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From page 12... ... 12 As part of this project, the research team conducted measurements along I-17 in Phoenix, Arizona, to quantify the effects of meteorology on highway noise. This chapter discusses how the measurements were made, the results of the measurements, and a comparison of the measurements to various highway noise models. Read the entire page →
From page 13... ... Measurement and Modeling of Roadway Noise 13 barrier on the home side of the frontage road, but away from the part where the microphones were located. This would diminish sound from the frontage road but would not affect traffic noise coming over the barrier from the highway. Read the entire page →
From page 14... ... 14 How Weather Affects the Noise You Hear from Highways Source: Wyle for NCHRP Project 25-52. a b Figure 9. Read the entire page →
From page 15... ... Measurement and Modeling of Roadway Noise 15 Source: RSG for NCHRP Project 25-52. Figure 11. Read the entire page →
From page 16... ... 16 How Weather Affects the Noise You Hear from Highways Source: Wyle for NCHRP Project 25-52. Figure 13. Read the entire page →
From page 17... ... Measurement and Modeling of Roadway Noise 17 the measurement team captured several aerial photos of the measurement area via a hot-air balloon. The photo in Figure 15 is looking north toward the upper air measurement station and the No-Barrier measurement positions. Read the entire page →
From page 18... ... 18 How Weather Affects the Noise You Hear from Highways Upper Air Measurement Station The "atmospheric boundary layer" is the part of the atmosphere adjacent to the ground and extending upward to a point where the atmosphere is no longer significantly influenced by the ground. The lowest part of the boundary layer is called the surface layer, which has a height of typically 100 meters. Read the entire page →
From page 19... ... Measurement and Modeling of Roadway Noise 19 The Leosphere WindCube v2 Lidar system measures the Doppler shift of five infrared beams as reflected off aerosols such as dust, pollen, precipitation, and pollutants. From these beam returns, the instrument computes various wind parameters, by height, every second. Read the entire page →
From page 20... ... 20 How Weather Affects the Noise You Hear from Highways sensor. The RNRG Symphonie system recorded in 10-minute intervals and was in operation from February 24 through March 7, 2016. Read the entire page →
From page 21... ... Measurement and Modeling of Roadway Noise 21 Source: Wyle for NCHRP Project 25-52. Symphonie Temperature Pressure Humidity Sensors Ultrasonic U-V-W Anemometer Figure 21. Read the entire page →
From page 22... ... 22 How Weather Affects the Noise You Hear from Highways Figure 23 shows the calculated sound power level of the highway. This is the sum of the sound emissions from all vehicles and is a function of vehicle speed, vehicle mix, and traffic volume. Read the entire page →
From page 23... ... Measurement and Modeling of Roadway Noise 23 levels between 50 and 54 dBA and the PM peak hours have sound levels of 32 to 36 dB -- an approximate 18 dB difference. This change in sound level cannot be explained by differences in traffic volume, mix, or speed as the highway sound power is roughly the same during the AM and PM peak hour. Read the entire page →
From page 24... ... 24 How Weather Affects the Noise You Hear from Highways variations in traffic volume and speed. Therefore, the sound level difference varies primarily due to meteorological effects. Read the entire page →
From page 25... ... Measurement and Modeling of Roadway Noise 25 Barrier Location The sound levels measured at the Barrier location behave differently than at the No-Barrier location. As shown in Figure 27, the traffic volume at the Barrier location showed a similar pattern to the No-Barrier location, with a distinctive diurnal pattern. Read the entire page →
From page 26... ... 26 How Weather Affects the Noise You Hear from Highways change during the day. As shown in Figure 29, the measured sound levels follow along the same general pattern as the highway sound power from Figure 28. Read the entire page →
From page 27... ... Measurement and Modeling of Roadway Noise 27 In this case, the research team concluded that sound levels at positions well inside the acoustic shadow region behind a tall barrier are less affected by meteorological effects than sound levels at unscreened positions are. Modeling Results Harmonoise Modeling TNM versions 2.5 and 3.0 assume an acoustically neutral atmosphere and neglect meteorological effects other than atmospheric absorption. Read the entire page →
