sound barriers on roads
Post on 01-Oct-2015
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DESCRIPTIONsound and acoustics
ROAD TRAFFIC ISSUES AND REMEDIESREPORTACOUSTICS
ADVANCED BUILDING SERVICES
CONTENTSINTODUCTION3TYPICAL NOISE LEVELS DUE TO FREE-FLOWING ROAD TRAFFIC3SOURCES OF NOISE POLLUTION4TRAFFIC OPERATIONS :4ROADWAY SURFACETYPES :4TIRE TYPES:5ROADWAY GEOMETRICSAND SURROUNDINGTERRAIN:5MICROMETEOROLOGY :6GEOMETRY OF AREA STRUCTURES6EFFECT OF SPEED ON TOTAL NOISE LEVELS6REMEDIES :6NOISE BARRIERS:6MATERIAL7DISTANCE8HEIGHT8CONTROL AT THE SOURCE8ACOUSTICAL SITE PLANNING9DISTANCE :9NOISE COMPATIBLE LAND USES AS BUFFERS9BUILDINGS AS NOISE SHIELDS10ORIENTATION10PLANTING IN BUFFER STRIP11CONCLUSION13
LIST OF FIGURESFigure 1 ROADWAY5Figure 2: SURFACES5Figure 3 : low rolling resistance tyres6Figure 4: ROADWAY GEOMETRICS6Figure 5: GRAPH- EFFECT OF SPEED7Figure 6: NOISE BARRIERS8Figure 7 BRICK NOISE BARRIER Figure 8: WOODEN NOISE BARRIER9Figure 9 RUBBERIZED ASPHALT10Figure 10: EFFECT OF DISTANCE10Figure 11: PARKING AS NOISE SHEILDS11Figure 12: BUILDINGS AS NOISE SHEILDS11Figure 13: STANDARD JUTTING BALCONY12Figure 14: HIGHWAY PLANTERS12Figure 15: CROSS SECTION OF BERM13Figure 16: WALL BARRIERS.13Figure 17 EARTH BERM14
INTODUCTIONRoadway noiseis the collectivesoundenergy emanating frommotor vehicles. It consists chiefly of road surface, tire,engine/transmission, aerodynamic, and braking elements.The level of noise generated by road traffic depends upon such factors as the number of vehicles passing per hour, the type of traffic, the preponderance of heavy vehicles, average speed, gradient and smoothness of traffic flow. The smoothness of traffic flow also affects variability of the noise and is governed by such things as roundabouts and traffic lights, and the volume of traffic and pedestrian movement with their effects on stopping, starting and overtaking. The level of traffic noise fluctuates continuously and the way it does has a considerable effect on the nuisance caused. For assessing traffic noise, noise is measured in dB(A).TYPICAL NOISE LEVELS DUE TO FREE-FLOWING ROAD TRAFFICslno. Type of Tr~lc L.1030 m from Edge No. of Road, dB(A) i) 5020 vehicles per 18 hoar day 65 (10 percentheavyvehicles),50kmph ii) 10000 vehicles per 18 hour day 70 (20pereentheavyvehicles),60kmphiii) 10000 vehicles per 18 hour day 75 (40percentheavyvehicles),80kmphiv) 20000 vehicles per 18 hour day 77 (40percentheavyvehicles),80kmphNOTE The values are applicable to free flowing traffic without honking.Source :nbc
Figure 1 ROADWAYSOURCES OF NOISE POLLUTIONThe intensity of roadway noise is governed by the following variables: traffic operations (speed, truck mix, age of vehicle fleet), roadway surface type, tire types, roadway geometrics, terrain, micrometeorology and the geometry of area structures. At lower speeds and/or when accelerating / braking, engine & power-train noise can dominate.TRAFFIC OPERATIONS :Noise is affected significantly by vehicle speeds, since sound energy roughly doubles for each increment of ten miles an hour in vehicle velocity.ROADWAY SURFACETYPES :Roadway surface types contribute to different noise levels. Of the common types of surfaces in modern cities, there is a 4 Db difference between the loudest and the softest: chip seal type and grooved roads being the loudest , andconcrete surfaces without spacers being the quietest, andasphalticsurfaces being about average.
Figure 2: SURFACES
TIRE TYPES:Tire types can cause 10 dB(A) variations in noise, base : d on a 2001 sample of 100 commercially available tires. As of 2001, there was no correlation between grip and noise. Quieter tires may have slightly lower rolling resistance.
Figure 3: low rolling resistance tyresROADWAY GEOMETRICSAND SURROUNDINGTERRAIN: are interrelated, since the propagation of sound is sensitive to the overall geometry and must considerdiffraction(bending of sound waves around obstacles),reflection,ground waveattenuation, spreading loss andrefraction. A simple discussion indicates that sound will be diminished when the path of sound is blocked by terrain, or will be enhanced if the roadway is elevated so as to broadcast; however, the complexities of variable interaction are so great, that there are many exceptions to this simple argument.
