ASTM E950_E950M-22.pdf

Designation: E950/E950M − 22

Standard Test Method for Measuring the Longitudinal Profile of Traveled Surfaces1

This standard is issued under the fixed designation E950/E950M; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.

A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This standard is device independent. Measurements may

be made by any device capable of producing a suitable longitudinal elevation profile for the vehicular traveled surface.

However, cellular phone-based road rating devices are not applicable. The vehicle-based profiling device, commonly described as the “inertial profiler,” is used as an example of one such device.

1.2 Elevation measurements may be used to validate or

certify a profiling device or to determine its suitability for a particular application by comparing measurements produced by a profiling device, called a candidate Production Class profiler, with measurements produced by a reference profiling device, called a Reference Class profiler. To conduct profile measurements for a particular application, the calculated pro-file shall meet the accuracy and repeatability requirements specified herein for that particular application or class. The selection of proper filtering allows the user to obtain suitable wavelength information for the intended application. For example, for application for road roughness evaluation, the precision and bias are determined using the cross-correlation method after filtering using the International Roughness Index (IRI) filter (1).2

1.3 The values stated in either SI units or inch-pound units

are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.

1.4 This standard 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 standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.

Specific precautionary information is given in Section 7.

1.5 This international standard was developed in accor-

dance with internationally recognized principles on standard-ization established in the Decision on Principles for the Development of International Standards, Guides and Recom-mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents

2.1 ASTM Standards:3

E178 Practice for Dealing With Outlying Observations E867 Terminology Relating to Vehicle-Pavement Systems E1489 Practice for Computing Ride Number of Roads from

Longitudinal Profile Measurements Made by an Inertial Profile Measuring Device

E1926 Practice for Computing International Roughness In-dex of Roads from Longitudinal Profile Measurements

E2560 Specification for Data Format for Pavement Profile F457 Test Method for Speed and Distance Calibration of

Fifth Wheel Equipped With Either Analog or Digital Instrumentation

2.2 AASHTO Standards:4

AASHTO R 56 Standard Practice for Certification of Inertial Profiling Systems

AASHTO R 57 Standard Practice for Operating Inertial Profiling Systems

AASHTO PP 106 Standard Practice for Assessment of Static Performance in Transverse Pavement Profiling Systems

AASHTO PP 107 Standard Practice for Assessment of Body Motion Cancellation in Transverse Pavement Profiling Systems

AASHTO PP 108 Standard Practice for Assessment of Navigation Drift Mitigation in Transverse Pavement Pro-filing Systems

AASHTO PP 109 Standard Practice for Assessment of Highway Performance of Transverse Pavement Profiling Systems

1 This test method is under the jurisdiction of ASTM Committee E17 on Vehicle

- Pavement Systems and is the direct responsibility of Subcommittee E17.31 on Methods for Measuring Profile and Roughness.

Current edition approved Nov. 1, 2022. Published November 2022. Originally approved in 1983. Last previous edition approved in 2018 as E950/E950M – 09

(2018). DOI: 10.1520/E0950_E0950M-22.

2 The boldface numbers in parentheses refer to the list of references at the end of this standard.

3 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.

4 Available from American Association of State Highway and Transportation Officials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001, http://www.transportation.org.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

MICHIGAN STATE DEPT. OF TRANSPORTATION CONSTRUCTION & TECH DIVISION pursuant to License Agreement. No further reproductions authorized.

Downloaded/printed by Copyright by ASTM Int'l (all rights reserved) Mon Aug 19 15:12:28 UTC 2024 https://doi.org/10.1520/E0178 https://doi.org/10.1520/E0867 https://doi.org/10.1520/E1489 https://doi.org/10.1520/E1489 https://doi.org/10.1520/E1489 https://doi.org/10.1520/E1926 https://doi.org/10.1520/E1926 https://doi.org/10.1520/E2560 https://doi.org/10.1520/F0457 https://doi.org/10.1520/F0457 https://doi.org/10.1520/F0457 http://www.astm.org/COMMIT/COMMITTEE/E17.htm http://www.astm.org/COMMIT/SUBCOMMIT/E1731.htm

AASHTO PP 110 Standard Practice for Assessment of Ground Reference Data for Transverse Pavement Profiling System Assessment

AASHTO PP 111 Standard Practice for Definition of Terms Related to Transverse Pavement Profiling Systems and Ground Reference Equipment

3. Terminology

3.1 Definitions:

3.1.1 accelerometer, n—a sensor that measures acceleration.

