VTechWorks Repository :: Browsing by Author "Sivanandan, R."

Browsing by Author "Sivanandan, R."

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An adaptive strategy for providing dynamic route guidance under non-recurrent traffic congestion
Lee, Sang-Keon (Virginia Tech, 1996-05-28)
Traffic congestion on urban road networks has been recognized as one of the most serious problems with which modern cities are confronted. It is generally anticipated that Dynamic Route Guidance Systems (DRGS) will play an important role in reducing urban traffic congestion and improving traffic flows and safety. One of the most critical issues in designing these systems is in the development of optimal routing strategies that would maximize the benefits to overall system as well as individual users. Infrastructure based DRGS have advantage of pursuing system optimal routing strategy, which is more essential under abnormal traffic conditions such as non-recurrent congestion and natural disaster. However user compliance could be a problem under such a strategy, particularly when some of equipped drivers are urged not to choose minimum travel time path for the sake of improving the total network travel time. On the other hand, In-vehicle based DRGS can utilize the user-specified route selection criteria to avoid "Braess Paradox" under normal traffic conditions. However, it may be of little use under abnormal traffic conditions and high DRGS market penetration. In conducting the comparative analysis between system optimal strategy and user equilibrium strategy, significant differences were found within the mid-range traffic demand. The maximum total travel time difference occurs when the level of traffic demand is half of the system capacity. At this point, system optimal route guidance strategy can save more than 11% of the total travel time of user equilibrium route guidance strategy. The research proposes an adaptive routing strategy as an efficient dynamic route guidance under non-recurrent traffic congestion. Computation results show that there is no need to implement system optimal routing strategy at the initial stage of the incident. However, it is critical to use system optimal routing strategy as freeway and arterial are getting congested and the queue delay in freeway increases. The adaptive routing strategy is evaluated using Traffic simulation model, INTEGRATION. According to simulation results using an ideal network, the travel time saving ratio is maximum when both arterial and freeway have normal traffic demand under incident. In case of a realistic network, the adaptive routing strategy also proved to save the total travel time between 3% to 10% over the traditional user equilibrium routing strategy. The reduction of total travel time increases as the incident duration increases. Consequently, it is concluded that the adaptive routing strategy for DRGS is more efficient than using user equilibrium routing strategy alone.
Decision support system for locating traffic information dissemination sites along freeway corridors
Nutakor, Christopher (Virginia Tech, 1996)
Dynamic route guidance systems which are products of the Intelligent Transportation Systems (ITS) Technology have been reasonably useful in guiding motorists from their origins to destinations. In general, transportation networks could be used more efficiently if dynamic route guidance information could be provided to motorists at all relevant locations along freeway corridors. This is however not possible, particularly because of financial constraints. It is therefore imperative that information be provided to motorists at locations where it will be of maximum benefit. The objective of this research is to develop methodologies and computer models for estimating utility of motorist information at different locations along freeway corridors. Such models will be very useful in guiding transportation professionals to optimize resources when providing guidance information to motorists. The methodologies have been developed based on both recurrent and non recurrent traffic congestion situations. The methodologies assume that motorists behave rationally and will divert from congested freeways to uncongested arterials based on the user equilibrium traffic assignment criteria. The utility of information estimation has however been based on total system time savings. Computer models have been developed based on the methodologies using the C++ programming language. Nonetheless, because the computer models have been developed based on historical traffic data, they have been validated using real time simulation models developed with the SIMSCRIPT II.5 programming language. The validation process proved reasonably successful. Many factors which include traffic volumes on alternate arterial routes to a given freeway link, the number of alternate routes to the freeway link especially under recurrent traffic congestion conditions, link lengths, volume of traffic on the freeway link and incident history in the case of non recurrent congestions influence the utility of information. With the particular networks investigated in this research however, the results indicate volume of traffic on the freeway links as the most influencing factor, since freeway links with relatively high traffic volumes tend to have relatively high utility values. The reason for this is probably because of the small size nature of the networks used, hence as a result all the freeway links tend to have only one or two alternate routes and the traffic volumes on the arterial links also do not differ significantly. The freeway link volumes therefore become the dominating factor in influencing the information utilities.
