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Traffic simulation models are increasingly being used in the transportation engineering profession--often, to solve complex problems that may not lend themselves to traditional analysis techniques. The application of traffic simulation models has traditionally been at the individual vehicle (microscopic) level or aggregate traffic stream (macroscopic) level. Recently, the Virginia Department of Transportation and other agencies have shown interest in mesoscopic traffic simulation models, which allow for a level of detail higher than macroscopic models and model execution times better than those of microscopic models. This study proposed a procedure for mesoscopic simulation model calibration and validation. The proposed procedure was demonstrated on a test bed along I-95 in the City of Richmond and Chesterfield County, Virginia, using Aimsun Next. Results of the case study indicated that the proposed procedure appears to be properly calibrating and validating the mesoscopic simulation model of the test bed.
A single source of information for researchers and professionals, Traffic Simulation and Data: Validation Methods and Applications offers a complete overview of traffic data collection, state estimation, calibration and validation for traffic modelling and simulation. It derives from the Multitude Project-a European Cost Action project that incorpo
Well-calibrated traffic simulation model predictions can be highly valid if various conditions arising due to time-of-day, work zones, weather, etc. are appropriately accounted for during calibration. Calibration of traffic simulation models for various conditions requires larger datasets to capture the stochasticity. In this study we use datasets spanning large time periods to, especially, incorporate variability in traffic flow and speed. However, large datasets pose computational challenges. With the increase in number of stochastic factors, the numerical methods suffer from curse of dimensionality. We propose a novel methodology to address the computational complexity in simulation model calibration under highly stochastic traffic conditions. This methodology is based on sparse grid stochastic collocation, which treats each stochastic factor as a different dimension and uses a limited number of points where simulation is performed. A computationally-efficient interpolant is constructed to generate the full distribution of the simulated output. We use real-world examples to calibrate for different times of day and conditions and show that proposed methodology is more efficient than traditional Monte Carlo-type sampling. We validate the model using a hold-out dataset and also show the drawback of using limited data for macroscopic simulation model calibration. Modelers could often face situations with limited data in calibrating for a particular condition, often when using traffic sensor data. We augment the current data with other sources when sensor data is missing. For calibrating microscopic traffic simulation models needing customized models augmenting the default modeling, require detailed site-specific data. In such cases same generic calibration methodology may not be applicable and specialized formulations are required. We propose the use of a simulation-based optimization (SBO) framework for calibration of toll plaza models that economizes on data requirements. The novelty of the SBO framework is that parameters corresponding to unavailable data can be used as calibration parameters. Using case studies the benefits of the SBO framework are demonstrated. Furthermore, we combine the sampling and interpolation using stochastic collocation with the SBO framework. Using this hybrid framework, we perform calibration to obtain distribution of output from the toll plaza model that closely follows the observed measures at the toll plaza.
The increasing power of computer technologies, the evolution of software en- neering and the advent of the intelligent transport systems has prompted traf c simulation to become one of the most used approaches for traf c analysis in s- port of the design and evaluation of traf c systems. The ability of traf c simulation to emulate the time variability of traf c phenomena makes it a unique tool for capturing the complexity of traf c systems. In recent years, traf c simulation – and namely microscopic traf c simulation – has moved from the academic to the professional world. A wide variety of traf- c simulation software is currently available on the market and it is utilized by thousands of users, consultants, researchers and public agencies. Microscopic traf c simulation based on the emulation of traf c ows from the dynamics of individual vehicles is becoming one the most attractive approaches. However, traf c simulation still lacks a uni ed treatment. Dozens of papers on theory and applications are published in scienti c journals every year. A search of simulation-related papers and workshops through the proceedings of the last annual TRB meetings would support this assertion, as would a review of the minutes from speci cally dedicated meetings such as the International Symposiums on Traf c Simulation (Yokohama, 2002; Lausanne, 2006; Brisbane, 2008) or the International Workshops on Traf c Modeling and Simulation (Tucson, 2001; Barcelona, 2003; Sedona, 2005; Graz 2008). Yet, the only comprehensive treatment of the subject to be found so far is in the user’s manuals of various software products.
