Motor vehicle accidents are often difficult to resolve since the data is conflicting and of questionable validity. Conventional analysis requires a great deal of expertise on the part of the accident investigator. Problems that are conceptual and cannot be reduced to numbers can often be solved using expert system technology.KAR is a prototype rule based Knowledge-based Accident Reconstruction system used at the initial stage of an investigation. The program is capable of calculating vehicle speeds using any combination of the following techniques: skid, roll, overturn, yaw, vault, momentum and energy. The system's most notable feature is its interpretive abilities. The program is able to determine how to solve the mechanics of the accident, and verifies the evidence before it uses a particular method in the calculations. Additionally, an interactive explanation facility allows the user to examine the program's reasoning.