Design framework for the graphical user interface of a terminal area air traffic advisory system
Beamon, Courtney A. (Virginia Tech, 1996-08-16)
The purpose of this research thesis was to develop a framework and methodology for the design of a graphical user interface to be used by air traffic controllers. The interface is intended to be only a part of a complete Advisory System designed to supplement the tasks of terminal area air traffic controllers. This research addresses many of the human factors issues associated with the development of the display. The research takes a user-perspective and applies the principles of rapid prototyping to develop the framework for the design of the interface. Attention is also given to the previous research that explores the implications of automating various air traffic control tasks. Finally, a prototype system was developed to fulfill one of the primary rapid prototyping steps. The prototype displays the general format for the various advisories and presents three typical scenarios where the system may be of particular use. In the future, the prototype can be used to gather additional information on the opinions and requirements of the future system users - air traffic controllers. It is anticipated that moderate benefits can be attained through the implementation of such a system, provided that the interface satisfies the user requirements.
Development and evaluation of traffic prediction systems
Kim, Changkyun (Virginia Tech, 1994-04-12)
Developing real-time traffic diversion strategies is a major issue of Advanced Traffic Management Systems (ATMS), a component of Intelligent Vehicle Highway Systems (IVHS). Traffic diversion utilizes available capacity in the urban network during a congestion-causing event. If an alternative route selected for diversion is not congested at the current time, a certain part of the route may become congested by the time the diverted drivers reach that part of the network. Thus the ability to forecast future traffic variables on each link along various routes in a prompt and accurate fashion may be necessary to ensure the success of a diversion strategy. Forecasting future traffic variables would also be helpful for urban traffic control. In addition, the forecasting model may help assign the vehicles onto the alternate roads, if the information on driver destinations and the routes between a diversion point and the destinations are available. This dissertation is aimed at developing and evaluating two prediction models: link-based model and network-based model. The link-based prediction model has two components. One component is an Auto Regressive Integrated Moving Average (ARIMA) time series model based on the latest (current) traffic data. The other component is the smoothed historical traffic volume (historical average) for that period as obtained from previous days. These two components are combined to represent the dynamic fluctuations in the traffic flow behavior. The combined model is designed to produce the predicted traffic volumes for a look-ahead period of 30 minutes, divided into 6-minute time intervals. The results show that the combined model is promising for light to medium congested traffic conditions. The network-based prediction model combines current traffic, historical average, and upstream traffic. It is presumed that traffic volume on the upstream can be used to predict the downstream traffic in a specific time period. Three prediction models are developed for traffic prediction: a combination of historical average and upstream traffic, a combination of current traffic and upstream traffic, and a combination of all three variables. The three models are evaluated through regression analysis. The third model is found to be the most applicable while the first model was the least. In order to consider current traffic conditions, a heuristic adaptive weighting system is devised based on the relationships between the origin of prediction and the previous periods. The developed models are applied to real freeway data in 15-minute time interval measured by regular induction loop detectors. The prediction models are shown to be capable of producing reliable and accurate forecasts under congested traffic condition. The prediction systems perform better in the 15-minute range than in the ranges of 30-minute or 45-minute. It is noted that the combined models usually produce more consistent forecasts than the historical average.
Development of a real-time and geographical information system-based transit management information system
Bae, Sanghoon (Virginia Tech, 1993-06-17)
The Tidewater Regional Transit (TRT) in Virginia has implemented an Automatic Vehicle Location (AVL) system into their bus system. However, there are some problems with the system that TRT is endeavoring to resolve in order to maximize its utilization. Therefore, the main goal of this research was to develop an automated Management Information System (MIS) that processes the overwhelming real-time incoming data from the AVL system in TRT, and to present it promptly in an easy-to-access, easy-to-understand, and easy-to-use format. In order to meet this goal, development of a graphics- and Geographical Information System (GIS)-based display system is essential. Classification of data from the AVL system according to its priority, relevancy, and demand level was the first step in achieving the goal of this research. The second step was to develop a user-friendly, menu-option display system. This step mainly focuses on the structured computer model construction so that its future potential for expansion and modification is easily accommodated. The last step of the research was to develop a GIS-based display system. For this task, the TIGER/Line Census file is utilized as the data file for map display. Since the topic of this research - MIS development - is a part of a proposed Advanced Public Transportation System (APTS) research project, its future research direction is also identified. One of the most important recommendations for the future research is the real-time operational application of the developed MIS model.
