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.

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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.

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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.

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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.

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Authors: Xin Zhang and Gang-Len Chang
Journal: Journal of Intelligent Transportation Systems: Technology, Planning, and Operations 2014
Abstract:  In most metropolitan areas, an emergency evacuation may require a potentially large number of pedestrians to walk some distance to access their passenger cars or resort to transit systems. In this process, the massive number of pedestrians may place a tremendous burden on vehicles in the roadway network, especially at critical intersections. Thus, the effective road enforcement of the vehicle and pedestrian flows and the proper coordination between these two flows at critical intersections during a multi-modal evacuation process is a critical issue in evacuation planning. This article presents an integrated linear model for the design of optimized flow plans for massive mixed pedestrian–vehicle flows within an evacuation zone. The optimized flow can also be used to generate signal timing plans at critical intersections. In addition, the linear nature of the model can circumvent the computational burden to apply in large-scale networks. An illustrating example of the evacuation around the M&T Bank Stadium in downtown Baltimore, MD, is presented and used to demonstrate the model’s capability to address the complex interactions between vehicle and pedestrian flows within an evacuation zone. Results of simulation experiments verify the applicability of our model to a real-world scenario and further indicate that accounting for such conflicting movements will yield more reliable estimation of an evacuation’s required clearance time.

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Authors: Yang (Carl) Lu, Xianfeng Yang, and Gang-Len Chang
Journal: Transportation Research Record 2014
Abstract:  Although average effective vehicle length (AEVL) has been recognized as one of the most popular methods for detecting data errors, how to set proper thresholds so as to prevent false alarms and missed detections remains a challenging ongoing issue. This study proposed a sequential screening algorithm that employed multiple comparisons with the best statistics to compare concurrently the estimated AEVLs between lanes and stations for assessment of the data quality of a target detector. With both the temporal and spatial information, the proposed method can reliably generate a confidence interval and determine whether the target detector is malfunctioning or in need of calibration. The proposed algorithm was tested with 2 weeks of detector data from Ocean City, Maryland. The analysis results demonstrate the effectiveness of the proposed sequential screening algorithm and its potential for field applications.

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Authors: Xin Zhang and Gang-Len Chang
Journal: Journal of Public Transportation, Vol. 17, No. 3, 2014
Abstract:  This paper develops a decision-support model for transit-based evacuation planning occurring in metropolitan areas. The model consists of two modules executed in a sequential manner: the first deals with determining pick-up locations from candidate locations based on the spatial distribution of the evacuees, and the second plans for the route and schedule for each transit vehicle based on vehicle availability and evacuee demand pattern. An overlapping clustering algorithm is first adopted in allocating the demands to several nearby clusters. Then, an optimization model is proposed to allocate available buses from the depots to transport the assembled evacuees between the pick-up locations and different safety destinations and public shelters. A numerical example based on the city of Baltimore demonstrates the applicability of the proposed model and the advantages compared to state-of-the-art models with overly strict and unrealistic assumptions.

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Authors: Chien-Lun Lan and Gang-Len Chang
Journal: IEEE Transactions on Intelligent Transportation Systems 2014
Abstract:  In response to the need for designing signal plans for congested intersections caused by heavy scooter–vehicle mixed flows, this paper presents our formulated model for optimizing both the cycle length and signal timings for isolated intersections. The proposed model accounts for the interactions between scooter and vehicle flows and reflects the maneuverability of scooters in the queue formation and discharging process. The robustness of the proposed formulations has been evaluated with field data and laboratory experiments. The signal optimization model, grounded on such formulations for scooter–vehicle mixed flows, has also been implemented at an intersection and assessed with a rigorous before-and-after field analysis. Our research concludes that incorporating the unique properties of scooter flows is essential for design and development of effective signal control strategies to contend with recurrent congestion caused by heavy mixed scooter–vehicle flows.

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