Coordinated Ramp Metering With Priorities

Ramp metering systems on motorways in urban areas need a level of coordination, otherwise, traffic on some on-ramps has much more difficulty entering the motorway than on others. The existing rule-based algorithms are a substantial improvement over the uncoordinated case, but this way of coordination still lacks flexibility. This is because the traditional algorithms take the existing ramp metering systems as starting point, which has inherent limitations, as these systems were not designed to operate in a setting with coordination. In this study, a more fundamental approach is taken, by considering the network of a motorway segment with a small number of on-ramps, and addressing both internal performance and the role the network should play in its surrounding network. The fundamental approach has been expressed in a generic, scalable model for network management, and the quantitative hierarchical model. When this model is applied to ramp metering, it becomes easy to assign priorities to the different on-ramps and to the motorway. This way of coordinating on-ramps offers far greater flexibility to support various traffic management policies. Moreover, it offers a perspective to extend the managed area to networks of virtually any size.