Development of automatic vehicle headway control law and a simulation tool
Yao, Mingdong (Virginia Tech, 1996)
Vehicle following and its effects on traffic flow has been an active area of research. Human Driving involves reaction, delays, and human errors that has adverse effects on traffic flow . We can eliminate human errors by introducing a computer control system. The purpose of this research was to develop and evaluate a control law and a simulation tool for the study of automatic vehicle headway control. This research considers longitudinal control of a platoon of vehicles on automated highways. A new way of designing control law for vehicle following is presented by introducing safe boundary concept - the trail vehicle should never exceed the maximum safe velocity and at the same time keeps the passengers comfort when accelerating or decelerating except under emergency circumstances. After finding the safe boundary, we design the automatic control law and then using our simulation tool to simulate its performance, adjust parameters until we reach a satisfactory result. System dynamics concept and basic individual vehicle motion laws are used through the research. System dynamics provides a common foundation that can be applied wherever we want to understand and influence how things change through time. We look at the platoon system as a whole and study all the objects, such as vehicle dynamics, road condition, motor dynamics, in this system interact with one another. A third-order nonlinear, Car-following, PID control law is designed using System Dynamics concept. System dynamics' simulation language DYNAMO and Spreadsheet are have been used for our development of a simulation tooL A Satisfactory result is found after the extensive simulation which indicates that the platoon assumptions are achievable using the advanced technologies, like automatic vehicle control, radar, and sensors.
Dynamic estimation of travel time on arterial roads by using automatic vehicle location (AVL) bus as a vehicle probe
Bae, Sanghoon (Virginia Tech, 1995-05-11)
A method of reducing congestion is to reduce the demand by providing the road network users with accurate and reliable travel time information for their pretrip planning and enroute guidance, and/or attracting more people to the public transit. For this purpose, this research concenturates on using Automatic Vehicle Location (AVL) system equipped bus as a probe vehicle for estimating bus arrival times and auto travel times. Since many transit organizations throughout the North America are currently operating these AVL buses on their bus routes, in a sense, existing AVL bus would be the most cost-effective traffic probe which can be utilized for data collection in the proactive mode. Therefore, the goals of this research are to enhance the current use of AVL systems by introducing a new module to estimate bus arrival time information for transit travelers, and use AVL systems-equipped bus as a probe vehicle to estimate the nontransit travel time for auto travelers.
A framework for dynamic traffic diversion during non-recurrent congestion: models and algorithms
Özbay, Kaan (Virginia Tech, 1996-04-30)
Real-time control of traffic diversion during non-recurrent congestion continues to be a challenging topic. Especially, with the advent of Intelligent Transportation Systems (ITS), the need for models and algorithms that will control the diversion in real-time, responding to the current traffic conditions has become evident. Several researchers have tried to solve this on-line control problem by adopting different approaches such as, expert systems, feedback control, and mathematical programming. In order to ensure the effectiveness of real-time traffic diversion, an implementation framework capable of predicting the impact of the incident on the traffic flow, generating feasible alternate routes in real-time, and controlling traffic in order to achieve a pre-set goal based on a system optimal or a user equilibrium concept is required. In this dissertation, a framework that would satisfy these requirements is adopted consisting of a "diversion initiation module", a "diversion strategy planning module", and a "control and routing module" which determines the route guidance commands in real-time. The incident duration data collected by the Northern Virginia incident management agencies is analyzed to determine major factors that affect the incident clearance duration. Next, prediction/decision trees are developed for different types of incidents. Based on the validation of these trees using the data that is not employed for the development of the trees, it is found that they perform well for the majority of the incidents. A simple deterministic queuing approach is used to predict the delays that will be caused by the incident for which the clearance duration is predicted using the prediction/decision trees. The diversion strategy planning module, Network Generator, is developed as a knowledge based expert system that uses simple expert rules in conjunction with historical and realtime data to determine the incident impact zone, and to eliminate links that are not suitable for diversion. Finally, it generates alternate routes for diversion using this modified network. Network generator is tested using simulation on a small portion of the Fairfax network. Finally, feedback control models for dynamic traffic routing models, both in distributed and lumped parameter settings, are developed. Methods for developing controllers for these models are also discussed. Two heuristic and analytic feedback controllers for the space discretized lumped parameter models are developed and their effectiveness for realtime traffic control is shown by simulating several scenarios on a simple network. An analytic feedback controller is also designed using a feedback linearization technique for the space discretized model. This controller also performed very well during simulations of various scenarios and proved to be an effective solution to this feedback control problem.
