NORDTEX FINAL REPORT ROAD SURFACE TEXTURE FOR LOW NOISE AND LOW ROLLING RESISTANCE

Transcription

1 NORDTEX FINAL REPORT ROAD SURFACE TEXTURE FOR LOW NOISE AND LOW ROLLING RESISTANCE VEJDIREKTORATET, RAPPORT 506, 2013

2 ROAD SURFACE TEXTURE FOR LOW NOISE AND LOW ROLLING RESISTANCE NORDTEX FINAL REPORT AUTHORS: Jørgen Kragh, Lykke Møller Iversen and Ulf Sandberg PHOTOS: Road Directorate p.31 Ulf Sandberg DATE: December 2013 ISBN (NET): LAYOUT: Road Directorate COPYRIGHT: Vejdirektoratet,

3 CONTENTS PREFACE 4 FORORD 5 SUMMARY 6 RESUMÉ 7 1. BACKGROUND AND AIM 8 2. METHOD APPLIED OVERVIEW 9 3. LIMITATIONS FIELD CALIBRATION NOISE AND TEXTURE DATA RELATION BETWEEN TEXTURE AND NOISE Relation between CPX noise levels and road surface texture levels Inter-correlations Correlations based on NordTyre data Estimated road noisiness parameters HOW CPX NOISE LEVELS REPRESENT TRAFFIC NOISE LEVELS ROLLING RESISTANCE Background Measurements in Denmark Measurements in Sweden and a synthesis of rolling resistance measurements CHANGING TEXTURE TO REDUCE NOISE ON SURFACES IN SERVICE HOW TO OPTIMIZE SURFACE TEXTURE FOR LOW NOISE Essential principles Limitations and sacrifices General advice on noise reducing road surfaces An example of a favourable surface identified in NordTex CHALLENGES IN SURFACE PROFILE MEASUREMENT Problems observed by ISO working group WG DRD investigation VTI problems WG 39 work on solutions and latest status DISCUSSION General Differences in texture spectra measured by the parties Ways to obtain texture for low tyre/road noise emission Small aggregate Steep grading curve Grinding the surface Rolling resistance and noise CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES 45 APPENDIX 1 PAVEMENTS AND SELECTED MEASUREMENT RESULTS 46 APPENDIX 2 TABLES OF CORRELATION 53 APPENDIX 3 DIFFERENCES IN TEXTURE SPECTRA MEASURED BY THE PARTIES 56 APPENDIX 4 ABBREVIATIONS USED IN THE REPORT 59 3

4 PREFACE Nordic road administrations face challenges in their effort to reduce population exposure to noise from road traffic. In Denmark, for example, Government strategy emphasizes the potential associated with the reduction of tyre/road noise. The Norwegian Government target has been defined as 10 % reduction of the number of annoyed persons before 2020 as compared to the situation in The most efficient way to reduce the general traffic noise is to reduce the source of noise emission. At present the most important part of this noise emission is tyre/road noise. Noise reducing road surfaces are mainly experimental although Danish national and municipal road administrations in recent years have applied thin asphalt layers with small aggregate, and experiments are going on to optimise noise reduction as well as structural and acoustical durability. To support such work the connection between surface texture and traffic pass-by noise levels should be clarified. This has been studied in the Nordic countries, in particular by the Swedish institute VTI, while little expertise existed in Denmark and Norway prior to the project reported on here. In 2006, exchange of information on road surface texture and tyre/road noise began between Nordic parties, attempting at creating a common knowledge base. In 2009 the NordTex project was initiated in order to establish new Nordic competence. This report documents the results of the project. The following persons have contributed to the project. The Project Steering Group Norway: Jostein Aksnes (chair), Norwegian Public Roads Administration (Statens Vegvesen, Vegdirektoratet) Denmark: Jakob Fryd, Danish Road Directorate (Vejdirektoratet) Sweden: Pereric Westergren, Jesper Elsander, Swedish Transport Administration (Trafikverket) The Project Advisory Luc Goubert, Belgian Road Research Centre, BRRC, Belgium Ragnar Evensen, ViaNova Plan og Trafikk AS, Norway The Project Group Denmark: Jørgen Kragh (project leader), Bent Andersen, Lykke Møller Iversen, Erik Nielsen, Jens Oddershede, Danish Road Directorate (Vejdirektoratet) Norway: Doreen Siebert, Odd Durban Hansen, Norwegian Public Roads Administration (Statens Vegvesen, Vegdirektoratet), Truls Berge, Svein Å. Storeheier, SINTEF Sweden: Ulf Sandberg, Mikael Ögren, Anders Genell, Swedish National Road and Transport Research Institute (VTI) 4

