Showing papers on "Traffic wave published in 2010"

A kinematic wave theory of lane-changing traffic flow

Abstract: Frequent lane-changes in highway merging, diverging, and weaving areas could disrupt traffic flow and, even worse, lead to accidents. In this paper, we propose a simple model for studying bottleneck effects of lane-changing traffic and aggregate traffic dynamics of a roadway with lane-changing areas. Based on the observation that, when changing its lane, a vehicle affects traffic on both its current and target lanes, we propose to capture such lateral interactions by introducing a new lane-changing intensity variable. With a modified fundamental diagram, we are able to study the impacts of lane-changing traffic on overall traffic flow. In addition, the corresponding traffic dynamics can be described with a simple kinematic wave model. For a location-dependent lane-changing intensity variable, we discuss kinematic wave solutions of the Riemann problem of the new model and introduce a supply-demand method for its numerical solutions. With both theoretical and empirical analysis, we demonstrate that lane-changes could have significant bottleneck effects on overall traffic flow. In the future, we will be interested in studying lane-changing intensities for different road geometries, locations, on-ramp/off-ramp flows, as well as traffic conditions. The new modeling framework could be helpful for developing ramp-metering and other lane management strategies to mitigate the bottleneck effects of lane-changes.

Generated Traffic and Induced Travel Implications for Transport Planning

Abstract: Traffic congestion tends to maintain equilibrium. Congestion reaches a point at which it constrains further growth in peak-period trips. If road capacity increases, the number of peak-period trips also increases until congestion again limits further traffic growth. The additional travel is called “generated traffic.” Generated traffic consists of diverted traffic (trips shifted in time, route and destination), and induced vehicle travel (shifts from other modes, longer trips and new vehicle trips). Research indicates that generated traffic often fills a significant portion of capacity added to congested urban road. Generated traffic has three implications for transport planning. First, it reduces the congestion reduction benefits of road capacity expansion. Second, it increases many external costs. Third, it provides relatively small user benefits because it consists of vehicle travel that consumers are most willing to forego when their costs increase. It is important to account for these factors in analysis. This paper defines types of generated traffic, discusses generated traffic impacts, recommends ways to incorporate generated traffic into evaluation, and describes alternatives to roadway capacity expansion.

Predicting expected road traffic conditions based on historical and current data

Abstract: Techniques are described for determining and using information regarding expected road traffic flow conditions information for vehicles traveling on roads. The expected road traffic flow conditions for a particular portion of a road may be generated by combining historical representative information about road traffic flow conditions for that road portion with current information about actual traffic flow on or near that road portion. The combination may, for example, provide benefits for estimating expected traffic flow conditions information for roads with structural flow obstructions that cause reduced traffic flow at certain road locations and times - for example, the expected traffic flow conditions information may be based at least in part on fitting or otherwise adapting partial actual traffic flow information about a vehicle's actual travel path to a historical travel profile for a road that includes representative traffic flow information for various combinations of road locations and time periods.

Traffic routing using intelligent traffic signals, gps and mobile data devices

Abstract: A traffic routing system reduces emissions from commuter and other traffic, eases congestion on roadways, and decreases transit time by use of communications among vehicles and traffic controls, such as traffic lights. In one aspect, a traffic light receives a signal that a vehicle is approaching and in response turns green to allow the vehicle to pass without impairment. In another aspect, a vehicle receives a signal to adjust a current rate of speed to arrive when a traffic signal allows vehicles to pass. In still another aspect, a combination of congestion, emergency traffic, roadwork and similar factors influence proposed routes sent to vehicles.

