Showing papers on "Traffic wave published in 1994"

The cell transmission model: a dynamic representation of highway traffic consistent with the hydrodynamic theory

Abstract: This paper presents a simple representation of traffic on a highway with a single entrance and exit. The representation can be used to predict traffic's evolution over time and space, including transient phenomena such as the building, propagation, and dissipation of queues. The easy-to-solve difference equations used to predict traffic's evolution are shown to be the discrete analog of the differential equations arising from a special case of the hydrodynamic model of traffic flow. The proposed method automatically generates appropriate changes in density at locations where the hydrodynamic theory would call for a shockwave; i.e., a jump in density such as those typically seen at the end of every queue. The complex side calculations required by classical methods to keep track of shockwaves are thus eliminated. The paper also shows how the equations can mimic the real-life development of stop-and-go traffic within moving queues.

Traffic at the edge of chaos

Abstract: We use a very simple description of human driving behavior to simulate traffic. The regime of maximum vehicle flow in a closed system shows near-critical behavior, and as a result a sharp decrease of the predictability of travel time. Since Advanced Traffic Management Systems (ATMSs) tend to drive larger parts of the transportation system towards this regime of maximum flow, we argue that in consequence the traffic system as a whole will be driven closer to criticality, thus making predictions much harder. A simulation of a simplified transportation network supports our argument.

Life times of simulated traffic jams

Abstract: We study a model for freeway traffic which includes strong noise taking into account the fluctuations of individual driving behavior. The model shows emergent traffic jams with a self-similar appearance near the throughput maximum of the traffic. The lifetime distribution of these jams shows a short scaling regime, which gets considerably longer if one reduces the fluctuations when driving at maximum speed but leaves the fluctuations for slowing down or accelerating unchanged. The outflow from a traffic jam self-organizes into this state of maximum throughput.

Stochastic Vehicle‐Queue‐Load Model for Large Bridges

Abstract: For long‐span bridges, the traffic load can be modeled as white‐noise‐load fields along the lanes. The mean and the intensity of the white‐noise field depend on the traffic situation. Theoretical expressions in terms of the traffic parameters are available for these white‐noise‐field characteristics covering the entire range from free Poissonian traffic to dense congested traffic that in the limit of zero vehicle velocity becomes a standing queue of vehicles. This paper presents a stochastic model for the load‐effect pulse process caused by the formation of queues of stopped vehicles. The key assumptions leading to the model are the following: (1) The probabilistic structure of the succession of cars and trucks in the queue is generated on the basis of the free Poissonian traffic situation; (2) the occurrences of standing queues are Poissonian and sufficiently rare to justify the neglect of the effect of within‐lane overlap; (3) the queue durations and lengths are exponentially distributed; and (4) the ce...

Traffic jams and the congestion toll

Abstract: The theory of congestion tolls, in particular, the traffic jam, is developed. A dynamic model of traffic flow is presented that describes the formation and development of the traffic jam based on the theory of kinematic waves. I demonstrate the dynamic externality present when traffic is jammed. Furthermore, I obtained some results that differ from those based on the conventional approach: (a) the cost curve for travel on a long road does not include the backward-bending section that appears in the conventional approach; (b) I allow for traffic jams during optimal use of road.

Effect of Jam-Avoiding Turn on Jamming Transition in Two-Dimensional Traffic Flow Model

Abstract: A stochastic cellular automaton (CA) model is presented to study traffic flow in cities. In order to avoid traffic jam, cars are allowed to turn with probability p turn when cars are blocked ahead by other cars. It is found that the jam-avoiding turn has an important effect on traffic jam. With increasing car density, jamming transitions occur from a maximal velocity phase, through a homogeneously moving phase, to a jamming phase, with a critical point. Above the critical point, the jamming transition does not appear. It is shown that allowing cars to turn results in a complex phase diagram.

