Protocols for Network-Level Macrotexture Measurement (2021)

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125   A P P E N D I X Draft AASHTO Protocols

126 Protocols for Network-Level Macrotexture Measurement Proposed Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds AASHTO Designation: M X1 INTRODUCTION The macrotexture of a pavement surface influences the friction between the tire and the road, noise at the tire-pavement interface, rolling resistance of vehicles, and tire wear. 1. SCOPE 1.1. The objective of this specification is to define the required attributes of equipment that can measure pavement macrotexture at highway speeds. This system may be added to a host vehicle as a single-function device or as a component of a multifunctional system that collects data relating to a variety of other properties including ride quality and cracking. The equipment may be used to collect network-level data or project-level data. The equipment shall be supplied with software that can compute macrotexture indices, particularly the Mean Profile Depth (MPD), from the measured data. 1.2. It is not the intent of this specification to relieve the supplier from the responsibility to provide an appropriate product for the intended function, nor is it intended to specify all the design details. The objective is to provide a sufficiently detailed specification in order to define the function of the equipment clearly. It is intended to have enough detail that the data collected from different equipment in each class of equipment (i.e., single-spot lasers, line lasers, and 3D equipment) will be identical. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R X2, [Proposed] Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds. R X3, [Proposed] Standard Practice for Certification of High-Speed Macrotexture Measuring Equipment. 2.2. ASTM Standard: E1845, Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 127   2.3. Other Documents: ISO Standard 13473-1:2019, Characterization of Pavement Texture by Use of Surface Profiles, Part 1: Determination of Mean Profile Depth. PIARC (2016). “Road Dictionary.” Available at: http://www.piarc.org/en/Terminology- Dictionaries-Road-Transport-Roads/ (accessed January 26, 2019). Katicha, S. W., D. E. Mogrovejo, G. W. Flintsch, and E. D. de León Izeppi (2015). “Adaptive spike removal method for high-speed pavement macrotexture measurements by controlling the false discovery rate.” Transportation Research Record: Journal of the Transportation Research Board, 2525(1): 100-110. doi: 10.3141/2525-11 Sayers, M. W., and S. M. Karamihas (1997). ERD File format for storage and analysis of road profiles, University of Michigan Transportation Research Institute, UMTRI-97-51, October 1997. Available at: https://deepblue.lib.umich.edu/bitstream/handle/2027.42/106533/ 102995.pdf?sequence=1&isAllowed=y (accessed January 27, 2019). 3. TERMINOLOGY 3.1. Definitions: 3.1.1. 3D system—a laser system that collects elevation data along the full width of a travel lane. Such transverse profiles are obtained at regular intervals as the host vehicle moves along the road. 3.1.2. Index—within the context of this standard, a suitably chosen index that quantifies the macrotexture of the pavement surface. 3.1.3. Mean Profile Depth (MPD)—an index used to quantify the macrotexture of a pavement surface that is computed by averaging the mean segment depth (MSD) values over a specified distance. The procedure for computing the MPD is described in ASTM E1845. 3.1.4. Mean Segment Depth (MSD)—an index used to quantify the macrotexture of a pavement surface over a distance of 100 mm (4 inches). The procedure for computing the MSD from macrotexture data is described in ASTM E1845. The MSD can be computed over a 100 mm distance for data collected along the travel direction, perpendicular to the travel direction, or at any orientation to the travel direction. 3.1.5. Line Laser—a line laser obtains a series of data points along a line, with the line typically being 100-mm (4 inches) long. The line laser is mounted such that it collects data perpendicular to the travel direction, or at a defined angle from the travel direction. 3.1.6. Macrotexture Profile—the vertical deviations of the pavement surface taken along a line with sufficient detail to capture the macrotexture-relevant features of the pavement surface; the

128 Protocols for Network-Level Macrotexture Measurement line can be along the direction of travel, perpendicular to the direction of travel, or at any orientation to the direction of travel. 3.1.7. Measurement Range—the detectable range of heights that can be accurately measured by the sensor. 3.1.8. Pavement Macrotexture—according to the World Road Association (Permanent International Association of Road Congress [PIARC]), macrotexture is defined as surface irregularities of a road pavement with horizontal dimensions ranging between 0.5 mm and 50 mm and vertical dimensions between 0.2 mm and 10 mm. 3.1.9. Report Interval—the longitudinal distance over which a macrotexture index is averaged and reported. 3.1.10. Sample Interval—the longitudinal distance between data capture points in a macrotexture profile. 3.1.11. Single-Spot Laser—a laser that projects a spot of light that typically has a diameter of 1 mm (0.04 in.) or less onto the pavement surface. 4. GENERAL EQUIPMENT REQUIREMENTS 4.1. General—The sensors that collect macrotexture profiles can be classified into the following categories: (1) single-spot laser sensors, (2) line lasers, and (3) 3D systems. Single-Spot Lasers—Single-spot laser sensors typically collect temporal data along the travel direction, and the collected data are stored in a file. As data at a fixed spatial data interval are needed for computing macrotexture indices, the temporal data are post-processed to output data at a fixed spatial data interval in order to compute macrotexture indices. Line Lasers—Line lasers collect data over a typical length of 100 mm (4 inches) either perpendicular or at an angle to the direction of travel. These data are collected at a fixed data recording interval in the longitudinal direction. 3D Systems—Equipment with 3D systems collect data along the full lane width typically approximately perpendicular to the travel direction, and obtain such full lane width transverse profiles at regular intervals. 4.1.1. The macrotexture profile shall be measured using equipment in which two primary transducers are used. The transducers are (1) a height sensor that measures the distance between the sensor and the pavement while the vehicle is traveling and (2) a distance measuring instrument (DMI) that provides a location reference for the vehicle as it travels. A Global Positioning System (GPS) receiver may be installed in the host vehicle and integrated into the system software to record GPS information during testing.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 129   4.1.2. The supplier shall provide all parts and labor necessary for the installation of the equipment. The computer system provided shall include a mounting arrangement that can be easily used by the operator sitting in the front passenger seat, or by the driver when a single person drives the vehicle and collects data. 4.2. Calculating Macrotexture Indices—The software shall be capable of calculating an appropriate macrotexture index such as the MPD from the data stored internally in the computer or on external storage media. The software shall be capable of computing the macrotexture index over any user-defined interval. If data are collected along the two wheelpaths using either single- spot lasers or line lasers, the macrotexture index shall be computed along each wheelpath, and the values for each wheelpath as well as the average value shall be reported. If a 3D system is used, the macrotexture index shall be computed for the portion of the data collected along each wheelpath, and the individual wheelpath values, as well as the average, shall be reported. 4.3. Calibration and Verification of Calibration—The equipment shall have provisions to facilitate the calibration of the distance measurement instrument (DMI) in the equipment and perform a verification of the measurements obtained from the height sensor. Any external devices required for calibration shall be included with the equipment. 4.4. All electronic components inside the vehicle shall be restrained with tie-downs or other applicable methods such that these components will not move during hard braking, accelerating, or a crash. 5. EQUIPMENT 5.1. General Requirements—The equipment shall meet the following requirements: 5.1.1. The equipment shall be capable of measuring macrotexture on pavements with MSD values ranging from 0.1 mm to 5 mm. 5.1.2. If macrotexture is being measured along both wheelpaths, mount the sensors on the host vehicle such that the center-to-center distance between the two sensors is between 1,650 mm and 1,800 mm (65 in. to 71 in.), with each sensor mounted equidistant from the center of the vehicle. Select a specific value for the distance between the sensors based on owner-agency requirements. If only a single sensor is used to collect data, collect data along the left wheelpath. 5.1.3. The equipment shall be capable of measuring macrotexture on pavements at vehicle speeds ranging from 0 to 112 km/hr (0 to 70 mph). 5.1.4. The data collected by the equipment shall not be affected by variations in the speed of the host vehicle caused by changing speed limits, braking, acceleration, or coming to a stop. 5.1.5. The computer in the equipment shall be capable of collecting and storing internally at least 80 km (50 miles) of macrotexture profile during a single data collection run.

