Roundabout Model Research Articles

SAFETY AND OPERATIONAL ASSESSMENT OF COOPERATIVE DRIVING SYSTEMS ON ROUNDABOUTS

This paper presents a simulation-driven method for assessing the safety and efficiency of traffic at roundabouts incorporating connected and automated vehicle (CAV) technology. Utilizing the newly proposed CAV-based factors specified by the Highway Capacity Manual (HCM) provided a practical framework for analyzing capacity dynamics across various traffic scenarios. Using microscopic traffic simulation on a roundabout model replicating real-world geometry and traffic attributes facilitated the identification of crucial behavioral parameters. This simulation spanned from smooth traffic scenarios to operational saturation, aiding in the study of mixed traffic scenarios during the transition to increasing CAV presence. Additionally, the study assessed the safety and traffic impact of a dedicated CAV lane using surrogate safety metrics. Aimsun software aided in model parameter calibration, which, combined with the Surrogate Safety Assessment Model (SSAM), supported safety analysis. Despite observed enhancements in roundabout performance with CAV integration, the benefits of a designated CAV lane highlighted the potential to reduce conflicts among vehicles. In conclusion, the paper emphasizes the overall performance enhancement achieved with CAVs at roundabouts while also providing insights for evaluating the potential of CAV technologies in future mobility management strategies.

Optimized path planning and scheduling strategies for connected and automated vehicles at single-lane roundabouts.

This paper focuses on the cooperative driving challenges of connected and automated vehicles (CAVs) at single-lane roundabouts. First, a geometric path planning method is proposed for CAVs navigating a single-lane roundabout. Based on this method, a vehicle roundabout model is established. Four potential traffic scenarios for CAVs are established, and the optimal arrival times at conflict points are analyzed. By correlating the optimal arrival times at conflict points with the optimal entry times into the roundabout, the multi-vehicle coordination problem in complex intersections is simplified to a speed control issue during entry. Utilizing the principles of optimal control and Pontryagin minimization, two speed optimization strategies are proposed. Finally, MATLAB is employed for simulation analysis. The results indicate that the control strategy proposed in this paper enables the system to clearly identify potential conflicts between vehicles and implement an optimal control strategy, ensuring that vehicles can navigate the roundabout efficiently in terms of time and fuel without collisions. Additionally, the minimum time interval is established at 0.2 seconds to completely prevent vehicle collisions. In this study, the fusion problem involving two vehicles at a single conflict point is further expanded to encompass multiple vehicles at multiple conflict points. Thus, the efficient scheduling of multiple vehicles in single-lane roundabouts is realized.

The fitting of roundabout model with gradient-based minimization

The objective of this research is to create an appropriate roundabout model for all countries. To date, the four-arm roundabout macroscopic model has been created. In order to ensure the feasibility and suitability of the model for all countries, the fitting process must be implemented since the speed of vehicles varies in each country. Thus, the parameter estimation on the rate of exiting roundabout is to be determined because the mean speed of vehicles is related to the rate of exiting the roundabout. In the minimization process, we have proposed an efficient and reliable framework as it includes the calculation of gradients used in minimization so called the user supplied-gradient minimization, as compared to non-user supplied-gradient minimization. The including of the calculation of gradient is to produce more accurate results by the built-in MATLAB minimization routine for parameter fitting. In this research, five pseudo experiments with numerous parameters are carried out. The rate of exiting the roundabout is set initially in order to compute the Total Travel Time and Total Waiting Time. The simulation showed a highly converged and accurate solution by the user supplied-gradient minimization. Lastly, this parameter estimation can be implemented that will enable the roundabout model to be applied worldwide if there is actual data for Total Travel Time and Total Waiting Time.

Two Stop-Line Method for Modern T-Shape Roundabout: Evaluation of Capacity and Optimal Signal Cycle

Uncoordinated traffic flows at the traditional roundabouts, especially with a small circumference and fewer lanes, are often heavily affected by congestion, which escalates fuel consumption, CO2 emissions, idling, and travel delay. An intriguing way to mitigate such uncoordinated flows at junctions would be facilitated through optimal traffic signalization. For this purpose, this paper presents a novel holistic Three-Leg Signalized Roundabout (TLSR) model based on two signalized stop lines (2SL). The first stop line is placed at each entry curve of a roundabout with effectual lane markings as usual. Hereafter, the second stop line is set exclusively in the circulatory roadway to improve left-turning mobility with an additional “short-lane model” to deal with heavy traffic, following specific patterns for smooth vehicle merging. The capacity and optimal signal cycle relationships are derived to evaluate the performance of the proposed TLSR-2SL, considering the internal space constraints of the roundabout. Under the various scenarios, the parameters’ sensitivity tests demonstrate that signal cycle and central radius play a significant role in enhancing the roundabout’s operational performance. From the executed simulation, the proposed framework improves the traffic flow by 15% and controls the relative error within 10% compared to benchmark methods.

