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Measurement of Highway-Related Noise

Appendix D Sample Report Documentation

The objective of this appendix is to exemplify the types of information to be documented in a field measurement report. For the purposes of this appendix, assume existing-noise measurements were performed (See Section 4).

D.1 Site Sketches

The measurement site was located on Route 95 (a 2-lane highway) 0.8 km past Exit 21. A reference microphone was attached to a mast, placed at a height of 1.5 m above the roadway pavement, and located at a 15 m offset position from the centerline of the near travel lane. Another portable mast was fitted with three microphones, placed at heights of 1.5 m (low), 4.5 m (middle), and 7.5 m (high), and located at a 30-m offset position. When referring to microphone heights, the high, middle, and low convention will be used for the remainder of this report. Figures D1 and D2 present the plan and elevation views, respectively.

Aerial view of the plan. Click on image for full description

Figure D1. Measurement site plan view.

Cross-section view of the microphone positions in relation to an uneven terrain and the near travel lane of the road. Click on image for full description

Figure D2. Measurement site elevation view.

D.2 Source Description

The source was constant free-flowing traffic traveling on Route 95. Traffic volume and mix were recorded on video cassette and used to obtain vehicle counts. Vehicles were counted and classified in three categories: automobiles (A); medium trucks (MT); and heavy trucks (HT). Vehicles were further grouped by direction (eastbound and westbound). Vehicle counts and average speed for each test run are presented in Table D1.




Table D1. 5-minute vehicle count and average speed data.

Test
Run #

Start
Time
Westbound Eastbound Avg
Speed
(km/h)
Std
Deviation( Σ )
A MT HT A MT HT
1 9:00 407 7 31 322 9 38 96.7 3.4
2 9:10 351 8 36 348 12 26 97.3 3.4
3 9:20 319 8 20 340 10 29 96.4 3.7
4 9:30 317 16 25 338 10 37 96.7 3.2
5 9:40 335 14 25 342 12 39 94.8 3.1
6 9:50 363 8 32 335 6 38 93.6 3.3
7 10:00 332 8 20 375 8 35 94.0 3.8
8 10:10 340 11 22 320 11 33 93.8 3.9
9 10:20 291 10 23 354 7 28 96.7 3.5
10 10:30 374 10 25 404 12 40 94.9 3.5
11 11:00 370 3 41 428 7 55 90.7 4.3
12 11:10 364 3 47 422 11 42 91.6 5.7
13 11:20 352 4 48 375 4 41 93.8 5.0
14 11:30 397 2 38 426 4 39 90.1 4.1
15 11:40 416 4 39 384 6 47 90.7 4.6
16 11:50 397 3 34 411 5 49 94.8 3.6
17 12:00 424 3 49 377 6 44 92.5 3.3
18 12:10 408 2 28 364 2 39 91.4 2.7
19 12:20 - - - - - - - -
20 12:30 346 3 37 342 8 30 93.6 5.0
21 13:30 385 8 49 427 11 33 93.6 3.8
22 13:40 391 4 40 459 5 42 94.3 3.6
23 13:50 409 1 39 463 14 30 94.4 3.1
24 14:00 - - - - - - - -
25 14:10 - - - - - - - -
26 14:20 - - - - - - - -
27 14:30 426 3 33 499 10 33 92.2 4.1
28 14:40 500 3 39 699 5 51 90.6 4.5
29 14:50 507 3 17 678 7 32 94.9 4.0
30 15:00 476 7 32 704 9 39 92.7 2.3


D.3 Instrumentation Description

Note: A list of instrumentation is presented in Table D2. Each noise measurement system consisted of a General Radio Model 1962-9610 random-incidence electret microphone, connected to a Larson Davis Model 827-0V preamplifier. The microphone/ preamplifier system was mounted in an insulated nylon holder and connected via cable to a Larson Davis Model 820 Type 1 Precision integrating Sound Level Meter/Environmental Noise Analyzer (LD820). The microphone/preamplifier combination was positioned 0.3 m from the mast and placed in its shadow as viewed from the roadway. This position insured minimum errors due to reflections from the mast structure.(11) Brüel & Kjær Model UA0237 windscreens were placed atop each microphone to reduce the effects of wind-generated noise on the microphone diaphragm.

Pre-processing and storage of the measured noise level data were accomplished by the LD820. Each unit was programmed to continually measure, energy average, and store A-weighted noise levels with fast-exponential response characteristics at a rate of two data records each second (1/2-second averages).

