LTPP Manual for Profile Measurements and Processing

CHAPTER 6. INTER-REGIONAL PROFILER COMPARISON TESTS

6.1 INTRODUCTION

This chapter describes a plan for periodic comparison of the inertial profilers that are used in the LTPP program. This comparison is usually performed on an annual basis at a date and location determined by the FHWA. The FHWA will select a host RSC who will be responsible for coordination of logistical arrangements (hotel, maps, traffic control, meeting places, etc.), selection and marking of comparison test sections, and measurement of the longitudinal profile on those test sections using a Dipstick^®. The annual profiler comparison will be rotated among the four RSCs, so that they are responsible for preparatory activities once every four years. After completion of preparatory activities, but within 14 days of the Dipstick^® measurements, nonhost RSCs will travel to the test sites and, together with the host RSC perform profile measurements over a two to four day period with their respective profilers.

A report summarizing the results of the profiler comparison tests and associated data must be submitted by each RSC to the FHWA LTPP Office, with a copy to the LTPP TSSC within 21 days after completion of the tests. Interregional comparison and analyses of the profiler test data will be performed by the TSSC, who will produce and submit to the FHWA LTPP Office a report of the results within 45 days after receipt of the individual RSC reports.

6.2 PREPARATORY ACTIVITIES

The host RSC will be responsible for the following activities:

1. Dates for profiler comparison tests in coordination with the FHWA, TSSC, and other RSCs.
2.  
3. Site selection.
4.  
5. Logistical arrangements (reserve block of rooms at or near selected site, meal arrangements, traffic control arrangements, etc.).
6.  
7. Communication of final logistical arrangements to FHWA, TSSC, and other RSCs.
8.  

6.3 TEST SECTIONS

The host RSC will be responsible for selecting and marking the test sites that will be used for the profiler comparison. Five test sections for profile testing and one test section for DMI testing should be selected by the host RSC. The five test sections for profile testing should be selected based on the following guidelines:

1. Section One (AC-l): Smooth AC: AC pavement with a mean IRI < 1.6 m/km.
2.  
3. Section Two (AC-2): Rough AC: AC pavement with a mean IRI > 2.2 m/km.
4.  
5. Section Three (PCC-l): Smooth PCC: Jointed PCC pavement with a mean IRI < 1.6 m/km.
6.  
7. Section Four (PCC-2): Rough PCC: Jointed PCC pavement with a mean IRI > 2.2 m/km.
8.  
9. Section Five: Chip sealed section.
10.  

The test sections used for profile testing should meet the following criteria:

1. The AC pavement sections should not be a PCC section that has been overlaid with AC.
2.  
3. The test sections should have a marked outside lane edge stripe that can be used as an outside lane edge reference.
4.  
5. The test sections should be located on flat tangent sections with sufficient length at each end to allow for acceleration to a constant speed prior to the section and safe deceleration past its end.
6.  
7. The speed limit of the roadways containing the test sections should be at least 80 km/h.
8.  
9. Each test section should be 152.4-m in length, with the beginning and end marked.
10.  
11. The test sections should be located within a centralized locale with short travel distances between each test section to reduce travel time where possible.
12.  
13. The test sections do not have to be located on LTPP test sections. However, LTPP test sections can be used when convenient.
14.  

An accurately measured section, 300 m long, should be established as the DMI test section. A standard surveying tape should be used in conformance with standard surveying practice to accurately locate the end point relative to the start point. The DMI test section should be located on reasonably level pavement suitable for such testing (i.e., low traffic volume, adequate sight distances, operator safety, etc.).

6.4 DIPSTICK^® MEASUREMENTS AT TEST SECTIONS

Dipstick^® measurements along both wheel paths at all test sections should be obtained using the procedures outlined in Chapter three. The Dipstick^® measurements should be performed within 14 days of the profiler comparison tests. On PCC test sections, the Dipstick^® measurements should be performed after noon, at the same approximate time of day as expected for the collection of profiler data. If sufficient resources are not available for performing Dipstick^® measurements at all test sections, with approval from the FHWA, the RSC should perform Dipstick^® data collection only at the smooth AC test section

6.5 PROFILER COMPARISON TESTS

The following sequence should be followed in performing tests during the profiler comparison test:

1. Full calibration check of laser height sensors.
2.  
3. Accelerometer calibration and bounce test.
4.  
5. Static height sensor test.
6.  
7. DMI calibration data collection to check bias and precision of DMI.
8.  
9. Test section profiling.
10.  
11. DMI verification.
12.  