Impact of Autonomous Vehicles on Roundabout Capacity

Studying the impact of AVs on our road infrastructure offers a lot of potential in the transportation domain; one of these issues is how capacity will be affected. This paper presents a contribution to this research area by investigating the impact of AVs on the capacity of single-lane roundabouts using a microsimulation model. For the development of the model, a roundabout situated in Győr (Hungary) was selected and field data on the roundabout geometric characteristics as well as traffic volumes were used. Simulations using Vissim were run for various scenarios based on varying input traffic volumes and market penetration rates of AVs to assess queue lengths. The highway capacity manual (HCM) roundabout model was used to estimate the capacity of the existing roundabout. Values of follow-up times and critical gaps were set to decreasing as the penetration rate of AVs increases. The results demonstrated that 20% and 40% AVs in the flow would increase leg capacities by about 10% and 20%, respectively. Furthermore, a reduction in excessive queue lengths was estimated and capacities and queue lengths were calculated by legs. It was found that these are highly influenced by the distribution of flows among legs, and the share of flows in various directions.

The Roundabout Model for Adjunct Clinical Nurse Faculty Retention.

The Roundabout Model was created to address the need for developing and retaining adjunct clinical faculty. Three interrelated evidence-based practices form the Roundabout Model: education, mentoring, and ongoing evaluation. Implementation of the model at one private not-for-profit school of nursing in the Midwest resulted in improved adjunct clinical faculty retention, from 50 percent to 100 percent, as well as improved student and clinical agency satisfaction. Students rated 88 percent of adjunct clinical faculty 3.5 or above on a 4.0 scale. Clinical agency complaints were reduced from three to four annually to zero.

Roundabout model with on-ramp queues: Exact results and scaling approximations.

This paper introduces a general model of a single-lane roundabout, represented as a circular lattice that consists of L cells, with Markovian traffic dynamics. Vehicles enter the roundabout via on-ramp queues that have stochastic arrival processes, remain on the roundabout a random number of cells, and depart via off-ramps. Importantly, the model does not oversimplify the dynamics of traffic on roundabouts, while various performance-related quantities (such as delay and queue length) allow an analytical characterization. In particular, we present an explicit expression for the marginal stationary distribution of each cell on the lattice. Moreover, we derive results that give insight on the dependencies between parts of the roundabout, and on the queue distribution. Finally, we find scaling limits that allow, for every partition of the roundabout in segments, to approximate (i) the joint distribution of the occupation of these segments by a multivariate Gaussian distribution, and (ii) the joint distribution of their total queue lengths by a collection of independent Poisson random variables. To verify the scaling limit statements, we develop a way to empirically assess convergence in distribution of random variables.

Predicting Agent Behaviour and State for Applications in a Roundabout-Scenario Autonomous Driving.

As human drivers, we instinctively employ our understanding of other road users’ behaviour for enhanced efficiency of our drive and safety of the traffic. In recent years, different aspects of assisted and autonomous driving have gotten a lot of attention from the research and industrial community, including the aspects of behaviour modelling and prediction of future state. In this paper, we address the problem of modelling and predicting agent behaviour and state in a roundabout traffic scenario. We present three ways of modelling traffic in a roundabout based on: (i) the roundabout geometry; (ii) mean path taken by vehicles inside the roundabout; and (iii) a set of reference trajectories traversed by vehicles inside the roundabout. The roundabout models are compared in terms of exit-direction classification and state (i.e., position inside the roundabout) prediction of query vehicles inside the roundabout. The exit-direction classification and state prediction are based on a particle-filter classifier algorithm. The results show that the roundabout model based on set of reference trajectories is better suited for both the exit-direction and state prediction.

