Hoe Kyoung Kim

Ad Hoc Distributed Simulations

An ad hoc distributed simulation is a collection of autonomous on-line simulations brought together to model an operational system. They offer the potential of increased accuracy, responsiveness, and robustness compared to centralized approaches. They differ from conventional distributed simulations in that they are created bottom-up rather than top-down. They combine concepts from conventional distributed simulations and replicated trials, raising new issues in data management and synchronization. The ad hoc simulation approach is proposed as well as an optimistic synchronization algorithm. A prototype coupling in-vehicle transportation simulations is evaluated, yielding promising results. Experiences applying this concept to a commercial transportation simulator in an emergency scenario are described.

Dynamic data driven application simulation of surface transportation systems

A project concerned with applying Dynamic Data Driven Application Simulations (DDDAS) to monitor and manage surface transportation systems is described. Building upon activities such as the Vehicle-Infrastructure Integration initiative, a hierarchical DDDAS architecture is presented that includes coupled in-vehicle, roadside, and traffic management center simulations. The overall architecture is described as well as current work to implement and evaluate the effectiveness of this approach for a portion the Atlanta metropolitan area in the context of a hypothesized emergency evacuation scenario.

An investigation of real-time dynamic data driven transportation simulation

Widespread deployment of sensors in roadways and vehicles is creating new challenges in effectively exploiting the wealth of real-time transportation system data. However, the precision of the real-time data varies depending on the level of data aggregation. For example, minute-by-minute data are more precise than hourly average data. This paper explores the ability to create an accurate estimate of the evolving state of transportation systems using real-time roadway data aggregated at various update intervals. It is found that simulation based on inflow data aggregated over a short time interval is capable of providing a superior representation of the real world over longer aggregate intervals. However, the perceived improvements are minimal under congested conditions and most pronounced under un-congested conditions. In addition, outflow constraints should be considered during congested flow periods, otherwise significant deviation from the real world performance may arise

Practical Procedure to Collect Arterial Travel Time Data Using GPS-Instrumented Test Vehicles

Arterial streets are interrupted flow facilities that balance two purposes: serving through trips and providing commercial and residential access to adjacent land. A dominant factor in urban arterial street operations is the presence of traffic signals, which govern the flow of vehicles entering and exiting an arterial segment. Consequently, the performance of an arterial street is predominately influenced by delays incurred at traffic signals, with measures of effectiveness primarily a function of the performance at the arterial segment level. This paper presents a practical procedure to collect and analyze travel time data, based on Global Positioning Systems (GPS), that readily reflect measures of performance for both segments and extended arterial sections. Underlying this procedure is an assumption that both average travel speed and average intersection approach delay can be calculated as a function of arterial segment travel time, resulting in travel time as a primary field measurement used for gaug...

A Probe-Vehicle-Based Evaluation of Adaptive Traffic Signal Control

In 2005, the Cobb County Department of Transportation, Cobb County, GA, conducted an adaptive signal control pilot study implementing the Sydney Coordinated Adaptive Traffic System (SCATS) on 15 intersections. This paper presents the results of a before-and-after probe-vehicle-based operational comparison of optimized time-of-day (i.e., before control) and SCATS (i.e., after control) traffic control system performance. The focus of this operational analysis is the typical operating performance during the weekday peak, weekday off-peak, and weekend travel periods. Travel time data were collected using Global-Positioning-System (GPS)-equipped test vehicles. The results showed that both systems provided good performance, whereas neither the before time-of-day or after SCATS is clearly dominant, except on Cumberland Parkway, where SCATS control consistently provides equivalent or superior performance to that of the time-of-day control.

Ad Hoc Distributed Dynamic Data-Driven Simulations of Surface Transportation Systems

An ad hoc distributed dynamic data-driven simulation is a collection of autonomous online simulations brought together to model an operational system. They offer the potential of increased accuracy, responsiveness, and robustness compared to centralized approaches. They differ from conventional distributed simulations in that they are created bottom-up rather than top-down. They combine concepts from conventional distributed simulations and replicated trials, raising new issues in data management and synchronization. In this article, the ad hoc simulation approach and an optimistic synchronization algorithm are proposed. A prototype coupling in-vehicle transportation simulation is evaluated and shown to yield results comparable to a traditional replicated experiment for the tested scenarios. Experiences applying this concept to a commercial transportation simulator in an emergency scenario are described.

A Case Study on Measuring Travel Time, Speed and Delay Using GPS-Instrumented Test Vehicles

The Georgia Institute of Technology research team has recently conducted an arterial performance monitoring study on a 15-intersection signal control system in Cobb County, Georgia, using GPS-instrumented test vehicles. This paper describes the defined GPS error detecting criteria and the data reduction procedure developed by the research team. Error detecting criteria are developed based on distance between two consecutive GPS points, acceleration rate, deceleration rate, horizontal dilution of precision (HDOP), and the number of satellites. The impact on percentage of GPS data eliminated as a result of these varying criteria is given and performance measures are calculated for several different criteria values, allowing for a determination of the sensitivity of the performance measures to the error checking criteria set.

A simulation-based investigation of a dynamic advanced traveler information system

Traffic congestion is a source of significant economic and social costs in urban areas. Intelligent Transportation Systems (ITS) are a promising means to help alleviate congestion by utilizing advanced sensing, computing, and communication technologies. This paper investigates a basic ITS framework — Advanced Traveler Information System (ATIS) — using wireless vehicle-to-vehicle and vehicle-to-roadside communication and assuming an ideal communication environment. Utilizing an off-the-shelf microscopic simulation model this paper explores both a centralized (CA) and decentralized (DCA) ATIS architecture. Results of this study indicate that an ATIS using wireless communication can save travel time given varying combinations of system characteristics: traffic flow, communication radio range, and penetration ratio. Challenges are also noted in relying solely on instrumented vehicle data in an ATIS implementation.

Ad Hoc Distributed Simulation of Surface Transportation Systems

Current research in applying the Dynamic Data Driven Application Systems (DDDAS) concept to monitor and manage surface transportation systems in day-to-day and emergency scenarios is described. This work is focused in four, tightly coupled areas. First, a novel approach to predicting future system states termed ad hoc distributed simulations has been developed and is under investigation. Second, on-line simulation models that can incorporate real-time data and perform rollback operations for optimistic ad hoc distributed simulations are being developed and configured with data corresponding to the Atlanta metropolitan area. Third, research in the analysis of real-time data is being used to define approaches for transportation system data collection that can drive distributed on-line simulations. Finally, research in data dissemination approaches is examining effective means to distribute information in mobile distributed systems to support the ad hoc distributed simulation concept.

On the Resilience of Ad Hoc Distributed Simulation of Surface Transportation Systems with Unreliable Communications

The Dynamic Data Driven Application Systems (DDDAS) concept is examined in the context of monitoring and managing surface transportation systems in day-to-day and emergency scenarios. An approach to predicting future system states termed ad hoc distributed simulations is described. This approach uses on-line distributed simulation models that can incorporate real-time data and utilizes rollback operations to update state predictions as new information becomes available. This paper focuses on examining the reliability of ad hoc distributed simulations in mobile computing environments, and specifically, assessing the accuracy of future state predictions in the face of unreliable communications.