Assessment of Data Collection for ESAL Determinations for the Kentucky Transportation Cabinet, Division of Planning

The Kentucky Transportation Cabinet's Division of Planning collects weight data, traffic volume data, and vehicle classification data. This information is used as inputs in determining ESAL' s (equivalent single axle loads). ESAL's are used in the pavement design process to determine pavement thickness. There have been inconsistencies observed during the computation of the ESAL's during the past three or four years. These inconsistencies have resulted in a significant inflation in the estimate of ESAL's per year, which if used in the design process would result in significantly thicker pavements. The inconsistent data is most obvious for Aggregate Class II (rural principal arterials and rural minor arterials), Aggregate Class V (urban other freeways and expressways and urban other principal arterials), and Aggregate Class VI (urban minor arterials, urban collectors and urban locals). More specifically, in Aggregate Class II between 1998 and 1999, the ESAL' s per truck axle more than doubled from, 0.275 to 0.555. However, there was only a small increase in the number of ESAL's per axle in Aggregate Class II after 1999, but these values remained significantly higher than expected. A substantial increase in the number of ESAL' s per truck axle was observed in both Aggregate Class V and Aggregate Class VI between 1999 and 2000, nearly tripling and quadrupling, respectively. The ESAL's per axle determined for the succeeding years in these two aggregate classes did not increase dramatically but again, were extremely higher than preceding year's data would have predicted through use of a trend line. The objective of this research study will be to examine in detail the weight data collection equipment, on-site calibration procedures, and sampling techniques used by the Division of Planning for the different Aggregate Classes of highways. This effort will attempt to standardize procedures used by the Division of Planning to collect weight data and ensure that a statistically valid sample is obtained for each of the Aggregate Classes to properly define traffic characteristics. Data collected during the years from 1998 through 2001 will be analyzed to determine if the data can be used to accurately calculate equivalent single axle loads. The data collected for all Aggregate Classes will be statistically evaluated and recommendations will be made to utilize only those data that exhibit a demonstrated confidence. The Kentucky Transportation Center will also initiate and complete a review of practices currently being used by states that collect traffic information used in the determination of equivalent single axle loads. It is anticipated that the review would encompass both equipment and procedures being used and what, if any, problems these states may have experienced. Because of the changes in coal truck configurations and loads during recent years, the use of the "coal haul" algorithm to determine coal trucks will be investigated to assess implications of its use in the determination of equivalent single axle loads. The work plan will be subdivided into the following tasks: Task 1: A vigorous examination of the weight data collection and related traffic classification equipment will be initiated. This examination will review the on-site calibration procedures used and the weigh-in-motion sampling techniques for the different Aggregate Classes, I through VI. The accuracy level between equipment permanently Task 2: Task 3: Task 4: Task 5: installed to collect weight data and portable equipment will be investigated. Systematic errors will be identified and corrected. Based on these findings, recommendations will be made to the Division of Planning to standardize sampling and calibration techniques. It is anticipated that the Division of Planning, prior to fourth quarter data collection activities, would consider any recommended procedural changes for implementation and that some evaluation of these changes is necessary. Unedited weigh-in-motion data will be statistically evaluated for an identifiable bias or pattern that would indicate unreasonableness. A bias or pattern in the data may be adjusted that will allow the information to be used in calculating equivalent single axle loads for those years already identified as questionable. A comprehensive review of available literature will be performed to determine what equipment and sampling methods other states are using to collect traffic weight and classification data and whether those states have experienced biases in the data collected. Investigate the implications of the use of the "coal-haul" algorithm in the determination of equivalent single axle loads. Recommendations to modify the methods used to collect and analyze data for determining equivalent single axle loads will be developed by the team of researchers at the Kentucky Transportation Center and presented to the Division of Planning.