130 Protocols for Network-Level Macrotexture Measurement 5.1.6. The equipment shall be capable of measuring macrotexture over an ambient temperature range of 0°C to 44°C (35°F to 110°F). 5.1.7. The equipment shall be capable of measuring macrotexture at a humidity up to 90 percent (non-condensing). Note 1—Local environmental conditions may require extending the suggested temperature and humidity limits. 5.1.8. The collected data shall not be affected by pavement color or by color changes of the pavement. 5.1.9. The collected data shall not be affected by ambient light. 5.1.10. The measurement system must be mounted on the vehicle such that vehicle vibrations do not influence the obtained measurements over the operating speed range, which is 0 to 112 km/hr (0 to 70 mph). 5.1.11. The equipment shall be equipped with an automated triggering system that can automatically initiate and terminate data collection using a reflective mark that is placed on the pavement surface or a reflective mark placed on a cone that is placed on the side of the road. The equipment shall also have the capability to initiate and terminate data collection using a manual method. 5.1.12. Power consumption of all installed equipment shall not exceed the capacity of the equipment providing operating power. Complete discharge of this system shall not impact the vehicle's regular electrical system. 5.1.13. The owner-agency shall specify the computer system parameters, including memory, operating system, interfaces, removable storage, etc. The computer must be ruggedized for the mobile environment. 5.1.14. Data Display—Data display parameters (computer monitor) shall be specified by the owner-agency. The size and type of display(s) shall be specified. 5.1.15. Keyboard—The keyboard shall be specified by the owner-agency. Specify the type of keyboard required. 5.1.16. Printer—The printer shall be specified by the owner-agency. Specify the type of printer required. The equipment shall not require the printer in order to function and shall be able to collect data without the printer being present. 5.2. Distance Measuring Instrument: A vehicle-mounted DMI shall be provided that is capable of measuring the traveled distance and the vehicle speed. The DMI shall be capable of measuring longitudinal distance data in an incrementing or decrementing mode from a selected starting point. Optionally, the equipment may also report distance in station format for project-level data

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 131   collection where data are collected to verify the macrotexture of a newly placed pavement. The measured distance shall be accurate to 0.15 percent over a distance of 1.6 km (1 mile) up to the maximum speed of the vehicle. Note 2—The measurements taken on a specific lane can differ significantly from the project stations due to the horizontal and vertical curvature of the pavement. 5.3. Sensors for collecting height data: The sensors that collect the height data should satisfy the following requirements: 5.3.1. The pavement height data shall be obtained using a non-contact height sensor. 5.3.2. The vertical resolution of the sensors that collect the height data must be at least 0.05 mm. 5.3.3. The measuring range of single-spot lasers or line laser sensors shall be at least 200 mm. The measuring range of 3D systems shall be at least 100 mm. 5.3.4. The angles between the axis of the emitting device and the axis of the receiving device shall be no more than 30°. Larger angles will underestimate deep textures. 5.3.5. The sensors shall have a standoff distance that provides sufficient clearance between the bottom of the sensor and the surface measured during vehicle operations. A standoff distance of at least 300 mm (12 in.) is recommended. 5.3.6. The sensors for collecting the height data may be a single-spot laser, a line laser, or a 3D system. 5.3.6.1. Single-spot laser sensor: The diameter of the spot projected onto the pavement by the sensor shall not be greater than 1 mm. Single-spot lasers typically store temporal data. Data at a fixed distance interval is needed in order to compute macrotexture indices. The data collected by a single-spot laser when post-processed to output data in the spatial domain shall have a fixed longitudinal data interval of 1 mm or less. The reference plane of the sensor shall not change significantly over each 100-mm distance interval to avoid vehicle motions influencing the computed macrotexture indices. Note 3—A method to avoid the issue of vertical motion of the vehicle is to use an accelerometer established inertial reference plane, which is the method used by inertial profilers to prevent vehicle motions from affecting the longitudinal profile data. Single-spot macrotexture data collection systems currently in use do not typically use such a method, and it is assumed that vehicle motions over a 100-mm interval (the distance of macrotexture data that is used to compute the MSD ) is negligible. 5.3.6.2. Line Laser—A line laser collects a series of data points along a line that is typically 100-mm long. The width of the line projected onto the ground shall not be more than 1 mm. The data points along this line shall be provided at a fixed longitudinal distance interval that is 1 mm

132 Protocols for Network-Level Macrotexture Measurement or less. The line laser shall be mounted on the host vehicle such that the collected data will be perpendicular to the travel direction or at an angle to the travel direction. The longitudinal distance between the locations where the line laser obtains measurements shall not be more than 25 mm. 5.3.6.3. 3D Sensor—A 3D sensor collects data along a transverse line that spans the full width of the pavement as the host vehicle travels along the roadway. The width of the line over which the data are collected shall not be more than 1 mm. The data points along this line shall be provided at a fixed longitudinal distance interval that is 1 mm or less. The collected data can be used to compute a macrotexture index along each wheelpath, or at any location within the lane. If the 3D sensor is capable of collecting transverse profiles along the travel direction at an interval not exceeding 1 mm, this data can be used to compute a macrotexture index along the travel direction. Note 4—On surfaces that have longitudinal texture such as longitudinally tined concrete, longitudinally diamond ground concrete, and longitudinally grooved concrete, macrotexture indices are computed from data collected by equipment with single-spot lasers can be very different from the data collected by equipment with a line laser or a 3D system. This is because equipment with single-spot lasers will take measurements on the trough of the texture as well as between the land area between the longitudinal texture. A line laser or a 3D system will be capable of accurately capturing the surface texture as measurements are obtained perpendicular to the travel direction. Note 5—Measurements obtained by line lasers and 3D systems on transversely tined concrete surfaces near a transverse tine may have a portion of the data collected on the trough of the tine and a portion of the data on the land area between the tines. This issue can be avoided by mounting the sensor at an angle to the travel direction. 6. SOFTWARE 6.1. Features of the Software The equipment computer shall contain the necessary software modules to perform the following tasks: Program initialization. Calibration or verification of transducers. Entering header information. Data collection. Ability to enter events. Saving collected raw data. Transferring data. Computation of macrotexture indices. Saving of computed macrotexture indices. Generation of reports detailing computed macrotexture indices and operator-entered events. Exporting data.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 133   Equipment shutdown. 6.1.1. Program Initialization—When loaded, the software shall perform a system self-check to ensure that all components of the data collection system are functioning properly. An error message should be displayed if a problem is detected in any component of the data collection system. 6.1.2. Calibration or verification of transducers—The software shall have a module for calibrating the DMI of the equipment and for performing a verification check of the height sensors. Calibration of the DMI and calibration verification of the height sensors are addressed in Section 7. 6.1.3. Entering Header Information—The software shall have a menu for entering header information associated with the data collection run prior to collecting data. This information shall be saved in the data file. Table 1 provides some examples of the header information that is typically entered before a data collection run. The owner-agency shall provide the fields that need to be associated with a data collection run in order for the vendor to provide software that will have the fields that are necessary for the owner-agency. Table 1. Typical Header Information. Variable Character Length Type Example Filename 12 AN Wayne12 Project 25 AN Gateway Route 15 AN I-94 Direction 2 A NB Lane 10 AN Outside County 10 AN Wayne Beginning Reference 25 AN Mile Marker 18 Operator 5 A CK Driver 5 A MS Vehicle ID 10 AN 830112 Comment 25 AN New Pavement A = Alphabetic, N - Numeric, AN - Alphanumeric The software shall ensure that the operator enters all required variables. Required numeric variables shall default to ASCII zeros. Alphabetic and alphanumeric variables shall default to blanks. 6.1.4. Data Collection—The software shall provide a set of operational functions that can be selected by the operator in the main menu for initiating and terminating data collection. The software shall provide options to initiate data collection manually or by using the automatic triggering mechanism that initiates data collection when a reflective mark placed on the pavement or on a cone that is placed on the side of the road is detected. The software shall have the capability to terminate data collection manually, after a specified distance has been traveled,

