Li Wen Chen

Development and Empirical Study of Real-Time Simulation-Based Dynamic Traffic Assignment Model

This research aims at developing a system of real-time simulation-based dynamic traffic model under mixed traffic flow conditions. The system consists of two layers, namely, simulation layer and real-time control layer. The system is implemented based on rolling horizon approach, which is advanced for each stage; thus real-time data can be incorporated within the framework. In order to predict normative, as well as predictive, information, a simulation-based dynamic traffic assignment model is employed within each stage. Empirical data for a real city network, such as flows from vehicle detectors, are used to validate the model in a real-time environment. The values of mean absolute percentage error and root-mean-squared percentage error are within 15%, and the results show promising agreements between observed and simulated flows.

Flow Equilibrium Under Dynamic Traffic Assignment and Signal Control—An Illustration of Pretimed and Actuated Signal Control Policies

Under intelligent transportation systems, the interaction between signal setting and traffic assignment is an important issue in designing efficient advanced traffic management systems. Most of the studies only describe the interaction under static assumptions, which do not consider possible temporal flow distribution. These assumptions limit the applicability in real-time management and control. This paper focuses on finding equilibrium under the interaction of signal setting and traffic assignment. The problem is constructed and solved through a bi-level framework. The upper level solves for signal setting parameters based on flow distributions, including cycle length and green splits. The lower level solves for user equilibrium dynamic traffic assignment (UEDTA) flows in a traffic network. The signal setting parameters are adjusted through pretimed and actuated signal controls. UEDTA flow patterns are generated through a simulation-based dynamic traffic assignment (DTA) model, DynaTAIWAN. Numerical experiments based on a real network in Kaohsiung City, Taiwan, are conducted to study the dynamic equilibrium. The numerical results indicate the existence of equilibrium flow under signal control and route assignment in a dynamic aspect. The results show that the average travel times under the pretimed signal policy are, in general, better than the times under the actuated signal policy.

Real-Time Implementation of Simulation-based Dynamic Traffic Assignment Model

This research aims at developing a real-time simulation-based dynamic traffic model for mixed traffic flow conditions for ATMS/ATIS applications. The real-time model is implemented based on rolling horizon approach. The rolling horizon is advanced for each stage, thus real-time data can be incorporated within the framework. In order to predict normative as well as predictive information, a simulation-based DTA model is employed within each stage. Empirical data for freeways, including flows from toll stations and vehicle detectors, are used to validate the model in a real-time environment.

Impact assessment of network reliability with route information under severe weather

Climate change and severe weather impacts on transportation and infrastructure have become global and environmental issues in the whole world. All human and transportation infrastructure systems are affected by climate change. Taiwan was hit by Typhoon Morakot and it caused a flood disaster in August 2009. This research focuses on the weather assessment measures of network reliability under route information. Two indexes are proposed to examine network reliability under route information, including: connectivity reliability and travel time reliability. Numerical experiments are conducted based on a real traffic network, the Jiaxian network, to illustrate the impact assessment of network reliability.

Dynamic flow equilibrium for flow-responsive signal settings and time-dependent traffic assignment

Under Intelligent Transportation Systems (ITS), the interaction between signal setting and traffic assignment is an important issue in designing efficient Advanced Traffic Management Systems (ATMS). This research focuses on finding dynamic user equilibrium between signal setting and route assignment. The problem is solved through a bi-level framework. The upper level solves for signal setting parameters based on flows, including cycle length and green splits. The lower level solves for time-dependent user equilibrium (UE) flows in a traffic network. The signal setting is adjusted through actuated signal control. Dynamic UE flow patterns are solved through a simulation-based DTA model, DynaTAIWAN. This bi-level framework can be applied in cities with signalized networks. Numerical experiments are conducted based on a subnetwork of the Kaohsiung City to study the dynamic equilibrium.

An object-oriented simulation-assignment model with consideration of mixed traffic flows for its applications

This paper aims at developing an integrated dynamic simulation-assignment model, DynaTAIWAN, for advanced traffic management systems as well as advanced traveller information systems. The model is composed of two layers, namely simulation-layer and real-time control layer. One of the key features of DynaTAIWAN is its ability to model multiple vehicle classes, especially motorcycles. Numerical experiments are conducted on two networks for illustrating possible capabilities of DynaTAIWAN