5 FORORD De nordiske vejforvaltninger står over for store udfordringer i arbejdet med at nedbringe den støjbelastning, som vejtrafikken påfører befolkningerne. I den danske regerings strategi for begrænsning af trafikstøj påpeges potentialet for at nedbringe støjen fra bildækkenes kontakt med vejbelægningen. Den norske regerings erklærede mål er en reduktion af antallet af generede personer i forhold til situationen i 1999 på 10 % før Den mest effektive måde at reducere trafikstøj på er at formindske støjen ved kilderne, og som situationen er i dag stammer størstedelen af den udsendte støj fra kontakten mellem dæk og vejbelægning. Støjreducerende vejbelægninger har hidtil overvejende været anvendt på forsøgsbasis, selv om det danske Vejdirektorat og danske kommunale vejadministrationer i de seneste år i stigende omfang har udlagt tynde asfaltslidlag med lille maksimal stenstørrelse: Der pågår løbende en indsats for at optimere støjreduktionen samtidigt med at slidlagene har en acceptabel holdbarhed, både strukturelt og akustisk. Denne indsats kan fremmes hvis man får større indsigt i sammenhængen mellem vejbelægningens overfladetekstur og støjniveauet fra forbikørende biler. Det har der i mange år været arbej det med i de nordiske lande, navnlig ved det svenske VTI, mens der var meget begrænset ekspertise til rådighed i Danmark og Norge forud for NordTex-projektet. I 2006 begyndte en proces med at udveksle viden mellem nordiske interessenter om vejbelægningers overfladetekstur og dæk/vejbanestøjen, og i 2009 blev NordTex projektet påbegyndt med henblik på at etablere ny nordisk kompetence. Nærværende rapport dokumenterer resultaterne af projektet. I projektets forløb har følgende personer medvirket. Styregruppe Norge: Jostein Aksnes (formand), Statens Vegvesen, Vegdirektoratet Danmark: Jakob Fryd, Vejdirektoratet Sverige: Pereric Westergren, Jesper Elsander, Trafikverket Rådgivningsgruppe Luc Goubert, Belgian Road Research Centre, BRRC, Belgien Ragnar Evensen, ViaNova Plan og Trafikk AS, Norge Projektgruppe Danmark: Jørgen Kragh (projektleder), Bent Andersen, Lykke Møller Iversen, Erik Nielsen, Jens Oddershede, Vejdirektoratet Norge: Doreen Siebert, Odd Durban Hansen, Statens Vegvesen, Vegdirektoratet, Truls Berge, Svein Å. Storeheier, SINTEF Sverige: Ulf Sandberg, Mikael Ögren, Anders Genell, Statens väg- och transportforskningsinstitut (VTI) 5

6 SUMMARY The present report documents results of a joint effort by research institutes in Denmark, Norway and Sweden. The NordTex project has looked at relations between road surface texture and tyre/road noise, by studying results of earlier research and by conducting new experiments. The results are valid for passenger car tyres running on dense (non-porous) pavement. Noise levels were measured by means of CPX trailers, and road surface profiles were measured with laser based equipment. The relations between these parameters were analysed. On some of the pavements, rolling resistance was measured using a special trailer. The following conclusions are drawn: 1. The general trends mentioned in 6) below confirms results found in earlier projects. This is remarkable, because tyre design and normal mix recipes have developed essentially in the meantime 2. Low texture levels at large texture wavelengths are associated with low tyre/road noise levels. This was the most important parameter for the pavements studied 3. High texture levels at small wavelengths are also associated with low noise levels, although in the present data this relation is less clear than the relation at larger wavelengths 4. The trends in 2) and 3) are valid for the overall group of data, but results from some pavements did not follow these trends. The reasons are not understood 5. CPX trailer noise levels measured with standard reference test tyres are strongly correlated with statistical pass-by vehicle noise levels from light vehicles, and pavement texture optimisation may be based on CPX trailer measurements 6. To obtain a surface texture for low noise levels, texture levels shall be low in the megatexture range, i.e. the third-octave bands with centre wavelengths 63 mm 500 mm. This may for example be obtained by a) applying aggregate with a small nominal maximum size and with a shape facilitating the aggregates to be seated closely together after compacting b) grinding off peaks of the surface of a pavement having large aggregates. These are more resistant to wear from studded tyres than is the case with smaller aggregates 7. Smaller maximum aggregates imply less durability, in particular less wear resistance to studded tyres. Texture change due to such wear may be reduced by having a large portion of high quality aggregate larger than 2 mm in the asphalt mix 8. Polymer or rubber modified bitumen may contribute in obtaining asphalt mortar more resistant to wear from studded tyres 9. Competence concerning road surface texture measurement and its interaction with tyre/road noise emission has been enhanced significantly among project partners during the course of the project 10. The Danish Road Directorate has decided to discontinue its default use of so-called enveloping when analysing pavement surface profiles. Such enveloping is an attempt to interpret the surface texture in a way corresponding to the impact it makes on a tyre. The procedure has not been developed sufficiently to be useful in practice 11. Lower noise levels also means lower rolling resistance as long as dense road surfaces are considered, and therefore efforts to reduce traffic noise do not counteract efforts to reduce fuel consumption or CO 2 emission 12. The so-called G factor did not provide any new correlation between surface texture profiles and tyre/ road noise, which is not already provided by other parameters 13. The parameter denoted Skewness is a parameter sensitive to whether the texture is positive or negative. This parameter should be considered in future research 14. The method proposed in ISO for predicting the change in tyre/road and vehicle noise levels as a consequence of changes in the surface profile gave results which agreed well with noise level differences measured in NordTex. This indicates that the project results are relevant and useful. 6

