DMRB VOLUME 10 SECTION 5 PART 2 - Standards …

1 February 2001 DESIGN MANUAL FOR ROADS AND BRIDGESVOLUME 10 ENVIRONMENTALDESIGN ANDMANAGEMENTSECTION 5 ENVIRONMENTALBARRIERSPART 2HA 66/95 environmental barriers :TECHNICAL REQUIREMENTSSUMMARYThis Advice Note accompanies HA 65/94 ( ) and gives guidance on acoustic performance,forms of construction and physical properties FOR existing title page, content page andGeneral Preface page on the Goods Roads Guideseries of Advice new title this sheet as : A new contents page for VOLUME 10 datedSeptember 1995 is available with HA 75 66/95 environmental barriers :Technical RequirementsDESIGN MANUAL FOR ROADS AND BRIDGESTHE HIGHWAYS AGENCYTHE SCOTTISH EXECUTIVE DEVELOPMENTDEPARTMENTTHE NATIONAL ASSEMBLY FOR WALESCYNULLIAD CENEDLAETHOL CYMRUTHE DEPARTMENT FOR REGIONAL DEVELOPMENT*Summary:This Advice Note accompanies HA 65/94 (DMRB ) and gives guidanceon acoustic performance, forms of construction and physical properties ofmaterials.

2 * A Government Department in Northern IrelandVolume 10 SECTION 5 Part 2 HA 66/95 September 1995 REGISTRATION OF AMENDMENTSA mendPage NoSignature & Date ofAmendPage NoSignature & Date ofNoincorporation ofNoincorporation ofamendmentsamendmentsRegistration of AmendmentsVolume 10 SECTION 5 Part 2 HA 66/95 September 1995 REGISTRATION OF AMENDMENTSA mendPage NoSignature & Date ofAmendPage NoSignature & Date ofNoincorporation ofNoincorporation ofamendmentsamendmentsRegistration of AmendmentsENVIRONMENTAL BARRIERSTECHNICAL REQUIREMENTSS eptember 1995 VOLUME 10 SECTION 5 Part 2 HA 66/95 Contents0/15. EARTH MOUNDS AND RETAINING STRUCTURESE arthmounds and LandscapingEarth Retaining StructuresTechnical Approval6. ACOUSTIC SCREEN DESIGNG eneralWind and aerodynamic LoadingVehicle ImpactSupports and FoundationsDynamic Loads from Snow ClearanceVertical LoadsPropriety Barrier Systems7.

3 MATERIALSM aterials Covered by SHWS pecification of AlternativesStructural PlasticsRecycled MaterialsTransparent MaterialsAirborne Sound InsulationSound Absorbent Materials1. INTRODUCTIONG eneralScopeImplementation2. NOISE FUNDAMENTALSG eneration and PropagationShielding and ReflectionDiffraction and Scattering3. NOISE CALCULATIONSP rediction MethodsPorous SurfacingNoise PropagationScreening by BarriersNoise ReflectionsWide Carriageways4. BARRIER EFFICIENCYB arrier Cross SectionReflection and AbsorptionDispersion and ScatteringSeptember 1995 VOLUME 10 SECTION 5 Part 2 HA 66/958. MAINTENANCED esign LifeVandalism and Fire RiskMaterials and Design DetailsCleaningOther Maintenance TasksAccess9. COST COMPARISONSI ntroductionInstallation Cost IndexMaintenance Cost Index10. SUPPLEMENT - NOISE AND TRAFFICD efinitionMeasurementRoad Traffic NoiseAtmospheric ConditionsTraffic Noise Spectrum11. REFERENCESAPPENDIX AWind Loading Design MethodAPPENDIX BSteel Sections for PostsAPPENDIX CMass Concrete Post FoundationsContents0/2 September 1995 VOLUME 10 SECTION 5 Part 2 HA 66 document provides general guidance on the criteriaused in designing environmental barriers .

4 The OverseeingOrganisations requirements for approval on the grounds of structuralintegrity are contained in BD 2/94: Technical Approval of HighwayStructures - Part 1: General Procedures (DMRB ). The particularfeatures required of contractor designed environmental barriers onindividual schemes are set out in Appendix 3/2 of the procurement of environmental barriers will normallybe carried out under contracts incorporating OverseeingOrganisations Specification for Highway Works (MCHW 1). Productsconforming to equivalent Standards and specifications of other statesof the European Economic Area and tests undertaken in other statesof the European Economic Area will be acceptable in accordancewith the terms of clauses 104 and 105 of MCHW 1. For contractsnot incorporating this form of specification, advice should be soughton suitable clauses of mutual recognition which would have the document should be read in conjunction with HA 65(DMRB ) Design Guide for environmental barriers .