Traffic Jam and Shock Formation in Stochastic Traffic-Flow Model of a Two-Lane Roadway

Abstract: We present a stochastic cellular automaton (CA) model to simulate the traffic jam induced by a car accident in the traffic flow of a two-lane roadway. The CA model is an extended version of the one-dimensional asymmetric exclusion model to take into account the stochastic exchange of cars between the first and second lanes. We study the traffic flow of the system when the translation invariance is broken by the insertion of a blockage which is induced by a car accident on the first lane. Using the computer simulation, it is found that the dynamical jamming transions occur successively from the phase 1, through the phase 2, to the phase 3 with increasing the density of cars. The phase 1 is characterized by the property such that no cars exist in the first lane and the cars on the second lane move with the maximal velocity. The phase 2 is characterized by the shock formation (a discontinuity of density) and the maximal current. In the phase 3, the discontinuity disappears and the traffic flow is not affecte...

Roadway traffic controller design for automated highway systems

Abstract: For manual driving, the traffic flow is often irregular, unstable leading to congestion and to low traffic flow rate during minor incidents. These irregularities are due to variation of vehicle speeds and headways that are selected by the individual drivers. It is expected that the congestion could be reduced and traffic flow rate could be increased, if the speed and density of the vehicles along a lane can be properly controlled by a roadway controller. In this paper we propose a roadway controller and investigate the benefits of controlling the density and speed of the vehicles along a lane by using the proposed roadway controller. The roadway controller sends the appropriate speed commands to vehicles in each section of the lane. The vehicles are equipped to follow each other automatically and respond to the roadway commands without any driver intervention. A macroscopic traffic flow model is used for analysis and simulations. Our results demonstrate significant benefits in terms of smooth and stable traffic flow that reduce congestion considerably. >

Competition and cooperation on a toy Autobahn model

Abstract: Traffic on an one-lane freeway is simulated using a continuous space-discrete time probabilistic cellular automata model.The effet of different individual driving patterns is estimated by monitoring the traffic flow, the velocity and acceleration distributions, the aver-age number of accidents, and the distribution of density-waves (traffic jams) as a function of traffic density. The number of accidents, traffic jams, and the fuel consumption are drastically reduced by driving strategies adapting to local traffic conditions. At high traffic densities this leads, however, to a decrease in the global traffic throughout.

The development and dispersal of area-wide traffic jams /

Abstract: The development and dispersal of area-wide traffic jams is a matter of considerable social concern. Work at Middlesex University has enabled the construction of a simulation model with greater geographical scope than most conventional congestion simulation models. This paper proposes a simulation model which concentrates on a holistic view of traffic jam formation in a setting of isotropic flow. In the model, traffic incidents can effectively be introduced anywhere in the network. The growth of traffic jams can be observed using a graphical display and options are included to disperse and control the formation of traffic queues. Simulation results have shown that the uncontrolled growth of the traffic jam is both rapid and potentially irreversible. Attempts to disperse the traffic jam appear to be hampered by 'gridlock' phenomena. The paper describes a number of strategies which could be exploited to achieve a controlled dispersion of traffic jams.

Incidents and Intervention on Freeways

Abstract: This paper focuses on the spatio-temporal aspects of congestion caused by an incident and the way in which this can be alleviated by a traffic management intervention. A kinematic wave model of traffic is applied to investigate the issues of congestion. Expressions are derived in closed form for a number of quantities of interest including the maximum extent of the region, the time at which that occurs, relevant times for an intervention, and the effects of that on the size of the congested region. Special forms of these expressions are established for the case of the linear speed-density relationship and calculations are performed to illustrate the application of the resulting analysis to examples of incidents both with and without intervention.