7 RESUMÉ Rapporten dokumenterer resultater af et samarbejde mellem forskere i Danmark, Norge og Sverige. NordTexprojektet har undersøgt sammenhængen mellem teksturen af vejes overflade og støjen fra kontakten mellem dæk og vejbelægning, ud fra både tidligere projekter og nye målinger og analyser. Resultaterne gælder alene for personbiler, der kører på tætte (ikke-porøse) vejbelægninger. Støjniveauet blev målt ved hjælp af CPX-trailere, og belægningens overfladeprofil blev målt med laser-baseret udstyr. Sammenhængen mellem disse parametre blev analyseret. På nogle belægninger blev rullemodstanden målt ved hjælp af en speciel trailer. Konklusionerne er: 1. De overordnede tendenser omtalt i punkt 6) herunder bekræftede resultater af tidligere projekter. Dette er bemærkelsesværdigt, fordi design af bildæk og asfaltrecepter har ændret sig væsentligt i den mellemliggende tid 2. Lave niveauer af teksturen ved store bølgelængder indebærer lave niveauer af støjen fra dæk/ vejbelægning. Denne parameter var den vigtigste på de undersøgte belægninger 3. Høje niveauer af teksturen ved små bølgelængder giver også lave støjniveauer, men i de foreliggende data er denne sammenhæng mindre for de længere bølger 4. Tendenserne under 2) og 3) gælder for det samlede datamateriale, men resultaterne fra nogle af belægningerne følger ikke de generelle tendenser, uvist af hvilke årsager 5. Støjniveauer målt med CPX trailer udstyret med standard referencedæk er stærkt korreleret med støjniveauerne (SPB) fra lette køretøjers forbikørsel, og optimering af belægningers tekstur kan baseres målinger med CPX-trailer 6. For at få en overfladestruktur der giver lavt støjniveau, skal teksturniveauet være lavt i området for megatekstur, dvs. i tredjedeloktavbåndene med center-bølgelængder 63 mm mm. Dette kan for eksempel opnås ved a) at anvende aggregater med en lille nominel maksimal størrelse og med en form, der gør at stenene lejres tæt sammen ved komprimeringen b) at slibe toppene af stenene i overfladen af en belægning stor maksimal kornstørrelse, som er mere modstandsdygtigt over for pigdæk-slitage end slidlag med mindre sten 7. En mindre maksimal kornstørrelse giver mindre holdbarhed, især mindre slidstyrke over for pigdæk. Teksturens modstandsdygtighed over for slid kan øges ved at tilsætte en stor andel stenmateriale af høj kvalitet med kornstørrelser over 2 mm 8. Polymer- eller gummimodificeret bitumen kan bidrage til at asfaltmørtlen bliver mere slidstærk over for pigdæk 9. Kompetencerne inden for måling af overfladetekstur er i løbet af projektet øget betydeligt hos projektets partnere. Det samme gælder indsigten i sammenhængene mellem teksturen og den udsendte støj fra kontakten mellem dæk og vejbelægning 10. Vejdirektoratet vil indtil videre undlade enveloping ved analyse af overfladeprofiler. Hensigten med enveloping-proceduren er at bedømmelsen af teksturen skal svare til den måde den påvirker et bildæk. Proceduren er endnu ikke udviklet til praktisk brug 11. Lavere støjniveau indebærer lavere rullemodstand på tætte vejbelægninger, og derfor modvirker indsatsen for at nedbringe støjen ikke bestræbelser på at reducere brændstofforbruget 12. Den såkaldte G-faktor giver ikke ny information om sammenhængen mellem overfladens tekstur og dæk/vejstøjen, som ikke allerede er indeholdt i de øvrige målte parametre 13. Parameteren Skewness er følsom for om teksturen er positiv eller negativ. Denne parameter bør indgå i fremtidige undersøgelser af sammenhængen mellem tekstur og støj 14. Metoden i ISO til at beregne ændringen i niveauet af dæk/vejbane- og forbikørselsstøj som følge af ændringer i overfladeteksturen gav resultater, som passer fint med niveauforskellene målt i NordTex. Det indikerer, at projektets resultater er relevante og anvendelige. 7

8 1. BACKGROUND AND AIM Understanding the relation between pavement surface texture and the generation of tyre/road noise, together with the effects of pavement acoustic absorption, if any, is a key to optimizing the noise reducing properties of road surfacings. The very ambitious aim of the project was to establish principles for the design of road surfacing mixes yielding lower tyre/road noise levels and to perform initial test of such mixes in full scale demonstration projects. This topic is important to all Nordic countries while the impact of studded tyres is of little interest to most European countries. According to the original project description the project should 1) Establish a base of data on texture and noise levels; 2) Analyse data and identify texture characteristics associated with low tyre/road noise levels; 3) Derive promising mix designs, and 4) Build test sections and test these initially and after their first winter in service. An important aspect pointed out in the process of establishing the project was the need for building Nordic expertise concerning road surface texture measurement and texture influence on tyre/ road noise. Prior to the project start, the Swedish Transport Administration (Trafikverket) funded a study resulting in a state-of-the art report on road surface texture influence on tyre/road noise [1]. During the initial project stages it became clear that measuring pavement surface properties was even more difficult than anticipated, and the project layout had to be revised several times so points 1) - 4) mentioned above could only be fulfilled to a limited extent. These somewhat modified aims are dealt with in the following sections of the report. The intention has been for the present final report to provide a summary of results with reference to details documented in project milestone reports. 8

9 2. METHOD APPLIED OVERVIEW The first stage of the project was a comparison of 1. noise levels measured by means of three different CPX noise measurement trailers [2], and 2. road surface profiles measured with different equipment [3] To be able to compare texture measurement results it was necessary to define a measurement method. In a second project stage CPX noise levels and road surface texture should be measured on existing roads and an initial analysis should be made of the relations between surface texture and noise. Originally it was the intention to utilise results of this analysis to construct new test sections of road with surface textures expected to provide low tyre/road noise levels and then repeat the procedure from project stage two to confirm that low noise levels had in fact been obtained. In reality it turned out to be necessary to select among sections of road which by experience were assumed to be associated with low tyre/road noise levels. The results from this phase of the project were reported in [4] - [7]. The noise and texture measurements should be supplemented by measurements of tyre rolling resistance to avoid sub-optimization based on noise alone. Due to challenges met in measuring road surface profiles only a few rolling resistance measurement were carried out. These results are documented in [8]. Microphone arrangement on DRD open trailer decibella 9

10 3. LIMITATIONS The project has been limited to nonporous pavement, and it deals only with surface properties at a specific point in time. Long-term testing has been outside the scope of the present project. Due to a limited budget, the project had to be based on data from a limited number of pavements and to take advantage of road sections built and data recorded in a variety of other projects. Finally, an important limitation is that much of the tyre/road noise data collected have been measured using a CPX reference tyre which is intended to represent light vehicle noise. Thus the data are focused on light vehicle traffic, while they do not represent heavy vehicle traffic. Texture influence on noise from light and heavy vehicle tyres is known to be different. 10