Data processing algorithms convert the vertical acceleration measure to an inertial reference that defines the instant height of the accelerometer in the host vehicle.

3.1.2 aliasing, v—in the context of this standard, the spec-trum of a digitized data record exists over the range of frequencies from zero to one half the sampling frequency.

Suppose the spectrum of the original signal extends beyond one half the sampling frequency. In that case, those compo-nents of the signal at frequencies higher than one half the sampling frequency will, when digitized, be folded back into the spectrum of the digitized signal. The excessively high-frequency components will thus be “aliased” into low-frequency components.

3.1.3 anti-aliasing filter, n—low-pass analog filter applied to the original analog profile signal to suppress those signal components at frequencies higher than one half the intended digital sampling frequency.

3.1.4 bias, n—the degree of cross-correlation between a candidate Production Class profiler and a Reference Class profiler (that is, accuracy).

3.1.5 carriage, n—a platform for mounting the profile-measuring equipment.

3.1.6 cross-correlation, n—an indicator of agreement be-tween two series of profile elevation measurements. A cross-correlation value of 1.0 indicates perfect agreement. A cross-correlation value of 0.0 indicates no agreement.

3.1.7 inertial profiler, n—the combination of the inertial profiling equipment and the host vehicle.

3.1.8 IRI waveband, n—slope profile with frequency

weighting determined by the quarter-car filter using the Golden Car Simulation at a standard speed of 80 kph. E1926

3.1.9 long waveband, n—band pass filter with cutoffs at 90 m [300 ft] and 8 m [26 ft] with optional longer wavelength cutoffs for airfield application.

3.1.9.1 Discussion—Longer wavelength cutoffs may be

specified for airfield applications.

3.1.10 medium waveband, n—band pass filter with cutoffs at 8 m [26 ft] and 1.6 m [5 ft].

3.1.11 phase shift, n—the distance offset between elevation points from two profiles.

3.1.12 precision, n—the degree of cross-correlation between a series of repeat profile elevation measurements conducted with the same device (that is, repeatability).

3.1.13 production class profiler, n—a production device used to collect profiles for construction project acceptance or road network surveys.

3.1.14 profile record, n—data record of arbitrary length of the surface elevation, slope, or acceleration.

3.1.15 profile segment, n—that part of a profile record for which the profile index will be calculated.

3.1.16 profile trace, n—that part of a profile record for which the measurement is made along the desired line.

3.1.17 recording interval, n—the longitudinal distance be-tween recorded data points.

3.1.18 reference class profiler, n—a device used to collect reference profiles for qualifying a candidate Production Class profiler.

3.1.19 reference profile, n—a series of profile elevation records deemed correct for a given segment of the traveled surface.

3.1.20 sampling rate, n—the rate at which the height sensor measures vertical displacement.

3.1.21 short waveband, n—high-pass filter with a cutoff at

1.6 m [5 ft].

3.1.22 signal-to-noise ratio (S/N), n—a measure that com-pares the level of the desired signal to the level of background noise.

3.1.23 transient, n—a filter response during a settling period until reaching steady-state response.

4. Summary of Test Method

4.1 The test apparatus, profiler, can be any device that

measures and records the elevation profile of the traveled surface.

4.2 For the example of inertial profiler technology, the test apparatus consists of a vehicle equipped with the necessary transducers, computing, and recording equipment to measure and record the elevation profile of the traveled surface.

4.3 The sampling rate is selected and depends on the

intended application’s anticipated roadway conditions and data requirements.

4.4 For inertial profiler technology, the test apparatus is

driven in the wheel tracks or in the correct lateral location over the section of the traveled surface to be profiled. The transduc-ers measure (1) the vertical acceleration of the vehicle, (2) the vertical distance between the accelerometer and the traveled surface, and (3) the longitudinal distance traveled by the vehicle. A computer combines these transducer signals to produce the longitudinal profile of the traveled surface.

