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18 Table 6. Passby test sites. Site # Location Description 1 US 30 near Marshalltown, IA PCC-Burlap Drag 2 US 30 near Marshalltown, IA PCC-Random Transverse Tine 3 US 30 near Marshalltown, IA PCC-Uniform Transverse Tine 4 US 30 near Marshalltown, IA AC-Dense Graded 5 US 30 near Marshalltown, IA PCC-Longitudinal Tine 6 LA 138 near Lancaster, CA AC-Dense Graded Overlay 7 LA 138 near Lancaster, CA AC-Open Graded Overlay 8 LA 138 near Lancaster, CA AC-Rubberized Open Graded Overlay 9 LA 138 near Lancaster, CA AC-Bonded Wearing Course 10 KN 58 near Mojave, CA PCC-Grooved on Burlap Drag 11 KN 58 near Mojave, CA PCC-Ground (2.67 Blade Spacing) 12 Shasta 299 near Redding, CA AC-Rubberized Open Graded Overlay the 60 mph samples were reanalyzed into shorter sample seg- provided from the RTA. The microphone output signals ments to assess the variation of OBSI level over the standard were also captured on a solid-state digital recorder as backup 440-ft test section. The microphones were calibrated at the and later use as required. Vehicle speed and type (light vehi- beginning and end of the measurement period. Three passes cle, medium or heavy duty truck, or "other") were manually were made for each test speed, which were averaged together recorded for each measured passby. Vehicle speed was mea- during post analysis. During the data acquisition, OBSI qual- sured with a radar gun and wind speed was documented from ity metrics of coherence between the two microphones com- an anemometer at regular intervals. Prior to testing, the test prising each probe and the difference between sound pressure vehicle speedometer was calibrated with the radar gun "shot" and sound intensity level were monitored. The actual time sig- in a direction very nearly parallel to the centerline of vehicle nals of the four microphones were monitored in order to travel. Vehicle speed measurements during the CPB tests were identify any data acquisition abnormalities. later used to adjust the recorded speed to the actual speed at the Statistical vehicle passby measurements were done generally measurement angle used for passby data collection. The total following the procedures described in the report "Measure- number of passby events acquired at each site ranged between ment of Highway-Related Noise" (20). Two microphone posi- 178 and 259 depending on the occurrence of sufficient (nom- tions were used: one at a distance of 25 ft from the centerline inally 40) heavy truck passby events. of travel and one at a distance of 50 ft at heights of 5 ft above Controlled vehicle passby measurements of the test vehicles the height of the pavement. An example passby measurement followed the same procedures as those described for the statis- setup is shown in Figure 12 for the longitudinally tined PCC tical passbys. A minimum of three passbys was measured at pavement (Site 5). The passby sound pressure levels were each test speed. measured using two-channel real time analyzers (RTA). The analyzers were set to "fast" response (1/8 second exponential average) and the 1/3 octave band and overall A-weighted sound Meteorological Conditions pressure levels occurring in 1/10th-second intervals were log- Testing in Iowa (Sites 1 through 5) was conducted over a ged during the passby. The maximum level for each passby 3-day period from September 26th to 28th, 2007, where clear was then determined from a plot of sound level versus time skies and calm to light winds (0 to 7 mph) prevailed. Temper- atures ranged from 48 to 60F for the morning testing on the 26th and 28th, from 60 to 68F on the afternoon of the 26th, from 59 to 73F on the morning of the 27th, and from 76 to 77F on the afternoon of the 27th. 25 ft Mic. 50 ft Mic. Measurements along LA 138 (Sites 6 through 9) and Mohave Position Position Bypass (Sites 10 and 11) were conducted on November 6th to 9th, 2007. The sky was clear during the testing with winds from the east of up to 9 mph. Air temperatures ranged from about 60F in the morning to highs of about 75 to 77F in the after- noon on all 4 days. The Shasta 299 (Site 12) monitoring was conducted on November 30, 2007, where clear skies and air temperatures ranging from 45F to about 55F, with winds Figure 12. Typical passby measurement setup. speeds of up to 6.7 mph prevailed.