Fault-tolerance in decentralized motorway traffic management

Abstract

In the Dutch motorway traffic management (MTM) system used by Rijkswaterstaat, a central system and multiple outstations alongside the road communicate with each other to keep highways safe. This makes the MTM system a form of distributed flow control system. However, Rijkswaterstaat faces 2 problems with regards to traffic control: the control system is hierarchical leading to a single point of failure and communication failures between the central system and the outstations lead to unsafe situations. A solution to both problems is the use of a multi-agent system (MAS). However, no fault-tolerant MAS solution exists for the type of flow network that the highway network is. We therefore design our own fault-tolerant MAS solution for flow networks where the failure of a controller does not change the characteristics of the flow network. Our design associates an agent with every outstation in the network giving it the ability to make its own decisions. The communication protocol used by these agents to communicate with each other is capable of detecting communication failures with outstations and rearrange them so that the control action remains unchanged. This results in a system which keeps the highway safe when one or more outstations or their communication abilities fail.