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Zhao J.,Key Laboratory of Road and Traffic Engineering | Ma W.,Key Laboratory of Road and Traffic Engineering | Zhang H.M.,University of California at Davis | Yang X.,Key Laboratory of Road and Traffic Engineering
Transportation Research Record | Year: 2013

Many congested intersections have a heavy traffic volume on movements for which capacity is insufficient because of geometric limitations. An unconventional approach that increases the capacity of heavily congested intersections is presented: this approach opens up exit lanes for left-turn traffic dynamically with the help of an additional traffic light installed at the median opening (the presignal); this situation is referred to as exit lanes for left-turn (EFL) control. An optimization problem for EFL control was formulated as a mixed-integer nonlinear program, in which the geometric layout, main signal timing, and presignal timing were integrated. The mixed-integer nonlinear program was solved by transformation into a series of mixed-integer linear programs. The latter problem can be solved with the standard branch-and-bound technique. The results of extensive numerical analysis and VISSIM simulation showed that the EFL approach could increase intersection capacity and reduce traffic delay substantially, especially under high left-turn demand. Moreover, the EFL control can be applied to one or multiple legs simultaneously; thus the control is particularly useful for intersections with an unbalanced left demand and a degree of saturation in travel directions.

Zhao J.,Key Laboratory of Road and Traffic Engineering | Ma W.,Key Laboratory of Road and Traffic Engineering | Zhang H.M.,University of California at Davis | Yang X.,Key Laboratory of Road and Traffic Engineering
Transportation Research Record | Year: 2013

At isolated signalized intersections, congestion problems are caused in part by an imbalance in supply and demand, which may be caused by the variability of turning-movement volumes. Although signal timing can be adjusted to handle varying demand, the effect of this adjustment alone is limited, especially when traffic demand fluctuates significantly. A two-step optimization model for dynamic lane assignment is presented: the model overcomes the shortcoming of static lane markings and fully utilizes the existing traffic facilities. The first step is to obtain the best lane assignment scheme by using an arm-group-based integer nonlinear program model. The second step is to identify a suitable implementation scheme by determining a binary-type threshold. The results of VISSIM simulation show that the proposed model can correctly choose the occasion to change the lane assignment by ignoring the small volume fluctuation and can improve traffic operations effectively when the traffic demand varies significantly.

Ma W.,Key Laboratory of Road and Traffic Engineering | Xie H.,Key Laboratory of Road and Traffic Engineering | Liu Y.,University of Wisconsin - Milwaukee | Head L.,University of Arizona | Luo Z.,University of Wisconsin - Milwaukee
Transportation Research Record | Year: 2013

Many congested intersections have heavy traffic volume on movements for which there is insufficient capacity because of geometric limitations. Installing presignals at midblock locations and reorganizing traffic upstream of the approach of an intersection combine to be a promising and cost-effective method for addressing these capacity limitations. A coordinated optimization model was developed for an isolated intersection approach with presignals to increase the protected left-turn phase capacity. The presignal model was based on two principles: (a) explicitly capture the interaction between the presignal and the main signal by modeling the queuing process and capacity constraints of temporal and spatial limitations of the intersection and (b) optimize the signal timings of both the presignal and the main signal as well as the offset between them to produce the best operational strategy for the approach. The minimum green time required and the delay-minimization problems are considered. Extensive experimental analysis has shown that the presignal model out-performs the conventional control method (without presignal). Sensitivity analysis of the signal timing method that will assist traffic engineers with selecting the appropriate length of the sorting area, phase sequence, and early starting time of presignals was conducted. The results from the study offer a basis for traffic practitioners, researchers, and authorities on which to design and utilize presignals in locations where there is a need to increase intersection capacity for congested movements.

Wang X.,Tongji University | Wang X.,Key Laboratory of Road and Traffic Engineering | Fan T.,Tongji University | Chen M.,Tongji University | And 3 more authors.
Accident Analysis and Prevention | Year: 2015

Traffic safety on urban arterials is influenced by several key variables including geometric design features, land use, traffic volume, and travel speeds. This paper is an exploratory study of the relationship of these variables to safety. It uses a comparatively new method of measuring speeds by extracting GPS data from taxis operating on Shanghai's urban network. This GPS derived speed data, hereafter called Floating Car Data (FCD) was used to calculate average speeds during peak and off-peak hours, and was acquired from samples of 15,000+ taxis traveling on 176 segments over 18 major arterials in central Shanghai. Geometric design features of these arterials and surrounding land use characteristics were obtained by field investigation, and crash data was obtained from police reports. Bayesian inference using four different models, Poisson-lognormal (PLN), PLN with Maximum Likelihood priors (PLN-ML), hierarchical PLN (HPLN), and HPLN with Maximum Likelihood priors (HPLN-ML), was used to estimate crash frequencies. Results showed the HPLN-ML models had the best goodness-of-fit and efficiency, and models with ML priors yielded estimates with the lowest standard errors. Crash frequencies increased with increases in traffic volume. Higher average speeds were associated with higher crash frequencies during peak periods, but not during off-peak periods. Several geometric design features including average segment length of arterial, number of lanes, presence of non-motorized lanes, number of access points, and commercial land use, were positively related to crash frequencies. © 2015 Elsevier Ltd. All rights reserved.

