Paul T. R. Wang

An object-oriented traffic simulation with IVHS applications

Many traffic simulation models have been developed over the years; however, most existing models are not well-suited for evaluating Intelligent Vehicle/Highway Systems (IVHS) concepts. This paper describes a new model, the Vehicular Traffic Analysis Capability (VTAC), specifically designed to model Advanced Traffic Management and Advanced Traveler Information systems. The model was developed using object-oriented analysis and design principles, and implemented in a relatively new, object-oriented, simulation language. VTAC is believed to be the first traffic model developed using the object-oriented paradigm. The principles used in the new models design and the preliminary results obtained to-date are described. The model can currently model arterial networks, and sufficient progress has been made to demonstrate the utility of the object-oriented approach to traffic modeling.

Modeling time and space metering of flights in the national airspace system

Metering flights at key points such as sector crossings is an important operational procedure in mitigating National Airspace System (NAS) traffic congestion due to high demand or changing weather conditions. The authors combine a mathematical model for minutes-in-trail or miles-in-trail (MIT) metering with discrete event simulation in a newly developed tool that can be used by analysts to examine or predict existing or developing bottlenecks within NAS. We define a penalty function recursively in terms of MIT delays between leading and following flights. With discrete event simulations, it is possible to examine the anticipated MIT delays for all the flights scheduled to arrive at any crossing point. Impacts of flight cancellations, route changes, and additional enroute delays as results of airport or sector congestion can all be evaluated during each simulation by updating the scheduled flight crossing times and the expected MIT delay penalties for all the trailing flights.

Modelling concepts for intelligent vehicle highway systems (IVHS) applications

The Federal Highway Administration (FHWA) in cooperation with other government agencies, private industry, and academia, has established the Intelligent Vehicle Highway Systems (IVHS) program to use advanced computer and communications technology to increase throughput on existing roadways, to improve the safety of the traveling public, and to improve productivity of vehicle operations. Communications and vehicle traffic control are two major technologies used directly or indirectly to support the above IVHS program. This paper describes vehicle traffic and communications system modeling concepts used to analyze IVHS applications. The modeling concepts for IVHS traffic analysis section focuses on issues, solutions, and the design principles of an object-oriented model. The modeling concepts for communications system analysis section discusses Commercial Vehicle Operations (CVO) related architecture alternatives and performance analysis considerations. The paper summarizes the experience gained from our simtdation/analysis and discussesthe future direction for IVHS modeling studies.

Distributed/parallel traffic simulation for IVHS applications

This paper presents two algorithms developed for a distributed, discretes-event, and object-oriented traffic simulation, such as the Raffle and Highway Objects for REsearch, Analysis, and Understanding (THOREAU) (McGurrin and Wang, 1991) and (Hsin and Wang, 1992). THOREAU was designed for the study and analysis of Intelligent Vehicle Highway Systems (IVHS) [1] applications. The purpose of using distributed processing for traffic simulation is to extend the scope which can be modeled at an individual vehicle behavior level, by significantly increasing execution speed. The first algorithm was derived to decompose a large traffic model into submodels distributed over a network of workstations, with a minimum amount of inter-processor interactions, and to achieve the highest degree of parallelism. The second algorithm is an improvement of the Floyd algorithm for finding shortest paths using submodel decomposition and node to are incidency to achieve a 10m/sup 3/- fold speed improvement using m distributed processors. Both algorithms are being implemented for IVHS-related applications in a new version of THOREAU.

IVHS traffic modeling using parallel computing

The THOREAU simulation of vehicular traffic which may help researchers to evaluate candidate algorithms for Advanced Traveler Information Services (ATIS) and Advanced Traffic Management Systems (ATMS) is discussed. The authors seek to establish a set of ATIS and ATMS algorithms for comparative studies. An important goal is to provide sufficient information to developers of ATIS and ATMS algorithms for them to determine whether they could benefit from using THOREAU. The THOREAU simulation models vehicles moving along arterial roads and freeways. Portions of Orlando, Florida, and Troy, Michigan, have been represented and modeled using a simple ATIS algorithm which reroutes vehicles to minimize travel time based on recent demand history.

