise level at which residents are exposed. The impact of noise emissions on human health is estimated and expressed in disability-adjusted life years (DALYs) and the related external cost have been calculated by monetarizing the environmental impacts and by integrating them within the cost assessment. The methodology followed allowed the comparison of different scenarios and the results show a huge potential for reducing environmental impacts and costs when using low-noise road surfaces although accurate information about the acoustic aging of the materials is key in order to ensure that benefits are obtained.

Latest Development of Low Noise Road Surfacing in Hong Kong - Application on Local Roads with Different Road Characteristics

Like other metropolitan cities in the world, road traffic noise is a major problem in Hong Kong. The Hong Kong Government endeavors to pre-empt road traffic noise issue through comprehensive noise planning process for new road projects or new residential developments. For traffic noise from existing roads, the Government has adopted various noise mitigation strategies, for example, resurfacing with Low Noise Road Surface (LNRS) material, retrofitting of noise barrier, etc., to combat the noise problem. As of today, Polymer Modified Friction Course (PMFC) is the most commonly adopted LNRS in Hong Kong, which serves as a standard road surface material for high-speed roads and expressways. Nonetheless, it is found to be less durable for local roads due to its open-texture, especially for common road characteristics such as frequent start stop, sharp turn, roadside parking, etc. To explore suitable LNRS material for local roads, a trial programme on a newly developed LNRS material - Polymer Modified Stone Mastic Asphalt (PMSMA6), has been launched to evaluate its noise reduction performance and engineering feasibility on local roads with common road characteristics. This paper attempts to share the experience and latest technical findings of the above trial programme on LNRS in Hong Kong.

Durability of the noise-reduction performance of the PMSMA and CRSMA pavements - a case study in Hong Kong

Tyre/road interaction noise is one of the main sources of urban traffic noise, which has aroused public concern about health and living environment. Low-noise road surface (LNRS) is a feasible solution to reduce tyre/road noise from its source. As a high-density city, Hong Kong has studied the noise-reduction performance of different LNRS materials in the past decade, such as the crumbed rubber modified stone mastic asphalt (CRSMA) and polymer modified stone mastic asphalt (PMSMA) with a small maximum aggregate size. This study aims to evaluate and compare the durabilities of the noise-reduction performance of CRSMA and PMSMA pavements. The close-proximity (CPX) method was applied to collect the tyre/road noise data over three consecutive years after the pavements were constructed. The sound pressure levels and spectrograms were investigated to compare the noise reduction durabilities of the two LNRS materials. The results showed that the CRSMA6 pavement showed good and relatively stable noise reduction performance during the whole observation period. In contrast, although PMSMA6 presented a lower noise level than CRSMA6 at the early stage, its noise reduction property gradually deteriorated. PMSMA6's noise value surpassed CRSMA6 in the third year.

Study on low noise pavements using waste plastics

The quality of life along heavily travelled roads is impacted by traffic noise. According to research on pavement noise, it is possible to plan and construct pavement surfaces that will result in quieter roads. Environmental contamination is a pressing problem today, and incorrect plastic waste disposal is a major contributor to it. Utilizing waste plastic has shown that it not only solves disposal issues, but also improves the qualities of bituminous mixtures. We propose use of PET waste plastic to build low-noise pavements in order to address the problems of waste plastic and traffic noise. By using a smooth surface texture and a tiny maximum size aggregate, a low-noise road surface can be constructed while also taking cost, durability, and safety into account. Current work includes testing of materials like aggregate, polymer modified bitumen and analysing them according to specifications and performing the mix tests with and without waste plastic in the mix. Optimum polymer modified bitumen content for Open Graded Friction Course (OGFC) and Stone Matrix Asphalt (SMA) mixes were found to be 5.5% and 6.0% respectively. Cantabro test results indicated very nominal wear and tear. Addition of waste plastic of 5% by weight of bitumen along with cellulose fibres in OGFC course yielded a considerable increase in sound absorption i.e 3.5 dB when compared to bituminous concrete course. Addition of waste plastic of 20% by weight of bitumen along with cellulose fibres in SMA course resulted a considerable increase in sound absorption i.e 6 dB when compared to BC course.

