Showing papers on "Traffic wave published in 1998"

Microscopic modeling of traffic flow: investigation of collision free vehicle dynamics.

Abstract: The continuous growth of road traffic volumes leads to significant environmental and economical problems. For more than four decades efforts have been done to understand the dynamics of traffic flow in order to find out how to optimize traffic with respect to a reduction of environmental impacts and economical loss due to congestion. A microsopic model of traffic flow is proposed, adding to the understanding of the different types of congestion found in traffic flow.

Intelligent Cruise Control Systems and Traffic Flow Stability

Abstract: In analogy to the flow of fluids, it is expected that the aggregate density and the velocity of vehicles in a section of a freeway adequately describe the traffic flow dynamics. The conservation of mass equation together with the aggregation of the vehicle following dynamics of controlled vehicles describes the evolution of the traffic density and the aggregate speed of a traffic flow. There are two kinds of stability associated with traffic flow problems - string stability (or car-following stability) and traffic flow stability. We make a clear distinction between traffic flow stability and string stability, and such a dis- tinction has not been recognized in the literature, thus far. String stability is stability with respect to intervehicular spacing; intuitively, it ensures the knowledge of the position and velocity of every vehicle in the traffic, within reasonable bounds of error, from the knowledge of the position and velocity of a vehicle in the traffic. String stability is analyzed without adding vehicles to or removing vehicles from the traffic. On the other hand, traffic flow stability deals with the evolution of traffic velocity and density in response to the ad- dition and/or removal of vehicles from the flow. Traffic flow stability can be guaranteed only if the velocity and density solutions of the coupled set of equa- tions is stable, i.e., only if stability with respect to automatic vehicle following and stability with respect to density evolution is guaranteed. Therefore, the ow stability and critical capacity of any section of a highway is dependent not only on the vehicle following control laws and the information used in their synthesis, but also on the spacing policy employed by the control system. Such a dependence has practical consequences in the choice of a spacing policy for adaptive cruise control laws and on the stability of the traffic ow consisting of vehicles equipped with adaptive cruise control features on the existing and future highways. This critical dependence is the subject of investigation in this paper. This problem is analyzed in two steps: The first step is to understand the effect of spacing policy employed by the Intelligent Cruise Control (ICC) systems on traffic flow stability. The second step is to understand how the dynamics of ICC system affects traffic flow stability. Using such an analysis, it is shown that cruise control systems that employ a constant time headway policy lead to unacceptable characteristics for the traffic flows. Key Words: Intelligent Cruise Control Systems, Traffic Flow Stability, String Stability, Advanced Vehicle Control Systems, Advanced Traffic Management Systems.

Coherent moving states in highway traffic

Abstract: Advances in multiagent simulation techniques1,2,3 have made possible the study of realistic highway traffic patterns and have allowed theories3,4,5,6 based on driver behaviour to be tested. Such simulations display various empirical features of traffic flows7, and are used to design traffic controls that maximize the throughput of vehicles on busy highways. In addition to its intrinsic economic value8, vehicular traffic is of interest because it may be relevant to social phenomena in which diverse individuals compete with each other under certain constraints9,10. Here we report simulations of heterogeneous traffic which demonstrate that cooperative, coherent states can arise from competitive interactions between vehicles. As the density of vehicles increases, their interactions cause a transition into a highly correlated state in which all vehicles move with approximately the same speed, analogous to the motion of a solid block. This state is safer because it has a reduced lane-changing rate, and the traffic flow is high and stable. The coherent state disappears when the vehicle density exceeds a critical value. We observe the effect also in real Dutch traffic data.

Reliability measures of an origin and destination pair in a deteriorated road network with variable flows

Abstract: A flow network should be studied for evaluating the reliability of a degraded road network, in which the inconvenience of travel may bring the reduction of travel demand and network flow pattern may change. This paper aims to show reliability measures of an origin and destination (OD) pair in a road network when some links are possibly damaged by natural disasters and may be closed to traffic. The UE model with variable demand and strict link capacity constraints is applied to describe flows in a network with some disconnected links. An approximation algorithm is proposed for estimating the cumulative travel time distribution between an OD pair. Small scale examples are calculated to test the performance of the proposed algorithm.