5. Significance and Use

5.1 For inertial profiler technology, measuring vehicular

traveled surfaces using an instrumented vehicle with a fluctu-ating inertial reference elevation provides a satisfactory method for acquiring profile elevation measurements (1).

5.2 The profile data can be processed to produce, by

simulation, the outputs of other devices. This can be done in real time or can be computed as a post-process. Some of the devices that can be simulated include road meters (2), various straightedge devices (3), profilographs (4), as well as pavers and grinders. Caution should be taken regarding the nonlinear

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Downloaded/printed by Copyright by ASTM Int'l (all rights reserved) Mon Aug 19 15:12:28 UTC 2024 phase shifts inherent in the measurements of the above simulated devices. Comparisons of various equipment and their profile computer programs are referenced (5, 6).

5.3 The raw data or the profile data can also be recorded

later for data processing and analysis and by more complex data processing procedures.

6. Apparatus

6.1 This section illustrates an example device based on

inertial profiler technology.

6.2 The test apparatus consists of a carriage equipped with

transducers, profile computing, and recording equipment. The transducers are used to measure vertical changes in the road surface (profile) and longitudinal distance traveled. The com-puter is used to process the transducer outputs to produce the computed profile of the traveled surface. The test apparatus shall be capable of one or more profile traces and a mass storage device for long-term data storage. If two profile traces are measured simultaneously, the vertical profile transducers shall be mounted 1.5 to 1.8 m [58 to 71 in.] apart so that they measure in the two wheel tracks of the traveled surface. Some form of data display shall also be included to ensure correct data are being collected. Other supporting apparatus can include an operator speed display and a graphical display of collected data.

6.3 Carriage Requirements—If the carriage is a motorized

vehicle, the vehicle shall be large enough to accommodate all the required equipment without major structural modifications.

The engine, steering mechanisms, and suspension components shall be adequate to allow smooth control of speed and direction of travel. The environment of the interior of the vehicle shall be maintained within tolerable limits of the instrumentation and operators. The manufacturer’s recommen-dations should be followed if specified.

6.4 Transducers:

6.4.1 Accelerometer—On inertial profilers, the accelerom-

eter measures the vertical acceleration used to establish the inertial reference. A high-quality accelerometer shall be used that meets the requirements of the profiling application. The accelerometer shall be mounted on the measuring vehicle with the accelerometer’s sensitive axis perpendicular to the traveled surface. The accelerometer range shall be large enough to accommodate the acceleration levels expected from the mea-suring vehicle’s bounce motions (typically 62 g for production level collection). The accelerometer shall be biased to account for the 1 g acceleration of gravity or be compensated for in the computations. A test method shall be provided to verify the calibration of the accelerometer. The accelerometer shall have a minimum resolution to allow profile calculation and accuracy and bias to meet the application requirements as given in this test method.

6.4.2 Vertical Profile Measurement—On inertial profilers, the vertical profile points are measured using an accelerometer and a vertical distance transducer such as a laser, combined with a longitudinal distance transducer. The vertical distance transducer shall be mounted on the vehicle with its measuring axis perpendicular to the traveled surface and in line with the accelerometer’s sensitive axis. The transducer shall continu-ously measure the vertical distance to the traveled surface or a sample at intervals not greater than needed to allow calculated profile meeting the requirements in Section 13. A set of gauge blocks shall be included to calibrate and validate vertical profile transducer operation. Tire bridging is recommended to manage coarse textures, tinings, and grooves. The vertical resolution is not required. Instead, the performance of the entire measurement system shall meet the precision and bias of this standard.

6.4.3 Longitudinal Distance Measurement—The longitudi-

nal distance transducer shall be able to measure the distance along the traveled surface to a resolution needed to satisfy the particular application requirements and to allow the calculated profile to meet the requirements given in Section 13. Any distance transducer that produces analog or digital signals with sufficient accuracy may be used. The accuracy of the distance measurement is established by calibration, as specified in 9.2.3.

6.4.4 Location Markers—A section start, intermediate fea-

ture location(s), and section end shall be identified by location marks that can be accurately detected by automatic means, such as magnetic detection, photocell detection of reflective tape, or similar means.