A safety analysis of roundabouts and turbo roundabouts based on Petri nets

Objective: In this work, a roundabout and a turbo roundabout model are compared and previous modeling with continuous Petri nets and safety are analyzed through indicators of complexity. Petri nets are a graphic and mathematical representation that allow a faithful modeling of urban systems.Method: The methodology has been designed for the transformation of a real system to small subgraphs that represent the maneuvers in roundabouts, approximated as roads and lanes of incorporation. Places within the roundabout have been located and defined as continuous places from their influence and visibility toward adjacent conditions. The transitions have been modeled by time and inhibitory arcs, which represent priorities and areas where drivers must pay attention. The created networks represent a faithful model of vehicle flow trajectories in the roundabouts.Results: The methodology is applied to the same real road intersection. The case study is a recent transformation from roundabout to turbo roundabout. The roundabout network complexity is corroborated by a greater number of entries and exits that lead to each roundabout place (reflected in the maneuvers that can be performed) and a greater number of inhibiting arcs. In most of the turbo roundabout places, the driver’s only option is reduced to occupying next place. The possibility of choosing between several places supposes a greater trajectory intersection and an increased time for decision making. The only situation where the complexity is the same between both systems is when a vehicle accesses the inner lane of the roundabout from the left lane on a single-lane road. The main maneuvers causing accidents have been modeled and their solution in a turbo roundabout is presented.Conclusions: The reduced complexity of the turbo roundabout is due to the strict limitations in lane changes, turning turbo roundabouts into a safer model: A lower number of possible movements that can be performed by drivers and a smaller number of trajectories with collision risk. Petri nets have proven to be perfectly applicable to the representation of traffic circular systems (such as roundabouts and turbo roundabouts) and to measure the complexity and security of the system.

Calibration of Aimsun roundabout model: Pedestrian and vehicles flow

Nowadays, pedestrians play an effective role on roundabout capacity and urban intersection. In this study, the results of stimulation and collaboration of Aimsun software are studied. First, the vo...

Riemann solver for a macroscopic double-lane roundabout model

In this article, we introduce a Riemann solver for traffic flow on a roundabout with two lanes. The roundabout is modeled as a sequence of 2 × 1, 1 × 2 and 2 × 2 junctions. The Riemann solver provides a solution at junctions by taking into consideration traffic distribution, priorities, and the maximization of through flux. We prove existence and uniqueness of the solution of the Riemann problem and show some results numerically.

Cellular Automaton to Study the Impact of Changes in Traffic Rules in a Roundabout: A Preliminary Approach

The current article presents a roundabout traffic model based on cellular automata for computer simulation. The model takes into account various sizes of roundabouts, as well as various types and maximum speeds of vehicles. A realistic vehicle braking phase is presented which is adjusted to the kind of vehicle and weather conditions. It also analyses roundabout traffic options including where the various rules for entering and exiting a roundabout apply. Traffic rules are contained in respective traffic scenarios. The simulation results indicate that there is significant scope for roundabout traffic reorganisation, with a mind to increasing roundabout capacity.

Phase transitions and optimal transport in stochastic roundabout traffic.

We study traffic in a roundabout model, where the dynamics along the interior lane of the roundabout are described by the totally asymmetric simple exclusion process (TASEP). Vehicles can enter the interior lane or exit from it via S intersecting streets with given rates, and locally modified dynamics at the junctions take into account that collisions of entering vehicles with vehicles approaching the entrance point from the interior lane should be avoided. A route matrix specifies the probabilities for vehicles to arrive from and to exit to certain intersecting streets. By subdividing the interior lane into segments between consecutive intersecting streets with effective entrance and exit rates, a classification of the stationary roundabout traffic in terms of TASEP multiphases is given, where each segment can be in either the low-density, high-density, or maximum current TASEP phase. A general methodology is developed, which allows one to calculate the multiphases and optimal throughput conditions based on a mean-field treatment. Explicit analytical results from this treatment are derived for equivalent interesting streets. The results are shown to be in good agreement with kinetic Monte Carlo simulations.

A Macroscopic Single‐Lane Roundabout Model to Account for Insertion Delays and O–D Patterns

Abstract: Available traffic simulation tools for roundabouts are exclusively based on a microscopic framework. This article provides a parsimonious macroscopic model able to replicate the main traffic features occurring at this kind of intersection. Especially, it accounts for time‐limited disruptions on the approach legs due to the insertion process, even when the entry demand does not exceed the merging capacity. It also computes circulating flows that are consistent with vehicle paths induced by the O–D traffic composition. The two‐step validation process using data collected at two different roundabouts is convincing. Moreover, the model appears to be computer‐efficient and has few easy‐to‐calibrate parameters. As a result, it can be easily linked to a traffic simulation package to model a whole urban network.