5 It supportsthe overall advice given in the Design Guide with guidance onacoustic performance, forms of construction and physical propertiesof materials and supersedes H14/76: Noise barriers - Standards andMaterials (DMRB ). essentials of noise propagation and attenuation aresummarised and the basis of standard noise calculations areexplained, covering the effect of barriers in particular. The relativeeffectiveness of different forms of barrier are discussed andreferences provided to permit further reading. environmental barriersin the form of thin panel constructions are given particular attentionunder the general heading of acoustic later chapters in this document describe the materialsand construction techniques which can be used in environmentalbarriers. Basic engineering requirements for the design of differentstructural forms are given with reference to the appropriatedocuments.

6 A design method is provided for acoustic screens,together with a review of current information on a range of materialswhich may be used in their construction. Indicators of relative costs,including those of maintenance, are given for various forms ofenvironmental 1995 VOLUME 10 SECTION 5 Part 2 HA 66 FUNDAMENTALSV ehicle and Traffic level of noise received at some distance from thesource is affected by a number of factors relating firstly to the amountof noise generated and secondly to the amount by which it isattenuated as it travels through the air. These effects are brieflysummarised here but covered in more detail in Chapter noise arises in different ways from the engine,transmission, bodywork, suspensions and tyres. The most significantfactors affecting the noise are the engine speed and the speed onthe road. The dominant source of noise from vehicles cruising inhigh gear often arises from the interaction of tyres on the roadsurface, but the engine noise of heavy vehicles can be significant,especially when they are going up noise generated by large numbers of vehicles passinga continuous stream merges together and can be characterised bya representative level of noise at a given distance from the road (forexample 10 metres from the edge of carriageway).

7 The noise leveldepends principally on the total flow of traffic, its average speedand the proportion of heavy vehicles, but may be modified by differentroad the purpose of assessment, the source of noise fromtraffic on a trunk road or motorway is normally taken as a line from the near edge of the carriageway and metres aboveit. Allowance is made for various factors which affect the noisereaching a distant receiver. The factors affecting propagation are:i)Distance - starting from any reference point, the noise levelat another point which is twice as far from the line source will beapproximately 3dB(A) less because of the dispersion of )Soft Ground - The simple reduction with distance assumesthat sound either travels through free space or passes over a hardreflecting surface. If sound passes over a more absorbent form ofsurface such as grassland, it will be attenuated more )Angle of View - The treatment of traffic noise as a linesource assumes that it stretches to infinity in either direction.

8 Whenthe length of road under consideration is comparable with thedistance to the reception point, the overall noise level is reduced inrelation to the angle subtended by the road at that )Screening - Solid objects which interrupt the line of sightbetween source and receiver will block the noise passing directly tothe receiver. Screening may be provided by hills or buildings, byboundary walls, by cutting slopes, or by environmental barriersincluded in the scheme )Wind - Standard calculations of average noise levels(CRTN) allow for a light breeze blowing from the road towards thereception point. In most locations wind direction varies considerablyand it is usually not necessary to take the prevailing wind into accountin assessing average noise Fundamentals2/1 September 1995 VOLUME 10 SECTION 5 Part 2 HA 66/95 Screening and tends to be diffracted around obstacles, but itsintensity is reduced in the shadow.

9 Examples of screenedpropagation are illustrated here. The basis of calculations used inassessing noise impacts and designing environmental barriers isfurther explained in chapter 3. It should be noted that discontinousvisual barriers such as vegetation or anti-dazzle screens have verylittle effect on noise by BuildingsScreening by Cutting or Elevated can be reflected off large flat surfaces such asbuilding facades, retaining walls and acoustic screens. This canincrease the noise level in some areas. The benefits of screeningmay also be reduced by multiple reflections and reverberation if thereare reflecting surfaces on both sides of a road. This case is illustratedon page 4 Fundamentals2/2 September 1995 VOLUME 10 SECTION 5 Part 2 HA 66 CALCULATIONSP rediction approved method for assessing road traffic noise inEngland and Wales is set out in Calculation of Road Traffic Noise1988 (CRTN).

10 This provides charts and formulae which allow thenoise generated by a specified traffic flow to be estimated and alsodefines the criteria to determine entitlement under the NoiseInsulation Regulations. For Scotland, a Memorandum on the NoiseInsulation (Scotland) Regulations 1975 gives the approved methodfor assessing entitlement to noise insulation. This contains similarcalculations to CRTN, except for the correction allowing foralternative forms of road surface. It also provides a nomogram forassessing the most effective height and location for a noise calculations, the road is modelled by a series of segmentswhich can be treated as line sources of noise. A basic noise levelgenerated by the traffic on each segment is calculated from the flow,average speed and proportion of HGVs. Corrections are applied forthe effects of gradients and road surface texture. The noise levelsat which properties are then calculated by summing the contributionsfrom each segment, suitably reduced by the effects of distance, softground and screening and increased by reflections porous road surface reduces both the amount of noisegenerated by tyres and the energy of sound waves as they spreadacross it.