Heuristic network generator: an expert systems approach for selection of alternative routes during incident conditions
Krishnaswamy, Vijay (Virginia Tech, 1994-06-23)
Congestion on the freeways of the U.S. has increased multifold over the past few years. A significant portion of this congestion is caused by non-recurring events such as incidents. Diversion has been accepted as a method that can reduce delays during incidents. The process of diversion involves the selection of the alternate routes, which is currently done off-line and is not responsive to each incident case. The volumes on these preselected routes on that particular day are also ignored. The preselected routes, in most cases, serve only to bypass the link on which the incident occurs. Considering the volumes that flow on the freeways, this leads to considerable delays in terms of lost time and productivity. Another important issue that is currently neglected is user compliance. The network generator is used to reduce the delays in selection of these alternate routes. It uses characteristics such as the congestion levels and available capacities in selection of alternate routes in real-time. Also, used in selecting alternate routes are feasibility criteria, that significantly affect the available capacities on the links. These include presence of trip generators (schools, offices, etc.) or safety factors (icy bridges, height restrictions, etc.). The model thus generates a reduced network and a set of alternate routes to divert the traffic upstream of the incident. Disutilities that drivers associate with route-choice, such as the number of left-turns and signals, the relative time spent on the freeway and arterials are attached to each route. The routes with the minimum disutilities are displayed to the user. A user-equilibrium assignment module to predict traffic flows in the future is also incorporated into the framework. As a precursor to the network generator, there is a module which calculates the clearance time for an incident. It uses other characteristics of the incident such as the weather and time of occurrence in order to predict if the delays are significant to initiate diversion. Numerous tests were conducted in order to validate the rules and functions developed. The tests were based on varying incident and traffic conditions. The results showed that the model, was able to select better routes for off-peak conditions rather than peak conditions. There is a threshold value of the delay caused by the incident, beyond which the model is very effective.
Integrated urban transportation and land use modeling by application of system dynamics
Erickson, Douglas J. (Virginia Tech, 1995-01-16)
The spatial allocation of land uses and vehicle route selection within an urban network are both dependent upon travel times between zones in an urban region. These location and accessibility components form the basis of a time dependent feedback structure linking land use and transportation planning. Integrating algorithms for land use allocation, mode choice, and route selection is the next step required for comprehensive urban planning. However, any integration of existing models still requires exogenous estimates of future population and employment. Predictions of the distribution of land uses, travel mode, and route selection are all based upon modeling choice behaviors. Similarly, choice behavior modeling can be extended to virtually all elements of the urban structure. Drawing upon System Dynamics, and utilizing Forrester's concepts of urban modeling, a truly integrated model can be developed free of outside input for future population and employment levels. The feasibility and utility of the Dynamic Urban Land Use - Transportation Model are demonstrated through the use of a hypothetical urban region. Given a set of initial conditions, the model simulates the choice behaviors that determine future population movement, employment opportunities, and housing availability, and allocates these elements to zones. Mode and route selection for the home-to-work journey are then simulated and become inputs for future spatial allocation. Analysis of the effects on the urban system as a result of a variety of transportation and land use policies is included to demonstrate the usefulness of the methodology as a decision making tool.