11 4. FIELD CALIBRATION Figure 1 shows, as an example, the mean profile depths, MPD, measured in 2009 by DRD, STF and VTI respectively, in Task 2, Calibration, see [3] and [9]. There is a reasonably good agreement, actually better than in most other comparisons made recently, as presented to ISO and CEN working groups. 2,5 2,0 1,5 1,0 MPD [mm] DRD SVV-STF VTI Figure 2 shows examples of surface profile texture spectra measured by DRD and SVV-STF, respectively. At wavelengths smaller than 10 mm or so SVV-STF spectral levels are higher than DRD spectral levels. When these results were first presented the reason for the deviation was thought to be insufficient spike removal from the SVV-STF profile data and perhaps remaining influence from electrical noise, even though SVV- STF had attempted to correct for this. Later the deviations were found to be caused mostly by DRD applying enveloping in its analyses while SVV- STF did not do so; see also Section 11. 0,5 0,0 HRA 11/16 AC 11d AC110 AC 60 SMA 6+ PA8/PA/16 Figure 1. MPD measured in the right wheel track on six 100 m long calibration sections on M10, Kongelundsvej and Vigerslevvej [3], [8], but adjusted in 2013 by DRD Note: The results in Figure 1 deviate slightly from data in [3], because 1) DRD has corrected errors in the order of mm made in its original analyses, based on reanalyses carried out in 2013; 2) The VTI result from the two-layer porous asphalt PA 8/PA 16 has been adjusted in May 2013 by DRD, because the original VTI data by mistake were from a 160 m long section of Vigerslevvej preceding the 100 m long calibration section, and not from the calibration section itself. On the first 160 m VTI measured MPD = 1.13 mm; DRD measured MPD = 1.17 mm; on the road section m DRD measured MPD = 1.51 mm. Measuring with SVV-STF trailer with enclosure 11

12 Figure 3 and Figure 4 show examples of the results of comparing the A-weighted CPX trailer noise levels [2]. Figure 3 shows the CPX noise levels measured with the same trailer equipped with four different reference tyres, SRTT. The results found with each of the four tyres running on seven different pavements are shown as a function of the average result of measurements with the four tyres. An old SRTT belonging to TUG and having a hard tread, probably as a result of ageing, yielded the highest noise levels. The remainder of tyres were in newer condition and yielded results within ± 0.5 or 0.6 db on all pavements, which is considered a normal variation. Figure 2: Texture spectra, examples from [3], [9] but showing final data for the full length of each road section Figure 4 shows CPX noise levels measured on the same seven pavements with the three different trailers with their new SRTTs. The range is larger than in Figure 3 and it was concluded in [2] that the reason why the TUG trailer yielded 1 db lower noise levels than the DRI 1) trailer, is a combination of 1) the individual TUG SRT tyre being a little less noisy than the individual DRI tyre and 2) that the TUG tyre on the average rolled slightly nearer to the less worn lane centre than the DRI tyre on the DRI trailer. This is a consequence of the two trailers having different test tyre setups: the DRI trailer has a test tyre in each wheel track while the TUG trailer has a single tyre in the middle of the trailer and attempted to drive with this tyre in the right wheel track. 1) DRI has changed its name to DRD during the NordTex project period 12

13 Figure 3. CPX noise levels measured with four different tyres SRTT on the same trailer, from [2] Figure 4. CPX noise levels measured with three different trailers with their new SRTTs, from [2] 13

14 5. NOISE AND TEXTURE DATA The amount of available data used for analysing the relationship between road surface texture and tyre/road noise is summarized in Table 1 to Table 3. These tables refer to tables in Appendix 1 which contain selected data for each pavement. The Danish road sections mentioned in Table 1 and Table 2 were built in the European project SILVIA (Kongelundsvej) and in a national Danish project (M10). On each site there was a reference section with AC 11d, and a number of noise reducing thin asphalt layers. The Danish road sections on Kastrupvej mentioned in Table 2 and the road sections mentioned in Table 3 do also comprise a reference section and some noise reducing thin asphalt layers on each site. The sections on Kastrupvej and on M68 were built as a part of the European project SILENCE, while the sections on M64 were built as a part of the Danish-Dutch cooperation in the Dutch IPG project. The road sections at Igelsø were built in a Danish project to demonstrate a variety of noise reducing thin asphalt layers. The Norwegian test sections were built in the Norwegian project Environmentally friendly road surfaces (Miljøvennlige vegdekker). 14

15 Table 1. Overview of CPX measurements made in 2009 with SRTT at 50 km/h; the total number of pavements was N = 34, 18 of which in the Copenhagen area and 16 Norwegian pavements; in some cases this set of data has been denoted Data set #1 or <ds1_50> Sub set No. Site Pavement Measured by N [-] Measured Listed in ID Table No. 1 Kongelundsvej DRI01-DRI06 DRD Table 10 2 M10 DRI07-DRI13 DRD Table 10 3 Norwegian pavements STF02-STF19 STF Table 11 Reference tyre: SRTT Speed [km/h]: 50 Table 2. Overview of CPX measurements made in with CPX reference tyre A at 50 km/h; the total number of pavements was N = 55, N 1 = 18 in Denmark and N 2 = 37 pavements in Norway; in some cases this set of data has been denoted Data set #2 or <ds2_50> Sub set No. 1 Site Pavement Measured by N [-] Measured Listed in ID Table No. Kongelundsvej, M45 Kastrupvej DRI01 DRI02, DRI03 DRI06, DRI14 DRI15, DRI20 DRI29 DRD Table 14 2 Norwegian pavements STF Table 15 Reference tyre: A Speed [km]: 50 Table 3. Overview of CPX measurements made in with SRTT at 80 km/h; the total number of pavements was N = 46 pavements, 41 in Denmark and 5 in Norway; in some cases this set of data has been denoted Data set #1 or <ds1_80> Sub set No. Site Pavement Measured by N [-] Measured Listed in ID Table No. 1 Igelsø DRI30-DRI41 DRD Table 12 2 M64 DRI42-DRI55 DRD Table 12 3 M68 DRI56-DRI64 DRD Table 12 4 M10 DRI07-DRI013 DRD Table 12 5 Norwegian pavements STF Table 13 Reference tyre: SRTT Speed [km/h]: 80 15

