Showing papers on "Traffic wave published in 2008"

Self-Control of Traffic Lights and Vehicle Flows in Urban Road Networks

Abstract: Based on fluid-dynamic and many-particle (car-following) simulations of traffic flows in (urban) networks, we study the problem of coordinating incompatible traffic flows at intersections. Inspired by the observation of self-organized oscillations of pedestrian flows at bottlenecks [D. Helbing and P. Moln\'ar, Phys. Eev. E 51 (1995) 4282--4286], we propose a self-organization approach to traffic light control. The problem can be treated as multi-agent problem with interactions between vehicles and traffic lights. Specifically, our approach assumes a priority-based control of traffic lights by the vehicle flows themselves, taking into account short-sighted anticipation of vehicle flows and platoons. The considered local interactions lead to emergent coordination patterns such as ``green waves'' and achieve an efficient, decentralized traffic light control. While the proposed self-control adapts flexibly to local flow conditions and often leads to non-cyclical switching patterns with changing service sequences of different traffic flows, an almost periodic service may evolve under certain conditions and suggests the existence of a spontaneous synchronization of traffic lights despite the varying delays due to variable vehicle queues and travel times. The self-organized traffic light control is based on an optimization and a stabilization rule, each of which performs poorly at high utilizations of the road network, while their proper combination reaches a superior performance. The result is a considerable reduction not only in the average travel times, but also of their variation. Similar control approaches could be applied to the coordination of logistic and production processes.

A dynamic and automatic traffic light control expert system for solving the road congestion problem

Abstract: Traffic congestion is a severe problem in many modern cities around the world. To solve the problem, we have proposed a framework for a dynamic and automatic traffic light control expert system combined with a simulation model, which is composed of six submodels coded in Arena to help analyze the traffic problem. The model adopts interarrival time and interdeparture time to simulate the arrival and leaving number of cars on roads. In the experiment, each submodel represents a road that has three intersections. The simulation results physically prove the efficiency of the traffic system in an urban area, because the average waiting time of cars at every intersection is sharply dropped when the red light duration is 65s and the green light time duration is 125s. Meanwhile, further analysis also shows if we keep the interarrival time of roads A, B, and C, and change that of roads D, E, and F from 1.7 to 3.4s and the interdeparture times at the three intersections on roads A, B, and C are equal to 0.6s, the total performance of the simulation model is the best. Finally, according to the data collected from RFID readers and the best, second and third best traffic light durations generated from the simulation model, the automatic and dynamic traffic light control expert system can control how long traffic signals should be for traffic improvement.

Mechanisms for spatio-temporal pattern formation in highway traffic models

Abstract: A key qualitative requirement for highway traffic models is the ability to replicate a type of traffic jam popularly referred to as a phantom jam, shock wave or stop-and-go wave. Despite over 50 years of modelling, the precise mechanisms for the generation and propagation of stop-and-go waves and the associated spatio-temporal patterns are in dispute. However, the increasing availability of empirical datasets, such as those collected from motorway incident detection and automatic signalling system (MIDAS) inductance loops in the UK or the next-generation simulation trajectory data (NGSIM) project in the USA, means that we can expect to resolve these questions definitively in the next few years. This paper will survey the essence of the competing explanations of highway traffic pattern formation and introduce and analyse a new mechanism, based on dynamical systems theory and bistability, which can help resolve the conflict.

Urban traffic congestion propagation and bottleneck identification

Abstract: Bottlenecks in urban traffic network are sticking points in restricting network collectivity traffic efficiency. To identify network bottlenecks effectively is a foundational work for improving network traffic condition and preventing traffic congestion. In this paper, a congestion propagation model of urban network traffic is proposed based on the cell transmission model (CTM). The proposed model includes a link model, which describes flow propagation on links, and a node model, which represents link-to-link flow propagation. A new method of estimating average journey velocity (AJV) of both link and network is developed to identify network congestion bottlenecks. A numerical example is studied in Sioux Falls urban traffic network. The proposed model is employed in simulating network traffic propagation and congestion bottleneck identification under different traffic demands. The simulation results show that continual increase of traffic demand is an immediate factor in network congestion bottleneck emergence and increase as well as reducing network collectivity capability. Whether a particular link will become a bottleneck is mainly determined by its position in network, its traffic flow (attributed to different OD pairs) component, and network traffic demand.