Integration of a GIS and an expert system for freeway incident management
Jonnalagadda, Srikanth (Virginia Tech, 1996-09-15)
Congestion due to traffic accidents and incidents can be reduced through effective freeway incident management. However, this is plagued by a number of problems and requires a high level of expertise and coordination among the involved personnel. The ill-structured nature of the problem, constantly changing conditions, the number of agencies involved, and the lack of current information often cause errors in decision and response. Under these conditions, there is need for computer based support tools to provide the required decision and information support and aid the entire process by improving coordination and communication. This study focuses on addressing this issue through the development of an Expert-GIS system which integrates the powerful spatial data handling capabilities of a Geographic Information System with the rule based reasoning logic of an Expert System. The system is designed as a Group Decision Support System that provides the required support for both the substance of the problem (decisions) and the agency level interactions that take place. The ability to support the process of response is modeled using a blackboard architecture for the system. The prototype developed fully integrates the software environments of Arc/Info and Nexpert-Object and presents a unified interface, from where different incident management functions can be accessed. A complete spatial database was designed for the Fairfax County in Northern Virginia as a part of this development effort. Decision support is provided through a set of six integrated modules - incident detection and verification, preliminary response, duration estimation, delay calculation, final response plan and diversion planning, and recovery. Coordination and communication were enhanced by ensuring the uniformity of information at different locations using the system, and through a messaging mechanism that informed users about the current status of incident. The prototype system was developed for two hypothetical agencIes called the Traffic Management Center and The Police Control Center. Historical incident cases were use to test these systems and check the accuracy of the database and the rule base. Both the tests and the development effort showed a strong need for established sources of network information, that could be readily incorporated into the database. Given the fact that the system works with real network data, the next phase of research in should focus on the deployment of the system at test sites. User feedback obtained from these tests would then serve as a basis for future enhancements.
A linear programming approach for synthesizing origin-destination (O-D) trip tables from link traffic volumes
Sivanandan, R. (Virginia Tech, 1991)
This research effort is motivated by the need to quickly obtain origin-destination (0-0) trip information for an urban area, without expending the excessive time and effort usually accompanying survey-based methods. The intent is to utilize this information to facilitate diversion of traffic in real time, in the event of congestion-causing incidents such as accidents. The O-D trip table information is a key to successful diversion planning, where user destinations are considered in developing the plans. Traffic volumes on the links of the road network contain information which can be exploited advantageously to derive the trip patterns. This approach of synthesizing a trip table from link volumes, and perhaps using a prior trip table to guide the derivation, has useful applications in the context of diversion planning. Unlike conventional O-D surveys, it has the potential of yielding results quickly, a requisite for real-time applications. This research work details a new methodology for synthesizing origin-destination (0-0) trip tables. The approach, which is based on a non-proportional assignment, user-equilibrium motivated, linear programming model, is the principal component of this dissertation. The model is designed to determine a traffic equilibrium network flow solution which reproduces the link volume data, if such a solution exists. If such alternate solutions exist, then it is designed to find that which most closely resembles a specified target trip table. However. it recognizes that due to incomplete information, the traffic may not conform to an equilibrium flow pattern, and moreover, there might be inconsistencies in the observed link flow data, or there might be incomplete information. Accordingly, the model permits violations in the equilibrium conditions as well as deviations from the observed link flows, but at suitable incurred penalties in the objective function. A column generation solution technique is presented to optimally solve the problem. The methodology also accommodates a specified prior target trip table, and drives the solution toward a tendency to match this table using user controlled parameters. Implementation strategies are discussed, and an illustration of the proposed method is presented using some sample test networks. The results from the model are discussed vis-a-vis other relevant, available approaches. The quality of the results and the computational effort required are used as a set of criteria in the comparisons. The comparisons of test results demonstrate the superiority of the linear programming model over the other models considered. The model is also applied to a real network of Northern Virginia, where congestion problems present a serious concern. As a result of this experience, several implementation strategies relevant to the application of the model on a real network are presented, and some general conclusions are derived. The potential application of the model in real-time traffic diversion planning for the study area is discussed. Recommendations for further research are also presented.
