Day-to-day dynamic models for Intelligent Transportation Systems design and appraisal

Transportation Supply Design (TSD) with demand assignment provides a powerful framework to support project appraisal, since modifications of existing and/or introduction of new transport facilities and/or services may greatly affect traveller behaviour, concerning path choice at least. TSD also includes the Design of Intelligent Transportation Systems (ITSs), such as Advanced Traveller Information Systems (ATISs) or Advanced Driver Assistance Systems (ADASs). Solution approaches available for all the above problems are based on user equilibrium (UE) assignment, with either Wardrop or (less frequently) probabilistic path choice models. Still, optimization of transportation supply under equilibrium assumption may not guarantee that an effective solution is obtained; indeed the system may not evolve towards the equilibrium state, if this state is not stable. Thus results of project appraisals based on equilibrium assignment only may be misleading. On the other hand, day-to-day dynamic models provide a more general approach to demand assignment, including as special cases equilibrium state.This paper aims at supporting this conclusion, by describing an extension of a deterministic process model to include the evolution over time of the total user surplus. According to this approach a project appraisal should be based both on the value of user surplus and its stability over time. A simple but effective application shows that the proposed approach can be applied to model the effect of ITS. Results for a small network show that an accurate design of ITS based on the effects on total user surplus requires a day-to-day dynamic analysis.

• A deterministic process is proposed to analyse equilibrium stability.
• Project appraisal should be based on user surplus value and stability.
• The proposed model can analyze the effects of the introduction of ITS.
• Design of ITS requires an analysis of the evolution over time.
• Carefully designed ITS may outperform improving of existing facilities.