Author(s)

A. Cartenì

Abstract

All the elements of a transportation system model generally suffer from some approximation. Normally the demand vector is considered the most crucial and problematic element to be simulated, and traffic counts are thus generally used to update it so that the whole model system is able to reproduce the observed link flows. Updating demand vectors using traffic counts has received considerable attention in recent years. In this paper the methodology proposed by Cascetta and Postorino (Fixed point models for the estimation of O-D matrices using traffic counts on congested networks. Transportation Science, Vol. 35, 2001) for updating the demand vector using traffic counts on congested networks is applied to a real case: the OD demand vectors for the city of Naples (Italy). The results show the good capacity of this methodology to reproduce the traffic counts measured. Furthermore, through the estimated OD vectors it was possible to make a structural analysis of transportation demand in Naples. Keyword: origin-destination demand updating; bi-level programming problem; transportation simulation model. 1 Introduction A transportation system can be defined as the combination of elements and their interactions, which produce the demand for travel within a given area and the supply of transportation services to satisfy this demand (Cascetta [7]). The interactions among the various elements of a transportation system can be simulated with mathematical models. Supply models simulate the performances of the transportation services available in the different zones and demand models simulate the aspects of travel demand as a function of the

Keywords

origin-destination demand updating; bi-level programming problem; transportation simulation model.