Hierarchical Control of Automated Highway Systems

Roberto Horowitz
Department of Mechanical Engineering
University of California at Berkeley
Berkeley CA 94720-1740

Automated Highway Systems (AHS) is a concept intended to increase capacity and safety in current highways. This talk discusses some aspects of the hierarchical control of a fully automated AHS design, currently under development at the California PATH program. In the first part of the talk, we present an overview of an AHS architecture that is composed of five hierarchical layers: physical, regulation, coordination, link and network layers. Subsequently, we briefly discuss the function and modeling abstraction used to describe each layer, as well as the structure of the control system at each layer of the AHS controller hierarchy.

In the second part of the talk we discuss in some detail two aspects of the control system design for this architecture. The first concerns the design of safe regulation layer controllers, the second the design of traffic flow link layer controllers. In the case of the regulation layer, we assume that AHS traffic is organized into platoons of closely spaced vehicles and present conditions to achieve collision free joining and splitting of platoons, under normal operating conditions. Velocity profiles for all single lane maneuvers are presented, as well as a nonlinear tracking controllers that execute these maneuvers in minimum time, without compromising safety. Link layer feedforward and feedback traffic flow controllers are presented for different highways topologies, including multiple lane highways with multiple vehicle destinations. Lyapunov stability techniques are used to show that decentralized feedback flow control laws can stabilize vehicular density and flow around predetermined profiles. Finally we present, as an illustrative example, the design of regulation, coordination and link layer maneuvers for the transit of automated emergency vehicles, such as ambulances, fire trucks or police cars. The goal of these maneuvers is to permit an emergency vehicle to transit on the AHS at a faster velocity than the rest of the traffic, with minimal repercussions on the overall traffic capacity of the system.