Noise Walls Some Noise Facts - Virginia Department Of Transportation
Noise wallsSome Noise FactsWhat is noise?Noise is unwanted sound. Noise is perceived differentlyby every individual. A noise that is irritating one personmay be tolerant to another.Sound is transmitted by pressure variations in air from itssource to the surroundings. Most sounds or noises weencountered in our daily life are from sources which canbe characterized as point or line sources.A point source occurs when a sound source isstationary. For point sources, sound is radiated equallyin all directions like a pulsing sphere, as illustrated inFigure 1. The noise level for a point source decreasesby 6 dB per doubling of distance from the source.Figure 2: Line Sourceloud to the average listener. Therefore, a source willsound twice as loud if the noise is increased from 65decibels to 75 decibels and four times as loud from 65decibels to 85 decibels.Doubling the sound source, such as doubling thenumber of traffic on the highway causes the noise levelto increases by 3 decibels. A 3 decibel change is barelynoticeable to most people. Since humans do not havethe same sensitivity to all frequencies, the A-weightedscale was developed, and is used for highway trafficnoise evaluation.The chart on the next page indicates common indoorand outdoor noise levels.Figure 1: Point SourceA line source occurs when many sources are moving ina line, the sound radiates like a pulsing cylinder from thesource, as shown in Figure 2. For a line source, thenoise level decreases by 3 dB per doubling of distancefrom it. Traffic noise is generated this way. A stream ofcars in the roadway produces noise as a line source.Noise is measured in decibels (dB) on a logarithmicscale. This scale does not work the same way as mostother familiar scales. An increase in 10 decibels willcause the noise to be perceived as sounding twice as1
Noise wallsSome Noise FactsFigure 3: Sound levels for common equipment and activities2
Noise wallsSome Noise FactsWhen adding decibels and a calculator is not available,the table below is accurate to 1 decibel. It should beunderstood, however, that in practical terms noise levelsare rarely known to this accuracy. When computerprograms produce noise level results in tenths ofdecibels, it is suggested that they be rounded off to thenearest whole decibel.When there are several noise levels to add such as theexample below, the noise levels should be added two ata time, starting with the lower-valued levels. Continuethe addition procedure of two at a time until only onevalue remains. This is illustrated in the example below.3
Noise wallsSome Noise FactsWhat Causes highway traffic noise?The principle noise sources of highway vehicles are theengine, the exhaust system and the tires. Exhaust noiseis usually controlled by mufflers, assuming they are usedand function properly. Engine noise can only becontrolled by vehicle manufacturers and propermaintenance, factors that typically beyond the control ofVDOT and FHWA. Tire noise is generated by theinteraction between each vehicle’s tires with the roadwaysurface. At speeds less than 30 miles per hour, engineand exhaust noise are usually louder than tire noise. Atspeeds greater than 30 miles per hour, the reverse istrue, that is tire noise becomes the dominant noisesource. Thus, highways are typically dominated by tirenoise while local streets are typically dominated byengine and exhaust noise.The overall noise level generated by vehicles on ahighway depends on the number of factors which includethe quantity of vehicles, the speed of the vehicles, andthe types of vehicles. Figures 4, 5 and 6 on the pagesthat follow show generally how these factors influencenoise levels.Noise BarriersWhen trying to mitigate a noise problem, we look forpractical solutions in terms of treating the source of thenoise, and the path between the noise source and thereceiver. This concept is illustrated in Figure 7. Since itis often impractical to reduce the noise at the source orat the receiver, the only practical option left would be toreduce the noise along the path between the source andthe receiver, thus the use of noise barriers.The use of Noise barriers is the most common trafficnoise mitigation. Barriers can take different forms, aslong as they break the line-of-sight (noise path) betweenthe vehicles on the highway and affected residentialcommunities. Barriers can be in the form of walls, berm,or combination.Figure 7: Source-path-receiver conceptBarriers are a popular solution because they have beenproven effective at reducing noise impacts fortransportation improvement projects and are typicallyavailable to the Department to provide noise mitigationfor Type I projects.Reflective/Absorptive wallNoise walls reduce noise by shielding receivers from