A stochastic wave propagation model

Abstract: We introduce in this paper gap time, the time taken for a following vehicle to travel at its current speed the distance between its head position and the position of the rear of its leading vehicle, as a fundamental parameter for modeling some prominent features of congested traffic, namely the scatter of the fundamental diagram and the growth and decay of traffic disturbances on highways. In the model, traffic waves propagate in a stochastic manner and their speeds are determined by the relative differences between gap times and the reaction times of drivers. The scatter on the fundamental diagram and the growth and decay of perturbations are explained by random fluctuations of gap time and random transitions of traffic states on the fundamental diagram, respectively. Empirical data are used to validate the model and the evaluation shows close correspondence between model predictions and field observations.

Fundamental Diagram Estimation Through Passing-Rate Measurements in Congestion

Abstract: Classically, fundamental diagrams are estimated from aggregated data at a specific location. Such a measurement method may lead to inconsistency which mainly explain the controversy about their shape. This paper proposes a new estimation method based on passing rate measurements along moving observer paths. Under specific assumptions, it can be proved that in congestion passing rate is constant whatever the traffic flow states are. This property allows (i) to prove that a linear fundamental diagram is suitable to represent traffic flow behavior involved in the NGSIM dataset; (ii) to fit its two parameters: the congested wave speed and the jam density. Finally, simulations of vehicle trajectories are carried out with the Newell's simplified car-following model to test the estimated fundamental diagram. It is found that the estimated parameters provide accurate vehicle trajectories.

A theory of traffic congestion at heavy bottlenecks

Abstract: Spatiotemporal features and physics of vehicular traffic congestion occurring due to heavy highway bottlenecks caused for example by bad weather conditions or accidents are found based on simulations in the framework of three-phase traffic theory. A model of a heavy bottleneck is presented. Under a continuous non-limited increase in bottleneck strength, i.e., when the average flow rate within a congested pattern allowed by the heavy bottleneck decreases continuously up to zero, the evolution of the traffic phases in congested traffic, synchronized flow and wide moving jams, is studied. It is found that at a small enough flow rate within the congested pattern, the pattern exhibits a non-regular structure: a pinch region of synchronized flow within the pattern disappears and appears randomly over time; wide moving jams upstream of the pinch region exhibit a complex non-regular dynamics in which the jams appear and disappear randomly. At greater bottleneck strengths, wide moving jams merge onto a mega-wide moving jam (mega-jam) within which low-speed patterns with a complex non-regular spatiotemporal dynamics occur. We show that when the bottleneck strength is great enough, only the mega-jam survives and synchronized flow remains only within its downstream front separating free flow and congested traffic. Theoretical results presented can explain why no sequence of wide moving jams can often be distinguished in non-homogeneous traffic congestion measured at very heavy bottlenecks caused by bad weather conditions or accidents.

Stochastic Description of Traffic Flow

Abstract: We propose a traffic model based on microscopic stochastic dynamics. We built a Markov chain equipped with an Arrhenius interaction law. The resulting stochastic process is comprised of both spin-flip and spin-exchange dynamics which models vehicles exiting, entering and interacting in a two-dimensional lattice environment corresponding to a multi-lane highway. The process is further equipped with a novel look-ahead type, anisotropic interaction potential which allows drivers/vehicles to ascertain local fluctuations and advance to new cells forward or sideways. The resulting vehicular traffic model is simulated via kinetic Monte Carlo and examined under both, typical and extreme traffic flow scenarios. The model is shown to correctly predict both qualitative as well as quantitative traffic observables for any highway geometry. Furthermore it also captures interesting multi-scale phenomena in traffic flows after a simulated accident which lead to oscillatory, dissipating, traffic waves with different periods per lane.