Details on each of these tests/checks are described in the following sections.

6.5.1 Full Calibration Check of Laser Sensors

A full calibration check of the laser height sensors should be performed following the procedures described in section 2.5.4 of this manual.

6.5.2 Bounce Test

The accelerometers should be calibrated prior to performing the bounce test following the procedures described in section 2.5.3 of this manual. Perform the bounce test using the procedures described in section 2.3.3.3. Record the IRI for the static test and the dynamic bounce test. Save the files created during the bounce test.

6.5.3 Static Height Sensor Test

This test is performed to determine the bias and precision of the laser height sensors. The following procedures should be followed for performing this test:

1. Measure the distance from the ground to the glass face of the laser sensor. Record the reading for each height sensor on the Static Height Sensor Measurements form that is included in appendix G.
2.  
3. Drive the vehicle such that all four tires will rest on the support blocks. The height of each support block should be 76 mm, as described in section 2.5.4.1.
4.  
5. Place a calibration base plate on the ground under each laser sensor. Place a calibration surface plate on top of each base plate. Let the computer take at least 500 readings.
6.  
7. Place a block on each base plate such that the 25 mm side of the block is vertical. Place a calibration surface plate on top of each block. Let the computer take at least 500 readings. Record the value shown under "Dif Ht" for each sensor on the data sheet (corresponding to cells Base Plate + 25 mm Block + Calibration Plate for Test 1). The value shown in "Dif Ht" is the height of the block that is measured by the data acquisition system in the profiler.
8.  
9. Repeat step 3. Place a block on each base plate such that the 50 mm side of the block is vertical. Place a calibration surface plate on top of each block. Let the computer take at least 500 readings. Record the value shown under Dif Ht for each sensor on the data sheet (corresponding to cells Base Plate + 50 mm Block + Calibration Plate for Test 1).
10.  
11. Repeat step 3. Place a block on each base plate such that the 75 mm side of the block is vertical. Place a calibration surface plate on top of each block. Let the computer take at least 500 readings. Record the value shown under "Dif Ht" for each sensor on the data sheet (corresponding to cells Base Plate + 75 mm Block + Calibration Plate).
12.  
13. Repeat step 3. Place two blocks on each base plate such that the two 50 mm sides are stacked on top of each other to give a total height of 100 mm. Place a calibration surface plate on top of each block. Let the computer take at least 500 readings. Record the value shown under "Dif Ht" for each sensor on the data sheet (corresponding to cells Base Plate + 100 mm Block + Calibration Plate).
14.  
15. Repeat steps 3 through 7 four more times and record readings on the data sheet.
16.  
17. Perform the following computations (Note: A spreadsheet can be used to perform these computations):
    1. Compute the average values obtained for tests one through five in the appropriate cell.
    2.  
    3. Enter the actual block height in the appropriate cells.
    4.  
    5. Subtract the average value computed previously from the actual block height and enter computed values in appropriate cells.
    6.  
    7. Compute the standard deviation of block height measured by the data acquisition system for each block position (values shown under Height of Block for Tests one through five) for all sensors and record values on the form.
    8.  
18.  

6.5.4 DMI Test

Calibrate the DMI following procedures described in section 2.5.2 of this manual. Then perform a profile run on the DMI section and record the distance shown under "Distance Old DCF" and the air temperature obtained from the temperature probe on the DMI Measurement form (see appendix G). Repeat this procedure five more times. The tire pressure may be checked and adjusted if necessary prior to performing each run. Compute the average and standard deviation of the six recorded distances.

6.5.5 Profile Testing

Profile data collection at each test section should be performed following the procedures that are used when performing data collection at GPS sections as outlined in this manual. Testing should be performed at a speed of 80 km/h. The PCC test sections should be profiled after noon.

6.5.6 Verification of DMI

The purpose of this test is to evaluate the stability of the DMI over time. This test should be performed after all five test sections have been profiled. The DMI should not be calibrated before doing the verification testing. Warm up the tires using the procedures that were used when the tires were warmed up prior to calibrating the DMI. Perform a profile run on the DMI section and record the distance shown under "Distance Old DCF" and the air temperature obtained from the temperature probe on the DMI Verification form (see appendix G). Repeat this procedure five more times. The tire pressure may be checked and adjusted if necessary prior to performing each run. Compute the average and standard deviation of the six recorded distances.

