This paper describes how an expert system shell was used to create a knowledge-based system for speed zone determination. Speed zoning must be rational and consistent if it is to contribute to a speed management programme. The development, within a traffic authority, of speed zoning processes and decisions necessarily falls to a small number of experts who are often confronted with conflicting pressures from a range of interest groups. The paper describes the process whereby the knowledge of experts in the speed zoning area was established and developed into a rationale for system rules. The knowledge-based system developed is proving operationally successful, being user-friendly for both the experts for testing and development, and those wishing to use the system for speed zone determination. An outline is then given of the iterative monitoring procedure whereby the system is being ‘tuned’ to match expert decisions.