Authors: Xianfeng Yang, Yang (Carl) Lu, and Gang-Len Chang
Journal: Journal of Advanced Transportation 2014
Abstract: This study presents two models for proactive variable speed limit (VSL) control on a recurrently congested freeway segment. The proposed model uses embedded traffic flow relations to predict the evolution of congestion patterns over the projected time horizon, and then computes the time-varying optimal speed limit to smooth traffic flows. To contend with the uncertainties associated with drivers’ responses to VSL control, this study has also proposed an advanced model that further adopts Kalman Filter to enhance the traffic state estimation. Both models have been investigated with two control objectives—travel time minimization and speed variance minimization. Our extensive simulation analysis with a VISSIM simulator, calibrated with field data from our previous VSL field demonstration, has revealed the benefits of the proposed VSL control models. Also, the experimental results indicated that the proposed advanced models with both control objectives can significantly reduce the travel time over the recurrent bottleneck locations. With respect to several selected measure of effectiveness (MOEs), such as average number of stops and average travel time, the research results confirm that the control models with the objective of minimizing speed variance can offer the promising properties for field implementation.
Authors: Xin Zhang and Gang-Len Chang
Journal: Transportation Research Part C 2014
Abstract: In urban emergency evacuation, a potentially large number of evacuees may depend either on transit or other modes, or need to walk a long distance, to access their passenger cars. In the process of approaching the designated pick-up points or parking areas for evacuation, the massive number of pedestrians may cause tremendous burden to vehicles in the roadway network. Responsible agencies often need to contend with congestion incurred by massive vehicles emanating from parking garages, evacuation buses generated from bus stops, and the conflicts between evacuees and vehicles at intersections. Hence, an effective plan for such evacuation needs to concurrently address both the multi-modal traffic route assignment and the optimization of network signal controls for mixed traffic flows. This paper presents an integrated model to produce the optimal distribution of vehicle and pedestrian flows, and the responsive network signal plan for massive mixed pedestrian– vehicle flows within the evacuation zone. The proposed model features its effectiveness in accounting for multiple types of evacuation vehicles, the interdependent relations between pedestrian and vehicle flows via some conversion locations, and the inevitable conflicts between intersection turning vehicle and pedestrian flows. An illustrating example concerning an evacuation around the M&T stadium area has been presented, and the results indicate the promising properties of our proposed model, especially on reflecting the complex interactions between vehicle and pedestrian flows and the favorable use of high-occupancy vehicles for evacuation operations.
Authors: Kyeong-Pyo Kang, Gang-Len Chang, and Jawad Paracha
Journal: Transportation Research Record, No. 1948
Publication Date: 2006
ABSTRACT:
The purpose of this study is to present the evaluation result of a dynamic late merge (DLM) system for highway work zone operations, experimented by the Maryland State Highway Administration and International Road Dynamics Inc. The evaluation focuses mainly on the operational efficiency such as the input–output analysis, work zone throughput, volume distribution, and resulting queue length. Evaluation results reveal that a properly deployed DLM system can indeed outperform the conventional merge control with respect to the total work zone throughputs. Such a system, however, may result in excessive traffic conflicts if not properly integrated with existing static warning signs for work zone operations. Some suggestions and guidelines developed from field observations and analysis results for potential improvement of the DLM performance are also presented in this paper.
Authors: Xianfeng Yang, Gang-Len Chang, Saed Rahwanji, and Yang Lu
Journal: Journal of Transportation Engineering 2013
Abstract:
Despite the increasing use of continuous-flow intersections (CFIs) to contend with the congestion caused by heavy through and left-turn traffic flows, a reliable and convenient tool for the traffic community to identify potential deficiencies of a CFI’s design is not yet available. This is due to the unique geometric feature of CFI, which comprises one primary intersection and several crossover intersections. The interdependent relationship between traffic delays and queues at a CFI with five closely spaced intersections cannot be fully captured with the existing analysis models, which were developed primarily for conventional intersections. In response to such a need, this study presents a comprehensive analysis for the overall CFI delay, identifies the potential queue spillback locations, and develops a set of planning stage models for the CFI design geometry. To facilitate the application of these proposed models, this paper also includes a case study of a CFI at the intersection of MD 4 and MD 235 constructed by the Maryland State Highway Administration.
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Authors: Xianfeng Yang, Gang-Len Chang, and Saed Rahwanji
Journal: Journal of Transportation Engineering 2014
Unconventional Design: DDI
Purpose: Developed a signal optimization model for DDI to achieve proper signal progressions.
Abstract:
As one of the most popular unconventional interchange designs, diverging diamond intersection (DDI) has received increased attention over the past decade. Through a reverse operation of traffic movements between its two crossover intersections, DDI can accommodate more traffic movements within each phase. To design an effective signal plan for DDIs, one needs to address the following two critical issues: (1) how to select the common cycle length and green splits at each crossover intersection under different geometric conditions, and (2) how to coordinate a DDI’s two crossover intersections with its adjacent conventional intersections. To contend with these issues, this paper presents an optimization model with the objective of maximizing intersection capacity to yield the optimal green splits and cycle length.
Also, in view of the potentially large left-turn traffic volumes from the freeway off-ramps, this study has further modified a model to provide progressions to both left-turn and through traffic paths. Using simulation software as an unbiased tool, this study has conducted extensive simulation comparisons between the optimized signal plans and the results from signal optimization software under various traffic scenarios. The experimental results confirm the promising properties of the proposed signal models for DDI, especially if the traffic progression between two crossover intersections is the major concern.
