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Yunhao Wang,Yiming Bie,Le Zhang 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.1
Bus holding strategy is an effective way for alleviating inevitable disruptions along a bus route, including decisions on the control point locations and slack duration. However, at present, the locations of the control points and corresponding slack times are largely determined by engineering experience and therefore lack theoretical optimization. The aim of this study is to develop a model which can jointly optimize the locations of the control points and corresponding slack times under a given number of control points. As locations of the upstream control points will influence the downstream operation states, this optimization problem is modeled as a multi-stage decision process. To evaluate the stability and efficiency of a bus system, we calculate the punctuality rate and travel time at each stage by taking into account the uncertainty along the route and propose a reasonable stage-utilization cost combing these two factors. A numerical case study based on a real bus route in Harbin of China is carried out to demonstrate our approach. The impacts of the weighting factor and slack times on the optimal control point plan are also discussed.
Identification of Spillovers in Urban Street Networks Based on Upstream Fixed Traffic Data
Dongfang Ma,DianHai Wang,YiMing Bie,Sheng Jin,Zhenyu Mei 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.5
This paper presents a method to identify spillovers based on upstream fixed detector data, using occupancy per cycle as thedetermination index. The key idea of this new method is that when the queues extend to the detector position, there will be unusablegreen time to a certain degree, and the occupancy will be greater than a particular threshold. Firstly, this paper introduces traffic wavemodels modified by a kinematic equation, and provides a calculation method for the occupancy per cycle under different trafficconditions, based on the relationship between the three basic traffic flow parameters, speed, traffic flow, and density. Secondly, thethreshold of occupancy, which characterizes the appearance of spillovers, is determined by the premise that the stopping and startingwaves have the same speed, and then the accuracy of the new method are verified by VISSIM simulation, using the ratio ofmisjudgment as the evaluation index. Finally, the precision stability of the method is analyzed, and the results show that the precisionof this method is affected by the the detector location and bus ratio insignificantly.
A Link Traffic Model by Incorporating both Merits of Vertical and Horizontal Queue Concept
HongSheng Qi,DianHai Wang,Peng Chen,YiMing Bie 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.5
With the development of traffic flow theory and practice, traffic models at different levels of analysis are expected to provide comprehensive outputs with satisfactory efficiency. Accordingly, this research proposes an Equivalent Link traffic State Model (ELSM) to meet this requirement. ELSM combines both advantages of Vertical Queue Model (VQ) and Horizontal Queue Model (HQ). On one hand, the structure of ELSM is similar to VQ; on the other hand, queue dynamics at any moment along the link can be available through deriving three “characteristic points” of each cycle based on shock wave theory. Thus spatial variation of vehicle queue can be obtained. As a result, common traffic performance indexes such as delay, stops and queue length can be directly obtained in addition to the microscopic level variables such as vehicle trajectories and travel time. It is shown that with the increasing of numerical resolution, the results of CTM (Cell Transmission Model) gradually converge to ELSM.