A Method to Enhance the Performance of Synthetic Origin-Destination (O-D) Trip Table Estimation Models
Sivanandan, R.; Nanda, Dhruv (Virginia Center for Transportation Innovation and Research, 1998-01)
The conventional methods of determining origin-destination (O-D) trip tables involve elaborate surveys, e.g., home interviews, that require considerable time, staff, and funds. To overcome this drawback, a number of theoretical models that synthesize O-D trip tables from link volume data have been developed. The focus of the research reported here was on two of these models The Highway Emulator (THE) and the Linear Programming (LP) model. These models use target/seed tables for guiding the development of output trip tables. In earlier research conducted by the Virginia Tech Center for Transportation Research for the Virginia Transportation Research Council, it was determined that the performance of these models could potentially be enhanced by using a superior target/seed table. The research in this report uses readily available socioeconomic data and link volume information to develop a methodology for obtaining an enhanced target/seed table through application of the trip generation and trip distribution steps of the four-step planning process. The enhanced table was then used as the target/seed to THE and LP models, and their performance evaluated. In addition to measuring the closeness of the output tables to surveyed tables and their capability to replicate observed volumes, their improvements over the case when a structural table is used as target was also studied. Tests showed that the use of the enhanced target/seed table significantly improved the performance of the LP model. However, mixed trends were obtained for THE.
A Method to Enhance the Performance of Synthetic Origin-Destination (O-D) Trip Table Estimation Models
Nanda, Dhruv (Virginia Tech, 1997-06-09)
The conventional methods of determining the Origin-Destination (O-D) trip tables involve elaborate surveys, such as home interviews, requiring considerable time, manpower and funds. To overcome this drawback, a number of theoretical models that synthesize O-D trip tables from link volume data have been developed in the past. The focus of this research was on two of these models, namely, The Highway Emulator (THE) and the Linear Programming (LP) models. These models use target/seed tables for guiding the modeled trip tables. In an earlier research effort conducted by Virginia Tech Center for Transportation Research, potential was noted for enhancing these models' performances by using a superior target/seed table. This research study exploits the readily available socio-economic/census data and link volume information and proposes a methodology for obtaining improved target/seed tables, by performing the trip generation and trip distribution steps. This table was provided as target to THE and LP models, and their performances evaluated using Pulaski town as case study. In addition to measuring the closeness of the output tables to surveyed tables and their capability to replicate observed volumes, their improvements over the case when a structural table is used as target was also studied. Tests showed that the use of the superior target/seed table significantly improved the performance of the LP model. However, for THE, mixed trends are seen in terms of different measures of closeness. The sensitivity of the user parameter to place certain degree of belief on the target/seed table for LP model was also analyzed.
Methodologies for integrating traffic flow theory, ITS and evolving surveillance technologies
Nam, Do H. (Virginia Tech, 1995)
The purpose of this research is to develop methodologies for applying traffic flow theories to various ITS categories through the utilization of evolving surveillance technologies. This integration of theory, measurement and application has been overlooked since the advent of ITS because of the number of disciplines involved. In this context, the following illustrative methodologies are selected, developed and presented in this study: - a methodology for automatic measurement of major spatial traffic variables for the present and the future implementation of various ITS functional areas, in general; and - a methodology for real-time link and incident specific freeway diversion in conjunction with freeway incident management, in particular. The first methodology includes the development of a dynamic flow model based on stochastic queuing theory and the principle of conservation of vehicles. An inductive modeling approach adapted here utilizes geometric interpretations of cumulative arrival-departure diagrams which have been drawn directly from surveillance data. The advantages of this model are real-time applicability and transportability as well as ease of use. Analysis results show that the estimates are in qualitative and quantitative agreement with the empirical data measured at 30-second intervals. The analytical expression for link travel times satisfies traffic dynamics where the new form of the equation of conservation of vehicles has been derived. This methodology has potential applicable to automatic traffic control and automatic incident detection. The methodology is then applied to freeway diversion in real-time in conjunction with freeway incident management. The proposed new form of the equation of conservation of vehicles is applied to detect recurring or non-recurring congestion analytically. The principle of conservation of vehicles is applied to develop the concept of progression and retrogression of incident domain, which turns out to be compatible with traditional shock wave traffic mechanism during incidents. The link and incident specific diversion methodology is achieved by using a delay diagram and volume-travel time curves, which can be plotted per link per incident. The use of such graphic aids makes problem solving much easier and clearer. The dynamic traffic flow model developed here can also be applied to estimate travel times during incidents as a function of time. The development of a computer program for freeway diversion concludes this research.
