Multilane Roundabouts Research Articles

A multi-objective method for large multi-lane roundabout design through microscopic traffic simulation and SSAM analysis

Urban traffic congestion poses a significant challenge, impacting both economic efficiency and environmental sustainability. Roundabouts, recognized for their ability to improve traffic flow and reduce collisions, have become a focal point in traffic management strategies in urban areas. Different types and sizes of single and multi-lane roundabouts can be used, including conventional and innovative roundabouts with small, medium or large size diameters. Many optimization models are available for designing conventional roundabouts but not large roundabouts. To partially cover this gap, the present paper introduces a novel approach integrating simulation-based analysis with a goal programming method to optimize large roundabout design. By leveraging advanced traffic simulation tools like AIMSUN Next and Surrogate Safety Assessment Models (SSAMs), this methodology evaluates multiple design scenarios to enhance traffic flow, safety, and environmental performance. A case study of a complex large roundabout in the Italian greenest and sustainable city demonstrates the efficacy of this methodological approach. The findings provide valuable insights for traffic and highway engineers, emphasizing a data-driven, holistic approach to sustainable traffic management and roundabout optimization.

Data-driven neural network model for maximum speed profile based on driver risk

In the field of vehicle control systems, the primary objective is to ensure the safety of road users. The intricate dynamics of road vehicles necessitate a high level of precision. Vehicle safety encompasses a multitude of considerations, including vehicle trajectory, prevailing traffic conditions, road structure, and meteorological factors. This study employs an Artificial Neural Network (ANN) trained with human driver data using SCANeR Studio software to evaluate the risk for the driver. The risk has been defined as a five-level parameter, which depends on the potential danger of a situation, where speed and direction play a crucial role. The system incorporates a simulator, an ANN, and a display interface to present the surroundings and communicate important information to the driver. This research employs a simulated driving scenario comprising a multi-lane roundabout with vehicles travelling in different directions to simulate real-world challenges. Risk estimation is achieved through a Time Delay Neural Network (TDNN) trained with various information about the environment in relation to the driven vehicle. The research employs a Jackknife technique for overall evaluation and introduces an adaptive algorithm for speed limit setting. The findings demonstrate the stability, generality, and practical applicability of the ANN in enhancing road safety.

Methodology to Counter Heterogeneity at Urban Multilane Roundabouts

Despite the adoption of roundabouts in developing countries for traffic management and smooth flow, the concept of traffic heterogeneity management at these intersections is relatively unexplored. Estimating passenger car units (PCUs) for different vehicle types to homogenize traffic is a recognized approach worldwide. In this study, vehicles were classified into five categories to provide a meaningful context for the analysis. The study proposes a model to estimate PCU values for different vehicle types, specifically at roundabouts, after identifying the potential influencing factors. The study was based on data collected from 10 roundabouts in three Indian cities, having different physical and geometrical characteristics. The proposed method yielded PCU values that were partially comparable with existing standards. Comparisons with the Indian Highway Capacity Manual (Indo-HCM) revealed that this publication underestimated PCU values for two-wheelers and three-wheelers by 20% and 11% respectively, but overestimated PCU values for big cars and heavy vehicles by 9% and 12%, respectively. Method appropriateness was ascertained from the lack of prior assumptions made about traffic and geometrical characteristics. To prevent unnecessary re-estimation of PCU values across locations, the idea of a heterogeneity counter component (HCC) was proposed. The model was trained using cross validation on a dataset of seven roundabouts, and its performance was evaluated on a separate dataset using mean absolute percentage error. The relationship between PCUs and the geometrical features of roundabouts, and the effect of traffic characteristics on HCC were studied. The findings might be considered while revising relevant codes and manuals (e.g., IRC-65:2017, Indo-HCM).

