1、Standard Specification for Smoothness of Pavement in Weigh-in-Motion (WIM) Systems AASHTO Designation: M 331-171Technical Section: 5a, Pavement Measurement Release: Group 1 (April 2017) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washin
2、gton, D.C. 20001 TS-5a M 331-1 AASHTO Standard Specification for Smoothness of Pavement in Weigh-in-Motion (WIM) Systems AASHTO Designation: M 331-171Technical Section: 5a, Pavement Measurement Release: Group 1 (April 2017) 1. SCOPE 1.1. Weigh-in-motion (WIM) is the process of measuring the dynamic
3、forces of moving vehicle tires on pavements and estimating the corresponding tire loads of the static vehicle. The dynamic forces of moving vehicles include the effects of road surface roughness and are modified by vehicle characteristics such as sprung and unsprung mass, tire inflation pressures, o
4、ut-of-round or dynamically unbalanced wheels and tires, vehicle cargo, suspension damping, and the vehicles aerodynamic characteristics. The smoothness of the pavement surface in WIM systems directly affects the scales ability to accurately estimate static loads from measured dynamic forces. Lack of
5、 smoothness can create difficulties in calibrating WIM equipment and may cause poor results from subsequent vehicle weight data collection efforts. 1.2. WIM system pavement smoothness is characterized by the output of a profiler in compliance with the Operator Certification section of R 56, collecti
6、ng data at 25-mm 1-in. or less intervals. The data produced by such a profiler will approximate the actual perpendicular deviation of the pavement surface from an established horizontal reference parallel to the lane direction in the wheel tracks. 1.3. The specification requires field collection of
7、pavement profile information of a WIM system or of a candidate WIM site. Computer software is then used to calculate a roughness index that has been correlated to distributions of single and tandem axle, and gross vehicle weight error levels through extensive simulations of truck dynamic loading ove
8、r measured profiles. Acceptable index levels are based on ensuring to a 95 percent level of confidence that the WIM system roughness will not produce errors that exceed the tolerance level limits recommended by ASTM E1318. 1.4. The profiler test vehicle, as well as all attachments to it, shall compl
9、y with all applicable state and federal laws. Necessary precautions imposed by laws and regulations, as well as vehicle manufacturers, shall be taken to ensure the safety of operating personnel and other traffic. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 56, Certification of Inertial Profilin
10、g Systems R 57, Operating Inertial Profiling Systems 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a M 331-2 AASHTO 2.2. ASTM Standards: E867, Standard Terminology Relating to Vehicle-Pavement Syst
11、ems E950/E950M, Standard Test Method for Measuring the Longitudinal Profile of Traveled Surfaces with an Accelerometer Established Inertial Profiling Reference E1318, Standard Specification for Highway Weigh-In-Motion (WIM) Systems with User Requirements and Test Methods 3. TERMINOLOGY 3.1. Definiti
12、ons: 3.1.1. dynamic axle load (kg or lb), nthe component of the time-varying forces applied perpendicularly to the road surface by the tires of any one axle of a moving vehicle. 3.1.2. index, na number or formula expressing some property, form, ratio, etc. of the relation or proportion of one amount
13、 or dimension to another. 3.1.3. roughness, nvertical deviation of a pavement surface from a horizontal reference along a wheel track with characteristics that affect vehicle dynamics, including dynamic axle loads. 3.1.4. profile record, na data record of the surface elevation or slope along one or
14、both wheel tracks of the road surface. 3.1.5. weigh-in-motion (WIM), nthe process of estimating a moving vehicles gross weight and the portion of that weight that is carried by each wheel, axle, or axle group, or combination thereof, by measurement and analysis of dynamic vehicle tire forces. (See A
15、STM E867.) 3.1.6. WIM scale roughness index, na summary index calculated from a profile trace that is correlated to the expected weighing error at a WIM scale placed within the trace. 4. TEST METHOD TO EVALUATE THE SMOOTHNESS OF PAVEMENT IN A WIM SYSTEM 4.1. Performance Requirements: 4.1.1. Function
16、al performance requirements for Types I and II WIM systems were established and tabulated within ASTM E1318. Table 1 summarizes the tolerance limits for 95 percent probability of conformity to WIM accuracy standards for axle loads, axle-group loads, and gross vehicle weights. This is accomplished us
17、ing a profile-based index that estimates the potential WIM error level due to roughness of the pavement, array, and sensing technology. Annex A, Section A1 summarizes the overall calculation procedure, and Sections A2 through A5 provide details of the calculation algorithms. 4.1.2. Each Type I WIM s
