查看更多>>摘要：Data for 44 days from live extended freeway sections around bottlenecks in the San Diego, California, area were analyzed to determine the stability of the point of initial flow breakdown and the feasibility of using similar data for more extensive research into the stability of bottleneck flow phenomena. The ultimate goal of such research is to shed light on the nature of transitions from uncongested to congested flow. Analysis of speed drop sequences suggests that there is rarely a single bottleneck location within critical freeway sections. This in turn suggests that many bottlenecks should be thought of as extended sections rather than points or isolated segments. This suggests an understanding of flow transitions intermediate between the conventional view that flow breaks down consistently at a few locations and the view that flow breakdown is spontaneous and that congested flow is self-organized. Data similar to those used in this study are adequate, but not ideal, for further investigation of the stability of bottleneck flow phenomena. Specific limitations relate to the locations of detector stations and the presence of chronic data errors. This approach to the study of bottlenecks can be improved by combining direct observation with analysis of loop detector data and by using cumulative flow counts to estimate changes in the numbers of vehicles stored in freeway segments.
查看更多>>摘要：An analytical methodology for prediction of the platoon arrival profiles and queue length along signalized arterials is proposed. Traffic between successive traffic signals is modeled as a two-step Markov decision process (MDP). Traffic dynamics are modeled with the use of the kinematic wave theory. The MDP formulation allows prediction of the arrival profiles several signals downstream from a known starting flow. This modeling approach can be used to estimate queue lengths and predict travel times, even in cases in which data from loop detectors are unknown, inaccurate, or aggregated. The proposed model was applied to two real-world test sites. The queues estimated with the model are in close agreement with the results from microscopic simulation.
查看更多>>摘要：Start-up delays of queued vehicles have been studied in past research for evaluation of their impacts on saturation flow rates at downstream traffic signals. A more crucial issue, however, can be the effect of start-up delays of queued vehicles at upstream locations where queued vehicles back up from a traffic signal across a railroad crossing. The relationship between queue start-up delays and track clearance times is important in establishing traffic signal preemption settings. This paper presents models that are developed for prediction of the expected maximum time required to mobilize a queue of any length. The models consider not only the average delay times but also the limiting delay times that are expected to accommodate high proportions of queues. For design convenience, queue lengths are converted into distance from the leading edge of a queue rather than being described only by the number of vehicles in a queue. Because the variations in start-up times, in addition to the average times reported in the literature, are needed, two sets of field studies were used to obtain data for model calibration and to investigate various traffic operation effects. Other factors that might be expected to influence queue start-up times are also analyzed.
查看更多>>摘要：Lane flow data for five extended freeway segments in the San Diego, California, area were used to examine the effects of freeway and ramp volumes on lane flow distributions and to explore the extent to which these relationships vary by time and location. The proportion of the flow using particular lanes varies significantly with the freeway volume but not with the on-ramp volume. Relationships between freeway volume and the proportion of flow in particular lanes vary significantly by time of day, with flows in different lanes more nearly equal in midday periods than before the morning peak period or after the evening peak period. Such relationships are relatively similar for different days at the same location and different locations within the same extended freeway section but are quite dissimilar for different sections. As a general rule, the proportion of flow in the median lane increases with increasing volume and is greater than that for other lanes in congested flow and high-volume uncongested flow; however, in some cases it increases continuously with increasing volume, and in others it increases up to a point and then decreases. The major implications for behavioral theories of traffic flow are that lane use behavior varies with driver population characteristics and that in making lane use decisions, drivers are sensitive to both speed and vehicle spacing.
查看更多>>摘要：Data from four merge locations in northern California and Toronto, Ontario, Canada, unveil a notable feature of driver turn taking. It was observed that queued vehicles from the on-ramp and freeway traffic streams entered a congested merge in some (nearly) fixed ratio that was independent of the merge outflow. Drivers in competing traffic streams thus entered the merge by adopting some definite turn-taking behavior, and this behavior was not influenced by the severity of the exogenous flow restriction from downstream. The findings validate part of an existing theory of merging traffic and should be considered when any new such theories are developed.
