Optimal Length of Transit Network with Traffic Performance Microsimulation

This paper examines the design of high-performance transit networks that minimize transit agency costs, the time of transit users in the system, and the travel time of car users. Surface transit services need segregated lanes to achieve a target cruising speed so that the transit network length has a significant effect on traffic performance. This effect is modeled with the macroscopic fundamental diagram (MFD). The optimization proceeds in two steps. First, an analytic model defines the optimal layout of surface transit networks according to the time headway, stop spacing, line spacing, and network size variables. Then, the average travel time of the traffic network is evaluated with the MFD curve corresponding to the former transit network length. The full methodology has been implemented in the city of Barcelona, Spain. MFD was calibrated in the city's central district by means of traffic microsimulation runs. The social optimum for the number of corridors is 15, somewhat smaller than the optimization that does not consider traffic (23 corridors).