Delay times in a cellular traffic flow model for road sections with periodic outflow

Abstract: A simple cellular automaton to model traffic flow is used to analyze the impact of traffic lights on travel times. The model is investigated on a stretch of road with open boundaries, where the inflow is driven stochastically, but the outflow is controlled by a traffic light with periodically changing outflow rates. Especially in the transition regime from free flow to oversaturated flow, the detailed space-time structure can be used to derive analytical lower and upper boundaries for the travel time function. The analytical results have been verified by a simulation study. The function displays a strong non-trivial dependency on the length of the system, which is at odds with a well-known formula derived almost 50 years ago by Webster. Such a model is interesting both from a theoretical point of view and for applications.

Dynamic Late Lane Merge System at Freeway Construction Work Zones

Abstract: In normal work zones with lane closures, drivers do not merge at any one definite point, a situation thus often causing a sudden interruption in traffic flow and sometimes higher delay and longer queue. The Dynamic Late Lane Merge System (DLLMS) is used to specify a definite merge point, improve the flow of congested work zones, and reduce queue lengths in travel lanes. The DLLMS was implemented in Michigan on three freeway segments that were reduced from two lanes to one lane because of highway construction work zones. The DLLMS directed traffic to use both lanes (open and closed lanes) until the designated "merge point" (close to the taper) where traffic from each lane was instructed to take turns merging into the open lane. On the basis of travel time characteristics, merge locations, and throughput, the effectiveness of the DLLMS was evaluated as a part of this study. The before period data were not available; therefore, a conventional work zone merge system, located on eastbound I-94, was used as a c...

Operational effects of acceleration lane on main traffic flow at discontinuities

Abstract: Recent studies have indicated that on-ramp flow is important in the formation of the stop-and-go traffic flow near the ramp Several models have been developed to explain the complex phenomena associated with ramps which result in the hysteretic phase transitions A good understanding of the mechanisms of congestion near on-ramps is very useful for the development of suitable control and highway design measures To this end, in this paper traffic flow operations on a freeway with an on-ramp are investigated based on a newly developed second order macroscopic model The proposed model allows to take into account the influences of the acceleration lane length on the flow dynamics of the main carriageway The main aim of this paper is, therefore, to investigate analytically and numerically the effects of acceleration lane length on traffic flow operations It is found that different acceleration lane lengths result in various congested traffic states

Traffic situation determination system

Abstract: In a traffic situation determination system, a vehicle side is formed to transmit information relating to the travel path of the vehicle specified by the GPS to the probe center when traveling on roads calculated to have the degree of traffic jam or congestion, while a probe center side is formed to acquire the travel path of the vehicle via a mobile phone communication network through a mobile phone, determine roads corresponding to the travel path of the vehicle specified by the GPS to be in the situation of traffic jam, and determine roads corresponding to the travel path of the vehicle specified in the mobile phone communication network to be in the situation of no traffic jams

Travel Time Reliability Model on Freeways

Abstract: Travel time reliability relates to both the variability in travel times and the predictability of travel times, the latter which is closely related to the probability of traffic breakdown. In this paper, a new analytical formula is proposed, which expresses travel time unreliability in terms of both these elements. This formula, which explicitly expresses the cost (severity) of travel time unreliability as a function of both inflow on a link and the characteristics of the route of interest, can be used for example in traffic assignment models, or road network performance analysis applications. In our model, the probability of traffic breakdown of a route is formulated on the basis of the probability of traffic breakdown of each section along the route. Empirical analysis on a basis of a large dataset of traffic flow data from loop detectors shows that there is a certain critical inflow value. Below the value, both the probability of traffic breakdown and travel time unreliability is small, but above the value, both the probability of traffic breakdown and travel time unreliability sharply increase with rising inflows.

Virtual Probe Approach for Time-Dependent Arterial Travel Time Estimation

Abstract: Travel time estimation on arterials is a challenging task for traffic engineers due to the interrupted nature of urban traffic flows. Many research efforts have been devoted on this topic, but their successes are limited and most of them can only be used for offline purposes due to the limited availability of traffic data from signalized intersections. With the advancement of intelligent transportation systems, high-resolution detector and signal status data are available but not fully explored. In this paper, we develop an innovative algorithm for time-dependent arterial travel time estimation by tracing a virtual probe vehicle. At each time step, the virtual probe has three possible maneuvers: acceleration, deceleration and no-speed-change. The maneuver decision is determined by its own status and its surrounding traffic conditions, which can be estimated based on the availability of traffic data at intersections. An interesting property of the proposed model is that travel time estimation errors can be self-corrected with the signal status data, because the differences between a virtual probe vehicle and a real probe can be reduced when both of them meet the red signal phase. A field study at an 11-intersections arterial corridor along France Avenue in Minneapolis, MN shows the proposed model can generate accurate time-dependent travel time under various traffic conditions.

