Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis (2017) / Chapter Skim
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17 Findings and Applications The measured data was reduced and analyzed during post-processing. (Table 2-1 provides nomenclature and summary information on the 20 test sites, which are used as designations in this chapter.)
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18 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis SIP Measurement Results Under the SIP procedure, the results are reported as a SIP Index (SIPI)
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Findings and Applications 19 Site Designated (Average) Speed, mph Level from Regression, dBA SIP Reference Level, dBA SIPI Level at 55mph, dBA Level at 65mph, dBA Level at 35mph, dBA Lakeville 51.4 90.3 87.8 2.5 90.7 505 SB1 57.3 86.0 89.6 -3.6 85.5 505 SB2 56.8 88.8 89.2 -0.4 88.1 505 NB1 58.4 90.5 89.6 0.9 88.6 NC1 65.9 93.2 91.6 1.6 92.9 NC2 66.8 94.0 91.8 2.2 93.5 NC3 63.4 91.9 91.0 0.9 91.9 NC4 67.7 90.9 92.0 -1.1 90.0 NC5 62.6 91.7 90.8 0.9 92.1 NC6 58.4 91.4 89.7 1.7 92.6 NC7 64.0 91.3 91.1 0.2 91.6 NC8 29.0 84.4 78.7 5.7 85.8 NC9 61.6 90.7 90.5 0.2 91.1 NC10 67.8 91.8 92.0 -0.2 90.9 NC11 63.4 91.9 91.0 0.9 92.3 NC12 63.8 90.2 91.1 -0.9 91.0 NC13 61.3 89.7 90.4 -0.7 90.0 NC14 38.0 82.5 83.0 -0.5 82.0 NC15 60.7 89.9 90.2 -0.3 90.4 NC16 53.2 88.9 88.2 0.7 92.5 Table 3-1.
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20 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis the uphill sites in North Carolina, the downhill sites in North Carolina, the flat sites in North Carolina, and the slower speed sites in North Carolina. Comparison With the REMELs Database One of the objectives of this research was to begin to populate a new heavy truck noise source database for potential use in future traffic noise models.
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Findings and Applications 21 the REMELs average, with differences of about 1.5 dB above 50 mph. At the slower speeds, the REMELs curve and the Project 25-45 trend line diverge considerably, with differences greater than 7 dB below 25 mph.
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22 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis has been reduced. In Figure 3-6, regression for the five higher speed, uphill sites is virtually identical to the REMELs curve for heavy truck cruise noise.
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Findings and Applications 23 Test Site Testing Date, Time Heavy-Duty Vehicles Medium-Duty Vehicles Light-Duty Vehicles Buses Lakeville 12/17/2013, 12:20-15:30 44 9 0 0 505 SB1 12/20/2013, 12:20-14:10 57 0 2 0 505 SB2 12/21/2013, 9:30-13:20 49 8 2 1 505 NB1 12/20/2013, 15:50-17:1012/30/2013, 13:10-15:00 24 49 2 1 0 9 0 0 NC1 9/18/2014, 14:00-16:00 69 0 9 0 NC2 9/19/2014, 10:00-12:30 61 1 0 0 NC3 9/19/2014, 15:30-17:00 66 0 7 0 NC4 9/22/2014, 10:30-12:00 73 4 0 0 NC5 9/22/2014, 14:30-16:00 76 0 0 0 NC6 9/23/2014, 10:00-12:00 71 5 13 3 NC7 9/23/2014, 14:00-16:00 72 3 9 1 NC8 9/24/2014, 10:00-13:00 58 8 12 0 NC9 9/24/2014, 14:30-15:009/25/2014, 14:30-16:00 80 0 13 0 NC10 9/26/2014, 10:00-11:30 66 5 7 0 NC11 9/26/2014, 13:00-15:00 67 4 8 0 NC12 9/29/2014, 10:00-12:00 65 4 10 0 NC13 9/29/2014, 13:30-14:309/30/2014, 10:00-11:00 66 1 0 0 NC14 9/30/2014, 12:30-17:30 46 15 0 4 NC15 10/1/2014, 11:00-13:00 62 4 0 0 NC16 10/1/2014, 14:00-17:0010/2/2014, 9:30-12:00 68 9 0 2 Table 3-2. Total vehicle counts per test site used for the noise source mapping analyses.
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24 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Figure 3-7. Sound level contours for a typical truck at the Lakeville site–overall A-weighted and one-third octave bands from 315 to 630 Hz.
