Tyre and Road Surface Optimisation for Skid Resistance and ...

ROlling resistance, Skid resistance, ANd Noise Emission measurement standards for road surfaces

Project Coordinator Manfred Haider, AIT Austrian Institute of Technology GmbH, Giefinggasse 2, 1210 Vienna, Austria. Tel: +43(0) 50550-6256 , Fax: +43(0) 50550-6599. E-mail: [email protected]. Website: http:/rosanne.fehrl.org

Collaborative Project FP7-SST-2013-RTD-1

Seventh Framework Programme

Theme SST.2013.5-3: Innovative, cost-effective construction and maintenance for safer, greener and climate resilient roads

Start date: 1 November 2013 Duration: 36 months

Deliverable 4.3

Reference tyres and road surfaces for skid resistance, noise and rolling

resistance measurements

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n°605368

Main Editor(s) Ulf Sandberg, VTI

Due Date 2015-12-31

Delivery Date 2017-01-17

Work Package WP 4

Dissemination level Public

mailto:[email protected]

http://pilot4safety.fehrl.org/

ROSANNE Deliverable D4.3: Reference tyres and reference road surfaces

Date: 2017-01-17, Version: 5.1 II (63)

Contributor(s)

Main Contributor Ulf Sandberg, VTI, Sweden

Contributor

Luc Goubert, BRRC, Belgium

Review

Reviewer(s) Luc Goubert

Tiago Vieira


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Control Sheet

Version History

Version Date Editor Summary of Modifications

1.0 2016-09-14 U. Sandberg First version of the document

2.0 2017-01-05 U. Sandberg Second version of the document

3.0 2017-01-10 U. Sandberg Third version of the document

4.0 2017-01-14 U. Sandberg Fourth version of the document

5.0 2017-01-16 U. Sandberg Fifth version of the document

5.1 2017-01-17 U. Sandberg Some corrections and additions made to the 5th version


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Table of Contents

Executive Summary .......................................................................................................... VII I. Introduction ................................................................................................................... 1

II. Purposes ........................................................................................................................ 2

III. A few notes on terminology .......................................................................................... 2

IV. Related general publications ........................................................................................ 2

PART A: REFERENCE TYRES ............................................................................................. 4

A1. Introduction and purpose ............................................................................................. 4

A2. A historical perspective (before 1990) ......................................................................... 4

A3. A historical perspective (1990-2010) ............................................................................ 6

A4. Status of work when ROSANNE started ...................................................................... 9

A5. Work done in ROSANNE ............................................................................................. 10 A5.1 General issues .........................................................................................................10 A5.2 Relation between CPX and SPB measurements for the reference tyres ..................11 A5.3 Reference tyre ageing and effect of rubber hardness ...............................................11 A5.4 The effect of rubber hardness ..................................................................................13 A5.5 Temperature effects .................................................................................................15 A5.6 Validation tests .........................................................................................................15

A6. Other reference tyres for noise monitoring ............................................................... 17

A7. Decision in ROSANNE about the reference tyres ..................................................... 18

A8. Availability of the tyres ............................................................................................... 20

A9. Implementation of the results as new ISO procedures ............................................. 21

A10. Reference tyres for skid resistance measurements ............................................. 22

A11. Future work ............................................................................................................. 23 A10.1 Introduction ........................................................................................................23 A10.2 Search for new tyres to become a reference tyre, especially H1 ........................23 A10.3 Reference tyre to represent worn tyres in traffic .................................................24 A10.4 Other studies and improvements for the ISO technical specification ..................24 A10.5 Issues concerning rolling resistance and skid resistance ....................................25

A12. Conclusions ............................................................................................................ 26

A13. References .............................................................................................................. 26

PART B: REFERENCE ROAD SURFACE FOR USE IN NOISE STUDIES ......................... 28

B0. Background ................................................................................................................. 28

B1. Introduction and purpose ........................................................................................... 29

B2. Scope and use of the concept .................................................................................... 29

B3. The CNOSSOS-EU approach ...................................................................................... 30 B3.1 Effect of road surface characteristics in the CNOSSOS-EU model............................30 B3.2 The CNOSSOS-EU reference road surface ..............................................................31


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B4. The noise properties of the actual surfaces on which the virtual reference is based – Data collected in ROSANNE ......................................................................... 32

B5. Problems with the CNOSSOS-EU approach .............................................................. 36

B6. Improved definition of the virtual reference surface ................................................. 37

B7. Practical example from annual Swedish tests........................................................... 40

B8. The ISO 10844 reference surface ............................................................................... 41

B9. Future work .................................................................................................................. 42

B10. Conclusions ............................................................................................................ 42

B11. Suggested terminology .......................................................................................... 43

B12. References .............................................................................................................. 43

PART C: REFERENCE ROAD SURFACE FOR USE IN ROLLING RESISTANCE STUDIES ....................................................................................................................... 45

C0. Background ................................................................................................................. 45

C1. Introduction and purpose ........................................................................................... 45

C2. Scope ........................................................................................................................... 46

C3. Normative references .................................................................................................. 46

C4. Terms and definitions ................................................................................................. 46

C5. Outline of the procedure ............................................................................................. 47

C6. The virtual reference surface ...................................................................................... 48 C6.1 General issues .........................................................................................................48 C6.2 Macrotexture ............................................................................................................48 C6.3 Megatexture .............................................................................................................48 C6.4 Longitudinal evenness .............................................................................................48 C6.5 Transversal evenness ..............................................................................................48 C6.6 Elasticity ...................................................................................................................48 C6.7 Longitudinal slope ....................................................................................................48 C6.8 Transversal slope .....................................................................................................48

C7. The actual reference (test) surface ............................................................................. 49 C7.1 General issues .........................................................................................................49 C7.2 Macrotexture ............................................................................................................49 C7.3 Megatexture .............................................................................................................49 C7.4 Longitudinal evenness .............................................................................................49 C7.5 Transversal evenness ..............................................................................................49 C7.6 Elasticity ...................................................................................................................49 C7.7 Longitudinal slope ....................................................................................................50 C7.8 Transversal slope .....................................................................................................50 C7.9 Homogeneity ............................................................................................................50 C7.10 Visual appearance .............................................................................................50 C7.11 Cleanliness ........................................................................................................50 C7.12 Dimensions of the actual test surface .................................................................50 C7.13 Acceleration and braking zone adjacent to the real test surface .........................50 C7.14 Surface temperature ..........................................................................................50


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C7.15 Measurement speed and operating concerns .....................................................50

C8. Procedure using an enveloped surface profile for texture calculation .................... 51

C9. Calculation of the rolling resistance coefficient reference value Cr,ref ..................... 52

C10. Discussion of the k factor ...................................................................................... 52

C11. Reporting ................................................................................................................. 53

C12. Uncertainty issues .................................................................................................. 53

C13. References .............................................................................................................. 54


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Executive Summary This deliverable starts with an introductory section, presenting the issues dealt with in this document, and continues with a few notes on terminology, and listing other relevant ROSANNE deliverables and international standards. Then, three parts follow that deal with the three major subjects of this deliverable. Part A: Reference tyres The CPX method needs reference tyres for testing the noise properties of road surfaces. The same applies to rolling resistance properties. As there is a decision in ROSANNE to use the CPX method for noise and a method for rolling resistance that uses a somewhat similar principle, both methods need to have reference tyres specified. It has been decided earlier in ISO/TC 43/SC 1/WG 33 to specify two reference tyres, denoted P1 and H1, and the task in ROSANNE has been to evaluate that decision and to select suitable tyres for the purpose. The work in ROSANNE about reference tyres has been extensive and provided results that have been very useful for ISO in the work to produce the standard on CPX measurements, as well as the technical specifications for two reference tyres and for the temperature corrections required for these tyres. Without the assistance of the ROSANNE work, the ISO work would have been seriously delayed. As there was a very stringent deadline for producing the ISO CPX standard (until the end of 2016), that deadline would not have been met if the ROSANNE work with reference tyres had not been done, and thus the work with the CPX standard would have needed to start with a proposal for a new work item. Clearly, this alone would have meant a delay of maybe a couple of years. ROSANNE work has indicated that tyres P1 (SRTT) and H1 (Avon AV4) are not only the best options, but also the only options for the CPX method, at the time of writing. They have also turned out to be useful as provisional references for rolling resistance measurements. ROSANNE has provided information about the influence of temperature on tyre rubber hardness, and on the influence of rubber hardness combined with temperature on CPX levels, without which the uncertainty of the CPX method would be substantially worse. The project has also highlighted the tyre mounting and run-in directional properties, as well as the variation between tyre samples that are nominally equal. Following the ROSANNE work, ISO is now in the final process of publishing three important documents, all of which are also used in the proposed draft to CEN for classification of noise properties of road surfaces, and where the TS on reference tyres is also used in the proposed draft to CEN on rolling resistance properties of road surfaces:

• ISO 11819-2: The standard presenting the CPX method • ISO/TS 11819-3: The technical specification for reference tyres • ISO/TS 13471-1: The technical specification for temperature correction

This deliverable also contains an extensive section on future work that should be done to improve the technical specification, to find a replacement for tyre H1 and for attempting to find a reference tyre representing worn and worn-out tyres, plus a few other issues.


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Part B: Reference road surface for use in noise studies There is a great need for a reference surface to be used when developing and implementing road traffic noise prediction models since the input noise levels and frequency spectra for various vehicle categories must be measured for a defined reference case. A second great need is to have a common reference when speaking about and reporting “noise reduction” for “low noise road surfaces”. As was first realized in project HARMONOISE, later carried over to IMAGINE and CNOSSOS-EU, the best option is to select a reference case that does not exist in reality but which is possible to define based on a couple of very common road surface types. Thus, a “virtual reference surface” has been defined in CNOSSOS-EU and used in the European Directive EU 2015/996. In summary, it is a mix (an acoustic average) of dense asphalt concrete with maximum aggregate size 11 mm (DAC 11) and stone mastic asphalt, also with maximum aggregate size 11 mm (SMA 11); each at an age between 2 and 7 years, and exposed to proper maintenance. These two surface types were chosen since they represent two of the most common types on European roads, and at least one of the types should be commonly available in each member state. In this deliverable, the virtual reference surface concept is explored based on experimental data collected and compiled in ROSANNE for the two reference tyres P1 and H1 on various DAC 11 and SMA 11 surfaces in the partners’ countries. Both typical CPX levels and typical frequency spectra are shown. It appears that the deviation between surfaces that are nominally equal is larger than one would like. It is hypothesized that the present measured noise properties of the virtual reference surface in the CNOSSOS-EU model that are input values to the model may need extensive checking. Proposals are made on how one can define a virtual reference surface practically and with lower uncertainty. Most important is to include not only one of each DAC and SMA surface, when attempting to assign reference noise levels and spectra to the virtual reference, but to make measurements on several surfaces that are nominally equal but constructed and laid independently and of different age. Several ways to improve the definition of the virtual reference and the associated noise level and frequency spectrum are presented. For example, it is recommended to attempt to find and document the original grading curve of the mix, as well as measuring the macrotexture represented by the MPD value. It may also be fruitful to use an enveloped MPD instead of the raw MPD for this purpose. In the future, it may be possible to define a reference MPD value (or reference enveloped MPD) for each of the ideal DAC 11 and SMA 11 pavements and to normalize measurement results on actual road sections with such pavements to the reference MPD. It is acknowledged that there already is a standard reference surface, according to ISO 10844, the properties of this surface are discussed, and it is motivated why this is not useful in this application.


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Part C: Reference road surface for use in rolling resistance studies A surface with a known rolling resistance for a given reference tyre would be very practical for the fast checking of a rolling resistance measurement device, for example of the trailer type. Rolling resistance measurement involves measurement of very small angles or forces and should be done with great care, which should involve a frequent checking of the equipment by comparing to a known standard, in order to avoid any drift. It could also serve as a reference in relation to which the rolling resistance of old or new road surfaces would be expressed. However, the construction of a dedicated test track with precise, predefined surface properties is a delicate and cumbersome (and hence costly) operation. Therefore, an alternative approach is proposed here: the virtual rolling resistance reference surface. This virtual surface is defined by a set of properties which are known to be relevant for the rolling resistance (texture, slope, elasticity, etc). The calibration of a rolling resistance device is then carried out by selecting a real road section with properties which deviate only within narrow limits from those of the virtual reference surface and measuring the rolling resistance coefficient on it. Then a correction is applied to the measured result to account for the deviations of the real surface from the virtual reference surface, yielding the rolling resistance coefficient as if measured on the virtual reference surface. The correction is based on a so-called k factor, which is the slope in the correlation between the rolling resistance coefficient and the texture values represented by the mean profile depth, MPD. A discussion is included regarding the preliminary status of the k factor.

Summarizing Part C of this document comprises the following steps:

1. The definition of a virtual rolling resistance reference surface by means of listing the relevant properties and appropriate descriptors, to which a standard value is assigned

2. Fixing of the boundaries regarding how far the real surface may deviate from the virtual surface

3. A method to calculate the rolling resistance coefficient on the virtual surface from the measurement on the real surface, using the k factor.

An alternative procedure for the enhanced compensation for the difference of the macrotexture between the virtual and the real surface – a simple but realistic surface profile enveloping procedure – is also outlined in this part and may be used to achieve a higher precision in the calibration.

ROlling resistance, Skid resistance, ANd Noise Emission measurement standards for road surfaces

Project Coordinator Manfred Haider, AIT Austrian Institute of Technology GmbH, Giefinggasse 2, 1210 Vienna, Austria. Tel: +43(0) 50550-6256 , Fax: +43(0) 50550-6599. E-mail: [email protected]. Website: http:/rosanne.fehrl.org

I. Introduction The three road surface parameters considered in ROSANNE, namely skid resistance, noise and rolling resistance, are results of interactions between tyres and the road surface. Consequently, one needs to consider both the road surfaces and the tyres rolling on the surfaces in this project. When testing the road surface influence and trying to quantify it, for practical and economic reasons, one must rely on a limited number of test tyres assumed to be representative of the tyres used by the entire road traffic fleet. These tyres, we may refer to as test tyres, but if they are intended for wide-spread and long-term use, while also being reasonably well specified, we call them reference tyres. Evidently, as the ROSANNE work aims at producing standard measuring methods, reference tyres are a very essential part of this project. In ROSANNE, it was decided to work with existing reference tyres in the work dealing with skid resistance; therefore, reference tyres for skid resistance measurements are not dealt with here. But, as reference tyres for noise and rolling resistance were not yet determined at the start of the project, tyres for those two parameters have been in focus. Other parts of ROSANNE are outlining draft standards on classification of noise properties of road surfaces (Deliverables D2.1, D2.4 and D2.6) and classification of rolling resistance properties of road surfaces (Deliverable D3.5). In order to make these classification methods complete, reference tyres must be designated. The purpose of the first Part (A) of this Deliverable is to document the work related to these tyres. There are also needs for specified reference (road) surfaces. One such case is when a certain performance of a road surface or range of road surfaces needs to be compared to some common and “normal” case. An example is when speaking or writing about “noise reduction” or “rolling resistance reduction”. “Reduction” always compares the object of interest (such as a new road surface type) to some other better known (reference) subject, which often can be a dominating road surface type in the road infrastructure in the region of interest. Consequently, ROSANNE has attempted to define reference surfaces which may be useful for two very common applications: (1) reference for calculation of road traffic noise emission, and (2) reference for a simplified calibration of rolling resistance measurement devices. In both cases, there may also be additional uses; for example, for noise, the reference surface may be a practical norm when reporting “noise reduction” of low noise road surfaces, in order that such reported quantities are comparable over time and location. For rolling resistance, the definition of a reference surface here may be a starting point for working out a model for predicting rolling resistance of road surfaces, something which may turn out to be useful for replacing survey measurements. Nevertheless, it is important that both reference tyres and reference surfaces are defined as precise and unambiguous as possible, taking state-of-the-art knowledge into consideration, which is the


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overall ambition in this deliverable. The purpose of the second Part (B) of this Deliverable is to document the work related to reference surfaces for noise and the purpose of the third Part (C) is to document the work related to reference surfaces for rolling resistance.