134 Protocols for Network-Level Macrotexture Measurement or when the automatic triggering mechanism detects a reflective mark placed on the pavement or on a cone that is placed on the side of the road. The equipment operation functions shall provide everything necessary for the operator to perform data collection in a user-friendly manner. 6.1.4.1. The macrotexture profile of the data shall be displayed in real time on the computer monitor. For data collected by a single-spot laser, display the macrotexture profile in the direction of travel. For data collected by a line laser or a 3D system, display the data at a specified longitudinal distance interval. 6.1.4.2. The monitor shall display the distance from the location where data collection was initiated. 6.1.4.3. The computed MPD value along the left and the right wheelpaths at 0.16-km (0.1-mile) intervals shall be displayed. 6.1.4.4. The software shall monitor the signals from the data collection system to verify that the testing is being performed properly and display an error message if a problem is detected with a sensor. 6.1.5. Ability to Enter Events—The software shall have a method for marking or recording various points of interest or events during data collection, such as bridges, intersections, etc. The software shall have the ability for the operator to enter pertinent comments entered from the keyboard relating to the testing (e.g., posted speed limit changes, surface changes, bridges, etc.) The software shall accept the operator input data in real time as the vehicle moves down the highway. The corresponding reference point shall be associated with the entered comment. The events and comments shall be saved in the data file. 6.1.6. Saving the Collected Data—The software shall automatically save the raw collected data when data collection is terminated. The start and end time of the data collection run, the distance over which the data were collected, and the average speed during testing shall be stored in the data file in addition to the header information that was described in Section 6.1.3. 6.1.7. Transferring Data—The computer system shall have the ability to transfer the collected macrotexture data files onto suitable high-density removable storage media. 6.1.8. Computation of Macrotexture Indices—The software shall have the capability to process the collected data and compute macrotexture indices such as MPD at user-defined intervals. 6.1.8.1. Before computing a macrotexture index (e.g., MPD), locations that have invalid height- sensor readings (dropouts) shall be replaced using the procedure described in this section. Sometimes the receiver in the sensor will not receive a sufficient intensity of reflected light from the pavement, and such an occurrence is termed a dropout. A valid reading is not obtained at the locations where dropouts occur. Such a situation can occur because of the reflective properties of the pavement surface or because of deep features on the pavement surface (e.g., chip seal surface). Locations where a dropout occurs must be marked in the raw data file. In some cases, a

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 135   single dropout will occur in the data stream, while in other cases, dropouts can occur over a series of connected data points. The invalid readings shall be replaced by interpolating between the first valid measurement before the dropout and the first valid measurement after the dropout. The following scheme shall be used to replace data points at the locations where dropouts occur: Yi = {(Yn – Ym) x (i-m)}/(n-m) + Ym i = sample numbers with invalid readings m = sample number of nearest valid value before i n = sample number of nearest valid value before i Yi = interpolated value for sample i Ym = value of sample m Yn = value of sample n 6.1.8.2. Spikes present in the data shall be removed before computing a macrotexture index (e.g., MPD). A spike is a data point that has a much higher elevation than the surrounding data points. A spike may be caused by a shiny surface, such as a shiny aggregate. Spikes may also be caused by contaminants present on the roadway (e.g., dirt or debris) or by leaves blowing under the sensor during data collection. An appropriate method for removing spikes from the macrotexture data before computing the MSD must be adopted. A relatively simple method for removing spikes is presented in ISO Standard 13473-1. Another approach is the method developed by researchers from Virginia Tech Transportation Institute (Katicha et al. 2015), which can address multiple spikes that are statistically different from most of the data. The method presented in ISO Standard 13473-1 for identifying spikes is presented below. As shown in the equation below, if the absolute difference in elevation between a data point and the point before that is greater than the data interval multiplied by 3, that data point is considered to be a spike. If |Yi – Yi-1| ≥ 3X, then Yi is considered to be a spike. Yi = elevation of point i Yi-1 = elevation of point i-1 X = data interval in mm The above procedure is applied to the raw data profile in the forward and the reverse direction to identify spikes. The identified spike is replaced by the interpolation technique that was described in section 6.1.8.1. If the data for a 100-mm segment that is used to compute the MSD has more than 5% spikes, discard that segment as having invalid data. 6.1.8.3. If the total of data points with dropouts and spikes in a 100-mm segment that is used to compute MSD is more than 10%, discard the segment as having invalid data.

136 Protocols for Network-Level Macrotexture Measurement 6.1.8.4. After addressing dropouts and spikes, compute the desired macrotexture parameter. For computing the MSD, use the procedures presented in ASTM E1845. Thereafter, compute the MPD over the specified distance, typically 0.16 km (0.1 mile), by averaging the MSD values. 6.1.8.5. Before computing the MPD, extreme MSD values can be addressed using the procedure presented in ISO Standard 13473-1 as an option in the software. Extreme MSD values may be caused by debris intersecting the laser light (e.g., leaves), contaminants on the pavement surface (e.g., stones), and so forth. The following are the three-point median filter procedures described in the ISO Standard 13473-1 to eliminate extreme MSD values. The median filter steps through all MSD values, considering three values at a time, replacing each individual value with the median of the three values. This procedure eliminates high or low MSD values. 6.1.9. Generation of Reports: The software shall be capable of generating a report of the computed macrotexture index (e.g., MPD). The index shall be reported at a user-selectable interval, such as 0.16 km (0.1 mile). Index values for each wheelpath as well as the mean computed by averaging the values for the left and the right wheelpath shall be included in the report. The generated report shall include the following items as a minimum at the start of the report: Route. Location of section. Lane. Measurement date. Start and end time of data collection. Type of surface. Comments made by operator (e.g., surface contamination locations, pavement condition that could affect measurements such as excessive cracking and potholes). Average test speed. Table 2 shows a format of the report for MPD. This report presents: MPD at a specified distance interval (e.g., 0.16 km) for each wheelpath and the average value. Percentage of MSD segments (i.e., 100-mm segments) within the 0.16-km length that had dropouts exceeding 10%. Percentage of MSD segments (i.e., 100-mm segments) within the 0.16-km length that had spikes exceeding 5%. Percentage of MSD segments (i.e., 100-mm segments) within the 0.16-km length that had dropouts plus spikes exceeding 10%.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 137   Table 2. Recommended format of the report. From To MPD (mm) Percentage of MSD Segments with: (km) (km) Left Right Mean Dropouts ≥10% Spikes ≥5% Total Invalid 0 0.16 0.16 0.32 0.32 0.48 Note: Total Invalid = Percentage of Segments with Dropouts ≥ 10% + Spikes ≥5% Also provide: Average MPD for the entire data collection run for the left wheelpath, right wheelpath, and the mean value. Standard deviation of MPD for the entire data collection run for the left wheelpath, right wheelpath, and the mean value. Percentage of data points in the data collection run with dropouts. Percentage of data points in the data collection run with spikes. 6.1.10. Exporting Data—The software shall be capable of producing macrotexture data files for data collected by equipment with single-spot lasers in the format described by the University of Michigan Transportation Research Institute as an .ERD file (Sayers and Karamihas 1997). For data collected by line lasers and 3D systems, the software shall be capable of producing an ASCII file where data collected by the line laser at each individual sampling location is provided in a horizontal line in the data at file. The user shall be able to specify a start distance and an end distance in the software to extract data within a specified distance interval, and the software shall be capable of extracting the data corresponding to these limits and create a data file as described previously. 6.1.11. Equipment Shutdown—The operational software shall provide a function to shut down the equipment that is activated via the keyboard. Prior to shutting down, the computer shall save all active parameters to the internal storage media for retrieval the next time the equipment is started up. 7. CALIBRATION AND VERIFICATION OF CALIBRATION OF TRANSDUCERS IN THE EQUIPMENT The software shall have a module for calibrating the DMI of the equipment and for performing a verification check of the height sensors. 7.1. Calibration of the DMI—The software shall have a module for performing a calibration of the DMI in the equipment. The operator shall have the capability to enter the distance of a pre- measured calibration section into the software. Then the operator shall drive over this calibration section where the automatic triggering system in the equipment will be able to detect the start and the end of the section using reflective marks placed on the pavement or on a cone placed on