18、cale location shall be chosen so that the WIM scale roughness index calculated from the pavement profile records of the WIM system do not exceed 1.34 m/km 84.8 in./mi in the left and right wheel tracks. Each Type II WIM scale location shall be chosen so that the WIM scale roughness index calculated
19、from the pavement profile records of the WIM system do not exceed 1.86 m/km 117.9 in./mi, in the left and right wheel tracks. The achievement of these values is needed to ensure that a WIM site is likely to produce load estimates that meet the requirements of ASTM E1318. When location requirements d
20、ictate scale placement in rough pavement, the existing pavement can be modified (overlaid, ground, etc.) or replaced to meet these smoothness requirements. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law
21、.TS-5a M 331-3 AASHTO 4.1.3. The very presence of a WIM scale may create localized roughness within the pavement in its vicinity. Therefore, when the WIM scale roughness index is used to select a location for WIM scale installation, the scale location must adhere to the roughness criteria in Section
22、 4.1.2 after the scale is installed. Table 1Functional Performance Requirements for ASTM E1318 Type I and II WIM Systems Function Tolerance for 95% Probability of Conformance Type I Type II Wheel load 25% Axle load 20% 30% Axle-group load 15% 20% Gross vehicle weight 10% 15% 4.1.4. In addition to th
23、e initial calculations of the WIM scale roughness index for WIM scale location acceptance, the pavement smoothness of each existing WIM scale shall be verified every two years. Profile records shall be collected and indices recalculated every two years to ensure that the scale remains likely to prod
24、uce load estimates that meet the functional performance requirements of ASTM E1318. 4.1.5. In specifying a location for a WIM scale with more than one sensor on a single wheel track (typical with piezoelectric WIM equipment), the position of the scale shall be defined as the location of the downstre
25、am sensor. The WIM scale roughness index is to be referenced to this point. 4.1.6. Under certain conditions, jointed concrete pavement surfaces may exhibit significant changes in roughness due to variations in the temperatures of the pavement. Profile records of these pavements shall be taken at lea
26、st twice, at times that correspond to approximate extremes of pavement (not air) temperature gradient that are likely to be experienced at the candidate location. The location for a WIM scale shall be chosen so that the WIM scale roughness index calculated from either of these profile records does n
27、ot exceed the limits. 4.2. Summary of PracticeTest methods for evaluating the smoothness of pavement in an existing WIM system are presented herein. These procedures are applicable for determining a WIM scale roughness index level that would indicate that a WIM scale is likely to produce acceptable
28、levels of weighing error as defined in Table 1. The smoothness tests require the collection of longitudinal profile data with a sampling rate of 25 mm 1 in. or less and otherwise in accordance with R 57. Computer analysis of these profiles serves to calculate the WIM scale roughness index that will
29、be compared to acceptable threshold values. 4.3. Significance and UseThe WIM scale roughness index was developed in a correlation of calculated roughness values to WIM scale error for a large-scale study of pitch-plane simulations of 3S2 (five-axle tractor-semitrailers) vehicles. The index was furth
30、er verified in a study of simulations of WIM scale errors associated with three-axle single-unit trucks. Subsequently, the index was refined using the same set of pitch-plane simulations on several existing WIM site profiles. This correlation allows the indexes to be used to determine whether the WI
31、M system pavement smoothness is sufficient to achieve weight measurements of 3S2 trucks and three-axle single-unit trucks that fall within ASTM error tolerance levels. The calculation of WIM scale roughness index values that fall within those that correlate to the scale measurement tolerances specif
32、ied in Table 1 means that the scale is very likely to produce an acceptable level of weighing error. 4.4. Procedure: 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a M 331-4 AASHTO 4.4.1. Profile Re
33、cordsObtain profile record s of both left and right wheel paths according to the procedures outlined in R 57 using a 25-mm 1-in. or smaller longitudinal sampling and reporting interval. These records should begin at least 122 m 400 ft prior to the WIM scale sensor and extend to 61 m 200 ft after the
34、 scale sensor or in accordance with R 57. For WIM scales that are comprised of two or more sensors, the location of the scale will be defined as the location of the downstream sensor. Record the WIM scale location as an Intermediate Feature Location Marker within the profile record as per Section 6.
