THE CELL TRANSMISSION MODEL .2. NETWORK TRAFFIC

This article shows how the evolution of multi-commodity traffic flows over complex networks can be predicted over time, based on a simple ma croscopic computer representation of traffic flow that is consistent w ith the kinematic wave theory under all traffic conditions. The method does not use ad hoc procedures to treat special situations. After a b rief review of the basic model for one link, the article describes how three-legged junctions can be modeled. It then introduces a numerical procedure for networks, assuming that a time-varying origin-destinati on (O-D) table is given and that the proportion of turns at every junc tion is known. These assumptions are reasonable for numerical analysis of disaster evacuation plans. The results are then extended to the ca se where, instead of the turning proportions, the best routes to each destination from every junction are known at all times. For technical reasons explained in the text, the procedure is more complicated in th is case, requiring more computer memory and more time for execution. T he effort is estimated to be about an older of magnitude greater than for the static traffic assignment problem on a network of the same siz e. The procedure is ideally suited for parallel computing. It is hoped that the results in the article wilt lead to more realistic models of freeway flow, disaster evacuations and dynamic traffic assignment for the evening commute.