II. Purposes The overall purposes of this work in ROSANNE are to:

• Study, select and define two reference tyres for noise and rolling resistance measurement of road surface properties

• Study, select and define a reference surface for acoustical properties of road surfaces • Study, select and define a reference surface for rolling resistance properties of road surfaces,

useful for simple calibration of measuring devices

III. A few notes on terminology Noise is defined as unwanted sound. Therefore, ideally, noise is a subjective entity. However, when it comes to studies or considerations related to the unwanted sound, it is common practice worldwide to use noise as a physical parameter similar to sound and quantified with the same physical units. Therefore, in this document, noise is considered as a physical parameter similar to sound, assuming that its effects are essentially unwanted. Another terminology issue relates to the term used for the wearing course of roads and streets; i.e. the surface on which road vehicles run. The features of these of interest on noise and rolling resistance studies are mainly related to the surface, but they may sometimes also depend on the structure a few centimetres under the surface. A common term in Europe and Australia is the term “road surface”, while in North America the term “pavement” is commonly used. Pavement may be considered as not only the surface which is in or near contact with the tyres but also the full layer of the wearing course, which in some cases may even include two layers. This document may not be consistent in the use of the terms road surface or pavement. However, unless something else is expressed, by “road surface” is meant the same part of the road as “pavement”; i.e. the wearing course, which in special cases (“low noise surfaces”) may include two layers near the top of the surface. Another potential inconsistency that may perhaps lead to confusion is the designation of the surface types DAC 11 and SMA 11, where DAC means dense asphalt concrete and SMA means stone mastic asphalt, and 11 is the maximum aggregate size. This is sometimes written as DAC 0/11 and SMA 0/11 (0/11 meaning that the mix includes aggregate and fine material from 0 to 11 mm), which is no technical difference to DAC 11 and SMA 11, but the latter is the standard designation according to the European series of standards EN 13108 and should be used.

IV. Related general publications The following deliverables in ROSANNE are related to this document:


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• D2.1 Outline of a draft standard for a procedure for the characterization of noise properties of road surfaces

• D2.2 Report on temperature influence and possible corrections for measurement of noise properties of road surfaces

• D2.3 Report on the analysis and comparison of existing noise measurement methods for noise properties of road surfaces

• D2.4 Draft standard for a procedure for the characterisation of noise properties of road surfaces

• D2.5 Report on the compatibility of the proposed noise characterization procedure with CNOSSOS‐EU and national calculation methods

• D2.6 Report on the development of the procedure for characterisation of noise properties of road surfaces including the updated draft standard

• D3.1 Draft standard outline: Methods of measuring rolling resistance — The road-based method

• D3.5 Draft standard for a trailer-based rolling resistance measurement method including robust calibration procedures

• D3.6 Experimental validation of the rolling resistance measurement method including updated draft standard.

These are available or will be available in 2017 on the ROSANNE website: http://rosanne-project.eu/ The following ISO documents are related to this Document:

• ISO 11819-2 Acoustics — Method for measuring the influence of road surfaces on traffic noise — Part 2: The close-proximity method

• ISO/TS 11819-3 Acoustics — Measurement of the influence of road surfaces on traffic noise — Part 3: Reference tyres

• ISO/TS 13471-1 Acoustics - Temperature influence on tyre/road noise measurement – Part 1: Correction for temperature when testing with the CPX method

• ISO 13473-1 Characterization of pavement texture by use of surface profiles: Part 1: Determination of Mean Profile Depth

The three first are all expected to be published by ISO in January-February of 2017. ISO 13473-1 is available in a version from 1997, but a new version is expected to be published in 2018. References related to the three annexes are published at the end of each annex.

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PART A: REFERENCE TYRES A1. Introduction and purpose When testing and trying to quantify the road surface influence on tyre/road noise with the CPX method (ISO 11819-2); for practical and economical reasons, one must rely on a limited number of test tyres assumed to be representative of the entire road traffic. These tyres may be referred to as “test tyres”, but if they are intended for wide-spread and long-term use, while also being reasonably well specified, they would be “reference tyres”. Reference tyres for the CPX method were specified already in the 1990’s; however, only as unofficial drafts by ISO/TC 43/SC 1/WG 33, and later developments made it necessary to look for new tyres. More about this is reported below. As the ROSANNE work aims at producing standard measuring methods, reference tyres are a very essential part of this project. In ROSANNE, it was decided to work with existing reference tyres in the work dealing with skid resistance; therefore, reference tyres for skid resistance measurements are not dealt with here. However, as reference tyres for noise and rolling resistance were not yet determined at the start of the project, tyres for those two parameters have been in focus in this work. Other parts of ROSANNE are outlining draft standards on classification of noise properties of road surfaces (Deliverables D2.1, D2.4 and D2.6) and classification of rolling resistance properties of road surfaces (Deliverables D3.1, D3.5 and D3.6). To make these classification methods complete, they must use designated reference tyres. Rather than including tyre specifications in the method descriptions, specifications for the tyres and their conditions are given in a document separate from but coordinated with the measurement methods, since tyres may have to be changed more often than the methods. The purpose of this Part of this Deliverable is to document the work related to these tyres. The results of this task (4.2 in ROSANNE) will greatly influence the resulting uncertainty and representa-tivity of the noise and rolling resistance measurement methods. The task has been performed in close cooperation with ISO/TC 43/SC 1/WG 33, which presently deals with this issue in the noise field, as well as earlier work in project MIRIAM on rolling resistance has been utilized.

A2. A historical perspective (before 1990) Extensive measurements with the CPX method (then called „The Trailer method“) took place in Sweden in 1984-1990 in cooperation projects between VTI and TUG. At that time, the following test tyres were used; see Figure A1:


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Tyre P: The non-patterned (“smooth“) reference tyre specified by PIARC (hence tyre P) primarily for friction measurements. This tyre was intended for representing cars with worn-out tyres. Tyre S: A car tyre for normal use (“summer“) produced by Firestone, product name Cavallino S1. This tyre was intended for representing cars with tyres in new condition. Tyre M: A car tyre for normal use (“summer“) produced by Michelin, product name XZX. This tyre was intended for representing cars with tyres in new condition. Tyre G: A car tyre for winter use produced by Gislaved Tyres (hence tyre G) in Sweden, product name Gislaved Frost M+S. This tyre was intended for representing cars with winter tyres in new condition. Tyre GS: A car tyre for winter use produced by Gislaved Tyres in Sweden, product name Gislaved Frost M+S. The tyre was equipped with steel studs (hence tyre GS). This tyre was intended for representing cars with studded winter tyres in new condition.

Figure A1: The five test tyres used by VTI/TUG in the 1980’s. From left: P, S, M, G and GS. Other research organizations used a variety of other normal car tyres, and in some cases, only the PIARC smooth tyre. There was also a PIARC tyre with a ribbed tread pattern which was favoured by Arsenal in Austria. On should note that the PIARC smooth tyre has a regular tread with thickness normal for a new tyre. It implies that it is not really representative of worn-out tyres since the latter have 6-8 mm thinner treads, and the tread thickness has a high influence.


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In the late 1980’s, the German Ministry of Transport proposed the use of the following tyres (in new condition), which also were used in cooperation with France, albeit the method preferred then was the controlled pass-by (CPB) [WG 33, 1995]:

• Michelin MXT, 155/70 SR 13 • Goodyear Vector, 175/70 SR 13 • Continental CH90, 195/65 HR 15 • Pirelli P600, 205/60 VR 15

A3. A historical perspective (1990-2010) The experience of “trailer measurements“ in countries such as Germany, France, Austria, Sweden and Poland in the 1980’s was assessed by ISO/TC 43/SC 1/WG 33, with the outcome that the following tyres were possible candidates [WG 33, 1995]: • ”PIARC smooth”: The standard reference tyre manufactured according to PIARC specifications. Steel radial, dimension 165 SR 15. Smooth (patternless) tread.

• ”PIARC rib”: The standard reference tyre manufactured according to PIARC specifications. Steel radial, dimension 165 SR 15. Longitudinally ribbed tread.

• ”ASTM E 501”: The standard reference tyre manufactured according to ASTM E 501-88 specifi-cations, for skid-resistance tests. Belted bias construction, dimension G78-15. Longitudinally ribbed tread. There is also a non-patterned version of this tyre.

• ”ASTM radial”: Standard reference tyre manufactured according to ASTM E 1136 specifications. Steel radial, dimension P195/75 R 14. ”All Season” tread (similar to a ”conventional” tyre tread). If one can accept the use of conventional, commercially available tyres, the tyres recommended by the mentioned guideline from the German Ministry of Transport were also considered. It was noticed that tyre G used in Sweden had another interesting feature: it classified road surfaces in a way similar to how truck tyres classified road surfaces, as noted when also SPB measurements were made. Thus, it was also becoming useful as a proxy for a truck tyre. The main reason for this performance was probably that the tread pattern featured relatively large blocks with relatively large air channels between them; something resembling truck tyres for drive axles. Consequently, it was considered to use this tyre as one of the reference tyres. After further discussions in WG 33, it was decided that four new tyres should be agreed on. These were specified in the first committee draft (CD) for the CPX method [ISO/CD11819-2, 1997]: Tyre A: Tread pattern “Summer A“ (Vredestein ProTrac, 185/65 R15) Tyre B: Tread pattern “Summer B“ (Avon Turbogrip, 185/65 R15) Tyre C: Tread pattern “Winter“ (Avon Enviro CR322, 185/65 R15) Tyre D: Tread pattern “Block“. This was in principle the tyre G mentioned above, intended as a proxy for truck tyres.


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The four tyres are illustrated in Figure A2.

Figure A2: The four test tyres first used in the CPX method in the 1990’s. However, it appeared that in the end of the 1990’s the Gislaved tyre was no longer available on the market, and WG 33 started looking for another tyre having similar features. This was soon identified by VTI as Dunlop Arctic M3 (dimension 185 R 14); see Figure A2.

Figure A3: The Tyre D used provi-sionally in the period 1998-2010; Dunlop Arctic MK3.

Production of this tyre had stopped in the late 1990’s but an oral agreement was reached with Dunlop tyres in the UK that this tyre would be transferred to the Dunlop vintage tyre store and thus produced also later as a special tyre, if needed.


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However, in 1999, Goodyear Tire and Rubber Company bought the major part of Dunlop. During the next few years it was attempted to get an agreement with Goodyear that the Arctic tyre would stay in the Dunlop vintage catalogue, but finally Goodyear (Luxembourg office) denied this. In 1998, a comprehensive round robin test of the CPX method including most CPX devices available in Europe, as well as a limited Japanese trial, was performed in the Netherlands and Germany, reported in 2000 as [Steven et al., 2000]. In this experiment, the Gislaved tyre had already been replaced with the Dunlop Arctic tyre. One of the major results of this was that tyres A, B and C gave very similar correlations with SPB car measurements and with each other, with a slight advantage of Tyre A, and that tyre G (only) gave a good correlation with SPB truck measurements. These results influenced WG 33 to decide that in the future, tyres B and C could be skipped, as they provided no new information compared to tyre A. Therefore, only Tyre A and Tyre D were used (provisionally) in the late 2000’s. In the late 2000’s two new developments occurred: In 2006, ASTM published a standard for a Standard Reference Test Tire (SRTT) as defined in ASTM F2493-06 (later updated to F2493-14), produced in USA. This looked interesting to WG 33 and trials were started to check whether this tyre could serve as the new Tyre A. Eventually, this was confirmed, and from about 2010 many CPX operators started to use this tyre. Since the Dunlop tyre was no longer available, searches were made for a new Tyre D that would correlate CPX measurements well with truck tyre SPB measurements. The new tyre identified to do this was Avon Supervan AV4, produced by Cooper/Avon Tyres in the United Kingdom. In 2006-2008, a number of candidate tyres, among them the SRTT and the Avon AV4, were tested for possible use in the CPX method. CPX tests included comparison with results measured with the SPB method. The experiments showed that these tyres represented rather well, for the particular purpose of characterising noise properties of road surfaces, a mix of passenger car tyres (SRTT) and a mix of truck tyres (Avon AV4). The conclusion was that the SRTT and Avon AV4 performed well for the purpose. The SRTT had the advantage of being available already as a reference tyre, while the Avon AV4 was an outgoing commercial light truck tyre; albeit still available on certain markets. Several reports were written by M+P about these studies, but they are summarized in [Morgan et al., 2009]. Following the encouraging results, the CPX operators using the old Tyre D soon switched to the Avon AV4 tyre. This happened around 2009-2010 and since then the SRTT and the Avon AV4 have been used widely as preliminary reference tyres.


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A4. Status of work when ROSANNE started As written above, in ISO/TC 43/SC 1/WG 33, which has the task to develop the CPX method for noise measurement and which includes several members of ROSANNE, two main candidate tyres had been identified and tested more extensively [Morgan et al., 2009]. These were:

• Standard Reference Test Tire (SRTT) as defined in ASTM F2493-14, produced in USA. Dimension: 225/60R16.

• Avon Supervan AV4, produced by Cooper/Avon Tyres in the U.K. Dimension: 195R14C.