A passive microphone simulator was used to establish the electronic noise floor of each system. In addition, the frequency response of each system was tested using pink noise generated by a Cetec Ivie Model IE-20b random noise generator.

Traffic speed was obtained with a CMI Doppler radar gun set up 6 m off the edge of the near travel lane, approximately 100 m west of the microphone centerline (See Figure D1). The Doppler radar was directed at the departing westbound traffic, thus minimizing the possibility of individual vehicles slowing down after detecting the radar signal. Readings were observed visually from the radar's digital display, and recorded continuously during each measurement period at a rate of approximately one reading every 10 seconds.

A Panasonic Model AG170 video camera was set up on a nearby overpass to record pass-by traffic at the measurement site. The camera was time-synchronized with the LD820's, so that the noise data could be correlated with the traffic data.




Table D2. Sample instrumentation log.
Item #: Quantity: Instrument Type: Serial #:
1 1 General Radio 1962-9610 Microphone & Preamp 43515
2 1 General Radio 1962-9610 Microphone & Preamp 43516
3 1 General Radio 1962-9610 Microphone & Preamp 43517
4 1 General Radio 1962-9610 Microphone & Preamp 43518
5 1 Larson Davis 820 Sound Level Meter 33768
6 1 Larson Davis 820 Sound Level Meter 33769
7 1 Larson Davis 820 Sound Level Meter 33770
8 1 Larson Davis 820 Sound Level Meter 33771
9 2 Brüel & Kjær Type 4231 Calibrator N/A
10 1 Cetec Ivie Random Noise Generator 501
11 2 Microphone Simulators N/A
12 6 Brüel & Kjær 0237 Windscreens N/A
13 1 Wind-Cup Anemometer N/A
14 1 Sling Psychrometer N/A
15 1 CMI Doppler Radar Gun 10331
16 1 Panasonic Model AF170 Video Camera 15095
17 1 Climatronics Model EWS Weatder Station 66881
18 20 9-Volt Batteries N/A
19 1 100' Tape Measure N/A

 

D.4 Meteorological Data

A Climatronics Model EWS weather station continually recorded temperature, humidity, wind speed, and wind direction data on a continuous strip-chart recorder with a paper speed of four inches per hour. Wind speed and direction were measured at a height of 7.5 m above the ground (height equivalent to the highest microphone position); temperature and humidity were measured at a height of 1.5 m above the ground. In addition, cloud cover was documented periodically, as well as significant changes in weather conditions.

Using the known recorder paper speed and the time marks produced on the strip-chart, a time scale was transposed on each chart and the 5-minute measurement period for each test was identified.

The average wind speed and average wind direction re magnetic north (degrees) were computed for each 5-minute test run. The 5-minute averaged wind speed (WS) and direction (WD) were then used to compute the vector component of wind speed in the x-y plane from the source to receiver (VWS) for each test run.

Meteorological data are presented in Table D3. Note: Cloud cover class 2 was observed for the duration of the measurement day.




Table D3. Meteorological data (5-minute average values).
Test
Run #
Start
Time
Wind
Speed (km/h)
Wind
Dir* ( ° )
Temp
( °F )
Rel
Hum (%)
VWS
(km/h)
1 9:00 10.5 65 13 46 4.3
2 9:10 11.3 80 14 45 1.9
3 9:20 6.4 130 14 44 -4.2
4 9:30 12.1 100 14 43 -2.1
5 9:40 8.8 105 14 43 -2.3
6 9:50 9.3 150 14 42 -8.0
7 10:00 12.1 115 15 41 -5.1
8 10:10 14.5 65 16 40 6.1
9 10:20 4.0 195 16 40 -3.9
10 10:30 12.9 155 16 40 -11.7
11 11:00 7.2 195 19 38 -6.9
12 11:10 0.0 - 18 36 0.0
13 11:20 7.7 15 19 34 7.4
14 11:30 10.0 35 19 33 8.2
15 11:40 8.8 325 19 32 7.2
16 11:50 13.4 10 19 32 13.2
17 12:00 7.7 350 19 32 7.6
18 12:10 5.3 45 19 32 3.7
19 12:20 - - - - -
20 12:30 7.2 330 18 32 6.3
21 13:30 10.9 345 19 32 10.6
22 13:40 6.9 20 19 32 6.4
23 13:50 8.2 50 19 32 5.3
24 14:00 - - - - -
25 14:10 - - - - -
26 14:20 - - - - -
27 14:30 8.8 30 20 30 7.7
28 14:40 6.3 30 20 30 5.5
29 14:50 10.5 40 19 29 8.0
30 15:00 0.0 - 18 29 0.0


D.5 Ground Surface Characterization

The roadway surface was composed of dense-graded asphaltic concrete. The roadside terrain between the road and the receivers was relatively flat and composed of packed clay with low-cut grass.

