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Wang X.,Tongji University | Wang X.,The Key Laboratory of Road and Traffic Engineering | Fan T.,Tongji University | Li W.,Tongji University | And 4 more authors.
Transportation Research Part C: Emerging Technologies | Year: 2016

Increased speed variation on urban arterials is associated with reductions in both operational performance and safety. Traffic flow, mean speed, traffic control parameters and geometric design features are known to affect speed variation. An exploratory study of the relationships among these variables could provide a foundation for improving the operational and safety performance of urban arterials, however, such a study has been hampered by problems in measuring speeds. The measurement of speed has traditionally been accomplished using spot speed collection methods such as radar, laser and loop detectors. These methods can cover only limited locations, and consequently are not able to capture speed distributions along an entire network, or even throughout any single road segment. In Shanghai, it is possible to acquire the speed distribution of any roadway segment, over any period of interest, by capturing data from Shanghai's 50,000+ taxis equipped with Global Positional Systems (GPS). These data, hereafter called Floating Car Data, were used to calculate mean speed and speed variation on 234 road segments from eight urban arterials in downtown Shanghai. Hierarchical models with random variables were developed to account for spatial correlations among segments within each arterial and heterogeneities among arterials. Considering that traffic demand changes throughout the day, AM peak, Noon off-peak, and PM peak hours were studied separately. Results showed that increases in number of lanes and number of access points, the presence of bus stops and increases in mean speed were all associated with increased speed variation, and that increases in traffic volume and traffic signal green times were associated with reduced speed variation. These findings can be used by engineers to minimize speed differences during the road network planning stage and continuing through the traffic management phase. © 2016 Elsevier Ltd. Source


Sun Z.,Shenyang Jianzhu University | Xu Z.,The Key Laboratory of Road and Traffic Engineering
WIT Transactions on the Built Environment | Year: 2013

The practice work state of a cement stabilized macadam base is to offer reference for the rationality strength limit value of a cement stabilized macadam base under over loading effect. The theory of an elastic layered system is applied to the change of stress in different depths of asphalt pavement under heavy load; uniform distributions of tire contact pressure in specifications are considered. The results of mechanical analysis show that the tensile stress comes forth primarily at the bottom of a cement stabilized macadam base course, not at that of asphalt layers, and the maximum tensile stress decreases with the thickening of asphalt layers. The maximum tensile stress increases evidently at the bottom of a cement stabilized macadam base course with the increase of axle load in the same pavement structure. The maximum tensile stress σymax value of the bottom of a cement stabilized macadam base course in pavement structure 2 is higher than in pavement structure 1. The asphalt surface layer thickness increase did not improve the road surface tensile stress in the condition of a cement stabilized macadam base course, and can't rely on increasing the thickness of asphalt layer to reduce the creation of the road surface cracks from top to bottom. © 2013 WIT Press. Source


Xiao L.,Tongji University | Xiao L.,The Key Laboratory of Road and Traffic Engineering | Wei C.,Beijing Jiaotong University | Chen X.,Tongji University | And 3 more authors.
Wuhan Ligong Daxue Xuebao (Jiaotong Kexue Yu Gongcheng Ban)/Journal of Wuhan University of Technology (Transportation Science and Engineering) | Year: 2015

Most of modal spit models were formulated based on the random utility theory that assumes that choice behavior of individuals completely follow compensatory rule; however some previous studies pointed that this assumption is strong, because individuals usually make decision dependent on some psychical thresholds. This paper proposes a semi-compensatory modal-split model based on mixed-logit model combined with psychical thresholds. The proposed model has two stages, and the model generates the choice set using psychical thresholds and then calculates the choice probability by a Mixed-Logit model in order to overcome IIA property and limitation of taste variation. Based on the sample data obtained by SP survey, we estimated the proposed model using a Markov chain Monte Carlo algorithm combined with data augmentation technique. We tested this model using Hit-Ratio method and compared with MNL model. Results show that the performance of the proposed model is better than that of the MNL model. ©, 2015, Wuhan University of Technology. All right reserved. Source


Yu R.,The Key Laboratory of Road and Traffic Engineering | Yu R.,Tongji University | Wang X.,The Key Laboratory of Road and Traffic Engineering | Wang X.,Tongji University | And 3 more authors.
Accident Analysis and Prevention | Year: 2016

Urban expressway systems have been developed rapidly in recent years in China; it has become one key part of the city roadway networks as carrying large traffic volume and providing high traveling speed. Along with the increase of traffic volume, traffic safety has become a major issue for Chinese urban expressways due to the frequent crash occurrence and the non-recurrent congestions caused by them. For the purpose of unveiling crash occurrence mechanisms and further developing Active Traffic Management (ATM) control strategies to improve traffic safety, this study developed disaggregate crash risk analysis models with loop detector traffic data and historical crash data. Bayesian random effects logistic regression models were utilized as it can account for the unobserved heterogeneity among crashes. However, previous crash risk analysis studies formulated random effects distributions in a parametric approach, which assigned them to follow normal distributions. Due to the limited information known about random effects distributions, subjective parametric setting may be incorrect. In order to construct more flexible and robust random effects to capture the unobserved heterogeneity, Bayesian semi-parametric inference technique was introduced to crash risk analysis in this study. Models with both inference techniques were developed for total crashes; semi-parametric models were proved to provide substantial better model goodness-of-fit, while the two models shared consistent coefficient estimations. Later on, Bayesian semi-parametric random effects logistic regression models were developed for weekday peak hour crashes, weekday non-peak hour crashes, and weekend non-peak hour crashes to investigate different crash occurrence scenarios. Significant factors that affect crash risk have been revealed and crash mechanisms have been concluded. © 2015 Elsevier Ltd. Source


Sun Y.,The Key Laboratory of Road and Traffic Engineering | Gao Y.,The Key Laboratory of Road and Traffic Engineering | Zheng W.,The Key Laboratory of Road and Traffic Engineering
Wuhan Ligong Daxue Xuebao (Jiaotong Kexue Yu Gongcheng Ban)/Journal of Wuhan University of Technology (Transportation Science and Engineering) | Year: 2014

This paper considers the passengers and freights. As for the freights, the traffic assignment model was built using the wardrop principle, then based on the characteristics of the logistics hub for passenger and freight, the transport path of mixed passengers and freights was discussed. In the end, by taking the Fujian ZhangLong park as example, the feasibility was validated. ©, 2014, Wuhan University of Technology. All right reserved. Source

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