This paper describes recent experience with the development and performance of OVERDRIVE 1.2. a central component of PARADIGM (the Pavement Rehabilitation Analysis and Design Mentor). PARADIGM is a microcomputer-based tool to integrate a set of knowledge-based expert systems (KBES) and algorithmic models for pavement rehabilitation decision-making, particularly at the local level. Because the analysis and design of pavement rehabilitation strategies relies so heavily on experts, and many of the tasks involved are both complex and ill-defined, conventional computer tools are of limited use in this domain. A basic premise of this research is that KBES can play a significant role in addressing these problems. OVERDRIVE is the Overlay Design Heuristic Adviser, and is a research prototype KBES to assist local engineers evaluate the structural adequacy of existing flexible pavement and design the structural thickness of an asphalt concrete overlay. In this paper the general domain, the domain tasks addressed by the current version of OVERDRIVE, knowledge acquisition, knowledge representation and inference, and hardware and software are described. A case-study application is presented using actual data. This application permits an initial assessment to be made of the comparative performance of OVERDRIVE versus alternative overlay design methods.