Integrated Equilibrium Flow Models for Transportation Planning

Abstract

The conventional transport model (recursive in character) is a combination of three submodels, trip generation, trip distribution and assignment. As a rule, these stages are treated separately as if the travel choices involved in each one were made independently of the other. A careful examination of this procedure, however, reveals some significant weaknesses. Although quite sophisticated models based on behavioral assumptions have been developed for the assignment stage, the models available for the distribution and generation stages are less refined. As a result, serious internal inconsistencies arise. For example, the travel costs that are used as inputs for the distribution and generation stage are not the same as those which are outputs from the assignment stage. As a partial remedy, practitioners have devised in recent years an iterative scheme, in which the above model is imbedded, in the hope that the interrelationship between demand, supply and cost will be taken into account. Unfortunately, the above scheme does not produce in general equilibrium flows (see e.g. [6]). For these reasons we strongly believe that the substitution of the “first generation” recursive transport model by a “second generation” integrated transport model based on behavioral assumptions and the equilibrium concept will be an important step towards better planning of transportation systems.

This research was supported by N.S.F. grant No. GP28931.