The practical use of these tyres in the years before ROSANNE started (2013) confirmed the experience of the initial tests. These tyres had already been used for some time in noise measurements in Sweden, Poland, the Netherlands, Germany and elsewhere; although the Avon AV4 had been used less frequently than the SRTT. The SRTT had also been used extensively in USA in the OBSI method, which is a “cousin” to the CPX method. Some studies of tyre-to-tyre differences and effects of rubber hardness and temperature effects had already been made. However, ROSANNE provided possibilities to make more measurements to fill the worst knowledge gaps. Meanwhile, the same tyres had been tried in rolling resistance measurements; most notably in the MIRIAM project [Bergiers et al., 2011]. The experience was fairly positive, even though the correla-tion of results from Avon AV4 tyre with truck tyres in general had been checked only in one experi-ment (but with reasonably good result). Lacking experience with other tyres, the same tyres as for the CPX method were used in the MIRIAM experiments; however, supplemented by a couple of other car tyres. A presentation in 2012 at the Tire Technology Expo summarized the status that far [Sandberg, 2012]. In a Nordic project – NordTex – a comparison of three CPX trailer constructions with different SRTT and Avon AV4 tyres was made in 2009. The results indicated that different samples of similar reference tyres were responsible for the variation in CPX levels between the trailers, but if tyres were of similar rubber hardness results differed only slightly [Kragh, 2009]. It seemed possible to make corrections for hardness to reduce the variation between the tyres. Two important papers, both made by members of WG 33 and initiated in WG 33, which were presented immediately before ROSANNE started are worth mentioning. In a Nordic project called NordTyre, a special study was made to see how the SRTT tyre compared to other market tyres. A total of 31 tyres from the NordTyre project, including the Uniroyal Tigerpaw SRTT tyre, were measured with the CPX method on the same (dense) road surfaces in Norway. The measurements confirmed that the SRTT tyre is a good choice of a tyre to represent tyre/road noise from passenger car tyres on Norwegian road surfaces [Berge, 2013].


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The other paper [Bühlmann et al., 2013] investigated the ageing process of the SRTT and Avon AV4 during one measurement season. CPX measurements and tests of rubber hardness with a type A durometer, were repeated monthly. This revealed substantial increases in rubber hardness during the 2012 measurement season, exceeding three units Shore A for the SRTT tyre and six units Shore A for the Avon AV4 tyre. This corresponded to a considerable increase in noise levels, suggesting that tyre ageing is a primary influencing factor when carrying out tyre/road noise measurements using the CPX method. The study provided a simple tyre specific model for estimating rubber hardness changes based on the number of measurement days. The data implied that individual corrections for the CPX reference tyres SRTT and Avon AV4 are needed with respect to hardness changes and usage. WG 33 decided to designate the two tyres by the symbols P1 and H1, where P1 stands for “passenger cars, generation 1” (which is the SRTT) and H1 stands for “heavy vehicles, generation 1” (which is the Avon AV4). The idea is that future reference tyre generations will be designated with 2, 3, 4, etc.

A5. Work done in ROSANNE

A5.1 General issues Work in ISO and project MIRIAM constituted a good base to start from. But there were several knowledge gaps and insufficient data that needed substantial experimental work to create robust standards. For quality assurance purposes, the reference tyres needed to be tested more comprehensively than done so far, which included specimen-to-specimen differences, wear influence, time stability, rubber hardness change with time and its influence, storage conditions, etc. Since temperature is an influencing factor, this task has also been coordinated with tasks T2.2 and T3.2, which have dealt with temperature corrections of measured results. ROSANNE confirmed the idea of WG 33 that the tyres should have dimensions that would be possible to use on cars or on trailers possible to tow by (powerful) cars. This meant that tyre H1 (proxy for truck tyres) could not be a tyre having the size for heavy trucks; it would be limited to light truck tyres of the smallest type. If a larger tyre would be used, the CPX method would need much larger test vehicles which would mean much higher costs and impractical operation. For practical reasons and following the experience in MIRIAM, it was an ambition to use the same reference tyres for noise and rolling resistance measurements; unless empirical data would speak against this solution. Of special concern was to find a car-sized tyre useful as a proxy for truck tyres in noise and rolling resistance measurements. The Avon AV4 was the only one that was been immediately tested and available for this purpose, as any other tyre would need extensive testing; not the least correlation with SPB results from trucks, before it may be considered. ROSANNE has not had a duration enough, neither the financial resources for such a study. Future work should be conducted to find a replacement for H1, but in the meantime H1 (Avon AV4) will have to serve its purpose.


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Much work has relied on laboratory testing on drums equipped with road surfaces or their replicas, at partners TUG and BASt. Some of the field measurements have also been useful; for example, the tests of rolling resistance measuring equipment in September 2016 in Nantes. A brief summary of the status of work for the CPX method, its reference tyres and temperature corrections, appear in [Sandberg, 2016].

A5.2 Relation between CPX and SPB measurements for the reference tyres A crucial issue is whether CPX measurements are representative of road traffic noise at the roadside, with respect to how road surfaces are classified, which is the purpose with the CPX method. This was the major issue studied in ROSANNE Deliverable D2.1 [Kragh, 2015]. The Danish Road Directorate (DRD) collected sets of data from different European countries on CPX noise levels and vehicle pass-by noise levels (mainly the SPB method) measured on the same pavements at approximately the same time. These data were pre-processed and sorted into two main groups: those where both types of noise level had been recorded at the same reference speed and those where CPX noise levels had been recorded at 80 km/h while vehicle pass-by noise levels had been measured at reference speeds 110 – 120 km/h. In the former group of data, there was a clear correlation between CPX noise levels measured with standard reference test tyres (SRTT) and pass-by noise levels from cars, according to which the average pass-by (SPB) noise level is 20.5 dB lower than the average CPX noise level. For the set of data where measurements were made at different speeds, the correlation was poorer and the spread in data was greater. Pass-by noise levels from multi-axle trucks had a clearer relation with CPX noise levels measured with reference tyre Avon AV4 than with CPX noise levels measured with SRTT. The average pass-by noise level from a multi-axle truck on dense pavement was 9.5 dB lower than the CPX noise level measured with Avon AV4 tyres. For two-axle trucks the corresponding difference is 12.0 dB. Please refer to Section B4 for further information about the acoustical performance of the tyres on the reference surfaces for noise studies. As a conclusion to this section, the two reference tyres seemed to fulfil the intended tasks in a satisfactory way.

A5.3 Reference tyre ageing and effect of rubber hardness The relations between age, tyre rubber hardness and CPX noise levels tested for several nominally identical samples of the reference tyres P1 and H1 were studied in a paper presented at Inter-Noise 2015 [Świeczko-Żurek, 2015]. During the last decade the Technical University of Gdansk (TUG) has tested 26 tyres designated as P1 and 34 tyres designated as H1. Approximately 10 of the H1 tyres were supplied from VTI for the


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ROSANNE project. Tyres P1 were manufactured in the period between week 14 of 2002 and week 3 of 2013, while tyres H1 were manufactured between week 20 of 2005 and 9 of 2012. Rubber hardness of the P1 tyres was within the range of 60 - 76 Sh while hardness of H1 tyres was within the 58-75 Sh range. Tyres were tested on the roadwheel facility of TUG with a drum of 1.5 m diameter fitted with a replica of an ISO reference road surface (designated as ISOr15). Results are summarized in Figure A4 below.

Figure A4: The relation between CPX levels and rubber hardness (upper half) and tyre age (lower half). The light brown diagrams are for tyre P1 and the blue diagrams are for tyre H1. Unfortunately, the diagrams have different scales so they are not easy to compare, but it appears that rubber hardness has a much better relation with noise than tyre age. One can also see that for tyre P1 the maximum deviation from the regression is about 0.7 dB (or ±1.4 dB), while it is 1.5 dB for tyre H1. Corresponding residuals are approx. 0.3 and 0.6 dB, respectively. Note that this was made on a smooth ISO surface (replica) which is by experience the surface which shows the greatest differences between tyres. For much more common surfaces, with higher texture, the differences are (by experience) believed to be significantly lower.


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A5.4 The effect of rubber hardness The most important influence factors, respectively sources of uncertainty, on the CPX measurements are temperature influences and the shore A hardness of the test tyre. In a study within ROSANNE, the general temperature influence on the tyre hardness, the tyre temperature behaviour during test runs and a combined approach of (tyre) temperature and tyre shore A hardness correction was made by AIT [Wehr and Fuchs, 2016]. Regarding the temperature effect on tyre rubber hardness, hardness measurements were conducted for five SRTT tyres of different hardness and age (two were one year old, two were three years, and one was nine years). The tyres were placed in a climatic chamber, where the ambient temperature was varied between 5 and 40 °C. At selected temperatures within this range, the tyre hardness was measured. Before each hardness measurement, the temperature was held constant for at least two hours for the tyres to reach an equilibrium temperature. Results of these measurements are shown in Figure A5. From this, it appears that a linear relation is a good estimation over a wide range of temperatures. Also, the slope of this trend is similar for all tyres within the uncertainty of the shore A hardness measurements.

Figure A5: Temperature influence on shore A hardness of five different SRTT:s; age of tyres is color-coded, their hard-ness increasing with increasing age. From [Wehr and Fuchs, 2016].

Thus, when determining the shore A hardness of the measurement tyre, temperature corrections can be applied according to:

with the coefficient β being -0.25 Shore A/°C. T is air and rubber temperature and HA is hardness in Shore A. Coefficients of determination are above 0.90 for all five tyres. Similar results could have been obtained for tyre H1, since rubber-temperature relation should not be very different for these tyre rubber compounds, but this is something needing a future check. In order to further investigate the temperature and shore A hardness effects on tyre/road noise emissions, CPX measurements were performed on two days on a highway section of 1 km length in


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Austria. Repeated measurement runs with a measurement speed of 80 km/h were carried out with four different SRTT:s (two were one year old, two were three years, and one was nine years with a Shore A hardness at 20 °C ranging from 67 to 77 Shore A units). Simultaneously, also air temperature as well as road surface and tyre surface temperature were measured. The latter two were acquired with infrared thermometers, where the tyre temperature sensor was oriented towards the tyre tread pattern. As expected, the differences in temperature and tyre yield large deviations in the resulting mean (as well as median) sound pressure levels ranging from 99.6 to 101.3 dB(A). The medians of sound pressure levels range approximately 0.5 dB(A) within one tyre set. The resulting relations are shown in Table A1, where one outlier has been omitted, namely the tyre that was nine years old (such age is not accepted in the ISO method). Table A1: Evaluation of hardness and temperature correction functions. From [Wehr and Fuchs, 2016].

The evaluation was made using three different methods, described in the paper by AIT. Here, it is mentioned only that the one which was finally used in the standard was the “standard” method. However, all three methods gave consistent hardness relations with a coefficient of approximately 0.20 dB/Shore A. The three different methods show comparable performance indicators, although leading to a final spread of the CPX level of approx. 0.5 dB (5 % - 95 %) resp. 0.2 dB (25 % - 75 %). It must be noted that the study indicated that the major reason for the effect of temperature on noise is that the tyre rubber is softened by higher temperatures, and vice versa. It was also noted, very importantly, that the relations between noise and rubber hardness seemed to be linear. Finally, it was noted that the relation between air and road temperatures are sometimes not very consistent, depending on solar radiation and surface albedo. This constitutes a factor of uncertainty that should be studied in the future. The AIT study also addressed the temperature effect, which is dealt with in the next section.


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A5.5 Temperature effects The effect of temperature on CPX levels and how to correct for it was the subject of ROSANNE Deliverable D2.2 [Sandberg et al., 2016]. These relations and corrections refer to the reference tyres P1 and H1; thus they are highly relevant here. Nevertheless, the reader is suggested to refer to D2.2. However, a couple of documents published after D2.2 was finished are worth mentioning here. The first one is the AIT paper mentioned above [Wehr and Fuchs, 2016]. As it is shown in Table A1, the temperature coefficient that AIT arrived at was -0.092 dB/oC, which is fully consistent with the proposed coefficient for 80 km/h in ISO/DTS13471-1 for dense asphalt. So far, so good. However, when making a multiple correlation analysis (the middle row in Table A1) the coefficient came out as -0.054 dB/oC, which may perhaps be interpreted as if some of the temperature effect is included already in the hardness coefficient. But this might be due to the special relation between air and road temperature in the AIT study, since they ran partly in a tunnel, and might not be generally valid. This matter may need some further study. The second document to mention is an attempt to see how the temperature effect is distributed on various frequency bands [Mioduszewski et al., 2016]. The correction procedure in ISO/DTS 13471-1 is neutral with respect to frequency as it only refers to the overall A-weighted sound level (the CPX level). Extensive studies of how temperature affects the tyre/road noise measured on a road using the CPX method and in laboratory with tyres rolling on drums equipped with replica road surfaces were conducted within ROSANNE at the Gdansk University of Technology (TUG) in Poland. Overall A-weighted sound levels and the one-third octave band frequency spectra were acquired during the tests. The temperature correction coefficients for overall sound levels were derived and published at previous Inter-Noise conferences (2014 and 2015). In the present paper, published at Inter-Noise 2016, the temperature influence on measured tyre/road noise one-third octave band frequency spectra are presented and discussed. The experiment showed differences in temperature effect on noise frequency spectra depending on the combination of tested tyre and road surface. A different temperature correction coefficient distribution over the frequency domain was observed for smooth-textured surfaces, different for rough-textured and a totally different for poroelastic ones. In general, the distribution for both reference tyres is rather similar, but the tyres differ, sometimes significantly, in values of the temperature coefficient for particular third-octave bands. In addition, some shifts were observed within the adjacent frequency bands. Consequently, no consistent proposals for frequency-dependent coefficients were possible, since the temperature effect on tyre/road noise frequency spectra is a rather complicated phenomenon that definitely needs more research.

A5.6 Validation tests At the Belgian Road Research Centre (BRRC), research was performed to fill up some gaps in the knowledge about reference tyre performance. CPX measurements were repeated with new P1 and


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H1 tyres with various distances of run-in, on 10 road surfaces to verify the influence of run-in. Additionally, measurements were performed with three sets of P1 tyres on these 10 road surfaces to verify the reproducibility. Influence of mounting direction of new P1 tyres was verified on a porous mastic asphalt to supplement available research [Bergiers & Maeck, 2016]. The results for the run-in tests are shown in Figures A6-A7. Based on all the findings it was recommended by the author to perform at least 400 km run-in of a new tyre before using it to perform CPX measurements, as well for P1 as for H1, and this was finally accepted by WG 33.

Figure A6: LCPX:P,80 as a function of run-in distance for 10 various test sections, for P1 tyre at 80 km/h.

Figure A7: LCPX:H,80 as a function of run-in distance for 10 various test sections for H1 tyre at 80 km/h. From [Bergiers & Maeck, 2016].


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The results of testing three samples of SRTT:s, run on 10 different road surfaces, are shown in Figure A8. Deviations of up to 1.2 dB occur. These CPX levels have been corrected for varying temperature and rubber hardness. Although the ranking of surfaces is similar for all tyres and correlation between the tyres is excellent, they differ in terms of absolute CPX levels. The results are unfortunately not very encouraging and seem to be worse than in other tests, such as [Kragh, 2009], but similar to [Świeczko-Żurek, 2015].

