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We propose a descent heuristic to solve the problem, which is an adaptation of the wellknown projected gradient method. After reformulating the problem to a single level problem, the objective function includes implicitly given link flow variables, corresponding to the given OD-matrix. We use a general nonlinear bilevel minimization formulation of the problem, where the lower level problem is to assign a given OD-matrix onto the network according to the user equilibrium principle. In this paper we consider the estimation of an origin–destination (OD) matrix, given a target OD-matrix and traffic counts on a subset of the links in the network. 339-354 Article in journal (Refereed) Published Abstract , K2, Kåkenhus, Linköpings universitet, Campus Norrköping, Norrköping, 13:15 (English)Ģ008 (English) In: Transportation Research Part B: Methodological, ISSN 0191-2615, E-ISSN 1879-2367, Vol. OD-matris, Trafikflödesobservation, Detektorallokering, Skattning, Trafikmodellering, Reseefterfrågan National CategoryĬomputational Mathematics Identifiers URN: urn:nbn:se:liu:diva-8859 ISBN: 978-91-8 (print) OAI: oai::liu-8859 DiVA, id: diva2:23558 Public defence Traffic modelling, Travel demand, Origin-Destination matrix, Traffic flow observation, Detector allocation, Estimation. Dissertations, ISSN 0345-7524 1102 Keywords Linköping Studies in Science and Technology. Place, publisher, year, edition, pagesInstitutionen för teknik och naturvetenskap, 2007.
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We formulate the problem to place link flow detectors as to achieve the least relaxation with a limited number of detectors. Presupposing that consistent flow observations from all the links in the network yields the best estimate of the OD-matrix, the lack of observations from some links results in a relaxation of the estimation problem, and a poorer estimate. There are different ways of quantifying a common goal to cover as much traffic as possible, and we create an experimental framework in which they can be evaluated. In the second study, an algorithm for time-independent estimation is extended to the time-dependent case and tested for a network from Stockholm, Sweden.įinally, we study the underlying problem of finding those links where traffic flow observations are to be performed, in order to ensure the best possible quality of the estimated OD-matrix. The first is a case study, where the conventional estimation technique is improved through introducing pre-adjustment schemes, which exploit the structure of the information contained in the OD-matrix and the link flow observations. The time-dependent OD-matrix estimation problem is the subject for two studies. Besides the problem of distributing the travel demand onto routes, the flow propagation in time and space must also be handled. When a time-dimension is considered, the estimation problem becomes more complex. A descent heuristic is proposed, in which special attention is given to the issue of calculating the change of a link flow with respect to a change of the travel demand in a certain pair of origin and destination nodes. We assume a user equilibrium to hold for the link flows in the network and recognize a bilevel structure of the estimation problem. Many methods have been suggested for OD-matrix estimation in time-independent models, which describe an average traffic situation. Both time-independent and time-dependent models are considered, and we also study the placement of link flow detectors. This thesis concerns the OD-matrix estimation problem, that is, the calculation of OD-matrices using observed link flows. 2007 (English) Doctoral thesis, comprehensive summary (Other academic) Abstract įor most kind of analyses in the field of traffic planning, there is a need for origin-destination (OD) matrices, which specify the travel demands between the origin and destination nodes in the network.