Study of the effect of traffic volume and road width on pcu value of vehicles using microscopic simulation

Abstract: The knowledge of traffic volume is an important basic input required for planning, analysis and operation of roadway systems. Expressing traffic volume as number of vehicles passing a given section of road or traffic lane per unit time will be inappropriate when several types of vehicles with widely varying static and dynamic characteristics are comprised in the traffic. The problem of measuring volume of such heterogeneous traffic has been addressed by converting the different types of vehicles into equivalent passenger cars and expressing the volume in terms of Passenger Car Unit (PCU) per hour. The vehicles of highly heterogeneous traffic with widely varying physical and operational characteristics such as the one prevailing on Indian roads, occupy based on the availability of space, any convenient lateral position on the road without any lane discipline. The interaction between moving vehicles under such heterogeneous traffic condition is highly com- plex. The results of the study, provides an insight into the complexity of the vehicular interaction in heterogeneous traffic. The PCU estimates, made through microscopic simulation, for the different types of vehicles of heterogeneous traffic, for a wide range of traffic volume and roadway conditions indicate that the PCU value of a vehicle significantly changes with change in traffic volume and width of roadway.

Traffic flow distribution system, traffic flow distribution method, traffic flow distribution program and program recording medium

Abstract: PROBLEM TO BE SOLVED: To provide a traffic flow distribution system which can reduce traffic congestion and CO 2 emission. SOLUTION: According to the current traffic information acquired from a road traffic quantity sensor 40 and a probe system 50 by a traffic information collection means 32a and travel schedule route information of each vehicle collected by a travel schedule route collection means 31a, distribution of traffic flows minimizing future traffic congestion and generation of CO 2 emission is determined by a traffic flow distribution means 31c as traffic flow distribution plans, and a change of travel route based on the traffic flow distribution plans is directed to each vehicle by a travel route change direction means 31d. Then, the record result of the travel route of each vehicle collected by a travel record route collection means 32c, its congestion occurrence and the CO 2 emission reduction effect are evaluated by a record management means 32d, and a traffic flow distribution algorithm of the traffic flow distribution means 31c is corrected. Moreover, an incentive is transmitted by an incentive providing means 32e to a vehicle which has changed the travel route following the change directions. COPYRIGHT: (C)2009,JPO&INPIT

Fundamental diagram in traffic flow of mixed vehicles on multi-lane highway

Abstract: We study the fundamental diagram for traffic flow of vehicular mixture on a multi-lane highway. We present the car-following model of multi-lane traffic in which slow and fast vehicles flow with changing lanes. We investigate the traffic states of the vehicular mixture under the periodic boundary. Two values of the current appear at a density and two current curves are obtained. Vehicles move with changing lanes in the traffic state of high current, while vehicles move without changing lanes in the traffic state of low current. They depend on the density, the fraction of slow vehicles, and the initial condition. In the high-current curve, the jamming transition between the free flow and the jammed state occurs at a low density. The fundamental diagrams (current–density diagrams) are shown for the single-lane, two-lane, three-lane, and four-lane traffics.

Fluctuations in urban traffic networks

Abstract: Urban traffic network is a typical complex system, in which movements of tremendous microscopic traffic participants (pedestrians, bicyclists and vehicles) form complicated spatial and temporal dynamics. We collected flow volumes data on the time-dependent activity of a typical urban traffic network, finding that the coupling between the average flux and the fluctuation on individual links obeys a certain scaling law, with a wide variety of scaling exponents between 1/2 and 1. These scaling phenomena can explain the interaction between the nodes' internal dynamics (i.e. queuing at intersections, car-following in driving) and changes in the external (network-wide) traffic demand (i.e. the every day increase of traffic amount during peak hours and shocking caused by traffic accidents), allowing us to further understand the mechanisms governing the transportation system's collective behavior. Multiscaling and hotspot features are observed in the traffic flow data as well. But the reason why the separated internal dynamics are comparable to the external dynamics in magnitude is still unclear and needs further investigations.

