VTechWorks Repository :: Browsing by Author "Hobeika, Antoine G."

Browsing by Author "Hobeika, Antoine G."

Now showing 1 - 20 of 101

Accounting for Risk and Level of Service in the Design of Passing Sight Distances
El Khoury, John (Virginia Tech, 2005-11-28)
Current design methods in transportation engineering do not simultaneously address the levels of risk and service associated with the design and use of various highway geometric elements. Passing sight distance (PSD) is an example of a geometric element designed with no risk measures. PSD is provided to ensure the safety of passing maneuvers on two-lane roads. Many variables decide the minimum length required for a safe passing maneuver. These are random variables and represent a wide range of human and vehicle characteristics. Also, current PSD design practices replace these random variables by single-value means in the calculation process, disregarding their inherent variations. The research focuses on three main objectives. The first goal is to derive a PSD distribution that accounts for the variations in the contributing parameters. Two models are devised for this purpose, a Monte-Carlo simulation model and a closed form analytical estimation model. The results of both models verify each other and differ by less than 5 percent. Using the PSD distribution, the reliability index of the current PSD criteria are assessed. The second goal is to attach risk indices to the various PSD lengths of the obtained distribution. A unique microscopic simulation is devised to replicate passing maneuvers on two-lane roads. Using the simulation results, the author is able to assess the risk of various PSD lengths for a specific design speed. The risk index of the AASHTO Green Book and the MUTCD PSD standards are also obtained using simulation. With risk measures attached to the PSD lengths, a trade-off analysis between the level of service and risk is feasible to accomplish. The last task is concerned with applying the Highway Capacity Manual concepts to assessing the service measures of the different PSD lengths. The results of the final trade-off analysis show that for a design speed of 50 mph, the AASHTO Green Book and the MUTCD standards overestimate the PSD requirements. The criteria can be reduced to 725 ft and still be within an acceptable risk level.
Adequacy of minimum passing sight distances for completing or aborting the passing maneuver
Ohene, Frederick A. (Virginia Tech, 1987-09-30)
Overtaking and passing maneuvers on two-lane rural roads is still one of the most complex situations drivers are faced with in everyday driving. In passing, drivers must judge the speed, acceleration and deceleration capabilities of their own vehicle, that of the impeding vehicle and the speed and rate of closure of the oncoming vehicle. They also have to make decisions on the adequacy of an acceptable gap and sight distance. This report presents an investigation of the adequacy of the current "Manual on Uniform Traffic Control Devices" (MUTCD) for marking on two-lane, two-way roads. It examines the existing criteria, problems associated with it and its reasonableness. Passing sight distances which incorporates both the option of aborting or completing the passing maneuver is presented. A model describing the kinematics of vehicle trajectories during the passing maneuver on two-lane roads is utilized for this purpose. The model is based on the presence of a delima zone during the passing maneuver. At this point, the decision to complete or abort the passing maneuver provides the same factor of safety. This critical position is located using the model. The parameters that strongly influence the required sight distance are investigated. Thus passing sight distances that will provide reasonable margin of safety throughout the passing maneuver will be achieved. It is realized from the results that the current MUTCD passing sight distance is inadequate from a safety standpoint, except for high accelerations and high decelerations.
Alternative Methodology To Household Activity Matching In TRANSIMS
Paradkar, Rajan (Virginia Tech, 2001-06-15)
TRANSIMS (Transportation Analysis and Simulation System) developed at the Los Alamos National Laboratory, is an integrated system of travel forecasting models designed to give transportation planners accurate and complete information on traffic impacts, congestion, and pollution. TRANSIMS is a micro-simulation model which uses census data to generate a synthetic population and assigns activities using activity survey data to each person of every household of the synthetic population. The synthetic households generated from the census data are matched with the survey households based on their demographic characteristics. The activities of the survey household individuals are then assigned to the individuals of the matched synthetic households. The CART algorithm is used to match the households. With the use of CART algorithm a classification tree is built for the activity survey households based on some dependent and independent variables from the demographic data. The TRANSIMS model assumes activity times as dependent variables for building the classification tree. The topic of this research is to compare the TRANSIMS approach of using times spent in executing the activities as dependent variables, compared to match the alternative of using travel times for trips between activities as dependent variables i.e. to use the travel time pattern instead of activity time pattern to match the persons in the survey households with the synthetic households. Thus assuming that if the travel time patterns are the same then we can match the survey households to the synthetic population i.e. people with similar demographic characteristics tend to have similar travel time patterns. The algorithm of the Activity Generator module along with the original set of dependent variables, were first used to generate a base case scenario. Further tests were carried out using an alternative set of dependent variables in the algorithm. A sensitivity analysis was also carried out to test the affect of different sets of dependent variables in generating activities using the algorithm of the Activity Generator. The thesis also includes a detailed documentation of the results from all the tests.