6.5 Profile Computation—A computer shall be used to

process the vertical measurement transducer outputs (acceler-ometer and vertical distance for an inertial profiler) and the longitudinal distance transducer outputs to produce measured traveled surface profile elevations. There are two basic meth-ods of computing measured traveled surface profile:

6.5.1 Spatial Based—In the spatial-based method, the trans-

ducer outputs are acquired and profile data points are computed as a function of the distance traveled.

6.5.2 Time Based—In the time-based system, the transducer

outputs are acquired and profile data points are computed as a function of a fixed-time interval. In the time-based method, the computation of the measured road profile depends on the profiler measuring speed.

6.5.3 For inertial profilers, filtering that permits elevation profile computation with a low attenuation or amplification limit of profile wavelengths at most 90 m [300 ft] long at test speeds of 25 to 95 km/h [15 to 60 mph] shall be provided. The computer and system shall not add noise over 10 % of the displacement measuring transducer’s resolution.

6.5.4 As part of the profile computation equipment, a

computer terminal shall be provided to allow the operator to perform system calibration, select system parameters, and monitor system outputs.

6.6 Driver Speed Display:

6.6.1 The profiler speed shall be displayed conveniently for

the driver to maintain the desired measuring speed on systems requiring constant speed. Some systems, especially spatial-based systems, are independent of speed and the speedometer is sufficient.

6.6.2 The displayed profiler speed, when required, may be

computed by the profile computer from the distance pulses.

Other means of measuring profiler speed are acceptable.

6.7 Display—A display shall be provided that allows visual

monitoring of the system’s outputs. Profile amplitudes shall be

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displayed as a function of time or distance traveled. The operator shall control amplitude and distance scaling through the profiler computer terminal.

6.8 Storage Device—A device shall be provided for record-

ing and long-term storage of data, computed profile, or both.

The device shall have playback ability for additional on-board processing or later processing. Profile data for recording shall be scaled by the computer to maintain the storage resolution of the computed profile and to accommodate the full range of amplitudes encountered during normal profile measuring op-eration. Signal-to-noise (S/N) ratio shall be 10 or better. S/N ratio can be calculated by dividing the mean value by the standard deviation of measurements.

6.9 Event Marker—The operator shall be provided the

means to mark event locations as part of the data records. The system may use a transducer (optionally) to automatically sense and record location markers typically placed on the traveled surface.

7. Safety Precautions

7.1 For vehicle-based profiling devices, the test vehicle and all attachments to it shall comply with all applicable state and federal laws. Necessary precautions imposed by laws and regulations and vehicle manufacturers shall be taken to ensure the safety of operating personnel and other traffic.

8. Digital Profile Recording

8.1 The computed profile elevations shall be recorded at

adequate intervals for an accurate representation of the traveled surface for the intended use of the data. Also, anti-aliasing filters are required when the folding frequency (one half of sampling frequency) is close to the upper frequency of interest (Terminology E867). Anti-aliasing filtering shall be applied to the accelerometer signal and the vertical profile measurement signal before computing profiles for inertial profilers. The upper filter cut-off frequency depends upon the intended use of the profile.

8.2 Where two or more profile traces are measured simul-

taneously (for example, wheel tracks), the recorded profile data for the profile traces shall begin and end at the same longitu-dinal locations. This requirement is unnecessary if the analysis to be used is independent of the wheel tracks (7).

NOTE 1—The recorded profile data files are recommended to comply with Specification E2560.

9. Calibration Procedures

9.1 The profiling system and its components shall be cali-

brated periodically as the manufacturer recommends.

NOTE 2—Because of the complexity of the calibration, it is recom-mended that the calibration procedure be automated to reduce or eliminate operator involvement and decision-making.

9.2 Transducers:

9.2.1 Acceleration Transducer—For inertial profilers, the

acceleration transducer shall have an internal or external calibration feature. A measure of the accelerometer error shall then be displayed for the operator’s acceptance. As an alternative, the acceleration transducer may be calibrated separately in the laboratory.

9.2.2 Vertical Profile Transducer—For inertial profilers, the vertical profile transducer shall be statically calibrated by introducing two or more accurately measured gauge blocks at least 25 mm [1.0 in.] and 50 mm [2.0 in.] (AASHTO R 57). A measure of the displacement transducer error shall be displayed for the operator’s acceptance or adjustment.