138 Protocols for Network-Level Macrotexture Measurement the side of the road. Thereafter, the software shall have the capability to automatically compute a calibration factor for the DMI, which is saved. 7.2 Verification of the Height Sensors—The software shall have a module for performing verification checks on the sensors that measure the height. One verification check shall consist of a static test where blocks of known height are placed under the sensor to determine if the system can measure the height of the block within a certain tolerance. The software shall provide the ability to use at least four different gauge blocks of different heights for this check. Gauge blocks needed for this test and other appropriate devices such as a base plate shall be provided with the equipment. The verification check shall also include a test where an object that contains shapes with known dimensions can be moved under the height sensor while the equipment is stationary to determine if the data collection system can measure the features of the object accurately. The vertical accuracy of the calibration surface in relation to its theoretical profile shall be less than 0.05 mm. For equipment with single-spot lasers, a disc-shaped object that contains known dimensions can be rotated under the sensor while the equipment is stationary. The shape of the profile collected by the sensor can be compared to the actual shape of the object to verify that the sensor is functioning properly. The MPD computed based on the shapes in the object can be compared to the MPD computed from the data collected by the measuring system. For verifying a line laser, an object that can be moved under the line laser back and forth can be provided to perform a verification of the sensor using the procedures described previously. Annex G of ISO Standard 13473-1 provides a description of the type of surfaces that can be used for this check. 8. MANUALS, TOOLBOX, AND SPARE PARTS 8.1. The following documents shall be provided with the delivery of the equipment: Two copies of the operating procedures for all operational software. Two copies of the schematic block diagrams and wiring diagrams covering the electronic circuitry of the installed equipment. A list detailing the components associated with the equipment. 8.2. A toolbox that has necessary tools that the operator can utilize to perform repairs on the equipment shall be provided. 8.3. Spare parts that are commonly needed to perform repairs shall be provided with the equipment. 9. KEYWORDS 9.1. Macrotexture, texture, macrotexture profile, texture profile, macrotexture indices, texture indices, Mean Profile Depth, MPD.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 139   10. REFERENCES ISO 13473-2, Characterization of Pavement Texture by Use of Surface Profile - Part 2: Terminology and Basic Requirements Related to Pavement Texture Profile Analysis. ISO 13473-3, Characterization of Pavement Texture by Use of Surface Profile - Part 3: Specification and Classification of Profilometers. ASTM E2157-15, Standard Test Method for Measuring Pavement Macrotexture Properties Using the Circular Track Meter. Goubert, L., and S. Katicha (2018). “Spike Removal from Texture Profiles: A Comparison of Two Approaches.” Proceedings, 8th Symposium on Pavement Surface Characteristics: SURF 2018 (May 2–4, 2018), Brisbane, Queensland, Australia.

140 Protocols for Network-Level Macrotexture Measurement Proposed Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds AASHTO Designation: R X2 1. SCOPE 1.1. This practice describes the procedure for operating and verifying the calibration of equipment that is used to measure pavement macrotexture at highway speeds. The procedures indicated in this standard can be utilized for network-level data collection, as well as project- level data collection. 1.2. This standard practice does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations related to and prior to its use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M X1, [Proposed] Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds. R X3, [Proposed] Standard Practice for Certification of High-Speed Macrotexture Measuring Equipment. R 57, Standard Practice for Operating Inertial Profiling Systems. 2.2. ASTM Standard: E1845, Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth. 2.3. Other Standards ISO Standard 13473-1:2019, Characterization of Pavement Texture by Use of Surface Profiles, Part 1: Determination of Mean Profile Depth. PIARC (2016). “Road Dictionary.” Available at: http://www.piarc.org/en/Terminology- Dictionaries-Road-Transport-Roads/ (accessed January 26, 2019).

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 141   Sayers, M. W., and S. M. Karamihas (1997). ERD File format for storage and analysis of road profiles, University of Michigan Transportation Research Institute, UMTRI-97-51, October 1997. Available at: https://deepblue.lib.umich.edu/bitstream/handle/2027.42/106533/ 102995.pdf?sequence=1&isAllowed=y (accessed January 27, 2019). 3. TERMINOLOGY 3.1. Definitions: 3.1.1. 3D system—a laser system that collects elevation data along the full width of a travel lane. Such transverse profiles are obtained at regular intervals as the host vehicle moves along the road. 3.1.2. Index—within the context of this standard, a suitably chosen index that quantifies the macrotexture of the pavement surface. 3.1.3. Mean Profile Depth (MPD)—an index used to quantify the macrotexture of a pavement surface that is computed by averaging the mean segment depth (MSD) values over a specified distance. The procedure for computing the MPD is described in ASTM E1845. 3.1.4. Mean Segment Depth (MSD)—an index used to quantify the macrotexture of a pavement surface over a distance of 100 mm (4 in.). The procedure for computing the MSD from macrotexture data is described in ASTM E1845. The MSD can be computed over a 100-mm distance for data collected along the travel direction, perpendicular to the travel direction, or at any orientation to the travel direction. 3.1.5. Line Laser—a line laser obtains a series of data points along a line, with the line typically being 100-mm (4-in.) long. The line laser is mounted such that it collects data perpendicular to the travel direction, or at a defined angle from the travel direction. 3.1.6. Macrotexture Profile—the vertical deviations of the pavement surface taken along a line with sufficient detail to capture the macrotexture-relevant features of the pavement surface; the line can be along the direction of travel, perpendicular to the direction of travel, or at any orientation to the direction of travel. 3.1.7. Measurement Range—the detectable range of heights that can be accurately measured by the sensor. 3.1.8. Pavement Macrotexture—according to the World Road Association (Permanent International Association of Road Congress [PIARC]), macrotexture is defined as surface irregularities of a road pavement with horizontal dimensions ranging between 0.5 mm and 50 mm and vertical dimensions between 0.2 mm and 10 mm. 3.1.9. Single-Spot Laser—a laser that projects a spot of light that typically has a diameter of 1 mm (0.04 in.) on to the pavement surface.