Analysis and Evaluation of Household Pick-up and Gathering Behavior in No-Notice Evacuations
Liu, Sirui (Virginia Tech, 2011-05-04)
No-notice incidents occur with no advance notice of time and place. Family members may be separated when a no-notice incident strikes during the daytime. They may seek to gather the household members first and evacuate as a unit, and parents may head in the "wrong" direction to pick up their children from schools/daycare centers. Many previous studies have acknowledged that such behavior exists but few, if any, have examined it in-depth. Additionally, this behavior has rarely been integrated with transportation simulation models of evacuation conditions. As shown through this work, such omissions generate overly optimistic network performance. Acknowledging the behavior also leads to potential network improvements by moving dependents (people being picked up by other household members) to more accessible locations. This study investigated no-notice evacuation household gathering behavior based on 315 interviews conducted in the Chicago metropolitan area, in which interviewees were asked about their evacuation and logistic decisions. The study analyzed household pick-up and gathering behavior from the interviews, developed models to represent the behavior, and integrated the household behavior models with network simulation modeling to examine the effects of household behaviors on network evacuation performance. Logistic regression models were built to predict the probability that parents retrieve children from school in normal and emergency situations. Gender, car availability, and travel distance (between parents and children) were the main influencing factors to determining child-chauffeuring travel behavior, where gender difference appeared to be most prominent. Women are more responsible for picking up children from school than men, and both women and men are more likely to pick up children under emergency conditions compared to a normal situation. A complex model to integrating human behavior analysis and network assignment modeling was presented in this study. The model follows the traditional four step urban transportation planning process and 1) estimates household gathering chains in an evacuation using a discrete choice (Logit) model and sequences chains following the principle of "nearest first", 2) assigns directions of destinations ensuring the least travel time to safe zones from the last stop within the hot zones, 3) applies decision tree based mode choice models to determine the mode used for evacuation, and 4) uses a dynamic assignment method to assign time-varying demand to the network. The whole framework was tested in the Chicago metropolitan region for two hypothetical incidents, one causing a 5-mile evacuation radius and the other a 25-mile radius evacuation. The results showed that considering household gathering behavior will reduce proportions of evacuees who reach safe zones by a certain time period, while not necessarily deteriorating overall network traffic performance. To facilitate the chain-based evacuations, a relocation model is proposed by moving carless dependents of facilities (such as schools and daycare centers) to more accessible locations for pickup; a linear integer program is presented to determine optimal sites. The optimization model uses estimated travel time obtained from a micro-simulation model and a procedure is presented to iterate between the two models (optimization and simulation). The methodology was applied to a sample network based on Chicago Heights, Illinois. The sample application involved four facilities with 780 dependents and three safe time thresholds, i.e., 30, 45 and 60 minutes. The sample application tested two scenarios - no mode shift and mode shift from car to bus - and introduced average speed and the number of successful evacuations of dependents to evaluate the performance of a relocation strategy. The safe evacuation time threshold was quite important for the relocation strategy; when it is adequate, relocating dependents benefits both those picking up dependents and the other vehicles in the network. This dissertation contributes to the fields of evacuation modeling and transportation engineering, in general. This study investigates child pick-up, spouse gathering, and home gathering behavior during hypothetical incidents, and identifies characteristics associated with household decision makers that influence this behavior. The study also presents a model to integrate the behavior with road network simulation modeling; the combined model could be used to investigate the effects of gathering behavior on network traffic performance and identify potential spatial and temporal bottlenecks. Finally, this work explored a strategy to facilitate household pick up chains by relocating facility dependents to more accessible site. The study can support any city evacuation plan development.