thenoise source. Sound that reaches a noise barrier iseither reflected or absorbed by the noise barrier. Insituations where noise-sensitive land uses exist on onlyone side of a roadway, walls are designed to adequatelyshield those receivers. Reflective barriers are oftenused in such situations, as they have the capability toreflect the sound to the opposite side of the roadway.This situation can become more complex where noisesensitive land uses exist on both sides of the roadway.Attempts to provide barriers for both communities cancreate what is referred to as a “parallel barrier” condition.In those situations, reflective noise from a barrier on oneside of the roadway can increase noise levels reachingthe receivers on the opposite side of the roadway by asmuch as 3 dBA. To combat this situation, noise barrierscan be designed with greater sound-absorbingcharacteristics to offset the affects of reflective noise.Sound-absorbing noise barriers allow sound waves toenter the wall. As the sound travels through the soundabsorbing material the sound waves change directionand follow a longer path. cont.to page 8 4
Noise wallsSome Noise FactsFigure 4: Effect of traffic volume on noise levels5
Noise wallsSome Noise FactsFigure 5: Effect of truck volume on noise levels6
Noise wallsSome Noise FactsFigure 6: Effect of traffic speed on noise levels7
Noise wallsSome Noise Facts cont from page 4 Every change in direction decreasesthe sound waves’ energy, limiting the amount of soundthat reenters the environment as reflective sound.Figure 8 provides examples of situations that canincrease reflective noise and identifies how absorptivebarriers can reduce this influence. Absorptive noisebarriers can effectively offset the affects of reflectivenoise, often reducing reflective noise by 2 to 3 dBA atreceivers on the opposite side of the road as a noisebarrier.Figure 9: Shadow zoneCut/FillRoadway design features can also dictate noise barrierplacement. In roadway cut conditions, where theroadway is located below the natural grade, barriers aretypically most effective when placed at the top of the cutslope, to take advantage of natural terrain, reducebarrier costs and increase barrier base elevations.Figure 8: Reflective/Absorptive wallsHorizontal placement of noise wallsThe horizontal placement of a noise barrier in relation tothe source and the receiver can also impact the overalleffectiveness of that barrier. In general, noise barriersare most effective when placed as close to the noisesource or as close to the noise receiver as possible.The relationship of roadway, barrier, and receiverelevations can also influence the effectiveness of noisebarriers, and in certain situations can render a noisebarrier ineffective. If noise-sensitive land uses adjacentto a roadway corridor are significantly above theroadway grade it may be impossible to effectively blockthe line-of sight (noise path) with a noise barrier.Receivers that are effectively shielded by a noise barrierare considered to be in the “shadow zone” of thebarrier. Figure 9 illustrates this.In roadway fill conditions, where the highway is abovethe natural grade, noise barriers are typically mosteffective when placed on the edge of the roadwayshoulder or on top of the fill slope. Figure 10demonstrates how barrier placement can affect barriereffectiveness.Figure 10: Barrier placement8
Noise wallsSome Noise FactsWall Length/Flanking NoiseFlanking noise refers to the noise component thatdiffracts around the ends of a noise barrier, as comparedto over the barrier, as illustrated in Figure 11.Wall HeightEffective noise barriers are both tall enough and longenough to significantly eliminate the line-of-sight fromthe roadway to the noise-sensitive sites. Generally,noticeable noise reductions (in the range of 5 dBA) arenot achieved until the line-of-sight between the source tothe receiver is effectively broken. Once that point isreached, additional 1-dBA reductions can typically beachieved with each 2-foot step of additional barrierheight, illustrated in Figure 13. While the maximumtheoretical limit of noise reduction in real-worldapplication is 10 to 15 dBA.Figure 11: Flanking NoiseFlanking noise must also be considered so as toeffectively mitigate for highway-noise with noise barriers.When considering the design of noise barriers to avoidflanking noise, barriers should extend well beyond thenoise-sensitive land uses they are designed to protect.FHWA recommends barriers to extend beyond impactedreceivers by as much as four-times the distance from theroad to the receiver to offset the effects of flanking noise.Often physical features or logical termini exist, such ashill sides or bridge structures that dictate the horizontallimits and termini of noise barrier designs. This isillustrated in Figure 12.Figure 12: Barrier design, minimizing flanking noiseFigure 13: Line of site blockage9
