Acoustic performances of roadside noise barriers: wide scale on-site measurement survey in Flanders
Peter HOUTAVE1, Jean-Pierre CLAIRBOIS2, Barbara VANHOOREWEDER3, Ann BUYTAERT4, Christ GLORIEUX5, Geert DIERCKX6 1,2A-Tech / Acoustic Technologies, Belgium
3,4AGENTSCHAP WEGEN & VERKEER, Belgium 5,6KUL Katholieke Universiteit Leuven, Laboratory of Acoustics, Belgium
ABSTRACT After 20 years of research and development, the (European) CEN standards on the (in-situ) intrinsic acoustic performances of roadside noise barriers are now completed. EN1793-5:2016 addresses the in-situ values of sound reflection under direct sound field conditions, while EN1793-6:2012 addresses the in-situ values of airborne sound insulation under direct sound field conditions. Thanks to the methods described within those 2 standards it is now possible to objectively measure and fairly compare noise barriers of different kinds and/or materials as they are installed along the roads, but also to establish a database of those performances, as well as their evolution all along the noise barriers lifetime. Thanks to the evidence of those standards, the Agentschap Wegen en Verkeer (Roads and Traffic Agency), the relevant Authority in Flanders, decided to start a wide scale systematic survey of the installed noise barriers along the Flemish road network, with 20 measured noise barriers per year (for both sound reflection and airborne sound insulation) for the next 4 years. This paper will introduce the context, objectives and methodology of the survey, as well as examples of the first tested sites. Keywords: Noise Barriers, Sound Reflection, Airborne Sound Insulation I-INCE Classification of Subjects Number(s): 31.1, 72.7, 73.4,74
1. INTRODUCTION Since the early stages of noise barriers characterization, the sound absorption and airborne sound
insulation characteristics of noise barriers have (almost always) been characterized using (reverberant room) laboratory-based tests methods (EN1793-1:1997 (1) and EN1793-2:1997 (2)): those tests methods were (respectively) based on the old ISO354 and ISO140.
In 2012, the scope of EN1793-2:2012 (3) had already been restricted to noise reducing devices (generic definition including noise barriers) that have an intended use under diffuse sound field conditions only. This had been possible then, thanks to the availability of the EN1793-6:2012 (4) for direct sound field intended uses. However, the scope of EN1793-1:2012 (5) was not yet restricted to this kind of intended uses, as the corresponding EN1793-5 for direct sound field intended uses was not yet fully available.
As of March 2016, after 20 years of research and developments, EN1793-5:2016 (6) has been finally published: a soon coming new revision of the EN1793-1:???? (7) will then have an adapted scope that will also be definitely restricted to intended uses under diffuse sound field conditions only. 1 firstname.lastname@example.org 2 email@example.com 3 firstname.lastname@example.org 4 email@example.com 5 firstname.lastname@example.org 6 email@example.com
This means that the old tests made inside (reverberant room) laboratories are no longer considered applicable for the assessment of noise barriers along roads, that is under direct field, non-reverberant conditions: since now, for assessing the acoustic characteristics of roadside noise barriers, the in-situ test methods according to the standards EN 1793-5:2016 and EN 1793-6:2012 are the reference.
Research has shown that there is a moderate correlation between sound absorption results measured according to EN 1793-5:2016 (under direct sound field conditions) and those measured according to EN 1793-1:2012 (under diffuse sound field conditions): when all barrier types are considered as a single dataset, the laboratory method dramatically over-estimates the sound absorption properties of a noise barrier compared to the in-situ method. For the airborne sound insulation, there is a potentially good correlation between the results measured according to both the laboratory method and the in-situ method. Further research is then required to investigate the correlation between the two methods for individual noise barrier types.
Despite good results in the laboratory, problems often arise during installation of the noise barriers. The weakest points of insulation are often the joints or post fixings or installed barriers with lower quality than tested. After installation, a visual and audible inspection of the whole barrier is recommended as the minimum requirement, supplemented by the in-situ test methods (EN 1793-5:2016 and EN1793-6:2012), the definitive references for assessing the acoustic performance of new barriers, as a form of project sign-off.