9.2.3 Longitudinal Distance Transducer—The longitudinal

distance transducer shall be calibrated by measuring a prede-termined distance other than the certification tracks, as given in Test Method F457. The measured distance shall be long enough to determine any significant difference between the measured distance and the predetermined actual distance. A measure of the distance transducer error shall be displayed for the operator’s acceptance or adjustment. An error larger than

0.1 % of the actual distance shall not be accepted. The transducer shall be calibrated at the measuring speed(s) for the intended application. If the distance transducer calibration is being performed as part of a profiler validation or certification effort, the distance transducer should be calibrated on the certification track.

10. Procedures

10.1 General:

10.1.1 System Power—Turn on electronic equipment before

testing to allow electronic components to stabilize (see manu-facturer’s operating manual).

10.1.2 System Parameters—If required, select the system

parameters that define the wavelength content of the surface profile to be measured (see manufacturer’s operating manual).

10.1.3 Calibration Checks—Perform calibration checks at

the beginning of a day of operation and at any other time the operator may suspect changes in system performance since the last calibration. Also, calibration checks should be made at the end of each day or before departing a region to ensure the collected data are valid (AASHTO R 57).

10.1.3.1 System—For inertial profilers, check the calibration by using the simple procedure of bouncing the vehicle while it is stationary on a flat surface. This checks the major portion of the system. In this mode of operation, the surface profile is unchanging, and the system output should be less than 1 % of the vehicle bounce amplitude (AASHTO R 57). A measure of the traveled surface profile measuring system error shall be displayed for the operator’s acceptance.

10.2 Measuring Speed:

10.2.1 For inertial profilers, more accurate profiles are

generally obtained at higher measuring speeds because of the filters used. However, higher measuring speeds may limit the transducer’s ability to capture relevant features of an extremely rough surface. Measuring speed might have to be reduced for a sampling of shorter intervals (7).

10.2.2 Avoid measuring speeds below or above manufactur-

er’s recommendations.

10.2.3 Avoid sudden speed changes to minimize unwanted

input to the acceleration transducer and transients to the filters.

10.3 Test Sections—In preparation for measuring short test

sections of a traveled surface, the operator should become

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acquainted with the test section to be measured, including the beginning, end, and any other features that should be identified within the test section. If identifying features within the test section are to be sensed automatically, the operator shall place the proper marker on the traveled surface at the locations to be identified. The wheel tracks must be identified on the roadway so that the measurements are made in the wheel tracks or the paths to be measured.

10.4 Data Acquisition:

10.4.1 Enter information about the test section and test

conditions (see Section 12).

10.4.2 Allow a lead-in distance and a lead-out distance of

the manufacturer’s recommendation or at least 150 m [500 ft] to allow the high-pass filter to stabilize. The lead-in distance is the distance from the point that the profiler reaches the desired measuring speed and the beginning of the test section. The lead-out distance is the distance from the end of the test section to the distance specified. This distance allows a zero-phase (forward/reverse) filter to stabilize.

NOTE 3—To ensure transient effect free zero-phase profile filtering, the surface elevation data needs to be recorded from the beginning of the lead-in to the end of the lead-out while marking the beginning and end of the test section.

10.4.3 Switch the system to test mode and start data

collection where the manufacturer recommends or at the start of the lead-in distance.

10.4.4 Mark the start of the test section. This can be done

automatically or manually with an event marker.

10.4.5 Maintain lateral position within the traveled lane as

closely as possible to mimic the track utilized by normal traffic.

If a single line is measured, it may be done in the center of either wheel path as defined by normal traffic. Alternatively, the single measurements could be taken in the center of the lane or feature of interest. If more than one line of the traveled surface is measured simultaneously, then one line of measurements should be taken in the center of the wheel path as defined by normal traffic (left or right, but should be the same each time the test section is measured). If the lateral distance between the vertical profile transducers does not coincide with the distance between the wheel paths, then the left vertical profile sensor should be aligned with the center of the left wheel path.

10.4.6 Observe and check that the data are reasonable as

they are recorded. If profile data are collected for multiple wheel paths, traces for the right and left wheel tracks should generally be very similar except in the longer wavelengths.