Investigation of electric vehicle noise sources on low-noise road surfaces

Electric vehicles (EVs) constitute an increasing share of the vehicle fleet, in particular regarding light vehicles. This ratio may be significantly enhanced in urban areas that favour access to low-emission vehicles. Acknowledged to be quieter than conventional vehicles due to a lower propulsion noise, EVs feature a comparatively heightened tyre-road noise contribution, further reduction of which can be achieved by selecting appropriate low-noise road surfaces. These factors may result in modified noise source distributions on the vehicles. In the framework of the LIFE E-VIA project, noise source contributions have been investigated on several light EVs from different segments on a reference ISO road surface, by using a microphone array with dedicated processing. Wide ranges of speeds and driving conditions were considered. In a second step, particular focus has been placed on the road surfaces, comparing the noise sources of selected EVs either driving on the ISO road surface or on low-noise prototypes optimized for EVs and developed within the project. These are two similar versions of a very thin asphalt concrete 0/6, one containing crumb rubber. The presentation gives an overview of the EV noise source behaviour and their ranking with regard to the various situations tested in the project.

Recommendations for the successful design of urban low-noise asphalts - findings from the statistics of over 200 mixtures

In many countries, low-noise road surfaces have become an established measure to reduce road traffic noise. The focus often is on the high-speed network, where porous asphalts (PA) have been used successfully for decades. For urban areas, however, the design of effective low-noise asphalt mixtures remains a challenge, as a pore structure is needed that does not clog at lower speeds. Frequently found solutions are fine textured asphalts in the medium void content range with small pores. The challenge in this particular range is to define mixtures that guarantee a certain acoustic performance. This is exactly where the study comes in: a combined statistical analysis of data from acoustic measurements and laboratory testing of over 200 road surfaces is performed to identify mixtures in the medium void content range (between 8-18% void content) that lead to reliable noise reduction. Multivariate statistical analysis on over 500 drill core examinations allowed us to identify meaningful subcategories of urban low-noise asphalt mixtures, each of which implying a certain effect mechanism and effectiveness in noise reduction. Based on this data, we give recommendations for successful grading curve ranges and other mixture design parameters for urban low-noise asphalts grouped into different performance categories.

Life E-VIA: Prototypal Low-Noise Road Surface for the Reduction of Electric Vehicle Rolling Noise in Urban Area

Abstract In both the current and foreseen context of significant development of the electric vehicle (EV) fleet, a future increasing ratio of EVs in the urban traffic is expected, still enhanced in low-emission zones involving bans or restricted access to other vehicles. EVs are known to be quieter than conventional vehicles at low speed because of a low motor noise emission, resulting in a higher prevalence of rolling noise in the environmental noise. EVs differ from conventional vehicles in several parameters that can influence tyre/road noise, like weight and torque. The LIFE E-VIA project objectives consist in developing, implementing and assessing a low-noise road surface for light EV traffic in urban conditions, optimised from an acoustical and life cycle perspective. In parallel, an optimisation of EV tyres is investigated. Prior to forthcoming layout in Florence (Italy) for assessment under real traffic conditions, a prototypal road surface has been implemented and evaluated on a test track in Nantes (France). Preliminary tests carried out with different EVs on several road surfaces highlighted the variability of noise emission over vehicle types and pavements, leading to specific ranking. Two prototype versions of a low-noise road surface have been laid out in Nantes, respectively without and with crumb rubber. Both of them have been acoustically assessed with on-board microphones (CPX method) and at roadside (CPB method and microphone array). Constant speed, acceleration and deceleration conditions were considered for pass-by tests. Other acoustical or physical parameters have been measured: acoustic absorption, 3D-texture, mechanical impedance and skid resistance properties (BPN and MPD). In comparison with a reference DAC 0/10 road surface, very usual in France, a roadside noise reduction up to 4 dB(A) was found at steady pass-by speed 50 km/h. Grip values are very high and macrotexture levels moderate. Lastly, mixtures durability is analysed with laboratory tests.

