Showing papers on "Traffic wave published in 2006"

Detecting anomalous road traffic conditions

Abstract: Techniques are described for automatically detecting anomalous road traffic conditions and for providing information about the detected anomalies, such as for use in facilitating travel on roads of interest. Anomalous road traffic conditions may be identified using target traffic conditions for a particular road segment at a particular selected time, such as target traffic conditions that reflect actual traffic conditions for a current or past selected time, and/or target traffic conditions that reflect predicted future traffic conditions for a future selected time. Target traffic conditions may be compared to distinct expected road traffic conditions for a road segment at a selected time, with the expected conditions reflecting road traffic conditions that are typical or normal for the road segment at the selected time. Anomalous conditions may be identified based on sufficiently large differences from the expected conditions, and information about the anomalous conditions may be provided in various ways.

Understanding widely scattered traffic flows, the capacity drop, and platoons as effects of variance-driven time gaps.

Abstract: We investigate the adaptation of the time headways in car-following models as a function of the local velocity variance, which is a measure of the inhomogeneity of traffic flow. We apply this mechanism to several car-following models and simulate traffic breakdowns in open systems with an on-ramp as bottleneck and in a closed ring road. Single-vehicle data and one-minute aggregated data generated by several virtual detectors show a semiquantitative agreement with microscopic and flow-density data from the Dutch freeway A9. This includes the observed distributions of the net time headways for free and congested traffic, the velocity variance as a function of density, and the fundamental diagram. The modal value of the time headway distribution is shifted by a factor of about 2 under congested conditions. Macroscopically, this corresponds to the capacity drop at the transition from free to congested traffic. The simulated fundamental diagram shows free, synchronized, and jammed traffic, and a wide scattering in the congested traffic regime. We explain this by a self-organized variance-driven process that leads to the spontaneous formation and decay of long-lived platoons even for a deterministic dynamics on a single lane.

A realistic two-lane cellular automata traffic model considering aggressive lane-changing behavior of fast vehicle

Abstract: In real traffic, a vehicle may perform different lane-changing behavior if its preceding vehicle is different. Fast vehicle usually has aggressive lane-changing behavior when its preceding vehicle is a slow one. In this paper, we take the factor into account and propose a new symmetric two-lane cellular automata model. It is shown that aggressive lane-changing behavior of fast vehicle can depress the plug formed by slow vehicles and improve traffic flow in mixed traffic in the intermediate density range. The simulation results also indicate that ping–pang lane-changing behavior is mainly caused by fast vehicles that are hindered by fast vehicles.

Deterministic microscopic three-phase traffic flow models

Abstract: Two different deterministic microscopic traffic flow models, which are in the context of the Kerner's there-phase traffic theory, are introduced. In an acceleration time delay model (ATD model), different time delays in driver acceleration associated with driver behaviour in various local driving situations are explicitly incorporated into the model. Vehicle acceleration depends on local traffic situation, i.e., whether a driver is within the free flow or synchronized flow or else wide moving jam traffic phase. In a speed adaptation model (SA model), vehicle speed adaptation occurs in synchronized flow depending on driving conditions. It is found that the ATD and SA models show spatiotemporal congested traffic patterns that are adequate with empirical results. In the ATD and SA models, the onset of congestion in free flow at a freeway bottleneck is associated with a first-order phase transition from free flow to synchronized flow; moving jams emerge spontaneously in synchronized flow only. Differences between the ATD and SA models are studied. A comparison of the ATD and SA models with stochastic models in the context of three-phase traffic theory is made. A critical discussion of earlier traffic flow theories and models based on the fundamental diagram approach is presented.

Flattened fauna and mitigation: Traffic victims related to road, traffic, vehicle, and species characteristics

Abstract: A model is developed to look at the probability of successful road traversing by mammals, based on Poisson-distributed arrivals of cars. It is a double ‘blind’ model presuming that a collision occurs when the animal and the car are on the same part of the road at the same time. When a car and an animal impact, two types of collisions can occur: ‘car hits animal’ and ‘animal hits car’. The probability of these events, and thus the probability of successful road traversing by animals, is determined by road, traffic, vehicle, and species characteristics. Use of the model shows that, for the parameter ranges, traffic volume and the animals’ traversing speed have the largest effects on whether a collision occurs. This model is applied to compare alternative network solutions and to evaluate traffic calming measures on a former arterial highway. It is shown that these measures are effective in mitigating traffic mortality among mammals.