Figure 4: ROADWAY GEOMETRICSMICROMETEOROLOGY :is significant in that sound waves can berefractedbywind gradientsorthermoclines, effectively dismissing the effect of somenoise barriersor terrain intervention.GEOMETRY OF AREA STRUCTURES:is an important input, since the presence of buildings or walls can block sound under certain circumstances, but reflective properties can augment sound energy at other locations.EFFECT OF SPEED ON TOTAL NOISE LEVELS
Figure 5: GRAPH- EFFECT OF SPEED
REMEDIES :NOISE BARRIERS: Reduce the sound which enters a community from a busy highway by either absorbing the sound, transmitting it, reflecting it back across the highway, or forcing it to take a longer path over and around the barrier. A noise barrier must be tall enough and long enough to block the view of a highway from the area that is to be protected, the "receiver." Noise barriers provide very little benefit for homes on a hillside overlooking a highway or for buildings which rise above the barrier. A noise barrier can achieve a 5 dB noise level reduction, when it is tall enough to break the line-of-sight from the highway to the home or receiver. After it breaks the line-of-sight, it can achieve approximately 1.5dB of additional noise level reduction for each meter of barrier height.
Figure 6: NOISE BARRIERS
MATERIALThe wall must be solid with no penetrations in order to be effective. Any penetration, opening or gate can degrade the effectiveness of the barrier. Concrete walls are preferred, but other types of walls can also be effective. A barrier does not have to be a wall, it could also be a large earthen berm. A common misconception is that typical landscaping or vegetation can act as an effective barrier for traffic noise. Unless the vegetation is 100' thick and very dense, it will provide very little if any noise reduction.
Figure 7BRICK NOISE BARRIERFigure 8: WOODEN NOISE BARRIERDISTANCETypically, a barrier is more effective the closer it is to the source or to the receiver. Noise barriers are generally only effective for homes within 300 ft. of the roadway.HEIGHTThe noise from automobile traffic is primarily from the tires on the pavement. This noise source is at 0' above the ground. Noise from large trucks is typically engine and exhaust noise and is approximately 8' above the ground. In order to be effective, a barrier wall must at least block the line of sight from the noise source to the receiver. Although a 6' high wall can help to reduce auto traffic noise, it will do little if anything for heavy truck traffic. On the same note, if a home is on a hill or elevated above the roadway, a 6' high wall may not be adequate in blocking the line of sight, even for auto traffic. CONTROL AT THE SOURCEAs a resident you may not be able to control traffic noise at the source, but there are ways of limiting problems with traffic noise in the design of future roadways. Traffic noise increases with higher speed limits and with shorter distances from the road to the home. Recessing the roadway can reduce the noise impact. Use of quiet pavement such as rubberized asphalt can also reduce the impact by 4-5 decibels . Unlike conventional asphalt, rubberized asphalt maintains its noise reduction properties over several years.
Changes in Sound Level, dBChanges in Apparent Loudness
5 - 6Clearly noticeable
10Twice (or half) as loud
Figure 9RUBBERIZED ASPHALTACOUSTICAL SITE PLANNINGThe arrangement of buildings on a site can be used to minimize noise impacts. If incompatible land uses already exist, or if a noise sensitive activity is planned, acoustical site planning often provides a successful technique for noise impact reduction.1. increasing the distance between the noise source and the receiver;2. placing nonresidential land uses such as parking lots, maintenance facilities, and utility areas between the source and the receiver;3. locating barrier-type buildings parallel to the noise source or the highway; and4. orienting the residences away from the noise.DISTANCE :Noise can be effectively reduced by increasing the distance between a residential building and a highway. Distance itself reduces sound: doubling the distance from a noise source can reduce its intensity.
Figure 10: EFFECT OF DISTANCENOISE COMPATIBLE LAND USES AS BUFFERSNoise protection can be achieved by locating noise-compatible land uses between the highway and residential units. Whenever possible, compatible uses should be nearest the noise source.In addition to protecting the residential development from the noise and dirt of highway traffic, the parking garage provides needed facilities for the residents
Figure 11: PARKING AS NOISE SHEILDSBUILDINGS AS NOISE SHIELDSAdditional noise protection can be achieved by arranging the site plan to use buildings as noise barriers. A long building, or a row of buildings parallel to a highway can shield other more distant structures or open areas from noise. One study shows that a two-story building can reduce noise levels on the side of the building away from the noise source by about 13dBA.
Figure 12: BUILDINGS AS NOISE SHEILDS
ORIENTATIONThe orientation of buildings or activities on a site affects the impact of noise, and the building or activity area may be oriented in such a way as to reduce this impact.Noise impacts can be severe for rooms facing the roadway since they are closest to