Cellular automaton model for traffic flow based on safe driving policies and human reactions

Abstract: This paper proposes a new single-lane cellular automaton model for traffic flow. The model takes into account normal drivers’ spacing policies and transportation engineering practices to guarantee that microscopic vehicle behavior is more in line with vehicular movement in the real world. As a result, drivers’ reactions are based on a safety analysis that determines the most appropriate action for a vehicle to take. Hence, the model introduces a new set of simple rules to change the speed of vehicles that incorporates three important thresholds required by the follower vehicle to accelerate, slow down or maintain its speed. Thus, the space gap, relative speed and limited acceleration/deceleration capabilities are introduced into simulations. Simulation results obtained from a system with periodic conditions show that the model can smooth the speed drop when vehicles approach the upstream front of the traffic jam. Therefore, the model avoids unrealistic deceleration behavior found in most previous cellular automata models. Besides, the model is also capable of reproducing most empirical findings including the three states of traffic flow, the backward speed of the downstream front of the traffic jam, and different congested traffic patterns induced by a system with open boundary conditions with an on-ramp. Moreover, the new model preserves the computational simplicity of the cellular automata models.

Influences of overtaking on two-lane traffic with signals

Abstract: Based on the cellular automata method (CA method), two-lane traffic flow with the consideration of overtaking is investigated. Discrete equations are proposed to describe the traffic dynamics by using the rules of CA model. Influences of signal cycle time ( t s ) and vehicular density ( ρ ) on the mean velocity 〈 v 〉 and mean overtaking times 〈 c 〉 of the traffic flow are discussed. The effects of slow vehicles and road barricades on the traffic flow are also studied. Simulation results shows that the vehicular density and the signal cycle time have significant influences on the traffic flow. The mean velocity of the traffic flow could keep a comparatively large value when ρ ≤ 0.45 . For a certain value of ρ , 〈 v 〉 displays a serrated fluctuation with t s . Therefore, there may exist a certain combination of ρ and t s which optimizes the traffic flow efficiency. As compared with the results in Nagatani (2009) [7] , the model proposed here and the simulation results which took into account the effects of signal cycle time, slow vehicles, and road barricades on the traffic flow with overtaking allowed, can reflect the situation of traffic flow in a more realistic way.

A theory of traffic congestion at moving bottlenecks

Abstract: The physics of traffic congestion occurring at a moving bottleneck on a multi-lane road is revealed based on the numerical analyses of vehicular traffic with a discrete stochastic traffic flow model in the framework of three-phase traffic theory. We find that there is a critical speed of a moving bottleneck at which traffic breakdown, i.e. a first-order phase transition from free flow to synchronized flow, occurs spontaneously at the moving bottleneck, if the flow rate upstream of the bottleneck is great enough. The greater the flow rate, the higher the critical speed of the moving bottleneck. A diagram of congested traffic patterns at the moving bottleneck is found, which shows regions in the flow-rate–moving-bottleneck-speed plane in which congested patterns emerge spontaneously or can be induced through large enough disturbances in an initial free flow. A comparison of features of traffic breakdown and resulting congested patterns at the moving bottleneck with known ones at an on-ramp (and other motionless) bottleneck is made. Nonlinear features of complex interactions and transformations of congested traffic patterns occurring at on- and off-ramp bottlenecks due to the existence of the moving bottleneck are found. The physics of the phenomenon of traffic congestion due to 'elephant racing' on a multi-lane road is revealed.

Optimization of Traffic Flow within an Urban Traffic Light Intersection with Genetic Algorithm

Abstract: Traffic flow control optimization in the traffic light systems is studied for improvement in this paper. Traffic light systems are built to control the traffic flows at the intersections to ensure the fluency of traffic flow within the traffic network. The increasing traffic flows that cannot be supported by the current traffic light systems cause lengthen of queue length at the intersection. The effect of queue length, green time, cycle time and amber time in the traffic system is observed and studied through simulations. Longer green time will pass through more vehicles, but it will increase the cycle time at the same time which causes more vehicles to accumulate at the intersection during the waiting time. Genetic algorithm is introduced in this paper for the optimization of the traffic flow control as its ability to find the optimized solution in its self tuning process. Genetic algorithm taking current queue length as its input then it will output the optimized green time for the intersection. The result of Genetic algorithm is further improved with the introduced of the incoming traffic flow during red time of each phase.