142 Protocols for Network-Level Macrotexture Measurement 4. SIGNIFICANCE AND USE 4.1. This practice outlines standard procedures for operating equipment for measuring macrotexture at highway speeds. The macrotexture measurement system may be added to a host vehicle as a single-function device. It can also be added to an inertial profiler that collects longitudinal profile data or be a component of a multifunctional data collection device that collects a variety of other data such as longitudinal profile and distress data. 4.2. The height sensor used to measure macrotexture profile may be a single-spot laser, line laser, or a 3D system. 4.3. Procedures for operating high-speed macrotexture measuring equipment that are applicable to network-level data collection as well as project-level data collection are described in this standard. 4.4. Procedures for calibrating or verifying the calibration of the components in the equipment are presented in this standard. 4.5. In many cases, it is expected that the macrotexture measurement equipment will be housed on the same vehicle that collects longitudinal profile data. The procedures to be followed for longitudinal profile data are described in AASHTO Standard R 57, Standard Practice for Operating Inertial Profiling Systems. The operating procedures described in this standard are in agreement with the operating procedures for inertial profiling systems described in R 57, and none of the operating procedures indicated in this standard will have an impact on the longitudinal profile data that may be collected in conjunction with the macrotexture measurement system. 5. EQUIPMENT 5.1. Minimum Requirements—The macrotexture measuring equipment must meet all requirements and specifications found in AASHTO Standard M X1 and must be currently certified in accordance with AASHTO R X3. Note 1—The host vehicle and all system components shall be in good repair and proven to be within the manufacturer's specifications. The operator of the macrotexture equipment shall have all tools and components necessary to adjust and operate the equipment following the manufacturer's instructions. 5.2. Repair, Adjustment, and Upgrade of Equipment 5.2.1. Major component repairs or replacement to a macrotexture measuring system that would require the recertification of the equipment include, but are not limited to, the following: The non-contact height sensor and its associated hardware. Any printed circuit board necessary for the collection of raw sensor data. Change of the host vehicle. Replacement of Distance Measuring Instrument (DMI).

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 143   5.2.2. The operator of the macrotexture equipment will be allowed to make minor adjustments to the equipment without having to complete the recertification process, as long as the adjustments allow the equipment to fulfill the verification of calibration that is described in Section 5.3. Minor adjustments to the system include, but are not limited to, the following: Inspecting, resoldering, or replacing connectors. Cleaning components, and normal adjustments to power supply voltage levels as required by the manufacturer. Setting software parameters and/or scale factors as required by the manufacturer in a routine calibration procedure. 5.3. Verification of Calibration—The components in the equipment that require verification of calibration are the Distance Measuring Instrument (DMI) and the height sensors. Verification of calibration of these components shall be performed at a minimum interval of 30 days, and when problems are suspected. 5.3.1. Verification of Calibration of the DMI—A straight and level roadway test section that is at least 161 m (528 ft.) long with sufficient lead-in distance for the vehicle to attain a constant speed before the start of the test section and a safe stopping distance after the end of the test section is required for the verification of calibration of the DMI. A test section that is 304.8-m long (1,000 ft.) is preferred. Layout the test section using a non-stretching measurement tape since the distance to be measured is the travel length the wheels of the host vehicle encounter. Check the cold tire air pressure, and adjust as needed to comply with the vehicle manufacture’s recommended value. Warm-up the tires before performing the verification test. Warm-up the equipment following the manufacture’s recommendations. Drive over the test section. The length of the test section determined from the DMI system in the equipment must be within 0.15 percent of the actual length of the test section. If the specified criterion is not met, calibrate the DMI using the manufacturer’s guidelines. Repeat calibration until the measured length of the test section is within 0.15 percent of the actual length of the test section. If this criterion cannot be met, contact the manufacturer and decide on a course of action to repair the DMI 5.3.2. Verification of Height Sensors—A static block height test and a stationary dynamic test as described in the following sections shall be performed on the height sensors for verification of the calibration of the height sensors. 5.3.2.1. Block Test—The static block height test shall be performed in accordance with the manufacturer's recommended procedures. In the absence of manufacturer's procedures, perform the block test described in this section. The height sensor check tests are run while the equipment is stationary after the equipment has reached operational stability as specified by the manufacturer. This test shall be conducted with the host vehicle parked on a relatively flat and level area. The purpose of the test is to verify that the measuring system in the equipment can accurately measure the height of blocks that are

144 Protocols for Network-Level Macrotexture Measurement placed under the sensor while the vehicle is stationary. During the test, do not lean on the vehicle or cause it to move in any way. Under windy conditions, it may be necessary to perform this test indoors. Use the base plate and gauge blocks provided with the equipment to perform this test. The thickness of the gauge blocks is determined by measuring the thickness at three different positions on each side of the block with a device capable of measuring to the nearest 0.00004 (0.001 in). For each block, an average thickness shall be determined from the measurements made, which shall be used in checking the height sensors as described in this test. The average thickness shall be marked on each gauge block. The test procedure consists of the following steps: 1. Position a smooth base plate under the height sensor of the equipment, level the plate, and take height measurements on the base plate. 2. Position a 6-mm (0.25-in.) block underneath the height sensor on top of the base plate, and take height-sensor measurements on the top of the block. 3. Carefully remove the 6-mm (0.25-in.) block from the base plate and replace it with a block having a height of 12 mm (0.50 in.). Obtain measurements on top of the 12-mm (0.5-in.) block. 4. Carefully remove the 12-mm (0.50-in.) block from the base plate and replace it with a block having a height of 25 mm (1 in.). Obtain measurements on top of the 25-mm (1-in.) block. 5. Carefully remove the 25-mm (1-in.) block from the base plate and replace it with a block having a height of 50 mm (2 in.). Obtain measurements on top of the 50-mm (2-in.) block. At a minimum, test a base plate and the 25-mm (1-in.) and 50-mm (2-in.) blocks. If the equipment fails the specified requirements for the minimum test, then perform the full range of tests to determine system linearity problems, standoff problems, or complete system failure. Determine the difference between each measurement on a gauge block and the measurement on the base plate to obtain the thickness of the gauge block as measured by the measuring system in the equipment. Repeat this calculation for each gauge block. The software on the equipment may have the capability to these computations automatically and display the measured height of each block. Determine the absolute values of the differences between the computed block thickness and the known average block thickness. The absolute difference should be less than or equal to 0.25 mm (0.01 in.) for each gauge block. If the specified tolerance is not met for any gauge block, repeat the test until two consecutive tests pass. If the specified requirement cannot be achieved on any block, contact the manufacturer to resolve the issue.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 145   The operator of the equipment should tabulate the measurements and record them in a calibration log. 5.3.2.2. Dynamic Test—The dynamic test to verify the accuracy of the height sensors consists of moving a calibration surface that contains shapes with known dimensions under the height sensor while the equipment is stationary to verify that the measuring system in the equipment will be able to capture the shapes on the object accurately. This test shall be performed in accordance with the manufacturer's recommended procedures. The vertical accuracy of the calibration surface in relation to its theoretical profile shall be less than 0.05 mm. For equipment with single-spot lasers, a disc-shaped object that contains known dimensions can be rotated under the height sensor while the equipment is stationary. The shape of the profile collected by the sensor can be compared to the actual shape of the object to verify that the sensor is functioning properly. The MPD computed based on the shapes in the object can be compared to the MPD computed from the data collected by the measuring system. For verifying a line laser, an object that can be moved under the line laser back and forth can be used to perform a verification of the sensor using the procedures described previously. Annex G of ISO Standard 13473-1 provides a description of the type of surfaces that can be used for this check. Maintain a log to be kept within the vehicle that documents the results from this test. 6. DATA COLLECTION PROCEDURE 6.1. Network-Level Data Collection—Use the procedures described in Table 1 to measure network-level macrotexture. 6.2. Project-Level Data Collection—Follow procedures described in Table 1 when measuring project-level macrotexture. When surveying new construction at the project level to verify the macrotexture of the newly constructed pavement, clean the roadway before data collection if debris or any loose material are present on the roadway. 7. QUALITY CONTROL CHECKS ON THE COLLECTED DATA 7.1. Review of Computed Macrotexture Indices—At the end of each day, generate a report of the selected macrotexture index (e.g., MPD) at 161-m (0.1-mile) intervals (see section 6.1.9 of AASHTO Standard M X1, [Proposed] Standard Specification for Equipment for Measuring Macrotexture on Pavements at Highway Speeds for format of such a report). Review the computed values for reasonableness. 7.2. Control Sections—For network-level data collection, set up several control sections within the state that are at least 161-m (528-ft.) long before collecting network-level data. These control sections should have a range of MPD values. Measure macrotexture on these sections using equipment that has been certified within 90 days. Perform five data collection runs at each test section and compute the average MPD for each wheelpath to establish the baseline MPD for each control section. Once established, the control sections can be used to validate if the equipment is functioning properly on a regular basis. Typically, no single MPD along a wheelpath shall vary by more than 5 percent of the baseline MPD.