An Analysis of Fare Collection Costs on Heavy Rail and Bus Systems in the U.S.
Plotnikov, Valeri (Virginia Tech, 2001-09-05)
In this research, an effort is made to analyze the costs of fare collection on heavy rail and motorbus systems in the U.S. Since existing ticketing and fare collection (TFC) systems are major elements of transit infrastructure and there are several new alternative TFC technologies available on the market, the need to evaluate the performance of existing TFC systems arises. However, very little research has been done, so far, to assess impacts of TFC technologies on capital and operating expenses in public transit. The two objectives of this research are: (1) to formulate a conceptual evaluation framework and a plan to assess the operating costs of existing TFC systems in transit and (2) to analyze the operating expenses associated with existing TFC systems on heavy rail and motorbus transit in the U.S. with the aid of the evaluation framework and plan. This research begins with a review of the current state of knowledge in the areas of transit TFC evaluation, the economics of public transit operations, and fare collection practices and technologies. It helps to determine the scope of work related to assessment of TFC operating costs on public transit and provides the basis for the development of a conceptual evaluation framework and an evaluation plan. Next, this research presents a systematic approach to define and describe alternative TFC systems and suggests that the major TFC system determinants are payment media, fare media, TFC equipment, and transit technology (mode). Following this is the development of measures of effectiveness to evaluate alternative TFC systems. These measures assess cost-effectiveness and labor-intensiveness of TFC operations. The development of TFC System Technology Index follows. This Index recognizes the fact that TFC systems may consist of different sets of TFC technologies both traditional and innovative. Finally, this research presents statistical results that support the hypothesis that TFC operating costs are related to transit demand, transit technology (mode) and TFC technologies. These results further suggest that: (1) TFC operating costs per unlinked passenger trip on heavy rail systems are higher than on motorbus systems and (2) TFC operating costs per unlinked passenger trip tend to increase as the use of non-electronic fare media increases. Actions for further research are also recommended.
Analysis of Freeway Weaving Areas Using Corridor Simulator and Highway Capacity Manual
Ramachandran, Suresh (Virginia Tech, 1997-12-01)
Weaving is defined as the crossing of two or more traffic streams traveling in the same direction along a significant length of the highway without the aid of traffic control devices . The traditional methods used for design and operational analysis of a highway is the Highway Capacity Manual (HCM). The traditional weaving methods in the highway capacity manual use road geometry and traffic volume as inputs and provide an estimate of speed as an output. CORSIM is a new computer simulation model developed by Federal Highway Administration (FHWA) for simulation of traffic behavior on integrated urban transportation networks of freeway and surface streets. The intent of this research is to identify the difference in the results by using the new CORSIM simulation and the traditional HCM approach in modeling the weaving sections on a freeway and make recommendations. The research will also compare the modeling strategy and provide analysis of the output.
Analysis of microprocessor based vehicular instrumentation and automatic passenger counting systems
Shankar, Sanjeev (Virginia Tech, 1985-08-05)
Information on transit ridership and operations is a necessary condition as far as efficient management is considered. Transit managements on the acquisition of such a data base can confirm predictions about scheduling, receive warnings about potential dangers and plan future operations on a much broader and precise base. Data from passenger counts provide essential information to marketing and scheduling personnel by identifying peak load-points and the such. Using manual collection methods for such data is expensive and prone to human errors. Automatic Passenger Counting (APC) systems are viewed as an improved and economical technique for data collection. Such systems monitor the progress of a particular vehicle — its position, number of passengers getting on and off, times and distances between stops — and make this data available for processing. These are state of the art systems, mostly microprocessor based and often embracing a modular structure. The Red Pine system is such a system with different dedicated modules for each bank of tasks. Multitasking software is seen to be an powerful tool for such systems and simplify the architecture of the system hardware. A CHMOS hardware design, suited for multitasking softwares is provided. Interfacing software for the Red Pine system has been developed and is explained. Debugging testing and simulation of the Red Pine hardware is detailed. Modifications have been recorded and improvements suggested.