Developing a method of multi-lane roundabouts capacity

Introduction. In recent years a number of methodological and regulatory documents have been developed for public road roundabouts in the Russian Federation. In particular it was proposed to evaluate the quality of traffic management at roundabouts by the level of service measured by the average delay at roundabout entrances. The extension of the average delay criterion to the design of roundabouts requires the development of a methodology for estimating the capacity of traffic lanes at multi-lane roundabout entrances.The aim of the study. Is to develop a methodology for estimating the capacity of multi-lane roundabouts.The object of the study. Is the functioning of multilane roundabouts. Subject of the research. Are the regularities of influence of traffic volume on the values of characteristics of transport streams interaction in the conflict points of multilane roundabouts.Theoretical foundations of the research. The model for estimation of carrying capacity of multilane roundabouts based on the use of conflict points and function of acceptance of intervals is offered.Research Methodology. The video footage of multi-lane roundabouts in the cities of Bratsk, Vladivostok, Irkutsk, Lipetsk, Nakhodka, Orenburg, Petrozavodsk and Pskov was processed. On each lane of the circular carriageway, intervals in the flow, measured between the front bumpers of vehicles, were recorded. The accepted and rejected headways were registered, as well as the number of vehicles using accepted intervals. The determination of the values of critical headways and follow-up time was performed using the Siegloch’s method based on linear regression.Results. A model for estimating capacity at the entrance to a multi-lane roundabout was validated. The values of critical intervals, queuing intervals of each of the entrance lanes to 2-lane and 3-lane roundabouts were determined. The values of the minimum headways in the flows moving on the circular carriageway are determined, also the dependences of the influence of traffic intensity on the free share of the traffic flow are established.

Effects of Phi and View Angle Geometric Principles on Safety of Multi-Lane Roundabouts

Conventional intersections that have been replaced by multi-lane roundabouts have experienced a substantial reduction in both injuries and fatal crashes. Property-damage-only (PDO) crashes have also been reduced at some of these roundabouts. However, some multi-lane roundabouts have experienced a significant increase in PDO crashes. The question arises as to why some U.S. multi-lane roundabouts have substantially higher numbers of PDO crashes while other outwardly similar roundabouts do not. In this paper, we examine the hypothesis that the cause of the higher numbers of PDO crashes at some U.S. multi-lane roundabouts is driver confusion, owing to the lack of adherence to horizontal geometric safety design principles related to entry angles. We review research and explore three case studies where adherence to the safety principles related to entry angles—Phi and left view angle—contributed to improved safety.

Comparative Evaluation of Roundabout Capacities Methods for Single-lane and Multi-lane Roundabout

A roundabout is a highway engineering concept meant to calm traffic, increase safety, reduce stop-and-go travel, reduce accidents and congestion, and decrease traffic delays. It is circular and facilitates one-way traffic flow around a central point. The first part of this study evaluated the principles and methods used to compare the capacity methods of roundabouts with different traffic conditions and geometric configurations. These methods include gap acceptance, empirical, and simulation software methods. Previous studies mentioned in this research used various methods and other new models developed by several researchers. However, this paper's main aim is to compare different roundabout capacity models for acceptable capacity predictions for single-lane and multi-lane roundabouts. In conclusion, previous studies such as RODEL, SIDRA, Swiss, HCM6, and IRC overestimate capacity, while the GHCM method underestimates it. Each VISSIM and SIDRA predicted higher capacity than HCM2010, Paramics, and Simtrafic capacity methods. Generally, the precise prediction of capacity value depends on the circulating flow, exiting traffic flow, driver behavior, and geometric variations. Also, a comparison between seventeen methods was made using virtual data. For a single-lane roundabout, Girabase and Swiss models estimated higher capacity values when compared with other models, while HCM 2010 estimated lower capacity. The Shamueli’s model provides an estimate of capacity about the same as the lower bound of the HCM 2000 model. Brilon’s model estimated lower capacity values for a multi-lane roundabout compared with other methods. At low circulating flow, the Girabase model estimated a higher capacity value, while with the increasing circulating flow, the FHWA2000 estimated a higher capacity than the Girabase model. Also, there is a bit of a difference between SIDRA 5 and 8.0. There is a small interval between models that are implemented in a single-lane roundabout. Therefore, the models are better at predicting the capacity of a single lane than they are at predicting the capacity of multiple lanes.

