Cities in western Europe are confronted with increasing problems not only in the transport sector but also in the environmental field, increasing social problems, city sprawl and loss of economic power. Economic activities are leaving the cities and settling along motorways, offering free parking opportunities for their customers. On the other hand, public transport, in former times the backbone of the transport system, is losing its customers and becoming a highly subsidised system. The increasing congestion on all carriageways for cars, particularly on motorways, is a clear symptom of a failing in the market economy in this sector. All kinds of treatment to mitigate or solve the problems have failed so far. The traditional approach seems to be totally wrong. The system has not been understood. A new approach, taking into account on one hand, individual human behaviour - which has not previously been the focus of traditional transportation planning - and, on the other hand, system behaviour, which has never been considered (although early studies from the end of the nineteenth century (Lill, 1889) point in this direction), offers the basis for understanding these unexpected effects. Countries in Southeastern Europe now have opportunities to avoid the main mistakes in city planning and transport system development, if they apply the scientific and empirically-sound findings. Motorisation in these countries is still much closer to a sustainable level than in most of the cities of western Europe. Although Newman and Kenworthy (1989) have no data from these cities in their diagram, it can be taken as given that most cities of Southeastern Europe are still in the sustainable position, considering density and energy for transportation.