An Integer Programming Formulation for Optimal Mode-Specific Route Assignment

Traffic in developing countries has a heterogeneous vehicular mix that uses all the network links and lacks lane discipline. Modeling and controlling such a mixed traffic system are challenging since most of the well-established models were developed for homogeneous traffic. It is hypothesized that segregating the mixed traffic by assigning a unique mode to each link will enhance system capacity. Towards achieving it, this paper proposes optimal mode-route assignment formulations with the objective of minimizing the total system travel time. However, perfect segregation is not always possible since the solution depends on the network topography. A viable solution is to make some links multi-modal. Another formulation is also presented in this paper to address this issue. Both the formulations are demonstrated using sample networks. Linear and nonlinear integer mathematical programming methods are used to explore the qualitative characteristics of optimal mode-route assignment using the single-path routing method. The results indicate that, in the worst case where perfect segregation is not possible, proposed formulation II can identify network with the least number of the multi-modal links. This research will help to develop effective strategies to model, control, and enhance the safety of mixed traffic networks.