A Freeway Traffic Control Model by First Order Hybrid Petri Nets

The paper proposes a model for real time control of freeways by ramp metering, an emerging technique for efficient freeway management. A modular framework based on first order hybrid Petri nets models the vehicle flows by a first order fluid approximation. Moreover, the lane interruptions and the signal timing plan controlling on-ramps are described by the discrete event dynamics using timed Petri nets. The proposed formalism enables the network designer to choose suitable ramp metering control signals in order to maximize the traffic flow by optimizing a suitable objective function. The optimal mode of operation is performed based on the state knowledge of the obtained linear discrete-time, time-varying state variable model of the freeway to react to unpredictable events such as the blocking of a lane due to an accident or to work in progress. The proposed model is applied to a case study to show its effectiveness.