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Page 37
Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
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Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
×
Page 38
Page 39
Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
×
Page 39
Page 40
Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
×
Page 40
Page 41
Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
×
Page 41
Page 42
Suggested Citation:"Chapter 4 - Proposed Revisions." National Academies of Sciences, Engineering, and Medicine. 2023. Enhancement of the Practice for Certification of Inertial Profiling Systems. Washington, DC: The National Academies Press. doi: 10.17226/27182.
×
Page 42

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37   Proposed Revisions The analyses described in Chapter 3 were used to develop a series of proposed revisions to AASHTO R 56-14. These revisions were tested in a field study described below. The proposed revisions to AASHTO R 56-14 standard practice are listed in Appendix A. This appendix is not published herein but available on the project web page. Summary of Proposed Revisions Operator Certification The section on operator certification needs to be revised to be more explicit in the require- ments associated with operator certification. The operator is required to undergo both a written examination and a practical test. The written examination is expected to cover the following items: • Operation of inertial profilers; • Collection of longitudinal profile data; • Processing and review of longitudinal profile data; and • State DOT test method and specifications. The practical portion of the certification is expected to encompass several items. These items include the equipment checks that are expected to be performed by the operator on a routine basis. The operator should be required to perform these tests before collecting the equipment certification data. These tests include the block check, bounce test, and check of the distance measuring instrument as described in AASHTO R 57-14. The final step of operator certification is a demonstration of the operator’s ability to operate the equipment to collect the data used to certify the equipment. Equipment Certification Test Sections The requirements for test sections needs to be revised to assist state DOTs in prioritizing the surface types. Ideally, test sections would represent the different surface types most commonly used for paving. However, in practice, it is difficult to maintain a large number of sections that represent every surfacing type used by a state DOT. Additionally, it is preferable to maintain these sections in a single location to allow for ease in collecting the reference profile data. There- fore, a prioritized list of surface types is identified in the revised standard. For example, if a state DOT typically uses open-graded or coarse-textured asphalt surfaces, the preferred test section is a smooth pavement section with a mean IRI between 50 and 95 in./mile with a coarse surface texture. C H A P T E R   4

38 Enhancement of the Practice for Certification of Inertial Profiling Systems A paragraph needs to be added with recommendations for marking the section to be used. It is recommended that a permanent marker be placed at the right edge of the pavement to mark the section location and establish the wheel path locations. The proposed revisions include marking the wheel paths with paint to guide both the reference and inertial profiler data collection. Data Analysis AASHTO R 56-14 did not identify a time limit for data submission. A time limit is expected to provide boundaries for the amount of post-processing that may be performed on the data before submission. A proposed revisions is to include the addition of a 2-hour time limit for data submittal. This time limit is intended to provide time to review the data before submitting it to the certifying state DOT or other certifying agency while still maintaining some boundaries on the data processing time after collection. The proposed revisions will add the option to allow for sample interval adjustment. AASHTO R 56-14 allowed for the profile to be shifted up to 3 ft in either direction to maximize the cross-correlation value. The addition of the sample interval adjustment will further improve the ability to match profile, particularly with another device. The recommended sample interval adjustment allows the distance between the points to be stretched or reduced up to a maximum of 0.1 percent. The data review presented in Chapter 3 suggests that the cross-correlation levels of AASHTO R 56-14 for repeatability may need to be revised to 94 percent with no change recommended for the accuracy requirement. Cross-correlation levels from AASHTO R 56-14 were expected to yield an approximate difference in IRI of 5 percent at a 95 percent level of confidence. The analyses described in Chapter 3 identified that the revised value of 94 percent for cross-correlation achieves the same 5 percent difference in IRI at the 95 percent level of confidence. The proposed revisions should also provide the equations for the 95th percentile line comparing cross-correlation and percent difference in IRI and adding tables to compare cross-correlation and percent differ- ence in IRI for different asphalt and concrete pavement texture types. These tables may be used to adjust the cross-correlation if a different level of accuracy in IRI is desired. Reporting Reporting the certification results is essential for the certification process, particularly with the proposed revisions. The variability allowed under the proposed revisions means that it is essential for the operator and equipment owners to understand the level of accuracy and repeatability demonstrated by their data collection system. A sample report with these additional details is provided in Figure 14. This report is an example of what an agency may use in presenting the results of the certification process. Field Test A field test of the proposed revisions was conducted by the MDOT in April 2022. The test section was located on MS 18 in Clinton County, Mississippi. It consisted of a single 528-ft section with a dense-graded asphalt surface, as shown in Figure 15. The mean IRI for the site was measured as 100 in./mile. Reference data were collected using a SurPRO model 3500 device. Reference data collection was repeated until an average of 98 percent cross-correlation was achieved between three runs. The average cross-correlation was 98.8 percent for the left wheel path and 98.3 percent for the right wheel path.

Proposed Revisions 39   Figure 14. Sample report format.

