Possibilities and limitations of decentralised traffic control systems

Due to steadily increasing mobility and the resulting rising traffic demands, serious congestion problems can be observed in many cities. One promising approach to alleviate the congestion effects is the coordination of the network´s traffic signals in response to the traffic flow. The recently introduced Decentralised Progressive Signal Systems approach is an adaptive coordination mechanism for traffic signals in urban road networks that relies on local traffic data only. Since the decentralised process cannot lead to optimal results in some special cases, it is extended with an optional hierarchical component introduced in this paper. Based on a broader view on the current network traffic, this Regional Manager is responsible for determining which intersections are coordinated. The efficiency of the coordination determined by the Regional Manager is demonstrated in a simulation-based evaluation that considers the decentralised mechanism and an uncoordinated system for comparison.