Numerical study of urban traffic flow with dedicated bus lane and intermittent bus lane

Abstract: Based on the cellular automaton traffic flow model and the concept of public transport priority, a two-lane traffic model with an intermittent bus lane is proposed and the properties of urban traffic flow are studied. The cases of traffic with a dedicated bus lane (DBL), an intermittent bus lane (IBL) and an ordinary two-lane traffic are simulated, and comparisons in the form of the fundamental diagrams and the velocity–density profiles are made between them. It is shown that the DBL has the advantage of freeing buses from traffic interference and also has the disadvantage of disrupting traffic, the IBL is more efficient in improving the bus flow than ordinary two-lane traffic and maintaining the car flow at a higher level at the same time than the DBL, while the ordinary two-lane traffic suppresses public transportation and is not advantageous in easing urban traffic congestion. Also it is indicated that the DBL is only appropriate for low traffic flow in a two-lane traffic system, and this limitation can be partly overcome by opening the bus lane to general traffic intermittently when the bus lane is not in use by buses.

Uncertainty and Predictability of Urban Link Travel Time: Delay Distribution–Based Analysis

Abstract: Travel times that vehicles experience in urban road networks are intrinsically uncertain because of the stochastic character of delays at signalized intersections. The ability to capture delay characteristics at signalized intersections is critical for estimating and predicting travel times on urban links. Much research has been done to predict travel time on urban links on the basis of traffic state information (e.g., volumes or speeds). However, the results have not been promising. One important reason is that delays experienced by vehicles on urban links are uncertain because of both traffic conditions and traffic control at intersections. This paper addresses the causes of travel time uncertainty. A probabilistic delay distribution model with stochastic arrivals and departures is proposed to investigate delay uncertainty in both undersaturated and oversaturated conditions. The delay distributions with the Poisson arrival process and with the binomial arrival process are compared. Results show that dif...

Modeling Vehicular Merging Behavior Under Heterogeneous Traffic Conditions

Abstract: In developing countries such as India, the traffic on roads is highly heterogeneous in nature, with vehicles of widely varying static and dynamic characteristics. This type of traffic is characterized by lack of lane discipline and free movement over the entire width of the roadway (laneless movement) based on availability of space. In such a regime of traffic flow, the phenomenon of merging of vehicles at junctions of two roads is complex and warrants further study. Merging maneuvers at T-junctions under congested traffic conditions were studied microscopically through video recordings. On the basis of these observations, models for normal and forced merging have been developed. Video data of merging maneuvers were employed to calibrate and validate the models. Such models can be used to simulate highly congested traffic flow in a realistic manner under heterogeneous traffic conditions. They can also give insight on devising better traffic control measures at such junctions.

New Signal Control Optimization Policy for Oversaturated Arterial Systems

Abstract: Growing traffic volume on the nation's urban highway infrastructure that exhibits limited opportunity for expansion inevitably produces traffic environments that are oversaturated. Oversaturated environments are caused by traffic demands that exceed available capacity and can produce queues that grow over time. These queues on an urban network can overflow the storage capacity of urban streets and physically block intersections, sharply reducing capacity when most needed. Even when intersection blockage is restrained by costly on-site enforcement, signal control policies designed for undersaturated conditions and based on an objective of minimizing delay and stops can be ineffective and even counterproductive. This paper presents an arterial control policy designed expressly for the oversaturated traffic environment. It is designed to maximize throughput while providing assurance that the intersections are clear of vehicles at signal phase changes (i.e. at the beginning of green). Features of this policy include: (1) Mandates queue spillback as a metering mechanism while ensuring clear intersections when needed; (2) Self-regulating; organically adjusts the metering rate through spillback blockage to compensate for fluctuating, cycle-by-cycle demand and service rates, with no adjustment in control parameters needed; (3) Straightforward application as a fixed time control policy with limited computational burden, with guidance for real-time application. The control policy is based on an analytical model of the queuing environment and its associated kinematic behavior of traffic. Selected results are presented.

