Browsing by Author "Farzaneh, Mohamadreza"

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    Empirical Studies on Traffic Flow in Inclement Weather
    Hranac, Robert; Sterzin, Emily; Krechmer, Daniel; Rakha, Hesham A.; Farzaneh, Mohamadreza (United States. Federal Highway Administration, 2006-10)
    Weather causes a variety of impacts on the transportation system. While severe winter storms, hurricanes, or flooding can result in major stoppages or evacuations of transportation systems and cost millions of dollars, day-to-day weather events such as rain, fog, snow, and freezing rain can have a serious impact on the mobility and safety of the transportation system users. These weather events can result in increased fuel consumption, delay, number of accidents, and significantly impact the performance of the transportation system. The overall goal of the research work undertaken in this study was to develop a better understanding of the impacts of weather on traffic flow. The research was intended to accomplish the following specific objectives: (1)Study the impact of precipitation on macroscopic traffic flow parameters over a full range of traffic states; 2) Study the impact of precipitation on macroscopic traffic flow parameters using consistent, continuous weather variables; 3) Study the impact of precipitation on macroscopic traffic flow parameters on a wide range of facilities; 4) Study regional differences in reaction to precipitation; and 5) Study macroscopic impacts of reduced visibility. The work documented in this report was conducted in two parts: 1) literature review and development of a data collection and analysis plan, and 2) analysis and interpretation of the results. The recommended plan combined the use of macroscopic traffic data archives with archived weather data in order to meet the research goals that include achieving better understanding of the impacts of weather on macroscopic traffic flow. The results of the research conducted for this study were helpful in identifying weather impacts of traffic flow in the three cities studied, Minneapolis-St. Paul, Baltimore and Seattle. No impacts were found on traffic stream jam density, but both rain and snow did impact traffic free-flow speed, speed-at-capacity and capacity and parameters varied with precipitation intensity. The results of these analyses are documented in the report. This report concludes with some recommendations of future research related to weather and traffic flow. Several ideas are presented including enhancing the macroscopic analysis used in this study. Additional work is proposed related to human factors and microscopic traffic modeling.
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    Modeling Traffic Dispersion
    Farzaneh, Mohamadreza (Virginia Tech, 2005-11-17)
    The dissertation studies traffic dispersion modeling in four parts. In the first part, the dissertation focuses on the Robertson platoon dispersion model which is the most widely used platoon dispersion model. The dissertation demonstrates the importance of the Yu and Van Aerde calibration procedure for the commonly accepted Robertson platoon dispersion model, which is implemented in the TRANSYT software. It demonstrates that the formulation results in an estimated downstream cyclic profile with a margin of error that increases as the size of the time step increases. In an attempt to address this shortcoming, the thesis proposes the use of three enhanced geometric distribution formulations that explicitly account for the time-step size within the modeling process. The proposed models are validated against field and simulated data. The second part focuses on implementation of the Robertson model inside the popular TRANSYT software. The dissertation first shows the importance of calibrating the recurrence platoon dispersion model. It is then demonstrated that the value of the travel time factor β is critical in estimating appropriate signal-timing plans. Alternatively, the dissertation demonstrates that the value of the platoon dispersion factor α does not significantly affect the estimated downstream cyclic flow profile; therefore, a unique value of α provides the necessary precision. Unfortunately, the TRANSYT software only allows the user to calibrate the platoon dispersion factor but does not allow the user to calibrate the travel time factor. In an attempt to address this shortcoming, the document proposes a formulation using the basic properties of the recurrence relationship to enable the user to control the travel time factor indirectly by altering the link average travel time. In the third part of the dissertation, a more general study of platoon dispersion models is presented. The main objective of this part is to evaluate the effect of the underlying travel time distribution on the accuracy and efficiency of platoon dispersion models, through qualitative and quantitative analyses. Since the data used in this study are generated by the INTEGRATION microsimulator, the document first describes the ability of INTEGRATION in generating realistic traffic dispersion effects. The dissertation then uses the microsimulator generated data to evaluate the prediction precision and performance of seven different platoon dispersion models, as well as the effect of different traffic control characteristics on the important efficiency measures used in traffic engineering. The results demonstrate that in terms of prediction accuracy the resulting flow profiles from all the models are very close, and only the geometric distribution of travel times gives higher fit error than others. It also indicates that for all the models the prediction accuracy declines as the travel distance increases, with the flow profiles approaching normality. In terms of efficiency, the travel time distribution has minimum effect on the offset selection and resulting delay. The study also demonstrates that the efficiency is affected more by the distance of travel than the travel time distribution. Finally, in the fourth part of the dissertation, platoon dispersion is studied from a microscopic standpoint. From this perspective traffic dispersion is modeled as differences in desired speed selection, or speed variability. The dissertation first investigates the corresponding steady-state behavior of the car-following models used in popular commercially available traffic microsimulation software and classifies them based on their steady-state characteristics in the uncongested regime. It is illustrated that with one exception, INTEGRATION which uses the Van Aerde car-following model, all the software assume that the desired speed in the uncongested regime is insensitive to traffic conditions. The document then addresses the effect of speed variability on the steady-state characteristics of the car-following models. It is shown that speed variability has significant influence on the speed-at-capacity and alters the behavior of the model in the uncongested regime. A method is proposed to effectively consider the influence of speed variability in the calibration process in order to control the steady-state behavior of the model. Finally, the effectiveness and validity of the proposed method is demonstrated through an example application.