A multimodal transit network design procedure for urban areas

The paper introduces a new method for solving the transit network design problem in a multimodal, demand elastic urban context. The mathematical formulation as an optimization problem explicitly takes into account the relationship between demand modal split, level of transit service and transport externalities. The solving procedure consists of a set of heuristics, which includes a first routine for route generation, a genetic algorithm for finding a sub-optimal set of routes with the associated frequencies and various practical rules for solution improvement. The performances of the network are estimated by a probabilistic modal split model, which reproduces the mode choice behaviour of users, a hyperpath transit assignment model, which reproduces the bus line choice behaviour of transit users, and a deterministic user equilibrium assignment model, which estimates the effect of the interaction between route choice behaviour of drivers and link congestion at the equilibrium.