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Findings and Applications 25 Figure 3-8. Sound level contours for a typical truck at the Lakeville site–one-third octave bands from 800 to 2,000 Hz.
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26 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis at lower frequencies it is difficult to localize the source given the size of the acoustic wavelengths involved. Figure 3-10 shows the 315 Hz contours for the loudspeaker along with the contours for the truck.
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Figure 3-10. Comparison of truck and loudspeaker contours for the 315 Hz one-third octave band.
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28 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Lakeville test site, only 9 (20.5% of the total) were identified as having some exhaust system noise; however, only in Run 55 were the levels high enough to be within 10 dB of the maximum A-weighted level.
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Findings and Applications 29 Lakeville Site. Figure 3-14 shows the vertical distributions for the acceptable heavy truck runs measured at the Lakeville site.
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30 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis 505 SB1 Site. Figure 3-15 shows the vertical distributions measured at 505 SB1.
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Findings and Applications 31 Figure 3-15. Overall A-weighted levels for all heavy-duty vehicles at Site 505 SB1 normalized to 93.1 dBA.
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32 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis for trucks with trailers. In general, the contours corresponding to the typical truck profiles of Figure 3-16 were similar to the contours from typical heavy-duty vehicles at the Lakeville site, (shown in Figures 3-7 through 3-9)
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Findings and Applications 33 North Carolina Sites The profiles of the North Carolina sites are categorized as follows: (1) uphill, (2)
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34 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis ranging from 3 to 9 dB lower than the maximum at ground level (5.8% of the total)
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Findings and Applications 35 Figure 3-20. Overall A-weighted levels for all heavy-duty vehicles measured at NC6 (uphill)
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36 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis additional trucks showed excessive low frequency content. Of all the uphill test sites, Site NC13 (Figure 3-23)
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Findings and Applications 37 Figure 3-23. Overall A-weighted levels for all heavy-duty vehicles measured at Site NC13 (uphill)
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38 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Figure 3-25. Overall A-weighted levels for all heavy-duty vehicles measured at Site NC4 (downhill)
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Findings and Applications 39 Figure 3-27. Overall A-weighted levels for all heavy-duty vehicles measured at Site NC10 (downhill)
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40 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Of these seven trucks, six had noise radiating from the exhaust outlets. The seventh truck (Run 21)
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Findings and Applications 41 maximum at heights at or below 9ft (2.7m)
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42 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Figure 3-31. Overall A-weighted levels for all heavy-duty vehicles measured at Site NC8 (slower speed)
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Findings and Applications 43 in North Carolina. More engine and exhaust noise would be expected for heavy trucks when accelerating.
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44 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis passing the measurement location, with a few accelerating from stop at the traffic light. For most of the trucks measured at this site, the noise levels reduced by 10 dBA from the ground-level maximum at heights at or below 10.5ft (3.2m)
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Findings and Applications 45 with uphill sites of the same/similar pavement, it was determined that the difference in the average maximum profile levels was less than 1 dBA in each case, and the average speeds measured at the downhill sites were faster than the corresponding uphill sites, which may be expected due to the grade. Similar to the OBSI results, the sites with the highest average maximum profile levels were Sites NC1 and NC2, which were the uphill and downhill sites, respectively, with transverse tine PCC.
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46 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis The lowest average maximum profile levels shown in Table 3-3 were measured at Sites NC14 (located along SR 211, downstream from a stoplight in a 45 mph zone) and NC8 (located at the southbound I-77 entrance ramp)
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Findings and Applications 47 Figure 3-35. Average overall A-weighted levels for all heavy-duty vehicles.
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48 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis the levels for all the profiles dropped quickly. At heights of 10ft (3m)
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Findings and Applications 49 For the trucks with noise levels at 12ft that were within 10 dB of the ground-level maximum, not all were due to exhaust noise. Of the 63 cases in Figure 3-37, only 56 (4.3%)
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50 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis noise in limited cases. In the Project 08-56 research, trailer tires were often identified as noise sources (similar to the current research)
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Findings and Applications 51 spot at lower frequencies is enlarged, getting larger with decreasing frequency. This occurs even if the actual source is small and acoustically compact, as illustrated by the contours for the 400 and 1,000 Hz frequency bands shown in Figure 3-40, where the actual noise source is the 4in-by4in (0.1m-by-0.1m)
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Figure 3-40. Contours for a small loudspeaker noise source on the pavement, as measured by the beamforming array for 400 and 1,000 Hz.