Effect of Addition of Rubber Granulate and Type of Modified Binder on the Viscoelastic Properties of Stone Mastic Asphalt Reducing Tire/Road Noise (SMA LA).

The use of rubber granulate in the composition of asphalt mixtures, as well as the use of poroelastic layers, is indicated by many research centers as a factor with a positive effect on tire/road noise reduction. Attention is however paid to their lower structural durability compared to asphalt concrete (AC) or stone mastic asphalt (SMA). Stone mastic asphalt reducing tire/road noise (SMA LA) layers have also been recently used as low-noise road surfaces. The article presents the test results of viscoelastic properties of asphalt mixtures SMA8 LA, SMA8 LA containing 10%, 20%, and 30% of rubber granulate, with bitumen 50/70, bitumen 50/70 modified with styrene butadiene styrene (SBS) copolymer, crumb rubber, and mixtures with bitumen modified simultaneously with crumb rubber and SBS copolymer. The reference asphalt mixture was the porous asphalt (PA8). The presented results of water damage resistance, degradation resistance in the Cantabro abrasion loss test, stiffness modulus as a function of temperature and hysteresis loop proved that the amount of rubber granulate and the type of binder significantly affect the values of these parameters. Attention was paid to the possibility of using the results of uniaxial cyclic compression tests when determining the proportion of rubber granulate in SMA8 LA mixtures. Tests of hysteresis loops and stiffness modulus confirm much higher elasticity of SMA8 LA mixtures with rubber granulate as compared to mixtures without the addition of granulate.

Modelling of the pavement acoustic longevity in Hong Kong through machine learning techniques

Traffic noise emission has long been a pervasive environmental and ecological problem, especially in the metropolitan cities with large-scale traffic network and high population density. Low noise road surface (LNRS) has been actively developed and applied as an effective measure to maintain the quieter environment of mobility service system. However, when LNRS is applied for noise abatement, the relationship between the acoustic performance and degradation of pavement has not been fully understood yet. To this end, this study aims to model the acoustic longevity of asphalt pavement as a function of the thickness, binder content, maximum aggregate size, and air void content of the pavement surface, as well as vehicle speed based on the long-term tyre-road noise data collected from 270 asphalt pavement sections in Hong Kong. Two machine learning techniques, namely artificial neural networks (ANN) and support vector machines (SVM), were employed and compared. It was found that both ANN and SVM could successfully model the pavement acoustic performance with acceptable model performance metrics. A case study showed that the ANN model was more aligned with the aging mechanisms of porous road surface, but the SVM model showed better training performance. The predicted acoustic deterioration rates of the porous surface case varied from −0.1 to 0.28 dB(A)/month rather than keeping a constant linear increasing trend, depending on pavement ageing periods and vehicle speed levels. The two-dimension sensitivity analysis (2D-SA) revealed the relative importance of pavement age and vehicle speed in controlling the acoustic performance.

Evaluation of tyre/road noise and texture interaction on rubberised and conventional pavements using CPX and profiling measurements

Road traffic noise is the most common source of environmental pollution in urban areas, and therefore, the study of noise mitigation actions is fundamental for urban planning. The use of low noise road surfaces is one of the most widespread intervention since it acts directly on the source of road traffic noise, represented by tyre/road interaction. In this work, the interaction between texture and tyre/road noise was studied from an experimental point of view, by comparing CPX and road texture measurements on rubberised and standard road surfaces. Tyre deformation was addressed by taking into account the indenter method proposed by Sandberg and Goubert in 2018. Regressions of CPX and enveloped road texture levels were performed separating rubberised from reference surfaces, and parallelism tests were performed on the slopes. Results show that the use of rubber influences the interaction of road texture and noise, especially at high frequencies.

