Modelling distributed real-time route guidance strategies in a traffic network that exhibits the Braess paradox

This paper examines the operational characteristics of a simple traffic network which produces a dynamic form of the Braess paradox when the in-vehicle link data base, that is used to guide vehicles in real-time through the network, is expanded to include a low capacity short cut link which was previously unknown to the drivers. The analysis focuses on the ways in which a route guidance system with distributed route selection logic, such as the TravTek system in Orlando, can be made to avoid the inefficiencies associated with the paradox without a priori knowledge of the existence of the paradox and while allowing each vehicle´s RGS computer to independently make routing decisions without the explicit knowledge of the concurrent routing decisions of other drivers. It is shown that this objective can be achieved by implementing a distributed form of a system optimum routing algorithm coupled with the use of a PROBIT type of error term to reduce some of the instabilities that are intrinsic in the travel time information feedback loop.