Ontario's OPAC design method, developed in the early 1970's,was mechanistic-empirically based. A key feature was the performancemodeling approach which separated traffic and environment associateddeterioration. A new, comprehensive "OPAC 2000" hasbeen developed as the successor to the original OPAC. This newpavement design method is also mechanistic-empirically based,with separate load-associated and environment associated performancemodels. However, the updated models have been calibrated froman extensive, long-term performance data base (incorporating agevs PCI, layer thicknesses, ESAL's, etc.). Moreover, they havebeen regionally adjusted using a clustering technique. As well,reliability analysis has been included based on the second momentapproximation method to obtain variance estimates for the parameters.Validation checks indicate very reasonable results.

While the framework of OPAC 2000 will be summatized in termsof the major modules and subsystems, including a comprehensiveeconomic analysis module, the paper concentrates on the performancemodeling effort and results. It is suggested that even thoughthe calibration has been carried out with the Ontario data base,the approach is generic in that the model form is transferableand could be calibrated to other regions.