Impact of Inconsistent Behavior of Drivers on Estimation of Critical Gap at Multi-Lane Roundabouts

Critical gap (CG) estimation, while taking into consideration inconsistent driver behavior resulting from heterogeneous traffic conditions, is a tedious task. Several methods dealing with CG estimation have been developed in the past but limited research has been done in this regard for developing countries and there is a lot of scope to explore this field considering varying traffic conditions on the roads. In this study, the maximum likelihood method (MLM), one of the most prominent methods of determining CG, has been compared with two other methods developed for traffic conditions prevailing in India. These methods use different techniques for calculating the CG, such as minimization of absolute differences of gaps given by Ahmad et al., and minimization of square root of standard deviation of actual gap value from the predicted CG as per the Indian Highway Capacity Manual (Indo-HCM). This paper discusses the estimation of CG for five different categories of vehicles using these methods to counter the heterogeneity of traffic. Data has been collected on two urban multi-lane roundabouts in India. SOLVER in MS Excel is used to optimize the functions defined in all three methods. The results reveal that the method suggested by Ahmad et al. gives the most consistent results which are close to actual value when driver behavior is inconsistent. The other two methods are also reasonably consistent, with the method given in Indo-HCM being slightly better than MLM. Further, two-way ANOVA was applied to check the consistency of results.

Turbo-Roundabouts as an Instrument for Improving the Efficiency and Safety in Urban Area: An Italian Case Study

In recent years, numerous turbo-roundabouts have been built in many European countries. To date, there are no turbo-roundabouts in Italy and even the regulations do not provide for their implementation. Turbo-roundabouts are considered the ideal alternative to multi-lane roundabouts as they have numerous advantages. However, they offer better operational performance only for specific traffic flow distributions. This research used the case study of an important and complex urban arterial road in eastern Sicily, Italy, to compare the operational and safety performance between multi-lane roundabouts and turbo-roundabouts. The evaluations were carried out with two simulation software: (1) AIMSUN Next 20.0.1 (operational performance); (2) SSAM 3.0 (safety performance). The results show that at medium/low traffic volumes, multi-lane roundabouts are significantly superior to turbo-roundabouts in terms of operational performance. At high traffic volumes, the operational performance of turbo-roundabouts improves significantly. As regards the safety parameters, for turbo-roundabouts there is always an increase in the TTC and PET, a reduction in maximum speeds and decelerations. There is also a significant decrease in conflict points. Ultimately, the safety and efficiency performance of turbo-roundabouts should: (1) Encourage administrations to replace the multi-lane roundabouts (illegal in Italy) with turbo-roundabouts; (2) encourage Italian legislators to revise intersection design legislation to include turbo-roundabouts among possible design solutions.

Intersection Sight Distance Requirements for Basic Turbo Roundabouts

Turbo roundabouts, emerging as a solution to conventional multilane roundabouts’ safety and operations concerns, are prevalent in Europe and are still new to North America. However, few studies and guidelines on intersection sight distance (ISD) requirements exist. This paper focuses on the basic turbo roundabouts, examines the circulatory roadway and approach design features, and develops ISD models with North American practices. The ISD requirements were identified for the vehicle approaching and entering the roundabout, which conflicts with the circulating vehicle in the circulatory roadways, and the entering vehicle at the upstream entry approach. Analytical models were developed to identify the required lateral clearance at the central island and clear sight triangles at the roundabout quadrants to satisfy the required ISD. The analyses were completed for four typical sizes of basic turbo roundabouts per Dutch design criteria. The design guidelines are provided for the required lateral clearance at the central island and the required clear sight triangles at the roundabout quadrants. They would be beneficial in establishing landscaping restrictions and determining the roadway right of way and property impacts at the intersections during the roadway planning stage.