Area occupancy characteristics of heterogeneous traffic

Abstract: Increasing congestion due to rapid urbanization in developing countries like India necessitates the study of traffic flow for effective traffic management. Most of the traffic studies conducted in this regard were on the lines of methods used in developed countries. These studies were able to represent the traffic behavior only in a very limited manner. In developing countries traffic is composed of several types of vehicles ranging from cars with high speeds to low speed non-motorized vehicles. Microscopic traffic characteristics such as time headway and space headway are difficult to measure due to the heterogeneous nature (no lane discipline, and two or three small vehicles occupying one lane in lateral direction) of the traffic. Even using some of the macroscopic traffic characteristics such as density or occupancy, to study this kind of traffic may lead to erroneous results. Thus it is desirable to have a metric that can represent the heterogeneous nature of traffic in these conditions. Since varying...

Effect of looking backward on traffic flow in a cooperative driving car following model

Abstract: An extended car following model is proposed by incorporating intelligent transportation system and the backward looking effect under certain condition in traffic flow The neutral stability condition of this model is obtained by using the linear stability theory The results show that anticipating the behavior of vehicles preceding and following one vehicle could lead to appreciable stabilization of traffic system From the simulation of space-time evolution of the vehicle headways, it is shown that the traffic jam could be suppressed efficiently via taking into account the information about the motion of two preceding vehicles and one following vehicle, and the analytical result is consistent with the simulation one

Intelligent redirection of vehicular traffic due to congestion and real time performance metrics

Abstract: An automated traffic control system provides real time alternative traffic flow solutions to address traffic congestion on a roadway. A process will pick routes to scan for real-time statistics on the traffic conditions and calculate an average vehicle speed (AVS) for that route, road, highway, etc. If the AVS drops below a historical threshold, a decision matrix is created, whereby all the real-time data is compared with historical data and provides an ideal or best alternative route for “route X”. The operator is provided this information within seconds and is allowed to make a decision to “accept pr decline” the proposed changes in routes. If the proposed changes are accepted, the changes begin to occur automatically such as but not limited to updating electronic signage, changing traffic control signals (all green to keep traffic moving), moving electronic barriers, etc.

Control of vehicular traffic through a sequence of traffic lights positioned with disordered interval

Abstract: We study the dynamical behavior of vehicular traffic through a sequence of traffic lights which are positioned with inhomogeneous interval on a roadway and turn on and off periodically with the synchronized strategy. The dynamics of vehicular traffic controlled by traffic lights is described in terms of the stochastic nonlinear map. When the interval between traffic lights fluctuates highly, vehicles cannot move together with the same tour time. While vehicles can move together with the other at less inhomogeneous interval between traffic lights for specific values of cycle time. If heterogeneity of traffic-light's interval is higher, it becomes more difficult to control vehicles moving together. The phase diagram (region map) is presented for controlling the vehicular traffic.

Traffic jam detection system and method

Abstract: A traffic jam detection system and method to estimate a traffic jam condition ahead of a vehicle. When a vehicle arrives at the tail end of a traffic jam, information is related to the tail end of the traffic jam is transmitted to an information center. The information center collects this information related to plural traffic jams from on-vehicle information terminals of a number of vehicles and develops estimated tail end information for each of the traffic jams. The information center transmits the estimated tail end information to vehicles approaching traffic jams for the driver to determine whether a traffic jam should be avoided or not.

Macroscopic Traffic Flow Propagation Stability for Adaptive Cruise Controlled Vehicles

Abstract: Traffic flow propagation stability is concerned about whether a traffic flow perturbation will propagate and form a traffic shockwave. In this paper, we discuss a general approach to the macroscopic traffic flow propagation stability for adaptive cruise controlled (ACC) vehicles. We present a macroscopic model with velocity saturation for traffic flow in which each individual vehicle is controlled by an adaptive cruise control spacing policy. A nonlinear traffic flow stability criterion is investigated using a wavefront expansion technique. Quantitative relationships between traffic flow stability and model parameters (such as traffic flow and speed, etc.) are derived for a generalized ACC traffic flow model. The newly derived stability results are in agreement with previously derived results that were obtained using both microscopic and macroscopic models with a constant time headway (CTH) policy. Moreover, the stability results derived in this paper provide sufficient and necessary conditions for ACC traffic flow stability and can be used to design other ACC spacing policies.