A theory of congested traffic flow

Abstract: Based on recent results on observations of traffic flow dynamics, new hypotheses about properties of congested flow are proposed. In particular, it is proposed that: 1) there are no fundamental diagrams which may describe the whole multitude of homogeneous states of traffic flow; 2) there are no unstable homogeneous states of traffic flow with respect to infinitesimal fluctuations, i.e., there is no critical density for traffic flow - in the whole possible range of the vehicle density homogeneous states of traffic flow can exist; 3) the characteristic line of the jam's downstream front separates the whole multitude of states of traffic in the flow-density plane into two different classes: (i) states below this line are stable with respect to any fluctuations and (ii) states above this line are metastable states where the nucleation effect leading to local phase transitions can occur. It is also noted that there is a reserve in the increasing of the highway capacity of about 50%, if an occurrence of any jams would be prevented.

Dynamics of Two Equivalent Lanes Traffic Flow Model: Self-Organization of the Slow Lane and Fast Lane

Abstract: A simple two-lanes traffic flow model using cellular automaton is investigated. In this model, if the car density is set within a certain range, the following characteristic behavior of traffic flow is observed. i) The self-organization of the slow and fast lanes in spite of the symmetry between these two lanes. ii) The appearance of several branches and hysteresis in the relation between traffic flow and car density.

Negative effects of mid-block speed control devices and their importance in the overall impact of traffic calming on the environment

Abstract: The purpose of this study is to investigate previously unknown effects of speed control devices on fundamental characteristics of traffic, such as vehicle headway distribution, absorption capacity and average delays to vehicles entering from driveways and pedestrian crossing opportunity. Headway data were collected at seven sites in the Sydney Metropolitan Area, under various levels of traffic flow and at various distances from the devices. The results demonstrate that although speed control devices do have some negative side-effects which are sometimes statistically significant, the magnitudes of the increase in average delays and the decrease in absorption capacities around the devices are below the level that would conceivably influence the practical crossing and merging abilities. These minor inconveniences to pedestrians and drivers are confined to the immediate vicinity of the devices and are, by far, outweighed by the benefits in terms of accident savings over the whole length of the street.

The influence of vehicle distribution models on packet success probability on a three lane motorway

Abstract: This paper evaluates the influence of vehicle distribution models on the packet success probability when used for vehicles sending data to a base station near the motorway. Four statistical models for the distribution of the vehicles on a three lane motorway are analyzed and compared with the results obtained when using real vehicle measurements. The measurements are split into three traffic conditions: queueing traffic with low speed, heavy traffic with small average headways and light traffic. The distribution models are used to calculate packet success probabilities using Rice distribution, capture effect and a single slope path loss model. The results show that, depending on the desired accuracy, fixed vehicle positions or exponential distributions can be chosen.

A simulation of a mobile highway traffic

Abstract: This paper presents the simulation model for two directional highway with multiple entrances and exits. The deterministic fluid model is used as a mathematical background. The system is described with ordinary differential equations, which are solved numerically. Parameters of interest are calling and non-calling vehicle's density, offered traffic, blocking probability, number of channels per cell. Different traffic scenarios along the highway are introduced assuming different vehicle's velocity pattern. The behavior of the system in case of a one directional and two directional highways are investigated separately.

Impacts on traffic congestion by switching routes and shifting departure time of trips

Abstract: This study evaluates the possibilities of traffic improvement by spatial and temporal demand spreading. It is understood that some vehicles can reduce the travel time and improve traffic condition by changing the route and departure time so as to avoid traffic jams. However, it is not clear to what extent such a demand spreading can improve traffic conditions. Therefore, the effects of demand spreading by quantitative analysis were investigated using actual road network and actual traffic. In the evaluation method, starting from the current traffic condition as an initial, some trips are shifted to other alternative routes or other departure times to reduce total travel time. In an application to a part of Tokyo, shifting departure times is understood as far more effective to reduce traffic congestion than switching routes, and the short degree of shifting time is enough to eliminate heavy traffic congestion. For the covering abstract see IRRD E102946.

An efficient algorithm for the continuous network loading problem: a DYNALOAD implementation

Abstract: The continuous dynamic network loading problem (CDNLP) consists in determining, on a congested network, time-dependent arc volumes, together with arc and path travel times, given the time varying path (departure) flow rates over a finite time horizon. This problem constitutes an intrinsic part of the dynamic traffic assignment problem. An efficient implementation is developed. Numerical examples are provided.

An Integrated Dynamic Model of Road Traffic Congestion based on Simple Car-Following Theory

Abstract: Abstract This paper presents a dynamic version of the standard static economic model of road traffic congestion, based on car-following theory. It is proven formally and illustrated numerically that the “hypercongested” equilibria found in the standard model are dynamically unstable. For arrival rates of users below the road's maximum capacity, the model reproduces the non-hypercongested stationary state outcomes found in the standard model. When the arrival rate exceeds this maximum capacity, however, the model produces outcomes consistent with Vickrey's model of bottleneck congestion. The model thus offers an integration and a generalization of these two archetype models.