Equilibrium analysis of macroscopic traffic oscillations

Abstract: Using a simple network model with two parallel links connecting a diverge and a merge, this paper studies under what conditions traffic oscillations may be initiated and propagated in a traffic stream, specially at freeway bottlenecks. Drivers are assumed to minimize either the experienced or instantaneous travel times, and in doing so, they settle at a Wardrop (day-to-day) equilibrium or a Boston (within-day) traffic equilibrium, respectively. We prove that the path travel time function in our model is not monotone, and show that this property leads to multiple Wardrop equilibria, of which only one is both stable and efficient. The paper shows that periodic traffic oscillations do not arise from Wardrop equilibria. Trivial oscillations exist at Boston equilibria, which are caused by drivers’ overreaction to traffic conditions. However, periodic oscillations are likely to emerge when (1) transitions between stable and unstable equilibria take place, and more importantly, (2) drivers make decisions based on out-of-date information of traffic conditions. The latter finding is useful in guiding control practice at freeway bottlenecks and work zones to prevent traffic oscillations.

Characterization and comparison of traffic flow on reversible roadways

Abstract: Reversible traffic operations have become an increasingly popular strategy for mitigating traffic congestion associated with the directionally unbalanced traffic flows that are a routine part of peak commute periods, planned special events, and emergency evacuations. It is interesting that despite its widespread and long-term use, relatively little is known about the operational characteristics of this form of operation. For example, capacity of a reversed lane has been estimated by some to be equal to that of a normal lane while others have theorized it to be half of this value. Without accurate estimates of reversible lane performance it is not possible to confidently gauge the benefits of reversible roadways or model them using traffic simulation. This paper presents the results of a study to measure and evaluate the speed and flow characteristics of reverse-flow traffic streams by comparing them under various operating conditions and locations. It was found that, contrary to some opinions, the flow characteristics of reverse-flowing lanes were generally similar to normally flowing lanes under a variety of traffic volume, time-of-day, location, and type-of-use conditions. The study also revealed that drivers will readily use reversible lanes without diminished operating speeds, particularly as volumes increase.

A Novel Intelligent Traffic Light Control Scheme

Abstract: Traffic congestion has become a major problem in today’s society. It may cause a great waste of material and human casualties. We think the fixed-time-state traffic light control scheme is one important reason. An intelligent traffic light control scheme is necessary in order to give a solution to this problem. The paper proposes a model to describe a road cross. In terms of dynamic and real-time traffic information, weights of all the serial lanes are dynamically computed, so as to automatically manage the current status and duration of traffic lights. The proposed novel control scheme consider traffic situations of both upstream lanes and downstream lanes, in order to reduce average vehicle waiting time at a road cross. The paper further performs simulations for the proposed scheme and gives detailed analysis on parameters which have great influence on scheme performance. Results show that the proposed scheme outperforms the fixed-time-state traffic light control scheme on average vehicle waiting time.

Modeling U-turn traffic flow

Abstract: Median U-turns are sometimes installed to improve the traffic flow at busy intersections by eliminating left turns. Using a microscopic traffic model, we confirmed the presence of transitions from free flow to congested flow with increasing car inflow density. In addition, our proposed rules inside a U-turn curve, which accounted for safety issues and an asymmetric lane changing behavior (outer-to-inner vs. inner-to-outer lane transitions), predicted the speed distribution of cars after the U-turn curve. We found that U-turn curves installed for improving traffic flow at busy intersections produced their desired effects only when there is minimal interaction between cars.

Dynamic highway congestion detection and prediction based on shock waves

Abstract: Existing highway traffic monitoring system requires to deploy a large number of sensors and video cameras to detect traffic congestions, which is costly and prone to errors and failures [1]. In this paper, we present a distributed traffic detection and prediction solution by using shock wave traffic model. We develop a Hello protocol to maintain the vehicle sequence on the same lane. Based on the measurements of velocity and distance between immediate leading and following vehicles, a vehicle can detect and compute shock wave velocity incurred by vehicle merges or obstacles on the highway. When velocity changes occur continuously, congestions will be formed, which can be detected and predicted by the vehicles through a shock wave detection procedure. Our solution is effective since we only require vehicles to communicate with its neighboring vehicles within its wireless communication range.

