1,721,315 research outputs found
Analysis and comparison of microscopic traffic flow models with real traffic microscopic data
Full text linkThe ever more widespread use of microscopic traffic simulation in the analysis of road systems has re-focussed attention on sub-models, including car-following models. The difficulties of micro-simulation models in accurately reproducing real traffic phenomena stem not only from the complexity of calibration and validation operations but also from the structural inadequacy of the sub-models themselves. These drawbacks both originate in the scant information available on real phenomena, due to the difficulty of gathering accurate field data. In this study, the use of K-dGPS instruments allowed trajectories of four vehicles in a platoon to be accurately monitored in real traffic conditions, both on urban and extra-urban roads. Some of these data were used to analyse the behaviour of four microscopic traffic flow models which differed greatly both in approach and complexity. The effect on model calibration results of the choice of performance measures was first investigated and inter-vehicle spacing was shown to be the most reliable measure. Model calibrations showed results similar to those obtained in other studies that used test track data. Instead, validations resulted in higher deviations compared to previous studies (with peaks in cross-validations between urban and extra-urban experiments). This confirms the need for real traffic data. On comparison, all the models showed similar performances (i.e. similar deviations in validation). However, if surprisingly the simplest model performed on average better than the others, the most complex one was the most robust, never reaching particularly high deviations
Conferimento di sismoresistenza a edifici storici: il caso della Pieve di S. Stefano di Sorano
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The effects of ATIS on transportation systems: theoretical analysis and numerical applications
No full textIn this paper some of the inconsistencies and limitations of other models in the simulation of the effects of ATIS (Advanced Traveller Information Systems) are discussed, with particular regard to the impact of pre-trip information on the day-to-day dynamics of transportation systems. An innovative model is proposed, where the compliance of travellers to ATIS is considered to be elastic and explicitly modelled; it is considered both variable within the whole dynamic process and dependent on the accuracy of the information. For the sake of simplicity, a fixed O/D demand is considered and the effects of ATIS are taken into account only on route choices. It is shown that in most cases ATIS cannot be used to optimise the performances of the traffic network (system optimum); rather, travellers are compliant to information only if supplied according to user optimum. Thus, the main role of ATIS in recurrent traffic conditions is shown to be the stabilisation of the transport systems. The first section of the publication introduces the motivations of the proposed model and how they have been addressed in literature, moreover it anticipates most of the innovative characteristic of the proposed model, as well as the expected accuracy of the results. In the second section the model is formalised as a dynamic process, which includes explicit simulation of compliance. In the third section the result of some numerical experiments, related to different information strategies, are presented; moreover, some theoretical analysis are carried out by determining the stability domain for the dynamic process in presence of information
Limits and perspectives of effective O-D matrix correction using traffic counts
No full textCorrection of the O–D matrix from traffic counts is a classical procedure usually adopted in transport engineering by practitioners for improving the overall reliability of transport models. Recently, Papola and Marzano showed through laboratory experiments that this procedure is generally unable to provide for effective correction of the O–D matrix. From a theoretical standpoint, this result can be justified by the lower number of (stochastic) equations (independent observed link flows) with respect to the unknowns (O–D flows). This paper first confirms that this represents the main reason for the failure of this procedure, showing that satisfactory correction is generally obtained when the number of equations is greater than the number of unknowns. Then, since this circumstance does not occur in practice, where the number of O–D pairs usually far exceeds the number of link counts, we explore alternative assumptions and contexts, allowing for a proper balance between unknowns and equations. This can be achieved by moving to within-day dynamic contexts, where a much larger number of equations are generally available. In order to bound the corresponding increase in the number of unknowns, specific reasonable hypotheses on O–D flow variation across time slices must be introduced. In this respect, we analyze the effectiveness of the O–D matrix correction procedure in the usually adopted linear hypothesis on the dynamic process evolution of O–D flows and under the assumption of constant distribution shares. In the second case it is shown that satisfactory corrections can be performed using a small number of time slices of up to 3 min in length, leading to a time horizon in which the hypothesis of constant distribution shares can be regarded as trustworthy and realistic
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