Analysis of Potential Wake Turbulence Encounters in Current and NextGen Flight Operations
Schroeder, Nataliya (Virginia Tech, 2011-01-31)
Wake vortices pose a threat to a following aircraft, because they can induce a roll and compromise the safety of everyone on board. Caused by a difference in pressure between the upper and the lower part of the wings, these invisible flows of air are a major hazard and have to be avoided by separating the aircraft at considerable distances. One of the known constraints in airport capacity for both departure and arrival operations is the large headway resulting from the wake spacing separation criteria. Reducing wake vortex separations to a safe level between successive aircraft can increase capacity in the National Airspace System (NAS) with corresponding savings in delay times. One of the main goals of the Wake Encounter Model (WEM) described in this thesis is to assess the outcome from future reduced separation criteria in the NAS. The model has been used to test probable encounters in today's operations, and can also be used to test NextGen scenarios, such as Close Parallel Approaches and reduced in-trail separation flights. This thesis presents model enhancements to account for aircraft turning maneuvers, giving the wake a more realistic shape. Three major airspaces, New York, Southern California and Atlanta, were analyzed using the original and the enhanced WEM to determine if the enhanced model better represents the conditions in today's operations. Additionally, some analysis on the wake lateral travel for closely spaced runways is presented in this thesis. Finally, some extension tools for post -analysis, such as animation tool and various graphs depicting the interactions between wake pairs were developed.
Analysis of truck overturn accidents on Virginia interstate systems: a case study of I-81
Azimi-Ghomi, Edreece A. (Virginia Tech, 1993-04-22)
In this study, trucks or large trucks are defined as straight trucks (ST-TR) also known as single unit trucks having a single body without any hitch between the loading section and front driving mechanism, tractor trailers (TR -TR) having two bodies coupled by a hitch, and twin tractor trailers (TW-TR) with front driving mechanisms towed by a double trailer. Vehicle miles of travel (VMT) for these trucks have been steadily increasing for the past five years (1986-1990) showing a continuous growth in transportation goods both inside and outside of the State of Virginia. The objective of this research is to identify the major factors associated with truck overturns occurring on which occurred between 1986 and 1990, on the main line of the Virginia Interstate System in general and 1-81 in particular.
Application of an automatic data acquisition system in mass transit
Raju, Srinath (Virginia Tech, 1987-10-14)
A robust algorithm has been developed to do data processing accurately, removing the need for a radio signal to be imbedded for locational accuracy. This, consequently eliminates the signposts installation and maintenance costs and worries. A sensitivity analysis of the algorithm using a real life data file revealed that the matching process change with changes in system parameters, adding credibility to the technique used for matching in the algorithm. Next, several new programs have been added to bring together a software package yielding management reports and plots. These reports and plots are tremendous decision aiding tools and since the programs are interactive, the package is easy to use. A user's manual has also been developed. Finally, an implementation of the Automated Data Acquisition System at TRT, Norfolk, is discussed. A systematic approach to the software development to meet the needs of the transit property has been conceptualized and specific software developed. A discussion of the details of this software development has been addressed, too. In essence, Automatic Data Acquisition systems research at Virginia Tech has now evolved to such a stage that with a little "tuning" of hardware & the associated software, a very powerful and versatile automated data collection and management aiding tool will be available for economical widespread implementation.
Application of user equilibrium traffic assignment in evacuation modelling
Kim, Changkyun (Virginia Tech, 1991-08-01)
The Mass Evacuation (MASSVAC) model was originally developed for analysis and evaluation of evacuation plan in a specific area facing natural disasters. It was later applied to deal with the problems of evacuation around nuclear power stations (MASSVAC 3.0). The purpose of this model is to simulate the network clearance time and evacuation routes. In the process, it employs the Dial's or the all-or-nothing method to assign the traffic on to the network. The major effort in this research is to include the user equilibrium assignment method to reduce the evacuation times and to improve highway network performance. Evacuation routes, number of links used, and evacuation times etc. are found to be influenced by the user equilibrium assignment method. Transportation System Management (TSM) strategies have also been incorporated in this enhanced model (MASSVAC 4.0) to improve the network performance during evacuation. The trip distribution process and the shortest path algorithm has been modified appropriately to suit the user equilibrium assignment.