Finally, monitoring of the condition and potentially the acoustic performance of noise barriers over their working lifetime will also be necessary for National Road Administrations to ensure tha t the barriers remain robust, intact and fit-for-purpose. It has also identified that there is a lack of published data on the long-term acoustic in-situ performance of noise barriers. Further practical data are then required too. For all those reasons, the Roads and Traffic Agency of Flanders (Belgium) decided to start a wide scale systematic survey of the installed noise barriers along their road network. This survey will consider 20 in-situ tested noise barriers per year for the next 4 years.
2. SITE SELECTION
2.1 The Flemish road network and noise barriers The Flemish road network is about 1.000 km of highways: along those highways, not less than 218
noise barriers have been installed some of those since about 30 years. The total length of those barriers corresponds to about 122 km, with a height varying from 2.4 m up to over 7 m. About 427.000 m of noise barriers of all kinds, shapes and materials are thus installed : the new in-situ methods now allow the Flemish Roads Authorities (as all the Roads Authorities of course) to check the effective acoustic performance (sound reflection and airborne sound insulation) of any existing, or new noise barrier in order to check the validity of the performances announced by the manufacturer at the contract stage , or even to monitor the evolution of their performances along time.
2.2 Site selection As specified in EN1793-5:2016 and EN1793-6:2016, in order to have the lowest frequency limit, as
low as possible, the tested samples should preferably have a height higher than 4 m. In that way, from the list of 218 possible noise barriers, a filter first selected the ones that have heights of minimum 4 meters: 78 noise barriers stayed in the list of potential sites (see table 1).
Table 1 part of the installed noise barriers database height 4m ( AWV) Provincie CODE Bouwjaar Materiaal Leeftijd H_MIN H_MAX Opmerkingen
Antwerpen 1_055 2013 Houtvezelbeton + PMMA 3 4.5 4.5 Mogelijke meetplaats voor lichtgewichtbeton aan het beginpunt van het scherm. Achterkant (behoorlijk) bereikbaar (mogelijks gracht aanwezig), voorkant (pechstrook + afrit)
Antwerpen 1_063 2013 Kokosvezel 3 4.5 4.5 Idem 1_065 (betere meetlocatie)Antwerpen 1_065 2013 Kokosvezel 3 4.5 4.5Antwerpen 1_069 2014 Houtvezelbeton 2 4.0 4.0 Geen plannen / foto'sAntwerpen 1_100 1950 Metaal onbekend 5.0 5.0 Zeer kort (4m)Antwerpen 1_121 2010 Kunststof 6 4.0 6.0 Combineren met 1_123, gebogen scherm, verhoogde
ligging A13, moeilijke bereikbaarheid, druk, geen pechstrook
Antwerpen 1_123 1999 Lichtgewichtbeton + PMMA 17 3.5 4.0 Combineren met 1_121, mogelijks moeilijk bereikbaar, druk, geen pechstrook
Limburg 2_005 2014 Metaal 2 4.0 4.0 SAS t.h.v. 39,550 (B = 3 m), mogelijks moeilijk bereikbaar, druk
Limburg 2_006 2014 Metaal 2 4.0 4.0 DEUR, mogelijks moeilijk bereikbaar, drukLimburg 2_008 2014 Metaal 2 4.0 4.0 DEUR, mogelijks moeilijk bereikbaar, drukLimburg 2_010 2011 Houtvezelbeton op sokkel 5 4.0 4.0 Idem 2_011, op- en afrit, mogelijks moeilijker
In this list, groups have established in order to merge all the noise barriers of the same type, as many different ones are installed: metallic barriers, concrete barriers, wood cement, wooden barriers, plastic ones, volumic concrete barriers (with plantations), and so on.
A first list of about 40 barriers appeared: further analysis of the location, the measurement conditions along highways, ease of access, ease of carrying out the measurements , possibility to reach both sides of the tested sampleOf the 20 targeted barriers, 10 of those have been actually found and checked, ready to be tested. Figure 1 shows 2 examples of those site locations.