Figure A8: LCPX:P,80 values for three tyre sets on 10 different pavements at 80 km/h. From [Bergiers & Maeck, 2016]. As to the effect of mounting direction of the SRTT:s, when comparing measurements from BRRC and BASt, performed in the run-in direction (BASt not respecting the arrow on the SRTT sidewall and BRRC respecting the arrow), differences up to 3.9 dB(A) were found, which was alarming. However, parts of the difference may be hardness difference and the effect of a winter which was in between the measurement campaign of BASt and BRRC, yielding about 1 dB(A) of noise deterioration of the road surface. However, the remaining 2 dB(A) remains unexplained. It demonstrates the importance of the mounting direction of the reference tyres since the arrow marking was introduced for recent tyres. This matter must be further studied, as there might be some unknown methodology problem here. The paper also reports some temperature effects, but these were included already in D2.2 so they are not further reported here.

A6. Other reference tyres for noise monitoring In Japan, noise properties of road surfaces are checked with a special type of CPX vehicle, of which there are several copies in operation, on which they have mounted a special reference tyre; see Figure A9. The tyre has a very special tread pattern, where one half is equipped with a “lug and


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block” pattern and the other half has a slick pattern (i.e. no pattern) with “pockets” or “cavities” in it. The idea is that the “lug” pattern shall excite the vibration mechanism and the “slick and pocket” pattern shall excite the air pumping mechanism of noise generation. It is quite possible that these mechanisms are generated. However, due to the lack of resemblance with real market tyres, it is most uncertain, or even unlikely, that the tyre classifies pavements in a representative way.

Figure A9: Japanese reference tyre for measurement of noise properties of road surfaces.

A7. Decision in ROSANNE about the reference tyres Based on a comprehensive overview of all available data and practical experience, the ROSANNE consortium has agreed to specify the following two reference tyres, for use in both the noise and rolling resistance work: Tyre P1: A steel-belted radial tyre for relatively large passenger cars or vans, specified in ASTM standard F2493-14, having the dimensional code P225/60R16 and referred to as a Standard Reference Test Tyre (SRTT). Both the text "Standard Reference Test Tyre" and the dimensional code P225/60R16 shall be displayed on the sidewall. Tyre H1: A steel-belted reinforced radial tyre for light trucks and vans, manufactured by Cooper Tire & Rubber Co. in the United Kingdom under the product name "Supervan AV4", having the dimensional code 195R14C. Both the text "Avon Supervan AV4" and the dimensional code 195R14C shall be displayed on the sidewall. The Supervan AV4 has a reinforced carcass construction to enable the carriage of heavy loads, and has a very robust rubber compound on the sidewall. It has also been decided in agreement with the ISO group that the test wheels and a number of other geometrical features shall be specified as follows:


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Table A2: Specifications of the reference tyres and test wheel

Tyre Basic dimension

code

Nominal cross-section

width

Nominal undeflected

diameter

Cross-sec-tional tread

radius

Load index

(LI)

Speed index

Rim code

P1 P225/60R16 231 mm 679 mm 308 mm 97 S 6.5 J

H1 195R14C 198 mm 666 mm 302 mm 106/104 N 5.5 J The designations P1 and H1 mean:

• P is for passenger car tyres; H is for Heavy vehicle tyres • The digit 1 is for the generation of such tyres. This is the very first generation (1), and future

changes of tyres will give the second generation (2), i.e. tyres P2 and H2, etc.

For noise it has been decided that both P1 and H1 are mandatory to use (D.2.4). For rolling resistance the two tyres are recommended, according to D3.5. Tyres other than the recommended reference tyres may be used for research or special survey purposes. However, it should be noted that in that case it is not possible to report results according to the method of D3.5. The tyres are extensively described in ISO/TS 11819-3. Figure A10 illustrates the tread patterns of the tyres.

Figure A10: The tread pattern of tyres P1 (left) and H1 (right).


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A8. Availability of the tyres The P1 tyre – the SRTT specified in ASTM 2493:14 - is used in some regulatory applications, most notably in the ECE Regulation R117 for tyres, as a standard reference tyre for measurement of “wet grip”. It follows that it must be available at least until another tyre is required or as long as the regulation exists. Another reference tyre - ASTM E 1136:10 – has been available now for approximately 30 years, and it is likely that also the ASTM 2493:14 SRTT will be available for a couple of decades or more. One may find the producing company listed in the standard, but more conveniently for at least Europe, one may purchase the tyre from

M+P Attn.: Mark Mertens ( [email protected] ) Wolfskamerweg 47

5262 ES Vught The Netherlands

Regarding the H1 tyre – Avon AV4 – finding a supplier is more complicated. Production of the tyre by Cooper-Avon has probably finished. However, at least until recently, there have been some supplies available among tyre dealers. VTI has been able for many years to purchase significant numbers of the tyre from Swedish dealers. The tyre has recently obtained a label according to EC/1222/2009 and on this label the noise level is given as 74 dB. This exceeds the present tyre noise limit in Europe and would prevent the selling of this tyre. However, the tyre type was produced before the limit was introduced and thus it may be exempted from the rule. When asking tyre organizations such as STRO in Scandinavia about how to interpret this special case no clear answer has been received. Nevertheless, VTI ordered 30 tyres of H1 type before the limit came into force, and these tyres are stored in a cold room for use by CPX operators who need the tyre in the next few years. Likewise, VTI already earlier purchased such tyres which were tested in ROSANNE and which are stored at TUG (it may be approximately 10-15 tyres). These will also be available. It appears that the problem of the 74 dB label value mentioned above has been solved by the suppliers by putting a special label on the tyre, stating that the tyre is designated for vehicles produced before 1990-10-01 and therefore is exempt from the tyre labelling and limits; see Figure A11. Consequently, the tyre is available in 2017 even in Europe. Furthermore, nothing prevents the selling of the Avon AV4 tyre outside the EU. It is not clear whether the tyre is available outside the EU, but it should be checked. CPX operators may contact VTI for the most current information; either at [email protected] or [email protected], or [email protected].






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Figure A11: Tyre label fixed on tyre H1 in 2017.

A9. Implementation of the results as new ISO procedures Based to a large extent on the work in ROSANNE, ISO/TC 43/SC 1/WG 33 has decided to specify the chosen tyres in a Technical Specification. A Committee Draft (CD) for ISO/TS 11819-3 was submitted to the ISO member bodies on 3 February 2016 for comments and voting. This was approved in the ballot and a new version was prepared for a new ballot in the autumn. Also this was approved and the final version is expected to be published in the first months of 2017. The final draft for the CPX standard, denoted as ISO/FDIS 11819-2, has been subject to a final ballot with a deadline of 2016-12-16. It was also approved by a great majority of ISO member countries. Final publication of ISO 11819-2 is expected in the first few months of 2017. This relies on ISO/TS 11819-3, without which it would be almost meaningless. D2.4 is largely based on these two ISO documents. It is also acknowledged by ISO that both documents have been produced with important contributions from work in ROSANNE, without which it is doubtful if the documents would be finished within a couple of years. Since both ISO 11819-2 and ISO/TS 11819-3 depend on ISO/TS 13471-1 (the temperature correction specification), it follows that all three ISO documents constitute a package that is crucial for the outcome of ROSANNE. ISO/TS 13471-1 also largely depends on ROSANNE work, as reported in D2.2. The objective of ROSANNE is to provide CEN/TC 227/WG 5 with drafts for classification of acoustic properties of road surfaces, which implies that the ISO 11819-2, ISO/TS 11819-3 and ISO/TS 13471-1 will be put forward to CEN for use also in the European standardization. WG 5 has been informed about the progress of this work during the active time of ROSANNE.


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A10. Reference tyres for skid resistance measurements This part of ROSANNE never intended to deal with reference tyres for skid resistance measurement, despite this is an extremely important issue. Both ASTM and PIARC have specified a number of such tyres; in addition there are special tyres produced for certain skid resistance measuring devices. See Figure A10. They range from truck tyres, through car and motorcycle tyres down to small tyres originally intended for off-road use. The multitude of different tyres for skid resistance testing is one of the reasons why it is so difficult to compare results of skid resistance measurements made with the various equipment of today. And yet, the only tyres that are really resembling tyres used in road traffic are the SRTT:s designed by ASTM in various sizes, of which the 16” SRTT of ASTM F2493:14 is one; and these tyres are not used for testing road surfaces. The SRTT:s have the advantage that they resemble regular tyres used on the vehicle fleet; i.e. they have tread patterns that are similar to many market tyres and they have an inner construction and tread rubber compounds that are typical of today’s common market tyres. Therefore, testing with such tyres should provide the best correlation with tests using market tyres. Unfortunately, very little attention has been assigned to the issue of correlation between skid resistance tests with today’s equipment and test tyres and with tests using sets of market tyres. Given all technical advances in rubber compounds and tread patterns, it is not clear that the skid resistance test tyres used today, which are obsolete designs, are the best for this purpose.

Figure A.10: Some examples of test (reference) tyres used for skid resistance measurements.


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The main reason why the ASTM SRTT:s have not become popular in road testing is that they have a “regular” and typical tread pattern (see for example the SRTT in Figure A8), and when they are worn it is assumed that they behave differently. It is assumed that they cannot be used in too long and frequent braking operations until the skid resistance coefficients are changed, since the tread thickness changes. However, the SRTT:s recently have become a necessity in skid resistance testing of tyres; as they are used as references against which market tyres are tested. The UN ECE Regulation R117 on noise, rolling resistance and skid resistance nowadays includes a method for “wet grip” testing; which is mandatory for all new tyres on the European market to pass. This applies to both legal safety limits and for the tyre labelling scheme. For type testing of all new car tyres (category C1), the same SRTT is used as the SRTT (P1) defined in this part of the deliverable. For larger tyres, there are larger SRTT:s. The new tyres are measured on the same test surface as the SRTT and they are classified with a number which is a fraction of the result of the SRTT tyre, which is normalised to 1.0. Good tyres from wet grip point of view would then usually get a number higher than 1.0. It follows that SRTT:s nowadays are used to a great extent in tyre comparison tests. If they work well in this application (which they seem to do) they should be possible to apply also in road testing, given that one must be careful not to wear them so much that the results will be influenced by the wear. One would need to study how measurement results depend on the tread wear, to determine how long each tyre can be used. This has not been possible to try in ROSANNE, but this author thinks that it should be considered for any major future project on skid resistance testing of road surfaces.

A11. Future work

A10.1 Introduction Frequently used ISO, CEN and ASTM standards are always “living” documents; i.e. they are regularly revised and improved, based on experience and new information. The three ISO documents considered here are the first official versions of its kind. It means that they are particularly subject to improvement considerations. The following mentions and discusses some future work which should be conducted. The extent of this section reflects the fact that the subject of reference tyres for noise and rolling resistance is quite new and not yet subject to much research.

A10.2 Search for new tyres to become a reference tyre, especially H1 Most important of all is to look for a replacement of tyre H1 (to become tyre H2). This tyre should have the same features as the H1 tyre; i.e. it should classify road surfaces in a way similar to how truck tyres classify road surfaces. By “truck tyres” we mean the bulk of tyres used on the heavy vehicle fleet running on European major roads. This should be checked by measuring tyre H2 (and H1 simultaneously) on the same roads as SPB measurements are made, including an appropriate number of heavy vehicles. Ideally, something like 20 different road surfaces should be included; or as an absolute minimum 10 surfaces if they are chosen to cover the most relevant surface types. It is known that plans to apply for such a project are considered in Belgium.


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A10.3 Reference tyre to represent worn tyres in traffic The reference tyres P1 and H1 are used only in new condition and until they are worn so much that the properties change in comparison to the new condition performance. Tyres on the vehicle fleet running on our roads are a mix of new and worn tyres; in fact most of them are worn. Many tyres are used until they pass below the common legal tread depth of 1.6 mm (for car tyres); some are almost slick. This would not be important in this subject if road surfaces would be classified in a similar way for new tyres as for the same tyres when they are worn or worn out. This is, unfortunately, not the case, as shown in [Sandberg & Glaeser, 2008]. Consequently, this is a factor that reduces the correlation between CPX measurements with the reference tyres and SPB measurements. Theoretically, CPX measurements with tyres in new condition (full tread pattern) should have lower sensitivity to the texture of the road surface as the road surface texture is usually smaller compared with the “texture” of the tread pattern; i.e. the noise level range is somewhat “compressed”, in comparison to when testing with worn-out tyres when the range tends to be “expanded”. However, this may be balanced to some extent by the effect of propulsion noise in the SPB method, which tends to have a similar “compression” of the noise level range. Why not use a slick reference tyre; i.e. a tyre with no tread pattern? There are such tyres for reference purposes designed by both PIARC and ASTM (see Section A3). Unfortunately, these slick tyres are not ideal, as they have a full tread thickness, despite they have no pattern. One would need a tyre with a tread of thickness equal to that of heavily worn tyres. Such reference tyres are not available. It is difficult to just (artificially) wear tyres P1 and H1 down to (say) 2 mm tread depth, as machines doing such wear will leave a different “microsurface” than tyres worn on the road, and this microsurface will rather soon be worn away when road testing has begun. Nevertheless, this is an important issue that rather soon should be subject of research. One may start with testing the smooth PIARC tyre, along with tyres P1 and H1 worn down to 2 mm tread depth in a tyre wear machine such as described in [Sandberg & Glaeser].

A10.4 Other studies and improvements for the ISO technical specification The study by AIT on rubber hardness and temperature influence on noise, as well as rubber hardness dependence on temperature, was made only on the P1 tyre. This study needs to be repeated; this time with the H1 tyre. As it was found in a couple of investigations mentioned above, there seems to be a larger variation between different samples of P1 and H1 tyres than one would like. This applies to the absolute CPX levels and not to the correlations when tested on various road surfaces. Other investigations have found only small variations between samples. This is something that should be studied more and under closely controlled conditions; preferably both in a laboratory facility and on roads. An indication was given above that further research is needed to investigate a possible change of noise level of reference tyre P1 when the rotational direction indicated with arrow mark was added on the recent tyres. It should be investigated further as to what extent the mounting, combined with


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run-in direction, influence noise levels, on both sides of the tyres. This study should be made under closely controlled conditions in a laboratory facility. The variations between similar tyres and with respect to mounting should be further checked not only for noise but also for rolling resistance. It may be an equally important issue for this parameter as for noise. If tyre-to-tyre noise levels differ too much it may be considered to apply some kind of pre-screening. That would involve the measurement of noise levels of a great number of tyres in new (but run-in) condition; i.e. before they are used in CPX measurements, and then eliminate tyres differing too much from the average tyre. One may also consider the application of a calibration factor for each tyre. Such pre-screening should probably be made in a laboratory facility having replica road surfaces. Finally, it was noted that the relation between air and road temperatures are sometimes not very consistent, depending on solar radiation and surface albedo. This constitutes a factor of uncertainty that should be studied in the future. Both air and road temperature influence tyre temperature, and the latter should be the most relevant one for the effect on tyre noise, but it is still extremely difficult to measure tyre temperatures with low uncertainty and it is not clear which part of the tyre, or even within the tread, that is the most important to measure. Further research on this is needed. This matter is probably even more important for rolling resistance than for noise; thus both parameters should be considered. As concluded in the study mentioned above on temperature coefficients for various frequency bands, more research is needed to try to find consistent variations of the temperature coefficient with acoustic frequency. This may be limited to the reference tyres.

