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119  This report has provided a comprehensive review of the state of the art and practice of network- level macrotexture and evaluated equipment repeatability, agreement, and accuracy of macro- texture parameters as measured with state-of-the-practice equipment. Several parameters were proposed and evaluated in terms of their ability to predict critical attributes, such as wet friction and tire-pavement noise. Based on the data collected and the analysis conducted, the research team proposed three draft AASHTO protocols, which have been included as an appendix. 5.1 Conclusions The main conclusions from the analyses were: 1. Single-spot and line-laser MPD results should not be used interchangeably 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 repeatable and generally agree well if similar sensing technologies (i.e., single-spot lasers) are used. In this research, the most repeatable measurements generally were provided by systems that used higher-frequency laser sensors operating at their recommended exposure times. 3. The use of a commercially available walking macrotexture measuring device equipped 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 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 with 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 device oriented at a 45° angle to the travel direction appears to be the most practical solution for measuring pavements with longitudinal or transversal engineered macrotexture. The experiments showed that this technology can produce relatively repeatable and accurate measurements on various types of surfaces, although the equipment experiences 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 RMS for random and transverse textures; however, alternative parameters to MPD and RMS should undergo continued testing on a greater variety of pavement surfaces before their adoption as standards. C H A P T E R  5 Conclusions and Recommendations
120 Protocols for Network-Level Macrotexture Measurement 5.2 Recommendations Based on the data collected and the analysis conducted, the research team proposed three draft protocols to be considered for approval and adoption by AASHTO: 1. Proposed Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds, 2. Proposed Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds, and 3. Proposed Standard Practice for Certification of High-Speed Macrotexture Measurement Equipment. The three proposed standards address equipment specifications, the operation of equip- ment for collecting data, and the certification of equipment, and are provided in the appendix to this report.