A hierarchical network model for road traffic control

Control of traffic in a network of roads may involve a large number of individual control loops, with various scopes and time scales, some of them working locally, such as traffic signals at a crossing, some of them coordinating a number of local control loops within its scope. In order to organize such a set of control loops, this paper proposes a hierarchical network model which is primarily based on a modularity property of networks. One of the prime applications of this hierarchical model is to derive an implementation architecture for the development of operational control systems, in order to achieve highly flexible control systems and thereby support the research in road traffic network control. The primary goal of this paper is to list the research issues in this approach.