A10.5 Issues concerning rolling resistance and skid resistance Work to find a H2 tyre should include testing the tyre properties not only for noise but also for rolling resistance; i.e. how well does it classify road surfaces with respect to their rolling resistance. Similar to the case for noise, the problem is also that the thickness of the tyre tread largely influences the rolling resistance coefficient [Sandberg & Glaeser, 2008]. It is known that when the tread is worn and getting thinner, less energy is lost in the rubber and rolling resistance is reduced. It also means that tyres with a thin tread are more sensitive to road surface texture changes than tyres with a full tread, and thus road surfaces will probably be classified differently if a worn reference tyre is used. It follows that one would need, also for rolling resistance measurements, reference tyres that are worn. The subject of skid resistance reference tyres is dealt with in Section A10, but it is reminded here that also this issue should be subject of future research.


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A12. Conclusions The work in ROSANNE about reference tyres has been extensive and provided results that have been most useful for ISO in the work to produce the standard on CPX measurements, as well as the technical specifications for two reference tyres and for the temperature corrections required for these tyres. Without the assistance of the ROSANNE work, the ISO work would have been seriously delayed. As there was a very stringent deadline for producing the CPX standard (until the end of 2016), that deadline would not have been met if ROSANNE did not exist and the work with reference tyres had not been done, and thus the work with the CPX standard would have needed to start with a new proposal for new work item. Clearly, this alone would have meant a delay of maybe a couple of years. ROSANNE work has indicated that tyres P1 (SRTT) and H1 (Avon AV4) are the currently best options, and in fact the only options, for the CPX method. They have also turned out to be useful as provisionally references for rolling resistance measurements. ROSANNE has provided information about the influence of temperature on tyre rubber hardness, and on the influence of rubber hardness combined with temperature on CPX levels, without which the uncertainty of the CPX method would be substantially worse. The project has also highlighted the tyre mounting and run-in directional properties, as well as the variation between tyre samples that are nominally equal. Following the ROSANNE work, ISO is now in the final process of publishing three important documents, all of which are also used in the proposed draft to CEN for classification of noise properties of road surfaces, and where the TS on reference tyres is also used in the proposed draft to CEN on rolling resistance properties of road surfaces (see Section IV in the main body for full titles):

• ISO 11819-2: The CPX method • ISO/TS 11819-3: Reference tyres • ISO/TS 13471-1: Temperature correction

A13. References Berge, Truls (2013): “Noise performance of the SRTT tyre compared to normal passenger car tyres”. Proc. of Inter-Noise 2013, Innsbruck, Austria.

Bergiers, Anneleen; Maeck, Johan (2016): “Validation of reference tyres and temperature correction for Close-ProXimity (CPX) method”. Proc. of Inter-Noise 2016, Hamburg, Germany.

Bergiers, Anneleen, et al. (2011): “Comparison of Rolling Resistance Measuring Equipment - Pilot Study”. MIRIAM SP1 Deliverable No. 3, Final version 2011-12-23. Downloadable at the MIRIAM website: http://www.miriam-co2.net/Publications/Publications.htm

Bühlmann, Erik; Schulze, Sebastian; Ziegler, Toni (2013): ”Ageing of the new CPX reference tyres during a measurement season”. Proc. of Inter-Noise 2013, Innsbruck, Austria.

http://www.miriam-co2.net/Publications/Publications.htm


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ISO/WD 11819-2 (1997): Acoustics - Method for measuring the influence of road surfaces on traffic noise - Part 2: "The Close-Proximity Method". Revised draft for first CD, meeting at Hamamatsu, Japan, 1997-10-20. This is document N 107 in the series of WG 33 numbered documents.

Kragh, Jørgen (2009): “Road surface texture – low noise and low rolling resistance. CPX trailer comparison – Copenhagen 2009”, Danish Road Institute Report 188 – 2010, ISBN Electronic 978-87-92094-71-1.

Kragh, Jørgen (2015): “Report on the analysis and comparison of existing noise measurement methods for noise properties of road surfaces”. ROSANNE Deliverable D2.3.

Mioduszewski, Piotr; Taryma, Stanisław; Woźniak, Ryszard (2016): “Temperature influence on tyre/road noise frequency spectra”. Proc. of Inter-Noise 2016, Hamburg, Germany.

Morgan, Phil; Sandberg, Ulf; van Blokland, G.J.; Schwanen, Wout (2009): “The selection of new reference test tyres for use with the CPX method, to be specified in ISO/TS 11819-3”. Proc. of Inter-Noise 2009, Ottawa, Canada.

Sandberg, Ulf; Glaeser, Klaus-Peter (2008): “Effect of tyre wear on noise emission and rolling resistance”. Proc. of Inter-Noise 2008, Shanghai, China.

Sandberg, Ulf (2012): “Reference tires and reference surfaces: necessary components of tire regula-tions”. Presentation at the Tire Technology Expo 2012, 14-16 February 2012, Cologne, Germany.

Sandberg, Ulf (2016): “Improving the CPX method by specifying reference tyres and including corrections for rubber hardness and temperature”. Proc. of Inter-Noise 2016, Hamburg, Germany.

Sandberg, Ulf, et al. (2016): "Report on temperature influence and possible corrections for measurement of noise properties of road surfaces". ROSANNE report D2.2 (2016), downloadable at http://rosanne-project.eu/

Steven, Heinz; Küppers, Dagmar, van Blokland, Gijsjan; van Loon, Ronald (2000): “International validation test for the “Close Proximity Method“ (CPX). Report from TÜV Automotive GmbH, Herzogenrath, Germany, and M+P Raadgevende ingenieurs b.v., Vught, The Netherlands.

Świeczko-Żurek, Beata; et al. (2015): “The effect of tire aging on acoustic performance of CPX reference Tires”. Proc. of Inter-Noise 2015, San Francisco, USA.

Wehr, Reinhard; Fuchs, Andreas (2016): “A combined approach for CPX tyre hardness and tempera-ture correction”. Proc. of Inter-Noise 2016, Hamburg, Germany.

WG 33 (1995): Minutes from the 12th meeting of ISO/TC 43/SC 1/WG 33, held in Madrid, Spain, 3-4 October 1995. This is document N 71 in the series of WG 33 numbered documents.

See also Section III of this report for ROSANNE deliverables and the formal designations of the ISO standards.



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PART B: REFERENCE ROAD SURFACE FOR USE IN NOISE STUDIES

B0. Background In prediction models for road traffic noise, it is necessary to base the calculations on vehicles running on some defined road surface for which vehicle noise, including tyre/road noise, is determined. Together with a definition of vehicle, speed and receiver (microphone) location, and a number of standard assumptions, this provides a reference noise level and frequency spectrum, from which one can calculate noise for any other combination of the said parameters. Thus, a reference road surface is a basic concept in road traffic noise modelling. This surface should be easy to find at various locations and have known properties; where measurements to develop and confirm the model can be made easy and fast and where results are reproducible. This would require that the surface is designed and specified in a suitable way, and that appropriate texture and other geometrical parameters having an acoustical influence are measured. Since there is no reference surface which is highly reproducible and stable in its performance, one may instead define an ideal (virtual) surface close in performance to an actual reference, but assumed to have permanent and defined properties, against which noise measurements on any actual road surface may be compared. Noise emission levels and frequency spectra may then be normalized to correspond to the ideal (virtual) reference surface. The concept of a virtual reference surface procedure was developed already in the HARMONOISE project more than 10 years ago [Sandberg, 2006], and was then taken over by the follow-up project IMAGINE and finally adopted in the work to develop a common European noise prediction model: CNOSSOS-EU [Kephalopoulos, et al., 2012]. When this was turned into a European directive [EU Com, 2015], the virtual reference surface concept was a major part of this regulation. Another useful noise-related application of a virtual reference surface is to use this surface when evaluating noise properties of other surfaces. The noise properties of the virtual reference surface may then be subtracted from those measured on other surfaces, resulting in a differential noise level and frequency spectrum. This is what is commonly known as “noise reduction” or “noise-reducing surface”, although this “reduction” may on some surfaces actually be negative; i.e. it would be a “noise excess”. This document discusses the definition of a suitable virtual reference (road) surface for use in noise measurement and calculations, and its potential applications and limitations. This is done from the perspective of the EU Directive specifications, but further suggests how the definition may be improved.


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B1. Introduction and purpose The concept of virtual reference surface for noise studies, as suggested in HARMONOISE and applied in the European Directive, is critically assessed in this deliverable. Problems are identified and proposals are made to alleviate them.

B2. Scope and use of the concept It is becoming more and more common to classify road surfaces (pavements), formally or informally, in terms of their noise influencing characteristics. Unless it is possible to assign an absolute, unambiguous and stable noise level to each pavement, one needs to use certain pavement categories defined in relation to each other; such as "high noise", “normal”, “low-noise” or "very low noise"; or perhaps associated with a number, such as "- 4 dB". When speaking about “noise reduction” of a pavement, this is meaningless unless a given reference has been used and is reported. In all such cases one will need some kind of standard or reference condition, representing “0 dB” or a “normal” pavement. Such a reference should be as generally and universally accepted as possible. The noise emission calculations in a traffic noise prediction model are normally based on some reference conditions. The substantial pavement influence on noise emission makes it necessary to define some reference pavement, or a range of pavements, for which the basic noise emission data can be calibrated. Other pavements will then be assigned some “delta decibel” value; i.e., a correction that brings the predicted level down or up to the level of the particular pavement used. Therefore, in all the mentioned cases there is a need for a defined “reference” pavement. Ideally, this should not depend on the region, state or country but be universal. To this end one would need one closely specified single pavement that could be used as a reference everywhere and always. In practice, this is not possible since there is no single pavement which is common in all countries or regions in the world. Unfortunately, when it comes to the choice of “reference” pavement in various studies or applications, against which a studied pavement is compared or “delta decibels” are presented, it is almost a total chaos. In some studies, a laterally tined cement concrete may be used as the reference while in other cases perhaps a dense-graded asphalt concrete having a certain maximum aggregate size may be used. Between these two cases, the noise level may differ by some 5 dB; meaning that a pavement found to be “low-noise” in the first case may be just “normal” in the second case. This document deals with the definition of a reference road surface for noise studies, allowing the actual reference used in any experimental study to be chosen within a range of very common pavements. After a set of defined, minor corrections to the measured values have been made, the actually measured or considered case can be related to a universal “virtual” pavement that can be common to almost all studies all over the world; albeit it does not exist in reality.


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B3. The CNOSSOS-EU approach

B3.1 Effect of road surface characteristics in the CNOSSOS-EU model This section is, to a large extent, copied from ROSANNE D2.5 [Anfosso, 2016]. It deals with the relevant content of the EU Directive [EU Com, 2015] which is taken from [Kephalopoulos, et al., 2012]. It must first be mentioned that CNOSSOS-EU and the EU Directive make a distinction between the two major noise components in road traffic noise:

• Tyre/road noise (noise from the tyre-to-road contact) • Propulsion noise (noise from sources such as engine, exhaust, transmission, fans)

In the Directive, tyre/road noise is designated as “rolling noise”, which is a term commonly used in legal documents from the EU or UN ECE; probably originating in a (poor) translation from the term “Rollgeräusch” (in German). This author strongly prefers the term tyre/road noise. The following text, in dark magenta colour, is copied from D2.5. The correction coefficients for road surface characteristics on, respectively, rolling noise emission and propulsion noise emission, are defined by the following formulae:

×+=∆

ref

mmmimiWR,road v

vlg L βa ,,, (1)

{ }0;,,, mimiWP,road min L a=∆ (2)

ai,m is the spectral correction in dB at the reference speed vref for vehicle category m (1, 2 or 3) and octave band i. In the case of a porous road surface the ai,m coefficient will decrease the propulsion noise, but dense surfaces will not increase it. βm is the speed effect on the rolling noise effect for vehicle category m (1, 2 or 3) and is supposed identical for all frequency bands. The experts in the ROSANNE project believe that equation (1) overestimates the effect of absorption on propulsion noise. They recommend that further investigation is made in order to check the relationship. ai,m and βm are derived to be representative for the acoustic performance of the road surface type averaged over its representative lifetime and assuming proper maintenance. Input data for the road noise model (such as AP,i,m , BP,i,m , AR,i,m , BR,i,m , ai,m and βm ) are provided in Appendix F of the Annex of Directive 2015/996/EC. Table B1 gives the list of the 14 road surfaces for which ai,m and βm data are provided in Appendix F and the associated speed range for validity. They are originated from the current Dutch road traffic calculation method.


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The Directive states that in cases where input data provided in Appendix F are not applicable or cause deviations from the true value (…), other values can be used, provided the values used and the methodology used to derive them are sufficiently documented, including demonstrating their suitability. This information shall be made publicly available. Table B1: Road surfaces types for which data are provided in Directive 2015/996/EC and associated speed range.

Code Road surface Speed range for validity (km/h)

Reference surface (virtual) corresponding to a mix of DAC11 and SMA 11: no correction All speeds

NL01 1-layer ZOAB1 50 - 130

NL02 2-layer ZOAB 50 – 130

NL03 2-layer ZOAB (fine) 80 – 130

NL04 SMA-NL5 40 – 80

NL05 SMA-NL8 40 – 80

NL06 Brushed down concrete 70 – 120

NL07 Optimised brushed down concrete 70 – 80

NL08 Fine broomed concrete 70 – 120

NL09 Worked surface 50 – 130

NL10 Hard elements in herring-bone 30 – 60

NL11 Hard elements not in herring-bone 30 – 60

NL12 Quiet hard elements 30 – 60

NL13 Thin layer A 40 – 130

NL14 Thin layer B 40 - 130

The road surfaces in Table B1 are drawn from a Dutch database. The noise properties of these (not indicated here) are given in relation to the CNOSSOS-EU reference road surface.

