Validation of the MEPDG Transfer Functions Using the LTPP Test Sections in Georgia

The Georgia Department of Transportation (GDOT) is transitioning from empirical design procedures to the Mechanistic-Empirical Pavement Design Guide (MEPDG) procedure for designing new and rehabilitated highway pavements. GDOT currently uses the 1972 AASHTO Interim Guide for Design of Pavement Structures as the standard pavement design procedure. As a part of the implementation process, GDOT has undertaken a project to verify the MEPDG global distress models and locally calibrate these models for local field conditions of Georgia, if determined to be necessary by the verification process, using the Long-Term Pavement Performance (LTPP) and non-LTPP sections in Georgia. One objective of this project is to verify or confirm that the MEPDG transfer functions and global calibration factors derived from NCHRP project 1-40D reasonably predict distresses and smoothness for the LTPP sites located in Georgia using proper design inputs. This report includes a comparison of the predicted and measured distress and International Roughness Index (IRI) values measured over time and between different projects, pavement design features, and/or site condition features. The confirmation process follows the procedure presented in the AASHTO MEPDG Local Calibration Guide (AASHTO, 2010). Specifically, this report documents use of the LTPP sites in Georgia to determine the bias and accuracy of the MEPDG transfer functions in predicting the distress and performance of those LTPP test sections. In summary, the number of Georgia LTPP sites and levels of distress exhibited on the test sections are considered inadequate for the validation or confirmation process of the global calibration coefficients from a statistical perspective. More importantly, bias between the measured and predicted distress for some of the transfer functions of both flexible and rigid pavements were found. Thus, it is recommended that GDOT proceed with the next phase of the study and select projects to fill in the many key gaps so that the calibration process can be used to adjust the calibration coefficients for each distress.