6.6 REPORTS

6.6.1 Submission of Reports and Data by RSCs

Within 21 days after completion of the comparison testing, each RSC should submit a report and the data collected during the comparison test to the FHWA LTPP Office, with a copy to the TSSC. Section 6.6.2 presents the format for this report and section 6.6.3 describes the profile data that should be submitted.

6.6.2 Format of Report

The report should consist of the following items:

1. Static Height Sensor Measurements form (see appendix G).
2.  
3. DMI Measurement for (see appendix G).
4.  
5. DMI Verification form (see appendix G).
6.  
7. IRI Values Table: Compute the IRI of the five runs at each site that would have been selected for upload to the LTPP database using the current version of ProQual. Enter the IRI values into the IRI Values table that is included in appendix G. Compute average and standard deviation of IRI for each wheel path at each site.
8.  
9. Profile Plots: Use ProQual to overlay the five selected runs at each site. Create the following graphs separately for each site and cut and paste them into the report: (a) five overlaid runs for left wheel path, (b) five overlaid runs for the right wheel path, (c) five overlaid runs for the center path, (d) overlay two runs and show left and right profiles on same graph. Create these graphs for all five sites. Indicate test section, surface type, and date of testing with each set of graphs.
10.  
11. Bounce Test Results: Create a table and show IRI values for static test and dynamic bounce test for each test day of profiler.
12.  
13. Site Visit report generated by ProQual for each site in the report.
14.  

If any data anomalies are noted for the static height sensor measurements, DMI testing, IRI values at a test section, or repeatability of profile plots, discuss the possible causes for these anomalies.

The host RSC should include the following items in the report:

1. Provide a description of structural attributes (if known) and observed distresses for all test sections. Details should be given on those attributes of the test section which are suspected of influencing profile measurements, such as meandering cracks in the wheel paths, highly variable transverse profile, etc. Detailed measurements are not required and subjective based descriptions are satisfactory. Include a photograph(s) of test sections in the report.
2.  
3. Include a table showing the IRI values computed from Dipstick^® measurements. Indicate date and time when Dipstick^® measurements were performed.
4.  

6.6.3 Data Submission

Organize the data into a CD in a logical manner. The following data should be submitted in a CD:

1. Bounce test files for each day (p, e and v files from the ICC profiler and ERD files created from this data).
2.  
3. Data collected by the ICC profiler at the five test sites. These are the files with extension p, e, and v, and the ERD files created from those data files.
4.  
5. Files created by ProQual when data were processed.
6.  
7. Excel file with separate sheets in the file for each of the following items: Static Height Sensor Test Results, DMI Measurements, DMI Verification Results, and IRI values.
8.  
9. Data files containing the Dipstick^® data, submitted by the host RSC.
10.  

6.6.4 Preparation of Report by TSSC

On receipt of the RSC reports and data, an interregional comparisons and analyses of the test results will be performed by the TSSC. A report summarizing the results of this effort should be submitted to the FHWA LTPP Office within 45 days after receipt of the individual RSC reports.

The report will document the results of the following analyses:

1. Evaluate the static accuracy of the profiler height sensors. The results from the static height sensor test will be evaluated to determine if the bias of each height sensor at each measurement position is within 0.25 mm, and if the precision of each height sensor at each measurement position is less than 0.125 mm.
2.  
3. Evaluate the results from the bounce test. The static and dynamic bounce test IRI values that were obtained for the profilers will be evaluated to determine if they meet the criteria specified in this manual.
4.  
5. Evaluate the accuracy of the DMI. The results obtained from the DMI test will be evaluated to determine if bias of the DMI is within 0.15 m (0.05 percent of the length of the section), and that the precision of the DMI is less than 0.075 m.
6.  
7. Compare the IRI values obtained by the profilers with those from the Dipstick^® and compare the IRI values between the profilers. The IRI values will be evaluated to determine if:
   1. The precision of the IRI along a wheel path for a profiler is less 0.04 m/km.
   2.  
   3. The difference in IRI for a wheel path between the Dipstick^® IRI and average profiler IRI obtained from the five runs is less than 0.16 m/km.
   4.  
8.  
9. Evaluate repeatability of each profiler along each wheel path at all sites by examining overlaid profile plots and by analyzing the point to point repeatability of each profiler.
10.  
11. Compare profile data obtained by the four profilers by preparing overlaid profile plots for each wheel path at each test section by selecting one representative profile run for each profiler at each test section.
12.