B3.2 The CNOSSOS-EU reference road surface The following text, in dark magenta colour, is copied from D2.5. Black text is added by this author. A virtual reference road surface is defined in CNOSSOS-EU, corresponding to an average of Dense Asphalt Concrete (DAC) 0/11 and Stone Mastic Asphalt (SMA) 0/11, between 2 and 7 years old and in a representative maintenance condition. The effect of other road surfaces is defined as a difference with this reference.

1 ZOAB is the Dutch term for ”very open asphalt concrete”; i.e. “porous asphalt”.


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In CNOSSOS-EU reference conditions, the road should be flat, the surface dry and the air temperature 20 °C. In ROSANNE, the road surface should also be dry and the reference air temperature is 20 °C. There is no specific requirement regarding the flatness of the road. An important point is that road surface correction data in the harmonised EU-model are representative for the acoustic performance of the road surface type averaged over its representative lifetime and assuming proper maintenance. It is well known that dense asphalt surfaces change a little in the noise properties when they are ageing and getting worn under proper maintenance conditions. Most commonly, there is a minor increase in noise levels: only a few dB over their lifetime, that is usually longer than 10 years (except in northern countries that allow the use of studded tyres, where lifetimes may be halved). The most important change occurs during the first or the two first years, when there is generally 1-2 dB of increased noise. On the contrary, noise levels on porous surfaces tend to increase significantly, more or less regularly over time, and can reach the noise levels of dense surfaces at the end of their lifetime. ROSANNE characterisation method focuses on new road surfaces, in the procedure for labelling new types of road surfaces as well as in the Conformity of Production check. However, in its principle, it is fully possible to characterise an “old” surface in the same way, for the purpose of getting input data for models. This is actually what the monitoring procedure aims at.

B4. The noise properties of the actual surfaces on which the virtual reference is based – Data collected in ROSANNE The following text, in dark magenta colour, is copied from D2.5. Black text is added by this author. In the final validation experiment of ROSANNE, taking place in the summer of 2016 but supplemented by some earlier measurements, partners collected and compiled available data of CPX measurements on DAC 11 and SMA 11. The grading size was extended to 0/10, as in some EU countries the standard includes this grading. The influence of this size difference on the noise emission is assumed negligible. Many more data were measured with the P1 tyre, in particular on SMA 11. They originate from Belgium (BRRC), Denmark (DRD), Poland (TUG) and Sweden (VTI). Data measured with the H1 tyre originate from Belgium, Poland and Sweden. Data for DAC are for surfaces aged from 2 to 7 years old with an average of 4 years. Data for SMA surfaces are from 2 months to 8 years of surface age, with an average of 3.4 years. The average overall noise levels (“CPX levels”) in A-weighted dB are presented in Table B2. The number of measurements and the standard deviations are also indicated. It appears that he standard deviation is quite consistently 0.8 to 0.9 dB, except for the case when there are only three measurements (which are too few for calculation of standard deviations, anyway). More about this deviation later in the document.


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Table B2: Average measured CPX levels and their standard deviations on reference surfaces at 80 km/h reference speed.

DAC 11 SMA 11 AVG REFERENCE

Tyre P1

LCPX,P [dB(A)]

98.5 99.6 99.4

No. of data 9 42 51

Std Dev [dB(A)] 0.85 0.80 0.90

Tyre H1

LCPX,H [dB(A)]

99.3 98.3 98.7

No. of data 3 5 8

Std Dev [dB(A)] 0.15 0.88 0.84

Third octave band spectra are presented in Figure B1 (DAC 11) and Figure B2 (SMA 11) for tyre P1, and in Figure B3 for tyre H1. In all the figures, the individual spectrum for each section appears in thin pale line whereas the thick black lines correspond to the calculated average spectrum. To enable the comparison with predictions from CNOSSOS-EU, the spectra for DAC 11 and SMA 11 are averaged and calculated in octave bands. The results are presented and compared with the predicted CPX spectra from CNOSSOS-EU reference data in Figure B4 for tyre P1 and passenger cars (vehicle category i=1) and in Figure B5 for tyre H1 and heavy vehicles (categories i=2 and 3). For passenger cars, the predicted spectrum is quite consistent with the measured average spectrum with the P1 tyre. However, the measured spectrum is somewhat sharper than the predicted spectrum, with a pronounced maximum at 1 kHz. The comparison is excellent for octave bands 250, 500 Hz. At 1 kHz, the predicted spectrum is 1 dB above the average measurement. At higher frequency bands, 2 kHz, 4 kHz and 8 kHz, the predictions are about 4 dB(A) higher than the average measured values. The overall overestimation of the prediction is 1.8 dB(A). This is an acceptable difference, bearing in mind the 0.8-0.9 dB(A) standard deviation for the measurements and the strong assumptions made for the prediction. For heavy vehicles, not surprisingly, the comparison leads to higher discrepancies. The overall average level measured with tyre H1 is 2.5 dB(A) below the CNOSSOS-EU predicted level for medium heavy vehicles (category 2) and 6.1 dB(A) below heavy vehicles (category 3). The predicted and measured spectra all show a peak at 1 kHz, but a marginally sharper one for the measurements. In the 1 kHz octave band, the measured spectrum is 1.7 dB(A) below the predicted spectrum for category 2 and 5.2 dB(A) for category 3, but the discrepancies are much higher for other octave bands. A lot of reasons can explain these differences; but the major difference is probably due to the very different size of the H1 tyre compared to real heavy truck tyres. As is written in Part A, the H1 tyre is a proxy for real heavy truck tyres, and is unable to distinguish between vehicle categories m = 2 and m = 3 in CNOSSOS-EDU. The task of tyre H1 is to provide a relative classification of road surfaces, representing traffic of heavy vehicles, but only in a relative way.


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Figure B1: CPX spectra measured at 80 km/h with tyre P1 on DAC 11 (red). Data from Denmark and Sweden. Calculated average (thick black) Figure B2: CPX spectra measured at 80 km/h with tyre P1 on SMA 11 (blue). Data from Belgium, Denmark, Po-land and Sweden. Cal-culated average (thick black) Figure B3: CPX spectra measured at 80 km/h with tyre H1 on DAC 11 (red) and SMA 11 (blue). Data from Belgium, Poland, Swe-den. Calculated ave-rage (thick black)


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Figure B4: Comparison of measured average CPX spectrum at 80 km/h using tyre P1 with predicted

CPX spectrum from CNOSSOS-EU reference data for light vehicles.

Figure B5: Comparison of measured average CPX spectrum at 80 km/h using tyre H1 with predicted

CPX spectrum from CNOSSOS-EU reference data for trucks. It is concluded that the possibility to establish for ROSANNE procedure a realistic reference CPX spectrum is rather consistent with the calculation from the CNOSSOS-EU reference data for light vehicles (category 1). However, this is not the case for heavy vehicles for the CPX level; although frequency spectra are quite similar. The problem may be overcome by adding an appropriate correction to the H1 spectrum.


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B5. Problems with the CNOSSOS-EU approach As written in B3.2, a virtual reference road surface is defined in CNOSSOS-EU, corresponding to an average of Dense Asphalt Concrete (DAC) 11 and Stone Mastic Asphalt (SMA) 11, between 2 and 7 years old and in a representative maintenance condition. It could also be 10 mm max. aggregate size pavement. Assume that somebody wants to set or check the reference noise level in the model. Then one shall find one DAC 11 and one SMA 11, with both being between 2 and 7 years old. Depending on the surfacing policy in the country or region, it may be possible to find either a DAC 11 or an SMA 11, but to find both could be a problem. Finding a few different ones of each kind, to reduce statistical uncertainty, may be even more difficult. Assume that the test crew finds one surface of each DAC and SMA, of 2-7 years of age. Table B2 then shows us that the standard deviation in CPX levels is around 0.8-0.9 dB. Experience suggests that when measuring with the SPB method one would not get lower standard deviations. Then, there is a great risk that one or both surfaces will have properties that are 2 dB different from the average. Such a difference will inevitably also be an uncertainty contribution in the model calculations, which is too large to be acceptable. It follows that it is necessary to make the reference measurements on several surfaces of the DAC 11 and SMA 11 type and calculate an average; surfaces that are independent samples. Four such surfaces would cut this part of the uncertainty to approximately half. But the above is not enough—one should attempt to avoid surfaces that are in some way “atypical”. It was found in ROSANNE that there are especially “SMA” surfaces that are deliberately designed to be somewhat quieter than an “average” SMA. For example, a road constructor may use an SMA mix within the grading limits of the EN 13108-5 standard and modify it, still within the limits, to reduce noise (or for another reason), and then it may become a proprietary surface which usually gets a unique name. Nevertheless, it happens sometimes that it is classified as an “SMA” surface. It may also be a recycled SMA, in which case some minor additions of material and binder are necessary. The same applies to DAC 11 or DAC 10; since there are variants that are constructed with a somewhat extra open texture with the objective to reduce noise or improve drainage. They are sometimes indicated with an extra “o” in the designation to indicate “open”, or corresponding in the respective language. For example, in Denmark one may find surfaces named AB 11å, which means AC 11 which is somewhat more open than a regular DAC 11. How is CEN defining the two surface types that are the basis for the virtual reference surface? In fact, there is no standard for design of a dense asphalt concrete (DAC); only a framework for design of an asphalt concrete (AC), namely EN 13108-1:2016. This standard, mandatory to use in the EU, has so wide tolerances in its grading curve, that it includes virtually all kinds of asphalt concrete, such as dense, semi-open, and open ones; probably also porous mixes. Figure B6 shows the grading limits of AC 11 as specified in EN 13108:2016. Note that specifications exist only for the sieve sizes indicated


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by a marker point. It is obvious to road engineers that this specification allows a wide variety of asphalt pavements, of which DAC 11 would be one. It is of no value in the context of a reference surface. The corresponding standard for SMA is EN 13108:2016. The grading limits for SMA 11 is shown in Figure B6. This is of course much narrower than the AC standard; yet, it allows several quite different variants within the SMA family. This one is of arguable value for the concept of a reference surface. In an earlier version of this standard, from 2000, the grading was much narrower, but this was soon changed to allow the required freedom in the member states for their own versions. As suggested above, member states have their own standards. They have to meet the requirements in the EN 13108 family of pavement standards, but as discussed above, there is considerable freedom to play with the design within the EN limits. Especially, one can “play” with the grading for the sieve sizes for which there are no specifications (such as for 0.5, 1, 4 and 8 mm). An example is shown in Figure B7, which shows that latest Swedish practice for DAC 11 and SMA 11, as defined by the Swedish Transport Administration [Trafikverket, 2015]. It is interesting to compare Figures B6 and B7, as the latter shows how a more useful specification for reference purposes may look. Other European countries, and some road construction companies, have different versions of the same, but still within the limits outlined in EN 13108. Consequently, it should be no surprise that there is considerable variation between surfaces nominally considered as DAC 11 and SMA 11. When testing reference surfaces, therefore, there is no other realistic solution to the variability problem than to measure noise on several samples of independent surface sections (by various contractors and/or of different ages) and calculate an average. If possible, it is a good idea to find and save the grading of the mix that the contractor used and compare it with Figures B6 and B7 to see if it seems to be near an “average” or near one of the limits (Figure B7 may then be more useful than B6). When the current reference noise levels in CNOSSOS-EU were determined, which occurred in the Netherlands many years ago, it is unclear how careful they were to select the reference surfaces. This matter should be explored from historical records, but more importantly, the data should be checked by modern measurements.

B6. Improved definition of the virtual reference surface It is suggested to add a note in the definition of the virtual reference surface (for noise purposes) saying approximately the following:


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Figure B6: The European standard grading limits for AC 11 and SMA 11, as specified in EN 13108-1 and EN 13108-5, respectively. See the text for comments.

Figure B7: The grading limits for DAC 11 and SMA 11, as specified in the design guidelines of the Swedish Transport Administration [Trafikverket, 2014]. See the text for comments.


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When making measurements to establish a reference noise level and frequency spectrum, one should be aware that tight specifications for the grading of the DAC 11 and SMA 11 mixes are not available in the CEN standards system. Instead, there may be national specifications in some member states which are much tighter than the specifications of EN 13108-1 and EN 13108-5. However, these may vary from country to country. Therefore, it is recommended to, if possible, find and record the actual grading of the mix of the tested surfaces, which may be compared to the standards and to each other. The presently best solution to address the uncertainty issue is to include many test surfaces when determining the noise properties of the virtual reference surface, and to document their gradings and texture (MPD values according to ISO 13473-1 are proposed). Testing for a reference noise value should include at least four independent SMA and/or four independent DAC, although the more surfaces one includes, the better it is. With some future research, it may be possible to define the tested surfaces by means of their MPD values and to determine a reference MPD value for each of an ideal DAC 11 and an ideal SMA 11. It may be an average or it may be another even number not far from the average. Then it may be possible to normalize noise levels from the actual MPD value to the reference MPD value. The relation between noise levels and MPD is not good in general, but for a particular (narrow) family of surfaces, there should be a fair correlation between noise (CPX) levels and the MPD value. The procedure in the previous paragraph may be improved by using the enveloped MPD value instead of the raw MPD. A procedure for the enveloping is described in C8. Research on this is recommended. Further, it is proposed that the age range is such that the surfaces have been exposed to road traffic with AADT above 3000 for no less than 30 months and no more than 90 months. It means that it is proposed that the age of two years is too young, as it risks increasing noise deviations; especially if traffic has been low. It also indicates that one shall avoid testing on roads with very low traffic. If there is a problem to find both DAC 11 and SMA 11 in the area of interest, one may provisionally relax the problem by letting one of them replace the other, provided one makes a correction for it. As shown in Table B2, an average DAC 11 is approximately 1.0 dB quieter than an SMA 11 for tyre P1 (representing light vehicles) and 1.0 dB noisier for tyre H1 (representing heavy vehicles). The experience of the author (US) is that this fits well with modern coast-by, CPB and SPB measurements; except that the difference for heavy vehicles is smaller (data for H1 in Table B2 are quite limited). Therefore, the suggestion is that one can convert from DAC 11 to SMA 11 by adding 1.0 dB to the DAC for light traffic, and vice versa. For heavy traffic the suggestion is that one can convert from DAC to SMA by subtracting 0.5 dB from the DAC value, and vice versa. By doing this, one does not necessarily need to find equal numbers of DAC and SMA surfaces for the reference testing. In case one makes the measurements on DAC 0/10 and SMA 0/10, one should subtract approx. 0.3 dB for tyre P1 (light vehicles) and add approx. 0.2 dB for tyre H1 (heavy vehicles) to convert from the 10 mm to 11 mm maximum aggregate size.


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Statistically, the above suggestions should work favourably to reduce uncertainties in the experimental procedure to determine the noise level and spectra representing the virtual reference surface. However, tests results in the future should be compiled to further confirm this, and minor adjustments may make the procedure even better.