10.4.7 Identify, as part of the recorded data, other physical features or known reference points within the test section that will assist in relating the calculated profile to the actually traveled surface profile.

10.4.8 Stop data recording at the end of the lead-out

distance.

10.4.9 Switch off the test mode at the end of the lead-out

distance.

10.5 Data Evaluation for Correctness:

10.5.1 If the performance of the test apparatus during a test run is questionable, perform an immediate check by measuring the test section again. The calculated profiles for the two test runs should agree with the cross-correlation levels specified in Section 13.

10.5.2 Occasionally, review and compare the profile or raw

data recorded on the storage device with the profile or raw data recorded during the data collection. The two data sets should be identical. Any difference between the two data sets indicates a problem with the storage device. A printing recorder is espe-cially helpful here.

11. Faulty Tests

11.1 Any observable differences between the measured

profiles of the left and right wheel tracks (see 10.4.6) that cannot be attributed to actual differences in the roadway mandate a repeat measurement. Following Practice E178, any observable differences between the two identical runs other than differences in the paths measured indicate an equipment problem and invalidate the test data.

12. Report

12.1 The field report for each test section shall contain data on the following items:

12.1.1 Date and time of day;

12.1.2 Operator, driver, and vehicle identification;

12.1.3 Weather conditions—principally temperature, cloud

cover, and wind;

12.1.4 Location and description of test section;

12.1.5 Surface description—type of pavement and condi-

tion;

12.1.6 Run number;

12.1.7 Measuring speed;

12.1.8 Direction measured;

12.1.9 Lane measured, transverse position;

12.1.10 Profile data; and

12.1.11 Other system-specific measurement options, for

example, filter wavelength data interval and resolution.

13. Precision and Bias

13.1 The precision and bias of a summary roughness index

measured by a profiling device are strongly related to the repeatability and accuracy of the measured profile, respectively, expressed in terms of cross-correlation (8, 9). The cross-correlation procedures are described in Appendix X1.

The procedures are implemented in the Profiler Certification Module (PCM) of the ProVAL software (10) that is recom-mended for the profiler repeatability and accuracy analysis with the cross-correlation method stated herein.

13.2 Development of the cross-correlation statement is as

follows:

13.2.1 Select a series of test sections adequate to cover the expected range of pavement types and textures.

13.2.2 Test sections should cover a range of IRI from 0.8 to

3.0 m/km [50 to 190 in./mile].

13.2.3 At least one section shall be 321.8 m [1056 ft] in

length. Others shall be at least 160.9 m [528 ft] in length.

Provide a minimum of 150 m [500 ft] of lead-in and lead-out for each section.

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13.2.4 Clearly mark the beginning of the lead-in and the

ending of the lead-out.

13.2.5 Clearly mark the beginning and end of each test

section.

13.2.6 Clearly mark at least one test line in each wheel path on each section.

13.2.7 Qualification of a Reference Class and a Production

Class profiler:

13.2.7.1 Calibrate the distance-measuring equipment on the

candidate Production Class profiler and a qualified Reference Class profiler to within 0.1 % of the accepted value of the length of each test section. Calibrate the distance-measuring equipment at the speed at which the test runs will be con-ducted.

13.2.7.2 Conduct at least three repeat runs on each section

with the qualified Reference Class profiler. If the repeatability of the repeat runs meets the minimum requirement in 13.3.1, select any repeat runs as the reference profile for use in 13.2.7.5.

13.2.7.3 Conduct ten repeat runs with the candidate Produc-

tion Class profiler on each test section. Conduct each run at the same speed used for distance measurement calibration. Main-tain constant speed throughout the test section.

NOTE 4—If possible, utilize the Production Class profiler’s automatic start/stop feature to maximize repeatability.

13.2.7.4 The maximum recording interval for the candidate

Production Class profiler is 70 mm [2.76 in.].

13.2.7.5 Determine the cross-correlation of the candidate

Production Class profiler in the wave bands of applications for each wheel track shown in 13.4.

13.3 A Reference Class profiler cross correlates between

repeated runs (that is, repeatability) over a range of pavement surface types as follows:

13.3.1 For the Reference Class profiler at the qualification

of a Production Class profiler, in IRI application, use the cross-correlation in the IRI waveband with the minimum repeatability of 0.98 (that is, 95 % of the time, the IRI agreement is within 2 %) (Practice E1926) (10).

