This paper describes the methodology used to adapt the 1993 AASHTO Guide for Design of Pavement Structures to Ontario conditions and the results achieved. The paper also outline additional work done to prepare the groundwork for the transition to the anticipated mechanistically-based 2002 AASHTO Guide. The discussion is confined to the design of flexible pavements only. The design inputs described in the paper include pavement load characterisation using equivalent single axle loads as well as axle load spectra, subgrade and material characterisation, initial and terminal serviceability, and reliability. The data used for the assessment and selection of design inputs were obtained from various sources including data collected on Ontario highway pavements and materials, results of previous research and development studies and laboratory investigations, a survey of opinions of many experienced pavement design engineers and other professionals working for the Ontario Ministry of Transportation, and a survey of the experience of other agencies. The work resulted in a new grouping of Ontario soils for pavement design purposes, recommended values for the resilient modulus of subgrade soils, recommendations for structural layer coefficients for Ontario smoothness specifications, and recommendations for design reliability based on value engineering principles. The paper provides a summary of specific changes and design recommendations. The recommended design inputs were subsequently verified to be appropriate by the results of the calibration and verification study. (Author/publisher)
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