16 6. RELATION BETWEEN TEXTURE AND NOISE 6.1 RELATION BETWEEN CPX NOISE LEVELS AND ROAD SUR- FACE TEXTURE LEVELS Figure 5 is a reproduction of a diagram from [4], showing the determination coefficient R 2 from linear regression analyses of the overall A-weighted CPX noise level on the third-octave band texture wavelength. The determination coefficient R 2 expresses the percentage of the variation in the measured noise levels which is explained by the variation in surface texture levels at that wavelength. The figure is based on a set of data from N = 29 roads with CPX noise levels measured using SRTT at 50 km/h: 13 DRD CPX and texture results from Kongelundsvej and M10, see Table 10 in Appendix 1, and data on noise levels and texture measured by SVV-STF on 16 roads in Norway, see Table 11. The highest percentage of explained variance R 2 = 72 % was found at 40 mm wavelength. These results are contaminated at small wavelengths, because DRD applied enveloping in the Danish results while STF did not do so in the Norwegian data. The enveloping caused lower texture levels than measured by SVV-STF and this has resulted in a lower percentage of explained variance. Figure 6 in the same way shows R 2 determined from Data set #2, see Table 2, for N =55 road sections with dense asphalt surfaces measured at 50 km/h with two old reference tyres A having slightly different age. The highest, although not high, determination coefficient R 2 is seen at 160 mm wavelength and there is virtually no correlation at small wavelengths. As Based on Data set #1 SRT tyres N = 29 roads M10, Kongelundsvej N 1 = 13 Norwegian roads N 2 = 16 Figure 5. Percentage of explained variance in overall A-weighted CPX noise level as a function of the texture wavelength; Data set #1, N = 29: L AcpxSRTT at 50 km/h [4] Figure 6. Percentage of explained variance in overall A-weighted CPX noise level as a function of the texture wavelength; based on Data set #2, N = 55: L AcpxTyreA at 50 km/h [4] Based on Data set #2 SRT tyres N = 55 roads N 1 =18 roads in DK N 2 = 37 roads in NO 16

17 already mentioned these results are contaminated at small wavelengths by DRD having applied enveloping while STF did not do so, and this probably has contributed to the lack of corralation at small wavelengths. Figure 7 is taken from [5] and shows the relation between the CPX noise levels from SRTT and the road surface texture levels at 80 mm wavelength for Data set #1, i.e. SRTT at 50 km/h on 34 roads (29 roads from Figure 5 plus 5 SVV-STF results from Kongelundsvej). As already mentioned, Figure 5 shows the highest R 2 at 40 mm wavelength while Figure 6 shows the highest R 2 at 160 mm. Nevertheless, in Figure 7 L tx80 has been chosen as an independent variable on the X-axis. This choice has also been made in various literature references, e.g. the octave band L tx80 in [10]. Based on Data set#1; N = 34 1= Kongelundsvej; N = 11 2 = M10; N = 7 3 = Norwegian roads; N = 16 The memo [5] contains several graphs of the type shown in Figure 7a and Figure 7b. Examples are shown in Figure 8 and Figure 9. The trend is for overall A-weighted CPX noise levels to be positively correlated with the surface texture third-octave band level at 80 mm wavelength. The same applies to some extent to the low frequency third octave band noise levels at 315 Hz but not to high frequency noise at 2000 Hz. Based on Data set#1; N = 34 1= Kongelundsvej; N = 11 2 = M10; N = 7 3 = Norwegian roads; N = 16 Figure 7b shows the same data as Figure 7a, but regression lines are shown for each of three sub sets of data. For the sub set shown in blue the range of texture levels is very limited and the texture/noise level relation is not significant. With the same texture level at 80 mm wavelength the pavements on M10 (green line) tended to yield about 3 db higher noise levels than the two other groups of pavement. This is looked into in some detail in Section Figure 7. Overall A-weighted CPX noise level from SRTT at 50 km/h as a function of the one-thirdoctave band texture level at 80 mm. N = 34 pavements in Data set #1. Fig. 7a (top): All data, L AcpxSRTT = L tx80 ; R 2 = Fig. 7b (bottom): Linear regression lines per sub set of data; taken from [5] 17

18 The data in Figure 9 illustrate the fact that there is a trend for the Norwegian pavements to have larger maximum aggregate size than the Danish wearing courses, and the higher noise levels on the Norwegian roads may be associated with this and with the use of studded tyres. The same trend was seen in data collected at 80 km/h [5]. Figure 10 shows 2-D correlation contours, i.e. the correlation 2) coefficient R from linear regression analyses for combinations of texture wavelength and acoustic third-octave frequency bands. The figure is a copy of Figures in [5] for the Norwegian pavements in Data set #2 ( Old reference tyre A at 50 km/h on N = 37 pavements) in the top part of the figure, and for the Danish pavements in Data set#1 (SRTT at 80 km/h on N = 41 pavements) in the bottom part of the figure. Table 17 and Table 18 in Appendix 1 give the values of R 2. Each table is based on data recorded with the same equipment, so the results are not contaminated by DRD having applied enveloping in the Danish results while STF did not do so in the Norwegian data. Figure 10 and Table 17 Table 18 show a positive correlation between the noise levels below 800 or at 1000 Hz and the surface texture levels at wavelengths larger than mm, and a negative correlation between high frequency noise levels and texture levels at small wavelengths. This has also been seen in earlier investigations. For example, the NordTex results in Figure 10 are in qualitative agreement with those in Figure 11 from [10]. Figure 11 was published in 1980, 2) Note, the figure shows the correlation coefficient R, not the determination coefficient R 2 as was the case in Figure 5 and Figure 6 Based on Data set#1; N = 41 1= Igelsø; N = 12 2 = M64; N = 13 3 = M68; N = 9 4 = M10; N = 7 Figure 8. CPX noise level from SRTT, L AcpxSRTT, at 80 km/h as a function of the one-third-octave band texture level at 80 mm, L tx80, for N = 41 pavements in Data set#1. The linear regression line is given by L AcpxSRTT = L tx80. R 2 = 0.462; taken from [5] Based on Data set #2; N = 55 1 = Kongelundsvej, M45, and Kastrupvej; N = 18 2 = Norwegian roads; N = 37 Figure 9. CPX noise level, L AcpxA, from old reference tyre A at 50 km/h as a function of the onethird-octave band texture level at 80 mm, L tx80, for N = 55 pavements in Data set #2. The linear regression line is given by L AcpxA = L tx80, R 2 = [5] 18

