Mechanistic-Empirical Pavement Design Guide (MEPDG)

Heavily trafficked highway

Challenge

Until recently, many state highway agencies were designing their highway pavements in accordance with the 1993 AASHTO Guide for Design of Pavement Structures or one of its predecessors. This procedure was considered the standard design procedure among virtually all states, as well as in several other countries, and is based on empirical relationships derived from the AASHO Road Test conducted from 1958 to 1960 in Ottawa, Illinois.

Since that time, changes in cross sectional design, advances in material science, vehicular design changes, and increased volume and weight distribution of traffic have all served to make this empirical data archaic. Because of these limitations, the majority of pavement designs conducted using the 1993 AASHTO Design Guide are outside the inference space of the original data.

The pavement engineering industry called for a more robust, mechanistic-based pavement design procedure that allowed designers to analyze the impacts of project-specific subgrade, climate, materials, and traffic and determine future performance in terms of pavement distress accumulation and ride quality deterioration.

Solution

To improve the design and performance of roadway pavements, ARA, in collaboration with our industry and university teaming partners, developed the Mechanistic-Empirical Pavement Design Guide (MEPDG) methodology and software as part of National Cooperative Highway Research Program (NCHRP) Project 1-37A. The MEPDG employs mechanistic-empirical approaches that promote accurate characterization of pavement structures and provide uniform guidelines for designing new and rehabilitated flexible, rigid, and composite pavements. By using these approaches, engineers can create more reliable pavement designs.

The MEPDG includes procedures for evaluating existing pavements and recommendations for rehabilitation treatments, drainage, and foundation improvements. In addition, there are procedures for performing traffic analyses, including options for calibrating to local conditions and incorporating measures for design reliability. Engineers can use the MEPDG to analyze common causes of pavement distress, including fatigue, rutting, thermal cracking in asphalt pavements, and cracking and faulting in concrete pavements.

ARA has continued to improve upon the software developed under NCHRP Project 1-37A, and the current version—AASHTOWare Pavement ME Design—is available through AASHTO.

Because the MEPDG procedure is so different from past, purely empirical procedures, agencies have found a need for training and assistance to implement and use it. Many have chosen ARA to provide products and services to aid in the implementation of the MEPDG. We work closely with an agency to define the goals and objectives of their MEPDG implementation, help generate a detailed implementation plan, and assist in the actual implementation process. Our assistance can include the development of pavement design protocols, establishing testing procedures, defining traffic input formats, materials characterization, environmental data applications, and addressing software issues. We also perform local calibration and validation of the MEPDG performance models to ensure that the resulting designs are appropriate for local conditions.

Impact

The MEPDG represents a significant advancement and paradigm shift in pavement design. The mechanistic-based nature of the methodology and the modular design of the software will allow for ongoing enhancement of the MEPDG as new material characterization, traffic, climate, and analysis models are developed. As such, the MEPDG is expected to drive the future of pavement design and analysis for the next 50+ years.

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Pavement Engineering

Pavement Engineering

Mechanistic pavement design, evaluation and testing, pavement management systems, performance modeling, life cycle cost analysis, accelerated... more