This paper presents an ongoing development of an architecture of travel behaviour models based both upon a system dynamics approach and an econometric approach. This system of models is intended to simulate the medium and long term effects of transport policies from a point of view of sustainable mobility. However, the necessary articulation of the behavioural change, the transformations of the activity locations and urban space, the socio-demographic tendencies and the transport supply, leads to an increasing complexity of the existing models. The control of this complexity seems increasingly difficult. The sensitivity of the results to the multiple parameters of a system of four-step models, to the specification of each model, and to the feedback mechanisms, seems quasi impossible to explore systematically, but only by empirical tests. The system dynamics approach makeS it possible to quickly implement tests on the structure of the models to answer questions such as 'if the predictive model is specified thus, how evolve the forecasts?'. The approach consists in building systems of models integrating at the same time the simulation techniques resulting from the system dynamics approach and various elementary 'bricks' of econometric models. A modelling platform of urban travel was developed by exceeding a sterile opposition between detailed quantitative econometric approach and qualitative approach of systems dynamics. In short it is a question of putting econometric equations in the feedback loops, and of avoiding everywhere where that is possible purely qualitative approaches. First of all the conceptual architecture of the various mechanisms of feedback between bricks of models are presented. Then the already validated bricks of model are presented, namely: an assignment model based on a shortest path algorithm and on a modelling of the congestion by a queuing model (capacity seen as a bottleneck); a model of departure time choice coupled with the previous queuing model, which allows to make endogenous the departure time choice and thus represents the dynamics of the congestion; a model of modal split based on a price-time model (distribution of values of time); a model of regulation of the public transport financing, taking into account the constraint of scarcity of the public resources and its consequences on the operation and attractiveness of public transport. Finally the linkage of these models will make it possible to illustrate the dynamics of the urban travel system, in particular how transport policies, jointly with demographic and economic dynamics, can make the system to branch out or even break down. For the covering abstract see ITRD E126595.
Abstract