Transportation network user equilibrium assignment by ant colony systems with a variable trail decay coefficient

The paper deals with deterministic and stochastic user equilibrium (DUE and SUE respectively) two well known problems in the transportation field where the transportation demand has to be assigned to the network. In order to solve these problems a modified version of the ant colony system is proposed evolving ACS from discrete to continuous optimization. The ant colony meta-heuristic is adapted theoretically in order to take into account many aspects characterizing the transportation problem: multiple ODs (Origin-Destination), link congestion, non-separable cost link functions different user cost models including stochastic cost perception. Other improvements are introduced into the ACS algorithm to speed up convergence for selecting the minimum cost path and especially for getting a variable trail decay coefficient, ρ. The application of the propose algorithm to the Sioux Falls test network is finally reported.