Authors: Xianfeng Yang, Yao Cheng and Gang-Len Chang
Journal: Journal of the Transportation Research Board (TRR),2015
Unconventional Design: Asymmetric Two-leg CFI
Purpose: Developed a signal optimization model for asymmetric Two-leg CFI by concurrently optimizing both the phase sequence and offsets.
Despite the increasing implementation of Continuous Flow Intersection (CFI) in practice, the development of reliable guidelines for its operational analysis and signal design remains at the infancy stage, especially for the popular two-leg asymmetric CFI design due to its relative low cost and desirable efficiency. To best utilize the capacity of such a CFI design, this paper presents a signal optimization model that can serve as an effective tool for engineers to design the cycle length, phase duration and sequences, and offsets for both its primary and sub intersections. By accounting for the commonly-encountered constraints of short bay length for turning movements and the interrelations between critical flow movements, the proposed model can prevent the queue spillover on left turn bays, and offer concurrent progression for both the through and left-turn flows. To ensure the applicability and effectiveness of the proposed model, this study has further used the data from a proposed asymmetric CFI in Maryland for performance evaluation. The results of extensive simulation with field data confirm that the proposed signal optimization with its capability to account for all physical constraints and flow conflicts can indeed perform as expected, that is, offering concurrent progression to both through and left-turning flows and preventing any queue from spilling over its designated bay.
Authors: Xianfeng Yang, Gang-Len Chang, Yang Lu, and Saed Rahwanji
Journal: Journal of Transportation Engineering 2013
Unconventional Design: CFI
Purpose: Developed a set of planning models for CFI geometry design based on the estimated maximal queue length for each link.
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.
Authors: Xianfeng Yang, Yao Cheng and Gang-len Chang
Journal: Transportation Research Part C, 2015
To contend with congestion and spillback on commuting arterials, serving as connectors between freeway and surface-street flows, this paper presents three multi-path progression models to offer progression bands for multiple critical path-flows contributing to the high volume in each arterial link. The first proposed model is a direct extension of MAXBAND under a predetermined phasing plan, but using the path-flow data to yield the progression bands. The second model further takes the phase sequence at each intersection as a decision variable, and concurrently optimizes the signal plans with offsets for the entire arterial. Due to the competing nature of multi-path progression flows over the same green duration, the third model is proposed with a function to automatically select the optimal number of paths in their bandwidths maximization process. The results of extensive simulation studies have shown that the proposed models outperform conventional design methods, such as MAXBAND or TRANSYT, especially for those arterials with multiple heavy path-flows. The research results from this study have also reflected the need to collect more traffic pattern data such as major path-flow volumes, in addition to the typical intersection volume counts.
Authors: Kyeong-Pyo Kang , Gang-Len Chang and Nan Zou
Journal: Transportation Research Record, No. 1877, 2004
Despite the well recognized fact that a proper control of traffic speed can contribute to both reduction in accidents and efficiency of highway operations, most existing speed control strategies implemented in Europe and U.S. tend to aim only at improving traffic safety. This research intends to present an on-line algorithm for variable speed limit (VSL) control at highway work zones that can take full advantage of its dynamic functions and concurrently achieve the objectives of throughput maximization as well as accident minimization.
Authors: Kyeong-Pyo Kang and Gang-Len Chang
Journal: IEEE Transactions on Intelligent Transportation Systems, Vol. 7, No. 1, March 2006
This paper proposes a new speed control strategy, named time-of-day speed limit (TOD SL) control, for highway work-zone operations. The main purposes of the TOD SL control are to overcome the difficulty in setting the optimal real-time speed limit due to the lack of detectors, and to maximize the use of available data such as the historical volume data on the target work zone. Its core logic is to divide the entire day of operations into a number of control periods and to accommodate the time-varying traffic conditions within each control period. The measure of effectiveness (MOE) selected in the TOD SL model takes into account both the operational efficiency and traffic safety. To encompass all possible traffic conditions during each control period, the control model employs traffic flow relations calibrated from historical data to estimate the speed and density data with available volume under possible traffic scenarios. The performance of the proposed TOD SL control has been evaluated with the simulation experiments, and compared with the other speed control strategies based on the selected measures of effectiveness.
Authors: PEI-WEI LIN, KYEONG-PYO KANG, and GANG-LEN CHANG
Journal: Journal of Intelligent Transportation Systems, 8:1–14, 2004
Despite the well recognized fact that a proper control of traffic speed can contribute to both reduction in accidents and efficiency of highway operations, most existing strategies for work-zone speed control in either Europe or the U.S. tend to primarily focus on improving traffic safety. This article presents two online algorithms for variable speed limit (VSL) controls at highway work zones that can take full advantage of all dynamic functions and concurrently achieve the objectives of queue reduction or throughput maximization. To evaluate the effectiveness of these proposed algorithms, this study has conducted extensive experiments based on simulated highway systems that have been calibrated with field data. The results of these simulation analyses have confirmed that VSL algorithms can yield a substantial increase in both work-zone throughputs and reduction in total vehicle delays. Moreover, traffic flows implementing VSL controls tend to exhibit lower speed variances than other non-controlled traffic scenarios. The speed variance reduction may indirectly contribute to improving the overall traffic safety in work zones.
Authors: Pei-Wei Lin and Gang-Len Chang
Journal: Transportation Research Record: Journal of the Transportation Research Board, No. 1923, Transportation Research Board of the National Academies, Washington, D.C., 2005, pp. 110?18.
This study presents a robust model for estimating the dynamic freeway origin-destination matrix with a measurable time series of ramp and mainline flows. The proposed model captures the speed variance among vehicles having the same departure time, origin, and destination with an embedded travel time distribution function that results in a substantial reduction in model parameters. With the developed solution algorithm, the proposed model offers the potential use in a network of realistic size such as the I-95 freeway corridor between the Maryland I-695 and I-495 beltways. Extensive numerical analyses with respect to the sensitivity of both input measurement errors and the selection of initial parameters have revealed that the proposed model is sufficiently robust for real-world applications.
Authors: Nan Zou, Shu-Ta Yeh, Gang-Len Chang, Alvin Marquess, and Michael Zezeski
Journal: Transportation Research Record, No. 1922, 2005, pp. 138–148.
This paper presents a simulation-based system for Ocean City, Maryland, evacuation during hurricanes. The proposed model features integration of optimization and simulation that allows potential users to revise the optimized plan for both planning and real-time operations. Since it is difficult to capture all network operational constraints and driver responses fully with mathematical formulations, six evacuation plans for Ocean City were investigated. Each was optimized initially with the optimization module and then revised on the basis of the results of simulation evaluation. To address potential incidents during the evacuation, the study presents a real-time operation plan with a developed system that allows the responsible operators to concurrently evaluate all candidate responsive strategies and to track the performance over time of the implemented strategy.
Authors: Ying Liu, Xiaorong Lai, and Gang-Len Chang
Journal: Transportation Research Record, No. 1964, 2006, pp 127-135
Staged evacuation is widely used under emergency situations where different parts of the target network may suffer different levels of severity over different time windows. By evacuating those populations in the network via an optimized sequence, the staged evacuation strategy can best utilize the available roadway capacity, optimally distribute the total demand over the evacuation time horizon, and thus minimize the network congestion level. This study has proposed a cell-based network model to capture critical characteristics associated with the staged evacuation operations. The proposed model features its capability in reflecting incident impacts and arrival patterns of evacuees in computing the optimal starting time and routes for each evacuation zone. The preliminary numerical results have demonstrated the potential for applying the proposed staged evacuation model in real-world emergency management and planning.
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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