The results of the comparative analysis showed that the AASHTO 1993 method generally under-predicted rigid pavement performance relative to the MEPDG, although the results varied widely between alternative rigid pavement designs. Many of the new flexible pavements and asphalt overlays of existing flexible pavements could not be re-designed to meet the MEPDG performance criteria by increasing the asphalt layer thickness. The asphalt layer thicknesses obtained using the MEPDG exceeded the asphalt layer thicknesses obtained using the AASHTO 1993 method, and a poor correlation was observed between the asphalt layer thicknesses obtained using the two methods. The MEPDG predicted that most of the new flexible pavements and asphalt overlays of flexible pavements designed using the AASHTO 1993 method would fail primarily due to permanent deformation and / or roughness. The results of the comparative analysis demonstrate that the AASHTO 1993 method generally over-predicted pavement performance relative to the MEPDG for new flexible pavements and asphalt overlays of flexible pavements.
Finally, the AASHTO 1993 and MEPDG methods were compared based on the thickness of the asphalt concrete or Portland cement concrete layers required to satisfy their respective design criteria. The purpose of this stage of the analysis was to determine whether the two methods predicted pavement performance in a consistent manner across a range of design conditions typical of Ontario. First, the nationally-calibrated MEPDG pavement distress models were used to predict the performance of the pavements designed using the AASHTO 1993 method. Historical flexible, rigid, and asphalt overlay pavement designs completed using the AASHTO 1993 pavement design method for the MTO were evaluated using a two-stage procedure. The purpose of this research was to conduct a comparative analysis of Ontario structural pavement designs using the AASHTO 1993 Guide for Design of Pavement Structures and the Mechanistic-Empirical Pavement Design Guide. Although the MEPDG provides a rational pavement design procedure with a solid foundation in engineering mechanics, a considerable amount of work is required to adapt and validate the MEPDG to Ontario conditions. The Mechanistic-Empirical Pavement Design Guide (MEPDG) was developed to address the perceived limitations of the AASHTO 1993 Guide.
Despite its widespread use, the AASHTO 1993 pavement design method has significant limitations stemming primarily from the limited range of conditions observed at the AASHTO Road Test from which its empirical relationships were derived.
The AASHTO 1993 Guide for Design of Pavement Structures is the most widely used pavement design method in both Canada and the United States, and is currently used by the Ministry of Transportation of Ontario (MTO) for both flexible and rigid pavement design.
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