Packet success probabilities for intelligent vehicle highway systems using measured headway distributions

Abstract: This paper evaluates the packet success probabilities for vehicles sending data to a base station near the motorway. An appropriate statistical model for the distribution of the vehicles on a motorway is investigated using measured data. The measurements were carried out on the A13 motorway in the Netherlands during relatively heavy traffic periods. The measurements were split into three traffic conditions: queuing traffic with low speed, heavy traffic with small average headways and free flowing traffic with larger headways. Six models for the distribution of the distances between the vehicles were considered. For the results presented in this paper the shifted negative exponential distribution was chosen. The success probabilities are calculated using Rician distribution, single slope path loss and capture effect. >

DRACULA Microscopic Traffic Simulator

Abstract: The DRACULA traffic simulator is a microscopic model in that the vehicles are individually represented. The movement of vehicles in the network are represented continuously and updated every one second. The network is modelled as a set of nodes and links which represent junctions and streets respectively. Vehicles are generated at their origins with a random headway distribution and are assigned a set of driver/vehicle characteristics (according to user-specified probabilities) and a fixed route. The movement of the vehicles on a network is governed by a car-following law, the gap acceptance rules and the traffic regulations at intersections. They can join a queue, change lane, discharge to another link or exit from the system. The traffic regulation at an intersection is actuated by traffic lights or right-of-way rules. The inputs to the simulation are network data, trip matrix, fixed-time signal plans, gap-acceptance and car-following parameters. Outputs are in forms of animated graphics and statistical measures of network performance. The program is written in C-language. All types of vehicle attributes are represented as one entity using the structure data type which provides a flexibility in storing and modifying various types of data. Attributes of nodes, links and lanes are also represented as structures. The large number of variables associated with vehicles and the network imply that the performance of the simulation depends on the size of the network and the total number of vehicles within the network at one time. The simulator can be applied in many areas of urban traffic control and management, such as detailed evaluation of traffic signal control strategies, environmental issues such as air pollution due to emission from vehicles in idling, accelerating, decelerating or cruising, and analyses of the effects of variable demand and supply upon the performance of a network.

Simulation of freeway incident restoration operations

Abstract: Incidents occurring on a highway decrease the number of lanes available to the through traffic, and cause congested situations, big delays, excess energy consumption and high air pollution. Non-recurring congestion becomes more pronounced during peak hour traffic. The main objective of this paper is to simulate the incident restoration operations and analyse their effects on the traffic flow in terms of travel delay and energy consumption. Various policies are tested, assuming different number of traffic restoring units, dispatching policies, and priority for service schemes. These policies are evaluated and a comparative analysis is incorporated to indicate the sensitivity of the various components against the selected restoration system. >

Dynamic traffic simulation to evaluate vehicle navigation systems

Abstract: This paper presents a macroscopic dynamic traffic simulation model called BOX-MODEL for evaluating information-oriented traffic control measures to reduce urban traffic congestion, for example advanced travelers information systems. This model simulates traffic condition in a large-scale network. Drivers are divided into groups according to patterns of route choice. One group is composed of drivers who get information of dynamic traffic condition and change route on the way to their destination according to the dynamic traffic condition. Another group is composed of drivers who do not get information of dynamic traffic condition but change route on the way to their destination according to dynamic traffic condition to some extent, and yet another group is composed of drivers who always use the same route. The authors examine the performance of the model through simulating traffic flow on an imaginary traffic network. The validity of the model is shown, and the effect of providing drivers information of dynamic traffic condition is estimated. >

The CARS demand-responsive traffic control system: recent improvements and experiences

Abstract: CARS is a third generation traffic control system that follows a centralised approach and can operate either on isolated junctions, arterials, or networks. It does not rely on the traditional concepts of cycle, split and offset, but calculates acyclic settings. Coordination between junctions is achieved through an underlying simulation model that deals with packets of vehicles moving according to an ad-hoc packet-following model, and stopping in horizontal queues. Tests by the AIMSUN microscopic simulation have showed a sustained improvement over optimal fixed-control settings on a wide range of traffic conditions.