Критические интервалы и интервалы следования из очереди на двухполосных кольцевых пересечениях

Over the past decade, a number of manuals have been developed for rural road roundabouts in the Russian Federation. However, two- and three-lane roundabouts are designed and operated in cities of the Russian Federation do not yet have manuals that take into account the specific features of this urban intersections. The development of such do not yet have manuals involves defining all multi-lane roundabout characteristics which used in consistent calculations of capacity, traffic delays and queue length. The objective of the study is to develop a methodology of multi-lane roundabout capacity estimation. At this stage, a study was done to determine the values of critical headway and follow-up time for two-lane roundabouts. Research methodology. Video rings were received from the city of Bratsk, Petrozavodsk, Pskov. The headways measured between the front bumpers of cars, were recorded on each lane of the circular roadway. Accepted and rejected headways were highlighted, as well as the number of vehicles using each accepted headway. Critical headway and follow-up time were determined using linear regression models. Study Result. It was found that the values of critical headway and follow-up time of the left and right entry lanes have different values. These results proved the validity of capacity calculation methods based on a separate consideration of each of entry lane. Objectives for further research. Further research will focus on estimation of critical headway and follow-up time for three-lane roundabouts. It is also necessary to establish the influence of traffic volumes on the headway distribution on two- and three-lane circular carriage way. Consistent solving of mentioned above research tasks will allow to form an estimation methodology for all characteristics of multilane roundabouts. Key words: two-lane roundabouts, conflict points, critical headway, follow-up time, regression analysis.

Critical headway and follow-up time analysis at two-lane roundabouts

Design of urban intersections, as well as the traffic control design on them requires the development of methods of capacity, traffic delays and queues estimation. Two and three-lane roundabouts are designed and operated in many cities of the Russian Federation. Currently there are no approved methods of performance estimation of such multilane roundabouts. The development of such methods would require the determination of all characteristics which are used in consistent calculations of capacity, traffic delays and queue lengths. Research target is to establish the values of multilane roundabouts critical headway and follow-up time. Two-lane traffic circles are analyzed at this research stage. Video records were received from the cities of Bratsk, Petrozavodsk, Pskov. The headways measured between the front bumpers of cars, were recorded on each lane of the circular roadway. Critical headway and follow-up time were determined using linear regression. It was found that the values of critical headway and follow-up time of the left and right entry lanes have different values. These results proved the validity of capacity calculation methods based on a separate consideration of each of entry lane. Further research will focus on estimation of critical headway and follow-up time for three-lane roundabouts. Consistent solving of mentioned above research tasks will allow to form an estimation methodology for all characteristics of multilane roundabouts.

Safety effects of roundabout conversions in Carmel, Indiana, the Roundabout City

Introduction: Roundabouts are a proven safety countermeasure for intersection safety. This study examined the safety effects of roundabout conversions in Carmel, Indiana, also known as the “Roundabout City.” Doing so is of particular interest because Carmel has a high density of roundabouts and its drivers understand their effectiveness and are familiar with navigating them. This study also adds to the current state of knowledge about innovative double-teardrop roundabouts (i.e., linked roundabouts with teardrop-shaped central islands). Method: Negative binomial models accounting for correlation within site pairs were applied to evaluate the safety effects of converting conventional intersections to roundabouts on total crashes, injury crashes, and property-damage-only (PDO) crashes between study sites and control sites for different roundabout types (single-lane, multi-lane, and double-teardrop). We compared crash data from a 2-year period before the installation of the roundabouts with the 2-year period after the conversions. Results: Injury crashes were 47% lower than what would have been expected without the roundabout conversions. The effects were strongest at the double-teardrop roundabouts, where injury crashes were significantly reduced by 84% and total crashes by 63%. Single-lane roundabouts experienced significant decreases of 51% in total crashes and 50% in PDO crashes (and a nonsignificant decrease of 50% in injury crashes). Multi-lane roundabouts were associated with increases in total and PDO crashes but a 15% decrease in injury crashes, though all were nonsignificant. Conclusions: Overall, the City of Carmel’s roundabout program is associated with reductions in injury crashes, which indicates improvements to safety. Single-lane and double-teardrop roundabouts are associated with improvements in the occurrence and severity of crashes. Practical Applications: Double-teardrop roundabouts should be considered for installation at interchange terminals to improve highway safety.

