Frequency optimization of a moderately congested public transit system

This paper addresses the problem of the frequency optimization of transit lines in a congested transit network. We consider the transit frequency optimization model proposed by Constantin and we modify it to consider vehicles capacity indirectly. The model is formulated as a two levels Min–Min optimization problem with the same objective function at both levels. This function represents the transportation time including a congestion penalty. The upper level corresponds to the transit operators' optimization problem and the lower level describes the users' behavior. A descent direction for the problem is obtained by using sensitivity analysis of the lower level problem. Computational results are presented for the Winnipeg (Canada) and the Stockholm (Sweden) transit networks.