In traditional assignment models, cars are assigned to a route and are therefore present on all links on that route simultaneously. Calculations from this type of model give few positive results. If the assignment is done in space with time as a third dimension, this problem can be overcome. The first part of the paper gives a simple example of the equilibrium assignment model showing that, in some parts of the network, congestion is unrealistically calculated as a consequence of bottlenecks upstream. The second part of the paper gives a description of the three-dimensional assignment models. The proposed algorithm conforms with existing two-dimensional assignment models, although details in the algorithm are different. The effect of improving the capacity of bottlenecks on congestion downstream is shown. A computer model of the assignment model works under ms-dos on a microcomputer. This paper appears in transportation research record no. 1220, Forecasting.
Abstract