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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.

Noise and vibration measurements were conducted on eight light vehicles ranging from small compact passenger cars to a large sport utility vehicle on and off shoulder rumble strips of two different designs to assess the input to a vehicle operator when the vehicle departed from the travel lane. The first design was a more conventional design, consisting of cylindrical indentions ground into the pavement at regular 30 cm intervals, and a continuous sinusoidal profile with a peak-to-peak length of 36 cm. Triaxial vibration measurements were made at six locations, including the steering wheel and column, the seat cushion and track, and the front and rear spindles. Interior noise was measured at six locations, one at the operator’s outward ear and five at the front seat passenger (three in the fore/aft locations of the seat and at outboard and inboard ear locations). In addition to the in/on vehicle measurements, pass-by noise levels were made.

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.

Typically, the noise emission from trucks under highway cruise conditions is not reduced as much as it is for light vehicles when quieter pavements are used. Potential reasons for this are that other noise sources beside tire/pavement noise are more significant for trucks than light vehicles and/or the effect of pavement on truck tire noise generation is different than it is for light vehicle. As the cruising passby noise levels of trucks are about 10 dB greater than for light vehicles, this becomes an important issue for highway noise abatement when trucks make up even a relatively small percentage of the traffic flow. To investigate this issue, beam forming and conventional passby testing methods were used to investigate the contribution of both tire/pavement noise and the other noise sources for common types of heavy trucks.

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.

With the growing recognition that pavement selection can be an effective traffic noise abatement tool, there has been increased need for developing methods to characterize tire/road noise generation for existing and experimental highway surfaces. To address this need, sound intensity measured on-board a test vehicle has been developed as an alternative technique to wayside, passby, or trailer methods. As part of this development, the relationship between sound intensity measured close to a moving tire contact patch and coastby sound pressure data measured at stationary point 7.5 meters away has been demonstrated for different tires and road surfaces. A protocol for sound intensity measurement on existing highways in traffic has also been developed. Using these, a library of the tire/road noise levels has been assembled for California State Highways and experimental highway test sections.

In previous literature, sound intensity has been used to quantify the strength of tire-pavement interaction noise sources very near an operating tire under non-driven, cruise conditions as measured on trailers or actual vehicles. In the current investigation, the relationship between such on-board sound intensity data and coast-by sound pressure levels measured 7.5 meters away from the centerline of vehicle travel were examined. When compared either in terms of overall A-weighted levels or 113 octave band spectra, these data demonstrate a strong correlation between the two types of measurements. Given this correlation, the sound intensity technique was then used to quantify the tire/pavement interaction noise for the driven tires of a passenger car under accelerating conditions such as those specified in the ISO 362/SAE 51470 or SAE 5986 passby noise procedures.