Queue Spillback and Demand Uncertainty in Dynamic Network Loading

In the field, queue spillback contributes substantially to urban congestion. Therefore, most dynamic network loading models either explicitly include spillback, or frame a failure to model spillback as an unfortunate consequence of mathematical or computational tractability that should be relaxed in future work. Although models with spillback are undeniably more realistic, they are also less robust to errors in input demand. We show that when there is high uncertainty in input demand, excluding spillback can actually reduce error by reducing sensitivity to demand errors. Our demonstrations include a small network that can be solved analytically, and dynamic user equilibrium on two real-world networks representing Austin, TX, and San Antonio, TX. We conclude that model realism must be carefully balanced against the accuracy of the input parameters, and the sensitivity of the model to any such errors in these inputs.

A Model to Simulate Multimodality in a Mesoscopic Dynamic Network Loading Framework

A dynamic network loading (DNL) model using a mesoscopic approach is proposed to simulate a multimodal transport network considering en-route change of the transport modes. The classic mesoscopic approach, where packets of users belonging to the same mode move following a path, is modified to take into account multiple modes interacting with each other, simultaneously and on the same multimodal network. In particular, to simulate modal change, functional aspects of multimodal arcs have been developed; those arcs are properly located on the network where modal change occurs and users are packed (or unpacked) in a new modal resource that moves up to destination or to another multimodal arc. A test on a simple network reproducing a real situation is performed in order to show model peculiarities; some indicators, used to describe performances of the considered transport system, are shown.