The Approach-dependent, Time-dependent, Label-constrained Shortest Path Problem and Enhancements for the CART Algorithm with Application to Transportation Systems
Jeenanunta, Chawalit (Virginia Tech, 2004-05-10)
In this dissertation, we consider two important problems pertaining to the analysis of transportation systems. The first of these is an approach-dependent, time-dependent, label-constrained shortest path problem that arises in the context of the Route Planner Module of the Transportation Analysis Simulation System (TRANSIMS), which has been developed by the Los Alamos National Laboratory for the Federal Highway Administration. This is a variant of the shortest path problem defined on a transportation network comprised of a set of nodes and a set of directed arcs such that each arc has an associated label designating a mode of transportation, and an associated travel time function that depends on the time of arrival at the tail node, as well as on the node via which this node was approached. The lattermost feature is a new concept injected into the time-dependent, label-constrained shortest path problem, and is used to model turn-penalties in transportation networks. The time spent at an intersection before entering the next link would depend on whether we travel straight through the intersection, or make a right turn at it, or make a left turn at it. Accordingly, we model this situation by incorporating within each link's travel time function a dependence on the link via which its tail node was approached. We propose two effective algorithms to solve this problem by adapting two efficient existing algorithms to handle time dependency and label constraints: the Partitioned Shortest Path (PSP) algorithm and the Heap-Dijkstra (HP-Dijkstra) algorithm, and present related theoretical complexity results. In addition, we also explore various heuristic methods to curtail the search. We explore an Augmented Ellipsoidal Region Technique (A-ERT) and a Distance-Based A-ERT, along with some variants to curtail the search for an optimal path between a given origin and destination to more promising subsets of the network. This helps speed up computation without sacrificing optimality. We also incorporate an approach-dependent delay estimation function, and in concert with a search tree level-based technique, we derive a total estimated travel time and use this as a key to prioritize node selections or to sort elements in the heap. As soon as we reach the destination node, while it is within some p% of the minimum key value of the heap, we then terminate the search. We name the versions of PSP and HP-Dijkstra that employ this method as Early Terminated PSP (ET-PSP) and Early Terminated Heap-Dijkstra (ETHP-Dijkstra) algorithms. All of these procedures are compared with the original Route Planner Module within TRANSIMS, which is implemented in the Linux operating system, using C++ along with the g++ GNU compiler. Extensive computational testing has been conducted using available data from the Portland, Oregon, and Blacksburg, Virginia, transportation networks to investigate the efficacy of the developed procedures. In particular, we have tested twenty-five different combinations of network curtailment and algorithmic strategies on three test networks: the Blacksburg-light, the Blacksburg-full, and the BigNet network. The results indicate that the Heap-Dijkstra algorithm implementations are much faster than the PSP algorithmic approaches for solving the underlying problem exactly. Furthermore, mong the curtailment schemes, the ETHP-Dijkstra with p=5%, yields the best overall results. This method produces solutions within 0.37-1.91% of optimality, while decreasing CPU effort by 56.68% at an average, as compared with applying the best available exact algorithm. The second part of this dissertation is concerned with the Classification and Regression Tree (CART) algorithm, and its application to the Activity Generation Module of TRANSIMS. The CART algorithm has been popularly used in various contexts by transportation engineers and planners to correlate a set of independent household demographic variables with certain dependent activity or travel time variables. However, the algorithm lacks an automated mechanism for deriving classification trees based on optimizing specified objective functions and handling desired side-constraints that govern the structure of the tree and the statistical and demographic nature of its leaf nodes. Using a novel set partitioning formulation, we propose new tree development, and more importantly, optimal pruning strategies to accommodate the consideration of such objective functions and side-constraints, and establish the theoretical validity of our approach. This general enhancement of the CART algorithm is then applied to the Activity Generator module of TRANSIMS. Related computational results are presented using real data pertaining to the Portland, Oregon, and Blacksburg, Virginia, transportation networks to demonstrate the flexibility and effectiveness of the proposed approach in classifying data, as well as to examine its numerical performance. The results indicate that a variety of objective functions and constraints can be readily accommodated to efficiently control the structural information that is captured by the developed classification tree as desired by the planner or analyst, dependent on the scope of the application at hand.