146 Protocols for Network-Level Macrotexture Measurement If a vendor is collecting network-level macrotexture data for an agency, and the agency also has equipment that can measure macrotexture, both the vendor and the agency should collect data at the control sections. The MPD values obtained by both parties’ equipment should be compared and must agree within 10 percent. If different, investigate to determine which equipment is not accurate by comparing collected data with data collected by a reference device (see AASHTO Standard R X3, [Proposed] Standard Practice for Certification of High-Speed Macrotexture Measurement Equipment. Table 1. Collection of Network-Level or Project-Level Macrotexture Data. Step Action 1 Check the cold tire pressure each day to ensure they meet the vehicle manufacturer's recommended value. If different, adjust tire pressure as differences in tire pressure will affect the measured distance. It is recommended that a static block check be performed using a 25-mm block on each height sensor following the procedures described in Section 5.3.2.1 before starting data collection each day. The height of block measured by the measuring system must be within 0.25 mm of the actual height of the block. 2 Warm-up equipment following manufacturer's recommendations before collecting data. 3 Make sure the lateral spacing between the height sensors is set according to agency guidelines, and each height sensor is equidistant from the center of the vehicle. 4 Enter all necessary header information into the software before collecting data. 5 Verify data collection is initiated at the correct location. 6 Drive along the center of the lane. 7 Collect data on dry pavement. Collecting data on damp pavement with no standing water is acceptable if it has been demonstrated that the height sensors can collect accurate data on damp pavements. 8 Try and maintain a constant speed by use of cruise control. Operate equipment within the speed range recommended by manufacturer. (Note 2) 9 Avoid rapid acceleration and deceleration. (Note 3) 10 If the manufacturer has specified a speed range for collecting macrotexture data, mark locations where the speed is outside the valid range so that data will not be used for computing macrotexture indices. 11 Monitor system warnings indicating a problem in the height sensor or the data collection system. Enter any relevant event information or comments during data collection as described in Section 6.1.5 of AASHTO M X1 [Proposed] Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds. 12 Monitor MPD values reported at 161-m (528-ft.) intervals to see if they are reasonable based on operator's experience for that surface type. Unreasonable MPD values could be due to equipment problems. Note 2—Equipment for measuring macrotexture may be able to collect accurate data at low speeds and even when coming to a complete stop. If an accelerometer is used in conjunction with the height sensor that measures macrotexture to adjust for vehicle movement, the accelerometer will not be able to collect accurate data below a specified lower speed limit. Note 3—Acceleration and deceleration may not have a noticeable effect on the quality of the macrotexture data that are being collected. However, if host vehicle is equipped with an inertial profiling system, rapid acceleration and braking can affect the longitudinal profile data.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 147   If an agency is measuring the macrotexture, and the equipment comes back to the office every weekend, establish at least two verification or control sections close to the office. One test section should have a low MPD (e.g., typically 0.6 mm) and the other sections should have a high MPD (e.g., typically 1.2 mm). Obtain measurements on the two verification sections every week before the equipment goes out to collect network-level data, and compare the obtained MPD values with baseline MPD values (determined as described in Section 7.2) at these control sections. The MPD values should not differ by more than 5 percent from the baseline values. Also, use this procedure if the equipment is only used to collect project-level data. 8. QUALITY ASSURANCE 8.1. Agencies using this standard practice are required to develop a satisfactory Quality Assurance (QA) plan. At a minimum, the plan shall include the requirements listed in the following sections (Pierce at al. 2013): 8.1.1. Qualification and training records of individuals operating the equipment. 8.1.2. Accuracy, repeatability, and calibration records of equipment used for data collection. 8.1.3. Periodic and ongoing quality control program and the content of the program. Note 4—The guidelines that can be used for the development of a Quality Assurance (QA) plan are provided in Appendix A. 9. KEYWORDS 9.1. Macrotexture, Macrotexture Data Collection, Mean Profile Depth, MPD. 10. REFERENCES Pierce, L. M., G. McGovern, and K. A. Zimmerman (2013). Practical Guide for Quality Management of Pavement Condition Data Collection. Federal Highway Administration, U.S. Department of Transportation.

148 Protocols for Network-Level Macrotexture Measurement APPENDIX A: GUIDELINES - QUALITY ASSURANCE PLAN A1.1. Quality Assurance (QA) Plan—Each agency shall develop a QA plan. The plan shall include survey personnel certification training records, accuracy and repeatability of equipment, daily quality control (QC) procedures, and periodic and ongoing QC activities. The following guidelines can be used for developing such a plan. A1.2. Certification and Training—Agencies are individually responsible for training and/or certifying their data collection personnel for proficiency in using the macrotexture measuring equipment according to this standard practice and other applicable agency procedures. The agencies should also implement a certification program to certify equipment that measures macrotexture at least annually to ensure repeatability and accuracy of the equipment. AASHTO Standard R X3, [Proposed] Standard Practice for Certification of High-Speed Macrotexture Measurement Equipment, describes procedures for the certification of equipment for measuring macrotexture. A1.3. Equipment Calibration—Verification of calibration of the DMI and the height sensors shall be done in accordance with manufacturer’s recommendations. The equipment must operate within the parameters specified in the manufacturer's specifications. A regular maintenance and testing program should be established for the equipment in accordance with the manufacturer's recommendations. A1.4. Verification Sections—Verification sections should be measured by the equipment on a regular basis. A baseline measurement should be obtained on the verification sections before starting data collection for the year. Evaluations of these measurements can provide information about the accuracy of field measurements and give insight into needed equipment calibration. A1.5. Quality Checks—Additional quality checks can be made by comparing the most recent historical MPD values with current measurements. At locations where large changes occur, the person in charge of data collection may require additional checks of the data.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 149   Proposed Standard Practice for Certification of High-Speed Macrotexture Measurement Equipment AASHTO Designation: R X3 1. SCOPE 1.1. This practice describes a certification procedure for equipment used to measure macrotexture of pavements at highway speeds. The minimum requirements stipulated in this standard are intended to verify that the equipment can collect repeatable and accurate macrotexture data at the project and network level. 1.2. This practice does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to its use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M X1, [Proposed] Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds. R X2, [Proposed] Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds. 2.2. ASTM Standard: E1845, Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth. 2.3. Other Documents: PIARC (2016). “Road Dictionary.” Available at: http://www.piarc.org/en/Terminology- Dictionaries-Road-Transport-Roads/ (accessed January 26, 2019). ISO Standard 13473-1:2019, Characterization of Pavement Texture by Use of Surface Profiles, Part 1: Determination of Mean Profile Depth.

