查看更多>>摘要：Computational efficiency and first in, first out (FIFO) are both important issues in applications such as dynamic traffic assignment. This paper first shows by example the FIFO properties of a computationally efficient commodity-based kinematic wave (CKW) model of network traffic flow. After the development of measurements of FIFO violation among commodities in location and time on the basis of the misplacement of vehicles in total and commodity traffic, it is argued theoretically that numerical CKW solutions converge to FIFO ones. Then, with numerical examples, it is shown that FIFO violation in CKW solutions is a function of the simulation time and the number of commodities but decreases with decreasing cell lengths, even for infinite number of commodities. Finally, the possible implications of this study are discussed.
查看更多>>摘要：Microscopic traffic simulation models have been playing an important role in the evaluation of transportation engineering and planning practices for the past few decades, particularly in cases in which field implementation is difficult or expensive to conduct. To achieve high fidelity and credibility for a traffic simulation model, model calibration and validation are of utmost importance. Most calibration efforts reported in the literature have focused on the informal practice, and they have seldom proposed a systematic procedure or guideline for the calibration and validation of simulation models. This paper proposes a procedure for microscopic simulation model calibration. The validity of the proposed procedure was demonstrated by use of a case study of an actuated signalized intersection by using a widely used microscopic traffic simulation model, Verkehr in Staedten Simulation (VISSIM). The simulation results were compared with multiple days of field data to determine the performance of the calibrated model. It was found that the calibrated parameters obtained by the proposed procedure generated performance measures that were representative of the field conditions, while the simulation results obtained with the default and best-guess parameters were significantly different from the field data.
Wilco BurghoutHaris N. KoutsopoulosIngmar Andreasson
p.218-225页
查看更多>>摘要：Traffic simulation is an important tool for modeling the operations of dynamic traffic systems. Although microscopic simulation models provide a detailed representation of the traffic process, macroscopic and mesoscopic models capture the traffic dynamics of large networks in less detail but without the problems of application and calibration of microscopic models. This paper presents a hybrid mesoscopic-microscopic model that applies microscopic simulation to areas of specific interest while simulating a large surrounding network in less detail with a mesoscopic model. The requirements that are important for a hybrid model to be consistent across the models at different levels of detail are identified. These requirements vary from the network and route choice consistency to the consistency of the traffic dynamics at the boundaries of the microscopic and mesoscopic submodels. An integration framework that satisfies these requirements is proposed. A prototype hybrid model is used to demonstrate the application of the integration framework and the solution of the various integration issues. The hybrid model integrates MITSIMLab, a microscopic traffic simulation model, and Mezzo, a newly developed mesoscopic model. The hybrid model is applied in two case studies. The results are promising and support both the proposed architecture and the importance of integrating microscopic and mesoscopic models.
查看更多>>摘要：The aim of this paper is to gather some observations resulting from the study of traffic data in an urban environment (Toulouse, France) rather than on freeways, as is often the case in papers that deal with flow-density relationship calibration. Methods developed for freeway data are studied and new ones are presented to address the specificity of traffic behavior in urban areas. A two-step approach is proposed. First, the data are processed to obtain consistent observations for simulation use. This processing includes the calculation of density from occupancy and space mean speed and the aggregation and the selection of data to make them suitable for equilibrium traffic state representation. Then, a best-fit curve is applied to the selected data to obtain flow-density relationships. Finally, the resulting relationships are studied to highlight the peculiarities of traffic behavior in urban streets.
Constantinos AntoniouMoshe Ben-AkivaHaris N. Koutsopoulos
p.235-245页
查看更多>>摘要：A methodology for the online calibration of the speed-density relationship is formulated as a flexible state-space model. Applicable solution approaches are discussed and three of them-the extended Kalman filter (EKF), the iterated EKF, and the unscented Kalman filter (UKF)-are selected and presented in detail. An application of the methodology with freeway sensor data from two networks in Europe and the United States is presented. The improvement in the estimation and prediction of speeds due to online calibration (compared with the speeds obtained from the relationship calibrated offline) is demonstrated. EKF provided the most straightforward solution to this problem and, indeed, achieved considerable improvements in estimation and prediction accuracy. The benefits obtained from the use of the more computationally expensive iterated EKF algorithm are shown. An innovative solution technique (UKF) is also presented.
查看更多>>摘要：One of the most critical aspects of effective microscopic traffic simulation models is proper calibration for accurate replication of both supply and demand characteristics, as well as their interaction. Recent research has begun automating the calibration process by using intelligent transportation system data. This research, however, has targeted automobile traffic and has not generally included commercial motor vehicle (CMV) impacts. Because CMVs are a significant part of the traffic stream and tend to have a disproportionate effect on the transportation system, it is theorized that these vehicles should be included in the calibration process. The objective of this research, therefore, is (a) to outline calibration parameters and network properties available (including site-specific vehicle distributions with weigh-in-motion and automatic vehicle classification data) for a freeway simulation of both passenger cars and CMVs and (b) to apply these parameters and network properties on an urban freeway system in Texas by using the microscopic traffic simulation model CORSIM and an automated genetic algorithm calibration methodology. The results of the analysis indicate that the overall calibration measurably improves the ability of the model to replicate observed conditions. The results for this corridor, however, do not support the need to include maximum nonemergency deceleration rates in the calibration process. The inclusion of site-specific vehicle distributions, however, was observed to provide a more accurate representation of vehicle composition and overall network results. This methodology has not been explored previously and provides a strong base for evaluating the impacts of CMVs on the transportation network by the use of microscopic traffic simulation models.
查看更多>>摘要：Occupancies and flows were jointly sampled from freeway segments in nearly stationary, unqueued traffic. When plots of occupancy per lane versus flow per lane were normalized by n (the number of travel lanes in the freeway segment from which a data set came), the plots took shapes that were piecewise linear in form (except for conditions that were near capacity) and were clearly influenced by n. Drivers adopted a higher speed (for a given occupancy) while traveling on segments of greater n. Yet, the speeds on these wider segments exhibited greater sensitivity: drivers began decelerating at relatively low occupancies. These findings came from a comparison of a data plot from each of five different freeway segments with the plot from its neighboring segment. Because each segment appeared to differ from its neighbor only in its n, the comparisons (approximately) controlled for other influential factors, including geometric design standards, speed limit, and driver population. The five pairwise comparisons, which verify the reproducibility of the effects of n on the data, were performed for freeways in and near Toronto, Ontario, Canada, and California. The findings are compared with the information currently provided in traffic handbooks.
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