California Partners for Advanced Transportation Technology

This paper presents a qualitative description of the evolution of traffic congestion during the morning rush hour in a long freeway leading to a single destination. Traffic is generated at the freeway’s many on - ramps during a short period of time and then is assumed to subside. Capacity limitations create queues on the ramps and the freeway, which is assumed to evolve according with the hydrodynamic theory of traffic flow. A special case that can be described with just a few parameters is analyzed in detail.

The simplicity of our scenario allows the results to be easily verified independently; they can then be used to check whether ‘the existing traffic assignment models are consistent with the basic laws of traffic flow. We found that unreasonable results are obtained with “point queue’’ models, currently a favored approach in the dynamic traffic assignment literature. A computer program, based on the cell transmission model (Daganzo, 1992), is put to the same test.