40 Enhancement of the Practice for Certification of Inertial Profiling Systems Seven high-speed inertial profilers performed a minimum of five repeat runs at two data collection speeds of 30 and 50 mph. One of the profilers (“zero speed”) reported the ability to collect data accurately in a stop-and-go situation. This device collected data under two addi- tional conditions. The first was starting from a dead stop and stopping at the end of the section such that there was no lead-in or lead-out in the data. The second condition was starting data collection at 30 mph, coming to a dead stop in the middle of the section, and then restarting and accelerating to the end of the section. Five of the seven devices used a line laser height sensor, one of the seven used a spot laser height sensor, and one of the devices used an LCMS sensor. Analysis The data from each device were analyzed for the cross-correlation. The cross-correlation values are provided in Table 27. These data were used to evaluate the accuracy and repeatability of each of the devices. Of the seven devices evaluated, two met the accuracy and repeatability requirements of AASHTO R 56-14 with respect to cross-correlations. All of the collectors achieved the repeatability of 94 percent for at least one data collection condition. For example, Collector 2 did not meet the repeatability requirements for the 30-mph speed of data collection but did for the 50-mph collection. Collector 3 met the repeatability requirement for data collection speed of 30 mph but not for the 50-mph collection. Similarly, for the check on accuracy, some of the collectors met the requirement of 90 percent cross-correlation for just one of the data collection speeds performed. For example, Collector 1 did not meet the accuracy requirement for the 30-mph data collection speed but did for the 50-mph collection. Collector 3 did not meet the requirement for the 30-mph data collection speed but did for the 50 mph. Collector 4 and Collector 7 met the accuracy requirement for all of the data collection speeds they performed. Figure 15. Overview of section used for field test. Source: Mississippi DOT.

Proposed Revisions 41   The result of these two checks might be summarized by data collector as follows: • Collector 1—50-mph collection • Collector 2—Does not pass • Collector 3—Does not pass • Collector 4—Range of data collection speed from 30 to 50 mph • Collector 5—Does not pass • Collector 6—Range of data collection speed from 30 to 50 mph • Collector 7—Range of data collection speed from stop-and-go to 50 mph From these data collectors, three require further review. Specifically, Collector 2’s data were reviewed further to identify the cause of the poor cross-correlations for accuracy. A synchroniza- tion analysis was performed using two of the runs at 30 mph. The synchronization analysis iden- tified that the maximum cross-correlation was seen at an approximate 15-ft offset. The equipment Unit Speed, mph Wheel Path Adjusted Non-Adjusted Accuracy, % Repeatability, % Accuracy, % Repeatability, % Collector 1 30 Left 89.8 94.0 88.6 93.9 Right 95.9 96.9 95.4 96.8 50 Left 93.4 95.8 92.3 96.8 Right 97.1 97.9 95.5 96.6 Collector 2 30 Left 10.5 91.0 7.5 91.0 Right 16.3 94.9 13.2 94.9 50 Left 42.9 96.3 43.0 97.8 Right 61.1 97.2 59.7 98.5 Collector 3 Spot Laser 30 Left 88.1 94.7 87.5 94.6 Right 89.4 97.4 89.4 97.3 50 Left 92.3 92.5 91.3 92.4 Right 92.6 95.7 92.3 95.7 Collector 4 LCMS 30 Left 95.5 95.4 94.8 97.3 Right 93.6 97.3 93.4 98.3 50 Left 94.3 96.4 93.2 96.2 Right 94.8 97.6 94.4 97.5 Collector 5 30 Left 74.7 78.0 74.6 78.0 Right 87.1 91.5 87.1 91.5 50 Left 79.2 95.5 78.9 95.5 Right 86.8 97.6 86.8 97.5 Collector 6 30 Left 95.2 99.1 94.0 99.1 Right 95.1 99.5 94.9 99.5 50 Left 92.4 97.5 91.2 97.5 Right 97.0 98.7 96.8 98.6 No Lead-in Left 20.3 44.3 20.1 44.2 Right 29.4 41.4 29.4 41.1 Stop- and-Go Left 0.8 22.1 0.8 21.2 Right 0.7 17.4 0.7 16.8 Collector 7 30 Left 93.5 98.8 92.3 98.8 Right 98.2 99.4 97.6 99.4 50 Left 92.4 97.5 91.2 97.5 Right 98.0 98.7 97.5 98.7 No Lead-in Left 96.3 98.8 94.7 98.8 Right 97.4 99.0 96.8 99.0 Stop- and-Go Left 96.6 96.3 95.9 96.2 Right 96.8 96.9 96.7 96.9 Table 27. Cross-correlations from field test.

42 Enhancement of the Practice for Certification of Inertial Profiling Systems had recently been updated to a GPS-based DMI from a wheel encoder, and the GPS receiver was mounted approximately 15 ft from the bar housing the inertial profiler sensors. As another example, assume that the state DOT is attempting to identify the accuracy and repeatability of the equipment to be used to collect network-level data. Furthermore, assume that, prior to certification testing for a data collection season, the state DOT or other certifying agency has reviewed the impacts of increasing the potential error and determined that they are willing to accept a 10 percent level of error in the accuracy of the IRI. Based on this error level, the state DOT would identify from Section 8.3.1.10.5 of the proposed revised AASHTO R 56 that a cross-correlation of 85 percent corresponds approximately to the 10 percent level of error in IRI at a 95 percent level of confidence for a smooth, dense-graded surface using a line laser. Based on a level of repeatability of 85 percent, Collector 5 and Collector 6 performed data collection at speeds that did not pass this check. Collector 5 had a cross-correlation of 78 percent in the left wheel path, and Collector 6 attempted collection at stop-and-go speed and with no lead-in, which demonstrated low values for cross-correlation. Using this same value for accuracy, Collector 2, Collector 5, and Collector 6 did not meet the requirement. Note that Collector 6 did meet cross-correlation of 85 percent at both 30- and 50-mph data collection speeds; therefore, data collected within this speed range are likely acceptable. However, the accuracy and repeatability requirements were not achieved in the other performed data collection speeds.

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Inertial profilers are used by state departments of transportation and others to produce an accurate and repeatable measure of the longitudinal pavement profile, which can be analyzed to produce various smoothness statistics such as the International Roughness Index.

NCHRP Research Report 1057: Enhancement of the Practice for Certification of Inertial Profiling Systems, from TRB's National Cooperative Highway Research Program, proposes revisions to AASHTO R 56-14 to enhance the practice for certification of inertial profiling systems.

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