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17 CHAPTER 5 Demonstration Testing of OBSI Procedure Introduction were also tested. In addition, a highly porous rubberized AC pavement along Shasta 299, about 5 miles east of Redding was The investigation was conducted to demonstrate the ability tested. The site location, photographs of the pavement sec- of the OBSI measurement method to quantify the relative tions, and the average 1/3 octave band spectrum for each sur- effect of different pavement types in comparison to total vehi- face under baseline conditions are provided in Appendix D. cle noise emissions measured with the CPB and SPB methods. All test sites followed the applicable criteria stipulated in the It included the simultaneous measurement of (1) OBSI on spe- FHWA document on highway noise measurement (20) and cific candidate test tires, (2) controlled passbys on test vehicles the ISO 11819-1 procedure (21). To the degree reasonable, sites equipped with the test tires, and (3) statistical passbys of both were selected to have acoustically hard (non-sound absorb- light- and heavy-duty vehicles on in-service payments. Using ing) surface characteristics between the vehicle lane of travel the SPB data, the relationship between OBSI tire-pavement and at least half of the distance to the 25-ft microphone fol- noise and average vehicle noise emissions was examined for lowing the ISO recommendation. Because the ISO procedure both light vehicles and heavy trucks. To account for site-to-site only addresses 25-ft distances, the FHWA criteria were used for variation, passby results were normalized using the measured the 50-ft microphone positions. To obtain comparable results, relationships between OBSI and CPB levels for each site. This sites were selected along roadways where the posted and typi- chapter describes the measurements performed, the results of cal vehicle speeds were 55 mph or higher. The designation, the OBSI and passby testing, and the relationships between the location, and description of each of the test sites are listed in OBSI and passby data. Table 6 (details of these sites are also provided in Appendix D). Description of Field Measurements Measurement Protocol Measurement Sites OBSI and controlled passby measurements were conducted The OBSI and passby testing was conducted at a total of using the 2007 Pontiac Grand Prix and the 2007 Chevrolet 12 sites (five in Iowa and seven in California). The sites in Iowa Impala with Michelin/Uniroyal SRTT and Dunlop SP Winter were located along U.S. Highway 30 between mileposts 178 and Sport M3 tires (Dunlop). The OBSI measurements followed 198, near Marshalltown. Portions of this section of highway the measurement protocol discussed for the parameter inves- were recently constructed to include many different types of tigation using the two-probe approach (2) with a vehicle load surface texturing (17). Along this section of highway, four sec- consisting of two people and the OBSI instrumentation. Mea- tions with different PCC texture were selected as test sites, surements were conducted at 60 mph and at test speeds vary- including a burlap drag surface, a random transverse tined ing from 50 to 70 mph, in 5-mph increments, depending on surface, a uniformly tined surface, and a longitudinally tined the typical speed of on-road vehicles, in order to match the surface. In addition, a nearby hot-mix AC pavement section speeds of the SPB measurements. The microphone signals were was selected as a test site. In California, four of the Caltrans test acquired using the same instrumentation and data analysis sys- sections on LA 138 (18), including DGAC, OGAC, rubber- tem described in Chapter 4. A standard 5-second averaging ized, and bonded wearing course AC pavements were tested. time was used for test Sites 1 through 9 and 12; a 4-second Two PCC sections, a grooved and a ground pavement, on the averaging time was used for Sites 10 and 11 because of the Caltrans research sites on the Mojave Bypass (KN 58) (19) shorter lengths of pavement sections. During post-analysis,