Supplemental Guidance on the Application of FHWA’s Traffic Noise Model (TNM) (2014) / Chapter Skim
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74 C H A P T E R 1 1 11.1 Introduction As sound travels from its source, the speed and direction of wind can increase or decrease the amount of sound energy that arrives at the receiver relative to a calm condition. This is primarily due to the refraction of the sound toward the ground in a downwind case or upward in the upwind case, as illustrated in Figure 49.
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75 FHWA's Traffic Noise Model (TNM) : Phase 1.42, 43 These studies provide measured sound levels under various meteorological conditions.
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76 adjustment. Although like Nord2000, the Concawe50 model can compute the effects of wind speed and direction, it was not selected because no equivalent measurement validation studies were identified for it.
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77 Automobiles and Trucks, Hard Ground, with Noise Barrier Receiver Distance (ft) Receiver Height (ft)
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78 Automobiles and Trucks, Soft Ground, without Noise Barrier Receiver Distance (ft) Receiver Height (ft)
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79 Automobiles Only, Hard Ground, without Noise Barrier Receiver Distance (ft) Receiver Height (ft)
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80 -30 -20 -10 0 10 20 10 100 1000 noitidnoC dni W ,ecnereffiD leveL dnuoS -C al m (d B) Distance (feet)
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81 11.4.1.3 Effect of Ground Type on Results The type of ground (either hard or soft) in the model also had a large effect on the results.
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82 11.5 Combined Effects of Wind and Temperature Gradients on Highway Noise Sources The focus of this research was primarily the separate effects of varying wind and temperature conditions on sound levels from highway noise sources. Often, wind and temperature gradients sufficient to affect sound propagation do not occur at the same time.57 However, it is possible that some moderate wind and temperature conditions may occur simultaneously.
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