A Comparison Of Travel Time Reduction Using Current Vs. Partially Predictive Travel Times

This paper describes an Advanced Traveler Information System which for the purposes of providing optimal route information for driver uses primarily current data, but also uses predictive data where incidents have sufficiently changed the capacity of a node or link. The prediction would be based on the expected demand and an estimate of the now-reduced capacity. The predictive data would only be used for links with incidents. A simulation study of such a system is described, and a comparison is made of the results of such a system to one using only current data and to the absence of a route guidance system.

DP AT FLIGHT DELAY MODELING AND ITINERARY TRACKING

MITREs Center for Advanced Aviation System Development (CAASD) has developed a high-speed parallel airframe and airspace simulation tool known as the Detailed Policy Assessment Tool (DPAT). The tool is used for delay analysis of aircraft itineraries as a function of airspace capacities, traffic demand and airline scheduling practices, specifically including schedule padding and slack. Schedule padding is extra time included in a flights scheduled gate-togate time, to allow for possible delays. Schedule slack is the extra time allowed between flights of the same airframe, to allow for possible delays. We will present a simple analytic model of flight delays that show the interrelation of these effects. Such an analysis is possible with a new feature of DP AT that allows analysts to trace itineraries from airport to airport, including traversal of every enroute sector and every restriction encountered. The DP AT itinerary trace is implemented in an XML framework to simplify program debugging, animation, and the external interface to other ATC modeling tools. The effect of airport/sector capacity increase or reduction, traffic demand changes, and schedule padding and slack on flight delays can be tracked explicitly in model validation and verification efforts.

Enhanced THOREAU traffic simulation for intelligent transportation systems (ITS)

Traffic and Highway Objects for Research, Analysis and Understanding (THOREAU) is an object-oriented microscopic and mesoscopic traffic simulation tool for traffic engineers. It emphasizes the simulation of advanced traveler information systems (ATIS) and advanced traffic management systems (ATMS) as components of intelligent transportation systems (ITS). This paper describes recent enhancements to THOREAU in the area of ATMS, namely the microsimulation of actuated signals and corridor-wide signal optimization in conjunction with route guidance and incident management. There are strong coupling effects among various trip time control parameters including signal cycle times, green wave offsets, and ATMS control strategies. Using sample urban traffic networks, the impacts of actuated signal controllers, the adaptive Webster-Cobbe (1966) algorithm for isolated intersection, traffic detector placement strategies and coordinated corridor-wide optimization can be quantified. Consequently, traffic engineers may use THOREAU to explore alternative ITS technologies or architectures for optimal signal control and to validate network performance estimates obtained through analytic or rule-of-thumb approaches.

VDL Mode 3 subnet simulation models in OPNET

The Very High Frequency (VHF) Digital Link (VDL) Mode 3 is based on a Time Division Multiple Access (TDMA) media access control (MAC) protocol. This MAC protocol incorporates priority queuing, slotted ALOHA, and polling by the ground station to handle channel contention and to achieve the speedy delivery of time critical ATC messages. This paper provides an overview of the VDL Mode 3 subnet simulation models in Optimized Network Engineering Tools (OPNET). Four different subnet models are available for the simulation of different system configurations, namely, 2V2D, 3V1D, 4D, and 3T. The usefulness of these simulation models is demonstrated by their capability in simulating a wide range of scenarios and protocol alternatives in dealing with various configurations, load factors, and protocol parameter settings.

Collision awareness multiple access networks performance optimization

Collision awareness (CA) multiple access networks i nclude the carrier sense multiple access (CSMA), ALOHA, and Ethernet networks. In order to maximize throughput with minimum network delay, these networks employ control parameters such as persistence and bac koff. Based upon previous analytic results, the authors derived an asymptotic closed form solution for CA ne tworks. It is demonstrasted that by dynamically changing the persistent value one can ensure that the offered traffic will stay optimal and hence protect the network from over saturation. This technique will greatly enhance the performance of CA networks. Opnet simulation is used to validate the analysis.