A control scheme for freeway traffic systems based on hybrid automata

  • Authors:

  • Simona Sacone;Silvia Siri

  • Affiliations:

  • Department of Communications, Computer and Systems Science, University of Genova, Genova, Italy 16145;Department of Communications, Computer and Systems Science, University of Genova, Genova, Italy 16145

  • Venue:
  • Discrete Event Dynamic Systems
  • Year:
  • 2012

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Abstract

In this paper a hybrid control scheme is devised in order to regulate traffic conditions in freeway systems. The considered control actions are ramp metering, i.e. using traffic lights at the on-ramps in order to regulate incoming traffic, and variable speed limits to be displayed on on-road variable message signs. The proposed scheme is composed of two levels: the lower level is characterized by different Model Predictive Control regulators, whereas at the higher level the different control actions are chosen according to a discrete-event dynamics. The overall scheme is then represented with the formalism of discrete-time discrete-event automata. More in detail, at the lower level, the prediction model used in the Model Predictive Control schemes is the first-order dynamical model of traffic flow in which we approximate the steady-state speed-density characteristic as a piecewise constant function. This approximation is motivated by the fact that we need a simpler finite-horizon problem to be solved on line, that in this case becomes a Mixed-Integer Linear programming problem. Depending on the system operating conditions, different regulators are determined by means of suitable Model Predictive Control schemes. The higher level of the control scheme has the function of identifying the present operating conditions and then switching to the suitable control action. The reported numerical results show the effectiveness of the proposed hybrid control framework.