Multilane Roundabout Capacity: Methodology Formation and Model Formulation

Multilane Roundabout Capacity: Methodology Formation and Model Formulation

Two-Geometry Roundabouts: Design Principles

Although multi-lane concentric roundabouts have a greater capacity than single-lane roundabouts, they may encourage increased driving speeds and decrease in safety. Furthermore, lane changing is possible in multi-lane roundabouts, thus increasing the risk of crashes. To address these drawbacks, the authors present the “Two-Geometry” Roundabout. This type of roundabout discourages lane changing within the roundabout, lowers driving speed through the roundabout, and facilitates the manoeuvres of larger and longer vehicles. The paper discusses the concept of the Two-Geometry Roundabout and outlines its principal advantages. We first delineate characteristics of single-roundabouts and multi-lane roundabouts, focusing on the problems of the latter. Next, the development, main characteristics and typologies of Two-Geometry Roundabouts are illustrated (with some examples attached); therefore, we focus on the positive effects of the Two-Geometry Roundabout with particular attention on heavy vehicles. Finally, we present methods for calculating the capacity of the Two-Geometry Roundabout and conclude the paper.

ОБОСНОВАНИЕ МОДЕЛИ ОЦЕНКИ ПРОПУСКНОЙ СПОСОБНОСТИ ГОРОДСКИХ ТРЕХПОЛОСНЫХ КОЛЬЦЕВЫХ ПЕРЕСЕЧЕНИЙ

Currently, three-lane traffic circles are widely used in cities of the Russian Federation. At the same time there are no methods for calculation of the capacity of such traffic circles, taking into account the peculiarities of traffic modes in urban conditions. The paper presents substantiation of development of a model for estimation of capacity of multilane roundabouts based on the conflict points. The development of such a model will allow to carry out a comparative analysis of the efficiency of multilane roundabouts with signalized roundabouts and turbo-roundabouts.

Exploring the safety level of a signalized roundabout with crossing BRT: an observational pilot, in Israel

Bus rapid transit (BRT) systems promote public transport use in big cities, but their implementation requires substantial changes in urban infrastructure, with impacts on road user behaviours and safety. In Israel, recently, a BRT system called "Matronit" was introduced in the Haifa metropolitan area. The extension of the BRT network included a new setting - a signalized multi-lane roundabout with a bi-directional BRT running through its center and traffic lights for the circular traffic when crossing the BRT route. Such a setting was not familiar to Israeli drivers and thus the initial operation of the roundabout was accompanied by an observational pilot. The study focused on safety-related behaviours of road users, e.g. drivers' compliance to the red-light; vehicle behaviours in the roundabout entrance areas; giving right-of-way to pedestrians. A before-after comparison was not possible, thus, the study aimed to characterize the safety level of the new setting by estimating the rates of risky behaviours observed and comparing them with indicators reported in the literature for similar traffic settings. The data were extracted from video-records of the traffic control center, in four areas of the roundabout, two near the traffic lights and at two entrance areas. The results showed that red-light violations were committed by 14% of the vehicles in one traffic-light area, with no cases in the other. On average, one-two red-light violations can be expected per hour, the frequency comparable with signalized intersections. Furthermore, 86% of the cases occurred during the first two seconds of the red-light, with no "near-collisions" between the vehicle and the BRT. In both entrance areas, when traffic was present inside the roundabout, 10%-20% of entering vehicles did not slow down, and this behaviour was more frequent under the red-lights. However, in most cases, the distance between the interacting vehicles was sufficient, while conflicts (with braking) were rare, in 1% of cases. Pedestrian appearance on the crosswalks was rare, but many of them (38%) were ignored by entering vehicles, while such behaviour is common for multi-lane roundabouts. In summary, the pilot demonstrated that the safety level of the roundabout was comparable to other settings, but risky driver behaviours were present both near the traffic lights and in the entrance areas. The findings seem to be site-specific and further research is needed to better fit infrastructure design solutions to various traffic volumes at roundabouts with crossing BRT.