B7. Practical example from annual Swedish tests In Sweden, VTI has monitored each year since 2010, once or twice a year, the noise properties on a Swedish low noise road surface on E4 in Huskvarna/Jönköping, and since 2014 such monitoring has also included a similar pavement of E4 in Rotebro, just north of Stockholm [Jacobson et al., 2016]. Also a number of other surfaces have been monitored in the same way. Since the by far most common surface on Swedish highways and motorways is SMA 0/16, this type of surface has been the actual reference each year. Then the reference noise level has been determined as the average level for each of tyres P1 and H1 for 4 to 7 SMA 0/16 surfaces (age 3-7 years). An example from the measurements in 2016 is shown in Table B3. Values are corrected for tyre hardness and temperature. It appears that the standard deviations are approx. 60 % of the standard deviations in Table B2; probably due to a closer control of the surfaces selected. The 95 % confidence limits of the average would be ± 0.3–0.4 dB around these (average) reference levels. Consequently, in this way (but in a European version for 11 mm max. aggregate size) one could determine the reference levels with very small uncertainty. This has been considered to provide a more stable and representative reference, changing marginally between years, than setting a certain noise level from each tyre as the reference, which would be the same each year. It all depends on which one considers more stable over time: the reference tyres or the average noise level of 4-6 SMA 0/16 pavements. Table B3: Example of Swedish reference surfaces SMA 0/16 used in the CPX monitoring measurements in 2016, and their CPX levels at 80 km/h.

Road number and location of tests LCPX,P,80 LCPX,H,80 Notes RV40 Mallsberg (Jönköping/Huskvarna) 98.9 98.8 This may be a questionable SMA RV47 Tokeryd (Jönköping/Habo) 100.4 99.5 LV636 Sjögestad (Mjölby/Linköping) 99.9 99.7 E22 Hörby 100.4 100.3 RV34 Flygrakan Kåparp (Linköping) 99.7 99.3 E4 Rotebro (Sollentuna/Stockholm) 100.2 99.8 E4 Rotebro (Sollentuna/Stockholm) 100.3 99.8 Average CPX level [dB] 100.0 99.6 Standard deviation [dB] 0.55 0.53


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B8. The ISO 10844 reference surface There has been a standard reference surface for noise testing since 1994, when ISO 10844 was first published. Since then, two updates have been made to the standard and the latest one is from 2014 [ISO 10844:2014]. It specifies the characteristics of a test surface intended to be used for measuring vehicle and tyre/road noise emissions. The surface is claimed to:

• produce consistent levels of tyre/road sound emission under a wide range of operating conditions including those appropriate to vehicle sound testing,

• minimize inter-site variation, • provide minor sound absorption.

It is used in several legal procedures, such as the EU tyre labelling regulation EC 1222:2009, the ECE Regulation 117 specifying noise limits to tyres, ECE Regulation 51, specifying noise limits to passenger cars, as well as corresponding regulations for trucks and motorcycles. ISO 10844 is quoted in several International Standards (e.g. the ISO 362 series and ISO 13325). Despite the surface is closely specified in its design, as well as in its laying, the tyre/road noise variation between different test tracks built and based on this standard may be 3-4 dB (A-weighted). There are no published data regarding this, but 3-4 dB seems to be used as a rule of thumb among users. The reasons are, according to this author, (1) the grading curve has relatively wide tolerances, most of all it allows maximum aggregate from 6.3 to 10 mm, and (2) it allows MPD variation from 0.3 to 0.7 mm. A further reason is that it is known that for very smooth-textured surfaces, such as the low-MPD variants of ISO 10844, variation in noise between tyres is larger than at more common textures on roads. The reasons why the ISO 10844 surface is not useful as a reference in the application discussed in this Part are:

• It is a surface originally intended to give as low tyre/road noise as possible (for an acoustically dense surface), although this matter is not something that the industry wants to hear nowadays

• The exact recipe is not used in any present road surface in service (although it would be rather similar to a DAC 8; i.e. like the DAC 11 in Figure A8 but with maximum 6.3-10 mm aggregate)

• The surface would not be safe in wet weather and at high speeds, as it allows far too smooth texture to provide the necessary water drainage on the low-MPD variants

• As its requirements are tailored to test tracks, some of the specifications are not very practical on actual roads

• Its properties are not known under normal road traffic, as it is only laid on test tracks with the special traffic of usually low intensity there.

It may be interesting to know that it is planned (unofficially) to specify a second ISO 10844 surface, with candidate surfaces being “normal” road surfaces, such as SMA 11. But this was proposed already in 2000 and has not happened since then, so it is most uncertain whether it will happen in the next few years. However, if it will happen, it will mean that it is consistent with the virtual reference surface in this Part, at least its SMA 11 variant.


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B9. Future work Many road and environment administrations are now struggling with conversion to the new CNOSSOS-EU model; i.e. the Directive EU 2015/996 [EU Commission, 2015]. The Annex to this Commission Directive sets out the common assessment methods. Member States are required to use these methods from 31 December 2018 onwards. This includes considering the issue of reference surfaces. Sweden is one of the countries in which work is ongoing to define new road surface correction levels and new frequency spectra. VTI has an ongoing project (sponsored by the Swedish organization BVFF) with this purpose; including to compile the results of all CPX measurements made from 2010 in the CNOSSOS-EU format. For the latter purpose, ROSANNE Deliverable D2.5 will be crucial. Most probably, the same applies to several other countries. A general problem in Europe is the various national terminology of road surfaces. Of course, there are European standards for such technology; mainly in the EN 13108 series of standards. Nevertheless, countries use their own terminology which is not always congruent with the one in CEN documents. Table B1 is an excellent illustration of this: in this table with 14 road surfaces, not a single one is clearly identifiable in the CEN terminology system. Therefore, CEN is suggested to issue a dictionary for the all road surface terms in the CEN system and how they correspond to surfaces in some of the national practices. It is suggested to monitor the work with updating the ISO 10844:2014 standard, as a second surface such as SMA 11 would give certain possibilities to compare measurements made for noise regulations and for labelling with the CNOSSOS-EU model. Furthermore, Chapter B6 presents numerous subjects that need more research, with the common aim to reduce uncertainties in determination of the virtual reference surface.

B10. Conclusions There is a great need for a reference surface to be used when developing and implementing road traffic noise prediction models since the input noise levels and frequency spectra for various vehicle categories must be measured for a defined reference case. A second great need is to have a common reference when speaking about and reporting “noise reduction” for “low noise road surfaces”. As was first realized in project HARMONOISE, later carried over to IMAGINE and CNOSSOS-EU, the best option is to select a reference case that does not exist in reality but which is possible to define based on a couple of very common road surface types. Thus, a “virtual reference surface” has been defined in CNOSSOS-EU and used in the European Directive EU 2015/996. In summary, it is a mix (an acoustic average) of dense asphalt concrete with maximum aggregate size 11 mm (DAC 11) and stone mastic asphalt, also with maximum aggregate size 11 mm (SMA 11); each at an age between 2 and 7 years, and exposed to proper maintenance.


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These two surface types were chosen since they represent two of the most common types on European roads, and at least one of the types should be commonly available in each member state. In this deliverable, the virtual reference surface concept is explored based on experimental data collected and compiled in ROSANNE for the two reference tyres P1 and H1 on various DAC 11 and SMA 11 surfaces in the partners’ countries. Both typical CPX levels and typical frequency spectra are shown. It appears that the deviation between surfaces that are nominally equal is larger than one would like. It is hypothesized that the present measured noise properties of the virtual reference surface in the CNOSSOS-EU model that are input values to the model may need extensive checking. In this deliverable, proposals are made on how one can define a virtual reference surface practically and with lower uncertainty. Most important is to include not only one of each DAC and SMA surface, when attempting to assign reference noise levels and spectra to the virtual reference, but to make measurements on several surfaces that are nominally equal but constructed and laid independently and of different age. Several ways to improve the definition of the virtual reference and the associated noise level and frequency spectrum are presented. For example, it is recommended to attempt to find and document the original grading curve of the mix, as well as measuring the macrotexture represented by the MPD value. It may also be fruitful to use an enveloped MPD instead of the raw MPD for this purpose. In the future, it may be possible to define a reference MPD value (or reference enveloped MPD) for each of the ideal DAC 11 and SMA 11 pavements and to normalize measurement results on actual road sections with such pavements to the reference MPD.

B11. Suggested terminology CNOSSOS-EU uses the term virtual reference surface. However, in Part C of this deliverable, another virtual reference surface is defined (for rolling resistance). These are quite similar but not identical. Therefore, it is useful to distinguish between them by adding the subject of each one when mentioning them in writing and orally. Here it is proposed to use this distinction:

• Virtual reference surface for noise, acronym VRSN • Virtual reference surface for rolling resistance, acronym VRSR

B12. References Anfosso-Lédéé, Fabienne (2016): “Report on the compatibility of the proposed noise characteri-zation procedure with CNOSSOS-EU and national calculation methods”. ROSANNE Deliverable D2.5, downloadable from http://rosanne-project.eu

EN 13108-1:2016, Bituminous mixtures - Material specifications - Part 1: Asphalt concrete

EN 13108-5:2016, Bituminous mixtures - Material specifications - Part 5: Stone mastic asphalt



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EU Commission (2015): “Establishing common noise assessment methods according to Directive 2002/49/EC of the European Parliament and of the Council”, COMMISSION DIRECTIVE (EU) 2015/996 of 19 May 2015, European Commission, Brussels (published in Official Journal of the European Union, L 168/1, 1.7.2015).

ISO 10844:2014: “Acoustics -- Specification of test tracks for measuring noise emitted by road vehicles and their tyres”. ISO, Geneva, Switzerland.

ISO 13473-1: “Characterization of pavement texture by use of surface profiles: Part 1: Determination of Mean Profile Depth”. ISO, Geneva, Switzerland.

Kephalopoulos, S; Paviotti, M.; Anfosso-Lédée, F. (2012): “Common Noise Assessment Methods in Europe (CNOSSOS-EU)”, EUR 25379 EN. Luxembourg: Publications Office of the European Union.

Sandberg, Ulf (2006): “The concept of virtual reference pavement for noise prediction and comparison purposes”. Proc. of Inter-Noise 2006, Hawaii, USA.

Trafikverket (2015): “KRAV - Bitumenbundna lager” (English translation: Requirements – Bitumen bound layers”. TDOK 2013:0529, Version 2.0, 2015-11-02, Trafikverket (Swedish Transport Admini-stration), Borlänge, Sweden. May be downloaded at: http://th.tkgbg.se/Portals/0/STARTFLIKEN/Checklistor%20och%20mallar/2_%20Projektering%20dokument/TDOK%202013%200529%20Bitumenbundna%20lager_2016-10.pdf

http://th.tkgbg.se/Portals/0/STARTFLIKEN/Checklistor%20och%20mallar/2_%20Projektering%20dokument/TDOK%202013%200529%20Bitumenbundna%20lager_2016-10.pdf

http://th.tkgbg.se/Portals/0/STARTFLIKEN/Checklistor%20och%20mallar/2_%20Projektering%20dokument/TDOK%202013%200529%20Bitumenbundna%20lager_2016-10.pdf


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PART C: REFERENCE ROAD SURFACE FOR USE IN ROLLING RESISTANCE STUDIES

C0. Background To make frequent and simple calibration checks of rolling resistance measuring devices, it is very useful to have a special test surface easy to find at various locations and with known properties; where measurements can be made easy and fast and where results are reproducible. Such a surface may be considered a reference surface. This would require that the surface is designed and specified in a suitable way, and that appropriate texture and other geometrical parameters are measured. One may then define an ideal (virtual) surface close in performance to the actual reference, but with permanent and defined properties, against which rolling resistance measurements on the actual reference surface may be compared. Rolling resistance values may then be normalized to correspond to the ideal (virtual) reference surface. Such a reference surface procedure, based on a type of surface relatively easy to find on the road network, provides a fast and simple day-to-day calibration possibility for rolling resistance of great value to the measurement procedures outlined in ROSANNE D3.5. This document defines a reproducible procedure for normalization of rolling resistance measure-ments on an actual reference surface to measurements that would be performed on a virtual reference surface. It is written in a format common to CEN and ISO standards to facilitate a future standardization of the procedure. Regarding terminology, please refer to B10, where it is proposed how one can distinguish between the reference surfaces for noise and rolling resistance.

C1. Introduction and purpose There is a need for simple checks and calibration of rolling resistance measuring devices. Such checks or calibrations are useful to conduct at the start and end of a measuring period (days, day or part of day) to make sure that there has been no drift with time. This can be achieved by running the device over a certain test surface on a road or test track for which the rolling resistance properties are known and defined. The purpose of this document is to describe a check and calibration procedure for rolling resistance measuring devices based on measurements of rolling resistance, road surface texture and other parameters that influence rolling resistance on a reference surface, and normalizing the results to those that would be obtained on a virtual reference surface. The latter is a non-existing, idealized surface that is defined by several parameters and whose rolling resistance properties are relatively similar to one of the most common road surfaces on European highways and streets.


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C2. Scope This document specifies a method for obtaining the rolling resistance coefficient, Cr, by measuring with a suitable device designed for rolling resistance measurements on a virtual reference surface on a road or test track. It is assumed that the device is equipped with some defined test or reference tyres. The method does not replace more elaborate calibration methods performed in a laboratory under closely controlled conditions, but will provide a simple check easy enough to be made once or twice per day. The method will also provide a defined road or test track surface that may be used as a reference against other road or test track surfaces may be compared. The method requires measurement not only of rolling resistance but also of road surface texture and some other geometrical parameters. However, the latter measurements do not need to be made simultaneously and not very often, as long as the surface does not change its properties. The described method can be used for the calibration of new or in use equipment and for comparing equipment without doing physically measurements on the same test track(s) or roads. Although the method may be used mainly to measure the rolling resistance properties of road surfaces using refe-rence tyres, it may in principle also be used for testing tyres on a defined virtual reference surface.

C3. Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including amendments) applies. ISO 13473-1:1997, Characterization of pavement texture by use of surface profiles - Part 1: Determination of Mean Profile Depth ISO 13473-2:2002, Characterization of pavement texture by use of surface profiles. Part 2: Terminology and basic requirements related to pavement texture profile analysis ISO 13473-3:2002, Characterization of pavement texture by use of surface profiles. Part 3: Specification and classification of profilometers ISO 13473-5:2010, Characterization of pavement texture by use of surface profiles. Part 5: Determination of megatexture ISO 18437-4:2008, Mechanical vibration and shock — Characterization of the dynamic mechanical properties of visco-elastic materials — Part 4: Dynamic stiffness method EN 13036-7:2003, Road and airfield surface characteristics - Test methods - Part 7: Irregularity measurement of pavement courses: the straightedge test prEN 13036-5:2006, Road and airfield surface characteristics - Test methods - Part 5: Determination of longitudinal unevenness indices.

