Assignment in the Integration of Urban Traffic Control and Dynamic Route Guidance

Higher levels of market penetration of dynamic route guidance systems, such as the EURO-SCOUT system from Siemens, require that some form of adjustment is made for the consequences of routeing recommendations. Ideally a procedure is required that generates route recommendations such that no guided driver could have taken a faster route. This is a form of Wardrop equilibrium, and necessitates a dynamic equilibrium assignment algorithm in order to obtain such a set of route recommendations. The determination of a dynamic equilibrium assignment requires the derivation of travel time functions. In this paper it is proposed that link travel time measurements from the dynamic route guidance system be combined with link flow measurements from a traffic signal control system, and that the coefficients of the link travel time functions be estimated recursively. A modified Frank-Wolfe algorithm. for solving the dynamic equilibrium assignment problem is proposed. This requires the iterative use of a shortest path algorithm, such as that currently implemented in the EURO-SCOUT system. The properties of the algorithm are explored using a small numerical example.