NOTE 5—For other applications than IRI, use cross-correlation within the long, medium, and short wavebands. The recommended minimum repeatability scores for RN-type (Practice E1489) or vehicle dynamics applications are 0.98 and 0.98 within the long and medium, respectively.

The short waveband requirements are not recommended due to tracking issues during profiling and complication caused by surface textures.

NOTE 6—The accuracy requirement for the Reference Class profiler will be defined in the Standard Test Method for Benchmark Profiler Measuring the Longitudinal Profile of Traveled Surfaces in the future.

13.4 A Production Class profiler cross correlates among

repeated runs (that is, repeatability) and to a Reference Class profiler (that is, accuracy) over a range of pavement surface types as follows (8):

13.4.1 For the IRI application, use the cross-correlation in

the IRI waveband with the minimum repeatability of 0.92 (that is, 95 % of the time, the IRI agreement is within 5 %) and the minimum accuracy score at 0.90 (that is, 95 % of the time, the IRI agreement is within 6 %) (Practice E1926, AASHTO R 56) (11).

NOTE 7—If the Production Class profiler accuracy requirement fails under 13.4.1, utilize one of the remaining Reference Class profiler runs and repeat the analysis until exhausting the options.

NOTE 8—For applications other than IRI, use cross-correlation within the long and medium wavebands. For the example of RN-type (Practice E1489) or vehicle dynamics applications, the recommended minimum repeatability scores are 0.92 and 0.92 within the long and medium wavebands; minimum accuracy scores are 0.90 and 0.90 within the long and medium wavebands. The short waveband requirements are not recommended due to tracking issues during profiling.

NOTE 9—Each waveband shall be isolated using a sixth-order Butter-worth filter (except for the low-pass filter for the short waveband). Filters shall be applied in both forward and reverse directions to eliminate phase shifts.

NOTE 10—The short waveband requirements may be recommended once the tracking issues are resolved with the advancement of technolo-gies.

NOTE 11—Further details on the basis for the correlation thresholds are described in Appendix D of Reference (11).

NOTE 12—The cross-correlation rating can be affected by the roughness levels, surface texture, grade, and other test track features. It is recom-mended to (1) avoid test tracks that are too rough and too smooth, (2) use line lasers for profiling on coarse surface textures and tinings, and (3) avoid test tracks with steep grades.

NOTE 13—Table 1 includes the summary of the cross-correlation threshold values of repeatability and accuracy for all types of profiles. The values for the IRI waveband are for the IRI applications. The values for the long and medium waveband are for the RN application.

14. Keywords

14.1 accuracy; cross-correlation; longitudinal profile; preci-sion and bias; profilers; profiling device; profilometer;

repeatability

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APPENDIX

(Nonmandatory Information)

X1. CROSS-CORRELATION PROCEDURES

X1.1 The computation procedure for cross-correlation used in this standard is described as follows.

X1.1.1 Identify a fixed profile (Q) that is already consistent with the desired longitudinal reference. It will be considered a location reference. The profile will have a sample interval ∆, a total length LQ, and a total number of samples NQ (=LQ / ∆).

The sample interval may be adjusted within 60.1 % to maximize cross-correlation.

X1.1.2 Cut a segment out of the correlated or shifted profile

(P) of shorter length than the reference profile, Lp. Preprocess it as follows.

X1.1.2.1 Filter it.

X1.1.2.2 Interpolate the filtered profile to the sample inter-val of the reference profile. The result is profile p, a portion of the original profile P. It will have Np samples (=Lp / ∆).

X1.1.2.3 Offset the profile vertically so that the mean is zero. The cropped, filtered, interpolated, and shifted version of profile P is given the symbol p̂, and will include Np samples.

X1.1.3 Apply a negative offset (δ0) to the correlated profile so that the first point in it is also the first point in the reference profile. This offset value equals XsQ – Xsp, where XsQ is the longitudinal position of the start of the broader reference profile (Q), and Xsp is the longitudinal position of the start of the correlated profile.

X1.1.4 Extract the portion of the reference profile (Q) that is covered by the correlated profile (p̂). The extracted segment, q, will cover the same number of samples as p̂.