150 Protocols for Network-Level Macrotexture Measurement 3. TERMINOLOGY 3.1. Definitions: 3.1.1. 3D System—a laser system that collects elevation data along the full width of a travel lane. Such transverse profiles are obtained at regular intervals as the host vehicle moves along the road. 3.1.2. Mean Profile Depth (MPD)—an index used to quantify the macrotexture of a pavement surface that is computed by averaging the MSD values over a specified distance. The procedure for computing the MPD is described in ASTM E1845. 3.1.3. Mean Segment Depth (MSD)—an index used to quantify the macrotexture of a pavement surface over a distance of 100 mm (4 in.). The procedure for computing the MSD from macrotexture data is described in ASTM E1845. The MSD can be computed over a 100-mm distance for data collected along the travel direction, perpendicular to the travel direction, or at any orientation to the travel direction. 3.1.4. Line Laser—a line laser obtains a series of data points along a line, with the line typically being 100-mm (4-in.) long. The line laser is mounted such that it collects data perpendicular to the travel direction, or at a defined angle from the travel direction. 3.1.5. Pavement Macrotexture—according to the World Road Association (Permanent International Association of Road Congress [PIARC]), macrotexture is defined as surface irregularities of a road pavement with horizontal dimensions ranging between 0.5 mm and 50 mm and vertical dimensions between 0.2 and 10 mm. 3.1.6. Single-Spot Laser—a laser that projects a spot of light that typically has a diameter of 1 mm (0.04 inches) on to the pavement surface. 4. SIGNIFICANCE AND USE 4.1. This practice describes a certification procedure for equipment that is used to measure macrotexture of pavements at highway speeds. Such equipment may be equipped with single- spot lasers, line lasers, or a 3D system for collecting the elevation data. The certification of equipment is aimed at verifying that the equipment can collect repeatable and accurate macrotexture data at project level and network level. In this practice, the MPD is used as the macrotexture index that is used to assess the repeatability and accuracy of the equipment. 5. EQUIPMENT 5.1. Minimum Requirements—The high-speed macrotexture measuring equipment shall meet all requirements and specifications found in AASHTO Standard MX1, [Proposed] Standard Specification for Equipment for Measuring Macrotexture of Pavements at Highway Speeds. 5.2. The software in the equipment must be capable of calculating and reporting MPD from data collected at test sections.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 151   5.3. The equipment must be equipped with a trigger that can automatically initiate and terminate data collection from reflective tape placed on the pavement surface or on a cone placed on the side of the road. 6. VERIFICATION OF CALIBRATION OF THE HEIGHT SENSORS AND THE DISTANCE MEASURING INSTRUMENT 6.1. Height Sensors—The first step of certification of the equipment is evaluating the ability of the equipment to pass the static block check and the stationary dynamic test that are described in Section 5.3.2 of AASHTO Standard R X2. The operator of the equipment shall be asked to perform the static block check and the stationary dynamic test according to the procedures described in Section 5.3.2 of AASHTO Standard R X2. The equipment must pass the block test by satisfying the specified criterion in AASHTO Standard R X2. The equipment must pass the stationary dynamic test by satisfying the criterion specified by the manufacturer. The equipment must pass both of these tests in order to proceed with the equipment certification procedures outlined in Section 7 of this standard. If equipment fails the block check, or the stationary dynamic test, or both tests, the operator should work with the manufacturer to adjust or repair the equipment such that the equipment will be able to pass both of these tests. 6.2. Distance Measurement Instrument (DMI) Test—The equipment must pass this test in order to proceed with the equipment certification procedures outlined in Section 7 of this standard. Check the accuracy of the DMI using the procedures described in this section. 6.2.1. Establish a test section that is at least 305-m (1,000-ft.) long for performing this test, with sufficient lead-in distance for the vehicle to attain a constant speed of 80 km/h (50 mph) before the start of the section and a safe stopping distance after the end of the section. Measure the distance between the starting and ending points with a measurement tape, pulled taut but following the pavement contour. Mark the starting and ending points of the test section. 6.2.2. Perform five repeat runs at the test section using the equipment by initiating and terminating data collection using the auto trigger, which is triggered at the start and the end of the test section by reflective tape placed on the pavement or by a cone with reflective tape that is placed on the side of the road. Maintain a constant speed of 80 km/h (50 mph) when traversing the test section. Record the distance of the test section that was determined by the DMI at the end of each run. 6.2.3. Distance Measurement Index (DMI) Accuracy—Compute the absolute difference between the DMI reading and the known distance of the test section for each run. The average of the absolute differences must be less than 0.15 percent of the length of the test section (i.e., 0.458 m for a 305-m long test section). 6.2.4. If the equipment is not able to meet this requirement, calibrate the DMI of the equipment using the manufacturer’s guidelines. Repeat steps 6.2.2 and 6.2.3. If the equipment is still not able to meet the requirement outlined in Section 6.2.3, the operator should work with the

152 Protocols for Network-Level Macrotexture Measurement manufacturer to adjust or repair the equipment such that the equipment will be able to pass the test. 6.3. Calibration Verification Log—Maintain a log that is to be kept with the equipment to provide a verification of calibration history. The results from the verification of height-sensor tests that are required to be performed at a minimum interval of 30 days (see Section 5.3.2 of AASHTO Standard R X2, [Proposed] Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds) should also be included in this log. The log should contain a record of any repairs, replacement of components, and changes in native software versions. If the log is electronic, a backup copy shall be kept in a secure location. 7. EQUIPMENT CERTIFICATION 7.1. Certification frequency shall be as specified by the owner-agency. It is recommended that the certification of equipment be performed at least annually. The macrotexture data collection equipment must successfully perform and pass the certification tests described in this section for repeatability and accuracy. The equipment shall be recertified after any major component repairs or replacements as described in Section 5.2.1 of AASHTO R X2, [Proposed] Standard Practice for Operating Equipment for Measuring Macrotexture at Highway Speeds. 7.2. Certification Testing—Certification testing shall be conducted at test sections established by the owner-agency. Reference data at the test sections will be collected using a suitable reference device, and the types of reference devices that can be used are described in this section. 7.3. Test Sections—The number of test sections to be used for certification shall be decided by the Owner-Agency. It is recommended at least two test sections be established on the surface type that is most common in the agency’s highway network (e.g., dense-graded asphalt concrete, open-graded friction course, stone-matrix asphalt). One of the test sections should have a low MPD and the other a high MPD based on the range of MPD values that are typically observed for that surface type. If the agency’s highway system contains concrete pavements that have a longitudinal texture (e.g., longitudinal tining, longitudinal diamond grinding), it is recommended that a test section also be established on this surface type. If the Owner-Agency has sufficient resources, it is recommended test sections to be established on all surface types on which the equipment is expected to collect data. Note 1—Research has shown equipment with single-spot laser sensors cannot collect accurate macrotexture data on surfaces that have a longitudinal texture (e.g., longitudinal tining, longitudinal diamond grinding). Therefore, certification of equipment with single-spot lasers on surfaces that have a longitudinal texture should not be performed. Each test section shall be 161 m (528 ft.) in length, with a sufficient lead-in distance to attain a speed of 80 km/h (50 mph) before the start of the test section and a safe stopping distance after the end of the test section. If testing is desired at a higher speed, establish the test sections such that testing can be safely performed. Test sections with significant horizontal curvature or superelevation should be avoided.

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 153   7.4. Reference Data Collection—Reference data at the test sections should be collected with a suitable reference device that has the capability to compute the MPD from the collected data. 7.4.1. Reference Devices—Reference devices for measuring pavement macrotexture that are currently available can be categorized as: (1) walk-along devices or (2) stationary devices. This standard covers only the walk-along devices. Select a reference device based on manufacturer’s documentation that shows the device is capable of collecting accurate macrotexture data. Such documentation can include test results where the equipment has collected data on artificial calibration surfaces with known shapes, where the data collected by the device has matched the actual shapes present on the calibration surface. A walk-along reference device is pushed along the test section at walking speed and will collect macrotexture data at specified data collection intervals. Such equipment may be equipped with a single-spot laser or a line laser. In the case of equipment with a single-spot laser, the equipment will collect data along the travel direction. Such equipment shall be capable of collecting data at intervals of 1 mm or less. For equipment with a line laser, data transverse to the travel direction will be collected at specified longitudinal distance intervals. Such equipment must be capable of collecting data along a transverse line at a longitudinal distance interval not exceeding 25 mm. Note 2—A walk-along reference device that is equipped with a single-spot laser will not be able to capture the shape of the texture on pavements that have longitudinal texture (e.g., longitudinal tining, longitudinal diamond grinding). Therefore, such a device should not be used to collect data on pavements that have a longitudinal texture. 7.4.2. Data Collection—Use procedures presented in this section to collect the reference macrotexture data at the test sections. Based on owner-agency guidelines, locate the left and right wheelpaths for testing. The transverse distance between the two wheelpaths must match the sensor spacing specified by the Owner-Agency for the high-speed macrotexture equipment. Push the walk-along device along the specified wheelpath within the test section to collect the macrotexture data. For devices equipped with a line laser, the center of the line projected onto the pavement must traverse along the specified path. Obtain five repeat measurements along each wheelpath. Compute the standard deviation of MPD for each wheelpath from the MPD obtained for the five runs. The standard deviation of MPD for each wheelpath should be less than or equal to 0.01 mm when rounded to two decimal places. If the standard deviation exceeds this value, evaluate the data and obtain additional runs until five runs that meet the specified standard deviation are obtained. Use the MPD values for the repeat runs to compute the average MPD. If more than five runs were obtained, use the five selected runs that provided a standard deviation of MPD of less than or equal to 0.01 mm to compute the average MPD. Note 3—When obtaining measurements on pavements having longitudinal texture (e.g., longitudinal tining, longitudinal diamond grinding) orient the device as needed such that the device will capture the shape of the longitudinal texture.

