Estimation of Equivalent Axleloads Using Data Collected by Automated Vehicle Classification and Weigh-in-Motion Equipment

The primary objective of this research study was to modify the existing EAL estimation system to include data obtained using the Golden River Weigh-In-Motion system and automated vehicle classification equipment. Data are to be collected over a three-year cycle in accordance with the FHWA Traffic Monitoring Guide. Having the capability of moving the portable weigh-in-motion scales to locations other than interstate sites permits the collection and analyses of specific data at sites on other highway functional classifications. Such data permits estimating both accumulated and future EAL requirements for that site. Such data permits estimating EAL requirements for sites on the same highway functional classification for which AADT is the only available data. An algorithm was developed to identify heavy/coal trucks weighed by W\M. The algorithm involves a minimum weight for straight-frame trucks and for semi-trailer coal trucks has the additional parameter of gross weight divided by the spacing between the last axle on the tractor and the first axle on the trailer. The algorithm works because the coal semi-trailer is shorter than a normal semi-trailer. Historical data files have been sorted by highway functional classification to permit calculating EAL requirements on a three-year cycle corresponding to the requirements of the FHWA Traffic Monitoring Guide. The revised computer programs use the same data format contained in historical files. The basic equation for estimating EALs contains the following seven parameters as independent variables; 1) annual average daily traffic volume, 2) average fraction of trucks in the traffic stream, 3) average fraction of coal trucks in the total truck population, 4) average number of axles per coal truck, 5) average number of axles per non-coal truck, 6) average number of equivalent axleloads per coal-truck axle, and 7) average number of equivalent axleloads per non-coal-truck axle

Comparison of Rigid Pavement Thickness Design Systems

Rigid pavement thickness design systems investigated during this study were the 1986 AASHTO, American Concrete Pavement Association (ACPA), Portland Cement Association (PCA), and Kentucky methods. The ACPA system is a computer program based upon the 1966 AASHTO design equation. It was difficult to evaluate and compare the Kentucky method to the PCA system because the input and analysis procedures differ greatly. The Kentucky method is based upon the fatigue relationship involving the value of work at the bottom of the concrete pavement caused by the applied load and repetitions of an 18-kip single axleload. The AASHTO method was derived from data obtained at the AASHO Road Test where the rigid pavements failed primarily due to pumping of the subgrade from under the slab. In Kentucky, pumping is a minor problem compared to failures caused by compressive forces at joint openings. Compression occurs due to annual temperature fluctuations resulting in slab movement and subsequent intrusion of debris into the joint openings. Eventually, the slab cannot move and compressive forces increase until failure occurs. Failure criterion used in the Kentucky thickness design system is quite different from the mode of failure observed at the AASHO Road Test and makes direct comparisons between design methods somewhat questionable. The expression of soil stiffness values is a major contributor to the confusion arising between design methods. Using elastic theory to develop load equivalency relationships, the ratio of rigid pavement EALs to flexible pavement EALs is approximately 1.1. According to W-4 Tables, the ratio of AASHTO rigid pavement EALs to AASHTO flexible pavement EALs is approximately 1.6. Thus, the AASHTO combination of pavement structures used in W-4 tables are not equivalent for fatigue calculations. Another combination should be chosen. Thickness designs using the 1966 AASHTO, ACPA, and Kentucky methods can be made to match provided the terminal serviceability varies with Kentucky CBR. To help understand the behavior at the AASHO Road Test, published data for the cracking index, pumping index, and serviceability index were investigated. All three data sets influenced one another and could be correlated fairly well for serviceability values greater than 1.5. A method was devised to normalize the data to account for tire load and pavement thickness variations. Serviceability data proved to be revealing. Of the 76 rigid pavement sections at the AASHO Road Test, 43 were given a serviceability rating greater than 1.5 at the end of testing operations. Of the 43, 10 had ratings between 2.5 and 4.0. The remaining 33 sections had ratings of 4.0, or greater. The 1986 AASHTO Guide recommends a terminal serviceability of 2.5 for major highway pavements. A 2.5 rating is appropriate for flexible pavements. From this investigation, a rating of 2.5 appears to be low for rigid pavements and suggests that a comparable set of serviceability values should be derived. It is recommended that Kentucky Department of Highways use the 1984 Kentucky Concrete Thickness Design Curves for design of rigid pavements