Efficiency Assessment of a Signalized Roundabout and a Traffic Intersection in Baghdad City

In Baghdad city, Iraq, the traffic volumes have rapidly grown during the last 15 years. Road networks need to reevaluate and decide if they are operating properly or not regarding the increase in the number of vehicles. Al-Jadriyah intersection (a four-leg signalized intersection) and Kamal Junblat Square (a multi-lane roundabout), which are two important intersections in Baghdad city with high traffic volumes, were selected to be reevaluated by the SIDRA package in this research. Traffic volume and vehicle movement data were abstracted from videotapes by the Smart Traffic Analyzer (STA) Software. The performance measures include delay and LOS. The analysis results by SIDRA Intersection 8.0.1 show that the performance of the roundabout is better than the signalized intersection but experiences high delay, and low LOS. Therefore, alternatives are proposed to improve the performance for current and future traffic volumes with low-medium delays.

Utilizing UAVs Technology on Microscopic Traffic Naturalistic Data Acquirement

Research into collecting and measuring reliable, accurate, and naturalistic microscopic traffic data is a fundamental aspect in road network planning scientific literature. The vehicle trajectory is one of the main variables in traffic flow theory that allows to extract information regarding microscopic traffic flow characteristics. Several methods and techniques have been applied regarding the acquisition of vehicle trajectory. The forthcoming applications of intelligent transport systems on vehicles and infrastructure require sufficient and innovative tools to calibrate existing models on more complex situations. Unmanned aerial vehicles (UAVs) are one of the most emerging technologies being used recently in the transportation field to monitor and analyze the traffic flow. The aim of this paper is to examine the use of UAVs as a tool for microscopic traffic data collection and analysis. A comprehensive guiding framework for accurate and cost-effective naturalistic traffic surveys and analysis using UAVs is proposed and presented in detail. Field experiments of acquiring vehicle trajectories on two multilane roundabouts were carried out following the proposed framework. Results of the experiment indicate the usefulness of the UAVs technology on various traffic analysis studies. The results of this study provide a practical guide regarding vehicle trajectory acquirement using UAVs.

Roundabouts - drivers' attitudes about the way of moving in two-lane roundabouts

In the last few years, there has been an expansion in the construction of roundaboust. The construction of roundabouts, raised the level of traffic safety. However, it can not be said that all roundabouts have the same level of traffic safety. One-lane roundabouts belong to the category of roundabouts with the fewest points of conflict, and then follow two-lane and multi-lane roundabouts. In general, in the Republic of Srpska there are certain deficiency in the statute and regulations, which refer to this area. These deficiency bring drivers to misapprehension how they should behave at roundabouts. In this labour will be presented the data obtained by surveying with random sampling. Attitudes refer to the way of direction of drivers, only in two-lane roundabouts. Also, in the labour we will provide a suggestion of measures. The suggested measures are practical and can be relatively easily applied in our country.

Intersection Sight Distance Characteristics of Turbo Roundabouts

A turbo roundabout uses spiral circulatory roads for effectively counteracting the problems faced in modern multilane roundabouts. First developed in 1996, the turbo roundabout has an advantage over the conventional roundabout regarding capacity and safety. Turbo roundabouts are still in the developing phase in North America, but even in the European subcontinent where they exist in large numbers, reliable analytical studies on the critical parameters of roundabout visibility are lacking. Visibility (sight distance) helps to shape the geometry of the intersection and aids in safety. This paper presents the mathematical characteristics of the intersection geometry and intersection sight distance (ISD) of the turbo roundabout. Mathematical formulas are presented for the sight distance from the approaching vehicle to the conflicting-entering and circulating vehicles. The maximum lateral clearances to the conflicting vehicles are derived using mathematical optimization. The developed analytical method is verified graphically using AutoCAD. To assist in practical applications, design aids for the maximum lateral clearance are presented. The presented method and design aids should aid in promoting safety at turbo roundabouts.