X1.1.4.1 Filter the extracted profile (q).

X1.1.4.2 Offset the filtered profile vertically so that the mean is zero. The result is q̂. This signal must be conditioned after it has been extracted from the broader reference profile.

This ensures the equal application of end conditions in the two signals correlated in Eq X1.1.

X1.1.4.3 Calculate the variance of the filtered and shifted profile over the range of interest (σq).

X1.1.5 Cross-correlate the signals. In this application, the variance must be calculated over the segment of interest only to account for the common situation in which the broader profile is not stationary.

ρm 5 σp·σq i51

Np p̂i q̂i1m (X1.1) σm 5 Xsq 2 Xsp1m ·∆ (X1.2)

X1.1.5.1 In the above equations, the value “m” is the number of samples skipped at the start of the long profile Q to create the shorter profile q̂. For each value of ρ, there exists an associated value of longitudinal offset, δ. In the first application, m is zero, and the offset between profiles is XsQ – Xsp. (The value of m is incremented from 0 to NQ – Np.)

X1.1.6 Shift the offset of the correlated signal by a distance equal to the sample interval of the reference profile. This amounts to shifting ahead of one sample on the reference profile. (Each time this is done, increment the value of “m.”)

X1.1.7 If the end of the reference profile has not been reached, return to X1.1.4.

X1.1.8 Search the function ρm for its maximum cross-correlation value, ρmax.

X1.1.9 Calculate the adjustment factor for overall rough-ness as follows:

f 5 min~σp,σq!

max~σp,σq!

(X1.3)

X1.1.10 Calculate the agreement score for the two profiles:

f·ρmax.

TABLE 1 Minimum Threshold Values of Repeatability and Accuracy

Waveband Reference Class Production Class

Repeatability AccuracyA Repeatability Accuracy

IRI 0.98 N/A 0.92 0.90

Long 0.98 N/A 0.92 0.90 Medium 0.98 N/A 0.92 0.90 A A placeholder for the accuracy requirement for the Reference Class profiler to be defined in the Standard Test Method for Benchmark Profiler Measuring the Longitudinal Profile of Traveled Surfaces in the future.

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REFERENCES

(1) Spangler, E. B., and Kelly, W. J., “GMR Road Profilometer—A Method for Measuring Road Profile,” Highway Research Record 121, Washington, DC, 1966.

(2) Gillespie, T. D., Sayers, M. W., and Segel, L., “Calibration and Correlation of Response-Type Road Roughness Measuring Systems,” NCHRP Report 228, National Cooperative Highway Research Program, National Academy of Science, Washington, DC, 1980.

(3) Wambold, J. C., et al., “State-of-the-Art of Measurement and Analysis of Road Roughness,” Transportation Research Record 836, Washington, DC, 1981.

(4) Kulakowski, B. T., and Wambold, J. C., “Development of Procedures for the Calibration of Profilographs,” FHWA Final Report, February 1989.

(5) Pong, M., “The Development of an Extensive-Range Dynamic Road Profile and Roughness Measuring System,” Ph.D. Dissertation, Penn State University, 1992.

(6) Sayers, M. W., and Gillespie, T. D., “The Ann Arbor Road Profilome-ter Meeting,” FHWA Report FHWA/RD-86/100, July 1986.

(7) Darlington, J. R., and Milliman, P., “A Progress Report on the

Evaluation of the General Motors Rapid Travel Road Profilometer,” Highway Research Record 214, Washington, DC, 1968.

(8) Karamihas, S. M., “Critical Profiler Accuracy Requirements,” Uni-versity of Michigan Transportation Research Institute, UMTRI-2005- 24, 2005.

(9) Karamihas, S. M., “Improving the Quality of Pavement Profiler Measurement,” Benchmark Test Evaluation Report, Federal Highway Administration Project, University of Michigan Transportation Re-search Institute, 2011.

(10) ProVAL—Profile Viewing and Analysis Software (www.RoadProfi-le.com).

(11) Karamihas, S. M., “Improving the Quality of Pavement Profiler Measurement,” Benchmark Testing Plan, Federal Highway Admin-istration Project, University of Michigan Transportation Research Institute, 2009.

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