Multi-level control of networks: the case of road traffic control

In this paper we illustrate multi-level network control by means of road traffic control. There is a natural and very common way of reducing the complexity of a network It consists of two steps: dividing the network into parts and introducing levels in the control of a network. Dividing a network into parts entails the introduction of levels: the internal control within each part is one level and the overall control of the parts is a second level. Applying these two steps recursively introduces a number of levels and a recursive decomposition of a network into a tree structure of parts. Each level has its own view on the network, its own control measures and objectives. A level's view on the network can often be represented by a simpler network. In two case studies we show how the levels and the subdivisions per level can be determined, which control measures and control objectives each level has and how the different levels interoperate. Moreover, we show why it is highly desirable that the simplified networks, representing the views on the network at each of the various levels, should be derived in an automated way, and how this can be done.