19 Third-octave band centre frequency [Hz] Third-octave centre wavelength [mm] Figure D correlation contours. The colours indicate the value of the correlation coefficient R. Figure 10a (top): Old reference tyre A at 50 km/h on N = 37 Norwegian roads, Data set #2; Figure 10b (bottom): SRTT at 80 km/h on 41 Danish roads, Data set #1. From [5] based on a Belgian and a Swedish study [11] attempting to determine noise-texture correlations as a function of the acoustic frequency and the texture wavelength. These Belgian- Swedish results were later confirmed by similar studies [10]. In Figure 11 top left, the maximum value of R = 0.95 at (315 Hz, 80 mm) and the minimum R = at (5000 Hz, 2 mm). Correspondingly: Top right: max 0.92 at (400 Hz, 80 mm); min at (3150 Hz, 2.5 mm); Bottom left: max 0.94 at (630 Hz, 80 mm); min at (4000 Hz, 2.5 mm); Bottom right: max 0.85 at (315 Hz, 63 mm), min at (2500 Hz, 2.5 mm). 19

20 Figure 11. Diagrams showing contours of correlation coefficients R from linear regression analysis of third-octave bands of acoustic frequency on thirdoctave band texture wavelength, originally from [10] but quoted here from [1]. All were radial tyres. Tyre P: PIARC reference tyre 165R15; Tyre S: Firestone 165R15; Tyre X: Michelin summer 175R14; Tyre W: winter tyre 165R15 What is unique about the NordTex study versus the Belgian-Swedish studies made before 1980 is that the NordTex study used the CPX method while the Belgian Swedish studies used the coast-by method, and that test tyres were different. Also, road surfaces were different, because in the late 1970 s there were few thin asphalt layers and no SMA surfaces. Despite these differences, the results are amazingly similar, and essentially the NordTex study confirms the results from the old Belgian-Swedish studies, although for modern tyres and roads. Thus, the noise/texture relations seem to be robust. However, these relations cannot be assumed to be valid for tyre/road noise from heavy vehicles. 6.2 INTER-CORRELATIONS Figure 12 [6] and Table 4 illustrate the relations between the overall A- weighted CPX noise levels and various pavement parameters: surface texture level L tx80 and L tx05 at third-octave band centre wavelength 80 mm and 5 mm, respectively, nominal maximum aggregate size, NMAS, and mean profile depth, MPD. L tx80 seems to be better correlated with the CPX noise levels than the other pavement parameters are, and L tx80 is highly correlated with MPD. These results are contaminated at small wavelengths because DRD applied enveloping in the Danish results while SVV-STF did not do so in the Norwegian data, and this probably contributes to the poor correlation between L tx05 and the CPX noise levels. 20

21 1 = Kongelundsvej; N = 11 2 = M10, N = 7 3 = Norwegian roads; N = 16 Figure 12. Relations between overall A-weighted CPX noise level and various pavement parameters, and interrelations between these. Based on measurements made by SVV-STF and DRD with SRTT at 50 km/h, <ds1_50>, see Table 10 and Table 11 Table 4. Values of R 2, summary from Figure 12, <ds1_50>; N = 34. Colours illustrate the degree of correlation L AcpxSRTT L tx80 NMAS MPD L tx05 L AcpxSRTT L tx NMAS MPD L tx Figure 13 illustrates the relations between the overall A-weighted CPX noise levels and the pavement parameters used in Figure 12 plus a so-called profile shape characteristic G (a German concept denoted Gestaltfaktor ). To calculate G, the cumulative probability distribution of the surface profile ordinates is generated. G is the percentage of this distribution which is higher than the average between the highest and the lowest individual points on the profile. The evaluation is made for every 100 mm of the profile length. A G value below 50 % indicates a peaky profile, while a G value larger than 50 % indicates a plateaulike profile with slits in it. Figure 13 is based on N = 21 pavements with available data on G [7]. The relations in the figure are all based on profiles measured by SVV-STF and therefore uncontaminated by DRD having applied enveloping while STF did not do so. 21

22 3 = Norwegian roads; N = 16 4 = Kongelundsvej, N = 5 Figure 13. Relations between overall A-weighted CPX noise level and various pavement parameters, and interrelations between these. Based on Data set #1; N=21; 3) Norwegian roads, red N = 16, Table 11; 4) Kongelundsvej, green N = 5, Table 10, with AC 8d excluded by mistake Table 5. Correlation coefficients R (Pearson correlation) summarised from Figure 13. The number of measurement results N = 21. Green = high positive; red = high negative correlation L CPXA L tx80 NMAS MPD G L tx5 Pearson Correlation L CPXA L tx NMAS MPD G L tx Table 5 summarises the correlation coefficients R based on the data illustrated in Figure 13. The highest correlation is between L tx80 and MPD. Best correlated with the CPX noise levels is the nominal maximum aggregate size NMAS, followed by L tx80. The G value is highly correlated with L tx05, but does not seem to provide new correlation with the noise levels that other parameters do not provide. MPD is sensitive to asymmetry of the profile and seems to represent the noise-texture relation better than G does. 22

