Analysis of Roundabout Stop-Line Delays: Effects Of Kinematic and Behavioral Parameters in Simulation Process of Observed Traffic Conditions (original) (raw)
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Nowadays, the functional design of a road junction is carried out by the use of the microsimulation models software, but it is important to underline that, despite the great diffusion of these instruments, there has not been the same improvement of appropriate methods in order to validate and calibrate these models. The main target to pursue is to know which and how many input parameters are most significant for the variation of output results that microscopic simulation software is able to provide. In this study, Authors present and complete a calibration procedure between observed performances of a roundabout placed in a city in province of Cosenza (ITALY) and performances obtained by the use of micro-simulation software (VISSIM). Two sets of scenarios different among them only for the traffic flow distribution were analyzed: Free Flow Condition (FFC), from which to derive the average speed profiles along a through movement; and Saturation Flow Condition (SFC), to determine the average stop-line delay along a particular branch. A total of 216+216 scenarios for single-lane roundabouts has been composed and analyzed in order to evaluate the best combinations of kinematic and behavioural (mainly in terms of acceptable gap) parameters in the simulation of roundabouts and to estimate of average percent errors between observed and simulated performances.
The performance of roundabouts can affect urban transport systems in terms of environmental and operational impacts, safety and efficiency. The development of roundabout traffic management and control systems can be carried out through road traffic micro-simulation models which are computer models where the movements of individual vehicles travelling around road networks are determined by using simple car following, lane changing and gap acceptance rules. Unfortunately, despite the great diffusion of these tools, appropriate methods are still needed in order to validate and calibrate these models. In general, the calibration process can be defined in this way: the process of comparing model parameters with real-world data to ensure that the model realistically represents the traffic environment. The objective is to minimize the discrepancy between model results and measurements or observations. The aim of this paper is the presentation of a first comparative approach between observed performances and performances obtained by the use of popular microsimulation software, in particular urban intersections such as roundabouts. In particular, an experimental investigation is designed and carried out in order to acquire some vehicular parameters for a roundabout placed in an urban contest of southern Italy. The calibration process is carried out by an analysis of variance of the kinematic parameters of an n-tuple of roundabout scenarios. This calibration procedure has permitted to derive some important conclusions about the choice of the most significant input parameters for the output results of each simulation scenario. Outcomes of this study are expected to benefit both practitioners and researchers.
Methodological Approach for Evaluation of Roundabout Performances through Microsimulation
Applied Mechanics and Materials, 2013
In the literature, there are many methodologies that allow the evaluation of roundabout performances (Capacity, Levels Of Service, etc.): analytical models (HCM, HBS etc.), statistical models (TRRL, SETRA) etc. Each technique considers some aspects of the roundabout in comparison to others (geometric elements, vehicular flow and behavioral parameters). Obtained results are often not comparable among themselves because of distinctive peculiarities of each method. Today, the best way to solve this problem is by using a refined simulation software of vehicular circulation. However, along with a more and more refined analysis of microsimulation software algorithms, it is frequently necessary for each user (researcher, engineer, planner, etc.) to know the real sensitivity of these packages with regard to the most important key parameters. In this paper the Authors introduce the results of a wide survey conducted on an ample range of virtual roundabout scenarios by the use of a modern simulation software. Each scenario describes a fixed roundabout phenomenon using the following variables: geometric elements (inscribed circle radius, circulatory roadway, central and splitter islands etc.); characteristics of the traffic flow (dynamic traffic assignment, approach speed, circulatory speed and reduced speed zones, etc.); behavioral features (priority rules, minimum gap, minimum headway, etc.). The results are presented from the evaluation of stop-line delays.
Operating speed profiles approaching a roundabout: experiments and micro-simulation
It is well known that roundabouts performance can affect urban transport systems in terms of safety, environmental and operational impacts. Roundabout traffic management and control can be carried out by using road traffic microsimulation models. Unfortunately, for these tools appropriate methods are still needed in order to validate and calibrate these models. On the other hand, the operating speed-profile is a useful tool for the analysis of safety issues on existing roads or intersections. As far as a roundabout is present, models and tools are needed to estimate a reliable operating speed-profile on the road section along which driver speed behaviour is affected by the intersection. Consequently, the object of the paper is to analyse operating speed vs. geometry relationship and to calibrate a micro-simulation model, based on experimental investigations and simulations. In light of the above fact, driver speed behaviour (approaching and departing from roundabouts) was studied and a procedure to predict the operating speed-profile along a road section characterized by the presence of a roundabout was developed. A traffic micro-simulation model was used and its results were compared with experimental data. Micro-simulation outputs and data modelling permitted to derive some important conclusions about operating speed-profiles of each simulation scenario. Outcomes of this study are expected to benefit both practitioners and researchers.
