Combined Model for Intermodal Networks with Variable Transit Frequencies

The formulation and solution of a combined mode choice and assignment, intermodal network equilibrium model with asymmetric link cost interactions are presented. Automobile, bus, and rail are the modes considered as travel options in the proposed formulation, along with the combined automobile-to-bus and automobile-to-rail intermodal options. Using park-and-ride facilities as transfer points, travelers may switch from automobile to transit. There is a two-way interaction between automobile and bus transit. The presence of transit vehicles on the highway links is registered through a bus–car equivalency factor, and the transit travel time depends on the highway link congestion level. Transit travel times are also subject to congestion at the transit stops because of boarding and alighting. Transit frequencies vary, depending on the level of congestion. The solution algorithm for the variational inequality and the derivation of the descent direction for the diagonalized problem are also presented. A test network is developed, and several tests are presented to show the convergence of the algorithm as well as the changes in the transit level of service due to transit and highway congestion