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Findings and Applications 53 the overall being approximately 4.8 dBA. The calculated differences between the spot levels and the maximum profile level at each frequency band were used as adjustment factors at each corresponding frequency band profile shown in Figure 3-41.
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54 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis each case, the calculated adjustment factors were similar, with variation at any given frequency of slightly more than 1 dBA. Figure 3-44 shows the correction factors calculated for the 3.3ft (1m)
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Findings and Applications 55 Figure 3-44. One-third octave band frequency corrections from ground level & 3.3ft (1m)
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56 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Carolina sites and a mix of trucks with relatively normal profiles; that is, where either the overall A-weighted profile did not extend above 8ft (2.4m) or where there was some profile content above 8ft (2.4m)
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Findings and Applications 57 frequencies ranging from 2,500 to 4,000 Hz, the average profiles were adjusted based on ambient levels determined at each site and for each frequency band. As shown in the high frequency contours of Run 38 at Lakeville (see Figure 3-9)
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58 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Source Height Distribution Analysis The first objective of this research was to develop heavy truck vertical source height distributions that could be used in traffic noise modeling. For this purpose, the average profiles from Figure 3-48 were developed as complete vertical distributions of source heights for each one-third octave band.
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Findings and Applications 59 Figure 3-49. One-third octave band and overall level profiles for a loudspeaker at ground level.
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60 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis for the 2,000 Hz band. Further, the profile for the loudspeaker measured 3.3ft (1m)
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Findings and Applications 61 Figure 3-52. Comparison of 630 Hz profiles for ground level and 3.3ft (1m)
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62 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis in TNM for heavy trucks consists of the same two heights (0ft and 12ft [0m and 3.7m]
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Findings and Applications 63 Figure 3-55. Initial application of a ground level and 5ft (1.5m)
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64 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis source at 1.6ft (0.5m) was required to get the fit shown in Figure 3-58.
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Findings and Applications 65 REMELs and TNM Source Height Distributions In the REMELs report,21 the issue of source height splits between ground level and 12ft (3.7m) for heavy trucks was addressed using the research performed at Florida Atlantic University (FLAU)
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66 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis where L is the sub-source height ratio at low frequencies, M is an empirical constant such that 1-M is the sub-source height ratio at high frequency, and N, P, and Q control the transition between the low and high frequencies For heavy trucks at cruise, it was determined that L = 0.054276, M = 0.973749, N = -36.503587, P = 102.627995, and Q = -132.679357. It was also noted that this value of L put only 5.4% source energy at 12ft (3.7m)
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Findings and Applications 67 Figure 3-60. Heavy truck pass-by spectrum for 55 mph cruise with and without the Frequency Correction Factors from the REMELs Report.
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68 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis For TNM 2.5,29 the values of for L, M, N, P, and Q were all changed again. The value of L was taken to be 0.8500, putting 85% of the energy at 12ft (3.7m)
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Findings and Applications 69 with and without the barrier; however, the contributions of some the frequency bands change significantly. As expected, the relative levels of the bands from 1,000 to 4,000 Hz are reduced significantly.
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70 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Figure 3-64. Levels with and without a 12ft (3.7m)
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Findings and Applications 71 average and the two-point source model ranges from about 1 to 2.5 dB. By adding the third source to the two-point source model at frequencies below 630 Hz, the three-point source model better replicates the NCHRP Project 25-45 average.
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72 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis the TNM distribution; however, the results of this research indicate that, with the current fleet of trucks in service, there are relatively few of these examples. Medium Truck Results The primary focus of this research was on the heavy vehicle noise source heights and, as a result, priority was placed on these measurements over other vehicle types.
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Findings and Applications 73 speed sites. Maximum profile level, average speed, and maximum height information is summarized in Table 3-6 for all medium trucks.
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74 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis instance, jumps from 79.4 dBA at 6.6ft (2m)
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Findings and Applications 75 level reduction of approximately 5 dBA from the medium truck maximum profile level to 6ft (1.8m) in the 4,000 Hz band.
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76 Mapping Heavy Vehicle Noise Source Heights for Highway Noise Analysis Figure 3-70. Corrected average one-third octave band vertical profiles for medium trucks.
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Findings and Applications 77 events, for which these data are available, compared to the cruise and interrupted flow REMELs curves. As discussed above, given the very low number of medium trucks, comparison to the REMELs curve is not as significant as was found in the similar comparison for heavy trucks.
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