Showing papers on "Traffic wave published in 1993"

Evolution of Traffic Jam in Traffic Flow Model

Abstract: Traffic flow is simulated in a three-state cellular automaton model. In a two-dimensional cell without a crashed car, the ensemble average of the velocity of the cars is enhanced by the self-organization in the low-density phase of cars. In the high-density phase above p =0.5 of car density, the velocity is decreased and the system then degenerates into a global jamming phase in which all cars are stopped. A crashed car provides the seed of a jamming cluster, which grows into a global traffic jam even in the low-density phase. The growth of the jamming cluster is studied, and the time dependence of the number of jamming cars and the scaling law for the cell sizes are discussed.

The Spatial Evolution of Queues During the Morning Commute in a Single Corridor

Abstract: This paper presents a qualitative description of the evolution of traffic congestion during the morning rush hour in a long freeway leading to a single destination. Traffic is generated at the freeway's many on-ramps during a short period of time and then is assumed to subside. Capacity limitations create queues on the ramps and the freeway, which is assumed to evolve according with the hydrodynamic theory of traffic flow. A special case that can be described with just a few parameters is analyzed in detail.

Car-following as a tool in road traffic simulation

Abstract: The car-following theory offers a mathematical description of how vehicles proceed in a platoon. The changes over time in the speed and acceleration of each vehicle, as a consequence of the speed and acceleration of the vehicles in front, are described. A new car-following model is suggested. The hypotheses is that a driver reacts to the stimuli from the surrounding traffic by choosing an acceleration or deceleration, which is proportional to two components, i.e., the difference between the preferred time gap and the actual time gap, and the difference between the preferred speed and the actual speed.

Dynamic traffic simulation for controlling traffic flow

Abstract: A method for managing traffic flow on roads which will help alleviate congestion is described. A road traffic simulator has been developed in which each vehicle can change route so as to reduce its travel time in accordance with travel time information provided. The simulator simulates the so-called Q-V relation, which means the average velocity on a link is determined in a nonlinear fashion by the quantity of traffic flow. Using this traffic simulator, an actual traffic network is evaluated, both with and without the traffic information. The delay in supplying information reduces the performance of the system at a particular location. Generally, the greater the number of locations for provision, the better. There is an optimum number that provides for fairly good performance in a relatively small number of places. This optimum information provision location is resolved using the traffic simulator.

Gating traffic into congested areas

Abstract: It is possible to use fixed time UTC systems to restrict traffic but it is necessary to calculate the restraint timings by hand, an expensive procedure. However, within version 2.4 of SCOOT there is a facility to restrict traffic, the 'gating' facility, in response to demand on particular 'bottleneck' links within the controlled network. When the saturation on a bottleneck link rises above a threshold, then the green time is reduced on defined gated links. The gated links can be at some distance from the bottleneck; the first time that 'action at a distance' has been included in SCOOT. In fact the gated links can be anywhere in the controlled network, but stability problems are expected if they are a long way from the associated bottleneck.

The Dynamic Behaviour of Road Traffic Flow

Abstract: This paper is a report on work in progress on a project concerned with models of road traffic flow. Results for two such models are described and illustrated. One model is the classical car-following model. A number of numerical simulations were carried out, but no evidence of chaos was found. The other model concerns trip distribution. Here a dynamic formulation of the model results in some solutions which appear chaotic, and evidence of a period-doubling sequence of bifurcations is found.

Road traffic simulation as a tool for estimation of road user effects

Abstract: This paper focuses on a road traffic simulation model called Mimic. It is a periodic-scanned microscopic traffic simulation model in which each vehicle and driver has individual characteristics, and with which the influence on each vehicle of other vehicles, road design, and physical environment can be calculated. The consequence models of the system estimate, for the road users and the environment, the most important effects of the road traffic. The road user effects considered in this system are traffic safety, travel time, vehicle costs and community serverance. The environmental impacts considered are air pollution, noise, and vibration.

A platoon dispersion concept for critical block length for coordinated traffic signal design

Abstract: Presently, signal grouping is determined by traffic engineers on the basis of experience and professional judgment. For general application it is desirable to establish measurable criteria to determine reasonable signal grouping in designing coordinated traffic signals. Since block length has a close relationship with vehicle platoon dispersion, it has been considered as one of the major factors for coordinating traffic signals for progressive traffic movements. The objective of this research is to investigate the effects of platoon size and degree of dispersion on dispersion distance and to establish a mathematical relationship for determining a critical block length for signal grouping.

Simulation of the dynamic traffic flow on urban road network.

Abstract: Methods of performing dynamic traffic assignment are needed to simulate traffic conditions on urban highways during peak periods of congestion. In this paper, the route choice behavior and two kinds o dynamic user optimum are analyzed first, then the constrains for dynamic traffic assignment problem are formulated. Finally, a practical simulation method is developed to perform dynamic traffic assignment for urban road network.

The use of traffic signals to improve the performance of roundabouts

Abstract: Congestion on roundabouts is often caused by a steady, but often relatively small circulating flow making entry of vehicles difficult. Traffic signals can help in two distinct types of situation: (a) where a flow imbalance prevents easy entry by a single major movement; and (b) where the roundabout is operating near capacity on several approaches. A solution to (a) is to signalise the major movement entry on a part-time basis. Optimising the signal timings may be achieved by modelling the junction as an isloated 'T' junction. A solution to (b) is to signalise most, or all the entries on a full-time basis. Combined with appropriate geometric changes, capacity can be improved. The signal timings are critical though and fixed time plans are usually appropriate. In Great Britain, the modelling program TRANSYT is used to optimise the timings, but there are special requirements to obtain the desired results, and these are presented. (A) For the covering abstract see IRRD 869558.

Effects of work zone detours on rural highway traffic operations

Abstract: This study examines two US 59 work zone sites and their impact on rural highway traffic. After first recording typical traffic under free-flow conditions (using infrared sensors and reflectors mounted just off the pavement), the researchers then monitored vehicle volume and vehicle speed both during and after work zone construction to identify the traffic operational effects resulting from work zone detours and lane closures. Vehicle speeds, along with the effects of various truck volumes, were analyzed. Two work-zone detour strategies were particularly studied: (1) those involving long-time lane closures using concrete barriers, and (2) those involving temporary lane closures using barrel-type barricades. Lane closures involving concrete traffic barriers produced a smaller reduction in free-flow speeds when compared with lane closures of temporary barrel-type barriers. Vehicle speeds through the two work zones were also determined to be influenced by truck volumes and total traffic, Moreover, vehicle speeds were found to vary at different times of the day and during weekdays and weekends. As this study confirmed, lane distribution of traffic on a normal four-lane divided highway varies with increased traffic volume, with a tendency for traffic to distribute equally between the two lanes.

The Spatial Evolution of Traffic Under the Two Wave Speed Assumption: A Shortcut Procedure and Some Observations

Abstract: This paper describes the behavior of traffic in a homogeneous highway according to the hydrodynamic theory, in the special case where the flow- density relationship is triangular, i.e., when only two wave velocities exist. It presents an exact formula that predicts the vehicle that would be found at position x at time t, given the locations of all the vehicles at time zero. The paper also introduces two graphical procedures. The first one identifies all the vehicle positions along the highway for any fixed t, and the second one identifies the traffic state on all the points in time-space.