Exploring the Effect of Turning Maneuvers and Route Choice on a Simple Network

Abstract: A simple symmetric network consisting of two tangent rings on which vehicles obey the Kinematic Wave Theory of traffic flow and can switch rings at the point of tangency is studied. An online adaptive simulation reveals that if there is any turning whatsoever the two-ring system becomes unevenly loaded for densities greater than the optimal density. This reduces flow. Furthermore, the two-ring system jams at significantly lower densities than the maximum density possible.

Continuum modeling for two-lane traffic flow with consideration of the traffic interruption probability

Abstract: Considering the effects that the probability of traffic interruption and the friction between two lanes have on the car-following behaviour, this paper establishes a new two-lane microscopic car-following model. Based on this microscopic model, a new macroscopic model was deduced by the relevance relation of microscopic and macroscopic scale parameters for the two-lane traffic flow. Terms related to lane change are added into the continuity equations and velocity dynamic equations to investigate the lane change rate. Numerical results verify that the proposed model can be efficiently used to reflect the effect of the probability of traffic interruption on the shock, rarefaction wave and lane change behaviour on two-lane freeways. The model has also been applied in reproducing some complex traffic phenomena caused by traffic accident interruption.

Study on traffic flow affected by the road turning

Abstract: Base on the NaSch model, an improved single-lane cellular automaton traffic flow model for especial road is proposed via considering effects of curvature radii, arc length and friction factor on the vehicle movement. By numerical simulation for the traffic flow with different curvature radii, arc length and friction factor, it is found that our improved model can reflect accurately the influence of special sections of a road on the running vehicles, meanwhile visualize the complex nonlinear phenomenon traffic waves of alternate running and stopping as in actual traffics. The reflecting phenomenon in actual traffics indicates that traffic accidents and congestion can be avoided by increase the curvature radii, friction factor of road turning, the capacity of road can be enhanced also.

Effects of the number of on-ramps on the ring traffic flow

Abstract: Since ramps are an important composition of traffic systems and there often exist multi ramps in a traffic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang et al. [2009 Communications in Theoretical Physics 51(1) 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex traffic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.

A Traffic Signal Optimization Strategy Considering Both Vehicular and Pedestrian Flows

Abstract: Current signal control strategies tend to ignore the pedestrian delays that may be imposed by reducing traffic delays. Such an objective is reasonable for motorways and rural roads where vehicular traffic is dominant over pedestrian traffic. However, it is not the case in metropolitan cities with large volume of pedestrian demands. This paper developed a traffic signal optimization strategy that considers both vehicular and pedestrian flows. The objective of the proposed model is to minimize the weighted vehicular and pedestrian delays. The deterministic queuing model is used to calculate vehicular traffic delay and pedestrian delay on sidewalk. Pedestrian delay on crosswalk is calculated based on an empirical pedestrian speed model, which considers interactions of pedestrian platoons and their impacts on average walking speed. The proposed model is first implemented at a Japanese intersection. MATLAB is utilized to solve the optimization problem and to output a set of MOEs. The results show that the proposed model improved average person delay (APRD) by 10% without changing the existing cycle length. Moreover, the model can optimize the cycle length and further improve APRD by as much as 44%. In order to demonstrate the applicability of the proposed model for general cases, this paper also conducted sensitivity analysis. According to the results, the proposed model is most significant and necessary for two circumstances: (1) metropolitan areas with high pedestrian demands and (2) major urban arterials with high pedestrian demands crossing the major streets.

Traffic Flow Monitoring in Crowded Cities.

Abstract: Traffic monitoring systems usually make assumptions about the movement of vehicles, such as that they drive in dedicated lanes, and that those lanes rarely include non-vehicle clutter. Urban settings within developing countries often present extremely chaotic traffic scenarios which make these assumptions unrealistic. We show how a standard approach to traffic monitoring can be made more robust by using probabilistic inference, and in such a way that we bypass the need for vehicle segmentation. Instead of tracking individual vehicles but treat a lane of traffic as a fluid and estimate the rate of flow. Our modelling of uncertainty allows us to accurately monitor traffic flow even in the presence of substantial clutter.

