Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 11
11
CHAPTER 4
Evaluation of OBSI Test Parameters
Introduction of tire wear and hardness were not evaluated and wheel align-
ment was not evaluated except as it occurred from test vehicle
As explained in Chapter 3, the OBSI method was selected as to test vehicle. Test execution variables including probe loca-
a basis for developing an onboard, at-the-source measure- tion, run-to-run and day-to-day repeatability, probe configu-
ment procedure for tire-pavement noise. As a portion of the ration, small variations in test speed, and reproducibility were
work conducted to develop such a procedure, test variables and also measured. Reproducibility across multiple users was not
measurement uncertainties were examined. Based on input assessed.
from current OBSI users as well as information contained in
the draft ISO CPX procedure, some pertinent variables that
could affect the measurement results were identified. The sen- Measurement Sites
sitivity of OBSI results to variations in pavement temperature,
The initial portion of this testing was conducted at
the configuration of the OBSI measurement fixture, tire infla-
Minnesota DOT's MnROAD Low Volume Road facility in
tion pressure, test vehicle type, test speed, and load were inves-
Albertville, MN. This facility is a 2.5-mile closed loop that
tigated. The intent of this investigation was to provide initial
contains 20 pavement test sections. Two of these sections, a
guidance on test variables and the control limits needed to
fine textured AC and a random transversely tined PCC, were
implement the OBSI procedure. This chapter summarizes the
selected as test surfaces. Due to an extended period of rain,
evaluation and results of the test parameter investigation and
testing was limited to the SRTT tire and only a portion of the
makes recommendations on parameter limits and controls
test matrix was completed. The remainder of the testing was
(additional information on the measurement sites and proto-
conducted at the General Motors Desert Proving Ground
col, along with a more detailed explanation of the results of this
(DPG) in Mesa, AZ, on relatively smooth AC and exposed
analysis, are provided in Appendix C).
aggregate PCC test sections. The site location, photographs of
the pavement sections, and the average 1/3 octave band spec-
Description of Field Measurements trum for each surface under baseline conditions are provided
in Appendix C.
Parameters Evaluated
Measurements were conducted to evaluate vehicle vari-
Measurement Protocol
ables and test execution variables on OBSI measurement
results. The test matrix is shown in Table 2. The baseline test condition for each test pavement and test
Environmental variables, such as air and pavement temper- tire followed the measurement protocol presented in Attach-
atures, wind conditions, and moisture conditions, could not ment 1 using "full-sized" rental vehicles along with a baseline
be systematically controlled for these tests. However, temper- load consisting of two people and the OBSI instrumentation.
ature and wind conditions were measured throughout, and A photograph of the OBSI equipment installed on a test vehi-
testing conducted over the extremes encountered was evalu- cle is shown in Figure 8.
ated. All testing was conducted under dry conditions. Vehicle Ideally, the same test vehicle would have been used as the
variables, including loading, tire inflation pressure, and baseline for all of the test scenarios. However, due to the relo-
vehicle-to-vehicle variation, were evaluated systematically. cation of the second portion of the testing, two different base-
Because of the time period of the testing, longer term variables line vehicles were used. The test vehicle used at MnROAD