Shao H.,Key Laboratory of Road and Traffic Engineering | Fan Y.,Chang'an University | Li J.,China Communications Construction Company Ltd.
Access Management Theories and Practices - Proceedings of the 2nd International Conference on Access Management, AM 2014 | Year: 2014

In order to improve the traffic safety and efficiency of new access roads in old city reconstruction, it is necessary to do research on site selection, layout design, and management of access road. By integrated analysis of multi-level road traffic operation, this paper determines the service level of access road using equivalent traffic capacity replacing intersection capacity as the representative value of road traffic capacity, and in according to the relationship of equivalent capacity and intersection spacing, back calculation of the optional areas of access roads is, which replaces the design method aimed at meeting the demands of the functional areas of intersection. Finally, according to this design idea, we use the road traffic simulation system to simulate the design of access road in the reconstruction of Qi county HeBi city Henan province. The results show that this method satisfies the road network service level and maximizes the system traffic capacity on the basis of traffic safety. © ASCE.

Yu H.-C.,Key Laboratory of Road and Traffic Engineering | Sun L.-J.,Key Laboratory of Road and Traffic Engineering
2011 International Conference on Electric Technology and Civil Engineering, ICETCE 2011 - Proceedings | Year: 2011

In order to investigate the strength of low dosage cement stabilized aggregates, and to provide reference for mixture design of anti-crack cement stabilized macadam base, intensity of pressure, splitting strength, compressive modulus of resilience and CBR were tested. Test results showed that low dosage cement stabilized aggregates much differ from conventional cement stabilized aggregates, when cement content was less than 5%, Cement dosage changes had little effect on maximum dry density, optimum water content rose as the increase of cement dosage. low dosage cement stabilized macadam with mechanical properties closed to inorganic binders, but it had higher structure bearing capacity than inorganic binders. Through reasonable structure combination design, use of low dosage cement stabilized aggregrates can reduce compressive modulus of resilience in road base, and reduce pavement reflection cracks. © 2011 IEEE.

Chen W.,Key Laboratory of Road and Traffic Engineering | Li H.,Key Laboratory of Road and Traffic Engineering | Xu Y.,Key Laboratory of Road and Traffic Engineering
Applied Mechanics and Materials | Year: 2012

With the increase in rail inspection technology, the whole rail profile can be measured by rail inspection cars or some typical static measurement instruments. Based on a large number of practical rail profile measurements, a whole rail profile auto-matching method is put forward to enhance the efficiency and accuracy of data analysis. An analytical tool applying this method is developed at the same time and the principle and calculation method of the tool will be introduced. Apart from this, data collected from in-situ measurements taken on line 2 of the Shanghai Metro will be performed and analyzed to verify this method. The main contributions of this paper are the generalization of an efficient analytical tool for the calculation of wear parameters at both specific and non-specific points and the practical application for comparison of data collected by both dynamic and static inspection with the standard, which proves that the method is correct and effective. © (2012) Trans Tech Publications, Switzerland.

Ma W.,Key Laboratory of Road and Traffic Engineering | Lu Y.,Key Laboratory of Road and Traffic Engineering
Proceedings 2011 International Conference on Transportation, Mechanical, and Electrical Engineering, TMEE 2011 | Year: 2011

With the goal of improving pedestrians' convenience and safety, signalized two-stage midblock crossings are increasingly installed in highly populated areas in developing countries such as China. Accurately design of crosswalk, especially the area of central refuge island is one of the most critical issues should be properly decided. In this paper, three signalization types for two-stage midblock pedestrian crossings are proposed. Pedestrian dynamics on central refuge island is formulated. Number of pedestrian waiting on central refuge island at any time of a cycle can be calculated by the model. Then, the maximum number of pedestrian waiting on central refuge island and the minimum needed area of central refuge island under a signal plan can be calculated. A case study is used to evaluate the proposed model. Sensitivity analysis has also been done to better assist traffic engineer in designing of two-stage midblock pedestrian crossing. © 2011 IEEE.

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