Real-Time Traffic Simulation With a Microscopic Model

Abstract: This paper describes a microscopic model that is able to simulate traffic situations in an urban environment in real time for use in driving simulators. Two types of vehicles are considered in the simulation, namely the user-driven vehicle at the center of the simulation model and the other vehicles that interact with it and its surroundings, which configure the developed traffic model. Simulation is performed in a reduced zone, called the control zone, surrounding the user-driven vehicle. This control zone is a mobile zone centered on the user-driven vehicle. The size of the control zone depends on the maximum number of vehicles involved simultaneously, the traffic density, and the driver's limit of visibility. The other vehicles involved in the traffic simulation are created or destroyed within the limits of the control zone. The general behavior of the traffic model is based on the following theory. Vehicles have an associated driver model that establishes several control functions for them to follow the path, while the steering, acceleration, and braking maneuvers follow certain models of behavior. A traffic light regulation is also included but only in the control area. The possibility of introducing anomalous traffic situations into the simulation is also considered, such as the presence of obstacles, abnormal maneuvers, etc. The developed model is immediately applicable to large-scale driving simulators for driver training, traffic control studies, and safety studies

Coupled vehicle and information flows: Message transport on a dynamic vehicle network

Abstract: A freeway with vehicles transmitting traffic-related messages via short-range broadcasting is a technological example of coupled material and information flows in complex networks: information on traffic flows is propagated via a dynamically changing ad hoc network based on local interactions. As vehicle and information propagation occur on similar time scales, the network dynamics strongly influences message propagation, which is done by the movement of nodes (cars) and by hops between nearby nodes: two cars within the limited broadcast range establish a dynamic link. Using the cars of the other driving direction as relay stations, the weak connectivity within one driving direction when the density of equipped cars is small can be overcome. By analytical calculation and by microscopic simulation of freeway traffic with a given percentage of vehicles equipped for inter-vehicle communication, we investigate how the equipment level influences the efficiency and velocity of information propagation. By simulating the formation of a typical traffic jam, we show how the non-local information about bottlenecks and jam fronts can travel upstream and reach potential users.

Adaptive decentralized congestion avoidance in two-dimensional traffic

Abstract: This paper studies congestion avoidance in a simple two-dimensional traffic system, using computer simulation. The mobile objects avoid congestion among themselves using simple congestion-avoiding traffic rules. The objects adaptively avoid congested regions and move towards less congested regions. The objects avoid congestion in decentralized manner based only on congestion levels in their local regions. It is found that the adaptive decentralized congestion-avoiding traffic rules prevent the traffic from undergoing congestion phase transition at low critical density. The congestion avoidance significantly increases the traffic capacity. The congestion-avoiding traffic rules increase the traffic capacity by keeping the emerging congestion and traffic hot spots small, localized, and temporary. Due to congestion avoidance, the travel time of objects is high and the amount of flow is low. The congestion-avoiding traffic eventually undergoes phase transition from free flow to jammed state, but at high critical density.

A stopped time dependent randomization cellular automata model for traffic flow controlled by traffic light

Abstract: Modelling road traffic behavior using cellular automata has become a well-established method to analyze, understand, and even forecast the behavior of real road traffic, because the automata's evolution rules are simple, computationally efficient. In this paper, we presented a new model. In this model, the randomization probability is defined to be function of the stopped time of the vehicle: the longer the vehicle stops, the larger the randomization probability is. This means that the sensitivity of the drivers depends on the stopped time. The simulations show that although the fundamental diagram of the new model is similar to that of Nagel–Schreckenberg model, the saturated current depends on the cycle time of traffic light. We have explained the dependence of saturated current on cycle time and made the outlook of the future work. Our results indicate that we can adjust the cycle time of the traffic lights to enhance the road capacity.

Control of traffic flow by sensing traffic states

Abstract: Traffic is controlled by sensing a current state of traffic and comparing it to a common state of traffic to determine deviations. A control scheme is determined based on the deviations, and control signals representative of the control scheme are generated to optimize the flow of traffic. The current state of traffic for an intersection or other advantageous monitoring location may be considered relative to a common state at the intersection or other location as well as relative to a current state of traffic at nearby locations, adjacent intersections, and locations where sensor equipped vehicles are traveling. Sensing occurs over time so the control scheme may be optimized based on consideration of historical data. Intersections or other locations may employ sensor devices to sense traffic state information, to communicate with other sensor devices of other intersections and/or a central controller, and to implement the control schemes to create a network of sensor devices each attempting to optimize traffic based on local and nearby traffic states.