C4. Terms and definitions Rolling resistance (force): symbol Fr: unit N force counteracting the motion of a rolling wheel


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NOTE: The term rolling resistance is also used as the general term for the force which must be overcome for a tyre to roll on a surface, which often implicitly in common speech includes the rolling resistance coefficient as the measured property. Rolling resistance coefficient: symbol Cr: unit N/N (non-dimensional) rolling resistance force divided by the vertical load on the wheel Measured rolling resistance coefficient; symbol Cr,meas: the rolling resistance coefficient actually measured on the real road or test track surface Rolling resistance coefficient reference value; symbol Cr,ref: the rolling resistance coefficient on the virtual rolling resistance reference surface Reference surface (test surface) wearing course of a road or test track on which the testing in this procedure or performed NOTE: this shall be a dense asphalt pavement that should be of type DAC 11, SMA 11 (see EN 13108-1 and EN 13108-5), or similar Virtual reference surface ideal wearing course of a road or test track which is defined in this procedure NOTE: this shall have properties not very different from those of a dense asphalt pavement of type SMA 11, DAC 11, or similar’ Enveloped surface (profile) the enveloped surface (profile) is the three (two) dimensional locus of the maximum penetration depth of the tyre tread when the tyre is rolling on the surface [ISO 13473-2:2002].

C5. Outline of the procedure This procedure comprises four main elements: 1. Definition of the virtual rolling resistance reference surface. First, a number of relevant proxy

parameters are chosen, such as texture, unevenness, elasticity, slope, etc, which are known to influence the rolling resistance. For each proxy parameter, a suitable descriptor is chosen (e.g. mean profile depth, MPD, for texture) and to each descriptor a reference value is attributed.

2. Fixing the boundaries for the actual reference (test) surface on which the measurements shall be carried out. These are carried out on real road or test track stretches which normally deviate a little from the virtual reference surface. The deviations are, however, limited and the boundaries of the descriptors of the relevant parameters for acceptable deviations are fixed.

3. Calculation procedure for the Cr on the virtual reference surface (indicated hereafter as Cr,ref), based on the measured Cr, indicated as Cr,meas.

4. Optionally, the texture (MPD) may be calculated for an enveloped surface profile, instead of for the raw profile curve. This will change the numerical values of the proxy parameters and their descriptors mentioned above.


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C6. The virtual reference surface

C6.1 General issues The virtual reference surface is defined by means of a set of descriptors of seven relevant proxy parameters, as described in the following sub-clauses. Since the reference surface is virtual, the descriptors have exact values by definition. The values chosen aims at representing an ideal pavement of a type SMA 11 or DAC 0/16 that has been in use for some time but is not yet worn.

C6.2 Macrotexture Macrotexture is described by the mean profile depth (MPD) [ISO 13473-1] and the skewness [ISO 13473-2]. For the virtual reference surface, the MPD shall be 0,8 mm and the skewness of the texture shall be 0,0.

C6.3 Megatexture Megatexture is described by the megatexture level LME [ISO 13473-5]. For the virtual reference surface LME shall be 0 dB. NOTE: As megatexture level is a logarithmic measure, 0 dB is close to, but not equal to, a perfectly smooth megatexture (close to 0,0 mm peak-bottom amplitude).

C6.4 Longitudinal evenness The International Roughness Index (IRI) is the descriptor for longitudinal evenness [prEN 13036-5:2006]. The IRI of the virtual reference surface shall be 0,0 mm/m.

C6.5 Transversal evenness For the transversal evenness the space under the 3 m straight edge is used as the descriptor [EN 13036-7:2003]. For the virtual reference surface this space shall be 0 mm. NOTE: This also implies that there shall be no wheel ruts.

C6.6 Elasticity The elasticity of the road surface is described by its Young’s modulus (of elasticity) [ISO 18437-4:2008]]. For the virtual reference surface the Young’s modulus shall be at least 15 000 MPa. NOTE: This corresponds to a common stone mastic asphalt pavement.

C6.7 Longitudinal slope The longitudinal slope of the virtual rolling resistance reference surface is 0,0 %.

C6.8 Transversal slope The transversal slope of the virtual rolling resistance reference surface is 2,0 %. NOTE: This represents a typical design of a straight section of a road.


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C7. The actual reference (test) surface

C7.1 General issues The calibration measurements can be carried out on any road section or test track, provided that it complies with a number of requirements, which are listed in this Clause. The values given refer to the average value over the test section, if nothing else is stated. The values chosen aims at allowing the use of a pavement of a type SMA 11 or DAC 0/16 that has been in use for some time but is not yet significantly worn, but it will also allow some pavements having maximum aggregate sizes, such as SMA 0/8, SMA 0/16 or DAC 11, provided these have values within the tolerance limits. It may also be any other dense asphalt pavement having gradings between those of SMA and DAC. Pavements with an “open texture” or porous pavements may not qualify since skewness might be too negative and newly laid SMA pavements, not yet exposed to a lot of traffic, may also have too negative skewness to be acceptable. The latter may also be too soft to meet the elasticity requirement. The first seven requirements are directly related to the proxy parameters and descriptors used to define the virtual reference surface. An additional set of requirements apply to the actual reference surface.

C7.2 Macrotexture MPD shall be between 0,6 and 1,0 mm and the skewness of the texture shall be between -0,5 and +0,5.

C7.3 Megatexture Megatexture level LME shall be within 0 and 60 dB (corresponding to 10-3 and 1 mm rms). NOTE: For real road surfaces, the MPD is very well correlated with LME, so there is no need for a tighter requirement. Essentially, the requirement means that the actual test surface shall be in good condition and that megatexture shall not be excessive.

C7.4 Longitudinal evenness The IRI value shall not be higher than 1,5 mm/m. NOTE: This implies that the test surface corresponds to the evenness of a good quality road offering a comfortable ride.

C7.5 Transversal evenness The result of the 3 m straight edge test shall not be higher than 3,0 mm on any longitudinal position of the test section.

C7.6 Elasticity The test surface shall be a dense asphalt pavement without any other elastic ingredient (such as rubber granulates) than bitumen and bitumen modifier (excluding rubber). See also the requirement of maximum surface temperature below.


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C7.7 Longitudinal slope The longitudinal slope of the test surface shall not be higher than 2,0 % on any part of the test section.

C7.8 Transversal slope The transversal slope of the test surface shall not be higher than 2,5 %.

C7.9 Homogeneity The surface shall be homogeneous over the entire length for the seven parameters listed above. The standard deviation for 20 m long sections shall not be higher than 20 % of the average or (if relevant) the maximum value.

C7.10 Visual appearance Regardless of the requirements above, the actual test surface shall be free of any visual degradation, such as potholes, severe cracking, ravelling or flushing.

C7.11 Cleanliness Regardless of the requirements above, the actual test surface shall be dry and free of any pollutant, such as oil, leaves, debris, dust, mud, sand, ice, or snow.

C7.12 Dimensions of the actual test surface The length of the test surface shall be at least 100 m and the minimum width at least 3,0 m. It shall be free of any curvature.

C7.13 Acceleration and braking zone adjacent to the real test surface There shall be an appropriate zone for acceleration before and a braking zone after the test section. The needed length depends on the desired measurement speed, the weight of the rolling resistance measurement device and the acceleration and braking power of the towing vehicle.

C7.14 Surface temperature The temperature of the test surface shall not exceed 40 oC, since higher temperatures may cause the surface to get soft enough to increase rolling resistance.

C7.15 Measurement speed and operating concerns The speed during the calibration measurement shall be close or similar to the speed used during regular measurements of rolling resistance. The operation for warming up the tyre and/or keeping the tyre at a reasonably constant operating temperature should be similar to that used when performing regular measurements of rolling resistance.


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C8. Procedure using an enveloped surface profile for texture calculation

As shown in ROSANNE D4.2, applying an enveloping procedure to the profile curve before calculating the MPD will be more representative of the actual tyre/road contact, and may thus provide a better descriptor for MPD. Therefore, this optional way to describe surface macrotexture would normally give lower uncertainty in normalizing the Cr,meas values to the nominal texture of the virtual reference surface. A method which is easy and yields a realistic enveloped surface profile is the “indentor method” as described in ROSANNE deliverable D4.2 and which works as described below. Suppose that the two-dimensional texture profile is available as equidistant discrete points (xi,yi). The procedure is as follows:

1. The profile is divided into equal intervals, “footprints”, each of length L, for example 90 mm.

2. For the first footprint, the regression line is calculated and subtracted from the profile in this footprint.

3. A horizontal line is drawn through the maximum value of the yi – k, with k = 0, if this step is executed for the first time.

4. The area under the profile and above the horizontal line, hereafter indicated as A, is calculated and compared to a predefined value S. If A < S, then k is increased with one step size (for example 0.01 mm) and one returns to step 3.

5. If A ≥ S, then all the points in this footprint with an amplitude above the horizontal line are assigned a status “remain” and the other points “to be interpolated”.

6. Then one shifts to the next footprint and one repeats the procedure from step 2 onwards, until the last footprint of the profile is processed.

7. One returns to the original profile (xi,yi). For all the points i which were flagged “remain”, the amplitude yi,env of the enveloped curve has the same value as the original amplitude yi. For the points with the status “to be interpolated”, yi,env is a value interpolated between the nearest points with the status “remain”. The interpolation scheme is to be chosen with care: a smooth connection with the adjacent “remain” points is preferable, but one has to avoid artificial and hence unwanted oscillations which may occur with higher order polynomial interpolation. A good choice is the cubic Hermite spline interpolation.

The procedure is schematically shown in Figure C1.


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Figure C1: Example of application of the indentor enveloping procedure on the original profile (in black). The distance between the adjacent vertical blue lines is the tyre/road footprint length. The green area equals the blue area (equalling predefined area S). The red line is the resulting enveloped profile. The MPD should then be calculated on the enveloped profile using the procedure outlined in ISO 13473-1. It is suggested that S = 6 mm2, but some further testing is after the end of the ROSANNE project ongoing at BRRC and will be published, presumably at the SURF 2018 conference.

C9. Calculation of the rolling resistance coefficient reference value Cr,ref

This clause describes how the measured rolling resistance values are normalized to correspond to similar measurements that would have taken place on the virtual reference surface. For this reason, Cr,ref is calculated from the average Cr measured on the actual reference (test) surface (Cr,meas) using the formula:

Cr,ref = Cr,meas - k ΔMPD (Equation 1) where • k is a constant factor, equal to 0.0011 (for an enveloped profile with S = 6 mm2 it is 0.0040) • ΔMPD = measured MPD – 0.8 mm • MPD is the mean profile depth on the actual reference (test) surface, expressed in mm, with the

additional requirement that MPD equals the arithmetic average of all the MSD values over the measurement length; see ISO 13473-1:2015.

C10. Discussion of the k factor It shall be noted that the suggested values of the k factor shall be considered as preliminary. In earlier research, in project MIRIAM, and in some national surveys, a value of k = 0.0019 was derived, as outlined in ROSANNE deliverable D4.1 [Goubert, et al., 2014]. It was also no sign of non-linear correlation between Cr and MPD. However, combined rolling resistance and texture measurements on the IFSTTAR test tracks in Nantes were carried out within the ROSANNE project and the findings were as follows, as summarized by the authors, based on results reported in [Anfosso-Lédéé, et al., 2016]:


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If one considers all the 12 test tracks (including the very rough ones) in the calculation of the regression line Cr as a function of MPD, then one gets a very high R². For the P1 tyre, one finds k = 0.0015 at 50 km/h and k = 0.0017 at 80 km/h, which is not too far below the value k = 0.0019, as mentioned above. For H1, k was found to be 0.0013 to 0.0015 at 50 km/h. There is only a weak (non-significant) sign of non-linearity, namely that the slope in the relation may be somewhat lower at low and medium MPD:s compared to the slope at high MPD:s. Therefore, if one considers only the test tracks with MPD < 1.5 mm, i.e. representative for the vast majority of real road surfaces, then one gets a lower R² and a lower k value, which is logical when the range is restricted, but also could be an effect on the possible non-linearity. Using this limitation in MPD range also makes sense for this purpose as this calibration procedure is designed for a limited MPD range that one wants to use the k coefficient, namely from 0.6 to 1.0 mm (see C7.2). Hence the proposal by the authors: for the P1 or the H1 tyre: k = 0.0011 for non-enveloped and k = 0.0040 for “indentor enveloped” profiles; the latter also based on the (average) results reported in [Anfosso-Lédéé, et al., 2016]. Considering that this lower k at low and medium MPD:s is not obvious in earlier studies, and is not clearly significant in ROSANNE, this issue should be further investigated. When considering the entire texture range on European road surfaces, it may be better to assume, preliminary, that k is equal to 0.0017. The difference between the k factors may have considerable effects, as 0.0017 is approxi-mately 50 % greater than 0.0011.

C11. Reporting Apart from reporting the measurements according to requirements in ROSANNE D3.6, in addition, the following should be reported here:

• The values describing the actual reference (test) surface and the operation; i.e. MPD, skewness, megatexture level, IRI, area under the 3 m straightedge, longitudinal slope, transversal slope, length of the test surface, test speed, and surface temperature.

• Whether MPD is based on the raw profile or the enveloped profile • The type of enveloping procedure (if appropriate) • Cr,meas • Cr,ref

C12. Uncertainty issues The uncertainty considerations are similar to those that appear in the new standard for rolling resistance devices (ROSANNE D3.5). However, there is one additional aspect; i.e., the extra uncertainty introduced by the calculation of the Cr,ref by means of Equation 1. An estimation of the additional uncertainty is displayed in Figure 1.


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Figure C2: Additional uncertainty introduced by the conversion from the Cr,meas to the virtual Cr,ref as a function of ΔMPD.

C13. References Anfosso Lédée, Fabienne; et al. (2016): “Experimental validation of the rolling resistance measurement method including updated draft standard”, ROSANNE deliverable D3.6; downloadable from http://rosanne-project.eu

Goubert, Luc; Do, Min Tanh; Bergiers, Anneleen; Karlsson, Rune; Sandberg, Ulf; Maeck, Johan (2014): “State-of-the-art concerning texture influence on skid resistance, noise emission and rolling resistance”, ROSANNE deliverable D4.1, April 2014; downloadable from http://rosanne-project.eu

EN 13108-1, Bituminous mixtures - Material specifications - Part 1: Asphalt concrete

EN 13108-5, Bituminous mixtures - Material specifications - Part 5: Stone mastic asphalt

ISO 13473-1, Characterization of pavement texture by use of surface profiles: Part 1: Determination of Mean Profile Depth. ISO, Geneva, Switzerland.

See further the normative references in C.3 and the list of ROSANNE deliverables in Section IV.



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