Methods of generating random air traffic are described for two- and three-dimensional computer models used in a study of the problem of managing off-route traffic. Edge effects which influence the estimation of conflicts taking place near the boundaries of such models are explained and quantified.The applications of computer models in air traffic management studies are many and varied. References 1 and 2 describe some of these for which the appropriate model required the generation of randomly distributed aircraft following straight-line flight paths at constant speeds. Such behaviour can be a plausible representation of that of off-route air traffic for many purposes and the main objective of this paper is to describe methods for generating random traffic of this nature, that is traffic outside airways, terminal control areas and aerodrome control zones.