35、3.4 of ASTM E950/E950M. Obtain a total of three records. Compare the outputs for each, and evaluate each for equipment-related spikes. Continue collecting profile records until the operator is satisfied that at least one error-free record has been obtained. Note 1Spacing of sensors, type of sensor t
36、echnology, and processing methods of such sensors also have an impact on the performance of the WIM system in addition to the pavement smoothness. 4.4.2. Calculation of IndexesA complete description of the procedure to calculate the WIM s cale roughness index is described in Annex AComputation of th
37、e WIM Scale Roughness Index. The procedure has been coded within the Optimal WIM Locator (OWL) in the Profile Viewer and Analysis (ProVAL) software program. ProVAL was developed for the Federal Highway Administration, which can be used to import, display, and analyze the characteristics of pavement
38、profiles from many different sources. This nonproprietary software, which is available on the web, performs the computations from Annex A with either R 57 or ERD text file versions of the profile records from any longitudinal profiler as inputs. 4.4.3. Although including pavement features located ou
39、tside the range of sensitivity of the WIM scale roughness index does not improve its predictive ability, the criteria might fail to screen out WIM sites with a major disturbance just beyond its range if the rest of the pavement is not as rough. Although this is unlikely to occur in practice, a usefu
40、l way to protect against very rough pavement features that are not captured by the index at the scale location is to inspect the value of WIM roughness index for 40 m 131 ft upstream of the scale to ensure that it does not exceed the threshold over this range. 4.5. Interpretation of ResultsTable 2 s
41、hows the upper threshold value indices for Types I an d II WIM scales in evaluating the smoothness of the pavement after a WIM scale installation. The upper threshold value of the index is that above which a WIM system is very likely to produce an unacceptable level of weighing error. Table 2WIM Rou
42、ghness Index Thresholds for Types I and II WIM Upper Threshold, m/km in./mi Type I WIM 2.70 171.1 Type II WIM 3.75 237.7 4.6. Precision and BiasThis is a test method that prod uces pass or fail results. The precision of the test is related to the degree of correlation between calculated index values
43、 and errors in measured values of tandem axle and gross vehicle weights. Since these relationships exhibited some scatter in a simulation study, conservative values for index cutoff values were chosen such that there was 95 percent confidence that a scale that met the index criteria would produce le
44、vels of weighing error that meet the ASTM E1318 standards in the study. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a M 331-5 AASHTO 5. TEST METHOD TO EVALUATE THE SMOOTHNESS OF PAVEMENT TO DETER
45、MINE THE OPTIMAL WIM SYSTEM LOCATION 5.1. Summary of Test MethodA test method for determining the optimal position for a WIM scale within a limited site is presented herein. The procedures are applicable for determining a precise placement of a WIM scale within the linear distance covered by a profi
46、ler record that will result in minimum WIM scale roughness index levels. The smoothness tests require the collection of longitudinal profile data with a sampling rate of 25 mm 1 in. or less and otherwise in accordance with R 57 according to the procedures in ASTM E950/E950M. Computer analysis of the
47、se profiles at varying longitudinal scale placements serves to place the WIM scale in a location that will minimize the WIM scale roughness index. Comparison of these values with acceptable threshold values will indicate whether the site is suitable. To protect against very rough pavement features t
48、hat are not captured by the index at the scale location, inspect the value of the index for 40 m 131 ft upstream of the scale to ensure that it does not exceed the lower threshold over this range. 5.2. Significance and UseA correlation has been established between calculated WIM scale roughness inde
49、x values and WIM scale. This correlation allows the index to be used to determine whether the WIM system pavement smoothness is sufficient to achieve weight measurements of 3S2 trucks and three-axle single-unit trucks that fall within ASTM error tolerance levels. The calculation of WIM scale roughness index for each candidate scale location within a profile record may be used to determine the correct positioning of a scale to maximize its likelihood of producing acceptable levels of weighing error as outlined in Table 1.