Modelling the acoustic performance of newly laid low-noise pavements

Road traffic in urban contexts produces noise mainly by the interaction of tyres with pavement surface and, therefore, the use of low-noise surfaces represents the best solution since they aim to mitigate the source. Moreover, in urban contexts it is often the only viable solution, together with a careful traffic planning. The main challenge in their adoption as noise mitigation actions is to be able to forecast the acoustical performances that the new road surface will be able to offer. In the UE, the new Green Public Procurement requires experimental verification of noise performance compliance: the designer must declare the acoustical performance of the proposed low-noise pavement and, a few months after the laying, the actual performance of the road surface must be tested using the Close Proximity Method (CPX). Due to the importance of being able to forecast CPX levels, the present work reports a novel way to model CPX broadband levels of newly laid low-noise road surfaces using only data available to the designer before the laying or easily obtained through coring tests, such as grading curve, fractal dimension, asphalt binder content, air voids, voids in mineral aggregates. Two models were elaborated, using two different frequency separations for tyre/road noise. The first model separates low and high frequency contributions, while the second one also considers noise around 1 kHz separately, using a three-band model. Both models are capable of forecasting the acoustic performance of newly laid low-noise road surfaces, using different road mixture parameters at different frequency ranges. The three band model shows a lower RMSE.

LOW-NOISE ASPHALT APPLICATION AND ITS EFFICIENCY ANALYSIS

Currently, the development of low-noise road surfaces in Europe, the United States and other countries is actively underway. The article describes the physical principles of noise generation when the under speed conditions, in particular rolling noise arising from the interaction of the wheel with the road, the reduction of which is the main purpose of low-noise surfaces. The types of compositions used in the world and the achieved efficiency are described. The advantages and disadvantages of each of them are analyzed. The summary on the main methods of experimental noise reduction efficiency determination using low-noise road surfaces is made. The importance of maintaining road safety and the need for additional research to determine the durability of the surfaces used.

Influence of texture on tyre road noise spectra in rubberized pavements

Road traffic noise is the most common source of environmental pollution in urban areas and therefore, the study of noise mitigation actions is fundamental for urban planning. The main source of road traffic noise is tyre/road interaction; thus, the use of low noise road surfaces represents an optimal solution for its mitigation. Several studies tried to find a correlation between road texture and broadband noise data, trying to provide guidelines for the development of acoustically optimised road surfaces.The present work studies the correlation between road texture and tyre/road noise from an experimental point of view, by analysing texture and noise spectra on ten different road surfaces. Tyre deformation has also been addressed by analysing two already existing tyre envelopment algorithms. The first algorithm, proposed by Von Meier and based on the limitation of the second order derivative of the profile signal, shows poor correlation with high frequency noise, while the second algorithm, based on a novel method proposed by Sandberg and Goubert and called indenter method, enhances correlation with low frequency noise and preserves information at higher frequencies. Correlation patterns show that rolling noise can be separated in three main contributions: low, middle and high frequency noise. Finally, experimental tyre/road noise and enveloped texture data obtained with the indenter algorithm have been used to elaborate a linear model that relates low and high frequency noise to texture one-third octave bands. This model deepens knowledge on tyre/road interaction.

Modelling of acoustic ageing of rubberized pavements

Tyre-road noise is the most important source of traffic noise in the mid-to-high speed range. The use of low noise road surfaces represents an ideal solution to mitigate traffic noise, because it directly affects the source, generating a widespread benefit for all the dwellings near the road and decreasing the number of people annoyed. More knowledge about long-term acoustic performance is required to promote the use of low noise road surfaces as mitigation action.In fact, as for a traditional road surface, the acoustic properties of low noise surfaces worsen over time: only by knowing the initial noise reduction and its time evolution, public administrations can design their application and related maintenance plans.In this work, an innovative approach was used to investigate and model acoustic ageing of some rubberized road surfaces surveyed for several years. This type of quiet pavements represents an efficient road surface technology in terms of traffic noise reduction. A new regression model was applied to estimate the acoustic ageing of the investigated pavements, considering the complex interacting system composed of three main elements: pavement type, traffic loads and climatic conditions.