Traffic jam prediction device and method

Abstract: A device and method to enable the prediction of a traffic jam even when the road environment changes. On the basis of up-to-the-minute, i.e., current, traffic jam information and changes from the preceding traffic jam information, the current traffic state is estimated. On the basis of the up-to-the-minute traffic jam information and the current traffic state, the current traffic jam degree is predicted. The results can be used in a conventional navigation method and apparatus to plot driving routes for a vehicle.

Traffic lights control with adaptive group formation based on swarm intelligence

Abstract: Several traffic control approaches address the problem of reducing traffic jams. A class of them deals with coordination of traffic lights to allow vehicles traveling in a given direction to pass an arterial without stopping. However, in cities where the business centers are no longer located exclusively downtown, this approach is not appropriate: simple offline optimization of the synchronization in one arterial alone cannot cope with changing traffic patterns.

Formation of density waves in traffic flow through intersecting roads.

Abstract: The formation of density waves in two intersecting roads, with a traffic circle at the intersection, is studied. It is found that, depending on the traffic densities in the two roads, density waves can form in the traffic circle and in one or both of the roads. Depending on the expression chosen for the optimal velocity, either the congestion moves entirely to the traffic circle or the congestion becomes confined to the traffic circle and a part of the road approaching the traffic circle.

Phase transition at an on-ramp in the Nagel–Schreckenberg traffic flow model

Abstract: Recent empirical observations show that traffic flow is related to various phase transitions, especially at bottlenecks. This paper studies traffic flow induced by an on-ramp in the Nagel–Schreckenberg model. It is shown that when considering the situation that vehicles on main road and on-ramp interact in a relatively long road section, first-order phase transition from free flow to congested flow occurs. In contrast, it is second-order phase transition from free flow to congested flow if the interaction road section is short. We have investigated the reason why first-order phase transition occurs. The interaction of vehicles may be viewed as a kind of cooperation behavior of drivers. Therefore, our results indicate that in future traffic flow research, investigation on cooperation behavior should be carried out.

Continuum Traffic Model for Freeway with On-and Off-Ramp to Explain Different Traffic-Congested States

Abstract: This paper presents a multilane continuum traffic flow model for traffic operations at on-and off-ramps, which is based on microscopic principles. One of the main contributions of the derived model is that it takes into account explicitly the impact of ramp length on traffic flow operations, as well as the willingness of drivers to accept smaller gaps when approaching at the end of on-ramps. Different congested states were investigated with the proposed model for specific values of both the upstream main carriageway flow and the on-ramp flow. Several types of congestion states consistent with well-known traffic-congested styles in the literature, such as a moving localized cluster, two moving localized clusters, triggered stop-and-go waves, and homogeneous congested traffic, were found. The simulation results show the stability states of traffic flow for different ramp lengths.

A macroscopic traffic model for highway work zones: Formulations and numerical results

Abstract: This paper focuses on two critical but neglected issues that are imperative for the design of effective control strategies for highway segments undergoing lane closure operations. The first issue is the impact of mandatory lane changes from the blocked lanes on the temporal and spatial evolution of traffic properties at the lane-closure highway bottleneck. The second issue is the interrelation between the critical density and its approaching traffic flow volume as well as characteristics under various types of lane-closure operations. A macroscopic multilane model is used for analyzing the dynamic traffic properties of the highway segment under a lane-closure operation. The proposed traffic flow formulations employ the hyperbolic model used in the non-Newtonian fluid dynamics, and assume the lane-changing intensity between neighboring lanes as a function of their difference in density. The results of extensive simulation experiments indicate that the proposed model is capable of realistically replicating the impacts of lane-changing maneuvers from the blocked lanes on the overall traffic conditions, including the interrelations between the approaching flow density, the resulting congestion level, and the exiting flow rate from the lane-closure zone. Extensive experimental analyses also confirm that traffic conditions will deteriorate dramatically and evolve to the state of traffic jam if the density has exceeded its critical level that varies with the type of lane-closure operations. This study provides a convenient way for computing such a critical density under various lane-closure conditions. It also offers a theoretical basis for understanding the formation and dissipation of traffic jams. Future extensions of the model are discussed.

Effects of Bottlenecks on Vehicle Traffic

Abstract: Traffic congestion is usually observed at the upper stream of bottlenecks such as tunnels. Congestion appears as stop-and-go waves and high-density uniform flow. We perform simulations of traffic flow with a bottleneck using the coupled map optimal velocity model. The bottleneck is expressed as a road segment with speed reduction. The speed reduction in the bottleneck controls the emergence of stop-and-go waves. A phenomenological theory of bottleneck effects is constructed.

