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3 ect was subsequently initiated with the objective of developing measured on a variety of pavement types using the same a rational procedure for measuring tire-pavement noise at the tires. Next, the results of the CPX and OBSI testing were source that could be implemented by highway agencies. analyzed and ranked on the basis of their ability to corre- late with the wayside passby levels. In addition, consider- ation was given to the expense/practicality and training/ Research Objectives and Scope expertise required for each method. Under the final sub- The objectives of this research were to (1) develop rational task, the OBSI method was recommended as the basis of procedures for measuring tire-pavement noise at the source the procedure to be demonstrated and refined in Phase II and (2) demonstrate the applicability of the procedures through based on the ranking of the techniques and their ability to testing of in-service pavements. This work was divided into meet the other identified criteria developed in Task 1. two Phases. Phase I of this project involved reviewing the rele- 3. Develop Work Plan to Demonstrate Recommended Method. In this task, a work plan for Phase II of the project was vant literature worldwide as documented in conference pro- developed. ceedings, technical papers, and other sources; evaluating the 4. Documentation and Interim Report. In this task, an interim several candidate techniques identified from the literature; and report of the research performed in Tasks 1 through 3 was then selecting a single approach for measuring tire-pavement prepared. The report included the results of survey work of noise at the source for further development. In Phase II, the Task 1, the experimental work and recommendations of effect of test parameters was examined and field tests were per- Task 2, and the updated and detailed work plan for Phase II formed on in-service pavements to compare source level, con- developed in Task 3. trolled vehicle passby, and statistical passby data collection. The results were used to develop a recommended test proce- Phase II included the following two tasks (5 and 6): dure for the measurement of tire-pavement noise at the source. 5. Field Measurements, Analysis, and Findings. This task Research Approach included three subtasks. The first subtask was the evalua- tion of repeatability issues and parameter dependencies of The research was performed in two phases comprising six the OBSI method using a preliminary test procedure. This tasks. Phase I included the following four tasks (1 through 4): evaluation was accomplished through testing conducted at Minnesota's DOT MnROAD Low Volume Road facility in 1. Identify Potential Tire-Pavement Noise Measurement Meth- Albertville, Minnesota, and at the General Motors Desert ods. In this task, information on methods for measuring Proving Ground (DPG) in Mesa, Arizona. The second sub- tire-pavement noise at the source was collected, reviewed, task was the assessment of the applicability of the OBSI and synthesized. The findings of this literature search are procedure through the testing of in-service pavements. summarized in Chapter 2 and documented in more detail This work consisted of conducting controlled vehicle in Appendix A. passby, statistical passby, and tire-pavement noise OBSI 2. Develop Recommendation for Tire-Pavement Test Method. measurements on 12 in-service pavement sections in Iowa The test methods identified in Task 1 were evaluated in and California. These tests included the simultaneous mea- regard to their potential for providing a rational test pro- surement of (1) OBSI on two specific candidate test tires, cedure for measuring tire-pavement noise at the source. (2) controlled passbys on test vehicles equipped with those Based on this evaluation, two candidate techniques were tires, and (3) statistical passbys of both light and heavy- identified for further investigation: CPX and OBSI. In duty vehicles. The third subtask involved the development order to develop a single recommended method, several of a draft OBSI procedure based on the results obtained subtasks were performed. First, the two candidate tech- through the test parameter investigation and the results of niques were evaluated in experiments conducted at and the in-service pavement testing. around the National Center for Asphalt Technology 6. Prepare Final Report. In this task, a report documenting (NCAT) test track facility in Opelika, Alabama. CPX, the research, findings, and recommendations resulting OBSI, and controlled wayside passby noise levels were from this research was prepared.