AQM Shell Development - Creating a Framework for Airspace and Airfield Operations and Air Quality Visualization Software
Peterson, Todd Alan (Virginia Tech, 1997-09-22)
It is believed that the analysis of air traffic impacts on air quality will benefit from attention to the three-dimensional nature of the air traffic network as well as the actions of individual aircraft during the study period. With the existence of air traffic simulation models, the actions of individual aircraft may already be defined in a simulated environment. SIMMOD, the Federal Aviation Administration's airport and airspace modeling software, performs such models of scheduled air traffic. The results of such models may be used to determine the impacts of scheduled air traffic on air quality as well as other parameters. This report addresses the interpretation of output from SIMMOD models for use in air quality analysis and visualization of the air traffic network, and the application of these techniques in a stand-alone computer program. This program, named AQM for its purpose in assisting development of Air Quality Models, provides a working framework for future development of software for detailed air quality analysis and visualization.
An Assessment Methodology for Emergency Vehicle Traffic Signal Priority Systems
McHale, Gene Michael (Virginia Tech, 2002-02-26)
Emergency vehicle traffic signal priority systems allow emergency vehicles such as fire and emergency medical vehicles to request and receive a green traffic signal indication when approaching an intersection. Such systems have been around for a number of years, however, there is little understanding of the costs and benefits of such systems once they are deployed. This research develops an improved method to assess the travel time impacts of emergency vehicle traffic signal priority systems for transportation planning analyses. The research investigates the current state of available methodologies used in assessing the costs and benefits of emergency vehicle traffic signal priority systems. The ITS Deployment Analysis System (IDAS) software is identified as a recently developed transportation planning tool with cost and benefit assessment capabilities for emergency vehicle traffic signal priority systems. The IDAS emergency vehicle traffic signal priority methodology is reviewed and recommendations are made to incorporate the estimation of non-emergency vehicle travel time impacts into the current methodology. To develop these improvements, a simulation analysis was performed to model an emergency vehicle traffic signal priority system under a variety of conditions. The simulation analysis was implemented using the CORSIM traffic simulation software as the tool. Results from the simulation analysis were used to make recommendations for enhancements to the IDAS emergency vehicle traffic signal priority methodology. These enhancements include the addition of non-emergency vehicle travel time impacts as a function of traffic volume on the transportation network. These impacts were relatively small and ranged from a 1.1% to 3.3% travel time increase for a one-hour analysis period to a 0.6% to 1.7% travel time increase for a two-hour analysis period. The enhanced methodology and a sample application of the methodology are presented as the results of this research. In addition, future research activities are identified to further improve assessment capabilities for emergency vehicle traffic signal priority systems.
Assessment of Vehicle-to-Vehicle Communication based Applications in an Urban Network
Kim, Taehyoung (Virginia Tech, 2015-06-23)
Connected Vehicle research has emerged as one of the highest priorities in the transportation systems because connected vehicle technology has the potential to improve safety, mobility, and environment for the current transportation systems. Various connected vehicle based applications have been identified and evaluated through various measurements to assess the performance of connected vehicle applications. However, most of these previous studies have used hypothetical study areas with simple networks for connected vehicle environment. This study represents connected vehicle environment in TRANSIMS to assess the performance of V2V communication applications in the realistic urban network. The communication duration rate and spatial-temporal dispersion of equipped vehicles are investigated to evaluate the capability of V2V communication based on the market penetration rate of equipped vehicles and wireless communication coverage in the whole study area. The area coverage level is used to assess the spatial-temporal dispersion of equipped vehicles for two study areas. The distance of incident information propagation and speed estimation error are used to measure the performance of event-driven and periodic applications based on different market penetration rates of equipped vehicles and wireless communication coverage in both morning peak and non-peak times. The wireless communication coverage is the major factor for event-driven application and the market penetration rate of equipped vehicles has more impact on the performance of periodic application. The required minimum levels of deployment for each application are determined for each scenario. These study findings will be useful for making decisions about investments on deployment of connected vehicle applications to improve the current transportation systems. Notably, event-driven applications can be reliably deployed in the initial stage of deployment despite the low level of market penetration of equipped vehicles.
