Secondary level bus network design: new method and case study

We propose a new method to generate a secondary level public transport network, which considers explicitly the interaction with an existing primary level trunk network. While the trunk network operates high speed and capacity services to support high demand corridors, the services of the secondary network are operated by regular buses running over the street network and include both feeder routes that connect to the trunk, and independent routes that serve demand which does not use the trunk network. The proposed method is an extension of an existing heuristic which generates routes based on shortest paths between high demand origin-destination pairs and the insertion of further nodes in existing routes, seeking to obtain solutions which are convenient to both users and operators. Due to the nature of the resolution method, the results are sensitive to the operational speed of the trunk network and to the imposed maximum route length. We apply the proposed methodology to a case study related to a medium-size city, where trunk corridors are planned to be deployed in an incremental way, which poses the need for having a systematic procedure to adjust the complementary secondary level bus network. Experimental results allow us to conclude that a fast trunk network reduces the user total travel time and the operational cost of the secondary bus network. Moreover, it reduces the usage of urban public space and improves its environment, by reducing the size of the operating fleet. This work provides a preliminary method to solve a relevant planning problem and formulates some conclusions regarding the relationship between the primary and the secondary public transportation networks. Finally, we identify some extensions to improve the proposed method toward its application to real settings.