Authors: Jie Yu, Yue Lie, and Xiaoguang Yang
Conference: 2008 TRB Annual Meeting
Type: Accepted for Presentation
Abstract:
Choosing proper locations of urban transit hubs has always been one of the critical concerns facing urban transportation planning agencies in China. This study proposes a mixed integer optimal location model for urban transit hubs, with the objective to minimize the demand-weighted total travel time, when explicitly taking into account Traffic Analysis Zones (TAZs) as demand origins or destinations in a target urban area. An Integer Non-linear Programming (INLP) reformulation was developed to significantly reduce the number of variables. Bilinear constraints in the proposed INLP formulation were then re-modeled into linear functions to ensure global optimal solutions obtained. The model was successfully applied to optimize the hub locations in Suzhou Industrial Park, China, with the result of significantly improved system performance. The impacts of several critical factors, such as the number of hubs and the travel time discount coefficient on the system performance are also investigated.

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Authors: Jie Yu, Yue, Liu, and Gang-Len Chang
Journal: ASCE Journal of Infrastructure Systems
Abstract:
This paper presents a robust multi-criteria model for prioritizing highway safety improvement projects, in which a set of criteria related to the project’s technical, economic, social and environmental impacts are properly weighted in consideration. The proposed model features an analytical hierarchy process (AHP) framework to tackle the multi-criteria decision making problem. Different from the conventional AHP, this paper adds a fuzzy scale level between the criteria level and the alternative level which offers the advantage of preventing the vagueness and uncertainty on judgments of the decision-maker(s). Such a unique modeling feature is further embedded with a nonlinear optimization formulation to maximize the consistency in pair-wise comparison and weight estimation for each criterion. Case study results reveal that the proposed model is efficient not only for selecting the most suitable project for a specific site, but also for determining the priorities for implementation those suitable projects among multiple sites given the budget constraint. Comparative study between the proposed model and the existing ranking methods has also indicated its capability to capture the comprehensive impacts of all contributory factors which have been neglected by most existing approaches during the safety project selection process. The clarity of model inputs, ease of synthesizing the final score of each candidate project, and the interpretation of results with respect to different selection criteria offer its best potential to be used as an effective tool for highway infrastructure manager and transportation authorities to assess and refine the highway safety improvement investments.

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Authors: Yue Liu, Gang-Len Chang, and Jie Yu
Journal: IEEE transaction on Vehicular Technology
Abstract:
This study presents an integrated model and its solution algorithm for freeway corridor control during incident management. With a parallel arterial as the detour route, the proposed model aims to produce the optimal diversion rates from the freeway mainline to relieve the congestion at the incident segment, and concurrently adjust signal timings at the arterial intersections to best accommodate the detour traffic. Different from previous studies, the presented model and algorithm have the following two critical features: (1) modeling explicitly the evolution of detour traffic along the ramps and surface streets with a set of dynamic network flow formulations so as to capture the local bottlenecks caused by demand surge due to diversion operations, and to properly set the responsive signal timing plans; and (2) developing a multi-objective optimization framework to maximize the utilization of the available corridor capacity via detour operations, but not to incur excessive congestion on the arterials and ramps. This study employs a Genetic Algorithm (GA) based heuristic to efficiently yield the reliable solution depending on decision maker’s preference. Extensive numerical tests on a segment along the I-95 corridor with its neighboring arterials have demonstrated the potential of the developed model for integrated freeway corridor control.

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Authors: Jie Yu, Sung Yoon Park, and Gang-Len Chang

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.

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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.

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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.

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