Evaluation of Roundabout Performances Using a Micro-Simulation Software
The growing use of roundabout to solve traffic problems has given rise to a large number of models to predict the performances of a roundabout. Each of these ones allows estimation of several features, such as capacity, approach delays and queue lengths through probabilistic or statistical formulations. The restrictions of these models, as well as the difficulty of their use, especially during oversaturation conditions, have driven researchers to use software that can simulate roundabout users behavior. In this regard the Authors present an extensive campaign of research based on several scenarios of roundabout with the aid of VISSIM micro-simulation tool. So three separate sets of scenarios for single-lane roundabouts are composed and analyzed, in total, 288 scenarios, considering as variables both the geometric features (width of splitter island, external roundabout radius, width of circulatory roadway) and the characteristics of traffic flow (distribution and assignment) and the circulation rules (approach and circulatory speed, priority rules). The evaluation of approach delay for each scenario allows to show the results in terms of level of service offered according to HCM 2010.
Analysis of Non-Conventional Roundabouts Performances through Microscopic Traffic Simulation
Applied Mechanics and Materials, 2014
This research is focused on the applicability, in particular contexts, of roundabouts characterized by a non conventional geometry configuration. The methodology is based on the microsimulation approach, validated through a series of surveys on real case studies and traffic conditions. A microsimulation model (VISSIM, PTV), was applied in order to reproduce roundabouts geometry and to define vehicle flow parameters. The research results allow to evaluate roundabouts level of service as a function of geometric features and to establish the limits connected to the employment of noncircular roundabouts in different traffic scenarios.
Comparison of SimTraffic and VISSIM Microscopic Traffic Simulation Tools in Modeling Roundabouts
Procedia Computer Science, 2015
SimTraffic and VISSIM are two microscopic traffic simulation tools that are capable of modeling arterial roads with signalized intersections and roundabouts. This study compares the performance of the two simulation tools in modeling dual lane and triple lane roundabouts under different scenarios such as traffic volume, proportion of left turning movement, and proportion of trucks in the traffic flow. The two simulation tools did not show statistically significant difference in general. However; in the case of high traffic volumes, VISSIM showed higher average delays than those from SimTraffic compared to nearly identical results in the case of low traffic volumes.
Procedia Social and Behavioral Sciences, 2014
Many researchers have shown in recent studies how roundabouts speed distribution, together with other features (entering flow, circulating flow, entry curvature, entry path radius, entry width, approach width, ratio of inscribed circle diameter/central island diameter, angle to next leg, etc.), can be used as a measure of safety level for these intersections. The wide use of different micro-simulation models for a preventive analysis of roundabouts performance (capacity, delays, levels of service, etc.) highlights the need for a deeper study of the most sensitive parameters for a better fitting between simulated and observed traffic conditions. This work is based on an experimental analysis of the crossing movement in two roundabouts characterized by different values of the inscribed circle diameter (D 1 D 2 ) and located close together on the same road in the University Campus of Arcavacata, Italy. The main aim of the research is the suggestion of a methodological approach to the simulation process of the through movement by the use of VISSIM ® micro-simulation software. Results concern the following issues: (i) coherence validation of experimental data regarding speed distributions along the crossing movement as a function of roundabout radius; (ii) methodological and procedural issues related to the implementation of simulation parameters in VISSIM, particularly referring to speed distributions along the crossing movement, in order to better understand the effects of the change of roundabouts geometric features on simulation results.
Transportation Research Record: Journal of the Transportation Research Board, 2012
A slip lane facilitates right-turning traffic flow, reduces approach delay, and reduces conflict points within a roundabout. In this paper the delay performance of a single-lane roundabout with an adjacent slip lane is modeled with the VISSIM microsimulation tool for three slip lane exit types (free-flow, yield, and stop) and the results are compared with a roundabout having no slip lane. The VISSIM assessment considers four experimental traffic percentage turning volume distributions as balanced flow scenarios (total traffic flow into and out of every roundabout approach is the same). Simulated slip lane right-turning traffic volumes range from 50 to 500 vehicles/h, and the four pedestrian volume levels range from 0 to 100 pedestrians/h. VISSIM results confirm that average delays in a roundabout with a slip lane are a function of circulating conflict volumes and are related exponentially to slip lane volumes regardless of the slip lane exit type. Results also indicate that a free-f...