Microscopic traffic simulation models have been widely accepted and applied in transportation engineering and planning practice for the past decades because simulation is cost-effective, safe, and fast. To achieve high fidelity and credibility for a traffic simulation model, calibration and validation are of utmost importance. Most calibration efforts reported in the literature have focused on the informal practice with a specific simulation model, but seldom did they propose a systematic procedure or guideline for simulation model calibration and validation. The purpose of this study was to develop and evaluate a procedure for microscopic simulation model calibration and validation. Three widely used microscopic traffic simulation models, VISSIM, PARAMICS, and CORSIM, were selected for model review and practice of model calibration and validation. The validity of the proposed procedure was evaluated and demonstrated via two case studies including an actuated signalized intersection and a 5-mile freeway segment with a lane-closure work zone. The simulation results were compared against the field data to determine the performance of the calibrated models. The proposed procedure yielded acceptable results for all applications, thus confirming that it was effective for the different networks and simulation models used in the study. Although the calibrated parameters generated the performance measures that were representative of the field conditions, the simulation results of the default parameters were significantly different from the field data.
The purpose of this research was to propose a multistage framework for the calibration and validation of the traffic simulation models and present results of a calibration and validation experience using CORSIM model for a network of urban streets. The study proposed a series of logical, sequential steps for the calibration and validation of micro-simulation traffic models. The test bed used for the study is an important network of traffic signals in the city of Chicago, Illinois. The internal network consisting of twelve nodes at the core of the network served as the main focus of the calibration and validation experience for this study. Base data was collected using video and manual counts for extended AM and PM peak periods. Two methods for determining the number of model repetitions were proposed: a) use of statistical formula based on desired confidence interval and degree of confidence, and b) model-based sensitivity test which examines the number of outlier runs and the variability (distribution) in the model output from running sets of 25, 50, and 100 model runs. The study showed that both methods compliment each other in arriving at the required number of model repetitions. Automation processes using the REXX code was used for extracting the required model outputs and perform analysis of repetitive and multiple model runs during the calibration and validation processes. The calibration strategy adopted for the test network consisted of four distinct stages: a) error checking, b) calibration of input parameters for capacity and demand (throughput comparisons), c) model tuning (link attributes), and d) demand adjustment. The study showed that the concept of split links in modeling long term blockages by curb side parked vehicles proved to be more useful as compared to the NETSIM record types for long term events and parking activity. The study also showed the use of 'In' and 'Out' throughput volumes as an efficient and effective tool in calibration of micro-s.
In recent years, the transport simulation of large road networks has become far more rapid and detailed, and many exciting developments in this field have emerged. Within this volume, the authors describe the simulation of automobile, pedestrian, and rail traffic coupled to new applications, such as the embedding of traffic simulation into driving simulators, to give a more realistic environment of driver behavior surrounding the subject vehicle. New approaches to traffic simulation are described, including the hybrid mesoscopic-microscopic model and floor-field agent-based simulation. Written by an invited panel of experts, this book addresses students, engineers, and scholars, as well as anyone who needs a state-of-the-art overview of transport simulation today.
A previous study developed a procedure for microscopic simulation model calibration and validation and evaluated the procedure via two relatively simple case studies using three microscopic simulation models. Results showed that default parameters were unacceptable while calibrated parameters were able to replicate field conditions. Consequently, the study recommended that microscopic simulation models be calibrated and validated before they were used for any evaluations and analyses. A technical review panel determined that the previously developed procedure might not be readily adoptable by Virginia Department of Transportation (VDOT) traffic engineers due to its extensive use of advanced statistical tools and a lack of hands-on case study material. In addition, the proposed procedure needed to be tested with complex network conditions such as urban arterial networks and congested freeway systems. Consequently, it was concluded that what is now needed is (1) a handbook for simulation model calibration and validation that can be easily used by VDOT engineers, and (2) tests of the procedure for various network conditions. The purpose of this project was to develop a handbook for simulation model calibration and validation for VDOT traffic engineers to use for their simulation work and to develop and conduct a hands-on short course to instruct them in the use of the handbook. This study recommended the following: 1.) VDOT traffic engineers should calibrate and validate microscopic simulation models by using the enhanced procedure (i.e., multiple performance measures-based procedure) before using them for any engineering applications to ensure reliable results provided for better decision-making. 2.) When VDOT traffic engineers conduct microscopic simulation model calibration and validation, multiple performance measures collected for multiple days should be used to obtain more reliable results. 3.) Additional hands-on short courses should be offered to expose the procedure to more VDOT traffic engineers and possibly others including consultants who would work for VDOT in the future. VDOT's Learning Center and UVA Center for Transportation Studies Local Technical Assistance Program (LTAP) are possible avenue to offer such short courses. 4.) The handbook should be distributed to VDOT traffic engineers who currently use or plan to use microscopic simulation models for engineering applications. In addition, the prototype program and hands-on short course material (Park, 2006) should be accessible to VDOT traffic engineers.
Keywords: Calibration, Validation, Traffic Simulation, CORSIM, TRAF-NETSIM, MOE's, Stop Delay, STVS, Urban Networks, RTTRACS.