1、TS-5a M 331-1 AASHTO Standard Specification for Smoothness of Pavement in Weigh-in-Motion (WIM) Systems AASHTO Designation: M 331-1311. SCOPE 1.1. Weigh-in-motion (WIM) is the process of measuring the dynamic forces of moving vehicle tires on pavements and estimating the corresponding tire loads of
2、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, out-of-round or dynamically unbalanced wheels and tires, suspension damping, and the vehicle
3、s 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 smoothness creates difficulties in calibrating WIM equipment and may cause poor results from subsequent v
4、ehicle 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 AASHTO R 56, collecting data at 25-mm 1-in. or less intervals. The data produced by such a profiler will approximate the ac
5、tual 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 pavement profile information of a WIM system or of a candidate WIM site. Computer software is then use
6、d to calculate a roughness index that has been correlated to distributions of tandem axle and gross vehicle weight error levels through extensive simulations of truck dynamic loading over measured profiles. Acceptable index levels are based on ensuring to a 95 percent level of confidence that the WI
7、M system roughness will not produce errors that exceed the tolerance level limits recommended by ASTM E 1318. 1.4. The profiler test vehicle, as well as all attachments to it, shall comply with all applicable state and federal laws. Necessary precautions imposed by laws and regulations, as well as v
8、ehicle 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 Profiling Systems R 57, Operating Inertial Profiling Systems 2013 by the American Association of State Highway and Transp
9、ortation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a M 331-2 AASHTO 2.2. ASTM Standards: E 867, Standard Terminology Relating to Vehicle-Pavement Systems E 950/E 950M, Standard Test Method for Measuring the Longitudinal Profile of Traveled Surfaces with an Accel
10、erometer Established Inertial Profiling Reference E 1318, Standard Specification for Highway Weigh-In-Motion (WIM) Systems with User Requirements and Test Methods 3. TERMINOLOGY 3.1. Definitions: 3.1.1. dynamic axle load (kg or lb), nthe component of the time-varying forces applied perpendicularly t
11、o 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 or dimension to another. 3.1.3. roughness, nvertical deviation of a pavement surface from a horizontal refer
12、ence along a wheel track with characteristics that effect vehicle dynamics, including dynamic axle loads. 3.1.4. profile record, na data record of the surface elevation or slope along one or both wheel tracks of the road surface. 3.1.5. weigh-in-motion (WIM), nthe process of estimating a moving vehi
13、cles 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 ASTM E 867.) 3.1.6. Definitions of Terms Specific to This Standard: 3.1.7. WIM scale roughness index, na summa
14、ry 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. Functional performance requirements for Types I and II WIM sy
15、stems were established and tabulated within ASTM E 1318. 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 using a profile-based index that estimates the potenti
16、al WIM error level due to roughness of the pavement. Annex A1 summarizes the overall calculation procedure, and Annexes A2 through A5 provide details of the calculation algorithms. 4.1.2. Each Type I WIM scale location shall be chosen so that the WIM scale roughness index calculated from the pavemen
17、t 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 from the pavement profile records of the WIM system do not exceed 1.86 m/km 117.9 in./mi, in th
18、e 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 E 1318. When location requirements dictate scale placement in rough 2013 by the American Association of State Highway and Transpor
19、tation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a M 331-3 AASHTO pavement, the existing pavement can be modified (overlaid, ground, etc.) or replaced to meet these smoothness requirements. 4.1.3. The very presence of a WIM scale will often create localized roug
20、hness 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 4.1.2 after the scale is installed. Table 1Functional Performance Requirements for AST
21、M E 1318 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 the initial calculations of the WIM scale roughness index for WIM scale location accepta
22、nce, the pavement smoothness of each existing WIM scale shall be verified annually. Profile records shall be collected and indices recalculated each year to ensure that the scale remains likely to produce load estimates that meet the functional performance requirements of ASTM E 1318. 4.1.5. In spec
23、ifying 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 downstream sensor. The WIM scale roughness index is to be referenced to this point. 4.1.6. Under certain c
24、onditions, 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 least twice, at times that correspond to approximate extremes of temperature gradient that are likely
25、 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 not exceed the limits. 4.2. Summary of PracticeTest methods for evaluating the smoothness of pavement in an existing W
26、IM 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 levels of weighing error as defined in Table 1. The smoothness tests require the collection of longitudinal profile d
27、ata 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 be compared to acceptable threshold values. 4.3. Significance and UseThe WIM scale roughness index was developed in a
28、 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 further verified in a study of simulations of WIM scale errors associated with three-axle single-unit trucks. Subsequently
29、, 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 WIM system pavement smoothness is sufficient to achieve weight measurements of 3S2 trucks and three-axle single-unit tr
30、ucks 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 specified in Table 1 means that the scale is very likely to produce an acceptable level of weighing error. 2013 by the Amer
31、ican 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. Procedure: 4.4.1. Profile RecordsObtain profile records of both left and right wheel paths according to the procedures outlined in R 57 using a 2
32、5-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 scale sensor or in accordance with R 57. For WIM scales that are comprised of two or more sensors, the location of th
33、e 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 6.3.4 of ASTM E 950/E 950M. Obtain a total of three records. Compare the outputs for each, and evaluate each for equipme
34、nt-related spikes. Continue collecting profile records until the operator is satisfied that at least one error-free record has been obtained. 4.4.2. Calculation of IndexesA complete description of the procedure to calculate the WIM scale roughness index is described in Annex A1Computation of the WIM
35、 Scale Roughness Index. The procedure has been coded within the Optimal WIM Locator (OWL) within ProVAL. This nonproprietary software performs the computations from Annex A1 with either R 57 or ERD text file versions of the profile records from any longitudinal profiler as inputs. 4.4.3. Although in
36、cluding pavement features located outside 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 un
37、likely to occur in practice, a useful 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
38、. Interpretation of ResultsLower threshold values of WIM roughness index are those below which a WIM system is very likely to produce an acceptable level of weighing error. The upper threshold value of the index is that above which a WIM system is very likely to produce an unacceptable level of weig
39、hing error. Threshold values for the index for Types I and II WIM scales are tabulated in Table 2 and Table 3, respectively. Table 2WIM Roughness Index Thresholds for Type I WIM Lower Threshold, m/km in./mi Upper Threshold, m/km in./mi 1.34 84.8 2.70 171.1 Table 3WIM Roughness Index Thresholds for T
40、ype II WIM Lower Threshold, m/km in./mi Upper Threshold, m/km in./mi 1.86 117.9 3.75 237.7 4.6. Precision and BiasThis is a test method that produces pass or fail results. The precision of the test is related to the degree of correlation between calculated index values and errors in measured values
41、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 levels of weighing error that mee
42、t the ASTM E 1318 standards in the study. 2013 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 DETERMINE THE OPTIMAL WIM SYSTEM LO
43、CATION 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 profiler record that will result in
44、 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 E 950/E 950M. Computer analysis of these profiles at varying longi
45、tudinal 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 that are not captured by the
46、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 of calculated WIM scale roughness index values to WIM scale error was conducted for a large-
47、scale study of pitch-plane simulations of 3S2 (five-axle tractor-semitrailers) vehicles. 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
48、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. 5.3. Tes
49、t Methods: 5.3.1. Profile RecordsObtain profile records 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 interval. These records shall meet the R 56 requirements for slope profile measured in the waveband specified for the WIM scale roughness index and should cover the entire longitudinal extent of roadway to be considered for the WIM scale placement. Obtain a total of three records, compare the outputs for each, and evaluate