Bluetooth based dynamic critical route volume estimation on signalized arterials
Gharat, Asmita (Virginia Tech, 2011-09-09)
Bluetooth Data collection technique is recently proven as a reliable data collection technique that provides the opportunity to modify traditional methodologies to improve system performance. Actual volume in the network is a result of the timing plans which are designed and modified based on the volume which is generated using existing timing plans in the system. This interdependency between timing plan and volume on the network is a dynamic process and should be captured to obtain actual traffic states in the network. The current practice is to calculate synthetic origin destination information based on detector volume that doesn't necessarily represent the volume scenario accurately. The data from Bluetooth technology can be utilized to calculate dynamic volume on the network which can be further used as input for signal timing design. Application of dynamic volume improves the system performance by providing the actual volume in system to design optimal timing plans. This thesis proposes a framework that can be used to integrate data obtained from the Bluetooth technology with the traditional methods to design timing plans. The proposed methodology utilizes the origin destination information obtained from Bluetooth data, detector data, characteristics of intersections such as number of lanes, saturation flow rate and existing timing plans as a basis for the calculation of the dynamic volume for the various movements at each intersection. The study shows that using the Bluetooth based OD matrix to calculate accurate dynamic volumes results in better system performance compared to the traditional way of using the static detector volume alone.
Co-Location Decision Tree for Enhancing Decision-Making of Pavement Maintenance and Rehabilitation
Zhou, Guoqing (Virginia Tech, 2011-01-17)
A pavement management system (PMS) is a valuable tool and one of the critical elements of the highway transportation infrastructure. Since a vast amount of pavement data is frequently and continuously being collected, updated, and exchanged due to rapidly deteriorating road conditions, increased traffic loads, and shrinking funds, resulting in the rapid accumulation of a large pavement database, knowledge-based expert systems (KBESs) have therefore been developed to solve various transportation problems. This dissertation presents the development of theory and algorithm for a new decision tree induction method, called co-location-based decision tree (CL-DT.) This method will enhance the decision-making abilities of pavement maintenance personnel and their rehabilitation strategies. This idea stems from shortcomings in traditional decision tree induction algorithms, when applied in the pavement treatment strategies. The proposed algorithm utilizes the co-location (co-occurrence) characteristics of spatial attribute data in the pavement database. With the proposed algorithm, one distinct event occurrence can associate with two or multiple attribute values that occur simultaneously in spatial and temporal domains. This research dissertation describes the details of the proposed CL-DT algorithms and steps of realizing the proposed algorithm. First, the dissertation research describes the detailed colocation mining algorithm, including spatial attribute data selection in pavement databases, the determination of candidate co-locations, the determination of table instances of candidate colocations, pruning the non-prevalent co-locations, and induction of co-location rules. In this step, a hybrid constraint, i.e., spatial geometric distance constraint condition and a distinct event-type constraint condition, is developed. The spatial geometric distance constraint condition is a neighborhood relationship-based spatial joins of table instances for many prevalent co-locations with one prevalent co-location; and the distance event-type constraint condition is a Euclidean distance between a set of attributes and its corresponding clusters center of attributes. The dissertation research also developed the spatial feature pruning method using the multi-resolution pruning criterion. The cross-correlation criterion of spatial features is used to remove the nonprevalent co-locations from the candidate prevalent co-location set under a given threshold. The dissertation research focused on the development of the co-location decision tree (CL-DT) algorithm, which includes the non-spatial attribute data selection in the pavement management database, co-location algorithm modeling, node merging criteria, and co-location decision tree induction. In this step, co-location mining rules are used to guide the decision tree generation and induce decision rules. For each step, this dissertation gives detailed flowcharts, such as flowchart of co-location decision tree induction, co-location/co-occurrence decision tree algorithm, algorithm of colocation/co-occurrence decision tree (CL-DT), and outline of steps of SFS (Sequential Feature Selection) algorithm. Finally, this research used a pavement database covering four counties, which are provided by NCDOT (North Carolina Department of Transportation), to verify and test the proposed method. The comparison analyses of different rehabilitation treatments proposed by NCDOT, by the traditional DT induction algorithm and by the proposed new method are conducted. Findings and conclusions include: (1) traditional DT technology can make a consistent decision for road maintenance and rehabilitation strategy under the same road conditions, i.e., less interference from human factors; (2) the traditional DT technology can increase the speed of decision-making because the technology automatically generates a decision-tree and rules if the expert knowledge is given, which saves time and expenses for PMS; (3) integration of the DT and GIS can provide the PMS with the capabilities of graphically displaying treatment decisions, visualizing the attribute and non-attribute data, and linking data and information to the geographical coordinates. However, the traditional DT induction methods are not as quite intelligent as one's expectations. Thus, post-processing and refinement is necessary. Moreover, traditional DT induction methods for pavement M&R strategies only used the non-spatial attribute data. It has been demonstrated from this dissertation research that the spatial data is very useful for the improvement of decision-making processes for pavement treatment strategies. In addition, the decision trees are based on the knowledge acquired from pavement management engineers for strategy selection. Thus, different decision-trees can be built if the requirement changes.
