Effect of Modeling Assumptions on Evolution of Queues in a Single Corridor

A qualitative description is presented of queuing patterns under an idealized scenario analogous to the evolution of traffic congestion during the morning peak hour in a long corridor leading to a single destination. The simplicity of the scenario allows the results to be verified independently by hand. Initially the corridor is assumed to consist of a single freeway. Traffic is generated at the freeway's many on-ramps during a short period and then is assumed to subside. Capacity limitations create queues on the ramps and the freeway, whose evolution is then described. A special case with just a few parameters is analyzed in detail. The solution obtained under the assumptions of the hydrodynamic theory of traffic flow (which explicitly recognizes vehicle storage limitations on the freeway) is shown to be drastically different from the solution obtained using "point queue" models, which ignore these limitations. Because the latter models are currently a favored approach in the dynamic traffic assignment literature, results of this study illustrate the need for reevaluating the conditions under which current theories may be applicable. The effect that a slower parallel arterial would have on the system's traffic is also discussed. It was found that a route choice mechanism in which drivers do not anticipate the system's evolution leads to unreasonable traffic patterns--that is, patterns that would not be expected in reality. The anticipation phenomenon must thus be incorporated into any realistic model of dynamic network flows, which unfortunately, increases the difficulty of developing detailed control strategies.