Optimizing contraflow scheduling problem: Model and algorithm

This article addresses the optimal contraflow scheduling problem that has arisen in the contraflow operation that has been implemented successfully in practice. The problem is formulated as a bilevel programming model in which the upper level problem is a binary integer programming formulation that aims to minimize the total travel time of a study area, while the lower level problem is a microscopic traffic simulation model that can simulate the dynamic reaction of drivers resulting from a contraflow scheduling scheme. As a consequence, such an adoption results in inexistence of analytical expression of the objective function in the upper level problem. Accordingly, conventional analytical solution methods for solving integer programming problems are no longer available for the proposed bilevel programing model. Therefore, this article develops a variation of the genetic algorithm that embeds with the microscopic traffic simulation module as well as a string repairing procedure to find the optimal contraflow scheduling solution. A case study in Singapore is carried out to evaluate the proposed methodology, in which PARAMICS as the microscopic traffic simulation model is applied.