Methodology for evaluating transportation-induced regional development
Ahn, Seung B. (Virginia Tech, 1996-06-05)
There has long been a recognition that efficient transport plays a key role in supporting a dynamic economy and a high quality of life. However, traffic increases along with population and income, and traffic congestion and accidents are negative results of this increase, as is environmental damage. There has been a need for a methodology to evaluate user, nonuser benefits and the environmental impacts of transportation investments and policies through rational, objective scientific analysis. This research aims to develop a methodology, termed the Transportation/Development Methodology, for evaluating transportation policies and projects, and also, to clarify the relationships between transportation investment and economic productivity. Transportation/Development Methodology, or TDM, conceptualizes the role of transportation in a broad socioeconomic and environmental context and enables scenario analysis. In addition to the development of the TDM, this research comprises a critique and discussion of the primary methodologies used for evaluating transportation effects. In both transportation and development management, policy processes tend to proceed in nearly total isolation from ongoing planning activities in estimating impacts induced by transportation investments and policies. To overcome that imbalance for current models, TDM uses a system dynamics approach and adopts concepts from other methodologies, such as Input-Output analysis, the Lowry Model, and the Urban Transportation Planning Process (UTPP). Finally, this research demonstrates the TDM by applying it in an analysis of a “real-life” situation, the Interstate 81 corridor, which goes through six states of the United States as a backbone of both passenger and freight transport. Development scenarios for improving regional economies, as well as for giving better service and reducing congestion, are analyzed by the TDM im order to evaluate their effectiveness. Application of the TDM to the I-81 corridor generates significant conclusions that would not have been possible using existing methodologies.
Micro-macroscopic modeling and simulation of an Automated Highway System
Nagarajan, Ramakrishnan (Virginia Tech, 1996)
Intelligent Transportation Systems (ITS), which uses modem electronics and communications technology to guide or control the operation of vehicles holds great promise for increasing the capacity of existing roads. reducing congestion and accident losses, and contributing to the ease and convenience of travel. The most sophisticated of all the ITS technologies that may ultimately yield the largest benefits is the Automated Highway Systems (AHS). The AHS approach to enhance the performance of our highways is to apply automation techniques to vehicles and roadways to increase the capacity and efficiency of existing facilities, while retaining the advantages of individual mobility. The idea is to have a system with instrumented highways and vehicles which allows the automation of the driving function. The overall objective of this research study involves the modeling and analysis of an AHS system, using a simulation tool specifically developed for this purpose. A multi-layer control system architecture that conforms to the one developed at the University of California, Berkeley, provides a framework for the micro and macroscopic modeling of the system. The focus of the system modeling is towards the lower layers of this control system architecture, involving a comprehensive modeling of the regulation and physical layers and a simple, yet realistic modeling of the functionalities of the link layer. The regulation and physical layer design incorporates a complete power train modeling of the vehicle that includes one-wheel rotational dynamics, linear vehicle dynamics, engine dynamics and actuator dynamics.