Reduction of road traffic noise by source measures â–” present and future strategies

The current trend worldwide is less focused on reducing road traffic noise. This is in strong contrast to the severe impact of traffic noise to the general health and quality of life. A more holistic and combined strategy is needed. Current international rules and regulations regarding vehicles and tyres are not sufficient to reduce traffic noise levels in an effective way. Calculations show that these regulations will only yield a reduction of approximately 1.5 dB in Lden levels for urban traffic. Additional measures need to be implemented. By combining optimized tyres and road surfaces, a noise reduction of 4â–“6 dB can be achieved. Such tyres are currently being developed for electric and hybrid-electric vehicles. In addition to noise reduction, these tyres have less rolling resistance that can reduce vehicle energy consumption up to 15% on normal road surfaces. However, there are several obstacles still to be removed, such as the effectiveness of the EU tyre labeling system, and the implementation and durability of low-noise road surfaces. These challenges are discussed in the article.

The influence of tyres on the use of the CPX method for evaluating the effectiveness of a noise mitigation action based on low-noise road surfaces

The usage of low-noise road surface can be an important and effective noise mitigation action and, in many cases, it might represent the only viable solution. After the laying of a low-noise road surface, it is necessary to verify if the planned objectives have been actually obtained: the Close Proximity Method (CPX) could be a possible method to achieve this result.The current release of the ISO 11819 draft regarding CPX redirects to a future third part for all details about the reference tyre to be used, while the previous one gave indications on dimensions, kind of tread pattern and maintenance conditions. As well known, tyre dimensions and tread pattern are the main sources of variability of rolling noise. Even though many tyres available on the market comply with all ISO requirements, the choice of a brand or a model rather than another one could nevertheless influence results of measurements.In this work, results obtained in several measurement sessions, repeated using different tyres, are compared, aiming to analyse the influence of the tyre choice in assessing the acoustic performance of a low-noise road surface. Limitations and advantages of the CPX method in regards to the evaluation of the effectiveness of a noise mitigation action are reported, and new perspectives are suggested, in order to improve the relationship with the noise level reduction at the receiver.

Performance Assessment of Low-Noise Road Surfaces in the Leopoldo Project: Comparison and Validation of Different Measurement Methods

In almost all urban contexts and in many extra-urban conurbations, where road traffic is the main noise pollution source, the use of barriers is not allowed. In these cases, low-noise road surfaces are the most used mitigation action together with traffic flow reduction. Selecting the optimal surface is only the first problem that the public administration has to face. In the second place, it has to consider the issue of assessing the efficacy of the mitigation action. The purpose of the LEOPOLDO project was to improve the knowledge in the design and the characterization of low-noise road surfaces, producing guidelines helpful to the public administrations. Several experimental road surfaces were tested. Moreover, several measurement methods were implemented aiming to select those that are suitable for a correct assessment of the pavement performances laid as mitigation planning. In this paper, the experience gained in the LEOPOLDO project will be described, focusing on both the measurement methods adopted to assess the performance of a low-noise road surface and the criteria by which the experimental results have to be evaluated, presenting a comparison of the obtained results and their monitoring along time.

Noise Impact on Inhabitants in Residential Areas under Various AntiNoise Measures

The sound environment is an inseparable part of the living environment. Noise is generally considered to be any sound or sounds which are undesirable, disturbing or harmful to people. Road transport has been the dominant source of noise in the environment for a number of years. Traffic noise modelling is used particularly for assessing the acoustic situation in the vicinity of roads, the identification of noise impact on population, designing anti-noise measures, strategic noise mapping, and action plans. Regarding noise impact within the assessment of sustainable transport development, the programme SoundPLAN assessed different types of noise impact on inhabitants in residential areas through the use of alternatives such as the reduction of vehicle speed, construction of anti-noise barriers, installation of low-noise road surface, and various combinations of these. For the production of noise maps, input data was combined with geographic data or map materials respectively, data on buildings, roads, inhabitants, and traffic data.The article presents the results of calculations of equivalent levels of acoustic pressure together with the division of impact on population into individual zones. Calculations are simulated on a terrain model of a part of the residential area surrounded by a busy trunk road and for the daytime. The residential area consists of detached houses and blocks of flats with a maximum height of 5 floors with the usual community amenities - garages, small shops, etc. Therefore, the application of simulated anti-noise measures may lead to a reduction of the negative impacts on the environment as well as on human health.