23 6.3 CORRELATIONS BASED ON NORDTYRE DATA A multiple correlation was made for the NordTex project based on the data in Table 19 of the NordTyre final report [12]. The result is shown in Table 6. The study (of noise from different tyres versus texture parameters) contained the following parameters for 31 different pavements, including an ISO test track: L A MPD NMAS Age SRF L Me Average A-weighted noise level measured with the CPX method, using a set of 24 different car tyres, in db Mean Profile Depth, according to ISO , in mm Nominal Maximum Aggregate Size, in mm Surface age in years at time of noise measurement Type of surface (SMA or DAC) Megatexture level, according to ISO , in db rel m. L ME is believed to be closely related to L tx80 used in Table 5 The analysis confirmed the strong correlation between MPD and L ME. NMAS was found to provide by far the best correlation with L A, as was the case in Table 5. Age and megatexture were next. MPD correlation with the noise level was not significant. Note: The significance test was run as two-tailed, although it would have been better with one-tailed (provided all relations would be only one-directional). All Sig values should be divided by 2 to get the one-tailed values. Table 6. Results of a correlation analysis based on data from the NordTyre project. Sig. is the level of significance in two-sided test. Note that N = 30 for parameter SRF (Surface type), but 31 in all other cases. The only porous pavement (PA 6) was omitted from that part of the analysis, because it does not belong to any of the types SMA or DAC. Note also that Pearson correlation is R and not R 2 L A MPD NMAS AGE SRF L ME L A Sig. (2-tailed) Pearson Correlation **.448 * * N Pearson Correlation *.791 ** MPD Sig. (2-tailed) N Pearson Correlation.670 ** * NMAS Sig. (2-tailed) N Pearson Correlation.448 * Age Sig. (2-tailed) N Pearson Correlation * ** SRF Sig. (2-tailed) N L ME Sig. (2-tailed) Pearson Correlation.446 *.791 **.374 * ** 1 N ** Correlation is significant at the 0.01 level; * Correlation is significant at the 0.05 level (2-tailed) 23

24 6.4 ESTIMATED ROAD NOISI- NESS PARAMETERS Figure 14 from [6] shows the measured CPX noise levels as a function of ENDt (the Expected pass-by Noise level Difference due to texture differences) calculated using a method described in ISO [13] for Data set #1, with 41 CPX noise levels measured with SRTT at 80 km/h and texture data from the Danish roads listed in Table 12 in Appendix 1. There is fair correlation, with 20 % larger range in measured CPX noise levels than in the calculated ENDt. A logarithmic fit would provide a slightly higher determination coefficient R 2 = Figure 15 from [6] shows the Estimated Road Noisiness Level ERNL from [10], as a function of the ENDt. ERNL is the pass-by noise level from a passenger car estimated, by means of Eq. 1, from the octave band road surface texture levels L tx80 and L tx05 at 80 mm and 5 mm texture wavelength, respectively, with constants a = 0.5; b = 0.25 and c = 60. There is fine correlation and an almost 1:1 relation between ERNL and ENDt in these data. Figure 14. CPX noise level (minus an arbitrary 90 db) as a function of ENDt ERNL = a L tx80 - b L tx05 + c Eq. (1) Figure 15. Estimated road noisiness ERNL as a function of ENDt 24

25 7. HOW CPX NOISE LEVELS REPRESENT TRAFFIC NOISE LEVELS Pass-by noise levels from passenger cars from Table 12 in Appendix 1 are shown in Figure 16 as a function of the CPX noise levels measured with SRT tyres on the same pavement. Figure 17 shows the same relation based on a larger set of data collected by DRD on 45 different pavements and repeated on these pavements plus another five new. Figure 17 includes the data from Figure 16. At 80 km/h the average difference between the CPX and the pass-by noise levels is 21.5 db and the correlation is high. 1 = Igelsø, N = 4 2 = M64 dense, N = 9 3 = M68 dense, N = 7 4 = M64 and M68 thin porous, N = 5 The noise levels measured with the CPX method using SRT tyres are well correlated with the noise levels measured with the SPB method for light vehicles. The residual standard deviation is approximately 1 db, which is roughly in line with earlier studies. Thus texture optimization based on the CPX method corresponds reasonably well with an optimization based on the SPB method. Figure 16. SPB noise levels from passenger cars at 80 km/h on 25 different pavements vs. CPX SRTT 80 km/h Figure 17. Passenger car pass-by noise levels as a function of the CPX noise level measured with SRTT. N = 95 on 45 and 50 pavements in Denmark 2010 and 2011, respectively 25

26 8. ROLLING RESISTANCE 8.1 BACKGROUND Projects on tyre/road rolling resistance, such as MIRIAM, COOEE, ROSANNE, and national Swedish activities during the last 10 years have demonstrated that new surface policies must consider tyre/road rolling resistance. Consequently, exploring low-noise surfaces by texture optimization must consider the effect that noise-optimization has on rolling resistance. Fortunately, low noise and low rolling resistance, when achieved by improved surface texture, do seem to go almost hand-in-hand. In the NordTex project, rolling resistance was measured in Denmark and Sweden by the Technical University of Gdansk (TUG) with a special trailer [8]. Measurements of rolling resistance were also intended in Norway but abandoned due to budget restraints. The trailer was run at 50 km/h and 80 km/h, sometimes also at 110 km/h. Three test tyres were used: SRTT (16 ), Avon AV4 and Michelin Primacy; see [8]. The first two of these tyres have been selected as reference tyres for noise measurements with the CPX method, and have also been used as temporary references for measuring rolling resistance. The SRTT and the Michelin Primacy are car tyres while the Avon AV4 is a tyre for light trucks, used as a proxy for heavy truck tyres. This tyre is known to work well for that purpose in noise measurements. The response of car tyres to various road surface textures differs from that of truck tyres. Within the NordTex project or in close connection with it 3), 14 road surfaces were measured in Denmark and 40 in Sweden. 8.2 MEASUREMENTS IN DENMARK As an example, Figure 18 shows the rolling resistance coefficients (RRC) measured at 110 km/h with three different tyres on the test sections of road on M10, while Figure 19 shows the 3) The Swedish Transport Administration funded rolling resistance measurements in Sweden to supplement the NordTex project RRCs measured at both 80 km/h and 110 km/h as a function of the mean profile depth MPD [8]. There is less variation between pavements than between tyres and there is a trend for higher rolling resistance with increasing MPD; see also Table 7. The large variation between tyres is due to the fact that the Avon AV4 light truck tyre has much higher RRC than the car tyres; AV4 tyre could not replace a car tyre. More comprehensive data, although not from the NordTex project, appear in a report from the MIRIAM project [14]. Most of those data have been collected at a later time, when methods and equipment had been improved and they represent a wider range of textures and more road surfaces 4). 4) These data contain information suggesting that something may be wrong with the data for SRTT in Figure 19, leading to too little sensitivity in RRC to variation in MPD. Most probably the RRC for HRA is too low 26

