Yuelong Su

Headway distribution modeling with regard to traffic status

Knowledge of vehicle headway distribution is very important for intelligent transportation and intelligent vehicle simulations. Various headway distribution models have been proposed, but most of them only fit for a certain traffic situation. To solve this problem, we study the dependence of headway distributions on traffic status in this paper. Results show that the log-normal distribution model is adequate in fitting headway data when the traffic is in free flow status; while the log-logistic distribution model is more suitable in fitting headway data when the traffic is in congestion status. This conclusion is useful in the traffic signal optimization algorithm, since it indicates that we should apply different delay estimation models during different traffic status so as to design optimal timing plan.

A Comparison of Phase Transitions Produced by PARAMICS, TransModeler, and VISSIM

Increasing efforts are devoted to test and improve the performance of commercial traffic simulation software now. However, most previous approaches emphasized microscopic car-following and lane-changing features but neglect the macroscopic traffic dynamics. In this paper, we compare the traffic flow phase transition behaviors of three popular simulation software: PARAMICS 6.5, TransModeler 2.0 and VISSIM 5.1 on a single yet typical scenario. Our testing re-sults show that their slight differences in microscopic models can be appropriately magnified and intuitively displayed in the phase diagram.

Behavior modeling and simulation for conflicts in vehicles-bicycles mixed flow

Great changes are taking place in Chinese economic and societal life during the last decade, which brings significantly increasing pressure to the transportation systems of most Chinese cities. For example, in Beijing, vehicles are now fiercely competing for the right of roads with the existing large amount of bicycles. Because many streets in Beijing are not fully channelized to separate vehicles and bicycles, such competition leads to notable growth of traffic accidents and decline of traffic efficiency. This important matter has attracted growing research interests recently. In this paper, a behavior modelling and simulation for conflicts in vehicles-bycicles mixed flow is proposed. The first part is driving-riding behaviors in vehicles-bicycles laminar flow, second part is a cellular automata model for vehicle-bycicle laminar flow, the third part is the simulation results and discussions, and the last part talks about the potential application.

A review of game theory applications in transportation analysis

Game theory has been widely used in various fields since its birth. Particularly, it plays an important role in transportation analysis and provides powerful tools to solve many difficult problems. This paper provides an overview of the numerous applications of game theory in transportation analysis and classifies these applications into two types. We aim to provide a clear framework of these applications and also a feasible solving process of problems. At last, we point out some drawbacks of game theory based applications and discuss how to adjust game theory method to deal with complex situations in future practice.

Delay estimates of mixed traffic flow at signalized intersections in China

Two characteristics of Chinese mixed traffic invalidate the conventional queuing delay estimates for western countries. First, the driving characteristics of Chinese drivers lead to different delays even though the other conditions are the same. Second, urban traffic flow in China is often hindered by pedestrians at intersections, such that imported intelligent traffic control systems do not work appropriately. Typical delay estimates for Chinese conditions were obtained from data for over 500 vehicle queues in Beijing collected using charge coupled device (CCD) cameras. The results show that the delays mainly depend on the proportion and positions of heavy vehicles in the queue, as well as the start-up situations (with or without interference). A simplified delay estimation model considers vehicle types and positions that compares well with the observed traffic delays.

Control Strategies for Transit Priority Based on Queue Modeling and Surrogate Testing

To explore the potential benefits of bus priority based on signal phasing strategy, this article proposes a simplified statistical sampling method to simulate vehicle delays at intersections instead of using conventional microscopic traffic simulations. This method greatly reduces the calculation cost and time while maintaining the estimation accuracy of the delay. This research provides a surrogate testing system and tests intuitive traffic signal phasing strategies that shorten average waiting time of queuing vehicles by letting certain buses pass the intersection with a higher priority. Interestingly, the results reveal that the length of the green time should be adaptive with the proportion of buses in the traffic flow. Moreover, a higher priority is suggested for the bus at certain positions in a queue so that it can pass the intersection in one green period with its preceding vehicles. The benefits of this approach include (1) reduced delay of both buses and other vehicles when the proportion of buses is small; (2) keeping the influence on network-wide traffic at a low level even when the proportion of buses is large, because the green time is only extended for a short while; and (3) ease to implement such control strategies by modifying current traffic control systems.

A CA model for intrusion conflicts simulation in vehicles-bicycles laminar traffic flow

Bicycle traffic serves as an essential trip mode in many Asian countries, i.e. China. But along with the economic developments, the intense competition of drivers and bicyclists for right of way brings significant trouble to city traffic. This paper studies the driving and riding behaviors during intrusion conflicts in vehicles-bicycles laminar flow, which means that some bicyclists will intrude the lanes reserved for vehicles from time to time. A cellular automata model is proposed to model such conflicts and examine the variation process of traffic flow rate according to the density of vehicles and bicycles. A useful suggestion is made in this paper finally, which will be further applied in infrastructure planning.

Majority-game based conflict modeling for pedestrians and right-turning vehicles in signalized intersection

Interactions between the crossing pedestrians and right-turning, left-turning, or through vehicles are frequently seen in cities. The resulting crowd dynamics is usually complex and of great difficulty to pedestrian clearance time estimation and signal phase optimization. Based on the study of abundant video data of competitive crossing, an elaborate but understandable cellular automata model is proposed in this paper to describe the competition behaviors of the pedestrians and right-turning drivers, when they are trying to pass the same crosswalk. The interaction between the drivers and pedestrians are viewed and simulated as a majority game between drivers and pedestrians. The simulation results show that this computationally efficient microscopic model fits well with the observed delay of vehicles and pedestrians.

Comparison of vehicle departure headways in Beijing and Atlanta

Two characteristics of traffic flows make the vehicle departure headways in Beijing, China different from that in Atlanta, USA. Urban traffic flows in China are often hindered by pedestrians at intersections and queuing vehicles often cannot be totally discharged during the green time, so most signalized intersections are over-saturated in the day time. The first characteristic makes the departure headways of the first and second vehicles in Beijing depend heavily on the start-up situations (with or without interference). The departure headways of the 3rd to 5th vehicles in Beijing have similar characteristics to those in Atlanta. The second characteristic makes the departure headways after the 5th vehicle significantly different from those in Atlanta. These comparisons show that the conventional delay estimate methods and signal control algorithms may not fit Chinese scenarios, which makes imported intelligent traffic control systems not work well in China without calibrations.

Optimal design of bus stops that are shared by multiple lines of buses

This paper studies a common traffic problem in China: a large number of bus lines share the same stop. In rush hours, a long queue of buses waiting to get into the stop, which causes a rise of bus delay and a drop of traffic capacity nearby. First, a cellular automaton model is proposed to simulate such traffic scenarios. Second, to re-designing such busy bus stops to enhance efficiency, some principles are proposed and evaluated by simulations. Finally, a specific design example is given.