Authors: Yue Liu, Gang-Len Chang, Ruihua Tao, Thomas Hicks, and Eric Tabacek
Journal: Transportation Research Record, In press (presented in Transportation Research Board 86th Annual Meeting, January, 2007)
In this paper the author presents the results of our empirical study on the distribution of dilemma zones for different groups of drivers at signalized intersections. Using a specially designed video-based system, this study has conducted extensive field observations of 1123 drivers’ responses to a yellow phase at six intersections of high accident frequency, including all critical data such as the speed evolution during the yellow phase, the acceleration/deceleration rates, and the approximate reaction time to an encountered yellow phase. Our empirical results have revealed that the dilemma zone is dynamic in nature with its location varying with the driving populations, and the commonly used practice of extending the yellow phase duration recommended may not eliminate all the dilemma zones.Two types of strategies which can effectively eliminate the dynamic dilemma zones are also designed to improve intersection safety.
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Authors: Ning Yang, Gang-Len Chang, and Kyeong-Pyo Kang
Journal: Journal of Transportation Engineering, 2007
This paper presents a new lane-based signal merge (LBSM) control system for freeway work zone operations. The proposed system applies the signal control concept to regulate the vehicles passing the work zone area at a lane-by-lane basis and offers an effective way to maximize the operational efficiency as well as safety. Introduction of the preliminary configuration and principal components associated with the proposed LBSM control contribute the core of this study.
To evaluate the effectiveness of the proposed system, this study has also conducted extensive simulation experiments, based on a freeway simulator calibrated with real-world work zone data. The experimental results show that under heavily congested traffic conditions the LBSM can outperform all existing control strategies with respect to the work zone throughput, the average vehicle delay, the average stop delay, and the average number of stops. This study has also investigated critical traffic flow related factors that may impact on the performance of such a system.
Authors: Yue Liu, Gang-Len Chang, Ying Liu and Xiaorong Lai
Conference: 2008 TRB Annual Meeting
Status: Accepted for Presentation
Evacuating large municipal areas during emergencies and disasters in an efficient manner is one of the critical tasks of emergency management agencies. This paper presents a corridor-based emergency evacuation system and its example applications for the Washington D.C. metropolitan area. The proposed system features its flexibility in accounting for various critical issues associated with both planning and real-time operations, including multiple data source integration, network decomposition, network-level traffic routing, contra-flow design, staged evacuation, optimal signal timing, and incorporating pedestrian and bus operations. Under a hypothetical emergency scenario for Union Station, the proposed system has demonstrated its effectiveness for producing evacuation routing strategies, identifying potential bottlenecks, and evaluating the performance of evacuation operations.
Authors: Yue Liu, Gang-Len Chang, and Jie Yu
Journal: ASCE Journal of Transportation Engineering
This paper presents the analysis results of driver responses during a yellow phase, based on field observations of 1123 drivers collected with a specially-designed system from six signalized intersections of high crash frequency in Maryland. By classifying drivers into aggressive, conservative, and normal groups based on their responses (i.e., stop or pass) and the distances to the stop line when the signal turns yellow, the statistical tests with the ordered-probit model clearly indicate some critical factors and their impacts on a driver’s decision at intersections. Such factors include average traffic flow speeds, traffic volume rate, the green split, the number of through and crossing lanes in the target approach, signal coordination, the difference between a vehicle’s approaching speed and the average traffic flow speeds, a driver’s gender, age, talking over cell phone or not, a vehicle’s type and model, and etc. The research findings for this study offer the basis for responsible agencies to identify underlying factors contributing to aggressive maneuvers at signalized intersections which often cause traffic crashes, and to develop improvement strategies, such as customized driver education and intelligent safety protection systems.
Authors: Jie Yu, Yue, Liu, and Gang-Len Chang
Journal: Journal of Transportation Engineering ASCE
This paper presents a comprehensive model for ranking candidate location plans of multiple urban transit hubs, which can effectively capture various aspects of concerns in the transit hub location planning process, including the overall efficiency of the transit network, the transfer intensity, the proximity to major passenger generators/attractors, the effectiveness of hub service coverage, the compatibility with land use restrictions, and the adaptability to future developable transit concepts. Grounded on an Analytical Hierarchy Process (AHP)-based framework integrated with the fuzzy logic, the proposed model offers the strengths to effectively determine the weights for multiple evaluation criteria, and to synthesize the final score of each candidate plan for comparison. Results from a case study in Suzhou Industrial Park, China reveal that the proposed model offers some promising properties for transportation planners to use in planning of transit hub locations. Comparative studies with respect to different evaluation criteria has further demonstrated the effectiveness of the proposed model in capturing the impacts of different criteria on the decision making process.
Authors: Yue, Liu and Gang-Len Chang
Journal: Transportation Research Part C， 2010
This paper presents an arterial signal optimization model that features its effectiveness on: (1) explicitly modeling physical queue evolution on arterial links by lane-group to account for shared-lane traffic interactions; and (2) capturing the dynamic interactions of spillback queues among lane groups and between neighboring intersections due to high demand, geometric constraints, or signal settings. Depending on the detected traffic patterns, one can select the control objective to be either minimizing the total travel time or maximizing the total throughput over the target area. The solution procedures developed with the Genetic Algorithm (GA) have been tested with an example arterial of four intersections under different demand scenarios. Extensive experimental analyses in comparison with results from TRANSYT-7F (version 8) reveal that the proposed model and solution method are quite promising for use in design of arterial signals, especially under congested, high demand traffic conditions.
Authors:Yongjie Lin, Xianfeng Yang, Gang-Len Chang, and Nan Zou
Journal: Transportation Research Record: Journal of the Transportation Research Board, No. 2356, 2013
This paper presents a transit signal priority (TSP) model designed to consider the benefits both to bus riders and to intersection passenger car users. The proposed strategy, which is mainly for headway-based bus operations, offers the responsible agency a reliable way to determine the optimal green extension or red truncation duration in response to multiple bus priority requests from different routes. The control objective is to minimize bus passenger waiting time at the downstream bus stop while ensuring that the delays for all passengers are not increased. In tests that used field data from Jinan, China, the proposed strategy showed promise in reducing bus passenger waiting time and total intersection delay. Further exploration with simulation experiments for sensitivity analysis found that TSP is most effective if the ratio between bus and passenger volumes exceeds a threshold of 2%.
Authors: Jie Yu, Yue Lie, and Xiaoguang Yang
Conference: 2008 TRB Annual Meeting
Type: Accepted for Presentation
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.
Authors: Jie Yu, Yue, Liu, and Gang-Len Chang
Journal: ASCE Journal of Infrastructure Systems
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.
Authors: Yue Liu, Gang-Len Chang, and Jie Yu
Journal: IEEE transaction on Vehicular Technology
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.