Effect of narrow lanes on the capacity of motorways: a trial in the paris region

Abstract: The trial described in this paper was realized during the spring 1996 on a 2.5 km section of the A6a motorway in the south of Paris. The initial cross section components were modified by narrowing the different lanes. An experimental design and a data collection campaign were set up in order to allow an assessment of the possible effects. This paper depicts the conditions of the trial. It consists of two parts which deal with assessment of behavior changes (positioning, motorcycle traffic) and macroscopic analysis in traffic flows. The conclusion summarizes the main findings. There was a reduction in the lateral spacing between vehicles. Heavy lorries in particular moved closer to the edge lines. Most motorcycles continued to ride between the streams of vehicles during peak hours. Capacity was almost maintained and the congestion level was equivalent. The practical results contribute to a better knowledge of the impact of narrow lanes on the functioning of urban motorways.

Empirical traffic flow modelling: “floating cars” in urban networks

Abstract: This paper discusses how floating probe vehicles can act as observers and provide the basis for an empirical model by measuring the state of traffic online. The authors discuss how the experience of these vehicles, compared with an idealized, predefined state, signals the emergence of increased traffic densities. The evolution and superposition of these partial flows can be given by means of empirical laws.

Communication equipment and communicating method

Abstract: PROBLEM TO BE SOLVED: To increase data quantity capable of being transmitted by stopping transmission by a 2nd transmitter for transmitting a signal to a 2nd traffic lane being adjacent to a 1st traffic lane when transmission by a 1st transmitter for transmitting a signal to the 1st traffic lane is performed. SOLUTION: Common information is transmitted to all traffic lanes. Next, respective different traffic lane information is transmitted to 1st and 3rd traffic lanes. In the meanwhile, communication is stopped in a 2nd and 4th traffic lanes. Next, respective different traffic lane information is transmitted to the 2nd and 4th traffic lanes. In such a case, communication is not performed in the 1st and 3rd traffic lanes. Thus, while a light beacon controlling part 102 performs data transmission with one head, transmission by a head being adjacent to the head is stopped. It is possible to transmit two times more quantity of different traffic lane information than in the conventional practice in each traffic lane by taking such a method.

Theoretical analysis of catastrophes in traffic

Abstract: Catastrophe theory has been applied to traffic analysis to account for discontinuous behavior of freeway operations. However, the reasons for catastrophe have not been developed, and there have not been any fundamental examination of whether catastrophe surfaces of the kinds proposed in the past are reasonable or even possible in traffic. This paper examines the short-time-period (30 seconds or less) dynamics of traffic flow based on fundamental considerations without making assumptions on the traffic relationships. The results show that the effect of vehicle length variations on occupancy calculations is one that could be leading to erroneous conclusions and that properly calculated occupancies for double loop detector stations show some interesting conclusions, that independent variation of the three variables (flow, occupancy and speed) is not possible, and that catastrophe folds showing a vertical drop of speed at constant flow and occupancy can not and does not exist. Finally, observed traffic data for freeway operation does not conform to a catastrophe surface, but a continuous fold-less surface.

Analysis of congested traffic flow

Abstract: Recent results of investigations of congested traffic flow are presented. It is noted that there are two qualitative different types of phase transitions from free traffic flow: (i) free flow to synchronized traffic flow and (ii) free flow to traffic jam. It is also noted that the flow rate out from a traffic jam qout can be considerably lower than the maximal possible flow rate in free flow q(free)max: q(free)max / qout approximates to 1.5. It is stressed that while traffic jams show characteristic parameters which do not depend on initial conditions, synchronized flow show a very complex spatial-temporal behavior. The properties of traffic flow found can be used for traffic forecasting with the aim of improvement of route guidance systems. For the covering abstract see IRRD E102946.

Driver behavior and congestion on highways

Abstract: Congestion on highways often occurs by sudden transitions from free flow traffic to synchronized traffic. Associated with such phase transitions are large decreases in speed. Such phase transitions seem to be often caused by temporal distortions in traffic flows, such as a short peak in the flow of traffic entering a highway from a ramp. If the traffic flow on the ramp has decreased after the peak, congestion on the highway may persist for a longer period. The paper develops a model of congestion for such situations that is based on assumptions about driver behavior and has these characteristics. Critical properties of driver behavior are that, for obvious reasons, sudden large changes in speed are avoided and that reactions to other drivers occur with some delay. In a model where speed can be changed immediately from to any desired value (and vice versa) and drivers react immediately to each other some of the typical characteristics of congestion on highways do not occur. The model suggests that control of the traffic flow, and especially of variations in traffic density, is of major importance in dealing with congestion. Measures for reducing congestion that intend to decrease the average flow of traffic (such as road pricing) should be supplemented by measures reducing the variation in that flow.

