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Local Calibration of the MEPDG Using Pavement Management Systems
Chapter 1. Introduction
The Mechanistic-Empirical Pavement Design Guide (MEPDG), prepared under NCHRP 1-37A and available from the Transportation Research Board (NCHRP 2004), is a significantly improved methodology for the design of pavement structures. Implementation of the MEPDG is expected to improve the efficiency of pavement designs and enhance the abilities of state transportation departments to predict pavement performance, which will thereby improve their ability to assess maintenance and rehabilitation needs over the life of the pavement structure.
Before the MEPDG can be fully implemented, it has to be calibrated using actual pavement design input and response data to ensure its validity and accuracy. As part of an initial calibration effort, the MEPDG performance models were calibrated and validated primarily using data from the Long-Term Pavement Performance (LTPP) program. Although the LTPP database represents a valuable resource, the enormous variability between the states in terms of geography, climatic conditions, construction materials, construction practices, traffic compositions and volumes, and numerous other pavement design variables make it desirable to calibrate the MEPDG at the local level using local field pavement data. This is not a simple task and requires a great deal of effort to evaluate the inputs needed to accurately reflect the uniqueness of pavement needs for an individual state. Of the three levels of input for MEPDG, the site specific materials, climatic, and traffic data (Level 1 data) most accurately reflects the local situation, the estimated regional data (Level 2 data) are more regionally based but less accurate, and the default data (Level 3 data) are for situations where more specific information is simply not available. The advantage of providing these three levels of input is that the MEPDG can still be used to design pavement structures with acceptable results even if specific Level 1 or Level 2 data are not available. Theoretically, the most accurate pavement design would be the one that used the MEPDG software that was calibrated using Level 1 data and used as many Level 1 and Level 2 data inputs as possible.
One of the first challenges in moving toward the use of the MEPDG is related to the collection of the data needed to support a local calibration effort. Pavement data collection and analysis is expensive, time consuming, and resource intensive, but significant savings could be realized by State Highway Agencies (SHAs) if existing pavement management system data could be used for MEPDG model calibration. An associated benefit of using pavement management data is the inherent improvement in coordination between pavement management and pavement design within each SHA. However, problems that may exist with regard to pavement management data must be resolved before such data can be successfully used to locally calibrate the MEPDG procedure. Some of these issues include:
In 2006, the FHWA launched a research study to evaluate the potential use of pavement management data for calibration of the MEPDG (FHWA 2006a; FHWA 2006b). Under that study, eight candidate states were selected to participate: Florida, Kansas, Minnesota, Mississippi, New Mexico, North Carolina, Pennsylvania, and Washington. The study concluded that all the participating states could feasibly undertake MEPDG calibration using PMS (Pavement Management System) data (FHWA 2006a; FHWA 2006b). The study went on to say that it seems likely many other states could do the same. One recommendation was that each SHA should develop a satellite pavement management/pavement design database, which should include the regular pavement management data for each project being designed and constructed using the MEPDG. The data used in the design phase would be tabulated in electronic format, transferred, and stored in a satellite database compatible with the pavement management system database. Such an approach would provide a methodology for preserving the design information that is used with the MEPDG on a project-by-project basis. It would also provide a more formal interface between pavement management and pavement design. However, it also requires the duplication of some data typically contained in a pavement management database, which may introduce data conflicts at some point in the future.
This project was initiated to assist state highway agencies with an important aspect of the MEPDG implementation by building on prior research activities and implementation efforts. In this regard, this projects objective is to develop a framework for using existing pavement management data to calibrate the MEPDG performance models. The feasibility of the framework will be demonstrated using actual data from a SHAs pavement management system. Specifically, the overall objectives of this project include:
The final report is presented in two volumes: Volume I (Final Report) and Volume 2 (Appendices). This report (Volume 1) documents the entire research effort that was conducted under the project, and contains eight chapters in addition to this introduction.Chapter 2 provides a summary of the process used for identifying three states to be further evaluated for use in this study. Chapter 3 presents the results of the three state selection process. Chapter 4 presents the selection of the single state. Chapter 5 summarizes the preliminary framework development for utilizing pavement management data in the calibration of the MEPDG. Chapter 6 presents the workplan for implementation of the final framework. Chapter 7 discusses the verification of the selected agency’s input data for use in the MEPDG calibration process. Chapter 8 presents the calibration results, and Chapter 9 presents specific recommendations on data needs for using pavement management data for calibration of the MEPDG.