Modeling of Airport Operations Using an Object-Oriented Approach
Zhong, Caoyuan (Virginia Tech, 1997-02-04)
This research develops an object-oriented approach to model airport ground network traffic operations. A generic modeling library is developed as a tool kit to model the basic traffic operations in the airfield using an object-oriented approach. The proposed generic modeling library for airfield operations is a collection of predefined abstract components implemented in the Java object-oriented programming language. Classes are defined and used as the basic components in a variety of airfield operation modeling, simulations, and optimizations. The generic airport modeling framework consists of a set the components that are necessary for modeling the basic activities of airfield traffic operations. By using the multi-threading techniques, components are integrated into the proposed modeling framework. Unlike traditional sequential simulation model, this framework organizes simulation activities into four major groups which are: flight schedule, aircraft movement, time, and animation. Instead of using built-in control logic, the framework adapts an open system policy which gives the flexibility to the end users to incorporate the user-preferred control logic into the end models. Another purpose in this research is to provide a future mechanism to study airfield ground traffic automated control systems with Just-In-Time forecasting and model system performance in a real-time ATC environment. The proposed generic library could be implemented into a Internet/intranet ready application which can query real time information and provide real time advice to pilots and air traffic controllers. This study is one of a few current research projects that are of using multiple threading technique to study traffic operation problems. The proposed generic library is originally implemented with C++ and, in the final stage, with Java, a truly cross-platform object-oriented language. Application written in Java can run on most of the mainstream computer operating systems without modifications. Although the proposed library is for airfield traffic control system, it could also be extended into air traffic control system as well as advanced transportation system.
Optimal traffic control for a freeway corridor under incident conditions
Zhang, Yunlong (Virginia Tech, 1996)
The non-recurring congestion, caused by incidents, is the main cause of traffic delays and causes up to 60 percent of the freeway delay in the United States. When severe incidents occur on freeways, capacity reduction due to lane blockages may cause an extremely high amount of traffic delay. In many cases, parallel surface arterials are available, and provide reasonably high speed and available capacity. In this scenario, to fully utilize the corridor capacity, diversion may be practical and necessary. With the changes of traffic demand levels and patterns on surface streets due to diversion, signal retiming for surface street intersections is necessary. A nonlinear programming model was formulated to provide an integrated traffic control strategy for a freeway corridor under incident conditions. The objective function of the optimization model considers the interactions among the corridor components, and clearly reflects the primary goals of corridor traffic control under freeway incident conditions: to divert as much traffic away from the freeway as possible, not to over-congest the arterial and surface streets; and properly reset the signal timing plans at all intersections to accommodate the changed traffic demand levels and patterns. The gradient projection method is employed to solve diversion and signal retiming control measures simultaneously. By using a specifically developed simple and realistic traffic flow model and employing a sequential optimization approach, the computer program COROPT can obtain optimal traffic control strategies quickly and effectively. The COROPT program also has the flexibility to deal with various corridor configurations, different size of the corridor system, and different timing phasings. The model can address the time-varying factor of traffic flow, and can handle changing traffic and incident conditions over the time. The model performance was evaluated and validated by running the simulation and optimization programs of TRANSYT-7F and INTEGRATION. It has been found that the proposed model and control strategy reduce the overall system delay, increase the throughput of the corridor, and thus improve the traffic conditions of the entire corridor.
Real-Time Advanced Warning and Traffic Control Systems for Work Zones: Examination of Requirements and Issues
Thommana, Jose (Virginia Tech, 1997-05-30)
The I-81 Corridor in Virginia traverses the western part of the state, connecting Bristol in the south to Winchester in the north. A study carried out at the Virginia Tech Center for Transportation Research identified traffic safety, work zone safety and traffic control, trucking issues, and intercity traveler information needs as important issues that deserve attention on the I-81 Corridor in Virginia. Analysis of work zone accident statistics showed a need for real-time systems to enhance work zone safety. Real-time advanced warning and traffic control systems provide a means of dynamic information dissemination and advanced warning, thereby enhancing work zone safety and facilitating traffic control. The focus of this research was on the development of functional and system requirements for a real-time advanced warning and traffic control system for work zones. This task was based on the examination of work zone accidents and their causes. The functional requirements include advanced warning, surveillance, advisory, and control functions. Each of these functions consists of several sub-functions. The needs with respect to each of these functions have also been identified. System requirements such as real-time operation, credibility, portability, ease of installation, and adaptability were also identified. Evaluation criteria and potential Measures Of Effectiveness (MOEs) for the evaluation of the system were also identified. Additionally, issues related to the evaluation of the system, such as time duration for evaluation and data collection techniques were identified and examined.

Browsing by Author "Sivanandan, R."

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