Hierarchical Centralized/Decentralized Event-Triggered Control of Multiclass Traffic Networks

Two hierarchical control schemes for regulating traffic in freeway networks via ramp metering are developed in this article. Both schemes are characterized by a multiclass nature and aim to jointly improve the total time spent by the vehicles and their pollutant emissions in the freeway network. Moreover, these schemes have been designed to be "implementation-oriented," i.e., they are characterized by a low computation and communication effort of the controllers while providing high performance in case of bottlenecks that may be far downstream on-ramp merging areas. The reduction of the computation and communication load is achieved through an event-triggered logic implemented at the higher level of the hierarchical scheme, in which the lower level is represented by extended multiclass ALINEA controllers characterized by time-varying parameters. The two proposed schemes differ for the fact that one is a centralized scheme, whereas the second one is decentralized. The effectiveness of the two schemes is evaluated by simulation in a realistic setting, also through a comparison with an optimization-based approach.