Effect of modeling assumptions on evolution of queues in a single corridor

Abstract: A qualitative description is presented of queuing patterns under an idealized scenario analogous to the evolution of traffic congestion during the morning peak hour in a long corridor leading to a single destination. The simplicity of the scenario allows the results to be verified independently by hand. Initially the corridor is assumed to consist of a single freeway. Traffic is generated at the freeway's many on-ramps during a short period and then is assumed to subside. Capacity limitations create queues on the ramps and the freeway, whose evolution is then described. A special case with just a few parameters is analyzed in detail. The solution obtained under the assumptions of the hydrodynamic theory of traffic flow (which explicitly recognizes vehicle storage limitations on the freeway) is shown to be drastically different from the solution obtained using "point queue" models, which ignore these limitations. Because the latter models are currently a favored approach in the dynamic traffic assignment literature, results of this study illustrate the need for reevaluating the conditions under which current theories may be applicable. The effect that a slower parallel arterial would have on the system's traffic is also discussed. It was found that a route choice mechanism in which drivers do not anticipate the system's evolution leads to unreasonable traffic patterns--that is, patterns that would not be expected in reality. The anticipation phenomenon must thus be incorporated into any realistic model of dynamic network flows, which unfortunately, increases the difficulty of developing detailed control strategies.

Development of a road traffic noise prediction model under interrupted traffic flow conditions using the shock wave traffic flow theory

Abstract: The paper concentrates on the development of an appropriate model for predicting the time averaged traffic noise level Leq db(A) under interrupted flow traffic conditions. Starting with an under-capacity signalised intersection, the aim of the model is to relate the time averaged noise level Leq db(A) to the vehicles' operating times in the four modes of acceleration, deceleration, cruising, and queuing as calculated from shock wave traffic flow theory. The paper illustrates the new modelling approach in two main stages; the source noise level stage and the propagation stage to predict the noise level at different receiver positions. It also assesses the prediction accuracy of the model against the UK CRTN,88 method. (A) For the covering abstract see IRRD 868006.

Why does traffic jam

Abstract: Scientists suspect that treating traffic as sound waves traveling through air might reveal how mysterious bottlenecks arise and then dissipate. This article focuses on the phenomenon of traffic bottlenecks and why they occur. Hours lost to traffic jams exceed 2.7 billion a year; idling cars and stop-and-go driving add to air pollution and guzzle gas. By examining driver delay behavior in the manner of sound waves, traffic scientists may be able to solve traffic delays on future highways.

Renewal model for entering highway traffic from on-ramps of given lengths

Abstract: A renewal traffic model is used to study the effect of different lengths of ramps on merging efficiency. The problem of awaiting a certain time gap in a renewal process is a classical one. An extended solution is presented with an expression for expected delay on the access road.

Traffic flow optimization using zone classification

Abstract: This paper proposes a new method of controlling traffic flow over the road network. This method first finds a critical subnetwork where the traffic demand exceeds the capacity of the subnetwork. Within the subnetwork a diversion of traffic is carried out by maximizing the over-all network evaluation function. Several numerical analyses are carried out. Outside the subnetwork another effort to reduce the demand to the over saturated network is carried out. This is done by recognizing the number of the vehicles within the subnetwork and tries to discourage vehicles not to proceed to the subnetwork. This combined control will regulate the traffic congestion.

Capacity and traffic conditions at unsignalised intersections approaches situated in traffic signal networks

Abstract: The studies and analyses undertaken by the authors were aimed at goals; first to select the proper method and work out a research (simulation model), and second to determine the parameters and magnitude of their impact on the capacity and traffic conditions minor approaches to unsignalised intersections. Results of the simulation experiment made it possible to quantify the impact of traffic flow disruptions caused by the traffic signals, on the capacity of minor approaches at priority type intersections. Comparison of results with the ones from the HCM procedure revealedits insensitivity to a few significant effects resulting adjacent traffic signals, namely rate of side inflows in traffic flows leaving signalised intersections, and the range of platoon dispersion or different impact of impedance than at isolated intersections. It has been shown that models of queue length and vehicular delay estimation, adequate for isolated priority intersections and applied in the case of the influence of traffic signals, can lead to significant errors. (a)