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1Â Â The various components of pavement surface texture have a high influence on vehicle- road interactions. In particular, macrotexture features contribute to pavement friction, tire- pavement noise, splash and spray, and rolling resistance. Therefore, the availability of robust macrotexture data in pavement management systems would significantly aid highway agen- cies in assessing the adequacy of pavement surface macrotexture and determining if corrective actions are required. The objective of this project was to develop and propose recommended protocols for test methods, equipment specifications, and data quality assurance (QA) practices for network-level macro texture measurement. The project identified equipment, environmental, and opera- tional factors that influence macrotexture measurements; the macrotexture characterization para meters used to represent the macrotexture; and improved methods for network-level macrotexture measurement that address these factors. This project developed protocols for equipment specifications, operational procedures for collecting data, and certification procedures for equipment to facilitate the use of these methods. The project started with a review of current practice that included a literature review, a survey of state highway agencies, and contact with equipment manufacturers and service providers to further assess the various technologies, methods, and approaches for collecting macrotexture data. The research team identified, summarized, and analyzed current and emerging measurement technologies for collecting macrotexture data at the network level, as well as current and emerging parameters for characterizing macrotexture. The project included three equipment comparison experiments to evaluate the main avail- able technologies in terms of repeatability, agreement, and accuracy: 1. The initial equipment comparison was conducted at the Virginia Smart Road in Blacksburg, Virginia, and included stationary, walking-speed, and high-speed macrotexture measuring equipment. The repeatability and agreement of measurements obtained from the equip- ment were tested on a variety of surfaces, including dense-graded hot-mix asphalt (HMA), open-graded friction courses, proprietary high-friction surfaces, as well as grooved, tined, and ground Portland cement concrete sections. 2. The second equipment comparison aimed to verify some of the first comparisonâs find- ings and to further assess and refine the most promising approaches for collecting data and characterizing pavement macrotexture as identified from the first experiment. The comparison was conducted at the MnROAD facility in Albertville, Minnesota, and included a variety of asphalt and concrete surfaces located in the mainline and the low- volume loop at the facility. 3. The third comparison, conducted at the Texas A&M Universityâs RELLIS Campus, focused on validating the recommended method for network-level macrotexture data collection S U M M A R Y Protocols for Network-Level Macrotexture Measurement
2 Protocols for Network-Level Macrotexture Measurement and processing. This experiment considered testing speed and exposure time for the laser sensors in the experimental design. The experiment also used a reference measurement beam manufactured to collect static reference texture data using a high-resolution laser and collected data on a series of manufactured surfaces. The data collected from the various experiments were used to evaluate equipment repeat- ability and agreement, and the accuracy of various macrotexture parameters measured with the state-of-the-practice equipment. In addition, several parameters were proposed and evaluated in terms of their ability to predict critical attributes such as wet-weather friction and tire-pavement noise. The main conclusions from the analyses were: 1. Single-spot and line-laser mean profile depth (MPD) results should not be used inter- changeably when longitudinal pavement texturing is present. Single-spot lasers are not capable of adequately capturing longitudinal pavement texture when compared to line lasers. 2. Most commercial off-the-shelf macrotexture equipment measurement results are repeat- able and generally agree well with one another if similar sensing technologies (e.g., single- spot lasers) are used. The systems that used higher-frequency laser sensors operating at their recommended exposure times generally provided the most repeatable measurements. 3. The use of commercially available walking macrotexture measuring equipment with a line laser appears to be the most practical method to collect reference profiles to verify and/or certify high-speed macrotexture measuring devices. The coefficient of repeatability of the walking macrotexture measuring device used in the experiments was 0.02 mm in the initial and verification experiments. The coefficient of repeatability is a precision measure that represents the value below which the absolute difference between two repeated test results may be expected to lie within a probability of 95%. 4. Engineered surfaces with properly prepared surfaces can and probably should be used to test the accuracy of line-laser-equipped reference walking devices. The surfaces can be scanned with a high-resolution laser texture beam to determine the reference measurements. 5. The use of a line laser oriented at a 45° angle to the travel direction appears to be the most practical solution for measuring pavements with a longitudinal or transversal engi- neered macrotexture. The experiments showed that this technology can produce rela- tively repeatable and accurate measurements on various types of surfaces, although they experience some problems on surfaces with high convex texture. 6. Macrotexture parameters that account for the enveloped shape of the tire on the pave- mentâs surface correlated better to friction and tire-pavement noise than did MPD and root mean square (RMS) values for random and transverse textures. However, alternative parameters to MPD and RMS should undergo continued testing on a greater variety of pavement surfaces before adoption as standards. Based on the data collected and the analysis conducted, the research team proposed three draft AASHTO standards. The proposed standards are provided in the appendix to this report and address equipment specifications, operation of equipment for collecting data, and certification of equipment.