D.6 Measurement Procedures

At the beginning of the measurement day, a complete system check was performed on the entire measurement system. To establish the electronic noise floor of each system, a passive microphone simulator was substituted for each microphone. The frequency response of each system was tested by recording a 30-second sample of pink noise. In addition, 30 seconds of calibration data were recorded at the beginning and end of the measurement day.

Data were collected at a rate of two samples per second. After collecting data for ten consecutive 5-minute test runs (5-minute spacing between each run), approximately 30 seconds of calibration data were measured and stored for all microphones. Data collection then calibration were repeated until a total of thirty 5-minute test runs were measured and stored.

At the end of the measurement day, the 1/2-second noise data stored in each LD820 were downloaded to an AST Premium Exec Model 386SX/20 notebook computer and stored on floppy disk for later off-line processing.

D.7 Acoustical Data

Processing of the noise data files stored on floppy disk was accomplished off-line, using the LD820 support software in tandem with the Acoustics Facility-developed computer program, RFILE. The LD820 software was used to obtain a graphical history plot (noise level versus time) for the test runs identified in the field as potentially contaminated. These plots were examined and all questionable test runs were removed from the population of events to be processed.

The RFILE program, using the 1/2-second data stored in each file, was used to compute the equivalent A-weighted sound levels for each 5-minute test run (LAeq,5min). The LAeq,5min values were adjusted for calibration drift. No ambient adjustments were necessary. The final LAeq,5min values are presented in Table D4. Computation of experimental error is shown below.

Experimental Data Error Calculation

  1. Compute Variance* for:
    • Background (Not computed if measured level background by 10 dB):

      Reference Microphone Position   0.0
      High Microphone Position   0.0

    • Difference (Corrected source levels at reference microphone position minus calibration corrected source levels at the

      High Microphone Position   0.012

    • Bias:

      Type Amount Amount/2 (Amount/2)2 Variance
      Calibrator 0.25 0.125 0.016 0.016
      Cal. Drift 0.23 0.115 0.013 0.013
  1. Sum of Variances (Sum of above items)   0.041
  2. Standard Error (Square root of Sum of Variances)   0.202

* Note:   Variance = ( Σ )2 = [n ∑ (Xi)2- (∑ Xi)2] / [n (n-1)]; where n is number of levels and Xi is value of ith level.




Table D4. Calibration corrected LAeq,5min data.
Test
Run #
Start
Time
REF HIGH MID LOW
1 9:00 80.65 79.30 72.50 65.65
2 9:10 80.15 78.90 71.60 64.95
3 9:20 80.05 78.80 71.40 64.75
4 9:30 80.55 79.30 71.80 64.15
5 9:40 80.25 79.10 71.50 64.85
6 9:50 80.15 79.00 71.20 64.75
7 10:00 80.05 78.80 71.40 64.65
8 10:10 80.55 79.10 71.10 64.25
9 10:20 80.15 78.80 71.10 64.45
10 10:30 80.55 79.20 71.50 64.85
11 11:00 81.15 79.95 73.25 64.75
12 11:10 81.55 80.25 74.35 64.15
13 11:20 80.95 79.45 72.35 64.85
14 11:30 80.75 79.35 72.05 64.75
15 11:40 80.95 79.65 72.75 64.65
16 11:50 80.75 79.45 72.45 64.25
17 12:00 80.95 79.55 72.45 64.45
18 12:10 80.25 79.15 72.15 64.85
19 12:20 - - - -
20 12:30 81.25 80.05 72.95 66.00
21 13:30 81.20 80.00 72.85 66.15
22 13:40 81.30 80.00 72.75 65.95
23 13:50 81.50 80.30 73.35 66.65
24 14:00 - - - -
25 14:10 - - - -
26 14:20 - - - -
27 14:30 80.80 79.50 72.35 65.75
28 14:40 81.80 80.50 73.15 66.75
29 14:50 81.20 80.10 72.85 66.15
30 15:00 81.40 80.30 73.15 66.45

Updated: 07/06/2011
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