This synthesis will be of interest to engineering managers, design engineers, traffic engineers, computer personnel, and others interested in advanced computer applications for highway design and operations. Information is provided on the history of knowledge based expert systems (KBES), current applications of these systems in transportation departments, potential applications, and hardware and software requirements. Additionally, some detailed programming information from two operational expert systems is included. There is growing use of computers in transportation departments, and KBES represent an area in which several highway agencies are gaining experience and obtaining promising results. This report of the Transportation Research Board describes the current state of the practice with respect to KBES, as well as the historical development of expert systems and the more general field of artificial intelligence. Experience with expert systems in transportation in summarized, including discussions of expert systems in operation and in development, based on a review of the literature and a survey of the states and experts in this field.