The introduction of new technologies into the field of transportation reformulates the question of the link between field studies and laboratory studies. With the use of computers, it has become possible to simulate the operator's behaviour, and to work out dynamic aids for displacement. The planning of taxi journeys is one of the many applications in which computers are contributing to the organization of displacements. At the same time, this approach has opened up new theoretical lines of research concerning the investigation of the cognitive processes involved in displacement planning.