A personal experience of a traffic conflict is given. It is a dramatic illustration of the result of a confusion of rules, which has many of the hallmarks of the typical rule-based errors which can potentially lead to accidents, and which can be very satisfactorily explained with the help of theories of cognitive psychology based on production systems of rules. Cognitive theories of this nature, stimulated by the development in the field of artificial intelligence of rule based "expert system" software, are now being increasingly applied to the analysis of accidents in complex systems. They are also being used to formulate new approaches to the analysis of the driving task and driver training. In this paper the implications of these theories for the designers of road system hardware and software are described, as is the information which designers need in order to adapt their designs to predictable road user behaviour. Suggestions are made which relate to a possible common language which can be used by designers, students of road user behaviour and safety experts so that they can communicate with one another. It provides a language in which behaviour can be described, design constraints can be specified, instructions for the use of designs and for the training of road users can be written, and the policing of road user behaviour against risk compensation can be discussed. For the covering abstract of the conference, session III, see IRRD 813211.
Abstract