Collision Warning and Avoidance System for Crest Vertical Curves
Kon, Tayfun (Virginia Tech, 1998-05-04)
In recent years, State Road Route 114 which is located in Montgomery County, Virginia, has gained a bad reputation because of numerous traffic accidents. Most of these accidents resulted in loss of lives and property. Although there are many suggestions and proposals designed to prevent these accidents, to date no actions is taken yet. The focus of this research is to explore a technology-based, low cost solution that will lower or eliminate the risk of accidents on this two-lane rural highway.
Combat aircraft mission tradeoff models for conceptual design evaluation
Malakhoff, Lev A. (Virginia Polytechnic Institute and State University, 1988)
A methodology is developed to address the analyses of combat aircraft attrition. The operations of an aircraft carrier task force are modeled using the systems dynamics simulation language DYNAMO. The three mission-roles include: surface attack, lighter escort, and carrier defense. The level of analysis is performed over the entire campaign, going beyond the traditional single·sortie analysis level. These analyses are performed by determining several measures of effectiveness (MOEs) for whatever constraints are applied to the model. The derived MOEs include: Campaign Survivability (CS), Fractlon of Force Lost (FFL), Exchange Ratio (ER), Relative Exchange Ratio (RER), Possible Crew Loss (PCL), and Replacement Cost (RC). RER is felt to be the most useful MOE since it considers the initial inventory levels of both friendly and enemy forces, and its magnitude is easy for the analyst to relate to (an RER greater than one is a prediction of a friendly force’s victory). The simulation model developed in this research is run for several experiments. The effects of force size on the MOEs ls studied, as well as a hypothetical multimission aircraft deployed to perform any of the three missions (albeit at lower effectiveness than the speciallzed aircraft for their given roles but nonetheless with a higher availability). Evaluation of specific technological improvements such as smaller radar cross section, higher thrust/weight, improved weapons ranges, is made using the MOEs. Also, a cost-effectiveness tradeoff methodology is developed by determining the acquisition cost ratio (ACR) for certain modified alternatives the baseline by determining the required initial inventory of modified aircraft to produce the same total effectiveness of the baseline aircraft.
A Comparative Analysis of Weaving Areas in HCM, TRANSIMS, CORSIM, VISSIM and INTEGRATION
Koppula, Nanditha (Virginia Tech, 2002-05-08)
Traffic simulation is a powerful tool that provides transportation engineers with the ability to test the feasibility and performance of a system before it is implemented and also helps in optimizing the proposed system. Over the past twenty years significant amount of work has been conducted on improving the quality and accuracy of transportation simulation models. Much of this work has been concentrated on microscopic simulation models because they provide traffic engineers greater opportunity to examine the inherently complex, stochastic, and dynamic nature of transportation systems when compared to traditional macroscopic models. In order to test the performance of some of the simulation models, a study is conducted on freeway weaving sections, which are considered to be one of the most complex regions to be modeled and analyzed. The intent of the research is to evaluate TRANSIMS, CORSIM, VISSIM and INTEGRATION and compare them with Highway Capacity Manual, which adopts a traditional methodology for carrying out the operational analysis of a highway system. The statistics collected for the simulation runs include weaving speeds, non-weaving speeds and density of the weaving section.

Browsing by Author "Hobeika, Antoine G."

Results Per Page

Sort Options