Lane Changing Rules Based on Cellular Automaton Traffic Flow Model

Abstract: Lane changing rules in freeway traffic were simulated by using cellular automaton model under condition of periodical boundary. The mean speed and flow volume under different lane changing rules were simulated, the difference of drivers£§ character was taken into account by introducing the flexible lane-changing rules and the influence of lane changing rules on traffic flow was discussed. In the process of computational simulation, the fundamental diagrams of traffic flow under different lane changing rules were obtained by changing traffic flow density. Result shows that models with new lane changing rules will enlarge traffic flow and suppress traffic jam; the best lane changing rule was obtained based on the analysis of point of view for safety.

Traffic flow impacts of a congestion assistant

Abstract: This paper presents the results from a microscopic traffic simulation study that was conducted to investigate the impacts of a so-called Congestion Assistant on traffic efficiency and traffic safety. The Congestion Assistant is an in-vehicle system that supports the driver with an Active pedal when approaching a traffic jam and a Stop & Go when driving in a traffic jam. Six variants of the Congestion Assistant with different equipment rates on a four-lane highway with a lane drop were assessed. The traffic simulation tool was calibrated and validated using measured loop data on a segment of the Dutch A12 highway. The Congestion Assistant was found to reduce the amount of congestion significantly, especially due to the Stop & Go. This function led to more efficient car-following behavior by adapting smaller headways and eliminating the reaction time of drivers. The Active pedal of the Congestion Assistant hardly influenced traffic efficiency; rather it affected traffic safety through a safer approach to a jam.

A Method for Tailback Approximation Via C2I-Data Based on Partial Penetration

Abstract: Optimizing traffic flow at signalized intersections is one approach to manage increasing traffic volume in metropolitan areas. This paper offers a method to use available C2I-communication data for tailback length approximation in urban networks. Tailback length can be used as criterion to be optimized within signal control methods, and can also be used for providing individual driver information like the optimal speed to pass the signalized intersection without needing to stop. The method merges current and historical C2I-communication data with information of the signal control in the access lanes and is implemented into the microscopic traffic simulator AIMSUN NG. The authors contend that even a low penetration rate of vehicles with communication tools is sufficient to obtain a reliable approximation. They conclude that, based on the good performance of the method so far, the currently used fixed time signal control will be changed into a traffic-responsive control strategy based on approximate dynamic programming techniques.

Research on model of traffic flow based on cusp catastrophe

Abstract: The phenomena of discontinuous jumping,which exist in the datum of observed traffic flow,are hard to be explained by traditional traffic flow model.But they can be explained better by using traffic flow model of catastrophe theory in three-dimensional space or more-dimensional space.To the traffic of high-speed way,by using traffic wave theory,three-parametric relation model of traffic flow is combined with cusp catastrophe mathematic model to analyze the critical state of high-speed way traffic flow model based on catastrophe theory.The results of analysis are coincided with the fact.Thereby the policy and measure of traffic control must be done when the observed density of practical traffic flow is nearby the critical density.

Departure Headways of Mixed Traffic Flow at Signalized Intersections: Distributions, Simulations and Validations

Abstract: A method to collect departure headways of mixed traffic flow at an urban signalized intersection was implemented. Mixed traffic flow in this paper refers to different vehicles in the queue including small vehicles and heavy vehicles, and different traffic participators at the intersections including pedestrians, bicyclists and vehicles. 500 groups of reliable departure headway data were extracted from videos. The distributions of departure headways are detailed and classified into categories according to two contents: the different positions of heavy vehicles in the queue and the different start-up situations with or without disturbances. The simulations based on above departure headway data are to compute needed minimal dissipating time of queues which heavy vehicles are located in different positions; possible start-up lost time with disturbance also included in the simulations. Dissipating times of vehicle queues at other signalized intersection are collected, the correctness of simulating results validated by these new traffic data.