Figure 1 location and measurement conditions of 2 chosen noise barriers ( AWV)
Except the safety conditions during the measurements, that imply stopping the closest lane to the measured sample, what also consequently reduces the traffic speed, all benef it for a better measurement, the weather conditions are crucial: wind of more than 5m/sec have to be avoided, rainy weather considerably slows down the measurement and, in some cases, might also block those. We thus chosen to wait for a better season: the first measurements are expected to start at the end of May 2016, what explains that, at the moment of writing this paper, the results are not yet available but will be presented during the conference.
2.3 Example of test reports All the testing conditions and the test results have to be presented in a standardized form that is
detailed in both EN1793-5:2016 and EN1793-6:2012: figure 2 shows an example of such a test report for the sound reflection performances, while figure 3 shows an example of such a test report for the airborne sound insulation performances. Every test reports has to detail: the noise barrier itself, all the measurements conditions, the equipment, the persons carrying out the measurement, the weather conditions, the lowest reliable frequency limit, then all the results in 1/3rd octave band as well as in a single number rating following the reference spectrum defined in EN1793-3:1997 (8).
For the airborne sound insulation measurements, tests have to be carried out in the middle of an acoustic element (i.e.: in the middle between two posts), as well as in front of the posts.
Figure 2 test report of sound reflection performance following EN1793-5 ( A-Tech / KULeuven)
Figure 3 test report of airborne sound insulation performance following EN1793-6
( A-Tech / KULeuven)
3. SUMMARY The Flemish Roads and Traffic Authorities has started an ambitious systematic program of
measurement of the in-situ performances of noise barriers along their highway network. The whole survey targets 80 noise barriers to be tested for both their sound absorption and their airborne sound insulation over the next 4 years, with an objective of 20 noise barriers per year.
Thanks to the now available standards EN1793-5:2016 and EN1793-6:2012, objective test methods
allow fair comparison of barriers from different manufacturers as well as of different materials and / or shapes. The long term evolution of those in-situ performances is now also possible to be monitored.
Many test results have now to follow: those results could be merged in the database that has been started within the QUIESST research (www.quiesst.eu), the dream being that other countries join the team and share their measurement results into a single European, or even Worldwide database of the intrinsic acoustic performance of noise barriers.
ACKNOWLEDGEMENTS This new survey is done for the Agentschap Wegen en Verkeer (Roads and Traffic Agency) of
Flanders: it will be done in common with A-Tech / Acoustic Technologies, and the Acoustic Laboratory of the University of Leuven.
REFERENCES 1. EN 1793-1:1997 Road traffic noise reducing devices Test method for determining the acoustic
performance Part 1: Intrinsic characteristics of sound absorption, CEN, 1997. 2. EN 1793-2:1997 Road traffic noise reducing devices Test method for determining the acoustic
performance Part 2: Intrinsic characteristics of airborne sound insulation", CEN, 1997. 3. EN 1793-2:2012 Road traffic noise reducing devices Test method for determining the acoustic
performance Part 2: Intrinsic characteristics of airborne sound insulation under diffuse sound field conditions, CEN, 2012.
4. EN 1793-6:2012 Road traffic noise reducing devices Test method for determining the acoustic performance Part 6: Intrinsic characteristics In situ values of airborne sound insulation under direct sound field conditions, CEN, 2012.
5. EN 1793-1:2012 Road traffic noise reducing devices Test method for determining the acoustic performance Part 1: Intrinsic characteristics of sound absorption, CEN, 2012.
6. EN 1793-5:2016 Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 5: Intrinsic characteristics - In situ values of sound reflection under direct sound field conditions, CEN, 2016.
7. EN 1793-1:???? Road traffic noise reducing devices Test method for determining the acoustic performance Part 1: Intrinsic characteristics of sound absorption under diffuse sound field conditions, CEN, revision currently under drafting.
8. EN 1793-3:1997 Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 3: Normalized traffic noise spectrum, CEN, 1997.