From page 28... ... 28 How Weather Affects the Noise You Hear from Highways the Harmonoise model is that it considers meteorological effects, including atmospheric refraction, the scattering by atmospheric turbulence, and related effects on ground attenuation. Analytical reflection and diffraction formulas are used for the calculation of the excess attenuation. Read the entire page →
From page 29... ... Measurement and Modeling of Roadway Noise 29 The values in Table 2 clearly illustrate the effects of wind and atmospheric stability on sound levels. • Sound levels are generally raised by downwind conditions and lowered by upwind conditions. Read the entire page →
From page 30... ... 30 How Weather Affects the Noise You Hear from Highways Vector Wind Class Stability Class Distance from Road (M) 15 30 60 120 240 480 960 V1 Strong Downwind S1 1 1 2 5 7 10 14 S2 1 1 2 5 7 11 12 S3 1 1 3 5 8 8 14 S4 1 1 3 5 6 7 10 S5 1 1 3 5 5 4 12 V2 Weak Downwind S1 0 -1 -4 -14 -19 -16 -9 S2 0 0 -2 -3 -2 1 2 S3 0 0 0 1 4 8 12 S4 1 1 2 4 8 7 13 S5 1 1 3 5 5 4 13 V3 Zero (Zero Wind Speed) Read the entire page →
From page 31... ... Measurement and Modeling of Roadway Noise 31 upward refraction. It will be shown later that the measurements yield a considerably smaller sound level difference between downward refraction and upward refraction (at most about 14 dB) Read the entire page →
From page 32... ... 32 How Weather Affects the Noise You Hear from Highways Vector Wind Class Stability Class Distance from Road (m) 70 100 130 160 V1 Strong Downwind S1 1 2 3 3 S2 1 2 3 4 S3 1 2 3 4 S4 1 3 4 5 S5 2 4 5 6 V2 Weak Downwind S1 -1 -2 -2 -3 S2 0 1 1 1 S3 0 2 2 3 S4 1 2 3 4 S5 1 3 5 6 V3 Zero (Zero Wind Speed) Read the entire page →
From page 33... ... Measurement and Modeling of Roadway Noise 33 Comparison of Modeled to Monitored Sound Levels Comparison to "Neutral" Conditions From the standpoint of outdoor sound propagation, acoustically neutral would be a situation where the vertical sound speed gradient is zero. That is, sound speed does not change with height. Read the entire page →
From page 34... ... 34 How Weather Affects the Noise You Hear from Highways The effect that the temperature profile has on sound levels relative to the neutral condition is shown in Figure 37. In this figure, a temperature inversion is where the temperature increases with height and a lapse condition is where temperature decreases with height. Read the entire page →
From page 35... ... Measurement and Modeling of Roadway Noise 35 conditions had a greater effect than strong upwind conditions. This is because intense winds can create turbulence in the air and this causes sound to scatter into the shadow zone. Read the entire page →
From page 36... ... 36 How Weather Affects the Noise You Hear from Highways Source: Bowlby & Associates for NCHRP Project 25-52. Figure 39. Read the entire page →
From page 37... ... Measurement and Modeling of Roadway Noise 37 most pertinent modeling results from Table 2. The results are shown in Table 5. Read the entire page →
From page 38... ... 38 How Weather Affects the Noise You Hear from Highways Vector Wind Class Stability Class Distance from Road (m) 15 30 60 120 240 480 960 V1 Strong Downwind S1 1 2 2 9 S2 S3 S4 S5 V2 Weak Downwind S1 0 -1 -4 -12 -16 -14 -8 S2 S3 S4 1 -1 -1 -2 3 16 S5 1 0 0 0 -2 -2 9 V3 Zero Vector Wind (No Crosswind) Read the entire page →
From page 39... ... Measurement and Modeling of Roadway Noise 39 Barrier Location The Barrier location was monitored for approximately 40 hours. During this period, most of the time there were clear conditions, other than a short cloudy period with weak upwind winds. Read the entire page →
From page 40... ... 40 How Weather Affects the Noise You Hear from Highways Vector Wind Class Stability Class Distance from Barrier (m) 15 60 90 120 150 V1 Strong Downwind S1 – – – – – S2 – – – – S3 – – – – – S4 – – – – – S5 – – – – – V2 Weak Downwind S1 – -1 -1 -2 -2 S2 – – – – – S3 – – – – – S4 – – – – – S5 – 2 3 4 7 V3 Zero Vector Wind (No Crosswind) Read the entire page →
From page 41... ... Measurement and Modeling of Roadway Noise 41 specified in NCHRP Report 791 (the maximum discrepancy resulting from this comparison is 7 meters at the 480-meter location; heights are identical) Read the entire page →

From page 12...

... 12 As part of this project, the research team conducted measurements along I-17 in Phoenix, Arizona, to quantify the effects of meteorology on highway noise. This chapter discusses how the measurements were made, the results of the measurements, and a comparison of the measurements to various highway noise models.