Cellular Automaton Traffic Flow Model Considering Flexible Safe Space for Lane-changing

Abstract: In real traffic,the lane-changing vehicles usually have different speeds and so their safe spaces for lane-changing are not same.That is to say,the high-speed vehicles change lanes swiftly and the low-speed ones vacillatingly.Therefore,the fixed safe space for lane-changing in some cellular automaton (CA) models is not appropriate.However,this effect has seldom been investigated before.A rule about flexible safe space was brought forward which made the CA model accord with the real traffic better.What’s more,the simulation shows that the new model will enlarge traffic flow and suppress traffic jam.

Dynamics of the congestion triggered by boundary

Abstract: We study the congestion on a homogeneous roadway with open boundaries. Three different phases are identified. Both numerical and analytical results are presented. For stationary boundaries, three different flow can be associated with a single density on the fundamental diagram. When the congestion is characterized by numerous jams, the system is homogeneous and the traffic flow is low. When the system is dominate by a single jam, the time trajectory traces out finite cycles and a higher traffic flow can be supported. If the cycles fill up a two-dimensional area, the traffic flow remains constant as the density changes; if the cycles collapse into a one-dimensional loop, a much higher traffic flow can be achieved. We also discuss the effects of dynamical boundaries.

Wave properties of a traffic flow model on highway with ramps

Abstract: In this paper, we use the model is recently presented by us to study the wave properties of the traffic flow on highway with ramps. The results show that the model can perfectly reproduce the effects that ramps have on the formation, the propagation and the evolution of the traffic waves on the main road. Finally, we study the propagating velocity of the first-order wave on the main road and we can further prove that ramps might destroy the stability of the main road traffic flow.

Study on the traffic behavior of on-ramp system with two-lane main road under signal controlling

Abstract: In this paper we investigate the two-lane main road on-ramp system with signal-controlling using the cellular automata traffic flow model. The traffic signal is setup at the merging part between the main road and the on-ramp so that it can control the vehicles of both roads. We simulate the effect of traffic signal on vehicle flows of main road and on-ramp, and the traffic capacity and average velocity at the merging part are discussed. Through the analysis of the phase diagram, it can be found that the on-ramp system with two-lane main road can embody more complicated and realistic traffic flow characteristics than the on-ramp system with single-lane main road. Compared with the model introduced by Jiang Rui ［Jiang R 2003 J. Phys. A 36 11713］, the simulation results indicate that the state of traffic flow is improved obviously and the capacity of the on ramp system has increased.

Improving Urban Traffic by Velocity Guidance

Abstract: In this paper, we use CA model to study the traffic flow on a ring road with one traffic light. A velocity guidance strategy is presented: when crossing traffic light, a message will give the driver a desired velocity in order that he can avoid sharply brakes when signal light turns red. The numerical results show that the velocity guidance strategy can efficiently reduce the ratio of the stopped vehicles and get relatively high and stable flow.

Outline of Diffusion Advection in Traffic Flow Modeling

Abstract: The quantity of data necessary in order to study traffic through a traffic network, and the large volume of information that is provided as a result renders the said model unmanageable in practice. A study of this kind is expensive and complex, with many sources of error connected to each step carried out. A simplification like the continuous medium is a reasonable approximation and, for certain dimensions of the actual problem, may be an alternative to be kept in mind. The hypotheses of the continuous model introduce errors comparable to those associated with geometric inaccuracies in the transport network, with the grouping of hundreds of streets in one same type of arc and therefore having the same functional characteristics, with the centralization of all journey departure points and destinations in discrete centroids, and with the uncertainly produced by a highly origin/destination matrix that is quickly phased out, etc. In the course of this work, a new model for characterizing traffic in dense network cities as a continuous medium, the diffusion/advection model, is put forward. The model is approached by means of the boundary element method that has the fundamental characteristic of only requiring the contour of the problem to be discretized, thereby reducing the complexity and need for information into one order. On the other hand, the boundary elements method tends to give a more complex mathematical formulation than that of other more diffuse methods. In order to validate the proposed technique, two examples in their fullest form are resolved with known analytic solution.