Part 2: Car-Following Models: Continuum Traffic Model for Freeway with On- and Off-Ramp to Explain Different Traffic-Congested States

Abstract: This paper presents a multilane continuum traffic flow model for traffic operations at on- and off-ramps, which is based on microscopic principles. One of the main contributions of the derived model is that it takes into account explicitly the impact of ramp length on traffic flow operations, as well as the willingness of drivers to accept smaller gaps when approaching at the end of on-ramps. Different congested states were investigated with the proposed model for specific values of both the upstream main carriageway flow and the on-ramp flow. Several types of congestion states consistent with well-known traffic-congested styles in the literature, such as a moving localized cluster, two moving localized clusters, triggered stop-and-go waves, and homogeneous congested traffic, were found. The simulation results show the stability states of traffic flow for different ramp lengths.

Measuring First-In-First-Out Violation Among Vehicles

Abstract: In reality, First-In-First-Out (FIFO) principle for vehicles on a link or path is often violated because of the heterogeneity in drivers’ behavior and traffic conditions on different lanes. It is important to understand how serious such FIFO violation can be, since the assumption of FIFO has been an important foundation for developing many dynamic traffic assignment strategies and traffic flow models. This paper first presents a measurement of FIFO violation among vehicles and then theoretically shows that this measurement is well defined. Then the paper applies this measurement in order to study scenarios simulated by a microscopic traffic simulator. In these scenarios, FIFO violation is linear to travel time or distance. This study will serve as a springboard for future studies on FIFO violation in real traffic and can have implications in calibrating traffic flow models and investigating dynamic traffic assignment methods.

Traffic control system and method

Abstract: The system and method disclosed utilize a smart metering system that combines real-time traffic data and statistical traffic models to control vehicle flow. Also disclosed are a system and method for using dual-use traffic lanes that function as regular traffic lanes under regular traffic conditions and as emergency traffic lanes in an emergency. Vehicle speed control devices can be used to prevent or break up slower traffic waves when they occur.

Hybrid Model Based on Second-Order Traffic Model

Abstract: The behaviour of traffic phenomena is described through three types of approaches. The first approach is macroscopic, based on the analogy with fluid mechanics through three basic variables: the flow rate q, the density p and the speed v. The second approach is microscopic, enabling one to point out the interaction phenomena between vehicles, through the vehicle speed v, the position x and the acceleration y. The third approach, which is the hybrid approach, is less known in the traffic domain. It makes it possible to combine the macroscopic and microscopic approaches. This paper proposes a hybrid model, based on a second order macroscopic modelling principle. As a first step, the models to be coupled will be chosen, and the analytical solution of the second order macroscopic model will be carried out. This model will be reformulated under the form of a supply and demand function, similar to the model by Lighthill-Witham-Richards. More precisely, two scenarios will be studied: first a hybrid model in the case of traffic at equilibrium, which will enable us to do a comparative study with an existing hybrid model in the literature. As a second step, the transition from a macroscopic representation of traffic to a microscopic representation in the conditions of an out of equilibrium traffic will be studied. The validation of the proper transmission of information from one traffic vision to another will be done, studying the propagation of congestion from upstream to downstream.

Perspective of Mitigating Shock Waves by Temporary In-Vehicle Dynamic Speed Control

Abstract: This paper describes how shock waves can be defined as upstream moving traffic jams on motorways that may remain unchanged in size for a long time. Suppression of such jams by speed limit control has been investigated before with good results. The basic idea is to decrease the inflow to the jammed area, by reducing the traffic speed in upstream segments of the road. The approach until now was to assume that the speed limits are communicated to drivers by variable speed limit (VSL) signs. Current developments of in-vehicle driving assistance systems, especially of speed assistance systems would enable a different approach. Speed assistance systems focus primarily of information and warning, although it has been suggested that in a hybrid layout such systems might assume vehicle control mode where desirable, e.g. in situations with mixed traffic of motor vehicles and vulnerable road users. Such temporary control could also be used to more directly, precisely and homogeneously adapt the traffic speed to the calculated values for shock wave suppression on motorways. This paper studies the feasibility of this scenario, in comparison scenarios using communication by VSL signs. The scenarios are modelled using an adapted version of the macroscopic simulation model METANET, and model predictive control (MPC) for optimal coordination of speed limits.