Effects of Construction Variations Upon Dynamic Moduli of Asphaltic Concrete

The two variables that most influence the behavior of asphaltic concrete pavements are subgrade modulus and thickness of the asphaltic concrete. Other significant variables are: temperature of the asphaltic concrete, asphaltic concrete modulus, frequency of the dynamic loading, asphalt content by weight in mix, and voids in the asphaltic concrete mix. During a series of Road Rater tests on a experimental pavement in Kentucky, deflection test data varied widely from expected values. Test data reported by Kallas and Riley permitted the development of an equation relating asphaltic concrete modulus to its temperature and to the frequency of loading. However, after deflection data were adjusted for temperature and frequency, the variation was still greater than expected. Construction records for each test station were examined; the void content and asphalt cement content of the mix were found to vary considerably

Economic Analyses of Millings

Economic analyses were made using 1984 and 1985 contract bid data. Data were identified as to who retained ownership. Recommendations as to who retains ownership are made based upon factors prevalent for a specific candidate pavement and other circumstances

An Analytical Investigation of AASHTO Load Equivalencies

An objective of this study was to develop procedures and/or refined relationships between Kentucky ESALs and AASHTO ESALs. Kentucky load equivalency relationships are the result of mechanistic analyses based on elastic theory. AASHTO load equivalency relationships were developed from recorded empirical data collected at the AASHO Road Test. Comparison of Kentucky and AASHTO ESALs necessarily in depth analyses of AASHTO load equivalency equations C-19, D-19, and their developmental equations given in the 1972 AASHTO Interm Guide. These equations evolved from the basic format used in analyzing AASHO Road Test data. In this investigation, the repetitions reported in Appendix A of AASHO Road Test Special Report 61E were converted to ESALs using Equation C-16. For Loop 3 (12-kip (53kN) single axieload and 24-kip (108-kN) tandem axieload), the ESALs at service facilities of 3.0, 2.5, 2.0 exceeded the ESALs at failure (Pt = 1.5). The AASHTO design equation, C-13, was used yo calculate the design ESALs for each of the AASHO Road Test pavement sections. The ratio of ESALs at a given P, to ESALs at failure and the ratio of repetitions at the same Pt to repetitions at failure were calculated. Direct correlations of the averages of these calculated ratios occurred for Lane 1 of Loops 5 and 6 and Lane 2 of Loop 6. This suggests that the AASHTO load equivalency relationships correlate best for loads greater than the legal limits. From recorded Kentucky loadometer data collected at stations located on Interstate routes, over 95% of all single and tandem axleloads are less than legal limits. This suggests that the AASHTO load equivalency relationships are not as appropriate to actual traffic loads. Ratios of AASHTO ESALs may be calculated using Equation 6 for flexible pavements and Equation 7 for rigid pavements to estimate combinations of Pt and SN, or Pt and slab thickness. AASHTO load equivalencies are based on pavement serviceability and structural number for flexible pavements, or slab thickness for rigid pavements respectively. Pavement serviceability is based upon measurements of surface roughness, cracking, patching, and rut depth. Pavement fatigue is an inherent parameter. In the Kentucky system, load equivalencies are based upon strain-repositions relationships developed from laboratory tests and matched with theoretical calculated strains based on elastic theory. Inherently included in the Kentucky system in the assumption that surface roughness will increase with traffic, cracking may develop, patches may be constructed, and ruts may develop. The common factor between the two systems is traffic. Measured parameters in on system are inherent in the other system and vice versa

Relationship Between Weights Measured by Permanent Truck Scales and Golden River Weigh-In-Motion Scales