Noise wallsSome Noise FactsBerm vs. WallEarth berms are often used as a practical alternative tonoise walls. An earth berm is generally created fromearthen-material that has been moved to a specificlocation during the highway construction process. Earthberms are often a preferred alternative to freestandingnoise walls since they can provide comparable (orgreater) noise reductions, require less maintenance,provide a natural appearance, and can typically beconstructed at much lower cost than typical post-andpanel noise wall systems. However, earth berms requireconsiderably more space than noise walls, oftenprecluding them from consideration.Noise walls options available in VirginiaAs a way to ensure high quality noise walls, VDOT onlyuses noise walls that have been approved through anextensive product evaluation process. The pictures onthe next pages show some of the several different typesof noise wall options VDOT has available.Often, typical berm designs include 2:1 slopes on eachside of the berm, with a level top. Assuming thisstandard design cross-section, a berm with a total heightof 12-feet above the roadway surface would requireapproximately 48-feet of horizontal width, as shown inFigure 14. These space requirements can often limit theuse of berms, especially in developed corridors withlimited space between the highway and adjacent noisesensitive land uses. This space requirement becomeseven more of a challenge on projects, where theroadway right-of-way is already established.Figure 14: Berm vs. Wall10
Noise wallsSome Noise FactsRoadway side-SanDiego DryStack11
Noise wallsSome Noise FactsRoadway side-NewEngland DryStack12
Noise wallsSome Noise FactsRoadway side-Fluted (Concrete)13
Noise wallsSome Noise FactsHomeowner’s side-Riverstone (Concrete)14
Noise wallsSome Noise FactsHomeowners side-Fuzzy raked (Concrete)15
Noise wallsSome Noise FactsPlastic used for light weight on structure e.g. Bridges16
Noise wallsSome Noise FactsMetal used for light weight on structure e.g. Bridges17
Noise wallsSome Noise FactsRoadway side Wooden barrier18
noise walls since they can provide comparable (or greater) noise reductions, require less maintenance, provide a natural appearance, and can typically be constructed at much lower cost than typical post-and-panel noise wall systems. However, earth berms require considerably more space than noise walls, often precluding them from consideration.
The following Fact Fluency Card labels are included in this pack: 1. Plus One Facts 2. Plus Two Facts 3. Plus Three Facts 4. Minus One Facts 5. Minus Two Facts 6. Minus Three Facts 7. Facts of Five 8. Doubles Facts (Addition) 9. Doubles Facts (Subtraction) 10. Near Doubles Facts (e.g. 6 7 6 6 1 12 1 13) 11. Facts of Ten: Addition 12.
Retaining walls may be non-proprietary systems such as gravity walls, cantilever walls, counterfort walls or tie-back walls, or may be proprietary systems such as mechanically stabilized earth walls or prefabricated modular walls. The tops of retaining walls shall not be determined by the exact fill slope but shall follow a
doubles-plus-one facts, doubles-plus-two facts, plus-ten facts, plus-nine facts, and then any remaining facts. For multiplication, the suggested sequence is the times-zero principle, times-one principle, times-two and two-times facts, times-five and five-times facts, times-nine and nine-times facts, perfect squares, and then any remaining facts .
Math Bee Practice . 1st Round Mixed Multiplication and Division Facts 2 seconds. Multiplication Facts 6 x 6 _ Multiplication Facts 6 x 6 36. Multiplication Facts 32 8 _ Multiplication Facts 32 8 4. Multiplication Facts 7 x 6 _ Multiplication Facts 7 x 6 42. Multiplication Facts 56 7 _
There are various external wall systems used in the local industry, including precast concrete walls, cast in-situ reinforced concrete walls, brickwalls, curtain walls, cladding walls, concrete block walls, etc. Due to volume constraint, this publication focuses on precast concrete walls, cast in-situ reinforced concrete walls and plastered .
6) Reinforced soil walls are generally less expensive to construct than "conventional" retaining walls. Figure 1.2 shows the comparative costs of reinforced soil retaining walls and conventional reinforced concrete walls. For walls with height less than 25 ft, reinforced soil walls using geosynthetics as
Noise Figure Overview of Noise Measurement Methods 4 White Paper Noise Measurements The noise contribution from circuit elements is usually defined in terms of noise figure, noise factor or noise temperature. These are terms that quantify the amount of noise that a circuit element adds to a signal.
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