$B9V;U(B:Dr.Vittorio Marzano, Universita degli studi di Napoli Federico II
$BBjL\(B:Developing effective O-D flow estimation/updating using traffic counts: Results and research prospects
Abstract: The seminar describes the main results of research activities on origin-destination (o-d) flows updating based on traffic counts, carried out by the research group at the University of Naples (Italy). A key issue in o-d flows updating is is the dimensionality of the problem: by means of laboratory experiments, o-d flow updating is shown effective generally only when the ratio between equations (i.e. independent counted link flows) and unknowns (i.e. o-d flows) is close to one. To achieve such balance, a within-day quasi-dynamic o-d flow estimator from traffic counts is presented, under the assumption that o-d shares are constant across a reference period, whilst total flows leaving each origin vary for each sub-period within the reference period. The advantage of this approach over conventional within-day dynamic estimators is to reduce drastically the number of unknowns, given the same set of observed time-varying traffic counts. The realism of the quasi-dynamic assumption and the theoretical and operational properties of the proposed quasi-dynamic estimator are discussed and tested on the real test site of A4-A23 motorways in North-Eastern Italy. Another possibility to balance unknowns and equations in o-d flows updating is to reduce the number of traffic zones in the study area, being the number of o-d flows proportional to the square of the number of traffic zones. Thus, an innovative optimization method for designing traffic zones to support o-d flows estimation/updating and relevant link flows estimation is also presented, and applied to a real case study in the Metropolitan Area of Napoli (Italy).