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Currently, the ASTM P225/60R 97S Radial Standard Reference Test Tire (SRTT) is used as a control test tire for calibrating test track surfaces over time and for rank ordering the noise performance of different pavement designs. As a result, variation from one SRTT to another and the effects of tire aging are important to quantify. Measurements of tire noise sound intensity on eight asphalt and two concrete test sections were conducted for eleven new and six older SRTT tires. The range in level for the new tires on each of the ten pavements was determined and was found to be 1.1 dB when averaged over all pavements compared to 0.7 dB for a single tire tested multiple times. As a group, the older tires produced levels 0.5 dB higher than the new tires when averaged for all pavements. The older tires had higher tread rubber durometer hardness values than the new tires, however, within the old and new groupings, no consistent trends could be identified.

Developing common methods of noise evaluation and facilities can present a number of challenges in the area of tire/pavement noise. Some of the issues involved include the design and construction of pavements globally, the change in pavement over time, and variation in the noise produced with standard test tires used as references. To help understand and address these issues for airborne tire/pavement noise, acoustic intensity measurement methods based on the On-board Sound Intensity (OBSI) technique have been used. Initial evaluations have included measurements conducted at several different proving grounds. Also included were measurements taken on a 3m diameter tire noise dynamometer with surfaces replicating test track pavements. Variation between facilities appears to be a function of both design/construction and pavement age. Consistent with trends in the literature, for smooth asphalt surfaces, the newest surface produced levels lower than older surfaces.

There is a growing interest in using a standard reference tire for both assessing changes in test track pavement over time and rank ordering of the performance of different highway pavements. Because of longer-term availability, the ASTM Standard Reference Test Tire (SRTT) is the primary candidate for these applications. Issues of concern for the SRTT include tire-to-tire variation, the relation of the SRTT to other tires currently in use, and the “break-in” period required for stable test tires. To address tire-to-tire variability, seven SRTT’s were tested on variety of asphalt concrete (AC) and Portland cement concrete (PCC) surfaces on two occasions. These included five new tires and two that had been in use for some time. Two of the new tires were re-tested with increasing use to examine any break-in period effect.

Acoustic beamforming was used to visualize the sound radiation of trucks under test track passby and actual highway operating conditions. The purpose of these measurements was to obtain an understanding of which sources contribute to the overall passby noise level and to determine the vertical distribution of noise sources. For trucks, drive axle tires were found to be the major contributor to passby noise at highway speeds, followed by powertrain noise to a much less degree, and very occasionally, exhaust stack outlet noise. For medium and heavy trucks, the acoustic mean source height was found to be about 0.5m and about 0.3m for light vehicles.

A road surface complying with the new International Standards Organization (ISO) specification was installed at an Arizona test facility (DPG site) in the winter of 1995/96. As part of the acoustic qualification of this site, comparative tests were conducted between this new surface, a Society of Automotive Engineers (SAE) sealed asphalt surface and an existing ISO surface in Michigan (MPG site). Initial testing with one vehicle and tire combination indicated that the new ISO surface produced ISO 362-1994 passby and coastby levels about 2 dB lower than sealed asphalt. Relative to the Michigan surface, the levels for the new Arizona ISO surface were 3 to 3½ dB lower. These differences were much greater than expected based on previously published studies of these two test surface types.