154 Protocols for Network-Level Macrotexture Measurement 7.5. Data Collection with High-Speed Macrotexture Equipment—Ensure that the sensor spacing in the equipment match the value specified by the Owner-Agency, and that each sensor is equidistant from the center of the vehicle. Obtain five repeat runs at each test section at a speed of 80 km/h (50 mph) with the vehicle aligned such that the sensors will obtain measurements along the path where reference data were collected. Data collection shall be initiated and stopped using the automatic triggering device in the equipment. Produce a report that shows the MPD of each wheelpath for each run at all test sections. 7.6. Repeatability—The repeatability of the equipment is determined by evaluating the standard deviation of MPD for each wheelpath at each test section. Use the MPD computed for the five runs along each wheelpath at each test section to compute the standard deviation of MPD for the equipment at each test section. The standard deviation of MPD along each wheelpath at all test sections should be less than 0.04 mm. If the equipment is able to meet this criterion for both wheelpath at all test sections, the equipment is considered to have passed the repeatability criterion. 7.7. Equipment Accuracy—Evaluate the accuracy of the equipment using the procedures described in this section. 7.7.1. Reference data collected using a walk-along device: For each wheelpath at each test section, compute the average MPD for the reference device for a wheelpath by averaging the MPD values obtained for the five runs as described in Section 7.4.2. For the high-speed equipment, for each wheelpath at each test section, compute the average MPD for a wheelpath by averaging the MPD values obtained for the five runs. For each wheelpath at each test section, the average MPD computed from the high-speed equipment data must be within 10 percent of the average MPD computed from the reference device data. 7.8. Passing Certification—If the equipment is able to pass the repeatability and the accuracy criterion described in Sections 7.6 and 7.7 for data collected along both wheelpaths at all test sections, the equipment has passed certification by demonstrating that the equipment can collect repeatable and accurate data. Note 4—If a single-spot laser passes certification on surfaces that have isotropic texture (i.e., same properties in all directions) this does not mean this equipment will be able to collect repeatable and accurate data on pavement surfaces that have texture in the longitudinal direction (e.g., longitudinal tining, diamond grinding). As described previously, research has shown that equipment with single-spot laser sensors cannot collect accurate macrotexture data on pavement surfaces that have texture in the longitudinal direction. Note 5—If one sensor passes the repeatability and accuracy criterion and the other sensor fails the repeatability criterion, accuracy criterion, or both criterion this may be an indication that there is a problem with that sensor. 7.9. Test Results—The results of the certification tests shall be documented by the testing agency. Results of certification shall include the following information:

Draft American Association of State Highway and Transportation Officials (AASHTO) Protocols 155   Identification of the equipment tested (i.e., make, model serial number, software version, owner). Date of last certification. Date of current certification. Operator of the high-speed equipment. Name of the individuals from the testing agency who conducted the test. Known longitudinal distance of the DMI test section and the average absolute difference between the DMI readings and the known distance, expressed in distance unit and as a percentage of the known longitudinal distance. Repeatability results: Standard deviation of MPD for each wheelpath at all test sections. Accuracy results: For each wheelpath at each test section report the following values: average MPD from the high-speed equipment, average MPD from the reference device, percentage difference of equipment MPD from the reference MPD. Overall determination from the test: Pass or Fail. A decal or other approved marking shall be placed on the equipment as evidence of certification. This decal shall show the expiration date (month and year) of the certification. 8. OPTIONAL TESTS 8.1. This section describes some optional tests that can be performed on the equipment to evaluate the capabilities of the equipment. 8.2. This section describes tests that can be performed to determine the influence of the following factors on the MPD computed from the collected data: operating at different constant speeds, effect of speed changes, and effect of coming to a stop. 8.2.1. Effect of speed on the collected data—Establish a test section that is at least 161 m (528 ft.) long. Obtain three repeat runs at the following speeds: 16, 32, 48, 64, 80, 96, and 112 km/h. Average the MPD from the repeat runs at each speed for each wheelpath. Compare the average MPD obtained at each speed to evaluate if relatively constant MPD values were obtained at all speeds or if there appears to be a relationship between MPD and testing speed (e.g., MPD increasing with testing speed). 8.2.2. Effect of changes in vehicle speed on the collected data: Establish a 305-m (1,000-ft.) long test section. Obtain three repeat runs at a constant speed of 80 km/h (50 mph), and compute the MPD of each wheelpath for each run. Average the results to obtain an average MPD for each wheelpath. Perform the following tests: (a) Enter the test section at 80 km/h (50 mph) and apply the brakes such that speed is reduced to about 40 km/h (25 mph) at the middle of the test section, then continue on until the end of the test section at a speed of 40 km/h (25 mph). This test is aimed at evaluating the effect of braking on MPD. (b) Enter the test section at 40 km/h (25 mph) and travel at this speed until approximately the center of the test section. Then accelerate such that a speed of 80 km/h (50 mph) is attained

156 Protocols for Network-Level Macrotexture Measurement approximately at the end of the test section. This test is aimed at evaluating the effect of acceleration on MPD. (c) Enter the test section at a speed of 80 km/h (50 mph) and apply the brakes such that speed is reduced to about 40 km/h (25 mph) at the middle of the test section. Then accelerate to reach a speed of 80 km/h (50 mph) approximately at the end of the test section. This test is aimed at evaluating the effect of braking followed by acceleration on MPD. (d) Enter the test section at a speed of 80 km/h and apply the brakes such that the vehicle comes to a complete stop at approximately the center of the test section. Thereafter, accelerate to reach a speed of 80 km/h approximately at the end of the test section. This test is aimed at evaluating the effect of a stop on the collected data. For each of the above cases, compute the MPD from the collected data for each wheelpath for the entire test section. Compare the obtained MPD with the average MPD computed from the data collected for the constant speed runs performed at 80 km/h. This comparison will provide information about how the MPD is affected by braking, acceleration, braking followed by acceleration, and coming to a complete stop. 8.3. Another test that can be performed to evaluate the performance of the equipment is to drive the vehicle over an object that is placed on the pavement that has features of known dimensions machined onto the surface. This test is similar to the stationary dynamic test described in Section 6.1 except that the equipment will collect data over the object at a high-speed. Annex G of ISO Standard 13473-1:2019 provides examples of artificial surfaces that can be used to perform the test. The object should be placed on the pavement such that the tires of the vehicle will not drive over it (i.e., place object at the center of the vehicle). For single-spot and line lasers, the sensor must have the capability of being moved to the center of the vehicle. After collecting data, compare the shapes of the features on the object that is measured by the equipment with the actual shapes on the object. 9. KEYWORDS 9.1. Macrotexture Data, Texture Data, Mean Profile Depth, MPD, Certification.

Abbreviations and acronyms used without denitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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