Expansion of bi-modal express transit networks − a hybrid optimization approach

Existing research has predominantly concentrated on designing a new transit network without considering the pre-existing network. However, the majority of problems involve redesigning or extending an already existing network. Considering the pre-existing multi-modal transit network in a city, we have integrated analytical methodologies and mathematical programming to formulate a two-stage approach for addressing the bi-modal express transit network design problem (ETNDP) within the context of a surface express transit system. In the first stage, we use analytical approaches and continuum approximations to identify the optimal locations of new stations. In the second stage, mathematical programming is proposed to simultaneously determine the optimal layout of express transit routes, the technology of each transit route, and the service headway associated with all transit routes (i.e., existing and new routes). Then, a metaheuristic algorithm based on a Genetic Algorithm is introduced to solve the proposed mathematical programming for real-size transit networks. The proposed approach has then been applied to the express transit network of Calgary, Canada, a large-sized bi-modal express network. The bi-modal ETNDP has been solved for Calgary under various scenarios, and the results have been discussed. Analyses show that, in the proposed hybrid approach, solving a part of the problem analytically reduces its complexity significantly and enables parametric analysis, while using mathematical programming helps to address the complexity of ETNDP for real transit networks. The proposed approach stands out from existing similar studies due to its departure from simplifying assumptions concerning network topology, the city’s structure, capturing any type of demand patterns, model flexibility to for existing transit network extension, and multi-modality of the express transit network.