The Division of Planning purchased a Golden River Weigh-in-Motion system. The first assignment was to determine the optimum calibration setting for operating each weigh mat. The second assignment was to determine the sensitivity of the weigh data. The third assignment was to develop appropriate relationships to adjust the dynamic data to equivalent static data. A series of correlation efforts established the appropriate calibration factor for each weigh mat. Then the mats were installed at a site on I 64 in Shelby County and data were collected for over 1,600 trucks. From these data, it became evident that equations to adjust dynamic loads to equivalent static loads should be developed for individual axle locations on the truck rather than the gross weight as recommended by the manufacturer. The primary reason was that the steering axle\u27s dynamic load was approximately 70 percent of the static axleload. The discrepancy is due to the torque transmitted from the engine to the drive axles which partially lifts the steering axle off the pavement. Therefore, equations were developed for: Steering Axle Single Drive Axle Single Axle on Trailer Drive Tandem Axles Trailer Tandem Axles Drive Tridem Axles Trailer Tridem Axles Observations of truck dynamics combined with literature review indicated that dynamic axleloads are affected by: Engine torque, Temperature of rigid pavements, Location of axle on truck, Pavement roughness rather than pavement type, and Suspension system between truck frame and axles

Recommendations for Implementation of Uniform Project Identification from the UPI Task Force

For years project identifications have been based upon county, section, subsection, and phase of work. While this system worked well in the beginning, overlay constructions, widening efforts, etc. have caused overlapping of projects to the point that identification of a given portion of a highway has become very difficult. Furthermore, each of the many separate phases of work has its own project number and may not be so readily identifiable as the succeeding work phase. Management came to realize there was a need for a numbering identification system that would be readily understandable. The direct result was the development of the Reference Point (RP) system and the resulting use of the Hardin County file on the GIM computer system. Subsequently, the Division of Planning was given the responsibility of assigning RP\u27 s to all state system highways and preparing a complete set of county RP maps and RP descriptions. On May 15, 1973, the Secretary of Transportation signed Official Order No. 80184 (see APPENDIX A) authorizing the formation of the Uniform Project Identification (UP!) Task Force, which was to be responsible to the Highway Indexing System Evaluation Committee. The Task Force personnel were assigned by mid-July, and the first meeting was held the end of July 1973. Meetings were conducted during August, September, early October, and late November 1973, and resulted in the issuance of memorandums dated August 15, 1973, and September 24, 1973 (see APPENDIX B)

Sensitivity Study of 1986 AASHTO Guide for Design of Pavement Structures

A sensitivity study of 14 items added to the 1986 AASHTO Guide for Design of Pavement Structures indicated: (1) variations in percent reliability were most influential on the design EAL for the same pavement structure while (2) variations in standard deviations had minimal effects. (3) Resilient moduli for base and subbase materials are very dependent upon stress state (or bulk stress). (4) A method was developed to quantify the effect of drainage capabilities for various soils and its effect upon reduction in structural coefficients for base and subbase materials. (5) Literature review revealed 13 relationships to define soil stiffness. The 1986 Guide has two equations for subgrade resilient modulus that yield results differing by factors of 2 to 10. Caution in their use cannot be over emphasized. (6) A method to account for environmental changes in subgrade materials is included in the 1986 Guide. (6) Temperature effects upon asphaltic concrete stiffness are not included. Sensitivity studies showed that temperature effects on pavement stiffness and variations in Structural Number far overshadow variations in subgrade stiffness. (7) The amount of material pumped from under rigid pavements appears to be a function of the number of axles passing over the spot rather than the number of groups of axles. (8) Kentucky and AASHTO load equivalencies were compared for the same stream of truck traffic. Fatigue data from the AASHO Road Test were used to compare the Kentucky and AASHTO thickness designs for the same soil stiffness. (9) The inclusion of mechanistic principles in pavement design was evaluated and discussed. (10) A value of 3.1 is recommended for the load transfer coefficient, J, because trucks travel with their tires located at the pavement-shoulder joint. (11) Kentucky employs most of the recommended rehabilitation procedures, or has more sophisticated procedures for those not being used. In some cases, economics has ruled out one, or more, of these procedures. (12) Kentucky thickness design methods include low volume roads. (13) Life cycle costs and pavement management were not included in this study because they are subjects of individual studies currently in progress