27 Figure 18. Rolling resistance coefficients measured with three different tyres on seven sections of M10, from [8] Figure 19. Rolling resistance coefficients measured with three different tyres on seven sections of M10 as a function of the surfaces mean profile depth; example from [8]. Data for UTLAC 8 are so close to data for AC 8o that the latter are difficult to see in the diagram 27

28 Table 7. Results of linear regression analyses of rolling resistance coefficients on MPD as measured on the seven sections of M10; based on [8] but with adjusted MPD-values; see the Note in Section 4. s R is the standard deviation of the residuals Tyre SRTT Avon AV4 Michelin Primacy HP Speed Slope Intercept R 2 s R [km/h] [-/mm] [-] [-] [-] In the MIRIAM report [14], the final relation between the rolling resistance coefficient RRC and MPD was suggested for light vehicles to be: RRC = Constant MPD + X IRI (Eq. 2) where MPD is Mean Profile Depth in mm, measured according to ISO IRI is the International Roughness Index X is a constant yet to be determined (but quite low for cars) Constant is a value unique to a certain tyre and several other circumstances; usually An important thing to notice in Eq. 2 is the slope of the relation with MPD, namely , which is larger than the value for SRTT in Table MEASUREMENTS IN SWEDEN AND A SYNTHESIS OF ROLLING RESISTANCE MEASUREMENTS This section presents a compilation made for the NordTex project of the results of rolling resistance measurements made by TUG at the request of VTI on 40 surfaces in Sweden, with three tyres, at two speeds. To reduce data, all measurement results from a certain road have been arithmetically averaged; i.e. for the two speeds and for the three tyres. This also reduces random errors. Speed is unimportant as speed influence is small and correlation between results measured at the two speeds is almost perfect. However, tyres may have slightly different sensitivity to texture, i.e. the RRC-MPD slope may differ, but it has been noticed that the ranking of surfaces is not affected by this. Thus, the grand averages given here represent an average for traffic having two thirds of light vehicles and one third of trucks and buses, assuming that tyre Avon AV4 represents the latter, which has been indicated in German results 5 ). The results are shown in Figure 20: RRC as a function of MPD. Each measurement series is distinguishable 5) A reference has not yet been approved for publication by the German sponsor by symbols and colours. The reason for distinguishing between series is that there are uncontrolled variations between these (and probably also within some series, although much less). Such variations are variations in temperature, and probably problems with stable calibration. For example, the two data sets yielding the highest rolling resistance coefficients were measured at 5-10 o C, while other data sets appearing in the lower part of the diagram were measured at o C. There could also be differences between data sets due to tyre changes between measurement series. No temperature correction has been made, since correction factors are unknown, while it is known that temperatures in south Scandinavian summer and autumn do affect rolling resistance as much as the road surface texture does. In Figure 20, the Danish measurements mentioned in Section 8.2, supplemented by results from Kongelundsvej have been added together with results of TUG measurements for the Round Robin Test (RRT) of MIRI- AM. Only the TUG data from MIRIAM were included, because other measur- 28

29 ing devices did not supply comparable data for all the surfaces. The most important result in Figure 20 is the slope of RRC versus MPD; i.e. the texture influence on rolling resistance. Regression data for all data sets are listed in Table 8. The slopes appear consistent ( ) when uncertain data sets (shown in parentheses) are neglected, although also the latter show reasonably consistent slopes. A slope of would be a good average for the three tyres used. If one would distinguish between the two car tyres on one hand and the light truck tyre on the other hand (these results are not shown in the figure), the slope for the car tyres would be approximately and for the truck tyre approximately This implies that, as is the case for noise [10], truck tyres are less sensitive to texture than car tyres, which is logical given the differences in dimension. RRC for average of 3 test tyres DK 2009 SE RV SE St Aska 2010 SE Skåne 2009 SE Skåne SE Skåne 2010 TAL MIRIAM RRT SE 2011 SE MPD [mm] Figure 20. Rolling resistance coefficients (RRC) measured with three different tyres at two speeds (RRC averaged over these) on 40 Swedish road surfaces as a function of the surface mean profile depth (MPD). Also results from Danish measurements mentioned in Section 8.2 and from TUG measurements in a Round Robin Test carried out in the MIRIAM project have been included Table 8. Results of linear regression analyses of rolling resistance coefficients RRC on MPD for the data in Figure 20. Each observation is an average for three tyres and two speeds. SE = Sweden, DK = Denmark. Values in () are uncertain due to small MPD range or too few observations Data set Number of observations Regression equation: RRC = Slope [-/mm] DK MPD SE RV MPD SE St Aska MPD (0.0017) (N.A.) SE Skåne MPD SE Skåne MPD SE Skåne 2010 TAL MPD (0.0021) (0.98) MIRIAM RRT MPD SE MPD (0.0012) (0.44) SE MPD (0.0009) (0.43) R 2 [-] 29