Download (Development_of_a_Signal_Optimization_Model_for_-Diverging_Diamond_Intechange.pdf)
Authors: Chenfeng Xiong, S.M. ASCE, Zheng Zhu, Xiang He, Xiqun Chen, Shanjiang Zhu, Subrat Mahapatra, Gang-Len Chang, M.ASCE, and Lei Zhang
Journal: Journal of Transportation Engineering 2015
Abstract: For determining highly dis-aggregate details about traffic dynamics, microscopic traffic simulation has long proven to be a valuable tool for the evaluation of development plans and operation/control strategies. With recent advances in computing capabilities, research interest in large-scale microscopic simulation has never been greater. This case study develops a 24-h large-scale microscopic traffic simulation model for the Washington, DC, metropolitan area. The model consists of over 7,000 links, 3,500 nodes, 400 signalized intersections, and over 40,000 origin-destination pairs. Various field measurements, such as time-dependent traffic counts and corridor travel times, have been used for model calibration/validation. The EPA’s Motor Vehicle Emission Simulator is linked with the microscopic simulation model for the estimation of environmental impacts. The calibrated model system has been used to comprehensively evaluate a newly built toll road in Maryland, the Inter-county Connector. Various network-level and corridor-level performance measures are quantified. The case study demonstrates the feasibility and capability of large-scale microscopic simulation in transportation applications. It establishes an example for modelers and practitioners who are interested in constructing a large-scale model system. The developed 24-h simulation model system of traffic and emissions has the potential to serve as a test bed for integration with other analysis tools, such as behavioral and optimization models.
Authors: Chenfeng Xiong, S.M. ASCE, Zheng Zhu, Xiang He, Xiqun Chen, Shanjiang Zhu, Subrat Mahapatra, Gang-Len Chang, M.ASCE, and Lei Zhang
Journal: Journal of Transportation Engineering 2015
Abstract: For determining highly dis-aggregate details about traffic dynamics, microscopic traffic simulation has long proven to be a valuable tool for the evaluation of development plans and operation/control strategies. With recent advances in computing capabilities, research interest in large-scale microscopic simulation has never been greater. This case study develops a 24-h large-scale microscopic traffic simulation model for the Washington, DC, metropolitan area. The model consists of over 7,000 links, 3,500 nodes, 400 signalized intersections, and over 40,000 origin-destination pairs. Various field measurements, such as time-dependent traffic counts and corridor travel times, have been used for model calibration/validation. The EPA’s Motor Vehicle Emission Simulator is linked with the microscopic simulation model for the estimation of environmental impacts. The calibrated model system has been used to comprehensively evaluate a newly built toll road in Maryland, the Inter-county Connector. Various network-level and corridor-level performance measures are quantified. The case study demonstrates the feasibility and capability of large-scale microscopic simulation in transportation applications. It establishes an example for modelers and practitioners who are interested in constructing a large-scale model system. The developed 24-h simulation model system of traffic and emissions has the potential to serve as a test bed for integration with other analysis tools, such as behavioral and optimization models.
Authors: Shanjiang Zhu, Woon Kim, Gang-Len Chang, M.ASCE, and Steve Rochon
Journal: Journal of Transportation Engineering 2014
Abstract: Both patrolling and prepositioned strategies for allocating emergency traffic response units have been implemented in practice. To compare the performance of both response strategies, this study has conducted an efficiency comparison based on the field data from the I-495/I-95 Capital Beltway. The extensive experimental results have revealed that the effectiveness of those response strategies varies with some critical factors, including the spatial distribution of incident frequency over different times of a day, the fleet size of the response team, the congestion level, and the available detection sources. In view of the resource constraints, the study has further presented a methodology to determine the most cost-beneficial fleet size operated with the proposed strategies, considering the marginal cost and the benefit of an additional response unit on the resulting total social benefits. The analysis results with the data from the Capital Beltway could serve as the basis for highway agencies to review and optimize their incident response and management program.
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Authors: Jie Yu, Yue Liu, Gang-Len Chang, Wanjing Ma, and Xiaoguang Yang
Journal: Transportation Research Record 2009
Abstract:
A cluster-based hierarchical location model for the selection of the proper locations and scales of urban transit hubs was developed with the objective of minimizing the demand-weighted total travel time. As an improvement to previous work, the proposed model has the following unique features: (a) it incorporates a hierarchical hub network topology that uses the concept of hub hierarchy establishment, route categorization, and service zone clustering to capture the critical operational issues for the transit network in an efficient manner and (b) it extends the previous nonhierarchical model to account for the impacts of hubs with various hierarchies as well as their interactions with lane use restrictions. An enhanced set of formulations along with the linearization approach was used to reduce significantly the number of variables and the computing time required to achieve the global optimum. The results of a case study in Suzhou Industrial Park in China revealed that the proposed model and solution method are quite promising for use in the planning of hub locations for the transit network. Sensitivity analysis of the performance
of the system was also done to assist planners with the selection of the hierarchical structure and the design of transit routes.
Download (Cluster_Based_Hierarchical_Model_for_Urban_Transit_Hub_Location_Planning.pdf)
Authors: Ying Liu , Xiaorong Lai , and Gang-len Chang
Journal: Journal of Transportation Engineering, Volume 132, Issue 10, pp. 800-807 (October 2006)
Abstract:
This paper presents a two-level integrated optimization system for use in generating the candidate set of optimal evacuation plans that serve as the input for simulation-based evacuation systems. In the proposed system, the high-level optimization aims to maximize the throughput during the specified evacuation duration, and the low level intends to minimize the total travel time as well as waiting time for the entire operation if the specified duration is sufficient for evacuating all demands. To effectively represent traffic flow relations with mathematical formulations, this paper employs the cell transmission concept, but with a revised formulation for large-scale network applications. The performance of the proposed models and their applicability has been tested with a microscopic simulation program that replicates the Ocean City evacuation network. Evaluation results from these numerical studies have demonstrated the promising properties of the proposed integrated optimization system.