查看更多>>摘要：A new approach to estimation of vehicle type-specific free speed distributions on multilane facilities is presented on the basis of the concept of censored observations. The original distribution-free method of Kaplan and Meier is generalized to include partially censored data, i.e., observations that are censored with a certain probability or to a certain degree. The method is applied with cross-section data collected at a busy two-lane motorway in the Netherlands. The results provide robust estimates of the speed distributions for different vehicle classes, while they remove the structural error made when more common approaches are applied.
Tomer ToledoCharisma F. ChoudhuryMoshe E. Ben-Akiva
p.157-165页
查看更多>>摘要：The lane-changing model is an important component of microscopic traffic simulation tools. With the increasing popularity of these tools, a number of lane-changing models have been proposed and implemented in various simulators in recent years. Most of these models are based on the assumption that drivers evaluate the current and adjacent lanes and choose a direction of change (or no change) on the basis of the utilities of these lanes only. The lane choice set is therefore dictated by the current position of the vehicle and in multilane facilities would be restricted to a subset of the available lanes. Thus, existing models lack an explicit tactical choice of a target lane and therefore cannot explain a sequence of lane changes from the current lane to this lane. In this paper, a generalized lane-changing model that explicitly incorporates the choice of target lane is presented. The target lane is the lane that the driver perceives to be the best when a wide range of factors and goals are taken into account. The immediate direction in which a driver changes lanes is determined by the target lane choice. All parameters of the model were jointly estimated with detailed vehicle trajectory data. The model was validated and compared with an existing lane-changing model with the use of a microscopic traffic simulator. The results indicate that the proposed model performs significantly better than the previous model.
查看更多>>摘要：In many countries the road mileage is dominated by rural highways. For that reason it is important to have access to efficient tools for evaluation of the performance of such roads. For other road types, e.g., freeways and urban street networks, a wealth of microsimulation models is available. However, only a few models dedicated to rural roads have been developed. None of these models handles traffic flows interrupted by intersections or roundabouts, nor are the models capable of describing the traffic flow on rural roads with a cable barrier between oncoming lanes. These are major drawbacks when Swedish roads, on which cable barriers and roundabouts are becoming increasingly important, are modeled. Moreover, as new areas of application for rural road simulation arise, a flexible and detailed model is needed. Such applications include, among other things, simulation of driver assistance systems and estimation of pollutant emissions. This paper introduces a versatile traffic microsimulation model for the rural roads of today and of the future. The model system presented, the Rural Traffic Simulator (RuTSim), is capable of handling all common types of rural roads, including the effects of roundabouts and intersections on the traffic on the main road. The purpose of the paper is to describe the simulation approach and the traffic modeling used in RuTSim. A verification of the RuTSim model is also included. RuTSim is found to produce outputs representative of all common types of rural roads in Sweden.
查看更多>>摘要：Because microscopic models are heavily used in applications, the appropriate calibration and validation of these models have been a recent concern. The contribution of this paper is to compare some of these models by calibrating and validating them with data from double loop detectors on a multilane freeway. To simplify this task, the models were tested by simplifying the multilane reality to a simulation of only a single lane. The results show that by simulating the multilane road with single-lane models, calibration errors (Theil's U-value, or the root mean square error) of 14% to 16% were obtained. A validation of the models, which was done by taking the calibrated parameters of one data set to reproduce the other data sets, gives additional errors of about 0.5 to 2.5 percentage points. This is in good agreement with other calibration and validation approaches performed recently.
查看更多>>摘要：Traffic oscillations such as stop-and-go waves in a traffic system can occur for a variety of reasons, such as instabilities. This paper describes a study of a type of periodic oscillations caused by network geometry with a microscopic simulation model, Paramics. With careful tuning in Paramics, periodic oscillations in which traffic states change periodically between a diverging junction and a merging junction are successfully simulated. The formation process is discussed in detail. The study suggests that, given an appropriate network structure and traffic conditions, the local oscillations caused by randomness in car-following and lane-changing models in Paramics can be maintained and can become periodic and global. Finally, the consistencies between a macroscopic kinematic wave model and Paramics are discussed, and future research topics and the implications of the findings of the study are presented.
NETL
NSTL