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Suggested Citation:"Summary." 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:"Summary." 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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1   Inertial profilers are used by state departments of transportation (DOTs) 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 (IRI). AASHTO’s standard AASHTO R 56-14, Standard Practice for Certification of Inertial Profiling Systems, describes a certification procedure for operators and test equipment used to measure a longitudinal surface elevation profile of a roadway based on an inertial reference system mounted on a data collection vehicle. The practice identifies minimum requirements intended to address the need for accurate and repeatable profile measurements for construction quality control/quality assurance, acceptance, and network-level data collection. The objective of this research was to propose revisions to AASHTO R 56-14 to enhance the practice for certification of inertial profiling systems. AASHTO R 56-14 was first pub- lished by AASHTO in 2014 and reaffirmed without changes in 2022; it will be referred to as AASHTO R 56-14 in this report. Review A review of the existing AASHTO R 56-14 standard practice was performed. One key aspect of that review was consideration of the elements from NCHRP Synthesis 526 (Perera 2018), which identified very few state DOTs using the AASHTO R 56-14 as written. Only seven state DOTs from the synthesis report were using more than two sections for certification of profilers, while the Critical Profiler Accuracy Requirements (CPAR) report (Karamihas 2005) identifies six surface types and four roughness levels for a recommendation of up to 24 sections to provide a complete matrix representing the range of surfaces that may be encountered in both construction acceptance and network-level data collection. However, the recommendations in the CPAR report allow for as few as four sections for certification if they are able to cover the levels of roughness and surface types used by an agency. The device for collection of reference data is not well-defined within AASHTO R 56-14, which identifies that the reference device should meet the criteria established in the Bench- mark Test Evaluation Report (Karamihas 2011); however, none of the potential reference devices evaluated met these requirements (Perera and Karamihas 2017). Further, AASHTO R 56-14 requires that the reference device be used to collect data immediately before mea- surements are made by an inertial profiler on jointed concrete pavements due to potential diurnal variation in slab shape and thereby pavement profile. The standard practice makes no requirement regarding the collection of reference data on asphalt pavements. S U M M A R Y Enhancement of the Practice for Certification of Inertial Profiling Systems

2 Enhancement of the Practice for Certification of Inertial Profiling Systems AASHTO R 56-14 requires the use of cross-correlation to compare profiles from the device to the reference device and to each other to assess accuracy and repeatability. The required cross-correlation is set to meet an approximate 5 percent level of error in IRI based on expe- rience. The level of cross-correlation does not account for recent experience in certification. In addition to the cross-correlation, AASHTO R 56-14 also requires the review of the IRI to assess that the equipment software is capable of computing the IRI. Proposed Revisions Data were collected from a variety of sources, including the Federal Highway Adminis- tration (FHWA) “rodeo” (i.e., a particular study that collected data through multiple passes) conducted in 2015, two Long-Term Pavement Performance (LTPP) profile “rodeos” con- ducted in 2010 and 2015, and certification data from Florida, Minnesota, Mississippi, and Tennessee. These data were reviewed, and analyses were performed to develop a series of proposed revisions in the AASHTO R 56-14 standard practice. From the analyses of these data, an estimated relationship between the percent differ- ence in IRI and the cross-correlation level was developed. The relationship was based on the 95th percentile data such that the percent difference in IRI would be less than the value estimated at a 95 percent level of confidence for a given cross-correlation. The surface type was a significant factor in the relationship such that the recommended level of cross- correlation for accuracy changes based on the surface type. The proposed revisions include a table that allows a state DOT to identify the level of cross-correlation based on the accept- able level of error in IRI. The analyses identified the prioritized list of surface types for certification based on the observed difficulty in achieving certification. The observed diffi- culty is impacted by such factors as high signal-to-noise ratio for very smooth sections and potential aliasing of profiles with a spot laser on coarse-textured and longitudinal-textured pavements. Additional revisions were proposed to refine language associated with the operator certification, test section marking, and reporting requirements. Each of the proposed revisions to AASHTO R 56-14 is expected to provide a more practical approach to equipment certification while maintaining confidence in the device’s accuracy and repeatability.

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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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