Road traffic: A case study of flow and path-dependency in weighted directed networks

Abstract: How much can we tell about flows through networks just from their topological properties? Whereas flow distributions of river basins, trees or cardiovascular systems come naturally to mind, more complex topologies are not so immediate, especially if the network is large and heterogeneously directed. Our study is motivated by the question of how the distribution of path-dependent trails in directed networks is correlated to the distribution of network flows. As an example we have studied the path-dependencies in closed trails in four metropolitan areas in England and the USA and computed their global and spatial correlations with measured traffic flows. We have found that the heterogeneous distribution of traffic intensity is mirrored by the distribution of agglomerate path-dependency and that high traffic roads are packed along corridors at short-to-medium trail lengths from the ensemble of nodes.

Analytical Models for Protected plus Permitted Left-Turn Capacity at Signalized Intersection with Heavy Traffic

Abstract: This paper presents theoretical analysis of left-turn operations under heavy traffic. When traffic demand is heavy, residual queues from previous cycles may occur and contribute to blockage of the left-turn bay by adjacent through traffic. Such blockage reduces the left-turn capacity and is a random phenomenon. An improved model for protected left-turn capacity is first proposed, taking into account the influence of residual queues and blockage by through traffic. In addition, the classic model always overestimates the potential permitted left-turn capacity when opposing traffic is heavy. The potential permitted left-turn capacity is then modeled in a probabilistic way, and a simple estimation is suggested by investigating its relation to the classic model. Furthermore, because left-turn capacity may vary in response to a blockage, the coefficients of variance for protected left-turn capacity and for queue clearance time are introduced to evaluate the protected left-turn timing plan. The developed analyti...

An Embedded Platform for Intelligent Traffic Control

Abstract: Safety and comfort of road users is fast becoming a matter of grave concern. The number of accidents on roads has shot up greatly with the increase in vehicle traffic, so has the race to build a safer and much more reliable system for traffic control and management. Traffic management rides on an extremely balanced equation. A change in timing of Traffic lights has adverse effects on traffic. A change applied too early may lead to congestion on other roads and a change too late may wreak havoc, long traffic jams, instance of road rage, accidents etc. The ideal automated traffic signal is yet to be built. This report presents an adaptive traffic control system where the traffic load is continuously measured by sensors connected to a micro controller-based system. The traffic lights of an area are interconnected with a communication network through which traffic load and synchronization information is exchanged. As a result, the duration of each traffic light cycle changes dynamically. This means that the timing of the traffic light changes according to the load, the side with the greatest load is given time wise priority.

Propagation Wave Speed Estimation of Freeway Traffic with Image Processing Tools

Abstract: In this paper, we present an automated and fast method to estimate the characteristic propagation wave speeds of freeway traffic, given spatiotemporal raw data, for example from a set of induction loops. This method, the Wave Speed Estimator, utilizes image processing methods to analyze the speed and flow data map for typical wave patterns. One of the applications is the estimation of parameters of the fundamental diagram, which in turn are crucial for the calibration of traffic state estimators. The application to real-world data from Dutch freeways shows promising results. This method can be used as a part of a traffic state estimator or as a parameterizing tool for estimators which depend on the fundamental diagram.

Queue spillovers in city street networks with signal- controlled intersections

Abstract: Quick and reliable estimation of traffic conditions is of critical importance for advanced traffic management systems, especially when heavy congestion occurs. This paper proposes a methodology to predict queue spillovers in city street networks with signalized intersections using data from loop detectors (counts and occupancy). The key idea of the developed methodology is that when spillovers from a downstream link, vehicle arrivals from the upstream signal line, queues discharge at rates smaller than the saturation flow. The paper underlines the significant effect of spillovers in congestion and analyzes an extension of the method to capture variations in vehicle lengths. It also shows that a macroscopic diagram connecting spillovers with car density exists for large scale urban networks which are homogeneously congested. The application of the methodology on an arterial site and the comparison with field data shows that it accurately identifies spillovers in city street networks with signal-controlled intersections.