Contribution to basic parameters analysis of the traffic flow on two-lane highways in the function of directional split of traffic flow of passenger cars

Abstract: In this paper the regularity of the changes of basic traffic flow parameters (flow rate, speed, and density) on the two-lane highway sections of ideal geometry, with the traffic flow of passenger cars being equal to the practical capacity, is analyzed in the function of directional split of passenger car (PC) traffic flow. The critical review of the way in which this question was treated in the Highway Capacity Manual (HCM), the leading publication dealing with the problems about the road capacity, is performed. Finally, all three basic traffic flow parameters (flow rate, speed and density) for the capacity of two lane highway section of ideal geometry and known PC-traffic flow, in the function of directional split of traffic flow, were defined.

Shifted and induced traffic

Abstract: New measures of traffic infrastructure (for example a new road link) and improvements on existing network elements (for example, shortening of travel time on a tram line by means of technological measures) lead to intermodal and intramodal shifts causing induced traffic at short notice. If a net is chosen of such a width, that all effects of one or more measures in respect of changes in traffic volume on all sections of the net can be shown, the traffic shifted from other modes, the traffic shifted within the same mode and the induced traffic can be described. Shifted traffic can be calculated quite accurately thanks to known traffic demand models, as long as the measures lead to alterations of time and/or costs (for example, Probit and Logit models). At the moment it is difficult to determine the induced traffic. Up to now there are only some initial models for these calculations. (a) For the covering entry of this conference, please see IRRD abstract no. 492019.

Optimizing Traffic Flow

Abstract: We present an economics-based method for deciding the optimal rates at which vehicles are allowed to enter a highway. The method exploits the naturally occuring fluctuations of traffic flow and is flexible enough to adapt in real time to the transient flow characteristics of road traffic. Simulations based on realistic parameter values show that this strategy is feasible for naturally occuring traffic, and that even far from optimality, injection policies can improve traffic flow. Our results also allow a better understanding of the high flows observed in ``synchronized'' congested traffic close to ramps.

An algorithm for vehicle queuing length during traffic jams

Abstract: When accidents happen on express trunk roads, it must be decided which entrance ramps need to be controlled in order to remove traffic jams. To achieve the above goal, the farthest distance of vehicle queues extending to upper reaches of the roads must be correctly estimated. In this paper, according to the extent and lasting time of traffic jams and changing demanded flow volume, the farthest distance of the vehicle queue extending to the upper reaches of roads is calculated using the gather-disperse wave theory. An illustrative example is given finally.

Microscopic simulation of freeway traffic - problems in widening the use of simulation program

Abstract: The application area of the traffic simulation program used in this study (HUTSIM) is widening to freeway surroundings. The new simulation environment causes new problems and development need to the program. The paper gives a discussion about the problems of microscopic freeway simulation based on general knowledge and experiences of a case study. Freeway as simulation environment requires a lot from the traffic simulation procedures. The interaction between drivers is very important. Realistic lane-change and car-following procedures have a great effect on the traffic flow and the lane distribution. Traffic has to be heterogeneous because the similarity of drivers gives too smooth traffic flow. Also the interaction between the driver and the environment and between the driver and the traffic control system should be calibrated carefully. The paper demonstrates that the use of a simulation tool is restricted by the environment where it has originally been developed and validated.

Beating red light runners

Abstract: The use of advanced radars to measure the speed, distance and direction of each individual vehicle in heavy traffic will make drivers think twice about running a red light. Over one million motor vehicle collisionsoccur in the United States at traffic signals, and most pf those are caused by red light runners. The article looks at a new intelligent transportation systems (ITS) project with a concept, referred to as Signalized Intersection Collision Alert System (SICAS), that is a traffic pre-emption systems. The system both helps avoid an accident and identifies the red light runner.

Analysis of structure parameters for urban traffic networks

Abstract: Studies the analysis of both structure parameters and dynamic traffic information for urban traffic networks. The structure parameters of urban traffic networks such as the lane number, type of signalized intersection, traffic regulation, phase, legal speed and link length are analyzed in relation to traffic flows in Hiroshima and Fukuyama cities, Japan. The dynamic traffic information of urban traffic networks are analysed quantitatively based on concepts and data analyses. Relationships between the structure parameters and the dynamic traffic information are described by equations or algorithms.